High temperature mass spectrometry, vaporization, and thermodynamics of vanadium monosulfide

Abstract

A high temperature mass spectrometric investigation of the congruent vaporization of vanadium monosulfide, VS(s), from 1700 to 2000°K has shown that the two principal vaporization reactions produce VS(g) and V(g) + S(g) with a minor contribution from the reaction to produce VS₂(g) + V(g). Thermodynamic results were obtained from three investigations of the congruent vaporization of the stoichiometric monosulfide. The second law enthalpy changes for the vaporization reactions at absolute zero were calculated from the experimental data and by use of a measured low temperature heat capacity for VS(s), estimated heat capacities for the solid above room temperature and for the vapor molecules, and literature values for the heat capacities of the atomic species. The $\Delta {\mathrm{H}}_0°$ values obtained and the estimated uncertainties are: 143±3 kcal for the reaction to form VS(g), 259±5 kcal for the reaction to form V(g) + S(g), and 144±5 kcal for the reaction to form ½ VS₂(g) + ½ V(g). Ionic fragmentation of VS⁺ is considered and shown to be unimportant. Approximate third‐law calculations of partial pressures of the important species are reported and the results are shown to be in acceptable agreement with the observed ion intensities.