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.

Silver powder was produced through water atomization at the high pressure of 80 MPa. Before the water atomization, silver was melted at 1330°C under nitrogen atmosphere. Scanning electron microscope observation showed that the as-prepared silver powder had various particles with morphologies such as spherical, irregular and coarse. The volume average particle size (D 50 ) of as-prepared silver powder determined by laser photo-scattering method was 7.7 μm. D 50 was influenced by the condition of atomization angle and drain rate. D 50 decreased with decreasing to atomization angle and drain rate. Electron probe micro analysis revealed that the oxygen content in as-prepared silver powder was 50 ppm. The specific resistivity of silver paste decreased to 1.75 × 10 −8 Ω·m with increasing the sintering temperature. When silver paste was sintered at 900°C for 10 min, the microstructure of silver paste was densified with the large grain growth.