The system NaAlSi3O8?H2O?H2 (1200� C, 2 kbar): the solubility and interaction mechanism of fluid species with melt

Abstract

The H2O and H2 solubilities in an albite melt at 1200° C and 2 kbar over the entire range of gas phase composition, from pure hydrogen to pure water were studied in gas-media pressure vessels. The water solubility initially increases with increasing hydrogen content until a maximum of 9.19 wt% H2O atXH 2 =0.1 is reached, withXH 2 >0.1 the water solubility decreases. The hydrogen solubility curve has a maximum atXH 2 =0.42 where the concentration reaches 0.206 wt% H2O. Over the entire compositional range1H NMR (nuclear magnetic resonance) spectra show distinct absorption lines due to protons bound to OH groups and to isolated firmly bound water molecules. In NMR and Raman spectra there were no bands attributable to the H−H vibrations of molecular hydrogen. The X-ray photo-electronic spectra of hydrogen-bearing glasses show the Si2p (99 eV) band which corresponds to the zero-valency silicon. The formation of OH groups and molecular water during interaction between hydrogen-bearing fluids and melts under reducing conditions has a qualitative effect, the same as for water dissolution. Another point of interest is that hydrogen-bearing melts undergo more depolymerization than do hydrous melts.