Incongruent vaporization of titanium carbide in thermal plasma

Abstract

Vaporization of TiC at the plasma high temperatures (4000–10 000 K) has been investigated by structural and compositional characterizations of the vapor-condensed products formed by Ar–H 2 and Ar–He heating followed by a thermodynamic calculation. An incongruent vaporization of TiC with preferential vaporization of titanium has been observed at higher temperatures, which is contrary to the behavior at lower temperatures observed previously. X-ray diffraction and chemical analysis revealed a significant reduction of carbon and correspondingly, a decrease of lattice parameters in the vapor-condensed product with respect to the starting TiC materials. The vapor-condensed products have a composition of TiC x ( x =0.38–0.58) and the lattice parameters are in range of a 0 =4.28420–4.30780 Å, depending on processing conditions. A calculation of equilibrium vaporization using Langmuir model shows that TiC vaporizes incongruently to Ti at high temperatures between 3150 and 4700 K, in agreement with the present experimental observations.