The high temperature vaporization of defect scandium monosulfide

Abstract

A high temperature vaporization study of the scandium–sulfur system has shown that a defect scandium monosulfide phase with composition Sc/S=0.8065 vaporizes congruently over the temperature range 1875–2220 K. High temperature mass spectrometric results show that the congruently subliming phase has two principle vaporization reactions producing ScS(g)+S(g) and Sc(g)+S(g). Thermodynamic results for Sc0.8065S(s) were obtained from both mass spectrometric and target collection investigations. Based on Mann’s cross sections for atoms, additivity for molecules, and the assumption of no fragmentation, the third-law mass-spectrometric enthalpy of vaporization at 298 K of Sc0.8065S to form Sc(g)+S(g) is 223.4±4.5 kcal and to form ScS(g)+S(g) is 133.8±4.5 kcal; the dissociation energy D°298 obtained for ScS(g) is 111.1±4.5 kcal. The third-law mass-spectrometric results are in good agreement with the target collection results. Ion intensity data were collected for ScS+ as a function of time upon vaporization of stoichiometric ScS(s) at 2035 K. The third-law value obtained for the enthalpy of atomization at 298 K of Sc1.0S(s) is 240.2±5 kcal.