Thermal plasma processing — syntheses of diamond and β″-alumina

Thermal plasma processing using a plasma jet with high speed and high heat capacity under reduced pressure (≦100 torr) is one of the most promising methods for synthesizing new materials. We have newly developed a thermal plasma reactor composed of a forced constricted type plasma jet generator with a feed ring, and confirmed that this reactor generates stable plasma jets with a high heat capacity under various operating conditions. In this paper, to realize the large area deposition at a high rate, synthesis of diamond films from gas mixtures of CH4 and H2 is studied. Synthesis of β″-alumina, thermoelectric materials for the alkali metal thermoelectric converter (AMTEC), from powder mixtures is also discussed.