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Shigeru Yamashita's

Reseach Interests


Thermodynamics of watersolubility in silicate melts under pressures

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).

(Left) An internally heated pressure vessel (IHPV, to 200MPa and 1700K) installed in our lab. In the water solubility measurements, a natural rhyolite glass was equilibrated with pure H2O vapor in this IHPV, and the water content of the quenched glass was determined by micro-FTIR spectroscopy.

(Above) A thermodynamically based solubility model for water in rhyolitic melts (Yamashita, 1999). A negative temperature dependence of water solubility becomes weaker at low water contents and high temperatures. This is a result of decreasing heat and increasing volume change of the water solution reaction, where the absolute value of both are negative. Further quantitative analysis of this subject is in progress.

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Link to: Shigeru Yamashita's Research Interests