Feature Article Earozoru Kenkyu, 26 1, Preparation of Nanoparticles by Ultrasonic Spray Pyrolysis 1 Takashi OGI 1 and Kikuo OKUYAMA 1 Rec

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1 Feature Article Earozoru Kenkyu, 26, Preparation of Nanoparticles by Ultrasonic Spray Pyrolysis Takashi OGI and Kikuo OKUYAMA Received 2 August 200 Accepted 29 September 200 Abstract In this review, we describe in detail the methods to produce various nanoparticles using ultrasonic spray pyrolysis. In general, droplets generated by an ultrasonic nebulizer have a size of approximately 5 micrometers so that submicrometer particles are typically produced by the conventional spray pyrolysis (CSP). In order to produce nanoparticles, modifications in technique such as adding salts or polymers to precursor solutions are necessary. However, salt assisted-sp requires an additional treatment of washing to dissolve and remove residual material from the produced nanoparticles. The addition of polymers does not require washing process because they are decomposed and volatilized during the pyrolysis. Both methods produce isolated nanocrystals. In flame spray pyrolysis, the formation of nanoparticles is dominated by the evaporation-condensation route, and therefore the flame temperature controls the formation of nanoparticles. This review concludes that ultrasonic nebulization with subsequent pyrolysis is one of the effective methods to produce nanoparticles. Keywords : Droplet, Particle Synthesis, Nanotechnology, Material Synthesis, Fine Particle Engineering, Flame Synthesis Chemistry and Chemical Engineering, Faculty of Engineering, Hiroshima University -4- Kagamiyama, Higashi-Hiroshima, Hiroshima, * Corresponding Author. okuyama@hiroshima-u.ac.jp (K. Okuyama) Fig. a Fig. b 2.75 MHz Fig. 2 span

2 Fig. Schematic diagram of droplet size measurement using laser diffraction particle size analyzer (a); and Particles generator using conventional and flame spray pyrolysis method (b). X Fig. 3 Fig. 2 Droplet size distribution of pure water at different (a) temperatures, and (b) carrier gas flow rates. (d v,90 d v,0 )/d v,50 5 μm 6 μm Rajian 3 Fig. 4 ODOP: One-Droplet-to-One-Particle ODMP: One- Droplet-to-Many-Particles d d Vol. 26 No

5 FE-SEM images and particle size analysis of ZrO 2 prepared at different conditions: (a) without cyclone; and (b) with

3 Fig. 4 Mechanism of nanoparticle formation from droplet in spray pyrolysis technique. Fig. 3 (a) Physicochemical properties and (b) droplet size distribution of water-alcol solutions. d p 2 dp CD dd MW n ρ Fig. 5 FE-SEM images and particle size analysis of ZrO 2 prepared at different conditions: (a) without cyclone; and (b) with cyclone. MW C D ρ n Fig. 5 Fig nm 5 2 Fig. 6 Comparison of mean diameters of ZrO 2 particles (theoretical values and the measured data)

4 2 3 τ sv τ sl τ sv τ sl τ sv τ sl τ sv <<τ sl Fig. 7 Conventional Spray Pyrolysis Method CSP Salt-Assisted Spray Pyrolysis Method SA-SP Fig. 7 a CSP ODOP 3 SA-SP Fig. 7 b Fig. 7 c Fig. 7 Schematic diagram of the Particle formation mechanism of spray pyrolysis (SP) (a) conventional SP (CSP), (b) particle breaking during SP, (c) salt-assisted SP. Vol. 26 No

SA-SP Fig. 8 Y 2 O 3 -ZrO 2 SEM 8 5. Fig. 9 Fig. 0 PEG Fig. 0 a 600 C 3 Fig. 0 b Fig. 0 b Fig. 0 c 9 2000 CVD Fig.

8 Y 2 O 3 -ZrO 2 samples synthesized by the CSP process (a, b) and the SA-SP process (c, d). a, c) SEM images of the samples before washing and b, d) TEM images after washing.

5 SA-SP Fig. 8 Y 2 O 3 -ZrO 2 SEM 8 5. Fig. 9 Fig. 0 PEG Fig. 0 a 600 C 3 Fig. 0 b Fig. 0 b Fig. 0 c CVD Fig. 9 Schematic diagram of nanoparticle formation and fragmentation by a polymer-assisted heat treatment. Fig. 8 Y 2 O 3 -ZrO 2 samples synthesized by the CSP process (a, b) and the SA-SP process (c, d). a, c) SEM images of the samples before washing and b, d) TEM images after washing. Note that the unwashed SA- SP particles (c) are larger than the unwashed CSP particles (a) due to the presence of salt. Fig. 0 FE-SEM images of SrTiO 3 : Pr, Al particles prepared from 0. M (aqueous solution+peg20000) at 600 C (a), with annealing at 600 C for 3 h (b), annealing with PEG 200 at 600 C for 3 h (c)

kg LED Fig. Flame-made BaTiO 3 nanoparticles prepared from different concentrations, (a) 0. M, (b) 0.4 M, and (c) HRTEM image of BaTiO 3 powder prepared using a precursor concentration of 0. M. The powder was fabricated under gaseous flow rates of CH 4 : 4 L/min, O 2 : 8.

6 kg LED Fig. Flame-made BaTiO 3 nanoparticles prepared from different concentrations, (a) 0. M, (b) 0.4 M, and (c) HRTEM image of BaTiO 3 powder prepared using a precursor concentration of 0. M. The powder was fabricated under gaseous flow rates of CH 4 : 4 L/min, O 2 : 8.4 L/min, O 2 (carrier gas): 4 L/min. Fig. 4 a BaTiO 3 TTIP BaTiO nm BaTiO 3 Fig. BaTiO 3 A No References Okuyama, K., Abdullah, M., Lenggoro, I. W. and Iskandar, F.: Preparation of Functional Nanostructured Particles by Spray Drying-A Review, Adv. Powder Technol., 7, (2006) 2 Wang, W. N., Purwanto, A., Lenggoro, I. W., Okuyama, K., Chang, H. and Jang, H. D.: Investigation on the Correlation Between Droplet and Particle Size Distribution in Ultrasonic Spray Pyrolysis, Ind. Eng. Chem. Res., 47, (2008) 3 Rajan, R. and Pandit, A. B.: Correlations to Predict Droplet Size in Ultrasonic Atomization, Ultrasonic, 39, (200) 4 Widiyastuti, Wang, W. N., Lenggoro, I. W., Iskandar, F. and Okuyama, K.: Simulation and Experiment of Spray Pyrolysis of Polydisperse Droplets, J. Mater. Res., 22, (2007) 5 Xia, B., Lenggoro, I. W. and Okuyama, K.: Novel Route to Nanoparticle Synthesis by Salt-Assisted Aerosol Decomposition, Adv. Mater., 3, (200) 6 Xia, B., Lenggoro, I. W. and Okuyama, K.: Synthesis of CeO 2 Nanoparticles by Salt-Assisted Ultrasonic Aerosol Decomposition, J. Mater. Chem., 3, (200) 7 Xia, B., Lenggoro, I. W. and Okuyama, K.: Synthesis and Photoluminescence of Spherical ZnS:Mn 2+ Particles, Chem. Mater., 4, (2002) 8 Wang, W. N., Kim, S. G., Lenggoro, I. W. and Okuyama, K.: Polymer-Assisted Annealing of Spray-pyrolyzed Powders for Formation of Luminescent Particles with Submicron and Nanometer Sizes, J. Am.Ceram. Soc., 90, (2007) 9 Purwanto, A., Wang, W. N., Lenggoro I. W. and Okuyama K.: Formation of BaTiO 3 Nanoparticles from an Aqueous Precursor by Flame Assisted Spray Pyrolysis, J. Eur. Ceram. Soc., 27, (2007) Vol. 26 No

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