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 0.8-2.0 GPa and 1200°-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 %), is:

XH2Omelt(CAS)=19±2-0.7±0.1XAl2O3+0.06±0.02(XAl2O3)2 +13.3±0.2P(GPa)-0.011±0.001T(K)

In alkali aluminosilicate melts, the solubility is considerably more sensitive to pressure, Al2O3, and temperature. The H2O-solubility data in the 0.8-2.0 GPa and 1200°-1400°C pressure- and temperature-range are consistent with constant activity coefficient of H2O in the melt. The partial molar volume of H2O, , 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 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 is invariant with temperature in contrast to along the joins, Na2Si4O9-Na2(NaAl)4O9 and K2Si4O9-K2(KAl)4O9, where in both cases decreases with increasing temperature.