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Alumina nanoparticles were directly synthesized by spray pyrolysis using radiofrequency (RF) plasma. The mist that was generated from the aqueous solution of aluminum nitrate by using an ultrasonic vibrator was continuously pyrolyzed in the RF plasma. Scanning-electron-microscope and transmission-electron-microscope images showed that as-prepared alumina nanoparticles exhibited spherical morphology with non-aggregation. The particle size and geometrical standard deviation of the alumina nanopowders obtained at 3000°C were 80 nm and 1.41, respectively. The average particle size of the alumina nanopowders decreased with increasing pyrolysis temperature. The average particle size and particle size distribution of the alumina nanopowders were independent of the concentration. X-ray diffraction revealed that as-prepared alumina nanopowders were crystallized to £-alumina. The crystallinity of the as-prepared alumina nanopowders increased with increasing pyrolysis temperature. BET revealed that the specific surface area (SSA) increased with increasing pyrolysis temperature. The as-prepared alumina nanopowders had a high SSA of 100 m 2 /g at 3,000°C.

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Spherical Ag-Pd alloy particles were prepared from aqueous solutions of AgNO 3 and Pd NO 3 2 by ultrasonic spray pyrolysis. As-prepared powders were dense and non-agglomerated particles, which had sub-micron size and narrow size distribution. XRD shows that as-prepared particles are polycrystalline and the crystal phase of the as-prepared particles has an alloy composition. Ag-Pd particles obtained from spray pyrolysis offer superior oxidation-resistivity of Pd as compared with those obtained from coprecipitation.