Incongruent vaporization of titanium carbide in thermal plasma

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–H2 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 TiCx (x=0.38–0.58) and the lattice parameters are in range of a0=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.