ИСТИНА

The paper completes the T-P-X diagram of the H2O-H2 system by an in situ volumetric investigation of phase transitions between the recently discovered unusual C0 hydrate [1] and the C1 hydrate (hydrogen-filled ice II) with a tentative H2/H2O molar ratio of XC0 = 1/6 ≈ 0.17 [2]. The C0↔C1 equilibrium line is positioned so as to leave all experimental points of the C0→C1 transition on the right of it and all points of the reverse transition on the left. Together with the available experimental data on melting of the C0 and C1 phases [1–3], this places the invariant “C0+C1+Liquid+H2 gas” point Q3 at P = 7.7(3) kbar and T = 22(2) °C. Our thermodynamical analysis showed that the hydrogen solubility in liquid H2O measured earlier at pressures below 1 kbar [4], reaches a maximum of H2/H2O ~ 0.02 at P ~ 3 kbar and monotonically decreases at higher H2 pressures. For the Q3 point, we obtained XL = 0.007(3), XC0 = 0.48(5) and XC1 = 0.17(5). The strong decrease in the H2 solubility in liquid H2O at high pressures is of interest for geophysics and planetology, because this suggests that the H2 and H2O fluids should not mix under the T-P interior conditions of the Earth, icy satellites and many other celestial bodies. [1] V.S. Efimchenko et al., J. Alloys Compd. 509S (2011) S860–S863 [2] W.L. Vos et al., Phys. Rev. Lett. 71 (1993) 3150–3153 [3] Y.A. Dyadin et al., Mendeleev Commun. 9 (1999) 209–210. [4] R. Wiebe and V.L. Gaddy, J. Am. Chem. Soc. 56 (1934) 76–79.