WATER IN PERALKALINE ALUMINOSILICATE MELTS TO 2 GPA AND 1400°C

Abstract

The solubility of H2O in melts along the join CaSi4O4-Ca(Ca0.5Al)4O9 (0, 3, and 6 mol% Al2O3) has been determined at 0.8 to 2.0 GPa and 1200 to 1400°C and compared with the solubility of H2O in melts along the joins Na2Si4O9-Na2(NaAl)4O9 and K2Si4O9-K2(KAl)4O9. The H2O solubility is a positive function of pressure and a negative function of temperature and Al2O3 content so that solubility, XH2Omelt (mol%), isXH2Omelt(CAS)=19+/-2-0.7+/-0.1*XAl2O3+0.06+/-0.02*(XAl2O3 )2+13.3+/-0.2*P(GPa)-0.011+/-0.001*T(K).In alkali aluminosilicate melts, the solubility is considerably more sensitive to pressure, Al2O3, and temperature.The H2O solubility data in the 0.8- to 2.0-GPa and 1200 to 1400°C pressure and temperature range are consistent with constant activity coefficient of H2O in the melt. The partial molar volume of H2O, VH2Omelt, derived from the solubility data, ranges between 12.4 cm3/mol for Al-free CaSi4O9 melt and 10.4 cm3/mol for CaSi4O9 + 6 mol% Al2O3. This decrease in VH2Omelt with increasing Al2O3 is similar to that reported for H2O in melts along the two alkali aluminosilicate joins (Na2Si4O9-Na2(NaAl)4O9 and K2Si4O9-K2(KAl)4O9). The VH2Omelt is invariant with temperature in contrast to VH2Omelt along the joins, Na2Si4O9-Na2(NaAl)4O9 and K2Si4O9-K2(KAl)4O9, where in both cases VH2Omelt decreases with increasing temperature.