Compression and Phase Transitions of Solid HCl, HBr, SiH4, and SF6

Abstract

Isothermal PV curves for solid HCl, HBr, SiH4, and SF6 have been determined by the direct piston displacement method up to pressures of 20 000 kg/cm2 at various temperatures between 50° and 190°K. Relative volume changes (and in some cases molar volumes) and compressibilities have been calculated for each substance. Phase transitions have been observed as discontinuities in the piston motion. First-order transitions have been observed in solid HCl, SiH4, and SF6. Phase diagrams are included. The expected second-order transition in solid HBr was not noted, probably because of impurities in the samples. The approximate volume changes accompanying the observed transitions have been determined. Their consistency with other data has been checked by means of the Clausius-Clapeyron equation.