RESUMEN

Powder samples of cristobalite-I are loaded with hydrogen at pressures up to 90 kbar and T = 250 °C and quenched under pressure to the liquid N2 temperature. The quenched samples are examined at ambient pressure by X-ray diffraction, Raman spectroscopy, and thermal desorption analysis. The hydrogen content of the samples is found to increase with pressure and reach a molecular ratio of H2/SiO2 ∼ 0.10 at P = 90 kbar. At ambient pressure, the samples consist of a mixture of approximately 80% cristobalite-I phase and 20% cristobalite-II-like phase, the crystal lattices of both phases being slightly expanded due to the hydrogen uptake. According to Raman spectroscopy, the hydrogen is dissolved in these phases in the form of H2 molecules.

Asunto(s)

Hidrógeno/química , Nitrógeno/química , Presión , Dióxido de Silicio/química , Solubilidad , Espectrometría Raman , Temperatura , Difracción de Rayos X

RESUMEN

The solubility of hydrogen in amorphous silica at a temperature of 250 °C and pressures up to 75 kbar is studied using a quenching technique. The molar ratio H(2)/SiO(2) is found to linearly increase with pressure from X = 0.16 at P = 6 kbar to X = 0.53 at P = 75 kbar. An investigation of a sample with X = 0.47 by Raman spectroscopy demonstrated that hydrogen dissolves in silica in the form of H(2) molecules, and these molecules occupy voids of, at least, two different types in the silica network. An X-ray diffraction study showed that the hydrogen molecules penetrating in the silica glass network prevented its irreversible densification occurring if the silica glass is compressed to the same pressure without hydrogen.

RESUMEN

Using a volumetric technique, a T-P diagram of phase transformations between the hydrogen-rich clathrate hydrate (sII phase), hydrogen-filled ice II (C(1) phase), and the liquid (L) is studied in the H(2)O-H(2) system at pressures up to 4.7 kbar and temperatures from -22 to +15 degrees C. The volume and entropy effects of these transformations are established in the vicinity of the triple point of the L + sII + C(1) equilibrium located at P = 3.6(1) kbar and T = +1(1) degrees C. The estimated molar ratios H(2)/H(2)O of phases at the triple point are X(L) = 0.04(2), X(sII) = 0.32(2), and X(C1) = 0.10(2).

RESUMEN

Using a volumetric technique, the deuterium solubility, X, in heavy water (L), low-pressure hexagonal ice (I h), and high-pressure cubic clathrate ice (sII) is studied at deuterium pressures up to 1.8 kbar and temperatures from -40 to +5 degrees C. The triple point of the L + I(h) + sII equilibrium is located at P = 1.07(3) kbar and T = -4.5(8) degrees C. The molar ratios D2/D2O of phases at the triple point are X(L) = 0.020(5), X(Ih) = 0.012(5), and X(sII) = 0.207(5).