Recently, I performed a series of water solubility measurements in rhyolite melt as a function of temperature between 1123 and 1473 K at pressures of 22 to 100 Ma, using an internally heated pressure vessel. Water solubility was determined by measuring the water content of the quenched glass using micro-FTIR spectroscopy. The temperature dependence of water solubility was modeled adequately, on the basis of the Stolper (1982) scheme, in which the speciation of dissolved water component was taken into account. The melt-H2O vapor equilibrium is governed by a coupled reaction: (1) H2Omolecular (melt) + O (melt) = 2OH (melt) (homogeneous reaction) and (2) H2O (vapor) = H2Omolecular (melt) (heterogeneous reaction). Under the assumption of ideal mixing of three melt components, a non-linear multiple regression successfully constrained the calorimetric parameters of the water solution reaction in rhyolite melt (the enthalpy of homogeneous reaction = 25.8ｱ11.8 kJ at P,T, the entropy of homogeneous reaction = 6.0ｱ8.7 J/K at P,T, and the enthalpy of heterogeneous reaction = -25.3ｱ4.8 kJ/mol at 1bar,T). The water solubility surface computed with these calorimetric parameters reproduces both the present and previously published solubility data for water in rhyolitic melts to 100 Ma and over a wide range of temperature from near the solidus to 1473 K. The major part of this study was published (Yamashita, 1999).
Link to: Shigeru Yamashita's Research Interests