The solubility and solution mechanisms of reduced C-O-H volatiles in Na(2)O-SiO(2) melts in equilibrium with a (H(2) + CH(4)) fluid at the hydrogen fugacity defined by the iron-wustite + H(2)O buffer [f(H2)(IW)] have been determined as a function of pressure (1-2.5 GPa) and silicate melt polymerization (NBO/Si: nonbridging oxygen per silicon) at 1400 degrees C. The solubility, calculated as CH(4), increases from similar to 0.2 wt% to similar to.5 wt% in the melt NBO/Si-range similar to 0.4 to similar to 1.0. The solubility is not significantly pressure-dependent, probably because f(H2)(IW) in the 1-2.5 GPa range does not vary greatly with pressure. Carbon isotope fractionation between methane-saturated melts and (H(2) + CH(4)) fluid varied by similar to 14%. in the NBO/Si-range of these melts.

The influence of ferrous and ferric iron on the low-temperature heat capacity and vibrational entropy of silicate glasses has been determined by adiabatic calorimetry. Two pairs of samples based on sodium disilicate and calcium Tschermak molecule compositions have been studied. Along with previous data for another Fe-bearing glass, these results have been used to complement the available set of composition independent partial molar relative entropies of oxides in silicate glasses with S-298 - S-0 values of 56.7 and 116 J/mol for FeO and Fe2O3, respectively. The calorimetric data indicate that the fraction of fivefold coordinated Al is significant in the CaO-"FeO"-Al2O3-SiO2 system and that association of Ca2+ and Na+ with Fe3+ in tetrahedral coordination for charge compensation does not entail significant changes in coordination for these two cations. At very low temperatures, however, the heat capacity is no longer an additive function of composition because of unexpectedly high positive deviations from Debye laws. These anomalies are stronger for the reduced than the oxidized glasses and considerably larger than for iron-free glasses, but their origin cannot be established from the present measurements. (C) 2009 Elsevier Ltd. All rights reserved.

The structure of H2O-saturated silicate melts, coexisting silicate-saturated aqueous solutions, and supercritical silicate liquids in the system Na2O center dot 4SiO(2)-H2O has been characterized with the sample at high temperature and pressure in a hydrothermal diamond anvil cell (HDAC). Structural information was obtained with confocal microRaman and with FTIR microscopy. Fluids and melts were examined along pressure-temperature trajectories defined by the isochores of H2O at nominal densities, rho(fluid), (from EOS of pure H2O) of 0.90 and 0.78 g/cm(3). With rho(fluid) = 0.78 g/cm(3), water-saturated melt and silicate-saturated aqueous fluid coexist to the highest temperature (800 degrees C) and pressure (677 MPa), whereas with rho(fluid) = 0.90 g/cm(3), a homogeneous single-phase liquid phase exists through the temperature and pressure range (25-800 degrees C, 0.1-1033 MPa). Less than 5 vol% quartz precipitates near 650 degrees C in both experimental series, thus driving Na/Si-ratios of melt + fluid phase assemblages to higher values than that of the Na2O center dot 4SiO(2) starting material.

Solubility and solution mechanism(s) of reduced (N+H)- and H-containing N-O-H volatile components in Na2O-SiO2 composition melts in equilibrium with NH3+H-2+N-2 and H2O+H-2 fluid and H- and N-isotope concentrations ill these melts were determined experimentally at 1.5 GPa and 1400 degrees C as a function of hydrogen fugacity,fa, and melt polymerization (composition), NBO/Si (NBO/Si = 0.4-1.18). This NBO/Si-range is similar to that between dacite and olivine tholeiite melt (NBO/Si similar to 0.4-1). The f(H2) was controlled between that of the iron-wftstite + H2O [logf(H2)(IW) similar to 3.42 (bar)] and that of the magnetite-hematite + H2O [logf(H2)(MH) similar to-0.91 (bar)] buffer.

The structure of H2O-saturated silicate melts and of silicate-saturated aqueous solutions, as well as that of supercritical silicate-rich aqueous liquids, has been characterized in-situ while the sample was at high temperature (to 800 degrees C) and pressure (up to 796 MPa). Structural information was obtained with confocal microRaman and with FTIR spectroscopy. Two Albearing glasses compositionally along the join Na2O center dot 4SiO(2)-Na2O center dot 4(NaAl)O-2-H2O (5 and 10 mol% Al2O3, denoted NA5 and NA10) were used as starting materials. Fluids and melts were examined along pressure-temperature trajectories of isochores of H2O at nominal densities (from PVT properties of pure H2O) of 0.85 g/cm3 (NA10 experiments) and 0.86 g/cm(3) (NA5 experiments) with the aluminosilicate + H2O sample contained in an externally-heated, Ir-gasketed hydrothermal diamond anvil cell.

The structure of silicate melts in the system Na2O center dot 4SiO(2) saturated with reduced C-O-H volatile components and of coexisting silicate-saturated C-O-H solutions has been determined in a hydrothermal diamond anvil cell (HDAC) by using confocal microRaman and FTIR spectroscopy as structural probes. The experiments were conducted in-situ with the melt and fluid at high temperature (up to 800 degrees C) and pressure (up to 1435 MPa). Redox conditions in the HDAC were controlled with the reaction, Mo + H2O = MoO2 + H-2, which is slightly more reducing than the Fe + H2O = FeO + H-2 buffer at 800 degrees C and less.