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

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 TBABwater system preferentially forms the TBAB.26H(2)O hydrate. Through in situ Raman spectral analysis, the stable crystal phase of the TBAB hydrate enclosing Xe changed from TBAB.26H(2)O to TBAB.38H(2)O during temperature ramping from 283.6 to 287.4 K at 0.3 MPa. No lattice vibration shift was observed for the TBAB.26H(2)O hydrate enclosing Xe, whereas the lattice vibration of the TBAB.38H(2)O 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.