Low Temperature Fabrication fo High Quality Powders by Ultra - fine Grinding under Electrical Discharge

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Composite particles are just key materials which create various kinds of new materials. This study aimed at developing novel powder processing technique to fabricate high quality composite particles rapidly under low temperature processing by making use of ultra-fine grinding mechanism assisted by electrical discharge. The formation mechanism of these powders was also discussed. The experiments started from the development of particle processing apparatus. Then, direct synthesis of composite oxide nanoparticles were conducted without any heat assistance, and the surface modifications of titanium dioxide nanoparticles were also conducted in NH3/N2 gas conditions with glow discharge. For the former experiment, La and Mn powders used in industries were selected, and both powders were processed by the apparatus with high mechanical energy. Consequently, nanosized particles of LaMnO_3 were synthesized only by mechanical energy input without any heat assistance. The reaction route was discussed by a mechanochemical reaction with the assistance of water in the atmosphere. For the latter experiment, nitrogen doping onto the surface of titanium oxide nanoparticles was conducted in the mixed gas of ammonium and nitrogen with glow discharge under mechanical processing. As a result, the nitrogen doping was successfully achieved without any grain growth of nanoparticles. The photocatalytic activity was also obtained by such surface modification under visible light. The doping mechanism was also discussed by a reaction model of nitrogen and titanium dioxides under plasma atmosphere. These results suggest that the processing technique developed by this study is promising for creating various kinds of high functional powders.