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Diffusion of Water in Silicate Melts

Wasserburg, G. J. (1988) Diffusion of Water in Silicate Melts. Journal of Geology, 96 (3). pp. 363-367. ISSN 0022-1376. http://resolver.caltech.edu/CaltechAUTHORS:20140909-141501428

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Abstract

The transport of water in silicate melts is examined from a theoretical point of view, taking into account the presence of both H_2O and OH^- species. It was assumed that only H_2O molecules may diffuse and that a constitutive relationship between the number density nH_2O of H_2O molecules and the total water content (n_Σ) exists such that nH_2O = g(n_Σ). This is related to dissociation or to chemical reactions such as H_2O molecular (melt) + Oxygen (melt) ⇌ 2 OH (melt). This approach leads to diffusion transport equations that are intrinsically nonlinear. Three regions are naturally defined: (I) high water content with a normal linear diffusion equation an: ∂n_Σ/∂t = DV^2n_Σ, where D is the intrinsic diffusion coefficient of a H_2O molecule in the silicate; (II) an intermediate or transitional region where the transport equation is ∂n_Σ/∂t = DV^2g(n_Σ); and (III) a region of low water concentration where the transport equation is an: ∂n_Σ/∂t = D^*V^2n^2_Σ. In the latter region, the equation is strongly nonlinear. D^* is a constant diffusion coefficient related to D. It follows that the dissociation of water molecules to form OH^- in silicates automatically implies a nonlinear transport behavior due to the storage of dissociated water molecules in immobile sites. This study of the kinetics of transport will aid in our understanding of speciation and structure in silicate melts.


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http://www.jstor.org/stable/30068734JSTORArticle
Additional Information:© 1988 by The University of Chicago. Manuscript received June 17, 1987; accepted November 25, 1987. This small contribution is dedicated to the late Hugh C. Heard. The author had the joy and privilege of working with Hugh on SiO_2-H_2O some 26 years ago. This work was done in response to a stimulating discussion with E. Stolper who had explored the speciation problem and the dissociation relationships. He was concerned with the interpretation of data on H20 diffusion in silicates. It is hoped that this simple analysis may be of use to other workers in discussing diffusion of dissociating molecules. Very helpful comments by O. Navon are gratefully acknowledged. This work supported by NSF EAR Grant No. 8618526. Division Contribution No. 4484 (569).
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NSFEAR 8618526
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Caltech Division of Geological and Planetary Sciences4484
Lunatic Asylum Lab569
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Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20140909-141501428
Official Citation:Diffusion of Water in Silicate Melts(pp. 363-367) G. J. Wasserburg Stable URL: http://www.jstor.org/stable/30068734
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:49501
Collection:CaltechAUTHORS
Deposited By: Ruth Sustaita
Deposited On:10 Sep 2014 20:17
Last Modified:10 Sep 2014 20:17

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