Thermodynamic Description of Crystalline Water Phases Containing Hydrogen

Abstract

Stability regions of crystal phases in the water–hydrogen system have been studied within our statistical thermodynamic model for describing clathrate compounds. The thermodynamic stability of hydrogen-containing ices I_h (C₀^Ih), II (C₁), I_c (C₂), classical clathrate hydrogen hydrate CS-II, and new hydrogen-filled ice phase C₀ has been analyzed. It has been shown that all considered phases are thermodynamically stable, but phase C₀ is metastable with respect to the other phases. The chemical potentials of water molecules in phases C₀ and C₁ are close to each other. As a result, metastable phase C₀ is experimentally observed in the stability region of phase C₁.