Phase transitions and equilibrium hydrogen content of phases in the water–hydrogen system at pressures to 1.8 kbar

Abstract

Using a volumetric technique, the hydrogen solubility X in liquid water (L), low-pressure hexagonal ice (I _h), and high-pressure cubic clathrate ice (sII) is studied at hydrogen pressures up to 1.8 kbar and temperatures from−36 to+20 ^°C. The triple point of the L+I _h+sII equilibrium is located at P=1.07(5) kbar and T=−10(1) ^°C. The hydrogen concentrations of phases at the triple point are X _L =0.17(5), and X _sII=2.3(1) wt.% H₂. The thermal stability and the process of decomposition of the clathrate phase at ambient pressure are studied by neutron diffraction.

Keywords:

• Clathrate hydrate
• Phase equilibria
• Thermal stability

Acknowledgements

This work was supported by Grant No. 05-02-17733 from the Russian Foundation for Basic Research and by the Program ‘Physics and mechanics of strongly compressed matter’ of the Russian Academy of Sciences. One of the authors (V.S.E.) thanks the Organizing Committee of the 44th EHPRG Conference for financial support to attend the Conference.