Vaporization Processes Involving Sulfur

Abstract

Free evaporation of rhombic sulfur is shown to give rise solely to S₈ vapor molecules, whereas the sublimation of an allotropic form (Engel's sulfur) produces only S₆ vapor molecules. The vapor composition characteristic of equilibrium can be produced by mixing any allotropic form of sulfur with commercial Al₂O₃, which evidently catalyzes the transformation among sulfur species. The evaporation coefficients of S₆ and S₇ molecules from a rhombic sulfur surface have been measured. The behavior of other allotropes (S_μ, S_π) is described as observed by mass spectrometry. Mass spectra of S₆ and S₈ molecules have been determined directly as a function of temperature and that of S₇ deduced from a vapor mixture of S₆, S₇, and S₈. Ionization efficiency curves and appearance potentials of the major ionic species are reported. Paramagnetic resonance measurements have been used to help elucidate the mechanism of catalysis.