INFLUENCE OF CARBON PRECURSOR ON THE GAS-PHASE CHEMISTRY OF THE Ti-C-Cl-H SYSTEM

摘要

The influence of carbon precursor, either methane (CH_4) or propane (C_3H_8), on the gas-phase chemistry of the Ti-C-Cl-H system used to deposit titanium carbide (TiC) from titanium tetrachloride (TiCl_4) was investigated using calculations of thermodynamic equilibrium, along with time-dependent simulations of rate equations from a proposed kinetic model. Differences in the resultant gas-phase chemistries between CH_4 and C_3H_8 are discussed for reactions under reduced pressure at 1500 K. Initial mixtures of TiCl_4, H_2, and hydrocarbon that produce identical equilibrium compositions were investigated. Results for the Ti-C-Cl-H system for both precursors are compared to those of Ti-Cl-H and C-H in order to further illustrate the differences in thermal stability of key constituents, as well as the extent of conversion. Regardless of which carbon precursor is present, species belonging to the Ti-Cl-H subsystem are near equilibrium within 5 s. Conversely, species emanating from CH_4 decomposition in the Ti-C-Cl-H system are predicted to be far from equilibrium and insensitive to reactions with TiCl_4. Finally, the stability of C_3H_8 in the Ti-C-Cl-H system is significantly enhanced over that of the C-H system. The enhanced stability is accompanied by a significant variation in the rate of byproduct formation, which suggests TiCl_4 and its subchlorides effectively compete with C_3H_8 for important reactive intermediates.