Treatment of refractory powders by a novel, high enthalpy dc plasma

Abstract

Thermophysical properties of CO2–CH4 mixtures at high temperatures are very attractive for materials processing. In comparison with argon, at the same temperature, such a mixture possesses much higher enthalpy and higher thermal conductivity. At high temperatures, CO2–CH4 mixture has a complex composition with strong presence of CO which, in the case of powder treatment, could reduce oxidation. In this work, a dc plasma torch with graphite cathode was used to study the effect of plasma gas composition on spheroidization of tungsten carbide and alumina powders. Two different gas compositions were used to generate the plasma while the torch current was kept at 300 A. Various techniques were employed to assess the average concentration of carbides and oxides and the final shape of the treated powders. Process parameters such as input power and plasma gas composition allow controlling the degree of powder oxidation and spheroidization of high melting point ceramic powders.