Flame spray pyrolysis

Novel Synthesis of Al2O3 Nano-particles by Flame Spray Pyrolysis : 

Novel Synthesis of Al2O3 Nano-particles by Flame Spray Pyrolysis A.I.Y. Tok *, F.Y.C. Boey, X.L Zhao School of Materials Science & Engineering, Nanyang Technological University, Nanyang Avenue, Singapore 639798, Singapore Sathya sadhasivam 26 MAR2009

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1.Introduction 2.Materials and methods 3.Result and Discussion 4. Conclusion

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Aluminium oxide (alumina, Al2O3) is currently one of the most useful oxide ceramics. Alumina is hard, highly resistant towards bases and acids, allows very high temperature applications and has excellent wear resistance. Flame spray pyrolysis method to produce nano-sized alumina particles using gas and aqueous precursors. This method has many advantages over the other methods as it is low-cost, easy to control particle size, simple processing, high production yield, and ease of conversion to mass manufacturing.

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Diagram of the flame spray pyrolysis apparatus Apparatus used to prepare the Al2O3 nano-particles The anhydrous AlCl3 powders were injected into the flame gun using the heating chamber at 300 ?C by means of nitrogen gas and were directly sprayed intothe collection chamber. Combustion occurred at less than 2000 ?C. In order to remove residual water and obtain fully crystallized particles with small particle size, the as-sprayed Al2O3 nano-particles were calcined at 1100 ?C for 2 h using a heating rate of 10 ?Cmin-1. Cooling rate was set to 50 ?Cmin-1 to reduce the possibility of agglomeration of nano-alumina powders.

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Characterization Gas sorption Differential thermal analysis X-ray diffraction Transmission electron microscopy Ceramic Powder Synthesis by Spray PyrolysisGary L. Messing, ? 1 Shi-Chang Zhang, ? 1 Gopal V. Jayanthi ? 1 1 Particulate Materials Center, The Pennsylvania State University, University Park, Pennsylvania 16802

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Results and Discussion There are three important aspects to flame spray pyrolysis Aerosol production, combustion and powder collection. Although it seems that these processes are independent, they are actually inter-related. For example, incomplete combustion occurs when large droplets are injected into the combustion zone, resulting in porous particles akin to those produced via spray pyrolysis G.L. Messing, S.C. Zhang, G.V. Jayanthi, Ceramic powder synthesis by spray pyrolysis, J. Am. Ceram. Soc. 76 (1993) 2707–2726.

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183ºc DSC analysis of anhydrous AlCl3 powder This represents the boiling point of the anhydrous AlCl3 powders. To obtain the AlCl3 vapour in this experiment Anhydrous AlCl3 was directly heated up to 300 ?C before it was carried out into the flame gun with nitrogen. In addition, a small exothermic peak was also observed at 760 ?C, measuring 107.6 J g-1. This represents the phase transformation of ?-Al2O3 to a-Al2O3. In order to fully convert the ? -Al2O3 to ?-Al2O3, the as-sprayed nano-particles had to be calcined at above 1000 ?C

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XRD Pattern of as-sprayed alumina nano-particles

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XRD pattern of alumina nano-particles calcined at 1100 ?C for 2 h.

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TEM micrograph of as-sprayed alumina nano-particles. TEM of alumina nano-particles calcined at 1100 ?C for 2 h.

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conclusion The novel flame spray pyrolysis method has successfully produced nano- sized Al2O3 of about 10–30 nm and 80–100 nm from AlCl3 vapour. Based on XRD results, the as-sprayed nano-particles consisted of -phase and -phaseAl2O3, which can be converted to -phase by calcination at 1100 ?C for 2 h. The particle size of calcined powders was about 80–100 nm. Although this work focused on the synthesis of Al2O3 nanoparticles, it can be seen that this method has the flexibility of easily producing other nano- particles by flame spraying other metal chlorides that have a low boiling point.