electrophoretic deposition

Complimentary Contributor Copy


MANUFACTURING TECHNOLOGY RESEARCH

ELECTROPHORETIC DEPOSITION (EPD) ADVANCES IN APPLICATIONS AND RESEARCH

No part of this digital document may be reproduced, stored in a retrieval system or transmitted in any form or by any means. The publisher has taken reasonable care in the preparation of this digital document, but makes no expressed or implied warranty of any kind and assumes no responsibility for any errors or omissions. No liability is assumed for incidental or consequential damages in connection with or arising out of information contained herein. This digital document is sold with the clear understanding that the publisher is not engaged in rendering legal, medical or any other professional services.


MANUFACTURING TECHNOLOGY RESEARCH Additional books in this series can be found on Nova’s website under the Series tab.

Additional e-books in this series can be found on Nova’s website under the e-book tab.


MANUFACTURING TECHNOLOGY RESEARCH

ELECTROPHORETIC DEPOSITION (EPD) ADVANCES IN APPLICATIONS AND RESEARCH

NATHAN BASS EDITOR


Copyright © 2017 by Nova Science Publishers, Inc. All rights reserved. No part of this book may be reproduced, stored in a retrieval system or transmitted in any form or by any means: electronic, electrostatic, magnetic, tape, mechanical photocopying, recording or otherwise without the written permission of the Publisher. We have partnered with Copyright Clearance Center to make it easy for you to obtain permissions to reuse content from this publication. Simply navigate to this publication’s page on Nova’s website and locate the “Get Permission” button below the title description. This button is linked directly to the title’s permission page on copyright.com. Alternatively, you can visit copyright.com and search by title, ISBN, or ISSN. For further questions about using the service on copyright.com, please contact: Copyright Clearance Center Phone: +1-(978) 750-8400 Fax: +1-(978) 750-4470 E-mail: [email protected].

NOTICE TO THE READER The Publisher has taken reasonable care in the preparation of this book, but makes no expressed or implied warranty of any kind and assumes no responsibility for any errors or omissions. No liability is assumed for incidental or consequential damages in connection with or arising out of information contained in this book. The Publisher shall not be liable for any special, consequential, or exemplary damages resulting, in whole or in part, from the readers’ use of, or reliance upon, this material. Any parts of this book based on government reports are so indicated and copyright is claimed for those parts to the extent applicable to compilations of such works. Independent verification should be sought for any data, advice or recommendations contained in this book. In addition, no responsibility is assumed by the publisher for any injury and/or damage to persons or property arising from any methods, products, instructions, ideas or otherwise contained in this publication. This publication is designed to provide accurate and authoritative information with regard to the subject matter covered herein. It is sold with the clear understanding that the Publisher is not engaged in rendering legal or any other professional services. If legal or any other expert assistance is required, the services of a competent person should be sought. FROM A DECLARATION OF PARTICIPANTS JOINTLY ADOPTED BY A COMMITTEE OF THE AMERICAN BAR ASSOCIATION AND A COMMITTEE OF PUBLISHERS. Additional color graphics may be available in the e-book version of this book.

Library of Congress Cataloging-in-Publication Data ISBN: H%RRN

Published by Nova Science Publishers, Inc. † New York


CONTENTS Preface Chapter 1

Chapter 2

Chapter 3

vii Alternating Current Electrophoretic Deposition (AC-EPD) and Infiltration of Nanomaterials in an Aqueous Suspension Kati Raju and Dang-Hyok Yoon SnO2-Thick Films Obtained by Electrophoretic Deposition and Their Technological Applications Glauco M. M. M. Lustosa, Guilhermina F. Teixeira, João Paulo C. Costa, Carla Y. Kisen, Leinig A. Perazolli and Maria A. Zaghete Synthesis and Characteristics of Silica-Coated Carbon Nanofibers on C-Fiber Textiles by Electrophoretic Deposition Chang-Seop Lez and Yura Hyun

Index

1

39

67 99



PREFACE Electrophoretic deposition (EPD) is attracting many researchers’ attention nowadays because of its numerous advantages, such as simple deposition apparatus, fast deposition rate, and the ease of deposition with a controlled thickness, compared to the other processing techniques. Chapter One reports the effectiveness of AC-EPD for the deposition and infiltration of various ceramic nanoparticles in an aqueous suspension. In Chapter Two, the authors discuss the functionalization of SnO2 thick films prepared by electrophoretic deposition. Chapter Three concludes that despite being a wet process, EPD offers easy control of the thickness and morphology of a deposited film through simple adjustments to the deposition time and the applied potential. Chapter 1 - Electrophoretic deposition (EPD) is attracting many researchers’ attention nowadays because of its numerous advantages, such as simple deposition apparatus, fast deposition rate, and the ease of deposition with a controlled thickness, compared to the other processing techniques. The basic concept involved in this method is the movement of charged particles in a stable suspension upon the application of an electric field. Generally, organic solvents, such as ethanol or acetone, are used over water in direct current (DC)-EPD because the formation of gas bubbles occurs by water electrolysis in an aqueous suspension. Recently, ecofriendly alternating current electrophoretic deposition (AC-EPD) using an


viii

Nathan Bass

aqueous suspension is emerging as a successful processing technique for the deposition of a range of particles, which was proven to minimize the water electrolysis. In the present work, the AC-EPD of various nanoparticles using an asymmetric signal, such as Si, C, β-SiC, TiO2, Al2O3, and BaTiO3, were examined. The rheological behavior of suspensions as a function of pH was studied using zeta potential, viscosity and conductivity measurements. By adding a suitable aqueous dispersant and binder at an optimal pH, a well-dispersed suspension containing nanoparticles was prepared. A square-shaped asymmetric signal with an optimum asymmetry factor was considered for AC-EPD, where homogeneous thick films over a large area could be deposited successfully. The microstructure of the deposited green films was observed by scanning electron microscopy. AC-EPD revealed uniform and crack-free films compared to the non-uniform film morphology prepared under a direct current. The effects of AC electric field, frequency and time on the deposition yield were also examined. In a following step, AC-EPD combined with the application of ultrasonic pulses was used to infiltrate the β-SiC nanoparticles effectively with suitable sintering additives into the fine voids of SiC fabrics to fabricate high density tubular- or planar-shaped SiC fiber-reinforced SiC composites (SiCf/SiC) for high temperature applications. Chapter 2 - The study of materials prepared as films unfolds a new generation of devices paving the way towards the development of new technologies. This ongoing progress in the study of materials clearly brings relevant advantages to the fore. Among such advantages includes the possibility of developing smaller and lighter materials, which help to improve their integration with technology. Among the deposition techniques for obtaining films, the Electrophoretic Deposition (EPD) method has attracted considerable attention owing to the possibility it provides for controlling film thickness by uniform deposition in a fast and less costly manner. The EPD method has been efficient in the production of SnO2 films with thickness controlled according to deposition time. SnO2 is categorized as an n-type semiconductor with electrical conductivity related to excess electrons and structural defects. SnO2 band gap (around


Preface

ix

3.6 eV) facilitates the electron excitation from the valence band (VB) to the conduction band (CB). This behavior enables the application of SnO2 as either photocatalysts, sensors, biosensors, varistors and solar cells in addition to its use for corrosion protection. Tin dioxide (SnO2) exhibits high thermal and mechanical stability besides showing electrical resistance behavior which is highly dependent on chemical composition and thermal treatment temperature. The authors’ objective here is to explain the chemical synthesis via the Polymeric Precursor Method aimed at obtaining SnO2 nanoparticles used for thick films deposition by EPD. The films’ characterizations show that they present a satisfactory response, rendering them suitable for application as varistors, gas sensors and photocatalysts. Chapter 3 - The electrophoretic deposition (EPD) technique, with its wide range of novel applications in the processing of advanced ceramic materials and coatings, has recently experienced an increased level of interest from both the academic and industrial sectors. This results, not only from its considerable versatility of use with different materials and their combinations, but because of its cost-effectiveness and the simplicity of required apparatus. Electrophoretic deposition (EPD) is one of the major colloidal processes in ceramic production, and has the advantages of short formation time, simple apparatus requirements, minimal restrictions on the shape of substrate, and no requirements for binder burnout, as the green coating contains few or no organic materials. In this study, nickel (Ni) and copper (Cu) catalysts were deposited onto C-fiber textiles by the electrophoretic deposition method. Carbon nanofibers (CNFs) were synthesized by chemical vapor deposition (CVD) to Co-Ni electroplated onto C-fiber textiles, and were coated with silica on the surface through the hydrolysis of tetraethyl orthosilicate (TEOS). In the second case, CNFs were synthesized by thermal CVD to Co-Ni electroplated onto C-fiber textiles. The spherical silica particles were coated to the surface of CNFs by hydrolysis of TEOS and were reduced to silicon by hydrogen gas (H2). The electrochemical characteristics of the silica/CNFs composite were investigated, and then these materials were applied as anode materials in lithium (Li) secondary batteries. Compared to other advanced shaping techniques, the EPD process is very versatile since it can be modified


x

Nathan Bass

easily for specific applications. For example, deposition can be made on flat, cylindrical, or any other shaped substrate with only minor modifications in electrode design and positioning. Despite being a wet process, EPD offers easy control of the thickness and morphology of a deposited film through simple adjustments to the deposition time and the applied potential.


In: Electrophoretic Deposition (EPD) ISBN: 978-1-53612-302-9 Editor: Nathan Bass © 2017 Nova Science Publishers, Inc.

Chapter 1

ALTERNATING CURRENT ELECTROPHORETIC DEPOSITION (AC-EPD) AND INFILTRATION OF NANOMATERIALS IN AN AQUEOUS SUSPENSION Kati Raju and Dang-Hyok Yoon* School of Materials Science and Engineering, Yeungnam University, Gyeongsan, Republic of Korea

ABSTRACT Electrophoretic deposition (EPD) is attracting many researchers’ attention nowadays because of its numerous advantages, such as simple deposition apparatus, fast deposition rate, and the ease of deposition with a controlled thickness, compared to the other processing techniques. The basic concept involved in this method is the movement of charged particles in a stable suspension upon the application of an electric field. Generally, organic solvents, such as ethanol or acetone, are used over water in direct current (DC)-EPD because the formation of gas bubbles *

Corresponding author: Email address: [email protected] Tel.: +82-538102561; fax: +82538104628.


2

Kati Raju and Dang-Hyok Yoon occurs by water electrolysis in an aqueous suspension. Recently, ecofriendly alternating current electrophoretic deposition (AC-EPD) using an aqueous suspension is emerging as a successful processing technique for the deposition of a range of particles, which was proven to minimize the water electrolysis. In the present work, the AC-EPD of various nanoparticles using an asymmetric signal, such as Si, C, β-SiC, TiO2, Al2O3, and BaTiO3, were examined. The rheological behavior of suspensions as a function of pH was studied using zeta potential, viscosity and conductivity measurements. By adding a suitable aqueous dispersant and binder at an optimal pH, a well-dispersed suspension containing nanoparticles was prepared. A square-shaped asymmetric signal with an optimum asymmetry factor was considered for AC-EPD, where homogeneous thick films over a large area could be deposited successfully. The microstructure of the deposited green films was observed by scanning electron microscopy. AC-EPD revealed uniform and crack-free films compared to the non-uniform film morphology prepared under a direct current. The effects of AC electric field, frequency and time on the deposition yield were also examined. In a following step, AC-EPD combined with the application of ultrasonic pulses was used to infiltrate the β-SiC nanoparticles effectively with suitable sintering additives into the fine voids of SiC fabrics to fabricate high density tubular- or planar-shaped SiC fiber-reinforced SiC composites (SiCf/SiC) for high temperature applications.

Keywords: aqueous electrophoretic deposition, nanoparticles, SiCf/SiC composites.

1. INTRODUCTION Electrophoretic deposition (EPD) is being widely used from both academic and industrial research fields because of its numerous advantages over other processing techniques. The basic concept involved in this method is the migration and deposition of charged powder particles to the counter electrode in a stable suspension upon the application of an electric field. Figure 1 shows the schematic of EPD of negatively charged particles onto the positive electrode. EPD can be used in the processing and integration of ceramics, coatings, and composite materials to deposit or infiltrate a range of materials, including metal, organic polymer and inorganic particles [1-12]. Therefore, EPD has emerged as one of the most


Alternating Current Electrophoretic Deposition (AC-EPD) …

3

promising technologies due to its versatility and simplicity among many other coating and deposition technologies, such as sol–gel [13], tape casting [14], physical vapor deposition [15, 16], pulsed laser deposition [17], RF sputtering [18], chemical vapor deposition [19] and many more. EPD has several advantages, such as (1) simple and inexpensive apparatus especially for mass production, (2) fast and high quality homogeneous film growth rate depending on the suspension concentration, (3) coating of a wide range of nanoparticles at ambient temperature and pressure, (4) no contamination or precise control over the desired composition, (5) flexibility of using either aqueous or non-aqueous suspensions, and (6) ease for the deposition of a variety of particles with controlled thickness on large and complex-shaped bodies. For example, EPD has been used for the deposition of various nano-materials, including gold and silica [20-22]. It has been also used to deposit oxides, such as Bi2O3 [23], ZrO2 [24], ZnO [25], TiO2 [26], Al2O3 [27], and BaTiO3 [28], as well as carbides and nitrides, such as SiC [29, 30] and TiN [31], respectively. Extensive reports on the fundamental theories and applications of EPD are available [32-37].

Figure 1. Schematic of EPD apparatus for negatively charged particles deposited onto the positive electrode.

Organic solvents, such as ethanol, isopropanol, acetylacetone, or acetone are used in EPD conventionally over water because of the


4

Kati Raju and Dang-Hyok Yoon

formation of gas bubbles and limited tolerance for drying when a suitable direct current (DC) is applied for an aqueous system. Because of the health and environmental hazards of the organic solvent-based EPD process, however, a slurry or suspension using non-flammable and low-cost water instead of toxic and expensive solvents is worthy to be investigated. Switching from a DC to AC electric fields is known to decrease the electrolytic decomposition of water, thus smooth and thick films can be deposited. EPD from aqueous suspensions using an asymmetric unbalanced alternating current (AC-EPD) has emerged as a successful processing technique for the deposition of a variety of particles [38-41]. By applying an unbalanced AC signal with sufficient amplitude and frequency, the decomposition of water becomes difficult, when most of current flows through the double layer capacitance [39, 42]. In addition, the potential that causes the electrochemical reactions also brings the current flow through the double layer capacitance, which is formed at the electrode–electrolyte interface. Moreover, the velocity of particle is known to have a non-linear dependence on the electric field under a strong AC field, causing the particle to travel a longer distance during one of the two half cycles, which results in a net particle movement during one period. Therefore, a combination of unbalanced AC electric field with nonlinear electrophoresis can create a drifting motion of particles. In order to solve the problems associated with water electrolysis under DC, therefore, AC has been considered in the present study. The theoretical aspects along with the advantages of AC-EPD have been extensively summarized in literatures [7, 9, 36-41]. In order to apply EPD effectively for nano-materials, the preparation of well-dispersed and homogeneous slurry is vital because the nano-sized particles themselves are inherently difficult to handle against agglomeration and settling. Many parameters must be taken into account for EPD, which can be classified into two categories: external and internal (suspension) parameters. The main external parameters include the applied electric field strength and frequency, the deposition time, the particle concentration, the cell geometry, and the type of electrodes. Suspension parameters mainly include zeta potential, viscosity, conductivity and



5

cohesion of the green deposit. These suspension parameters play a vital role compared with the external parameters, where rheological study permits to evaluate and control the suspension behavior. Although, EPD has been performed using aqueous suspensions, the effects of rheological behavior on the film microstructure have not been fully understood. Therefore exploring suitable conditions in an aqueous medium by alternating current to deposit a smooth and crack-free film is very essential to understand AC-EPD. In the present work, the deposition of various nanoparticles by ACEPD in an aqueous system, such as, Si, C, β-SiC, TiO2, Al2O3, and BaTiO3, were studied. Highly dispersed slurries suitable for EPD were obtained by adding an adequate dispersant and subsequent milling process. By optimizing the various parameters for EPD in detail, homogeneous thick films could be obtained. To realize the concept of AC-EPD for practical application, EPD combined with the application of ultrasonic pulses was demonstrated to infiltrate the β-SiC nanoparticles with sintering additives into the fine voids of SiC fabrics effectively. Resultantly, high density tubular- and planar-shaped SiC fiber-reinforced SiC composites (SiCf/SiC) for high temperature applications could be manufactured.

2. EXPERIMENTAL Commercially available high purity nanoparticles, including β-SiC (Dm ~ 52 nm, > 97.5% pure, 4620KE, NanoAmor Inc., USA), carbon black (Dm ~ 50 nm, > 98.5% pure, HiBlack 50L, ShinWoo Materials, Korea), Si powder (Dm ~ 100 nm, Alfa Aesar, USA), BaTiO3 (Dm ~ 100 nm, BT-01, Sakai Chemicals, Japan), Al2O3 (Dm ~ 100 nm, NABALOX, Nabaltec, Germany), and TiO2 (Dm ~ 50 nm, Cosmo Chemical, Korea), are used for AC-EPD after dispersing in deionized water in this study. Ammonium polycarboxylate (Cerasperse 5468CF, San Nopco, Korea) and a watersoluble acrylic binder (WB4101, Polymer Innovations, USA) were used as the dispersant and binder phase, respectively. Aqueous suspensions were prepared by ball milling using 0.8 mm SiC beads for 24 hrs. The zeta


6


potential and conductivity of the suspensions containing 1 wt. % of nanoparticles was measured using an electroacoustic-type zeta potential analyzer (Zeta Probe, Colloidal Dynamics, USA), while the rheological behavior was characterized using a computer controlled viscometer (LVDV-II+Pro, Brookfield, USA) with a small sample adapter and a SC418 spindle at room temperature. The pH of the suspensions was adjusted using NH4OH and HNO3 for basic and acidic conditions, respectively. The suspension was ultrasonicated for 10 minute and then stirred mechanically for 10 minute before the measurements. An average of five measurements at least for each sample was reported. After achieving a stable aqueous suspension of nanoparticles, EPD was performed to obtain homogeneous and crack-free films on stainless steel electrodes. A programmable function generator (Agilent 3322A), power amplifier (Trek Model PZD 700A M/S) and digital oscilloscope (Agilent DSO-X 2002A) were used for AC signal generation, amplification and monitoring, respectively. Figure 2 shows the experimental set-up and Teflon chamber used for AC-EPD in the present work. A square-shaped asymmetric waveform with an asymmetry factor of 4, frequencies ranging from 0.01 to 1 kHz, different peak-to-peak voltages, and deposition times from 5 to 30 minute were considered. Figure 3 presents a typical square-shaped asymmetric AC signal used for EPD. After drying the deposited films in a hot oven for overnight, the resulting green microstructure was characterized by scanning electron microscopy (SEM: S-4200, Hitachi). The deposition yield (mass/area) was evaluated as a function of the applied frequency and deposition time.

Figure 2. (a) Experimental set-up and (b) Teflon chamber used for EPD in the present work.


Alternating Current Electrophoretic Deposition (AC-EPD) … E.dt  0

Potential (V)

+V

7

Aymmetry factor = t1/t2 = 4

0

t1

-V

t2 Time/s

Figure 3. Typical square-shaped asymmetric AC signal used for EPD.

3. RESULTS AND DISCUSSION The most important concern for the successful deposition of particles is in finding the suitable conditions at which the suspended particles possess a high zeta potential, while the ionic conductivity of suspension remains low. A well-dispersed stable suspension will always result in better deposition. Dispersion of nano-sized particles is difficult because of their strong tendency to form aggregates, while the surface behavior of nano-materials depends on the pH and temperature. Moreover, a suitable dispersant must be added at an appropriate concentration to prepare a stable aqueous suspension because the dispersant affects to the surface charge, which is an important property for particle dispersion. When a particle is dispersed in an aqueous solution, surface ionization and the adsorption of cations or anions result in the generation of the surface charge. Resultantly, the electric potential will be developed between the


8


particle surface and the bulk of dispersion medium. This surface charge can be evaluated by measuring the particle’s zeta potential, where the zeta potential equals to zero is defined as isoelectric point (IEP). The selection of a suitable dispersant is affected by the liquid media used and the pH of suspension. In general, a good dispersant is characterized with high solubility and high dissociation rate in the liquid media. Because ammonium polycarboxylate (APC) was found as a suitable dispersant for increasing zeta potential, it was adopted as a dispersant in this study. To attain high stability of the colloidal suspension for EPD as well as to increase the particles adhesion, a water-soluble acrylic binder (WB4101) was also added as a binder phase.

3.1. AC-EPD of β-SiC In this work, β-SiC was used at different concentrations up to 30 wt. % in a deionized water for AC-EPD. Because SiC is a promising high performance ceramic that can be used under extreme conditions, the techniques for fabricating thick SiC films are important for practical applications. Several studies have reported the use of EPD for the deposition of SiC nanoparticles from organic suspensions. For example, DC-EPD was performed at a constant voltage of 60 V by Bouyer and Foissy [30] using an ethanol-based suspension. In addition, the effects of suspension parameters and deposition parameters on the quality of deposits were examined using the SiC content of 15 to 70 wt. %. [43]. In another study, DC-EPD from high solid content of 70 wt. % aqueous SiC suspensions using submicron and nano-sized powders was studied by Noval et al. [44]. DC-EPD was also successfully applied to fabricate the reaction-bonded joints using a variety of SiC and Si3N4 compositions. The suspension was prepared by a mixture of acetone and n-butylamine, where it was demonstrated that the EPD technique could be applied to join butt,



9

lap and scarf-type geometry [12]. A ceramic composite composed of Al2O3 particles and SiC whiskers has been also prepared by EPD in an isopropanol suspension, while the effects of processing parameters, such as applied voltage, solid loading, and the concentration of nitric acid and water on the preparation of a green ceramic composite have been examined [45]. Functionally graded Al2O3/SiC/ZrO2 composite material was prepared effectively by DC-EPD using a suspension with 2-butanone [46]. SiC/TiC laminar ceramic composites were also fabricated from acetonebutylamine suspensions by You et al. [47] and demonstrated that EPD is an effective technique in synthesizing laminar ceramic composites. In our previous study [29], homogeneous SiC thick films were deposited by ACEPD using an aqueous suspension. For this purpose, a well-dispersed suspension containing 10 wt. % β-SiC nanoparticles was prepared considering both electrostatic and steric dispersion mechanisms. The film deposited by DC-EPD showed a non-uniform surface with many craters caused by gas bubbles, whereas that by AC-EPD showed a smooth surface without visible defects. Figure 4 shows the microstructural difference between the DC- and AC-EPD deposited using 10 wt. % β-SiC suspension for 30 minutes.

Figure 4. Microstructural difference between (a) DC- and (b) AC-EPD SEM images. (Reprinted from Ref. [29], Copyright with permission from Elsevier).


10

Kati Raju and Dang-Hyok Yoon (a)

0 wt% 0.2 wt% 0.5 wt% 1 wt%

40

Zeta potential (mV)

20

0

-20

-40

-60 2

4

6

8

10

12

pH 1.8

(b)

Viscosity (cPs)

1.6

1.4 0 wt% 0.2 wt% 0.5 wt% 1 wt%

1.2

1.0

0.8 2

4

6

8

10

12

pH 8

(c)

0 wt% 0.2 wt% 0.5 wt% 1 wt%

7 Conductivity (mS/cm)

6 5 4 3 2 1 0 2

4

6

8

10

12

pH

Figure 5. Variation of (a) zeta potential, (b) viscosity, and (c) conductivity of β-SiC as a function of pH at different dispersant concentrations.



11

Aqueous suspensions for rheological studies were prepared by mixing 1 wt. % of SiC powders in a deionized water with various concentrations of ammonium polycarboxylate dispersant in our study. To identify the optimum pH and dispersant content for stable slurries, the zeta potentials of SiC powder by varying dispersant contents and pH were tested. As shown in Figure 5 (a), IEP of the SiC particles was found at pH = 5.46 in the absence of dispersant, which is consistent with those reported in other studies [48, 49]. In the absence of ammonium polycarboxylate, the maximum absolute zeta potential value did not exceed 40 mV, which meant that the electrostatic repulsion between the SiC particles was not sufficient to stabilize suspensions if no dispersant was added. The IEP moved from pH = 5.46 to pH = 3.32, when 0.2 wt. % ammonium polycarboxylate was added, where the zeta potential is increased in the whole range of pH with a maximum absolute zeta potential of 50 mV approximately at pH ≈ 10. When the concentration was increased to 0.5 wt. % then IEP was further decreased to 2.95, further enhancing its zeta potential to 60 mV. However, the IEP and zeta potential does not change significantly when the concentration was further increased to 1 wt.% [50], indicating that 0.5 wt. % dispersant would be the optimum concentration. Ammonium polycarboxylate is a dispersant showing both of an electrostatic and steric stabilization mechanism, which greatly influences the interaction between colloidal particles in an aqueous suspension. Distinct changes of surface charge in SiC suspensions were due to the adsorption of ammonium polycarboxylate on the surfaces of the particles, inducing more negative charges to the double layer because ammonium polycarboxylate becomes alkaline and electronegative when it is dissolved in water. Figure 5 (b) shows the effect of dispersant concentration on the viscosity of suspension by varying pH. The dispersant forms a polymeric barrier layer on the particle surface when it is added, and increases the stability of the suspension via a steric mechanism. Therefore, a welldispersed suspension has a lower viscosity due to the particle mobility offered by the fluid. Suspensions containing insufficient or excessive amounts of dispersant show a relatively higher viscosity than those with


12


adequate amount due to the insufficient surface coverage or bridging flocculation between polymeric species, respectively [51]. It is clearly shown that the viscosity was increased in the entire pH range as the concentration of dispersant increased. The viscosity behavior for the suspension added with 0.5 wt. % dispersant is similar to that of 1 wt. % added one. The effect of dispersant on the conductivity behavior is also shown in Figure 5 (c) because the conductivity of the suspension should be as low as possible. It can be observed that the conductivity increased by increasing the concentration of dispersant in the entire pH range. It is also evident that there is a small difference in the conductivity for the 0.5 and 1.0 wt. % dispersant addition. From the above zeta potential, viscosity and conductivity results, it is clear that 0.5 wt. % ammonium polycarboxylate dispersant is the optimal concentration and therefore further investigations were performed by fixing at this concentration. To examine the effect of binder adsorption on the surface of SiC, suspensions were prepared by mixing 1 wt. % SiC powder in deionized water with various concentrations of water-soluble acrylic binder (WB4101). The effect of WB4101 binder concentration on zeta potential by varying pH is shown in Figure 6 (a). It is clear that the zeta potential is decreased in the whole range of pH when 0.5 wt. % binder is added, while the IEP remains at pH = 5.46. When the concentration is increased to 1 wt. %, IEP still does not change but the zeta potential is decreased further, indicating that 0.5 wt. % is enough as a binder phase. To further evaluate the effect of binder addition on its rheological behavior, viscosity measurements were also performed and the results are shown in Figure 6 (b). It is evident that the addition of binder increases the viscosity of suspension for the entire pH range. It was also found that the addition of binder phase decreased the conductivity of suspension, which is desirable for EPD. Therefore, we may conclude that the addition of WB4101 binder phase decreases the zeta potential and conductivity, while increasing the viscosity of suspension. Based on the above results, therefore, the binder concentration was fixed to 0.5 wt. %.


Alternating Current Electrophoretic Deposition (AC-EPD) … 30

(a)

0 wt% 0.5 wt% 1 wt%

20

Zeta potential (mV)

13

10 0 -10 -20 -30 -40 -50 2

4

6

8

10

12

8

10

12

pH

Viscosity (cPs)

1.6

(b)

1.4

1.2

0 wt% 0.5 wt% 1 wt%

1.0

0.8 2

4

6

pH

Figure 6. Variation of (a) zeta potential and (b) viscosity of β-SiC as a function of suspension pH at different binder concentrations.

Meanwhile, the rheological investigations for suspension were also carried out after adding 0.5 wt. % of both dispersant binder phases. The effect of both polymeric species on the suspension zeta potential and conductivity was shown in Figure 7 (a) and (b), respectively. It is clear that IEP is decreased from pH = 5.46 to 3.5 approximately. From the above results, it is clear that the aqueous suspension of SiC is showing the optimum properties at 0.5 wt. % dispersant and 0.5 wt. % binder at pH 10.


14


Therefore further investigations were performed by fixing both at this concentration. AC-EPD was performed using a 30 wt. % SiC suspension containing both of 0.5 wt.% binder and dispersant on a stainless steel electrode, where a homogeneous thick film could be obtained, as shown in Figure 8. The 3 main parameters related with AC-EPD process that affect to the deposition yield are time, electric field and frequency of the applied AC signal. In general, the yield is directly proportional to the electric field and deposition time, until the depletion of particles begins in the suspension. Figure 9 shows the deposition thickness as a function of time for a typical frequency of 100 Hz and 20 V for a 30 wt. % SiC suspension. Table 1 shows the linear dependence of deposition yield with respect to the voltage at a fixed frequency of 100 Hz for 5 minute deposition. The frequency variation of deposition yield at a fixed voltage of 20 V and deposition time of 5 minutes is shown in Table 2. Frequency-dependence on the yield would be the most important factor for AC-EPD because different types of particles may have their own response under an AC field [29]. Based on the experimental results, β-SiC thick films up to 2.5 mm could be deposited by varying the deposition time, voltage and frequency using AC-EPD. Table 1. Effect of applied voltage for the yield of β-SiC deposited using AC- EPD for 5 minute at 100 Hz No. 1 2 3 4 5

Peak-to-Peak Voltage (V) 4 8 20 40 200

Deposition rate (g/cm2) no deposition 0.116 0.176 0.197 0.215



40

(a)

SiC SiC+0.5 wt% dispersant SiC+0.5 wt% binder SiC+0.5 wt% dispersant+ 0.5 wt% binder

20

Zeta potential (mV)

15

0

-20

-40

-60 2 8

4

(b)

pH

8

10

12

SiC SiC+0.5 wt% dispersant SiC+0.5 wt% binder SiC+0.5 wt% dispersant+0.5 wt% binder

7

Conductivity (mS/cm)

6

6 5 4 3 2 1 0 2

4

6

8

10

12

pH Figure 7. Variation of (a) zeta potential and (b) conductivity of β-SiC as a function of suspension pH with/without 0.5 wt. % dispersant and binder additions.


16


Figure 8. Digital image of the thick film deposited on a stainless steel electrode by ACEPD using a 30 wt. % β-SiC suspension, 20 V, and 100 Hz for 10 minute.

3.2. AC-EPD of Carbon Black and Si A model system consisting of carbon black particles with an average particle size of 26-30 nm and polystyrene in tetrahydrofuran was employed by Modi et al. for DC-EPD [52]. In another study, carbon particles were infiltrated into the synthesized porous Sn foams by EPD using an ethanol solution, containing sulfuric acid and amorphous carbon nanopowders [53]. DC-EPD was used to deposit graphene oxide onto a carbon steel from a graphene oxide aqueous suspension [54]. In addition, graphene oxide nanosheets were deposited at fluorine-doped tin oxide glass substrate by EPD technique as an easy short-time method [55]. The aqueous EPD of a diamond laminate with diamond particles of average particle sizes 0.5 μm and 2 μm were successfully deposited in an alternating manner onto a tungsten carbide substrate [56]. Table 2. Effect of frequency for the yield of β-SiC deposited using an ACEPD for 5 minute at 20 V No. 1 2 3

AC Frequency (Hz) 20 100 1000

Deposition rate (g/cm2) 0.133 0.176 0.165



Deposition @ 100 Hz for 20 V

2.1

Thickness (mm)

17

1.8

1.5

1.2

5

10

15

20

25

30

Time (minutes) Figure 9. Deposition thickness for 30 wt. % β-SiC suspension as a function of time for a typical frequency of 100 Hz and 20 V.

Because a uniform particle dispersion is a critical for achieving a high quality thick film by EPD, both electrostatic and steric dispersion mechanisms were considered by checking the zeta potential at pH 2 – 11 and adding a polymeric dispersant, respectively. In addition, a watersoluble acrylic binder was added to enhance the adhesion of carbon particles to the electrode in this study. Figure 10 shows the zeta potential behavior of a carbon with and without the dispersant and binder. The IEP for carbon was pH ~ 7.7 in the absence of a dispersant and binder. The maximum absolute zeta potential did not exceed 30 mV in the absence of a dispersant in a basic medium, indicating electrostatic repulsion might not be sufficient to stabilize the suspension. When both of 0.5 wt. % dispersant and binder were added, the maximum zeta potential was increased to -50 mV approximately in the pH range of 3 – 11, which is sufficient to confer a stable dispersion via an electrostatic mechanism. Upon the addition of dispersant and binder, the IEP shifted from pH = 7.7 to 3.6 because of the anionic nature of the dispersant. Based on these results, the pH of the suspension was set to 9 for AC-EPD. Using a 10 wt. % carbon black suspension containing both of 0.5 wt. % binder and dispersant, AC-EPD


18


using a typical frequency of 100 Hz and 10 V was performed for 10 minute on a stainless steel electrode. The digital image of the carbon deposit on a stainless steel electrode is shown in Figure 11 (a), while Figure 12 (a) and (b) presents the corresponding surface and cross-sectional SEM images, respectively.

carbon black carbon black+disp.+binder

60

Zeta potential (mV)

40 20 0 -20 -40 -60 2

4

6

8

10

pH Figure 10. Zeta potential behavior of carbon black as a function of suspension pH with and without the dispersant and binder addition.

Figure 11. Images for the thick films deposited by AC-EPD using (a) 10 wt. % carbon black and (b) 5 wt. % Si suspensions.



19

Figure 12. SEM images for the (a) surface and (b) cross-sectional of carbon black film.

Regarding the deposition of silicon particles, one should consider the physical properties of the starting silicon surface can be changed because the formation of SiO2 layer is inevitable because of the highly negative Gibbs formation free energy. Several studies have reported the use of EPD for silicon and SiO2 nanoparticles from organic suspensions. Methoxynonafluorobutane was used as a solvent for the DC-EPD of SiO2 powder [57]. In another study, AC-EPD was performed using a 0.1 wt. % silicon powder having a particle size of 4 µm approximately in pure acetylaceton, where the deposition yield decreased as the frequency of the electric field increased from 0.01 Hz to 1,000 Hz. When 3 different waveforms, i.e., rectangular, sinusoidal, and triangular were used, the deposition yield was highest with the rectangular wave, which was explained using the effective voltage of the applied AC field [58]. However, crystalline silicon in an aqueous medium can theoretically release two moles of H2 per mole of silicon by the reactions [59]: Si(cr.) + 4H2O(l) → Si(OH)4(aq.) + 2H2(g) Si(cr.) + 2H2O(l) → SiO2(s) + 2H2(g)

Therefore, EPD can be performed after removing the gas bubbles by keeping the suspension for some time. When 0.5 wt. % of the dispersant and binder were added, the IEP was at pH ~ 2.8 and the maximum zeta potential was about -80 mV at pH ~ 8.8, which is sufficient to confer a


20


stable dispersion. Therefore, AC-EPD was performed at pH ~ 8.8 on a stainless steel electrode using a typical Si suspension (5 wt. %) containing both of 0.5 wt. % binder and dispersant AC-EPD. The deposit using a typical AC frequency of 100 Hz and 20 V applied for 5 minutes is shown in Figure 11 (b), whereby a uniform deposition can be observed.

3.3. AC-EPD of Al2O3, BaTiO3 and TiO2 According to the previous reports, Al2O3 films were deposited compactly and uniformly on the substrate by DC-EPD in water using a nanopowder having a mean particle size of 50 nm. Within the range of the experiments, the optimal parameters determined were nanofluid concentration of 2 wt. %, deposition time of 15 minute, applied voltage of 23 V and suspension pH of 3 [27]. By using an ethanol-based colloidal suspensions with the addition of 4-hydrobezoic acid, EPD was also performed to fabricate an α-alumina matrix composites having a high volume fraction of woven fiber mat [60]. Alumina Alumina+disp.+binder

90

Zeta potential (mV)

60 30 0 -30 -60 -90 2

4

6

8

10

pH

Figure 13. Zeta potential behavior of Al2O3 with and without the dispersant and binder addition.



21

Figure 14. Digital images of (a) Al2O3 and (b) BaTiO3 film deposited by AC-EPD.

Figure 13 shows the zeta potential behavior of Al2O3 with and without the addition of dispersant and binder, which was performed in this study. The IEP of Al2O3 was pH ~ 9.8 in the absence of a dispersant and binder, where the maximum zeta potential was about -40 mV. When 0.5 wt. % of both dispersant and binder were added, however, the maximum zeta potential was increased to -75 mV at pH ~ 10, which is enough to confer a stable dispersion via an electrostatic mechanism. Because the IEP shifts its value from pH ~ 9.8 to 7.9 upon the addition of dispersant and binder, the pH of the suspension was set to 10. AC-EPD was performed after optimizing the parameters at 100 Hz and 20 V for 20 minute using a 15 wt. % Al2O3 suspension containing both of 0.5 wt. % binder and dispersant, and the result is shown in Figure 14 (a). On the other hand, the use of DC-EPD for the deposition of BaTiO3 nanoparticles from organic suspensions was reported by several researchers [61-65]. Nano-structured BaTiO3 thin films were electrophoretically deposited by using a stable suspension after adding a mixed solvent of 2-methoxyethonal and acetylacetone. The distance between the cathode and anode was 2 cm and the DC voltage varied from 1 to 15 V [61]. The effects of some parameters, such as applied voltage, deposition time, suspension concentration, and separating distance between two electrodes, on the thickness of the as-deposited BaTiO3 films were investigated [62]. In other work, DC-EPD was performed at 100 V for 1 hour at room temperature with an electrode distance of 3.5 cm using a 4


22


vol. % of BaTiO3 dispersed in ethanol. A vertical magnetic field of 17.4 T was applied to the suspension during EPD at room temperature with magnetic and electric field directions perpendicular to each other [63]. Polycrystalline BaTiO3 thin films were electrodeposited on a titanium foils from a colloidal aqueous solution of barium titanyl oxalate nanoparticles, which were synthesized by a hydrothermal process. EPD was performed with a DC voltage of 10 V for 10 minute between the titanium foil and a platinum electrode [64]. Stable aqueous suspension of 5 wt. % BaTiO3 was chosen for the DC-EPD using 0.3 wt.% poly(acrylic acid-co-maleic acid) as a dispersant at pH 10. Dense, uniform and defect-free BaTiO3 films with a thickness up to 20 µm could be formed under a low applied DC voltage of 2 – 6 V [65]. However, reports on the use AC-EPD for BaTiO3 deposition are scarcely available. Therefore, AC-EPD using 10 wt. % BaTiO3 aqueous suspension was performed in this study, where a uniform thick film could be deposited on alumina foil, as shown in Figure 14 (b). TiO2 coatings from an aqueous suspension have been also successfully prepared by the application of AC electric field. The quality of the TiO2 coatings deposited using AC-EPD was superior to that of DC-EPD coatings made from the same type of suspensions in terms of homogeneity and the extent of micro-cracking [41]. EPD of TiO2 nanoparticles under a symmetric uniform AC electric fields at 1 Hz in acetone showed that the ceramic particles would be able to deposit on both electrodes [66]. Recently, a review on the different aspects involved in the fabrication of TiO2 coatings by EPD was reported elsewhere [26]. After checking the zeta potential behavior without adding any organic additives, as shown in Figure 15 (a), the AC-EPD of TiO2 was performed in this study, which resulted in a smooth and homogeneous surface, as shown in Figure 15 (b).

3.4. Fabrication of Planar and Tubular SiCf/SiC by AC-EPD and Hot Pressing Different methods have been reported to fabricate high-quality SiCf/SiC composites, such as chemical vapor infiltration (CVI) [67],



23

polymer impregnation and pyrolysis (PIP) [68], nano-infiltrated transient eutectic-phase (NITE) process [69], and reaction sintering (RS) [70]. These methods are very slow and costly processes, which also result in an incomplete matrix phase filling into the gaps between fibers. Moreover, the presence of glassy phases originating from the sintering additives and the difficulty in infiltrating matrix particles into the fine voids between fibers are still challenges. Therefore, attempts have been made to combine different techniques to enhance the degree of matrix slurry infiltration for the fabrication of dense SiCf/SiC [71, 72]. On the other hand, EPD-based technique is relatively a new method for slurry infiltration into a tightly woven structure. A modified process originating from EPD, termed electrophoretic particle infiltration (EPI), has been used to infiltrate ceramic particles into the fibrous preforms [73]. Several studies have reported the EPD-based techniques to fabricate SiCf/SiC composites because of the lower manufacturing cost and shorter processing time compared to the other methods [50, 74-79]. The feasibility of DC-EPD for fabricating a dense SiCf/SiC was evaluated by Lee et al. [79], where 9 types of ethanol-based slurries with different powder contents, binder resin amounts and slurry pH were deposited on the SiC fabrics by EPD at 135 V for 10 minute to determine the optimal conditions. The deposition electrode was determined by the zeta potential of the β-SiC particles and sintering additives, whereby the acidic slurry pH was chosen for homogeneous deposition due to the positive zeta potentials for all constituents. The prepared SiCf/SiC composites showed the highest density and flexural strength of 94% and 342 MPa, respectively. In another study [77], the effectiveness of DC-EPD combined with ultrasonication was demonstrated for the infiltration of an nm-sized SiCbased matrix phase into the fine voids of a SiC preform to fabricate a dense SiCf/SiC. The zeta potential and viscosity of the suspension were controlled to achieve a uniform and simultaneous deposition of all constituents. EPD was performed under a 10 V DC electric field for 30 minute after adjusting the suspension pH to 3, in which the zeta potentials for all constituents were ≥ + 40mV. The matrix suspension composed of SiC, Al2O3-Y2O3-MgO as a sintering additive, and ethanol as a solvent,


24


was infiltrated into the preform with/without the application of ultrasonic pulses. Novak et al. [74] demonstrated the effectiveness of the electrophoretic infiltration of particles into the SiC fabrics for the production of SiCf/SiC, where they explained the influence of surface charge on the EPD of SiC powder in an aqueous suspension by adding different types of surfactants. SiCf/SiC was also manufactured using EPD followed by polymer infiltration and pyrolysis technique by Ivekovic et al. [71]. For this purpose, aqueous suspensions with a solids content of up to 60 wt. % were prepared from β-SiC powder having the particle size of 0.5 µm after adding tetramethylammonium hydroxide as a dispersant. The EPD was performed in a Teflon cell with graphite electrodes, which were separated at a distance of 2 cm, with an applied voltage of 30V for 10 minute. A cellulose membrane was placed in front of the anode to prevent the porosity caused by bubble formation at the electrode due to the electrolysis of water. In our previous study [50], an aqueous AC-EPD was used to infiltrate a SiC-based matrix phase containing Al2O3–Sc2O3 sintering aids into the fine voids of a two-dimensionally woven SiC fabric preform for the fabrication of a dense SiCf/SiC. The density higher than 94% along with a flexural strength of 413.9 ± 18.5 MPa was achieved due to the high degree of matrix phase infiltration. 40

(a)

Zeta potential (mV)

20 0 -20 -40 -60 -80 2

4

6

8

10

pH

Figure 15. (a) Zeta potential behavior and (b) SEM images for TiO2.



25

Addition of sintering additives is generally needed to increase the density of SiCf/SiC because of the high covalent bonding nature and low self-diffusivity of SiC. Most sintering additives enhance the densification of SiC by a liquid phase sintering mechanism, where Al2O3 and Sc2O3 have been considered frequently to achieve high density SiCf/SiC at relatively lower temperatures based on thermodynamic calculations and experimental observations [50, 80]. Commercial -SiC (Dm = 52 nm, > 97.5% pure, 4620KE, NanoAmor Inc., USA), Al2O3 (99.9% pure, Baikowski, Japan), Sc2O3 (99.9% pure, Alfa Aesar, USA) and two-dimensionally woven TyrannoTM-SA Grade-3 SiC fabrics (Ube Industries LTD., Japan) were used to fabricate SiCf/SiC. The fabrics had a 0/90o plain woven structure containing 1,600 filaments per yarn. Fine SiC powder containing 7 or 12 wt. % of eutectic Al2O3– Sc2O3 sintering additives was used as the matrix phase for the planar and tubular SiCf/SiC fabrication. Coarse Al2O3 and Sc2O3 were high-energy milled (MiniCer, Netzch, Germany) for 3 hour using 0.8 mm ZrO2 beads at 3000 rpm, where a mean particle size of 100 nm was obtained. To prepare slurry composed of β-SiC and Al2O3–Sc2O3 particles for matrix phase infiltration, 0.5 wt. % ammonium polycarboxylate dispersant and 0.5 wt. % WB4101 water-soluble acrylic binder were added. After preparing a stable aqueous suspension, AC-EPD was performed using a dual electrode system for a disc-shaped SiC preform. Optimal parameters, such as squareshaped asymmetric waveform with an asymmetry factor of 4, peak-to-peak voltage of 20 V, 100 Hz were used for AC-EPD. Selected deposition times were 30 and 60 minute for planar and tubular SiCf/SiC fabrication, respectively. Ultrasonic pulses of 10 W with a 1 second cycle were applied using a probe-type ultrasonicator (HD 2070, Bandelin, Germany) for the first 20 and 50 minute for planar and tubular structures, respectively, to minimize the surface sealing effect. After drying the infiltrated fabrics overnight, 20 layers of fabrics were stacked and laminated uniaxially under a pressure of 10 MPa to prepare a planar SiCf/SiC. After performing a binder burn-out at 350°C for 2 hour, hot pressing was carried out at 1750°C for 1 hour in an Ar atmosphere under a pressure of 20 MPa.


26


Figure 16. SEM image of the SiC fabric after infiltration of matrix phase into the fine voids of fabric by AC-EPD.

For the fabrication of tubular SiCf/SiC composite, a preform with a diameter of 20 mm and height of 35 mm was prepared by wrapping the SiC fabric 12 times on a graphite rod. The preform was located at the center of the Teflon chamber with a stainless steel inner wall for EPD, which was filled with slurry. The cylindrical stainless steel wall and graphite rod were connected to the AC source to infiltrate the matrix particles into the SiC fabric preform. The distance between the stainless steel wall and the preform was 25 mm. At the same time, a 30 μm-thick green tape composed of SiC and 12 wt. % of Al2O3–Sc2O3 sintering additive was prepared using a tape casting method. More details about the apparatus are given elsewhere [81]. The tubular preform infiltrated with the matrix phase along with green tape insertion between the preform layers was exposed to binder burn-out. Hot pressing was carried out at 1750°C for 2 hour under a pressure of 20 MPa using an out → in type graphite mold [81]. As two-dimensionally woven SiC fabrics have large inter-bundle voids and small intra-bundle gaps between each fiber, fine β-SiC particles would be essential to enhance the degree of matrix phase infiltration. One important barrier to be overcome for the fabrication of highly dense SiCf/SiC associated with matrix phase infiltration is ‘surface sealing,’



27

which is a preferential deposition of the matrix phase at the surface without penetrating into the deep voids during EPD. If surface sealing occurs, many unfilled voids will exist in the SiC fabric preform, resulting in a low composite density. Ultrasonic pulses can minimize this surface sealing by releasing the preferentially surface-adsorbed particles and enhancing infiltration into the deep voids of the preform during the EPD process. This study adopted a dual electrode system [50], which was also expected to enhance the degree of infiltration compared to the widely used single electrode system due to deposition from both sides. Homogeneous and thick infiltration of matrix slurry into the fine voids of SiC fabric can be achieved after EPD, as shown in Figure 16. Figure 17 (a) and (b) shows the corresponding digital images for planar SiCf/SiC, while 17 (c) shows the tubular SiCf/SiC after hot pressing, revealing a perfect cylindrical shape. Figure 18 (a) – (d) show SEM images of the hot-pressed tubular SiCf/SiC composites, which reveal a highly consolidated SiCf/SiC surface morphology, indicating the efficient infiltration of SiC and Al2O3-Sc2O3 particles by EPD combined with ultrasonication. The microstructure shown in Figure 18 is composed of the fiber-rich and matrix-rich region, where the fiber-rich region is the SiC fabric preform infiltrated with SiC particles with the sintering additive, while the matrix-rich region is formed mainly by the inserted green tape. Because large voids were not filled with the matrix phase, green tape was inserted between the preform layers, which can enhance the density of the composite by filling the voids during sintering. The fiber-rich region shown in Figure 18 (c) reveals the presence of small inter-fiber pores. On the other hand, the matrix-rich region in Figure 18 (d) shows a dense morphology without the presence of pores. Even though the top, middle and bottom parts were observed using SEM, all showed the similar microstructural behavior, while the final tubular sample revealed gas tightness because of the high density of 94.8%.


28


Figure 17. Digital camera images for (a), (b) planar and (c) tubular-shaped SiCf/SiC composites fabricated by infiltration using an AC-EPD and hot pressing.

Figure 18. SEM images of the hot-pressed tubular SiCf/SiC composites.

CONCLUSION This chapter reported the effectiveness of AC-EPD for the deposition and infiltration of various ceramic nanoparticles in an aqueous suspension.



29

After preparing well-dispersed nanoparticle suspensions in water by considering both electrostatic and steric stabilization mechanisms, homogeneous thick films could be deposited using AC asymmetric signals. Thick films with a more uniform surface morphology could be acquired by AC-EPD because of the suppressed water electrolysis and effective particle packing by a vibrating deposition mechanism under an AC signal compared to those with DC-EPD. Microstructural studies showed that the frequency of AC signal has a pronounced impact on the surface of deposited films and 100 Hz was selected as the optimal frequency for the deposition and infiltration of most nanoparticles. Microscopic images revealed that the AC-EPD combined with ultrasonic pulses was quite effective in infiltrating the matrix phase, containing SiC particles and sintering additives, into the 2-dimesionally woven SiC fabrics for the fabrication of dense planar and tubular SiCf/SiC composites. Overall, ecofriend AC-EPD in aqueous suspensions can be used to fabricate SiCf/SiC composites instead of organic solvents, which is economically viable from an industrial point of view.

REFERENCES [1]

[2] [3]

[4]

Boccaccini, A. R. & Zhitomirsky, I. (2002). Application of electrophoretic and electrolytic deposition techniques in ceramics processing. Curr. Opin. Solid State Mater. Sci., 6, 251-260. Zhitomirsky, I. (2006). Electrophoretic deposition of organic– inorganic nanocomposites. J. Mater. Sci., 41, 8186-8195. Boccaccini, A. R., Roether, J. A., Thomas, B. J. C., Shaffer, M. S. P., Chavez, E., Stoll, E. & Minay, E. J. (2006). The electrophoretic deposition of inorganic nanoscaled materials. J. Ceram. Soc. Japan., 114, 1-14. Besra, L. & Liu, M. (2007). A review on fundamentals and applications of electrophoretic deposition (EPD). Prog. Mater. Sci., 52, 1-61.


30 [5]

[6]

[7]

[8]

[9]

[10]

[11] [12]

[13]

[14]

Kati Raju and Dang-Hyok Yoon Corni, I., Ryan, M. P. & Boccaccini, A. R. (2008). Electrophoretic deposition: from traditional ceramics to nanotechnology. J. Eur. Ceram. Soc., 28, 1353-1367. Seuss, S., Chavez, A., Yoshioka, T., Stein, J. & Boccaccini, A. R. (2012). Electrophoretic deposition of soft coatings for orthopedic applications. Ceram. Trans., 237, 145-152. Yoshioka, T., Chávez-Valdez, A., Roether, J. A., Schubert, D. W. & Boccaccini, A. R. (2013). AC electrophoretic deposition of organic– inorganic composite coatings. J. Colloid Interface Sci., 392, 167-171. Chen, Q., Cordero-Arias, L., Roether, J. A., Cabanas-Polo, S., Virtanen, S. & Boccaccini, A. R. (2013). Alginate/Bioglass® composite coatings on stainless steel deposited by direct current and alternating current electrophoretic deposition. Surf. Coatings Technol., 233, 49-56. Neirinck, B., Van Mellaert, L., Fransaer, J., Van der Biest, O., Anné, J. & Vleugels, J. (2009). Electrophoretic deposition of bacterial cells. Electrochem. Commun., 11, 1842-1845. Boccaccini, A. R., Peters, C., Roether, J. A., Eifler, D., Misra, S. K. & Minay, E. J. (2006). Electrophoretic deposition of polyetheretherketone (PEEK) and PEEK/Bioglass® coatings on NiTi shape memory alloy wires. J. Mater. Sci., 41, 8152-8159. Simchi, A., Pishbin, F. & Boccaccini, A. R. (2009). Electrophoretic deposition of chitosan. Mater. Lett. 63, 2253-2256. Lessing, P. A., Erickson, A. W. & Kunerth, D. C. (2000). Electrophoretic deposition [EPD] applied to reaction joining of silicon carbide and silicon nitride ceramics. J. Mater. Sci., 35, 29132925. Lifshitz, E., Dag, I., Litvin, I., Hodes, G., Gorer, S., Reisfeld, R., Zelner, M. & Minti, H. (1998). Optical properties of CdSe nanoparticle films prepared by chemical deposition and sol–gel methods. Chem. Phys. Lett., 288, 188-196. Meier, L. P., Urech, L. & Gauckler, L. J. (2004). Tape casting of nanocrystalline ceria gadolinia powder. J. Eur. Ceram. Soc., 24, 3753-3758.



31

[15] Cross, C. E., Hemminger, J. C. & Penne, R. M. (2007). Physical vapor deposition of one-dimensional nanoparticle arrays on graphite: seeding the electrodeposition of gold nanowires. Langmuir, 23, 10372-10379. [16] Lyu, S. C., Zhang, Y., Lee, C. J., Ruh, H. & Lee, H. J. (2003). Lowtemperature growth of ZnO nanowire array by a simple physical vapor-deposition method. Chem. Mater., 15, 3294-3299. [17] Dikovska, A. O., Alexandrov, M. T., Atanasova, G. B., Tsankov, N. T. & Stefanov, P. K. (2013). Silver nanoparticles produced by PLD in vacuum: role of the laser wavelength used. Appl. Phys. A, 113, 8388. [18] Horikawa, T., Mikami, N., Makita, T., Tanimura, J., Kataoka, M., Sato, K. & Nunoshita, M. (1993). Dielectric properties of (Ba,Sr)TiO3 thin films deposited by RF sputtering. Jpn. J. Appl. Phys., 32, 4126-4130. [19] Okumura, M., Nakamura, S., Tsubota, S., Nakamura, T. & Azuma, M. (1998). Haruta, M., Chemical vapor deposition of gold on Al2O3, SiO2, and TiO2 for the oxidation of CO and of H2. Catal. Lett., 51, 53-58. [20] Bailey, R. C., Stevenson, K. J. & Hupp, J. T. (2000). Assembly of micropatterned colloidal gold thin films via microtransfer molding and electrophoretic deposition. Adv. Mater., 12, 1930-1934. [21] Xiong, X., Makaram, P., Busnaina, A., Bakhtari, K., Somu, S., McGruer, N. & Park, J. (2006). Large scale directed assembly of nanoparticles using nanotrench templates. Appl. Phys. Lett., 89, 193108. [22] Zhang, Q., Xu, T., Butterfield, D., Misner, M. J., Ryu, D. Y., Emrick, T. & Russell, T. P., (2005). Controlled placement of CdSe nanoparticles in diblock copolymer templates by electrophoretic deposition. Nano Lett., 5, 357-361. [23] Zhu, G., Yang, W., Lv, W., He, J., Wen, K., Huo, W., Hu, J., Waqas, M., Dickerson, J. H. & He, W. (2017) Facile electrophoretic deposition of functionalized Bi2O3 nanoparticles, Mater. Des., 116, 359-364.


32


[24] Das, D., Bagchi, B. & Basu, R. N. (2017). Nanostructured zirconia thin film fabricated by electrophoretic deposition technique. J. Alloys Compd., 693, 1220-1230. [25] Hasanpoor, M., Aliofkhazraein, M. & Delavari, H. H. (2016). In-situ study of mass and current density for electrophoretic deposition of zinc oxide nanoparticles. Ceram. Int., 42, 6906-6913. [26] Cabanas-Polo, S. & Boccaccini, A. R. (2016). Electrophoretic deposition of nanoscale TiO2: technology and applications. J. Eur. Ceram. Soc., 36, 265-283. [27] Song, G., Xu, G., Quan, Y., Yuan, Q. & Davies, P. A. (2016). Uniform design for the optimization of Al2O3 nanofilms produced by electrophoretic deposition. Surf. Coat. Tech., 286, 268-278. [28] Raju, K. & Yoon, D. H. (2013). Electrophoretic deposition of BaTiO3 in an aqueous suspension using asymmetric alternating current. Mater. Lett., 110, 188-190. [29] Raju, K., Yu, H. W. & Yoon, D. H. (2014). Aqueous electrophoretic deposition of SiC using asymmetric AC electric fields. Ceram. Int., 40, 12609-12612. [30] Bouyer, F. & Foissy, A. (1999). Electrophoretic deposition of silicon carbide. J. Am. Ceram. Soc., 82, 2001-2010. [31] Mendoza, C., González, Z., Castroa, Y., Gordo, E. & Ferrari, B. (2016). Improvement of TiN nanoparticles EPD inducing steric stabilization in non-aqueous suspensions. J. Eur. Ceram. Soc., 36, 307-317. [32] Sarkar, P. & Nicholson, P. S. (1996). Eletrophoretic deposition (EPD): mechanism, kinetics, and application to ceramic. J. Am. Ceram. Soc., 79, 1987–2002. [33] Zhitomirsky, I. (2002). Cathodic electrodeposition of ceramic and organoceramic materials: Fundamentals aspects. Adv. Colloid Interface Sci., 97, 279-317. [34] Ferrari, B. & Moreno, R. (2010). EPD kinetics: a review. J. Eur. Ceram. Soc., 30, 1069-1078. [35] Dickerson, J. H. Boccaccini, A. R. (Eds.) (2012). Electrophoretic Deposition of Nanomaterials, Springer, London.



33

[36] Ammam, M. (2012). Electrophoretic deposition under modulated electric fields: a review. RSC Adv., 2, 7633-7646. [37] Chávez-Valdez, A. & Boccaccini, A. R. (2012). Innovations in electrophoretic deposition: alternating current and pulsed direct current methods. Electrochim. Acta, 65, 70-89. [38] Nold, A. & Clasen, R. (2010). Bubble-free electrophoretic shaping from aqueous suspension with micro point-electrode. J. Eur. Ceram. Soc., 30, 2971–2975. [39] Neirinck, B., Fransaer, J., Vander Biest, O. & Vleugels, Jef. (2009). Aqueous electrophoretic deposition in asymmetric AC electric fields (AC–EPD). Electrochem. Commun., 11, 57-60. [40] Tang, F., Uchikoshi, T., Ozawa, K. & Sakka, Y. (2006). Effect of polyethylenimine on the dispersion and electrophoretic deposition of nano-sized titania aqueous suspensions. J. Eur. Ceram. Soc., 26, 1555-1560. [41] Chávez-Valdez, A., Herrmann, M. & Boccaccini, A. R. (2012). Alternating current electrophoretic deposition (EPD) of TiO2nanoparticles in aqueous suspensions. J. Colloid Interface Sci., 375, 102-105. [42] Dukhin, A. S. & Dukhin, S. S. (2005). Aperiodic capillary electrophoresis method using an alternating current electric field for separation of macromolecules. Electrophoresis, 26, 2149-2153. [43] Novak, S., Mejak, K. & Drazic, G. (2006). The preparation of LPS SiC-fibre-reinforced SiC ceramics using electrophoretic deposition. J. Mater. Sci., 41, 8093-8100. [44] Novak, S., Ivekovic, A. & Hattori, Y. (2014). Production of bulk SiC parts by electrophoretic deposition from concentrated aqueous suspension. Adv. Appl. Ceram., 113, 14-21. [45] Jean, J. H. (1995). Electrophoretic deposition of A12O3-SiC composite. Mater. Chem. Phys., 40, 285-290. [46] Askaria, E., Mehralib, M., Metselaara, I. H. S. C., Kadri, N. A. & Rahman, Md. M. (2012). Fabrication and mechanical properties of Al2O3/SiC/ZrO2 functionally graded material by electrophoretic deposition. J. Mech. Behav. Biomed. Mater., 12, 144-150.


34


[47] You, C., Jiang, D. & Tan, S. (2004). Deposition of silicon carbide/titanium carbide laminar ceramics by electrophoresis and densification by spark plasma sintering. J. Am. Ceram. Soc., 87, 759761. [48] Sun, J. & Gao, L. (2001). Dispersing SiC powder and improving its rheological behavior. J. Eur. Ceram. Soc., 21, 2447-2451. [49] Singh, B. P., Jena, J., Besra, L. & Bhattacharjee, S. (2007). Dispersion of nano-silicon carbide (SiC) powder in aqueous suspensions. J. Nanopart. Res. 9, 797-806. [50] Raju, K., Yu, H. W., Park, J. Y. & Yoon, D. H. (2015). Fabrication of SiCf/SiC composites by alternating current electrophoretic deposition (AC–EPD) and hot pressing. J. Eur. Ceram. Soc., 35, 503-511. [51] Lee, S. K., Ryu, S. S. & Yoon, D. H. (2007). Synthesis of fine Cadoped BaTiO3 powders by solid-state reaction method-Part II: Rheological study on milling. J. Electroceram., 18, 1-7. [52] Modi, S., Wei, M., Mead, J. L. & Barry, C. M. F. (2011). Effect of processing parameters on the electrophoretic deposition of carbon black nanoparticles in moderately viscous systems. Langmuir, 27, 3166-3173. [53] Jeun, J. H., Kim, W. S. & Hong, S. H. (2013). Electrophoretic deposition of carbon nanoparticles on dendritic Sn foams fabricated by electrodeposition. Mater. Lett., 112, 109-112. [54] Park, J. H. & Park, J. M. (2014). Electrophoretic deposition of graphene oxide on mild carbon steel for anti-corrosion application. Surf. Coat. Tech., 254, 167-174. [55] Ghasemi, S., Hosseini, S. R. & Mousavi, F. (2017). Electrophoretic deposition of graphene nanosheets: a suitable method for fabrication of silver-graphene counter electrode for dye-sensitized solar cell. Colloid. Surf. A: Physicochem. Eng. Aspects, 520, 477-487. [56] Dzepina, B., Sigalas, I., Herrmann, M. & Nilen, R. (2013). The aqueous electrophoretic deposition (EPD) of diamond–diamond laminates. Int. J. Refract. Met. Hard Mater., 36, 126-129.



35

[57] Negishi, H. (2016). Uniform and ultra low-power electrophoretic deposition of silica powder using a nonflammable organic solvent. J. Eur. Ceram. Soc., 36, 285-290. [58] Gardeshzadeh, A. R., Raissi, B. & Marzbanrad, E. (2008). Preparation of Si powder thick films by low frequency alternating electrophoretic deposition. J. Mater. Sci., 43, 2507-2508. [59] Erogbogbo, F., Lin, T., Tucciarone, P. M., LaJoie, K. M., Lai, L., Patki, G. D., Prasad, P. N. & Swihart, M. T. (2013). On-demand hydrogen generation using nanosilicon: splitting water without light, heat, or electricity. Nano Lett., 13, 451-456. [60] Stoll, E., Mahr, P., Kruger, H. G., Kern, H., Thomas, B. J. C. & Boccaccini, A. R. (2006). Fabrication technologies for oxide–oxide ceramic matrix composites based on electrophoretic deposition. J. Eur. Ceram. Soc., 26, 1567-1576. [61] Wu, Y. J., Li, J., Tanaka, H. & Kuwabara, M. (2005). Preparation of nano-structured BaTiO3 thin film by electrophoretic deposition and its characterization. J. Eur. Ceram. Soc., 25, 2041-2044. [62] Wang, J. Q. & Kuwabara, M. (2008). Electrophoretic deposition of BaTiO3 films on a Si substrate coated with conducting polyaniline layers. J. Eur. Ceram. Soc., 28, 101-108. [63] Vriami, D., Beaugnon, E., Cool, P., Vleugels, J. & Vander Biest, O. (2015). Hydrothermally synthesized BaTiO3 textured in a strong magnetic field. Ceram. Int., 41, 5397-5402. [64] Bacha, E., Renoud, R., Terrisse, H., Borderon, C., Plouet, M. R., Gundel, H. & Brohan, L. (2014). Electrophoretic deposition of BaTiO3 thin films from stable colloidal aqueous solutions. J. Eur. Ceram. Soc., 34, 2239-2247. [65] Zhao, J., Wang, X. & Li, L. (2006). Electrophoretic deposition of BaTiO3 films from aqueous suspensions. Mater. Chem. Phys., 99, 350-353. [66] Esmaeilzadeh, J., Ghashghaie, S., Dehkordi, B. R. & Riahifar, R. (2013). Role of the electric field affected zone (EFAZ) on the electrophoretic deposition of TiO2 nanoparticles under symmetric low-frequency AC electric fields. J. Phys. Chem. B, 117, 1660-1663.


36


[67] Yamada, R., Taguchi, T. & Igawa, N. (2000). Mechanical and thermal properties of 2D and 3D SiC/SiC composites. J. Nucl. Mater., 283-287, 574-578. [68] Ortona, A., Donato, A., Filacchioni, G., Angelis, U. D., Barbera, A. L., Nannetti, C. L., Riccardi, B. & Yeatman, J. (2000). SiC–SiCf CMC manufacturing by hybrid CVI–PIP techniques: process optimization. Fusion Eng. Des., 51-52, 159-163. [69] Katoh, Y., Dong, S. M. & Kohyama, A. (2002). Thermo-mechanical properties and microstructure of silicon carbide composites fabricated by nano-infiltrated transient eutectoid process. Fusion Eng. Des., 61-62, 723-731. [70] Taguchi, T., Igawa, N., Yamada, R. & Jitsukawa, S. (2005). Effect of thick SiC interphase layers on microstructure, mechanical and thermal properties of reaction-bonded SiC/SiC composites. J. Phys. Chem. Solids, 66, 576-580. [71] Ivekovic, A., Drazic, G. & Novak, S. (2011). Densification of a SiCmatrix by electrophoretic deposition and polymer infiltration and pyrolysis process. J. Eur. Ceram. Soc., 31, 833-840. [72] Yonathan, P., Lee, J. H., Yoon, D. H., Kim, W. J. & Park, J. Y. (2009). Improvement of SiCf/SiC density by slurry infiltration and tape stacking. Mater. Res. Bull., 44, 2116-2122. [73] Streckert, H. H., Norton, K. P., Katz, J. D. & Freim, J. O. (1997). Microwave densification of electrophoretically infiltrated silicon carbide composite. J. Mater. Sci. 32, 6429-6433. [74] Novak, S., Rade, K., Konig, K. & Boccaccini, A. R. (2008). Electrophoretic deposition in the production of SiC/SiC composites for fusion reactor applications. J. Eur. Ceram. Soc., 28, 2801-2807. [75] Yoshida, K., Matsukawa, K., Imai, M. & Yano, T. (2009). Formation of carbon coating on SiC fiber for two-dimensional SiCf/SiC composites by electrophoretic deposition. Mat. Sci. Eng. B, 161, 188192. [76] Yoshida, K., Matsukawa, K. & Yano, T. (2009). Microstructure and mechanical properties of silicon carbide fiber-reinforced silicon



[77]

[78]

[79]

[80] [81]

37

carbide composite fabricated by electrophoretic deposition and hotpressing. J. Nucl. Mater., 386-388, 643-646. Gil, G. Y. & Yoon, D. H. (2011). Densification of SiCf/SiC composites by electrophoretic infiltration combined with ultrasonication. J. Ceram. Process. Res., 12, 371-375. Park, J. Y., Jeong, M. H. & Kim, W. J. (2013). Characterization of slurry infiltrated SiCf/SiC prepared by electrophoretic deposition. J. Nucl. Mater., 442, S390-S393. Lee, J. H., Gil, G. Y. & Yoon, D. H. (2009). Fabrication of SiCf/SiC composites using an electrophoretic deposition. J. Kor. Ceram. Soc., 46, 447-451. Raju, K. & Yoon, D. H. (2016). Sintering additives for SiC based on the reactivity: A review. Ceram. Int., 42, 17947-17962. Yu, H. W., Fitriani, P., Lee, S. H., Park, J. Y. & Yoon, D. H. (2015). Fabrication of the tube-shaped SiCf/SiC by hot pressing. Ceram. Int., 41, 7890-7896.

BIOGRAPHICAL SKETCHES Dr. Kati Raju Affiliation: Yeungnam University Education: PhD Business Address: #310, Materials building, Gyeongsan, South Korea Research and Professional Experience: 10 years Publications from the Last 3 Years: 22 Dr. Kati Raju is a research professor at the School of Materials Science and Engineering, Yeungnam University, South Korea. He received his


38


Ph.D. in 2012 from Osmania University, India. His research interests include AC-and DC-EPD of nanomaterials, fabrication of SiCf/SiC composites and reactive air brazing for metal-ceramic joining. His Ph.D. included significant studies at Osmania University in the synthesis and magneto-transport studies of magnetic materials. He holds a patent and has authored or co-authored 31 international peer-reviewed publications on different materials. He may be reached at [email protected].

Dang-Hyok Yoon Affiliation: Yeungnam University Education: PhD Business Address: #404, Materials building, Gyeongsan, South Korea Research and Professional Experience: 20 years Publications from the Last 3 Years: 18 Professor Dang-Hyok Yoon is a Head of The School of Materials Science and Engineering at Yeungnam University, South Korea. He studied at KAIST, POSTECH and Clemson University (USA) for his undergraduate, master and PhD, respectively, majoring in ceramics. He worked for Samsung for 10 years as a senior researcher, working on MLCC and 6-Sigma methodology for industrial innovation as a Master Black-belt, before joining Yeungnam University in 2005. Prof. Yoon has published more than 100 publications in peer-reviewed journals. His research interests are in ceramic processing, including slurry preparation, dispersion, tape-casting, electrophoretic deposition, joining and composite fabrication. His recent research focuses on the SiCf/SiC fabrication using both of DC- and AC-EPD combined with hot pressing for high temperature applications. He may be reached at [email protected].



Chapter 2

SNO2-THICK FILMS OBTAINED BY ELECTROPHORETIC DEPOSITION AND THEIR TECHNOLOGICAL APPLICATIONS Glauco M. M. M. Lustosa1,2,, Guilhermina F. Teixeira1, João Paulo C. Costa1, Carla Y. Kisen2, Leinig A. Perazolli1,2 and Maria A. Zaghete1 1

Laboratory of Interdisciplinar Electrochemistry and Ceramics - Chemistry Institute of Araraquara, UNESP, Araraquara/Brazil 2 Laboratory of Microwave Sintering and Photocatalysis - Chemistry Institute of Araraquara, UNESP, Araraquara/Brazil

ABSTRACT The study of materials prepared as films unfolds a new generation of devices paving the way towards the development of new technologies. This ongoing progress in the study of materials clearly brings relevant advantages to the fore. Among such advantages includes the possibility of 

Corresponding Author Email: [email protected].


40

G. M. M. M. Lustosa, G. F. Teixeira, J. Paulo C. Costa et al. developing smaller and lighter materials, which help to improve their integration with technology. Among the deposition techniques for obtaining films, the Electrophoretic Deposition (EPD) method has attracted considerable attention owing to the possibility it provides for controlling film thickness by uniform deposition in a fast and less costly manner. The EPD method has been efficient in the production of SnO 2 films with thickness controlled according to deposition time. SnO 2 is categorized as an n-type semiconductor with electrical conductivity related to excess electrons and structural defects. SnO2 band gap (around 3.6 eV) facilitates the electron excitation from the valence band (VB) to the conduction band (CB). This behavior enables the application of SnO2 as either photocatalysts, sensors, biosensors, varistors and solar cells in addition to its use for corrosion protection. Tin dioxide (SnO2) exhibits high thermal and mechanical stability besides showing electrical resistance behavior which is highly dependent on chemical composition and thermal treatment temperature. Our objective here is to explain the chemical synthesis via the Polymeric Precursor Method aimed at obtaining SnO2 nanoparticles used for thick films deposition by EPD. The films’ characterizations show that they present a satisfactory response, rendering them suitable for application as varistors, gas sensors and photocatalysts.

Keywords: tin dioxide, chemical synthesis, electrophoretic deposition, microwave sintering.

INTRODUCTION Tin dioxide is categorized as a semiconductor and presents intermediary electronic conduction between the conductors and insulating compounds. To be characterized as semiconductor, the material needs to show a forbidden energy region (Egap or Eg, band gap) between the valence band and the conduction band in the gap ranging from 1 eV to 5 eV (Viana Junior, 2014). SnO2 is one of the most widely employed semiconductors. It exhibits a rutile-type crystalline structure (Figure 1) with tetragonal unit cell and lattice parameters a = b = 0.473 nm and c = 0.318 nm which were experimentally determined by Yamanaka (Yamanaka, 2000) based on X-ray Diffraction technique (XRD).


SnO2-Thick Films Obtained by Electrophoretic Deposition …

41

Figure 1. SnO2 unit cell. (Winter, 2016).

The band gap of tin dioxide is 3.60 eV (Ahmed, 2011), and this enables its applicability in several areas as a result of its electronic and optical properties in the nanostructured form. The addition of dopants changes SnO2 band gap, leading to alteration of the electrical properties, and thus allowing its use as varistors (Glot et al., 2015; Lu et al., 2012; Lustosa et al., 2015; Maleki Shahraki et al., 2015), gas sensors (Brunet et al., 2012; He et al., 2012; Yang et al., 2017), batteries (Wang, Y., 2006; Wang, Z. et al., 2011), photocatalysts (Guan et al., 2013; Rashad et al., 2014), solar cells (El-Etre et al., 2010; Senevirathna et al., 2007), among others. The electron conduction in SnO2 occurs as a result of the presence of intrinsic defects such as oxygen vacancy, interstitial Sn atoms and other defects related to the addition of dopants in the oxide structure that act as electron acceptors or donors (Leite et al., 2010), as shown by Equations 1 and 2, where Kröger and Vink notations are used: 𝑆𝑛𝑂2

𝑆𝑛𝑂 →

𝑆𝑛𝑂2

𝑆𝑛𝑂2 →

′′ 𝑆𝑛𝑆𝑛 + 𝑉𝑂•• + 𝑂𝑂𝑋 ′′′′ 𝑆𝑛𝑖•••• + 𝑉𝑆𝑛 + 2𝑂𝑂𝑋


(1) (2)

42

G. M. M. M. Lustosa, G. F. Teixeira, J. Paulo C. Costa et al.

SnO2 doping can be carried out via the synthesis step and through the use of elements that have either excess electrons (generating an electron donating energy level ED– n-type doping) or elements with less electrons (in this case generating holes in an energy acceptor level of E A electrons – p-type doping). The defects generated through the dopants introduction into SnO2 lattice change the Fermi Energy level in the electron structure (Viana Junior, 2014). Numerous studies have been published in the literature regarding SnO2 with several different doping elements with different morphologies (nanoparticles, nanobelts, nanorods, etc.) processed with thin or thick films, bulk and nanoparticles. In this chapter, we will discuss about the functionalization of SnO2 thick films prepared by electrophoretic deposition.

SYNTHESIS AND DEPOSITION OF SNO2 PARTICLES Apart from the use of SnO2-commercial particles for use in photocatalysis studies, we also carried out the synthesis of tin dioxide doped with 1% of cobalt and 0.05% of niobium by the Polymeric Precursors Method (Lustosa et al., 2016; Stojanovic et al., 2001) for application as varistor and gas sensor. In the polymeric precursor method, metallic cations are complexed or chelated by hydroxycarboxylic acid in an aqueous solution at 90-100°C. The solution is mixed with ethylene glycol and heated at around 130°C aiming at promoting polymerization and water evaporation. Thermal treatment at higher temperatures helps to eliminate the excess of organic components in addition to promoting cation oxidation and producing the oxide stoichiometric phase of interest. This method homogeneously disperses the metallic ions and immobilizes them in a rigid polymeric network at atomic scale, avoiding precipitation and phase segregation (Leite et al., 1995; Qiu et al., 2007; Teixeira et al. 2017). Figure 2 shows the polymeric precursor method mechanism.



43

Figure 2. Schematic depiction of the synthesis by the Polymeric Precursors Method. (By authors).

Through this method, one can obtain SnO2 nanoparticles (Figure 3a) with rutile crystalline phase (Figure 3b) based on the peaks of SnO2-rutile in JCDPS nº 41-1445 card (Figure 3a). The study of materials prepared as films leads to the development of a novel generation of devices which contributes towards the emergence of new technologies. A further advantage of this study lies in obtaining materials with relatively smaller size and being easily integrated with technological circuits. As a well-known fact, there is a wide range of deposition techniques employed for obtaining films. Some of these techniques that merit mentioning include sputtering, spray pyrolysis, spinor dip-coating, chemical vapor deposition and electrophoretic deposition (EPD). The EPD technique is recommended in nanoparticles processing as a result of the ease encountered with regard to films thickness control, which contributes towards promoting a uniform deposition in a short time with low cost of production. The material deposition on a substrate occurs through the application of electric tension of 2 kV during a defined period of time in a stable suspension containing nanoparticles. The EPD technique involves the use of a cell containing two electrodes (working electrode which contains the target substrate for deposition and the counter


44


electrode) in parallel immersed into the suspension (Corni et al., 2008; Bersa et al., 2007; Sarkar et al., 1996; Boccaccini et al., 2006) Figure 4 shows the system used for deposition of SnO2-particles by EPD. It indicates the movement of the particles according to the electrodes polarity through the application of an electric field. The particles in suspension migrate towards the working electrode where the substrate is placed, forming a dense and homogeneous film (Corni et al, 2008; Caproni et al., 2012).

Figure 3. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) of SnO2 powder doped with cobalt and niobium. (By authors).



45

Figure 4. Electrophoretic deposition system scheme. (By authors).

The EPD deposition mechanism requires that the particle possesses surface charge so as to be attracted by the current generated by the electric field applied in the system. This electric field is responsible for transporting the particles to the electrodes. The appearance of these charges leads to the formation of electric double layer on the particles surface, aiding in the solvent stability as well as in movement when the electric field is applied (Caproni et al., 2012; Zhitomirsky et al., 2001; Will, 2001). The EPD technique can be used towards the deposition of powders with particle size between1 μm and 0.001 μm suspended in organic or aqueous solution (Corni et al., 2008; Van der Biest et al., 1999). Organic solvents are relatively more employed as suspension medium for the particles. This is largely as a result of the fact that when water is used there is the risk of the occurrence of the electrolysis phenomenon which causes the release of hydrogen gaseous on the electrode surface, thereby interfering in the film characteristics such as thickness and density. Organic solvents promote better stability when it comes to forming the particle suspension as they are less polar and more viscous than water. Furthermore, the low conductivity of organic solvents minimizes the occurrence of Joule Heating promoted by the passage of current in the


46


system and the electrochemical attack on the electrodes (Matheus et al., 2000; Harbach et al., 1988). In the suspension prepared for the EPD, the surface charge of the particles interacts either with the solvent molecules or with the soluble ions (H+ and OH-), producing adsorbed electric charges (Zeta potential effect) which contribute towards the stabilization of the suspension and the deposition process (electrokinetic phenomenon) (Castro, 2004). When the total sum of the particles surface charges is almost zero (ZCP - the zero charge point or isoelectric point), the suspension becomes less stable as a result of the absence of charges that can cause formation of particles agglomerate besides increasing the suspension viscosity. The theoretical ZCP for SnO2 is 3.5. Above this pH, more adsorption of hydroxyl groups (OH-) occurs. In addition, with the proximity of the tin dioxide particles, there is the formation of a hydrogen bond between the hydroxyl groups, contributing towards the particles stabilization.

TECHNOLOGICAL APPLICATIONS OF SNO2 THICK FILM Photocatalysis Photocatalysis was developed in 1972 (Fujishima, 1972) with the aim of developing an efficient system for water treatment so as to ensure its reuse. Nowadays, this process has attracted great interest owing to the rise in water pollution coupled with the mismanagement of natural resources associated with industrial development and the little attention on the part of governments in addressing environmental issues. The photocatalysis process can be defined as a photoreaction caused by light energy absorption in a semiconductor material used as catalyst. This reaction accelerates the water reduction process in compounds with oxidation power to degrade organic compounds as in the scheme shown in Figure 5. In the photocatalysis mechanism, the energy absolved by a semiconductor leads to electron excitation from the valence band (VB) to the conduction band (CB). This electron transfer generates a hole in the



47

VB and a free electron in the CB, giving rise to the oxidation and reduction processes known as electron-hole pair (e-/h+). This process promotes chemical reactions that degrade the water molecules in hydroxyl and superoxide radicals. These radicals present high reduction-oxidation potential which enables them to react with organic compounds adsorbed on the semiconductor surface (Konstantinou et al., 2004; Serpone, 1995; Ziolli et al., 1998).

Figure 5. Simple schematic representation of the electronic excitation in a semiconductor for application in photocatalysis. (By authors).

Nowadays, the immobilization of photocalytic particles onto substrate surface as films makes more practical the industrial applications of photocatalyst (Mill et al., 2003; Xianyu et al., 2001). In this case, the oxyreduction reactions occur on the film surface, and the efficiency of photocatalysis is dependent on surface area and film thickness, being that ticker films present more photocatalytic efficiency. This behavior is due to the large surface area presented by ticker films, since surface roughness increase as film thickness that may increase the number of active sites available to photocatalysis. Besides a higher concentration of electron-hole


48


pair is presents on ticker films. In addition, the diffusion process of some impurities from substrate to surface of film is more difficult to happen for ticker films, avoiding negative impacts on photocatalytic activity (Xianyu et al., 2001). TiO2-based materials are the most used on photocatalysis applications, however other oxides such as ZnO (Moore et al., 2014; Podporska-Carroll et al., 2015; Wang et al., 2016) and SnO2 (Saravanakumar et al., 2017; Stojadinović et al., 2017; Yang et al., 2017) also show great results about their photocatalytic activity, being that this last is our object of interest here. The investigation of SnO2 film photocatalytic property was conducted by the photo-discoloration of Rhodamine B aqueous solution. Our interest in studying the photo-discoloration of Rhodamine B was driven by the fact that it is frequently applied as dye in the textile industry and regarded one of the main compounds responsible for the contamination of water bodies. In the study presented here, SnO2 films were obtained by EPD (Figure 4) from 20 mg of powder obtained via the polymeric precursor method which were subsequently suspended in 20 mL of isopropyl alcohol. The film deposition was carried out through the application of 2 kV for 1 minute on a titanium metal substrate (size of 2x1 cm and thickness of 0.9 mm). The nanoparticles deposition was followed by thermal treatment at 450 °C/1 hour with the aim of increasing the adhesion of the deposited layer and the substrate. Through scanning electron microscopy (Figure 6), the film was found to present homogeneous thickness with 24.8 μm of size.

Figure 6. Cross-sectional view of the SnO2-thick film to be used as photocatalyst (By authors).



49

To carry out the photocatalysis, three SnO2 films were fixed and immersed into 700 mL of Rhodamine B aqueous solution with concentration of 1x10-5mol/L exposed to UV-C radiation with 11W germicidal lamp (with emission at 254 nm) keeping the system under constant agitation and aeration. The maximum period of exposure to ultraviolet radiation was 2 hours, with aliquot removal at predetermined times (0, 5, 10, 15, 30, 60, 90 and 120 minutes) in order to obtain and evaluate the absorption spectrum through UV-Vis spectroscopy and to verify the decay evolution of Rhodamine B main absorption peak (554 nm). The efficiency (%) of the solutions photo-discoloration was calculated by Equation 3 as follows: 𝐸𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑐𝑦 =

𝐴0 − 𝐴𝑡 𝐴0

𝑥 100

(3)

where A0 is the initial absorbance intensity of the main peak at time = 0 min, and At is the absorbance of the peak at the aliquot removal time. Figure 7 shows the absorbance decay evolution of the maximum absorption peak (554 nm) from the UV-vis spectrum of the solution exposed to ultraviolet radiation. Photolysis experiments (only with the use of UV-radiation) and photocatalysis with TiO2-thick film were carried out for the purpose of comparing the photocatalytic activity of tin dioxide, since titanium dioxide presents high efficiency as a photocatalyst. Based on the data obtained, it was possible to verify the efficiency of the systems with regard to photolysis. While photolysis showed almost 62% of photo-discoloration efficiency of Rhodamine B aqueous solution following 120 minutes of exposure to UV-radiation, the use of SnO2 and TiO2 presented efficiency of 91% and 93% respectively. These results imply that SnO2 thick film has similar potential to TiO2 for application as photocatalyst. The photocatalytic behavior of tin oxide films can be improved by doping SnO2 particles, promoting an increase in the electron trapping behavior delaying the recombination of electron-hole pairs due to the


50


modification of the band-gap because the presence of dopant (Ran et al., 2015). By studies about Ce-doped SnO2 Wu et al. verified that the dopant addition improved the photocatalytic activity. This behavior is related to the increase of SnO2 surface area due to the size particles decrease promoted by introduction of Ce (Wu et al., 2010). In addition, the higher surface area of the sample may influence the diffusion process between reactant molecules and active sities easier and improving the photodegradation (Shanmugam et al., 2016). There are several reports about doped-SnO2 particles, such as Zn-doped SnO2 (Shanmugam et al., 2016), Co-doped SnO2 (Entradas et al., 2014) and rare-earth doped SnO2 (AlHamdi et al. 2014). The polymeric precursor method may be adapted to synthesize these compounds to posteriorly film processing by EPD and apply as photocatalystic under the experimental showed here.

Figure 7. Graph of decreasing relative concentration of Rhodamine B aqueous solutions with photocatalyst and exposed to ultraviolet radiation for 120 minutes (By authors).



51

Varistor A varistor is an electronic device responsible for protecting the electronic equipment when voltage surges do not occur in an electric power system (Pianaro et al., 1998). In an electrical system operation, when voltage spikes occur, the varistor can store the excess voltage inside the semiconductor grains and dissipates it as heat, thus protecting the system where it is applied. Tin dioxide-based varistors were first reported by Pianaro (Pianaro et al., 1995). They were introduced as alternative to ZnO commercial varistors due to similarities in their non-linear electrical characteristics. In addition, SnO2 presents a simpler microstructure avoiding the formation of secondary phases and requiring a smaller amount of dopants to improve the varistor property. The varistors have non-linear relationship between the voltage vs electric current. In other words, they do not vary constantly as determined by Ohm's Law, this is referred to as non-ohmic behavior. The electric conduction in SnO2 varistors is of the thermionic type, i.e., it is influenced by temperature and characterized as a Schottky-type conduction model (Felix et al., 2011), where the electrical conduction occurs through the potential barrier formed in the grain boundary region. The coefficient of nonlinearity (α) is regarded an important parameter in the quality of a varistor device and it is determined by the curve profile after electrical characterization. It can be calculated according to Equation 4, where J is current density and E stands for electrical field (Feng et al., 2011; He et al., 2012; Ma et al., 2015; Zang, G-Z et al., 2016). α=

𝐿𝑜𝑔𝐽2 − 𝐿𝑜𝑔𝐽1 𝑙𝑜𝑔𝐸2 − 𝑙𝑜𝑔𝐸1

(4)

The nominal voltage of a varistor is proportional to the number of barriers. The electric field of rupture (ER) is equivalent to the field when the current density is 1 mA/cm² while the leakage current (IF) is equivalent to the current when the voltage is 70% of the ER. The potential barrier is


52


formed by the dopants and depends on the amount and type of defect induced by the dopants in the grain boundary region. For the calculation of α, the current density range of 1 to 10 mA / cm² is adopted, where J1 = 1 and J2 = 10 are obtained. Thus, Equation 5 is simplified in the following equation: 𝛼 = (𝑙𝑜𝑔𝐸2 − 𝑙𝑜𝑔𝐸1 )−1

(5)

The deposition of the SnO2-based nanoparticles to be applied as varistors is similar to the procedure involving the obtaining of the photocatalytic film. The sample was prepared by EPD through the application of 2 kV for 40 seconds. The film obtained with equal or higher deposition times presented particles accumulation forming very clear deposit “islands”. In other words, they had quite irregular thickness and surface. Following deposition, the samples were thermally treated by microwave heating at 900 °C for 30 minutes aiming at promoting the sintering process. Through the use of SEM (Figure 8), one can observe a regular surface with thickness of around 78.8 µm, and average grain size ranging from 105.8 nm. It is worth pointing out that sintering is undoubtedly an important process in experimental procedures in that it promotes the densification of the material. During the sintering process, several steps take place. One of such steps involves the increase in grain size which leads to pore reduction by the formation of particles among the grains (which is referred to as grain boundary). Several mechanisms are involved in these steps. Some of the mechanisms found to be present include mass diffusion (within and on the surface of the grain), evaporation and condensation in the region between the grains in addition to superficial mass redistribution. The use of microwave in the sintering process is a relatively recent technology that has advantages over conventional sintering largely because it is a fast heating method. Sintering by microwave is seen to promote a more even grain diffusion and growth, since the heating occurs in a more uniform manner throughout the interior of the material resulting in substantial reduction of energy costs (Pereira et al., 2003; Menezes et al., 2007; Santos et al., 2006).



53

Figure 8. SEM of (a) surface and (b) cross-sectional of SnO2-based film electrophoretically deposited using 2 kV for 40 seconds and sintered at 900 °C/30 minutes in a microwave oven, for varistor application. (By authors).

After the sintering step, the films were modified through the deposition of chromium ions via EPD (application of 2 kV/3 minutes). The deposition was followed by drying at 100 °C and subsequent heat treatment in a microwave oven at 900 °C/15 minutes aiming at the diffusion of chromium. In this case, the addition of chromium acts directly in the grain boundary region as an electron acceptor leading to an increase in resistivity. The increase in resistivity is attributed to the generation of defects on the nanoparticles surface which contributes towards improving the potential barrier formed in the region. The films electrical properties were evaluated by Voltage vs Current measurements (Figure 9) which provide information about Current Density vs Electric Field. Based on these results, it was possible to calculate parameters such as nonlinearity coefficient (α), electric field (ER), rupture voltage (VR) and leakage current (IF).


54


Figure 9. Current Density vs. Electric Field (J vs E) for SnO2-based thick film electrophoretically deposited using 2 kV for 40 seconds. (By authors).

According to Figure 9, one can observe that the film shows characteristic curve of a varistor system, exhibiting an initial resistivity behavior of up to ~26 kV (breakdown electric field) where a rise in current is observed thereafter, thus characterizing the conductivity behavior of the SnO2-based thick film. From Equation 5, the nonlinear coefficient (α) was found to be 7.2. The rupture voltage was equivalent to ~205 Volts, and it is directly related to the thickness of the sample, which implies a higher amount of potential barriers that block the transport of electric current through the sample. In cases of low voltage applications (as seen in automotive components), the film preparation may be carried out with a relatively lower thickness. In addition to that, it is possible to use a solution with a lower concentration of chromium ions. One can also make use of a lower heat treatment in order to reduce the chromium ions diffusion in the grain boundary, since it is one of the most important factors that provide resistivity in the region.



55

Gas Sensor Gas sensors are used for controlling the emission of pollutants into the atmosphere and are widely used in both laboratories and industries, places that need rapid detection due to the possibility of small leaks that can lead to accidents. At first, the sensors were developed for the detection of explosive gases in the 1920s (Pandeeswari et al., 2016). With the advancement of technology and improved knowledge in chemistry, several types of sensors have been studied according to the detection mechanism. Some of the most studied sensors worth mentioning include infrared, electrochemical, catalytic and semiconductor sensors (Lee, E. et al. 2011; Lee, M. et al., 2007; Pradhan et al., 2008). The semiconductor-based sensor consists of a substrate with a pair of interdigital electrodes that increase the film area and a semiconductor metal oxide layered on the interdigital electrodes, as shown in Figure 10. The interdigital electrodes improve the analysis and/or gas detection by an in-situ heating (known as self-heating).

Figure 10. (a) Front-to-back image of the sensor with the electrodes and the (b) tin dioxide electrophoretic deposited on device (By authors).


56


A number of research studies have been conducted regarding tin dioxide-based semiconductor gas sensor. The considerable attraction drawn by this semiconductor gas sensor lies in its thermal and chemical stability when subjected to different atmosphere (Miller et al., 2006; Salehi, 2003; Suman et al., 2015; Wu et al. 2010; Yang et al., 2017; Zhan et al., 2013). The electrical behavior of these different nanostructured morphologies coupled with the possibility of introducing different dopants in SnO2 structures improve the sensorial behavior. This behavior is based on surface reactions that alter the electrical characteristics (resistance or impedance) of the semiconductor grains, thus indicating the presence of gas in the analysis atmosphere (Gasparetti, 2007; Suman et al., 2015; Weber et al., 2000). The sensitive principle occurs through the chemical interaction between the adsorbed gas and the semiconductor, leading to modification of the electron density in grain-grain region, changing the potential barrier formed in the junction (Uddin et al., 2015). When the sensor is exposed to an atmosphere rich in O2, the oxygen molecules are absorbed by the sensor surface capturing the free electrons (from the oxygen vacancy) from the conduction band and increasing the potential barrier formed in the grain boundary region while reducing the electronic conduction. This adsorbed oxygen can react with another gas leading to the electrons release while reducing the potential barrier and increasing the sensors conductivity. The electronic mobility is also favored by the use of high temperatures (Gasparetti, 2007; Uddin et al., 2015). To prepare the SnO2-based films, 12 mg of iodine was added to the solution used in the electrophoretic deposition system with the aim of increasing the surface charge of the particles, thus leading to an increase in the deposition rate. 2 kV was applied for 1 minute followed by heat treatment in a microwave oven at 500 °C for 10 minutes. As shown in Figure 11, the deposited film was found to be thicker and exhibited porosity, a typical characteristic that should influence the sensorial response once porosity leads to an increase in superficial area which tends to promote greater interaction of the grain with the gas present for analysis, thereby generating the gas sensor response.



57

Figure 11. SEM of SnO2-film surface electrophoretically deposited for 1 minute on alumina substrate and heat treated at 500 °C/10 minutes in a microwave oven for gas sensor application. Different magnifications. (By authors).

The SnO2-based film deposited on alumina substrate was electrically characterized by exposure to carbon monoxide gas for 5 minutes in varying concentrations at 300 °C. DC voltage of 1 V was applied and monitoring of the changes in film resistance was conducted using voltage source (Keithley, model 6487). Initially, the characterization was carried out at 10 ppm and was then gradually increased to 20, 40 and finally 100 ppm, performing a cleaning step of the film surface via the use of synthetic air flow for 30 minutes in the analysis chamber in-between analyses. The gas sensor property was evaluated according to its electrical response in different gas concentrations (Figure 12). The approximate conductance


58


sensor, both in air (GAir) and for gas (GGas), and the sensitivity of the response (S) can be expressed by Eq. 6 to 8. 𝐺𝐴𝑖𝑟 = 𝐺0 exp(𝑒𝑉𝐴𝑖𝑟 ⁄𝐾𝑇)

(6)

𝐺𝐺𝑎𝑠 = 𝐺0 exp(𝑒𝑉𝐺𝑎𝑠 ⁄𝐾𝑇)

(7)

𝑆 = 𝐺𝐺𝑎𝑠 ⁄𝐺𝐴𝑖𝑟

(8)

Figure 12. Graph of the gas sensor response using SnO2-based film characterized with carbon monoxide gas in different concentrations and at 300 °C. Film deposited by applying 2 kV/1 minute. (By authors).

As observed in the SnO2-based film, in the presence of carbon monoxide gas, the O- species adsorbed on the film surface interact with the gaseous particles (oxidation process) leading to the release of electrons from the surface. This causes in a decline in the film resistance as a result of the modification of the potential barrier between the grains. The gas sensor response, determined by the relationship between the resistance values in the presence of both synthetic air and the analyzed gas (RAir/RGas), is found to increase with an increase in the concentration of the



59

analyzed gas. According to the data, the responses obtained were 1.2, 1.4, 1.5 and 1.8 respectively for the concentrations of 10, 20, 40 and 100 ppm. These results are in agreement with the reports published in the literature. Saheli et al., (2003) reported the results of their investigation regarding the chemical synthesis of SnO2 and the obtaining of the film by chemical vapor deposition which showed a response of 2.1 (RAir/RGas) when analyzed at 150 °C in a self-heating system with 1000 ppm as the concentration of CO gas. While this result merits great consideration in its own right and especially by virtue of its similarity with our work, one should note that it was obtained from higher concentration and using a voltage of 50 V. In the work reported by Li et al., (2015), the films obtained from SnO2 particles (synthesized by hydrothermal method followed by tape casting deposition) showed a response of 1.5 for the analysis conducted at 300 °C with CO gas at the concentration of 500 ppm. It is worth noting that the concentration in their report is 5 times higher when compared to the sensor response presented by the film obtained in our work.

CONCLUSION The EPD method is considerably effective for the preparation of SnO2 thick films. This material has shown to be suitably efficient for application in photocatalysis, varistors and gas sensoring systems. In photocatalysis, SnO2 thick films showed 91% efficiency in Rhodamine B degradation. This behavior was similar to that of TiO2 films, which is known to be one of the most widely employed in photocatalyst application. Furthermore, the surface modification of SnO2 using chromium ions improves the varistor property by increasing the resistivity. Finally, the efficiency of SnO2 films as gas sensors was found to increase with the increase in gas concentrations in the analysis chamber. As it has been clearly demonstrated here, the EPD process can produce efficient SnO2-based materials with multifunctional applications.


60


ACKNOWLEDGMENTS The author is thankful to the coauthors for their invaluable dedication and collaboration in this project. We would like to express our deepest gratitude and indebtedness to the LMA-IQ for providing the FEG-SEM facilities and to the Brazilian research funding agencies CAPES, CNPq, CEPID/CDMF 2013/07296-2 and FAPESP 2014/11314-9 for the financial support granted in the course of this project.

REFERENCES Ahmed, A. S., Shafeeq, M. M., Singla M. L., Tabassum S., Naqvia, A. H., Azam, A., (2011). Band gap narrowing and fluorescence properties of nickel doped SnO2 nanoparticles. J. Lumin. 131, 1-6. Al-Hamdi, A. M., Sillanp, M., Dutta, J., (2014). Photocatalytic degradation of phenol in aqueous solution by rare earth-doped SnO nanoparticles. J. Mater. Sci., 49, 5151-5159. Bersa, L., Liu, M., (2007). A review on fundamentals and applications of electrophoretic deposition (EPD). Prog. Mater. Sci. 52, 1-61. Boccaccini, A. R., Roether, J.A., Thomas, B.J.C., Chaves, M.S.P.E., Shaffer, E. S., Minay, E.J. (2006). The electrophoretic deposition of inorganic nanoscaled materials. J. Ceram. Soc. Jpn. 114, 1-14. Brunet, E., Maier, T., Mutinati, G. C., Steinhauer, S., Köck, A., Gspan, C., Grogger, W., (2012). Comparison of the gas sensing performance of SnO2 thin film and SnO2 nanowire sensors. Sensor Actuat. B-Chem. 165, 110-118. Caproni, E., Muccillo, R., (2012). Application of the electrophoretic deposition technique for obtaining yttria-stabilized zirconia tubes. Cerâmica 58, 131-136. Castro, R. H. R., Murad, B. B. S., Gouvêa, D., (2004). Influence of the acid–basic character of oxide surfaces in dispersants effectiveness, Ceram. Int. 30, 2215-2221.



61

Corni, I., Ryan, M. P., Boccaccini, A. R., (2008). Electrophoretic deposition: from traditional ceramics to nanotechnology. J. Eur. Ceram. Soc. 28, 1353-1367. El-Etre, A. Y., Reda, S. M., (2010). Characterization of nanocrystalline SnO2 thin film fabricated by electrodeposition method for dyesensitized solar cell application. Appl. Surf. Sci. 256, 6601-6606. Entradas, T., Cabrita, J. F., Dalui, S., Nunes, M. R., Monteiro, O.C. Silvestre, A. J, (2014). Synthesis of sub-5 nm Co-doped SnO2 nanoparticles and their structural, microstructural, optical and photocatalytic properties. Materials Chemistry and Physics, 147, 563571. Felix, A. A., Orlandi, M. O., Varela, J. A., (2011). Schottky-type grain boundaries in CCTO ceramics. Solid State Commun. 151,1377-1381. Feng, H., Peng, Z., Fu, X., Fu, Z., Wang, C., Qui, L., Wao, H., (2011). Effect of SnO2 doping on microstructural and electrical properties of ZnO-Pr6O11 based varistor ceramics. J. Alloys Compd. 509, 7175-7180. Fujishima, A., Honda, K., (1972). Electrochemical photolysis of water at a semiconductor electrode. Nature 238, 37-38. Gasparetti, A. C., (2007). Gas sensor of tin dioxide. Integração 48, 67-70. Glot, A. B., Bulpett, R., Ivon, A. I., Gallegos-Acevedo, P. M., (2015). Electrical properties of SnO2 ceramics for low voltage varistors. Physica B. 457, 108-112. Guan, M., Zhao, X., Duan, L., Cao, M., Guo, W., Liu, J., Zhang, W., (2013). Controlled synthesis of SnO2 nanostructures with different morphologies and the influence on photocatalysis properties. J. Appl. Phys., 114, 114302/01-114302/07. Harbach, F., Nienburg, H., (1998). Homogeneous functional ceramic components through electrophoretic deposition from stable colloidal suspensions ~I. Basic concepts and application to zirconia. J. Eur. Ceram. Soc. 8, 675-683. He, J., Peng, Z., Fu, Z., Fu, X., (2012). Effect of ZnO doping on microstructural and electrical properties of SnO2-Ta2O5 based varistors. J. Alloys Compd. 528, 79-83.


62


Konstantinou, I. K., Albanis, T. A., (2004). TiO2-assisted photocatalytic degradation of azo dyes in aqueous solution: kinetic and mechanistic investigations: a review. Appl. Catal. B-Environ. 49, 1-14. Lee, E. B., Hwang, I. S., Cha, J. H., Lee, H. J., Pak, J. J., Lee, J. H., Ju, B.K., (2011). Micromachined catalytic combustible hydrogen gas sensor. Sensor Actuat. B-Chem. 153, 392-397. Lee, M. S., Sohn, J., Shim, J., Lee, W. M., (2007). Miniaturized electrochemical methanol sensor without gas diffusion backings. Sensor Actuat. B-Chem. 124, 323-328. Leite, D. R., Cilense, M., Orlandi, M. O., Bueno, P. R., Longo, E., Varela, J. A., (2010). The effect of TiO2 on the microstructural and electrical properties of low voltage varistor based on (Sn,Ti)O2 ceramics. Physica Status Solidi A 207, 457-461. Leite, E. R., Sousa, C. M. G., Longo, E., Varela, J.A., (1995). Influence of polymerization on the synthesis of SrTiO3: Part I. Characteristics of the polymeric precursors and their thermal decomposition. Ceramics International 21, 143-152. Li, C., Lv, M., Zuo, J., Huang, X., (2015). SnO2 highly sensitive CO gas sensor based on quasi-molecular-imprinting mechanism design. Sensors 15, 3789-3800. Lu, Z. Y., Glot, A. B., Ivon, A. I., Zhou, Z. Y., (2012). Electrical properties of new tin dioxide varistor ceramics at high currents. J. Eur. Ceram. Soc. 32, 3801-3807. Lustosa, G. M. M. M., Costa, J. P. C., Perazolli, L. A., Stojanovic, B. D., Zaghete, M.A., (2015). Electrophoretic deposition of (Zn, Nb)SnO2films varistor superficially modified with Cr3+. J. Eur. Ceram. Soc. 35, 2083-2089. Lustosa, G. M. M. M., Costa, J. P. C., Perazolli, L. A., Stojanovic, B. D., Zaghete, M.A., (2016). Potential barrier of (Zn,Nb)SnO2-films induced by microwave thermal diffusion of Cr3+ for low-voltage varistor. J. Am. Ceram. Soc. 99, 152-157. Ma, S., Xu, Z., Chu, R., Hao, J., Li, W., Cheng, L., Li, G., (2015). Influence of SnO2 on ZnO-Bi2O3-Co2O3 based varistor ceramics. Ceram. Int. 41, 12490-12494.



63

Maleki Shahraki, M., Bahrevara, M. A., Mirghafourian, S. M. S., Glot, A.B., (2015). Novel SnO2 ceramic surge absorbers for low voltage applications. Mater. Lett. 145, 355-358. Matheus, T., Rabu, N., Sellar J. R., Muddle, B. C., (2000). Fabrication of La1-xSrxGa1-yMgyO3-(x+y)/2 thin films by electrophoretic deposition and its conductivity measurements. Solid State Ionics 128, 111-115. Menezes, R. R., Souto, P. M., Kiminami, G. A., (2007). Sintering of ceramics in microwave oven: Part I: fundamentals aspects. Cerâmica 53, 1-10. Miller, T. A., Bakrania, S. D., Perez, C., Wooldridge, M. S., (2006). Nanostructured tin dioxide materials for gas sensor applications. Funct. Nanomater. 1, 1-24. Mills, A., Hill, G., Bhopal, S., Parkin, I. P., OŃeil, S. A., (2003). Thick titanium dioxide films for semiconductor photocatalysis. J. Photochem. Photobio. A. 160, 185-194. Moore, J. C., Louder, R., Thompson, C. V., (2014). Photocatalytic activity and stability of porous polycrystalline ZnO thin-films grown via a twostep thermal oxidation process. Coatings 4,651-669. Podporska-Carroll, J., Myles, A., Quilty, B., McCormack, D. E., Fagan, R., Hinder, S. J., Dionysiou, D. D., Pillai, S. C., (2015). Antibacterial properties of F-doped ZnO visible light photocatalyst. J. Hazard. Mater. 324, 39-47. Pandeeswari, R., Jeyaprakash, B. G., (2016). Vapour sensing property of metal oxide thin films at ambient condition: influencing factors: a review. Res. J. Pharmac. Biol. Chem. Sci. 7, 1221-1231. Pereira, G. J., Gouvêa, D., (2003). Densificação rápida de cerâmicas de SnO2. Cerâmica, 49: 116-119. [Fast densification of SnO2 ceramic. Ceramic, 49: 116-119]. Pianaro, S. A., Bueno, P. R., Olivi, P. Longo, E., Varela, J. A., (1998). Electrical properties of the SnO2-based varistor. J. Mater. Sci.- Mater. El. 9, 159-165. Pradhan, B., Setyowati, K., Liu, H., Waldeck, D. H., Chen, J., (2008). Carbon nanotube-polymer nanocomposite infrared sensor. Nano Letters 8, 1142-1146.


64


Qiu,S., Fan, H., Zheng, X., (2007). Pb(Zr0.95Ti0.05)O3 powders synthesized by Pechini method: Effect of molecular weight of polyester on the phase and morphology. Journal of Sol-Gel Science and Technology. 42, 21-26. Ran, L., Zhao, D., Gao, X., Yin, L., (2015). Highly crystalline Ti-doped SnO2 hollow structured photocatalyst with enhanced photocatalytic activity for degradation of organic dyes. CrystEngComm 17, 42254237. Rashad, M. M., Ismail, A. A., Osama, I., Ibrahim, I.A., Kandil, A. H. T., (2014). Photocatalytic decomposition of dyes using ZnO doped SnO2 nanoparticles prepared by solvothermal method. Arab. J. Chem. 7, 7177. Salehi, A., (2003). A highly sensitive self heated SnO2 carbon monoxide sensor. Sensor Actuat. B-Chem. 96, 88-93. Santos, P. A., Maruchin, S., Menegoto, G. F., Zara, A. J., Pianaro, S. A., (2006). The sintering time influence on the electrical and microstructural characteristics of SnO2 varistor. Mater. Lett., 60, 15541557. Saravanakumar, K., Muthuraj, V., (2017). Fabrication of sphere like plasmonic Ag/SnO2 photocatalyst for the degradation of phenol. Optik - Int. J. Light Electron Opt. 131, 754-763. Sarkar, P., Nicholson, P. S., (1996). Electrophoretic deposition (EPD): mechanism, kinetics and application to ceramics. J. Am. Ceram. Soc. 79, 1987-2002. Shanmugam, N., Sathya, T., Viruthagiri, G., Kalynasundaram, C., Gobi, R., Ragupathy, S., (2016). Photocatalytic degradation of brilliant green using undoped and Zn doped SnO2 nanoparticles under sunlight irradiation. Appl. Surf. Sci. 360, 283-290. Senevirathna, M. K. I., Pitigala, P. K. D. D. P., Premalal, E. V. A., Tennakone, K., Konno, A., (2007). Stability of the SnO2/MgO dyesensitized photoelectrochemical solar cell. Sol. Energ. Mat. Sol. C. 91, 544-547. Serpone, N., (1995). Brief introductory remarks on heterogeneous photocatalysis. Sol. Energ. Mat. Sol. C. 38, 369-379.



65

Stojanovic, B. D., Foschini, C. R., Cilense, M., Zaghete, M.A., Cavalheiro, A. A., Paiva-Santos, C.O., Varela, J. A., (2001). Structural characterization of organometallic-derived 9.5/65/35 PLZT ceramics. Mater. Chem. Phys. 68, 136-141. Stojadinović, S., Tadić, N., Radić, N., Grbić, B., Vasilić, R., (2017). TiO2/SnO2 photocatalyst formed by plasma electrolytic oxidation. Mater. Lett. 196, 292-295. Suman, P. H., Felix, A. A., Tuller, H. L., Varela, J. A., Orlandi, M. O., (2015). Comparative gas sensor response of SnO2, SnO and Sn3O4 nanobelts to NO2 and potential interferents. Sensor Actuat. B-Chem. 208, 122-127. Teixeira, G. F., Lustosa, G. M. M. M., Zanetti, S. M., Zaghete, M. A., (2017). Chemical Synthesis and Epitaxial Growth Methods for Preparation of Ferroelectric Ceramics and Thin Films. (In press). In: Magnetic, Ferroelectric and Multiferroic Metal Oxides, Elsevier, cap.6. Uddin, A. S. M. I, Phan, D. T., Chung, G. S., (2015). Low temperature acetylene gas sensor based on Ag nanoparticles-loaded ZnO-reduced graphene oxide hybrid. Sensor Actuat. B-Chem. 207, 362-369. Viana Junior, E. R, (2014). Propriedades elétricas e fotoelétricas de nanofitas de SnO2. Thesis, Universidade Federal de Minas Gerais UFMG. Wang, J., Xia, Y., Dong, Y., Chen, R., Xiang, L., Komaeneni, S., (2010). Defect-rich ZnO nanosheets of high surface area as an efficient visiblelight photocatalyst. Appl. Catal. B-Environ. 192, 8-16. Wang, L., Kank, Y., Liu, X., Zhang, S., Huang, W., Wang, S., (2012). ZnO nanorod gas sensor for ethanol detection. Sensor Actuat. B-Chem. 162, 237-243. Wang, Y., Zeng, H. C., Lee, J. Y., (2006). Highly reversible lithium storage in porous SnO2 nanotubes with coaxially grown carbon nanotube overlayers. Adv. Mater. 18, 645-649. Wang, Z., Luan, D., Boey, F. Y. C. and Lou, X. W., (2011). Fast formation of SnO2 nanoboxes with enhanced lithium storage capability. J. Am. Chem. Soc. 133, 4738-4741.


66


Weber, I. T., Andrade, R., Leite, E. R., Longo, E., (2001). Study of the SnO2-Nb2O5 system for an ethanol vapour sensor: a correlation between microstructure and sensor performance. Sensor Actuat. B-Chem. 72, 180-183. Will, J., Hrushka, M. K. M., Gubbler, L., Gauckler, L. J., (2001). Electrophoretic deposition of zirconia and porous anodic substrates. J. Am. Ceram. Soc. 84, 328-332. Wu, Q., Li, J., Sun, S., (2010). SnO2 gas sensors. Curr. Nanosc. 6, 525538. Xianyu, W. X., Park, M. K., Lee, W. I., (2001). Thickness Effect in the Photocatalytic Activity of TiO2 Thin Films Derived from Sol-Gel Process. Korean J. Chem. Eng. 907, 2-6. Yamanaka, T., Kurashima, R., Mimaki, J., (200). X-ray diffraction study of bond character of rutile-type SiO2, GeO2 and SnO2. Z. Kristallogr. 215, 424-428. Yang, J., Wang, S., Zhang, L., Dong, R., Zhu, Z., Gao, X., (2017). Zn2SnO4-doped SnO2 hollow spheres for phenylamine gas sensor application. Sensor Actuat. B-Chem. 239, 857-864. Yang, L., Huang, J., Shi, L., Cao, L., Zhou, W., Chang, K., Meng, X., Liu, G., Jie, Y., Ye, J., (2017). Efficient hydrogen evolution over Sb doped SnO2 photocatalyst sensitized by Eosin Y under visible light irradiation. Nano Energy 36, 331-340. Zang, G.-Z., Wang, X. F., Li, L. B., Zhou, F. Z., (2016). Varistor and dielectric properties of SiO2 doped SnO2-Zn2SnO4 ceramic composites. Ceram. Int. 42,18124-18127. Zhan, S., Li, D., Liang, S., Chen, X., Li, X., (2013). A novel flexible room temperature ethanol gas sensor based on SnO2 doped polydiallyldimethylammonium chloride. Sensors 13, 4378-4389. Zhitomirsky, I., Petric, A., (2001). The electrodeposition of ceramic and organoceramic films for fuel cells. J. Min. Met. Mat. S. 53, 48-50. Ziolli, R. L., Jardim, W. F., (1998). Mecanismo de fotodegradação de compostos orgânicos catalisada por TiO2. Quimica Nova 21, 319-325.



Chapter 3

SYNTHESIS AND CHARACTERISTICS OF SILICA-COATED CARBON NANOFIBERS ON C-FIBER TEXTILES BY ELECTROPHORETIC DEPOSITION Chang-Seop Lee1,* and Yura Hyun2 1

Department of Chemistry, Keimyung University, Daegu, Republic of Korea 2 Department of Pharmaceutical Engineering, International University of Korea, Jinju, Republic of Korea

ABSTRACT The electrophoretic deposition (EPD) technique, with its wide range of novel applications in the processing of advanced ceramic materials and coatings, has recently experienced an increased level of interest from both the academic and industrial sectors. This results, not only from its considerable versatility of use with different materials and their combinations, but because of its cost-effectiveness and the simplicity of required apparatus. Electrophoretic deposition (EPD) is one of the major *

Corresponding Author: [email protected].


68

Chang-Seop Lee and Yura Hyun colloidal processes in ceramic production, and has the advantages of short formation time, simple apparatus requirements, minimal restrictions on the shape of substrate, and no requirements for binder burnout, as the green coating contains few or no organic materials. In this study, nickel (Ni) and copper (Cu) catalysts were deposited onto C-fiber textiles by the electrophoretic deposition method. Carbon nanofibers (CNFs) were synthesized by chemical vapor deposition (CVD) to Co-Ni electroplated onto C-fiber textiles, and were coated with silica on the surface through the hydrolysis of tetraethyl orthosilicate (TEOS). In the second case, CNFs were synthesized by thermal CVD to Co-Ni electroplated onto Cfiber textiles. The spherical silica particles were coated to the surface of CNFs by hydrolysis of TEOS and were reduced to silicon by hydrogen gas (H2). The electrochemical characteristics of the silica/CNFs composite were investigated, and then these materials were applied as anode materials in lithium (Li) secondary batteries. Compared to other advanced shaping techniques, the EPD process is very versatile since it can be modified easily for specific applications. For example, deposition can be made on flat, cylindrical, or any other shaped substrate with only minor modifications in electrode design and positioning. Despite being a wet process, EPD offers easy control of the thickness and morphology of a deposited film through simple adjustments to the deposition time and the applied potential.

Keywords: transition metals, electrophoretic deposition, chemical vapor deposition, carbon nanofibers, silica

1. INTRODUCTION Carbon nanofibers (CNFs) refers to a class of materials characterized by fibers that are 1㎛ or narrower in diameter and contain more than 90% carbon content. CNF can be fabricated using several methods, including electrospinning, CVD, and laser ablation [1-5]. Fully grown carbon nanofiber is bonded and hybridized, either with sp, sp2, or sp3, depending on the requirement for specific characteristics, such as advanced heat resistance, chemical stability, electrical conductivity, mechanical strength, and large specific surface area. Carbon nanofibers also have flexibility and super elasticity, making it one of the most suitable materials for developing electrodes, catalysts, sensors, and electromagnetic wave-shielding


Synthesis and Characteristics of Silica-Coated Carbon …

69

materials. Carbon nanofiber is also appropriate for application to advanced materials such as electrodes used in secondary batteries or fuel cells used in the life sciences [6-15]. While carbon-series material is preferred for use in the anodes of lithium secondary batteries, they limit the maximum charging capacity to 372 mAh/g because only one lithium ion can reversibly be intercalated/ deintercalated per six carbon atoms. Silicon can improve such limitations, due to its theoretical capacity of 4,000 mAh/g, which is more than ten times that of the carbon-series materials [16-27]. The crystal structure of silicon optimizes the intercalation/deintercalation of the lithium ion by lowering the electrical conductivity and. creating a 300%-expansion in volume allowing the intercalation/deintercalation of the lithium ion to hinder the reversible cycling. Numerous researchers are searching for methods to stabilize the anode structures without an expansion in volume, by utilizing the potential of the nano-granulation of silicon, silicon-metallic alloys, silicon-nonmetallic alloys, and silicon-carbon composites [27-32]. In this study, EPD was used to deposit the transition metal catalyst onto the C-fiber textiles, followed by the CVD method to facilitate the growth of the carbon nanofibers on the C-fiber textiles. The CVD method takes advantage of ethylene gas as a carbon source. Tetraethyl orthosilicate (TEOS) was hydrolyzed to coat the surface of the carbon nanofibers with silicon dioxide (SiO2), synthesizing the SiO2/CNF composite. The physicochemical and electrochemical properties were then analyzed.

2. SYNTHESIS AND CHARACTERISTICS OF SILICA-COATED CNFS ON ELECTROPLATED NI-CU/C-FIBER TEXTILES [33] 2.1. Deposition of Ni-Cu Catalysts on C-Fiber Textiles Ni and Cu catalysts were deposited onto C-fiber textiles using the electrophoretic deposition method. A schematic diagram of the


Chang-Seop Lee and Yura Hyun

70

experimental apparatus is demonstrated in Figure 1. In this method, a carbon electrode was used as an anode and the C-fiber textiles were treated as the cathode, with a distance of 85 mm between each electrode. Three experimental conditions were considered in depositing the catalyst onto the C-fiber textiles. (1) Ni was deposited onto the C-fiber textiles with a nickel (II) acetate tetrahydrate aqueous solution (Ni). (2) Ni and Cu were deposited onto the C-fiber textiles with a mixed solution of nickel (II) acetate tetrahydrate and copper (II) acetate monohydrate (NiCu). (3) Cu was pre-deposited onto the C-fiber textiles and Ni was subsequently deposited onto the C-fiber textile in a nickel (II) acetate tetrahydrate aqueous solution (Ni/Cu).

Figure 1. Synthesis and Electrochemical Properties of Carbon nanofibers and SiO2/Carbon nanofiber composite on Ni-Cu/C-fiber textiles.

2.2. Reduction A reduction step was applied. This was done in order to convert the metal oxides that were on the surface of C-fiber textiles into elemental



71

nickel and copper using a tube furnace. Hydrogen mixed with nitrogen gas was used for the reduction process, and the flux of the reaction gas was controlled by a Mass Flow Controller (MFC). The reactor temperature was raised at the rate of 12 °C/min, until it reached 700 °C, with only pure nitrogen gas flowing while the temperature was raised. Once the temperature reached 700 °C, nitrogen gas mixed with 20% hydrogen gas flowed into the reactor. This reduction process was carried out over a period of two hours.

2.3. Growth of CNFs Carbon nanofibers were grown on C-fiber textiles by CVD, in a horizontal quartz tube reaction apparatus, following completion of the reduction process. The reaction apparatus was manufactured as a metal heating element, and a horizontal quartz reaction tube of 80 mm (diameter) x 1400 mm (length) was divided into 3 zones, to achieve a uniform temperature profile. The flux of the reaction gas was controlled by an electronic MFC; ethylene gas (C2H4) was used to grow the carbon nanofibers as a carbon source; and hydrogen was used to eliminate the remaining hydroxyl group after the reduction process, while nitrogen was used to stabilize the reaction. A prepared metal catalyst was evenly spread on a quartz boat, which was then placed into the reactor under a nitrogen atmosphere, and the reactor temperature was raised at 12 °C/min. Once the temperature reached 700 °C, this temperature was maintained for thirty minutes; nitrogen gas and 20% hydrogen (N2 balance) gas were flowed together into the reactor. For a period of three hours, the hydrogen (N2 balance) gas and 20% ethylene (N2 balance) gas were flowed together into the reactor. The flow of ethylene and hydrogen gases was cut off after the reaction completed; then, nitrogen, under an inactive reactor atmosphere, was passed through the reactor to cool it to room temperature.



72

2.4. Oxidation and SiO2 Coating on Carbon Nanofibers A hydroxyl group was introduced as an anchor for the SiO2 -coating on the surface of carbon nanofibers. The hydroxyl group was oxidized for 30minutes in 80℃-nitric acid and rinsed with distilled water. The synthesis of the SiO2-coated carbon nanofibers involved dissolving TEOS in ethyl alcohol, followed by dispersion of the carbon nanofibers grown onto Cfiber textiles in the solution and adding ammonia water for a period of twenty-four hour at 50 ℃.

2.5. Electrochemical Measurements For the SiO2 -coating on the surface of carbon nanofibers, the hydroxyl group was introduced as an anchor group. This was done by having the hydroxyl group oxidized for half an hour in 80 ℃-nitric acid and rinsed by distilled water. Then, for synthesis of a composite that was SiO2 -coated carbon nanofibers, TEOS was dissolved in ethyl alcohol, followed by dispersion of carbon nanofibers grown onto C-fiber textiles in this solution and addition of ammonia water for a twenty-four hour reaction at 50 ℃.

(a)

(b)

(c)

Figure 2. SEM images of CNFs grown on the catalysts Ni (a), Ni-Cu (b), and Ni/Cu (c) on C-fiber textiles.



73

Figure 3. Raman spectra of CNFs grown under three different deposition conditions.

2.6. Analyses 2.6.1. SEM SEM images of CNFs grown with the Ni (a), the Ni-Cu (b), and the Ni/Cu (c) catalysts that were deposited onto C-fiber textiles are shown in Figure 2. As shown in Figure 2 (a), the Y-shaped CNFs were grown with an average diameter of 40 nm that was Ni-catalyst only, representing growth of carbon nanofiber branches that stem from a single origin. Meanwhile, in Figure 2 (b), another type of Y-shaped CNFs stemming from a single catalyst in various directions was shown. This figure is relevant to the size of catalysts created because of the differential in the average diameters. Further, in Figure 2 (c), the helically grown CNFs with a uniform diameter of 33 nm are shown. With Ni deposited onto the predeposited C-fiber textiles, no Y-shaped carbon nanofiber was observed in


74


Figure 2 (c), due to the tendency of the catalyst deposit and the introduction of Cu affecting the growth mechanism of CNFs.

(a)

(b)

(c)

(d)

Figure 4. TEM images of CNFs (a) and SiO2/CNFs composite (b, c, d).

2.6.2. Raman The results of the Raman analysis of the CNFs grown under the three conditions mentioned above, are shown in Figure 3. As shown in Figure 3, the D-band and the G-band appearing around 1,350 cm-1 and 1,590 cm-1 represent the disordered graphite and the ordered graphite structures,



75

respectively. Either impurities or a defective graphite structure gave rise to the sp3 hybridization and the D-band while the G-band signified the existence of graphitic CNFs comprised from sp2 hybridization. The increasing trend of D-band/G-band Intensity (D/G) signifies a higher content of impurities and structural defects reflected in the increasing Dband and the eventual low degree of CNFs crystallization. As shown in Figure 3, the G-band Intensity of (a) is lower than those of (b) and (c) (a) had a higher D/G ratio at 0.94 compared to 0.80 for (b) and 0.83 for (c), indicating a high crystallization level in CNFs grown under the conditions (b) and (c) because they were more graphitized than those grown under the condition (a). This also signifies that the co-catalyst Cu might contribute to the growth of CNFs with a higher crystallization degree.

2.6.3. TEM TEM images were analyzed in order to investigate the structure of SiO2-coated layer in the SiO2/CNFs composite after the growth of CNFs onto C-fiber textiles. These images are shown in Figure 4. Among the other conditions, the CNFs grown under the condition (c) was used for the preparation of SiO2/CNFs composite, taking advantage of its higher crystallization degree, as proven by the Raman analysis. As shown in Figure 4 (a), the TEM image of CNFs represents the multi-layer graphite forming wires with the central micro-hollow. As for the TEM images from the SiO2/CNFs composite (b, c, d), they represent the SiO2, from the output of TEOS-hydrolysis, that was uniformly coated onto the CNFs for layered structure. 2.6.4. XRD The XRD results of CNF (a) and SiO2/CNF composite (b) are shown in Figure 5. As represented in Figure 5(a), the XRD pattern of (a) shows the C-characteristic peak of CNFs and the peak of Ni that was deposited onto the C-fiber textiles. The XRD pattern of (b) shows the broad SiO2 peak and the C-peak of CNFs, excluding Ni. This signifies that the state of Ni was refined by the acid treatment of CNFs and that the amorphous SiO2 was coated onto the surface of the CNFs.


76


2.6.5. XPS The X-ray Photoelectron Spectroscopy (XPS) survey spectra confirmed the state of CNFs and SiO2-coated CNFsas shown in Figure 6. As shown in (a), The sp2 and sp3 structures of the carbon in CNFs, in (b), Si2p and O1s represents the SiO2-coating of the CNFs. A hyperfine spectrum of Si was measured to analyze the binding property of the Si-O in the coated layer (Figure 6). Figure 6, shows the Si2p Scan of the SiO2/CNFs composite with the Si2p A~D, that corresponds to SiO, SiO2, and SiOX, indicating that the coated surface comprises the siloxane network as shown in Table 1.

Figure 5. X-ray diffraction patterns of CNFs (a) and SiO2/CNFs composite (b).



77

Figure 6. XPS survey spectra of CNFs (a) and SiO2/CNFs composite (b).

Table 1. XPS results of the SiO2/CNFs composite Element

Component

Si

SiO2/CNF

Name Si2pScanA Si2pScanB Si2pScanC Si2pScanD

Binding energy 102.81 103.66 104.79 105.74

Chemical bonding SiOx

2.6.6. Cyclic Voltammetry The open circuit voltage of the SiO2/CNFs composite was about 2.6 V, with respect to Li/Li+. Cyclic voltammograms of the SiO2/CNFs composite electrode measured within a potential window of 0.1-2.6 V at a 1.0 mV/s sweep rate. This is shown in Figure 7. Reduction peaks appear at 0.5 V and 0.3 V, and the oxidation peak appears at 0.4 V during the cathodic and anodic sweep. A decrease in the reduction peak in subsequent cycles was mainly attributed to the irreversible generation of a solid electrolyte interface (SEI) on the surface of SiO2. An increase in the second oxidation peak at 0.4 V represents the reversible deintercalation of lithium from the


78


SiO2 matrix. It showed that the SiO2/CNFs composite electrode could accommodate Li+ ion as a host.

2.6.7. Galvanostatic Charge-Discharge The SiO2/CNFs composite was subjected to a repeated cycling test at a current density of 100 mA g−1 within a voltage window of 0.1−2.6 V, and, for comparison, the CNFs electrode was tested at the same condition. The cycling performances of the CNFs and the SiO2/CNFs composite electrodes for Li secondary batteries are shown in Figure 8. The early-stage discharge capacity of the CNFs electrode was 300 mAh/g which maintained a near-stable discharge capacity after thirty cycles. In the case of the SiO2/CNFs composite, a comparatively high discharge capacity of 2,053 mAh/g was observed in the second cycle, and the discharge capacity of the twenty-ninth cycle was significantly reduced to 1,295 mAh/g with 63% of the capacity retention as compared to that of the second cycle. This indicates that the discharge capacity of the CNFs electrode nearly reached its theoretical capacity (372 mAh/g) and exhibited no fading capacity. The SiO2/CNFs composite had a high discharge capacity of 2,053 mAh/g, but the cycle performance was not as good as that of the CNFs.

Figure 7. Cyclic voltammograms of SiO2/CNFs composite.



Figure 8. Discharge capacity of CNFs and SiO2/CNFs composite.

Figure 9. Discharge and charge capacity and the columbic efficiency of SiO 2/CNFs composite.


79

80


The curves of capacity versus cycle number for the SiO2/CNFs composite are shown in Figure 9. The discharge and charge capacity of the second cycle was 2,053 and 1,866 mAh/g, respectively. The columbic efficiency of the second cycle was 82%. However, as further cycles were performed, the columbic efficiency reached 96% at twenty-nine cycles, representing a higher reversible insertion and deinsertion of Li ions into the SiO2/CNFs composite structure. There was an irreversible capacity loss at the early stage of cycling that was apparently due to an irreversible reaction between SiO2 and an electrolyte forming the SEI. This was evidenced by the cyclic voltammetry observed. This suggests that the SiO2/CNFs composite electrode accommodates Li, without a significant volume variation, in which an Si anode was generally used.

3. SYNTHESIS AND CHARACTERISTICS OF SILICA-COATED CNFS ON ELECTROPLATED CO-NI/C-FIBER TEXTILES [34] 3.1. Deposition of Co-Ni Catalysts on C-Fiber Textiles Co-Ni catalysts were deposited on C-fiber textiles using the electrophoretic method. Carbon electrodes and carbon sheets were respectively used as the anode and cathode, while a mixture of cobalt nitrate and nickel nitrate was used as the electrolyte. To analyze the characteristics of the CNFs according to the cobalt and nickel contents, cobalt nitrate and Nickel nitrate with weight ratios of 6:4 and 8:2 were used as the electrolyte for the deposition of Co-Ni catalysts. The catalysts were applied with 0.04-0.05 A current for 5 minutes.



81

3.2. Reduction of Catalysts and Synthesis of CNFs The C-fiber textiles with deposited catalysts were placed in a furnace, with nitrogen atmosphere and the temperature was increased at12 ℃/min until it reached 700 °C. H2 gas was flowed into the furnace for an hour for t0 reduce the catalysts, while the temperature was maintained at 700 °C. The CNFs were synthesized to electroplated Co-Ni/C-fiber textiles by CVD. Ethylene gas, as the carbon source, was flowed into the furnace for an hour at 700 ℃, to complete the reduction process. After the completion of the reaction, the temperature was lowered to room temperature in a nitrogen atmosphere.

3.3. Synthesis of SiO2-CNF Composite To apply the silica coating, a hydroxyl group was attached to the surface of the CNFs as an anchor group, and oxidized for 30 minutes in 80 °C nitric acid [21]. Using the sol-gel process, SiO2 was applied as a coating through the hydrolysis of TEOS on the surface of the reduced CNFs. TEOS was hydrolyzed by dissolving hydrochloric acid and distilled water with ethanol and stirring it for 6 hours at room temperature. After soaking the CNFs/C-fiber textiles in this solution, and adding ammonia solution for gelation, the solution was stirred for 12 hours and SiO2 was coated on the surface of the CNFs. Table 2. EDS results of CNFs on Co-Ni/C-fiber textiles Element

C (%)

O (%)

Co (%)

Ni (%)

CNFs/Co-Ni(8:2)

87

7

5

1

CNFs/Co-Ni(6:4)

88

7

3

2



82

Co-Ni (8:2)

Co-Ni (6:4)

Figure 10. SEM images of CNFs grown on Co-Ni/C-fiber textiles.

3.4. Electrochemical Measurements To investigate the electrochemical characteristics of the CNFs and the SiO2-CNF composite, a coin cell was fabricated. The CNFs and SiO2CNFs deposited on C-fiber textiles were used without a binder as the working electrode, Li metal was used for the counter electrode, and polyethylene was used for the separator. A solution of LiPF6 dissolved in ethylene carbonate (EC) and diethyl carbonate (DEC) (1:1vol.%) was used as the electrolyte. The coin cell was fabricated in a glove box filled with argon (Ar) gas.

3.5. Analyses 3.5.1. SEM and EDS Figure 10 shows the SEM images of CNFs synthesized according to the Co-Ni ratio. Table 2 shows the EDS results for the SEM images. In both samples, CNFs in a curved form with a uniform diameter were synthesized. With a Co-Ni ratio of 8:2, 40nm CNFs were synthesized while 30 nm CNFs were synthesized with a ratio of 6:4. In both samples, the carbon content was above 85%, and increased after the synthesis of



83

CNFs. As the carbon content increased, the catalyst content decreased at a relative rate.

Figure 11. XPS spectra of CNFs grown on Co-Ni/C-fiber textiles.

Figure 12. Raman spectra of CNFs grown on Co-Ni/C-fiber textiles.


84


Figure 13. TEM image of SiO2 coated CNFs composite.

3.5.2. XPS Figure 11 shows the XPS spectra of CNFs that were synthesized using Co-Ni catalysts. With Co-Ni ratios of 8:2 and 6:4, a C=C (sp2) bond, a C-C (sp3) bond, a -C=O bond, and a –COO bond were observed respectively around 285 eV, 286 eV, 288 eV and 292 eV. It was found that the catalyst ratio did not affect the binding energy of CNFs, as the same carbon binding energy was observed with both catalyst ratios. 3.5.3. Raman Figure 12 shows the Raman spectra of CNFs according to the Co-Ni ratios. a G band indicating a Carbon-Carbon double bond (sp2) around 1,590 cm-1, was observed. A D band indicating a Carbon-Carbon single bond (sp3) around 1,350 cm-1 was observed. Considering that the intensity ratio of the D band and B band at both ratios was close to 1, it was determined that CNFs were synthesized with a 1:1 ratio of sp2 bonds and sp3 bonds. The intensity of CNFs synthesized at the Co-Ni ratio of 8:2 was higher than that of the CNFs synthesized at the 6:4 ratio. This indicates that CNFs with higher crystallizability were synthesized. 3.5.4. TEM The TEM images of the silica coated layer on the surface of the CNFs were examined and are shown in Figure 13. The CNFs synthesized at a CoNi ratio of 8:2, with relatively high crystallizability were used. A layer of



85

silica at a thickness of about 10 nm in a hollow form with about an 8 nm center diameter was applied evenly to the surface of the CNFs.

Figure 14. XPS spectra of SiO2-CNFs composite. 1600 SiO2-CNFs CNFs/Co-Ni(8:2) CNFs/Co-Ni(6:4) C-fiber textiles

Discharge capacity(mAh/g)

1400 1200 1000 800 600 400 200 0 0

5

10

15

20

25

30

Cycle

Figure 15. Discharge capacities of C-fiber textiles, CNFs/Co-Ni, and SiO2-CNFs composite.



86

Table 3. Discharge capacities and retention rates of C-fiber textiles, CNFs/Co-Ni, and SiO2-CNFs composite

Discharge capacity at 1st cycle Discharge capacity at 30th cycle Retention rate (%)

C-fiber textiles

CNFs/ Co-Ni(8:2)

CNFs/ Co-Ni(6:4)

SiO2-CNFs

190

258

234

1468

183

244

220

705

96

95

94

47

3.5.5. XPS Figure14 shows the XPS spectra of the as-synthesized SiO2-CNFs composite. Binding energy of around 103-105 eV for silicon, SiO2 and SiO were found. Considering that the intensity of SiO2 bonding is higher than that of SiO bonding in larger areas, the coated layer on the surface of CNFs consisted mostly of SiO2. 3.5.6. Cycle Performance The discharge capacities of C-fiber textiles, CNFs, and SiO2-CNFs composites were measured and are shown in Figure 15. The results are summarized in Table 3. The respective initial discharge capacities of the CNFs synthesized with Co-Ni ratios of 8:2 and 6:4 were 258 and 234 mAhg-1, which are higher than that of the C-fiber textiles with an initial discharge capacity of 190 mAh/g and a retention rate of 95%. The SiO2CNFs composite showed the highest initial discharge capacity at 1,468 mAhg-1 and a retention rate of 47%.

CONCLUSION Carbon nanofibers, with Transition metal catalysts deposited through the electrophoretic method, were synthesized on the surface of C-fiber textiles using CVD. Following hydrolysis of TEOS, silica was coated on the surface of CNFs to synthesize SiO2-CNF composites. The characteristics



87

of the as-synthesized CNFs and SiO2-CNF composites were analyzed through SEM, EDS, TEM, Raman, and XPS spectroscopy. A coin-type half-cell without a binder was fabricated for the as-synthesized sample, and its cycle performance as an anode material in Li secondary batteries was investigated. Based on the results, the following conclusions were reached. The CNFs synthesized on Ni-Cu/C-fiber textiles have diameters of 33300 nm. According to galvanostatic charge-discharge, the SiO2/CNF composites have a superior discharge capacity at 1,295 than the CNFs, which maintains at 304 mAh/g, after twenty-nine cycles. A capacity retention, 63% occurred after the completion of twenty cycles. The results of the analyses show that the diameter of the Silica-coated CNFs on Co-Ni/C-fiber textiles was 30-40 nm and the SiO2 layer was uniformly coated at a thickness of 10nm onto their surface. The electrochemical characteristics of the CNFs and the SiO2-CNF composites were investigated using galvanostatic charge-discharge with coin cells. The as-synthesized CNFs and SiO2-CNFs composites were directly employed as anode materials without any binder. The CNFs had a discharge capacity of 258 mAhg-1 during the initial cycle with a retention rate of 95% after 30 cycles. The discharge capacity of the SiO2-CNFs composite was 1,486 mAhg-1 with a retention rate of 47%, which was greater than that of the CNFs.

ACKNOWLEDGMENTS This research was financially supported by the Ministry of Education, Science Technology (MEST) and National Research Foundation of Korea (NRF) through the Human Resource Training Project for Regional Innovation (NO.2015035858).


88


REFERENCES [1]

Gu, S. Y.; Ren, J.; Vancso, G. j. Process optimization and empirical modeling for electospun polyacrylonitrile (PAN) nanofiber precursor of carbon nanofibers. Eur. Polymer J., 2005, 41, 2559-2568. [2] Zhu, Y. A.; Sui, Zh. J.; Zhao, T. J.; Dai, Y. Ch.; Cheng, Zh. M.; Yuan, W. K. Modeling of fishbone-type carbon nanofibers: A theoretical study. Carbon, 2005, 43, 1694-1699. [3] Guo, T.; Nikolev, P.; Thess, A.; Colbert, D. T.; Smalley, R. E. Catalytic growth of single-walled manotubes by laser vaporization, Chemical Physics Letters, 1995, 243, 49-54. [4] Yoon, Y. J.; Baik, H. K. Catalytic growth mechanism of carbon nanofibers through chemical vapor deposition, Diamond and Related Materials, 2001, 10, 1214-1217. [5] Wieczorek-Ciurowa, K.; Kozak, A. J. The Thermal Decomposition of Fe(NO3)3·9H2O, Journal of Thermal Analysis and Calorimetry, 1999, 58, 647-651. [6] Boccaccini, A. R.; Cho, J.; Roether, J. A.; Thomas, B. J. C.; Minay, E. J.; Shaffer, M. S. P. Electrophoretic deposition of carbon nanotubes, Carbon, 2006, 44, 3149-3160. [7] ChandraKishore, S.; Pandurangan, A. Electrophoretic deposition of cobalt catalyst layer over stainless steel for the high yield synthesis of carbon nanotubes, Applied Surface Science, 2012, 258, 79367942. [8] Wang, H. W.; Lin, H. C.; Yeh, Y. C.; Kuo, C. H. Synthesis of Fe3O4 nanoparticles and formation of nanowire by electrophoretic deposition, Journal of Magnetism and Magnetic Materials, 2007, 310, 2425-2427. [9] Wang, R.; Wan, Y.; He, F.; Qi, Y.; You, W.; Luo, H. The synthesis of a new kind of magnetic coating on carbon fibers by electrodeposition, Applied Surface Science, 2012, 258, 3007-3011. [10] Park, K. H.; Lee, S.; Koh, K. H. Growth and high current field emission of carbon nanofiber films with electroplated Ni catalyst, Diamond and Related Materials, 2005, 14, 2094-2098.



89

[11] Cheng, J.; Zou, X.; Zhang, H.; Li, F.; Ren, P.; Zhu, G.; Su, Y.; Wang, M. Growth of Y-shaped Carbon Nanofibers from Ethanol Flames, Nanoscale Res Lett., 2008, 3, 295-298. [12] Zhang, Q.; Coi, Zuolin. Synthesis and characterization of Y-shaped carbon fibers by chemical vapor deposition, Materials Letters, 2009, 63, 850-851. [13] Okpalugo, T. I. T.; Papakonstantinou, P.; Murphy, H.; McLaughlin, J.; Brown, N. M. D. Surface-enhanced Raman scattering studies on C60 fullerene self-assemblies, Carbon, 2005, 43, 1-9. [14] De Jong, K. P.; Geus, J. W. Carbon nanofibers: catalytic synthesis and applications. Catalysis Reviews, 2000, 42, 481-510. [15] Iijima, S. Helical microtubules of graphitic carbon. Nature, 1991, 354, 56-58. [16] Choi, Y. G.; Yu, S. C.; Kim, N. Hydrogen adsorption and storage in carbon nanotubes. Synth. Met., 2000, 113, 209-216. [17] Williams, K. A.; Eklund, P. C. Monte Carlo simulations of H2 physisorption in finite-diameter carbon nanotube ropes. Chem. Phys. Lett., 2000, 320, 352-358. [18] Hwang, J. Y.; Lee, S. H.; Sim, K. S.; Kim, J. W. Hydrogen adsorption properties of multi-walled carbon nanotubes. J. of the Korean hydrogen energy society, 2001, 212(1), 65-73. [19] Schimmel, H.; Nijkamp, G.; Kearley, G.; Rivera, A.; De Jong, K.; Mulder, F. Hydrogen adsorption in carbon nanostructures compared. Mat. Sci. Eng. B., 2004, 108, 124-129. [20] Youn, H. S.; Ryu, H.; Cho, T.; Choi, W. Purity enhancement and electrochemical hydrogen storage property of carbon nanofibers grown at low temperature. Int. J. Hydrogen Energy, 2002, 27, 937940. [21] Davis, W.; Slawson, R.; Rigby, G. An unusual form of carbon. Nature, 1953, 171, 756. [22] Baker, R.; Harris, P.; Thomas, R.; Waite, R. Formation of filamentous carbon from iron, cobalt and chromium catalyzed decomposition of acetylene. J. catal., 1973, 30, 86-95.


90


[23] Cordier, A.; Rossignol, F.; Laurent, C.; Chartier, T.; Peigney, A. A new fast method for ceramic foam impregnation: Application to the CCVD synthesis of carbon nanotubes. Appl. Catal. A, 2007, 319, 713. [24] Zhang, Y.; Zhang, J. Synthesis of carbon nanofibers and nanotubes by chemical vapor deposition using a calcium carbonate catalyst. Mater. Lett., 2013, 92, 342-345. [25] Martin-Gullon, I.; Vera, J.; Conesa, J. A.; González, J. L.; Merino, C. Differences between carbon nanofibers produced using Fe and Ni catalysts in a floating catalyst reactor. Carbon, 2006, 44, 1572-1580. [26] Merkulov, V. I.; Guillorn, M. A.; Lowndes, D. H.; Simpson, M. L.; Voelkl, E. Shaping carbon nanostructures by controlling the synthesis process. Appl. Phys. Lett., 2001, 79, 1178-1180. [27] Han, Y.; Lee, J. Improvement on the electrochemical characteristics of graphite anodes by coating of the pyrolytic carbon using tumbling chemical vapor deposition. Electrochim. Acta, 2003, 48, 1073-1079. [28] Deck, C. P.; Vecchio, K. Growth mechanism of vapor phase CVDgrown multi-walled carbon nanotubes. Carbon 2005, 43, 2608-2617. [29] Lee, C. J.; Kim, D. W.; Lee, T. J.; Choi, Y. C.; Park, Y. S.; Lee, Y. H.; Choi, W. B.; Lee, N. S.; Park, G.; Kim, J. M. Synthesis of aligned carbon nanotubes using thermal chemical vapor deposition. Chem. Phys. Lett., 1999, 312, 461-468. [30] Norinaga, K.; Deutschmann, O.; Hüttinger, K. J. Analysis of gas phase compounds in chemical vapor deposition of carbon from light hydrocarbons. Carbon, 2006, 44, 1790-1800. [31] Hyun, Y. R.; Choi, C. Y.; Bae, J. Y.; Park, H. K.; Lee C. H., Synthesis and electrochemical performance of Mesoporous SiO2Carbonnanofibers composite as anode materials for lithium secondary batteries, Materials Research Bulletin, 2016, 82, 92-101. [32] Hyun, Y. R.; Choi, C. Y.; Park, H. K.; Lee C. H., Synthesis and electrochemical performance of Ruthenium Oxide-coated Carbon nanofibers as anode materials for lithium secondary batteries, Applied Surface Science, 2016, 388, 274-280.



91

[33] Nam, K. M.; Park, H. K.; Lee, C. H., Synthesis and Electrochemical Properties of Carbon Nanofibers and SiO2/Carbon Nanofieber Composite on Ni-Cu/C-Fiber Textiles. J. Nanosci. Nanotechnol., 2015, 15, 8989-8995. [34] Jang, K. H.; Lee, S. H.; Han, S. J.; Yoon, S. H.; Lee, C. S. Synthesis and Characteristics of Silica-Coated Carbon Nanofibers on Electroplated Co–Ni/C-Fiber Textiles, J. Nanosci. Nanotechnol., 2016, 16, 10767–10771.

BIOGRAPHICAL SKETCH Chang-Seop Lee Affiliation: Keimyung University, Daegu, Republic of Korea Education:  BS, Chemistry, 1979, Kyungpook National University, Korea  MS, Physical Chemistry, 1981, Kyungpook National University, Korea  PhD, Surface Chemistry, 1991, Oregon State University (Thesis Advisor: Prof. P. R. Watson) Business Address: 1095 Dalgubeol-daero, Dalseo-gu, Daegu 42601 Korea Research and Professional Experience:  Synthesis and characterization of catalytic materials and functionalized ceramic materials or composite materials  Kinetics and mechanisms of surface chemical reactions significant in heterogeneous catalysis, especially de-NOx mechanism, cold start hydrocarbon oxidation in automobile exhausts.  Development of gas sensors based on metal oxides detecting various VOCs and toxic gases from industrial fields.



92 

Synthesis and characterization of Si/carbon nanofibers and graphene/carbon nanotube/carbon nanofibers composites and testing of electrical performances as an electrode material for Li secondary batteries.

Professional Appointments:  Chair, Surface Science Division, Korean Vacuum Society, 19961998  Editor, Journal of the Korean Vacuum Society, 1996-1998  Editor, Analytical Sciences and Technology, 2005 – 2010  Editor, Advances in Chemical and Biological Engineering, 2015 – present  Editor, International Journal of Materials Science and Application, 2016 – Present  Director (2004-2005), Inspector (2013-2014), Chair, DaeguKyungpook Chapter (2015-Present) Korean Chemical Society  Director, Research division of atmospheric pollution and anti vibration-noise(1996-8) Director, External Affairs (2001-2004), Center for Automotive Parts Technology of Keimyung University designated by Ministry of Science and Technology (MOST) and Korea Science and Engineering Foundation (KOSEF)  Secretary General, Traditional Microorganism Resources Development and Industrialization Center designated by Ministry of Science and Technology (MOST) (2004-2005)  Head, Nano Materials and Process Research Center, Keimyung University (2005-2006)  Vice President, Daegu Regional Federation, Korean Federation of Science and Technology Societies (2016-Present) Honors:  Teaching award, The Third Military Academy, 1985  Christensen Award, Oregon State University, 1990



   

93

BISA Outstanding Research Professor, Keimyung University, 1996-1997 Industry-Academy Outstanding Research Professor, Keimyung University, 2012-2013 BISA Academic Award, Keimyung University, 2016 IAAM Award, International Association of Advanced Materials, 2017

Publications within three years: 1. Ki-Lyong Seo, Yura Hyun and Chang-Seop Lee, “Ultrasonochemical Coating and Characterization of TiO2-coated Zirconia Fine Particles”, J. Ind. & Eng. Chem., 19(3), 1819(2014). 2. Jae-Min Son, Young-Ho Park, Chang-Seop Lee, “The Development of Nano-Polyplex Efficacious against Osteoarthropathy”, J. Ind. & Eng. Chem., 19(3), 2490(2014). 3. Eunsil Park, Jong-Won Kim, Chang-Seop Lee, “Synthesis and Characterization of Carbon nanofibers on Co and Cu Catalysts by Chemical Vapor Deposition”, Bulletin of the Korean Chemical Society, 35(6), 1687(2014). 4. Dohyun Moon, Chang-Seop Lee, Jong-Ha Choi, “Two Conformational Isomers in a Crystal of trans-Dibromobis(2,2-dimethyl-1,3diaminopropane)chromium(III) Bromide”, Journal of Chemical Crystallography, 44(6), 306(2014). 5. Ki-Mok Nam, Karina Mees, Ho-Seon Park, Monika Willert-Porada, Chang-Seop Lee, “Electrophoretic Deposition for the Growth of Carbon nanofibers on Ni-Cu/C-fiber textiles”, Bulletin of the Korean Chemical Society, 35(8), 2431(2014). 6. Sang-Won Lee, Chang-Seop Lee, “Electrophoretic deposition of Iron catalyst on C-fiber textiles for the growth of Carbon nanofibers”, Journal of Nanoscience and Nanotechnology, Vol 14, 8619 (2014). 7. Byung-Sam Min, Young-Ho Park, Chang-Seop Lee, “Fabrication and Characterization of SnO2/ZnO Gas Sensor for detecting Toluene gas”, Journal of Nanoscience and Nanotechnology, Vol 15, 8495 (2014).


94


8. Ki-Mok Nam, Karina Mees, Ho-Seon Park, Monika Willert-Porada, Chang-Seop Lee, “Electrophoretic Deposition for the Growth of Carbon nanofibers on Ni-Cu/C-fiber textiles”, Bulletin of the Korean Chemical Society, 35(8), 2431-2437 (2014). 9. Dohyun Moon, Chang-Seop Lee, Jong-Ha Choi, “Two Conformational Isomers in a Crystal of trans-Dibromobis(2,2-dimethyl-1,3diaminopropane)chromium(III) Bromide”, Journal of Chemical Crystallography, 44(6), 306-311 (2014). 10. Dohyun Moon, Chang-Seop Lee, Keon-Sang Ryoo, Jong-Ha Choi, “Synthesis, Characterization and Crystal Structure of transAquahydroxobis(2,2-dimethyl-1,3-propanediamine)chromium(III) Diperchlorate”, Bulletin of the Korean Chemical Society, 35(10), 3099-3102 (2014). 11. Yura Hyun, Eun-Sil Park, Karina Mees, Ho-Seon Park, Monika Willert-Porada, Chang-Seop Lee, “Synthesis and Characterization of Carbon nanofibers on Transition Metal Catalysts by Chemical Vapor Deposition”, Journal of Nanoscience and Nanotechnology, 15(9) 7293 (2015). 12. Sang-Won Lee, Chang-Seop Lee, “Growth and Characterization of Carbon Nanofibers on Fe/C-fiber Textiles coated by DepositionPrecipitation and Dip-Coating”, Journal of Nanoscience and Nanotechnology, 15(9), 7317 (2015). 13. Eun-Sil Park, Heai-Ku Park, Ho-Seon Park, Chang-Seop Lee, “Synthesis and electrochemical properties of CNFs-Si composites as an anode material for Li secondary batteries”, Journal of Nanoscience and Nanotechnology, 15(11), 8961 (2015). 14. Ki-Mok Nam, Heai-Ku Park, Chang-Seop Lee, “Synthesis and Electrochemical Properties of Carbon nanofibers and SiO2/Carbon nanofiber composite on Ni-Cu/C-fiber textiles”, Journal of Nanoscience and Nanotechnology, 15(11), 8989 (2015). 15. Yura Hyun, Heai-Ku Park, Ho-Seon Park, Chang-Seop Lee, “Characteristics and Electrochemical performance of Si-Carbon Nanofibers composite as anode material for binder-free lithium



16.

17.

18.

19.

20.

21.

22.

23.

95

secondary battery”, Journal of Nanoscience and Nanotechnology, 15(11), 8951 (2015) Eun-Sil Park, Jong-Ha Choi, Chang-Seop Lee, “Synthesis and Characterization of vapor grown Si/CNFs and Si/PC/CNFs composites based on Co-Cu catalysts”, Bulletin of the Korean Chemical Society, 36(5), 1366 (2015). Eunyi-Jang, Heai-Ku Park, Jong-Ha Choi, Chang-Seop Lee, “Synthesis and Characterization of Carbon nanofibers grown on Ni and Mo Catalysts by Chemical Vapor Deposition”, Bulletin of the Korean Chemical Society, 36(5), 1452 (2015). Chang-Seop Lee, Jong-Ha Choi, Young-Ho Park, “Development of metal-loaded mixed metal oxides gas sensors for the detection of lethal gases”, J. Ind. & Eng. Chem., Vol. 29, 321-329 (2015). Eunyi-Jang, Heai-Ku Park, Chang-Seop Lee, “Synthesis and Application of Si/Carbon Nanofiber Composites based on Ni and Mo Catalysts for Anode Material of Lithium Secondary Batteries”, Journal of Nanoscience and Nanotechnology, 16(5), 4792 (2016). Yura Hyun, Jin-Young Choi, Heai-Ku Park, Chang-Seop Lee, “Synthesis and electrochemical performance of Ruthenium oxidecoated Carbon nanofibers as anode materials for Lithium secondary batteries”, Applied Surface Science, 388, 274-280 (2016) Yura Hyun, Jin-Young Choi, Jae-Young Bae, Heai-Ku Park, ChangSeop Lee, “Synthesis and electrochemical performance of mesoporous SiO2-Carbon nanofibers composite as anode materials for lithium secondary”, Materials Research Bulletin, 82, 92 (2016). Kun-Ho Jang, Sang-Hoon Lee, Yujin Han, Seong-Ho Yoon, ChangSeop Lee, “Synthesis and Characteristics of Silica-Coated Carbon Nanofibers on Electroplated Co–-Ni/C-Fiber Textiles”, Journal of Nanoscience and Nanotechnology, 16, 10767 (2016). Soo-Jin Kim, Yura Hyun, Chang-Seop Lee, “Physicochemical and Electrochemical Characteristics of Carbon nanomaterials and Carbon nanomaterial-Silicon Composites”, Journal of The Korean Chemical Society, 60(3), 299 (2016).


96


24. M. A. Subhan, S. W. Ng, C.-S. Lee, J.-H. Choi, “Synthesis, Crystal Structure, and Spectroscopic Properties of Isothiocyanato [(3,14dimethyl-2,6,13,17 tetraazatricyclo (16.4.0.07,12) docosane)] copper(II) Thiocyanate”, Journal of Structural Chemistry, in press (2017). 25. Min-Sun Kim, Eun-Sil Park, Yura Hyun, Heai-Ku Park and ChangSeop Lee, “Synthesis and Application of CNFs-Si Composites Based on Transition Metal Catalysts for Anode Material of Li Secondary Batteries”, Journal of Nanoscience and Nanotechnology, 17, 2970 (2017). 26. Chang-Seop Lee, Yura Hyun, “Nanofibers”, InTech, ISSN: 978-95351-4828-9, 2016. 27. Chang-Seop Lee, Yura Hyun, “Chemical Vapor Deposition”, InTech, ISSN: 978-953-51-4733-6, 2016. 28. “CNFs Growth method using of iron catalyst coating”, Korea patent: 10-1377691 (March 18, 2014). 29. “Growth method of Carbon Nanofibers based on Co catalyst”, Korea patent: 10-1398165 (May 15, 2014). 30. “Synthetic method of CNFs using of Fe catalyst, and CNFs by this method”, Korea patent: 10-1421188 (July 14, 2014). 31. “Synthesis method of CNF on transition metal by Chemical Vapor Deposition, and CNF thereof”, Korea patent: 10-1471625 (December 4, 2014). 32. “Synthesis method of Carbon nanofibers on Co and Cu Catalysts by Chemical Vapor Deposition, and there of Carbon nanofibers”, Korea patent: 10-1452728 (October 14, 2014). 33. “Growth method of carbon nanofibers using of electrophoretic deposition”, Korea patent: 10-1493469 (July 14, 2014). 34. “Growth method of Carbon nanofibers based Ni/Cu catalyst, and there of Carbon nanofibers”, Korea patent: 10-1577360 (December 8, 2015). 35. “Synthesis method of silicon/carbon nanofibers based on Co-Cu catalyst”, Korea patent: 10-1090928 (December 22, 2015).



97

36. “Manufacturing method of Si-CNFs composite and Lithium Secondary battery using of Fe-Cu catalysts”, Korea patent: 10-1608049 (March 25, 2016). 37. “Synthesis method of CNFs grown on Ni and Mo Catalysts, and manufacturing method of secondary cell using of it”, Korea patent: 101608052 (March 25, 2016). 38. “Manufacturing method of secondary batteries using Si-CNFs based on Co-Cu catalysts”, Korea patent: 10-1616083 (April 21, 2016).



INDEX A AC electrophoretic deposition (AC-EPD), v, vii, 1, 2, 4, 5, 8, 9, 14, 16, 17, 18, 19, 20, 21, 22, 24, 25, 26, 28, 30, 34, 38 acetone, vii, 1, 3, 8, 22 acetylene gas, 65 acid, 9, 20, 22, 42, 60, 72, 76, 81 additives, viii, 2, 5, 22, 23, 25, 29, 37 adhesion, 8, 17, 48 adsorption, 7, 11, 12, 46, 89 Al2O3 particles, 9 ammonia, 72, 81 ammonium, 8, 11, 12, 25 aqueous electrophoretic deposition, 2, 34 aqueous solutions, 35, 50 aqueous suspension, vii, 2, 3, 4, 5, 6, 7, 9, 11, 13, 16, 22, 24, 25, 28, 32, 33, 34, 35 asymmetry, viii, 2, 6, 25 atmosphere, 25, 55, 56, 72, 81

B bacterial cells, 30 band gap, viii, 40, 41

barriers, 51, 54 batteries, ix, 41, 68, 69, 78, 87, 90, 92, 94, 95, 97 binding energy, 84 biosensors, ix, 40 bonding, 77, 86 burnout, ix, 68

C calcium carbonate, 90 carbon, 5, 16, 17, 18, 19, 34, 36, 57, 58, 64, 65, 68, 69, 70, 71, 72, 74, 76, 80, 81, 82, 84, 88, 89, 90, 92, 96 carbon atoms, 69 carbon monoxide, 57, 58, 64 carbon nanofibers, 68, 69, 71, 72, 86, 88, 89, 90, 92, 93, 94, 95, 96 casting, 3, 26, 30, 38, 59 catalyst, 46, 69, 70, 72, 74, 75, 83, 84, 88, 90, 93, 96 ceramic, vii, ix, 8, 22, 23, 28, 32, 35, 37, 38, 39, 61, 62, 63, 65, 66, 67, 90, 91 ceramic materials, ix, 67, 91 chemical deposition, 30 chemical interaction, 56


Index

100

chemical reactions, 47, 91 chemical stability, 56, 68 chemical synthesis, ix, 40, 59 chemical vapor deposition, ix, 3, 31, 43, 59, 68, 88, 89, 90 chromium, 53, 54, 59, 89, 93, 94 coatings, ix, 2, 22, 30, 67 cobalt, 42, 44, 80, 88, 89 composites, viii, 2, 5, 9, 20, 22, 23, 27, 28, 29, 34, 35, 36, 37, 66, 69, 86, 87, 92, 94, 95 compounds, 40, 46, 48, 50, 90 conduction, ix, 40, 41, 46, 51, 56 conductivity, viii, 2, 4, 6, 7, 10, 12, 13, 15, 45, 54, 56, 63 copper, ix, 68, 70, 96 corrosion, ix, 34, 40 cost, ix, 4, 23, 43, 67 covalent bonding, 25 crystal structure, 69 crystalline, 19, 40, 43, 64 CVD, ix, 68, 69, 71, 81, 86, 90 cycles, 4, 77, 78, 80, 87 cycling, 69, 78, 80

D decomposition, 4, 64, 89 defects, 9, 41, 42, 53 degradation, 50, 59, 60, 62, 64 deposition, vii, viii, ix, 1, 2, 3, 4, 5, 6, 7, 8, 14, 19, 20, 21, 23, 25, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 40, 42, 43, 44, 45, 46, 48, 52, 53, 56, 59, 60, 61, 62, 63, 64, 66, 67, 68, 69, 73, 80, 88, 93, 96 diallyldimethylammonium chloride, 66 diffusion, 48, 50, 52, 53, 54, 62 diffusion process, 48, 50 dispersion, 7, 9, 17, 20, 21, 33, 38, 72 distilled water, 72, 81 dopants, 41, 42, 51, 52, 56

E electric charge, 46 electric current, 51, 54 electric field, vii, 1, 2, 4, 14, 19, 22, 23, 32, 33, 35, 44, 45, 51, 53, 54 electrical characterization, 51 electrical conductivity, viii, 40, 68, 69 electrical properties, 41, 53, 61, 62 electrical resistance, ix, 40 electrode surface, 45 electrodeposition, 31, 32, 34, 61, 66, 88 electrodes, 4, 6, 21, 22, 24, 43, 44, 45, 46, 55, 68, 78, 80 electrolysis, vii, 2, 4, 24, 29, 45 electrolyte, 4, 77, 80, 82 electromagnetic, 68 electron, viii, ix, 40, 41, 42, 44, 46, 47, 49, 53, 56, 58 electron microscopy, 44 electrophoresis, 4, 33, 34 electrophoretic deposition, v, vii, viii, ix, 1, 2, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 42, 43, 45, 56, 60, 61, 62, 63, 64, 66, 67, 68, 69, 88, 93, 94, 96 electrospinning, 68 emission, 49, 55, 88 energy, 25, 40, 42, 46, 52, 77, 84, 86, 89 environmental issues, 46 ethanol, vii, 1, 3, 8, 16, 20, 22, 23, 65, 66, 81 ethanol detection, 65 ethyl alcohol, 72 ethylene, 42, 69, 71, 72, 82 ethylene glycol, 42 excitation, ix, 40, 46, 47 experimental condition, 70 exposure, 49, 57


Index

F fabrication, 22, 23, 24, 25, 26, 29, 33, 34, 35, 37, 38, 63, 64, 93 fiber, ix, 20, 23, 26, 27, 36, 68, 69, 70, 71, 72, 73, 75, 76, 80, 81, 82, 83, 85, 86, 87, 88, 89, 93, 94 film thickness, viii, 40, 47 films, vii, viii, 2, 4, 5, 6, 8, 14, 18, 20, 21, 29, 30, 35, 39, 42, 43, 47, 48, 49, 53, 56, 59, 62, 63, 66, 88 financial support, 60 flexibility, 3, 68 formation, vii, ix, 1, 4, 19, 24, 45, 46, 51, 52, 65, 68, 88 free energy, 19 fuel cell, 66, 69 fullerene, 89 functionalization, vii, 42

G gas diffusion, 62 gas sensors, ix, 40, 41, 55, 59, 66, 91, 95 gel, 3, 30 gelation, 81 grain boundaries, 61 graphite, 24, 26, 31, 75, 90 growth, 3, 31, 52, 69, 74, 75, 88, 93 growth mechanism, 74, 88

101

hydrogen, ix, 35, 45, 46, 62, 66, 68, 70, 71, 72, 89 hydrogen gas, ix, 45, 62, 68, 70, 72 hydrolysis, ix, 68, 75, 81, 86 hydrothermal process, 22 hydroxide, 24 hydroxyl, 46, 47, 71, 72, 81

I images, 9, 16, 18, 19, 21, 24, 26, 27, 28, 29, 55, 73, 74, 75, 82, 84 immobilization, 47 impregnation, 23, 90 industrial sectors, ix, 67 insertion, 26, 80 integration, viii, 2, 40 ions, 42, 46, 53, 54, 59, 80 irradiation, 64, 66

L laminar, 9, 34 laser ablation, 68 lattice parameters, 40 leakage, 51, 53 life sciences, 69 light, 35, 46, 63, 65, 66, 90 linear dependence, 4, 14 liquid phase, 25 lithium, ix, 65, 68, 69, 77, 90, 94, 95

H M heterogeneous catalysis, 91 homogeneity, 22 hot pressing, 25, 27, 28, 34, 37, 38 hybrid, 36, 65 hybridization, 75 hydrocarbons, 90

macromolecules, 33 magnetic field, 22, 35 magnetic materials, 38 manufacturing, 23, 36, 97 mass, 3, 6, 32, 52


Index

102

materials, viii, ix, 2, 3, 4, 7, 29, 32, 38, 39, 43, 48, 59, 60, 63, 67, 68, 69, 87, 90, 91, 95 matrix, 20, 23, 24, 25, 26, 27, 29, 35, 36, 78 measurements, viii, 2, 6, 12, 53, 63 mechanical properties, 33, 36 metal oxides, 70, 91, 95 microstructure, viii, 2, 5, 6, 27, 36, 51, 66 microwave heating, 52 microwave sintering, 40 molecular weight, 64 molecules, 47, 50, 56 morphology, vii, viii, x, 2, 27, 29, 64, 68

N nanobelts, 42, 65 nanocomposites, 29 nanofibers, ix, 68, 69, 71, 72, 86, 88, 89, 90, 92, 93, 94, 95, 96 nanomaterials, 37, 95 nanoparticles, vii, viii, ix, 2, 3, 5, 8, 19, 21, 22, 28, 31, 32, 34, 35, 40, 42, 43, 48, 52, 53, 60, 61, 64, 65, 88 nanorods, 42 nanostructures, 61, 89, 90 nanotechnology, 30, 61 nanotube, 63, 65, 89, 92 nanowires, 31 natural resources, 46 nickel, ix, 60, 68, 70, 80 niobium, 42, 44 NiTi shape memory, 30 nitrogen, 70, 71, 72, 81

O optical properties, 41 optimization, 32, 36, 88 organic compounds, 46 organic solvents, vii, 1, 29, 45

oxidation, 31, 42, 46, 58, 65, 77, 91 oxygen, 41, 56

P pH, viii, 2, 6, 7, 10, 11, 12, 13, 15, 17, 18, 19, 20, 21, 22, 23, 46 phenol, 60, 64 photocatalysis, ix, 40, 41, 42, 46, 47, 48, 49, 59, 61, 63, 64 photolysis, 49, 61 physical properties, 19 platinum, 22 polymer, 2, 23, 24, 36, 63 polymerization, 42, 62 polystyrene, 16 porosity, 24, 56 precipitation, 42 preparation, 4, 9, 33, 38, 54, 59, 75 protection, ix, 40 pyrolysis, 23, 24, 36, 43

R radiation, 49, 50 Raman spectra, 73, 83, 84 reactions, 4, 19, 47 repulsion, 11, 17 resistance, 56, 57, 58, 68 response, ix, 14, 40, 56, 57, 58, 59, 65 restrictions, ix, 68 retention rate, 86, 87 room temperature, 6, 21, 66, 72, 81 rutile, 40, 43, 66

S scanning electron microscopy, viii, 2, 6, 48 scattering, 89 seeding, 31


Index segregation, 42 semiconductor, viii, 40, 46, 47, 51, 55, 56, 61, 63 semiconductor sensors, 55 sensor, ix, 40, 42, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 68 showing, ix, 11, 13, 40 Si3N4, 8 SiCf/SiC composites, 2, 22, 23, 27, 28, 29, 34, 36, 37 signals, 29 silica, v, ix, 3, 35, 67, 68, 69, 80, 81, 84, 86, 87, 91, 95 Silica, v, 67, 69, 80, 87, 91, 95 silicon, ix, 19, 30, 32, 34, 36, 68, 69, 86, 96 sintering, viii, 2, 5, 23, 24, 25, 26, 27, 29, 34, 40, 52, 53, 64 SiO2, 19, 31, 66, 69, 71, 72, 74, 75, 76, 77, 78, 79, 80, 81, 82, 84, 85, 86, 87, 90, 91, 94, 95 SnO2 nanoparticles, ix, 40, 43, 60, 61, 64 solar cells, ix, 40, 41 solution, 7, 16, 22, 42, 45, 48, 49, 54, 56, 60, 62, 70, 72, 81, 82 solvent molecules, 46 solvents, 3, 45 specific surface, 68 spectroscopy, 49, 87 stability, ix, 8, 11, 40, 45, 63 stabilization, 11, 29, 32, 46 steel, 6, 14, 16, 18, 20, 26, 30, 34, 88 storage, 65, 89 structural defects, viii, 40, 75 structure, 23, 25, 40, 41, 42, 75, 80 substrate, ix, 16, 20, 35, 43, 44, 47, 48, 55, 57, 66, 68 sulfuric acid, 16 surface area, 47, 50, 65 surface modification, 59 surfactants, 24 suspensions, viii, 2, 5, 8, 11, 12, 18, 19, 20, 21, 22, 24, 29, 61

103

synthesis, ix, 38, 40, 42, 43, 59, 61, 62, 72, 82, 88, 89, 90

T techniques, vii, viii, ix, 1, 2, 8, 23, 29, 36, 40, 43, 68 temperature, viii, ix, 2, 3, 5, 7, 22, 31, 38, 40, 51, 65, 70, 71, 72, 81, 89 TEOS, ix, 68, 69, 72, 75, 81, 86 textiles, ix, 68, 69, 70, 71, 72, 73, 75, 76, 80, 81, 82, 83, 85, 86, 87, 93, 94 thermal decomposition, 62 thermal oxidation, 63 thermal properties, 36 thermal treatment, ix, 40, 48 thermodynamic calculations, 25 thick films, vii, viii, ix, 2, 4, 5, 9, 14, 18, 21, 29, 31, 35, 40, 42, 59, 63 tin, 16, 40, 41, 42, 46, 49, 55, 56, 61, 62, 63 tin dioxide, 40, 41, 42, 46, 49, 55, 56, 61, 62, 63 tin oxide, 16, 49 titania, 33 titanium, 22, 34, 48, 49, 63 toxic gases, 91 transition metal, 68, 69, 96 transport, 38, 54 treatment, 42, 46, 53, 54, 56, 76 tungsten carbide, 16

U uniform, viii, 2, 9, 17, 20, 22, 23, 29, 40, 43, 52, 71, 74, 82 UV-radiation, 49

V valence, ix, 40, 46


Index

104 vapor, 3, 22, 31, 90, 95 varistors, ix, 40, 41, 51, 52, 59, 61 versatility, ix, 3, 67 viscosity, viii, 2, 4, 10, 11, 12, 13, 23, 46

W water, vii, 1, 3, 5, 8, 11, 12, 17, 20, 24, 25, 29, 35, 42, 45, 46, 48, 61, 72 water evaporation, 42 wires, 30, 75

X XPS, 76, 77, 83, 84, 85, 86, 87 X-ray diffraction (XRD) , 40, 44, 66, 75, 76

Y yield, viii, 2, 6, 14, 16, 19, 88

Z Zeta potential, 18, 20, 24, 46 zirconia, 32, 60, 61, 66 ZnO, 3, 31, 48, 51, 61, 62, 63, 64, 65, 93
