Automated spray pyrolyser for continuous production

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suitable precursors such as aluminium nitrate, zirconium nitrate and titanium hydroxide. The prepared nano particles have been potentially applied in ...
1 CiiT international Journal of Automation and Autonomous System, DOI: AA052009005, May 2009

Automated spray pyrolyser for continuous production of nano metal oxides for industrial applications V. Rajendran, P. Manivasakan and B. Saravanakumar P. R. Rautaa, B. B. Shaua, B. K. Pandaa, P. Renukadevib and P. Kolandaivelc



Centre for Nano science and Technology, K.S.Rangasamy College of Technology Tiruchengode-637 215, Tamil Nadu, India a Dalmia Institute of Scientific and Industrial Research, Rajgangpur-770 017, Orissa, India b Department of Nanotechnology, Anna University, Coimbatore-641 047, Tamil Nadu, India c Department of Physics, Bharathiar University, Coimbatore-641 049, Tamil Nadu, India attracted due to their properties like high surface to volume ratio, chemical stability, heat resistance and unique electronic, magnetic, optical and catalytic properties. The other major technological areas of nano metal oxides and their composites are in advanced composite materials, catalysts, high energy batteries, automobile and aerospace components, optical devices, radiation shielding and energetic materials. Many techniques have been developed and applied for the synthesis of nano powders. The same can be classified according to the strategy applied which includes both top-down and bottom-up approaches. The main difference between nanotechnology and conventional technologies is that the bottom-up approach is preferred in nanotechnology, whereas conventional technologies usually use top-down approaches [15]. The difference between these two approaches can be explained simply with an example of powder production, wherein the chemical synthesis represents the bottom-up approach, while crushing and milling of chunks represents the equivalent top-down process. The utility of nano metal oxides such as alumina, titania, zirconia and silica has been explored to the world community, still there is a deficiency in making it more popular to the common people. The heavy cost of material due to the precursor, sophisticated infrastructure, intricate process and lack of research in common field leads to little interest for common people. It is interesting to note that the production of nano metal oxide powders in large quantity is essentially required for their potential applications in refractories and ceramics. A variety of synthesis methods are being explored and developed for the production of nano metal oxide powders such as mechanical milling [16], thermal decomposition [17], hydrothermal [18] chemical [19] and sol-gel methods [20]. Every method has its own advantages and disadvantages. Synthesis of nano metal oxides through numerous solution based techniques such as ball milling, hydrothermal, sol-gel and spray pyrolysis have been reported elsewhere [20]. On comparison with several synthesis methods, spray pyrolyser has been found to be an ecofriendly method to produce the mass quantity of nanoparticles through continuous process. It has been found that the materials produced through this process possesses spherical morphology with uniform particle size and all most free flowing structure with quite reduced particle size. The present technology can be used for bulk production of nano particles with low cost from natural minerals employing

Abstract— The spray pyrolyser experimental set-up has been automated for large scale production of nano metal oxides from naturally available resources. The independent operation of spray set-up has promoted cost effective nanotechnology in industries. The present system operates continuously to produce mass quantity of nano powder with controlled particle size and morphology. The stoichiometric compositions of precursor and operational parameters have been controlled. The proposed experimental set-up can be efficiently used for commercial production of different nano metal oxides in continuous manner. Industrial application testing of nano metal oxides developed employing the above method is under progress. Keywords—Automation, Spray Pyrolysis set-up, Nano metal oxides, Particle size.

I. INTRODUCTION anotechnology is the science which deals with the study and manipulation of materials at their nanoscale length. The advancements in nanotechnology have an impact almost in all fields such as materials, instrumentation, electronics, healthcare, defense, sensors, energy, manufacturing and environments [1-5]. One particular subsection of nanotechnology can be distinguished as nanostructured materials i.e., materials in which certain elements of material structure exist at their nanoscale. The structure refers to chemical compositions, arrangement of atoms (atomic structure), and size of a solid in one, two or three dimensions. The size effects such as changes in dimensionality of system, changes in atomic structure and alloying of components are the effects which control the properties of nanostructured materials [6-8]. Nanostructured materials can exhibit higher electrical resistivity and lower thermal conductivities than bulk materials. The synthesis, characterisation and processing of nanostructured materials are quiet important in the emerging and rapidly growing nanotechnology field. Owing to their small size and high surface area to volume ratio, nano powders have created huge interest in recent years by virtue of their unusual magnetic, electrical, electronic, optical and mechanical properties [9-14]. Nano metal oxides have been

N

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2 CiiT international Journal of Automation and Autonomous System, DOI: AA052009005, May 2009 suitable precursors such as aluminium nitrate, zirconium nitrate and titanium hydroxide. The prepared nano particles have been potentially applied in refractories to improve their physico-chemical properties such as thermal expansion, densification and sintering temperature. The spray pyrolysis has been identified as the desirable method for mass production of nano powders for refractory applications. Spray pyrolyser is an automated system which provides significant benefits such as scale up the productivity in a manufacturing environment and vigorous change in technology advancements with increasing automation leads to faster tools for continuous production of nano powders. In the present investigation, an attempt has been made to produce nano metal oxides for industrial applications with controlled size and morphology.

The total automated experimental set-up is controlled by single control panel. The working features of automated system are explained in the following headings. a) Atomiser It consists of two-fluid nozzle with different size such as 0.7 mm, 1.0 mm and 1.5 mm diameter made of titanium metal. The atomiser is used to convert the precursor solution into fine droplets called atomisation. The atomised droplets size depends on the nozzle size and pressure of compressed air. The atomised spherical droplets get decomposed to form spherical particles. b) Automated anti-block unit The blocking of nozzle has been anti-blocked by a sharp stainless steel rod (AISI 316L) which is automatically operated in a fixed interval of time. It is an essential process for continues operation of the system. c) Tubular electric furnace with Hot air blower It consists of one main heater and one auxiliary heater (supporting heater) with temperature controller. The auxiliary heater is used to produce hot air up to the required temperature to air blower. The temperature of air flow has been monitored by inlet temperature controller which is present in hot air blower. An effective temperature sensor (Maxthermo, MC-2438) has been used to monitor the fixed temperature with an accuracy of ± 5° C. The blower speed is controlled employing Selec, PIC 101 RPM controller.

II. EXPERIMENTAL SET-UP The block diagram of automated spray pyrolysis experimental set-up used for mass production of nano metal oxide particles is shown in Fig. 1. The present independent spray pyrolyser experimental set-up primarily consist of a) an atomiser which converts the starting solution into droplets, b) automated anti-blocking unit, c) a tubular electric furnace with hot air blower, d) two-fluid nozzle with compressed air inlet and sample feeding port, e) feed pump which facilitate the flow rate of precursor, f) reaction chamber, g) cyclonic sample collectors and h) purification system.

1.

Two-Fluid Nozzle

9.

2.

Feed Pump

10. Compressed Air Inlet

3.

Nozzle

11. Heater

4.

Spray Angle

12. Air-Blower

5.

Air-Broom

13. Compressed Air Inlet

6.

Chamber

14. Exhaust

7.

Collection Port

15. Water In

8.

Cyclone

16. Drain

d) Two-fluid nozzle with compressed air inlet and sample feeding port In spray pyrolyser, two way fluid nozzle is located at the top of reaction chamber which consists of one compressed air inlet port and one sample feeding port. The atomiser is formed by mixing the precursors with pressurised air at the edge of two fluid nozzle. The pressure of compressed air is regulated in PSI employing waaree pressure gauge regulator. e) Feed pump Peristaltic feed pump with precise RPM controller (Selec, PIC 101) is used in the system to control the flow rate and uniform feeding of precursors in sample port. Adjustable speed pump is operated at a constant speed which is selected by the user. The pump is made up of stain steel (AISI 316L) corrosion resistance material. The pump is capable to run continuously and it can maintain the performance of atomiser. The compressed fluid goes from initial stage to reaction chamber by constant and continuous manner and it have the ability to pump in respective direction with equal efficiency. The operation of the pump is controlled using control panel. f) Reaction chamber A cylindrical stainless steel (AISI 316L) tubular reaction chamber is connected with hot air blower and two fluid nozzles which are located at the top of chamber. At the other end of reactor, three different cyclones in zigzag arrangements are connected. It consists of four different parallel temperature zones which have been used to identify chamber temperature at different places. The atomised droplets get decomposed at the reaction chamber to form ultra fine spherical particles which are forced out to cyclones by internal air pressure.

Sample holding vessel

17. Anti-block unit

Fig. 1 Block diagram of automated spray pyrolyser experimental set-up 2

3 CiiT international Journal of Automation and Autonomous System, DOI: AA052009005, May 2009 sequences of formation of atomiser droplets and nano sized entities are shown in Fig.3. The sprayed and atomised nano entities are decomposed to obtain nano metal oxide powders which have been collected at different cyclones. The decomposed mass like H2O, NO2 etc., can be eliminated by ceramic water filter which is in the purification system. After the completion of one full cycle, the produced nanoparticles are collected from the cyclones. There are two main parts of cyclones which are used for the powder collection such as second and third cyclones. These two cyclones consist of fine powders which are in nano range. The above process is known as spray pyrolysis or aerosol decomposition synthesis or droplet-to-particle conversion. The total process is automated using a single power control panel which controls the process automatically. Development of this method is based on thermal decomposition which is proved to be a milestone for inorganic powder materials technology. In the present investigation, attempts have been made to employ this method to obtain titania and zirconia nano particles by continuous process.

(g) Cyclonic sample collectors The decomposed nano powders have been collected on three different cyclonic collection ports. The tangential location of orifice develops a downward, spiraling flow of solid particles. The centrifugal force developed at the collection chamber walls is a downward direction which is greater than that of gravity. This centrifugal force spins out the solid particles from the orifice. The solid particles strike and deposited on the collector wall. The coarse, fine and ultra-fine particles have been collected respectively at the initial, middle and end of collection port. (h) Purification system It consists of two main parts such as reverse air jet filter and wet scrubber to avoid the fine particles enter into environments. The few uncollected ultra fine particles have been deposited by reverse air jet filter and the decomposed gas molecules like NO2 have been dissolved in flow water at wet scrubber which prevents the air pollution. In addition, wet scrubber contains an out let port to release the drain. The automated spray pyrolyser experimental set-up is as shown in Fig.2

Precursor solution

Atomized droplet

Fig.2. Automated spray pyrolyser experimental set-up

Pressurised droplet

Nano sized entities

III. WORKING PRINCIPILE Fig.3. Two-fluid nozzle- atomisation process

The true homogeneous solution is the starting phase in spray-pyrolysis method which is used to obtain nano powders. In spray-pyrolysis, reaction often takes place in solution in droplets, followed by solvent evaporation. The method is based on atomising the precursor and injecting the spray into a tubular reaction chamber. The atomised droplets of the precursor are converted into nanosized oxide crystallites or nano sized entities during their flow through the tubular reaction chamber. The hot air is introduced into the reaction chamber followed by the precursors are sprayed into chamber with use of two-fluid nozzle along with compressor air in let. The feed pump is used to control the flow rate of processors and formation of atomiser. The formation of atomiser is controlled by controlling the pressure of compressed air. The process

Decomposition reaction In spray pyrolysis, metal hydroxides and metal nitrates are the frequently used precursors for production of nano metal oxides powders. A typical decomposition reaction of zirconyl nitrate and zirconium hydroxide precursors is given in equation 1 and 2 respectively. ZrO(NO3)

ZrO2 + NO2

(1)

Zr(HO)2

ZrO2 + H2O

(2)

The precursor such as zirconyl nitrate, zirconium hydroxide, titanium hydroxide, aluminium nitrate and aluminium hydroxide are obtained respectively from natural 3

4 CiiT international Journal of Automation and Autonomous System, DOI: AA052009005, May 2009 minerals such as zircón sand, rutile sand and bauxite. The spray pyrolyser is a unique method for mass production of nano powders from precursors which are obtained from natural minerals. The important results of zirconia nanoparticles obtained from zirconyl nitrate through the automated spray pyrolysis are as shown in Figs.4 and 5.

flexibility with respect to the composition superior to any other methods.  Sub-micron (nanosized) oxide-based ceramic powders are produced directly from a homogeneous aqueous solution of metal salts (precursor).  This method produces identical size of particles (also called mono sized with uniform size distribution), identical shape or morphology, identical chemical composition and individually dispersed or mono dispersed particles (i.e., no agglomeration).  The products find application in areas such as structural (mechanical properties) as well as functional (electric, magnetic, etc. properties).  Economically spray pyrolysis is more advantageous when compared with other traditional methods offering high-quality ceramic powders. Considerable work has yet to be done to develop and improve the process technique for mass production of nano powders efficiently. In most of production processes of nano powders, there are still few requirements.  to control the nucleation and grain growth  to develop a technique capable of controlling particle agglomeration and size distribution  to develop methods to scale-up the systems effectively to shorten their manufacturing cycle time.

Density Distribution (q)

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2.0

1.5

1.0

0.5

0.0 0

20

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60

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Particle Size (nm)

Fig.4. Particles size of zirconia (ZrO2) nanoparticles Fig.4 depicts that the synthsised powder consists of particle size in the range of 20-80 nm and the maximum distribution of particles is at 38 nm. The results are effective when compared to other conventional methods. The specific surface area of spray synthsised powders are 38 m2 g-1.

IV. CONCLUSIONS Among all other methods, automated spray pyrolyser has many advantages compared to other classical process routes such as simple process, continuous production and ease scaling for mass production of nano metal oxides. As synthesized nano powder has unique spherical morphology with uniform particle size distribution. Automation of this process facilitates to scale up for large scale production of nano metal oxides. ACKNOWLEDGMENT The authors are very much thankful to Department of Science and Technology, New Delhi for the financial support to carry out this research project (SR/S5/NM-40/2005 dt. 26.06.07). V. Rajendran and P. Renukadevi are very much thankful to Dr. N. M. Ramaswamy, Director, Biotechnology, Anna University, Coimbatore for his valuable guidance and support.

Fig.5. SEM micrographs of zirconia nanoparticles Uniform spherical morphology of particles has been confirmed from SEM analysis (Fig.4). All the above results confirm the feasibilities of present automated spray pyrolysis experimental set-up for large scale production. Salient features The following are the salient features of automated spray pyrolysis experimental set-up:  Spray pyrolysis produces powders with small particle size down to nm range with a high degree of purity and crystallinity.  Spray pyrolysis as a method can meet all the specific requirements and at the same time exhibit a relatively high production rate and demonstrates a high

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Balasubramanium Saravanakumar obtained his post graduate degree from Nallamuthu Gounder Mahalingam College, Pollachi. Now he is pursuing his doctorial studies at Anna University, Coimbatore on development of nanobioactive glass for different biomedical applications.

Prema Ranjan Rauta obtained his post graduate degree from Utkal University, Orissa. He has two years experience in R&D. Currenly, he is pursuing his doctorial studies at Anna University, Coimbatote on sythesis and charactrisation of nano titania for industrial applications.

Bhakta Bandhu Sahu has received post graduate degree in geology from Sambalpur University, Orissa. He finished Master of Philosophy in the field of hydro geology at Sambalpur University, Orissa. Since 2002, he has been working as a scientist in Dalmia Institute of Scientific and Industrial Research. He has submitted his Ph. D. thesis in the field of plasma mediated synthesis of nano materials at Sambalpur University, Orissa. He published more than 10 research articles in different international journals. Dr. Bharati Krushna Panda has obtained his Doctoral degree in Chemistry at Sambalpur University, Orissa in the year 1994. Currently working as Director in Dalmia Institute of Scientific and Industrial Research at Rajgangpur and engaging in R & D work in ceramics and allied fields. He worked as Technology Manager in R & D, Tata refractories Limited, Belpahar for 26 years and engag -ing in R & D of refractory, ceramic raw materials and products. He is a member in Indian Institute of Ceramics, Indian Institute of Refractory Engineers and Indian ceramic society. He has rich experience in development of refectories for various industrial applications.

Dr. P.Renuka Devi received her post graduate degree in the field of Biochemistry at Maharaja College for Women, Erode during April 1998. She finished Master of Philosophy in the field of Biochemistry at Kongunadu Arts and Science College, Coimbatore during December 2003. She received Doctor of Philosophy in the field of Biochemistry at Kongunadu Arts and Science College, Coimbatore during March 2009. Smt. P. Renuka Devi has served different positions from June 1999 to August 2008 in Kovai Kalaimagal College of Arts and Science, Coimbatore. Currently working as lecturer in Biotechnology Centre, Department of Nanotechnology, Anna University Coimbatore, Coimbatore. She has published 6 research articles in different international journals. She is a member in Board of studies, Department of Biochemistry of Bharathiar University from 2007-2009, Microbiological Association of India and Indian Council of Science Congress.

Dr. Venkatachalam Rajendran, presently working as a Director, R&D, Centre for Nano Science and Technology, K. S. Rangasamy College of Thechnology, Tamilnadu, India. He has more than 15 years of rich academic experience at different Institutions. He has many research achievements during the same period. He has developed a Centre for Nano Science and Technology at K. S. Rangasamy College of Technology. He is at the verge of completion of M.Tech degree in NanoTechnology. Presently he developed nano metal oxides from natural minerals for diffent industrial applications. He visited number of Research Centres and Universities in India and abroad. He has completed 10 research projects. He has received number of awards and fellowship including Tamilnadu Young Scientist Award. He has published more than 85 research articles in different national and international journals. He has written 16 books in different topics and one among them is a R&D book.

Dr. P. Kolandaivel has received his Doctoral degree in Physics from University of Madras in the year 1987. He worked as Assistant Professor of Physics till 1988 at Government Arts College, Madras. Then, he joined at Bharathiar University, Coimbatore. He has served different positions in Department of Physics, Bharathiar University. Presently he is heading the Department of Physics. He has guided many young researchers for M. Phil and Ph. D degrees. His research area includes the quantum mechanics concepts of atomic and molecular properties of diverse biomolecules like proteins, nucleic acids. He has more than 90 publications in well-reputed journals with an overall citation around 300. He has collaboration with many researchers and research groups within India and abroad.

Palanisamy Manivasakan received his post-graduate degree from Gandhigram Rural University. He received his M.Phil. Degree in chemistry at School of Chemistry, Madurai Kamaraj University. He has developed monometal and bimetal nanoparticles based modified electrodes. Currently he is pursuing his doctoral studies at Anna University, Coimbatore on synthesis and characterisation of nano metal oxides for industrial applications.

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