Thermodynamic and Raman Spectroscopic Studies on Pressure-Induced Structural Transition of SF₆ Hydrate

Abstract

The SF 6 hydrate system has been investigated by use of a laser Raman spectroscopic analysis in a temperature range from 274 K to 313 K and pressure up to 155 MPa. Two quadruple points have been determined at (286.6 ± 0.2) K, (1.79 ± 0.01) MPa (SF 6 hydrate + water + liquid SF 6 + gas) and at (300.3 ± 0.2) K, (131 ± 1) MPa (SF 6 hydrate + water + liquid SF 6 + solid SF 6 ), respectively. The structure-II SF 6 hydrate changes to the structure-I type hydrate around 33 MPa, which is a so-called “pressure-induced structural transition” of SF 6 hydrate crystal.