Stolper, Edward (1982) The speciation of water in silicate melts. Geochimica et Cosmochimica Acta, 46 (12). pp. 2609-2620. ISSN 0016-7037 http://resolver.caltech.edu/CaltechAUTHORS:20120821-143130371
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Previous models of water solubility in silicate melts generally assume essentially complete reaction of water molecules to hydroxyl groups. In this paper a new model is proposed that is based on the hypothesis that the observed concentrations of molecular water and hydroxyl groups in hydrous silicate glasses reflect those of the melts from which they were quenched. The new model relates the proportions of molecular water and hydroxyl groups in melts via the following reaction describing the homogeneous equilibrium between melt species: H_2O_(molecular) (melt) + oxygen (melt) = 2OH (melt). An equilibrium constant has been formulated for this reaction and species are assumed to mix ideally. Given an equilibrium constant for this reaction of 0.1–0.3, the proposed model can account for variations in the concentrations of molecular water and hydroxyl groups in melts as functions of the total dissolved water content that are similar to those observed in glasses. The solubility of molecular water in melt is described by the following reaction: H_2O (vapor) = H_2O_(molecular) (melt). These reactions describing the homogeneous and heterogeneous equilibria of hydrous silicate melts can account for the following observations: the linearity between f_(H2O) and the square of the mole fraction of dissolved water at low total water contents and deviations from linearity at high total water contents; the difference between the partial molar volume of water in melts at low total water contents and at high total water contents; the similarity between water contents of vapor-saturated melts of significantly different compositions at high pressures versus the dependence on melt composition of water solubility in silicate melts at low pressures; and the variations of viscosity, electrical conductivity, the diffusivity of “water,” the diffusivity of cesium, and phase relationships with the total dissolved water contents of melts. This model is thus consistent with available observations on hydrous melt systems and available data on the species concentrations of hydrous glasses and is easily tested, since measurements of the concentrations of molecular water and hydroxyl groups in silicate glasses quenched from melts equilibrated over a range of conditions and total dissolved water contents are readily obtainable.
|Additional Information:||© 1982 Pergamon Press Ltd. Received 26 April 1982. Accepted 21 September 1982. Available online 22 May 2003. Discussions with T. L. Grove, H. Helgeson, J. R. Holloway, Henry F. Shaw, Lynn A. Silver, D. J. Stevenson, D. Walker, and G. J. Wasserburg have been helpful. This work was supported by NSF grant EAR-8009798. Division of Geological and Planetary Sciences. Contribution Number 3775.|
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|Official Citation:||Edward Stolper, The speciation of water in silicate melts, Geochimica et Cosmochimica Acta, Volume 46, Issue 12, December 1982, Pages 2609-2620, ISSN 0016-7037, 10.1016/0016-7037(82)90381-7. (http://www.sciencedirect.com/science/article/pii/0016703782903817)|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Ruth Sustaita|
|Deposited On:||21 Aug 2012 21:48|
|Last Modified:||21 Aug 2012 21:48|
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