WATER SOLUBILITY MECHANISMS IN KALSI3O8 MELTS AT HIGH-PRESSURE

Al-27, Si-29 MAS NMR, Raman, and IR spectroscopic techniques were empl oyed to investigate water solubility mechanisms in KAlSi3O8 melt. Anhy drous glasses were produced by isobarically quenching melts at 0.1 MPa and 2 GPa. Hydrous glasses with 2.5 wt% [H2O]tot were quenched isobar ically from 5 and 7 GPa. Hydrous glasses with 2.5, 5.0, and 7.5 wt% [H 2O]tot were quenched isobarically at 2 GPa. A peak near 900 cm-1 appea rs in the Raman and IR spectra of all hydrous KAlSi3O8 glasses. The in tensity of the 900 cm-1 peak relative to the intensity of the high-fre quency envelopes remains constant for all of the hydrous 2 GPa glasses . The intensity of the 900 cm-1 peak decreases with pressure at consta nt [H2O]tot. The Al-27 resonance is at more positive parts per million in the hydrous 2 GPa glasses relative to the anhydrous 2 GPa sample. Hydrous glasses have narrower linewidths than the 1 atm and 2 GPa anhy drous glasses. We suggest that this spectroscopic information indicate s two stages to the water dissolution mechanism. In the initial stage, we propose that water interacts with the aluminosilicate network to f orm Al-(OH) terminal bonds. At higher water contents (>25-30 mol% [H2O ]tot), the solubility mechanism occurs solely by the exchange of H+ fo r M+ (M = Na, K, Li), and the formation of partial hydration complexes around the alkali cation.