High-Temperature Mass Spectrometry, Vaporization, and Thermodynamics of Titanium Monosulfide

Abstract

A high‐temperature mass spectrometric investigation of the vaporization of titanium monosulfide, $\mathrm{TiS}\mathrm{(s)}$ , from 1700–2150°K has shown that the three principal vaporization reactions produce $\mathrm{TiS}\mathrm{(g),}\mathrm{Ti}\mathrm{(g)\hspace{0.17em}+\hspace{0.17em}S(g),}\mathrm{and}\mathrm{Ti}\mathrm{(g)\hspace{0.17em}+\hspace{0.17em}}\frac{1}{2}{\mathrm{S}}_2\mathrm{(g)}$ , the second being about four times as important as the first and both more important than the third. The disulfide ${\mathrm{TiS}}_2\mathrm{(g)}$ comprises less than 1% of the vapor. Thermodynamic results were obtained from five investigations, three with stoichiometric samples, one with excess titanium metal, and one with excess sulfur produced from admixed $\mathrm{SrS}\mathrm{(s)}$ . Equations representing partial pressures as functions of temperature are given. Based on Mann's cross sections for atoms, additivity for molecules, and the assumption of no fragmentation, the third‐law enthalpy of vaporization to form $\mathrm{TiS}\mathrm{(g)}$ is 140.7 ± 1.3 and to form one‐half mole each of $\mathrm{Ti}\mathrm{(g)}$ and $\mathrm{S}\mathrm{(g)}$ is 121.2 ± 1.1 kcal; the dissociation energy, $D_{298}°$ , of $\mathrm{TiS}\mathrm{(g)}$ is 101.8 ± 1.8 kcal/mole; the enthalpy of formation at 298°K of $\mathrm{TiS}\mathrm{(s)}$ is − 62.7 ± 2.5 kcal/mole. Earlier vapor pressure data were corrected for the partial dissociation of the vapor, and thermodynamic data derived from them are in excellent agreement with the new results. Appearance potentials are reported for several ionic species. Effects of ionic fragmentation and ionization cross section errors on the thermodynamic results are discussed, and a method for measuring these effects is described.