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 with a pressure of 80 MPa and a flow rate of 220 L/min. Scanning electron microscopy analysis showed that as-prepared silver particles were aggregated and had various types of morphologies such as spherical, spheroidal and irregular. The volume average particle size of as-prepared silver powder was 7.7 μm at the drain rate of 0.024 kg/s. The particle size decreased with decreasing the drain rate. Powder X-ray diffraction revealed that the silver powder with a single phase and high crystallinity was formed. Surface treatment of silver powders classified to 5 μm was performed at 10,000°C by radio-frequency (RF) plasma under argon atmosphere. RF plasma treatment led to the formation of spherical particles from irregular particles. The crystallinity and crystallite of silver powder were increased by RF plasma treatment. X-ray photoelectron spectroscopy showed that the oxygen content in silver particles decreased from 500 ppm to 45 ppm. Thermomechanical analysis revealed that the shrinkage of silver powder reduced by the RF plasma treatment. It was clear that the particle characterization of silver powder was significantly modified by RF plasma treatment. The specific resistivity of silver paste sintered at 900°C exhibited 1.89×10 -8 Ωm.

No abstract

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.

Monodispersed silver particles were prepared through wet chemical reduction method. As prepared silver particles had uniform polyhedron morphology with narrow size distribution. Powder X ray diffraction analysis showed that the silver powders had high crystallinity. The particle size of silver powders was controlled by adjusting the concentration of starting reagents and temperature. In a wet chemical reduction reaction, monodispersed silver particles were formed when the molar ratio of reducing agent and silver nitrate was 0.5. It was possible to control the particle size from 120 nm to 800 nm by adjusting the concentration of silver nitrate. The particle size of silver powders decreased to 70 nm with increasing the concentration of gum Arabic. Thermal mechanical measurement showed that the shrinkage of silver paste was 25 at 900. Electrical measurements revealed that the speci c resistivity of the silver paste sintered at 900 for 10 min was 1.81 × 10 −8 Ω m. It was expected that the silver powders exhibited excellent electrical property as electrode materials for integrated circuits, multilayer ceramic capacitor and solar cells etc.