Change in the Stable Crystal Phase of Tetra-n-butylammonium Bromide (TBAB) Hydrates Enclosing Xenon

Abstract

This article reports the inversion of the stable phase of tetra-n-butyl ammonium bromide (TBAB) hydrates in the xenon (Xe)–TBAB–water system. In the TBAB solution (mass fraction of TBAB in the water solution, w = 0.40) under atmospheric pressure, the TBAB–water system preferentially forms the TBAB·26H2O hydrate. Through in situ Raman spectral analysis, the stable crystal phase of the TBAB hydrate enclosing Xe changed from TBAB·26H2O to TBAB·38H2O during temperature ramping from 283.6 to 287.4 K at 0.3 MPa. No lattice vibration shift was observed for the TBAB·26H2O hydrate enclosing Xe, whereas the lattice vibration of the TBAB·38H2O hydrate enclosing Xe shifted to a lower wavenumber. When conducting temperature ramping in a pressure vessel, it was observed that phase transformation of the TBAB hydrates enclosing Xe occurred at a pressure and temperature higher than 0.2 MPa and 287 K, respectively.