Effect of Ball-Milling Parameter on the Synthesis of ...

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3Cluster for Polymer Composite (CPC), Science and Engineering Research Center, Engineering. Campus, Universiti Sains Malaysia, 14300 Nibong Tebal, ...
Advanced Materials Research Vol. 620 (2013) pp 309-313 © (2013) Trans Tech Publications, Switzerland doi:10.4028/www.scientific.net/AMR.620.309

Effect of Ball-Milling Parameter on the Synthesis of Mwcnt/Alumina Hybrid Compound NORLIN NOSBI1, a, and HAZIZAN MD AKIL2,3,b 1,2

School of Materials and Mineral Resources Engineering, Engineering Campus, Universiti Sains Malaysia, 14300 Seberang Perai Selatan, Pulau Pinang, Malaysia.

3

Cluster for Polymer Composite (CPC), Science and Engineering Research Center, Engineering Campus, Universiti Sains Malaysia, 14300 Nibong Tebal, Pulau Pinang, Malaysia. a

[email protected], [email protected]

Keywords: ball-milling, carbon nanotubes, alumina, chemical vapour deposition, synthesis.

Abstract. The effects of ball-milling parameter on the structures and properties of the synthesis of multi-walled carbon nanotubes (MWCNT)/alumina hybrid compound via methane decomposition process using Ni-Alumina catalyst were researched. The structural evaluation of particles compound was investigated by particle size analysis, energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), FTIR spectrometer and scanning electron microscopy (SEM). The results indicated that with 300rpm 15h, the microstructure of the hybrid compound is greatly refined, and methane decomposition process distributed uniformly, thus increasing the efficiency of the carbon nanotubes growth process. Introduction Over many existing nanostructures materials, carbon nanotubes (CNTs) have extensively attracted the attention of researchers. All researchers knew that CNTs were first recognized by Sumio Iijima [1]. Therefore lots of researchers had dedicated their studies based on CNTs since then [2, 3]. The CNTs were concentrically rolled graphene sheets with a large number of helicities and chiralities of a grapheme sheet rolled up like a scroll [4]. Their unique physical properties and other potential applications had contributed towards the use of CNTs as fillers and binders to improve the mechanical, thermal, electrical properties of the nanocomposites [5, 6, 7]. It includes conductive and high-strength composites; energy storage and energy conversion devices; sensors; field emission displays and radiation sources; hydrogen storage media; and nanometres-sized semiconductor devices, probes, and interconnects [8]. The formation of CNTs are dependent on the temperature, pressure, feedstock gas, reaction time and gas, reaction time and gas flow rate, and the catalyst that are used. Therefore, the effects of the particle size which correlated to the yield of MWCNT growth were investigated and the possibilities of the effect are discussed. The present study performed the synthesis of multi-walled carbon nanotubes/alumina hybrid compound via methane decomposition method. For this purpose, the effect of milling parameter, the morphological and the structural changes of MWCNT/alumina hybrid compound were investigated in detail. The hybrid compound were characterized using particle size analysis, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD) and Fourier Transform Infrared (FTIR) spectra. Materials and Methodology In the fabrication of the catalyst, 1L of distilled water were used to mix the aluminium powder [0.38mol, 99% purity], and Ni (NO3)2.6H2O [0.01mol, 98% purity], together with NaOH [0.01mol, 98% purity] (dissolved in 50ml of distilled water) with constant stirring. The green precipitate formed and then aged at room temperature for 24h without stirring, and the colloid (Ni (OH)2Al) was attained. Then the colloid was washed and filtered and dried for 2 hours at 80°C. The catalyst was milled in a planetary ball-mill for 5, 10 and 15 hours at room temperature. Details of milling conditions are given in Table 1. Further, the catalyst was calcined at 900°C. All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP, www.ttp.net. (ID: 202.170.51.238-15/10/12,03:45:01)

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Table 1: Details of milling conditions. Ball mill machine Planetary mill Retsch(PM100) Rotation speed of vial 300rpm Time [hours] 5, 10, 15 Vial material Alumina Ball material Alumina Diameter of balls [mm] 10 Number of balls 35 Balls to powder ratio 1:1 To synthesize CNTs, the Ni/Al2O3 was reduced at 400°C for 2hours in H2 gas. Then, CNTs grown process at 800°C in flow rates ratio of CH4/N2 (1:7) into the tube furnace. Characterizations. The particle size analysis was carried out using Malvern machine. The yields properties of samples were analysed using XRD method (10°-90°). The morphology and elemental analysis of samples was analysed using FESEM and EDX. Fourier transform infrared (FTIR) spectra of the samples were performed in a scan range wave number of 4000-400 cm-1 with a resolution of 2 cm-1. Results & Discussion Mechanochemical. The changes in crystal structural and chemical composition were analysed using X-ray diffraction. XRD patterns of the milled sample at of various part of milling time are shown in Fig. 1. It shows that the appearance of reflections at 33.92° (hkl: 107), 62.00° (hkl: 1014) are related to the NiO phase. The NiO phase sharp was seen which implies that at less milling time the agglomeration of NiO form large crystallites. After grinding in prolonged time the formation of the peaks were broader with lower intensities and the crystalline structure of the Al2O3and NiO compound collapsed. As mentioned in a previous study [9], the peak intensities were reducing because of the formation of amorphous materials in the milled powders. The reflections phases of NiO mislaid indicated that the compounds were well mixed with Al2O3 while being prepared. It also showed that Ni-Al2O3 was united to form a greater compound for 15 hours at 300rpm.The optimum conditions of milling can be selected in order to synthesize Ni-Al2O3 via mechanochemical method. These milling mechanisms changed the structure and surface properties of the compound due to the stress field and energy transfer within the compound along the highenergy grinding. The concentration of mechanochemical effect depended on the diversity forces of shear, impact, compression and attrition among particle compound by means of grinding media, milling time and the gravitational acceleration.

Fig. 1: XRD patterns of samples milled for 5, 10 and 15 hours.

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Fourier Transform Infrared Spectroscopy. In order to confirm the influence of the milling time on the compound, further investigations were analysed with FTIR spectrometer. Fig. 2 indicates the transmittance peaks which are assigned to various level of milling time. The absorption peaks around 3700-3600cm-1 arise from stretching of –OH group of alcohols. The absorption peak around 3435 cm-1 refers to the O-H stretch of the hydroxyl group. The adsorption of carbon monoxide on the Ni-Al sample occurs in the CO gas-phase 2000-2200 cm-1region.The peaks at 1634.99 cm-1 in the samples could be due to the O-H bending vibration of weakly bound molecular water [10]. The band obtained at 1384 cm-1 was due to the presence of carbon-carbon (C-C) deformation. The weaker bands at around 1000 cm-1 was an out-of-plane CH bending for the alkene. Absorption peaks between 600 and 800 cm-1 were featured to the librational and stretching modes of AlO4, AlO6 and OH groups [10]. The peak observed at 500 cm-1 assigned the stretching and bending vibration of the Al-O bond. The findings above were attributed to the hydrate and residual carbon to the Al2O3.

Fig. 2: FTIR spectra of samples 0 (before milling) and milled for 5, 10 and 15hours.

Milling time [hours] 0 5 10 15

Table 2: Size measurement results. Diameter size [nm] Atomic percentage of Before After Carbon [At. %] CNT milling milling 315.47 25.46 36.09 32.77 19.21 19.97 30.48 18.41 46.48 21.21 15.79 51.49

Weight percentage of Carbon [Wt.%] 23.29 11.42 31.26 36.37

In order to investigate the effect of mill rotation time on size reduction, the time course of size reduction was taken at 300rpm speed in 5, 10 and 15 hours. The diameter size of the sample compound powders before and after ground at each milled rotation time 5, 10 to 15 hours are shown in Table 2. As the milled rotation time was elevated, the particle size of the compound became smaller. It shows that the single MWCNT has a diameter size of about 15-19 nm after ground compared without ground, 25.46 nm. Moreover, the table exhibits that the amount of the carbon content has been achieved for the entire compound whereas small diameter size contained more

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At% and Wt% of carbon as confirmed by the EDX. SEM images views further confirmed the sizes of CNTs as shown in Fig.3. Therefore, the recommendable conditions are in small diameter size which it appears satisfaction in production of carbon nanotubes with crystalline structure necessity. As reported previously, the changes in size of CNT were shown to affect the conductivity, electronic and mechanical properties [11, 12, 13, 14]. That was why the size reduction rate was observed in this study.

(b)

(a) 100nm

200nm

100nm

CNT

(c)

CNT

200nm

(d) 100nm

100nm

CNT 200nm

CNT

200nm

Fig. 3: SEM micrographs of MWCNTs diameter size (a) before milled (0) and after milled; (b) 5 hours, (c) 10 hours and (d) 15 hours. Conclusions The results of this study are summarized as follows: • Ni-Al2O3/MWCNT had been synthesized using CVD process. • MWCNT with diameter of around 19-15 nm had been successfully fabricated assist by milling. • The phase detection of 51.49 atomic percentage (At%) and 36.37 weight percentage (Wt%) of carbon exhibited more traces in the compound phases that were milled with the speed 300 rpm at time 15 hours. • More carbon content in the CNT compound and composite fields had offered a higher potential to be accepted in many applications.

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Acknowledgment The authors wish to thank USM grant (Cluster for Polymer Composite: 1001/PKT/8640013 and ERGS: 6730007) and Malaysia Ministry of Higher Education (MyBrain15) for the financial support to carry out this research work. References [1]

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