Viscosity and configurational entropy of silicate melts |
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| Authors: | Pascal Richet |
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| Institution: | Laboratoire de Géochimie, Institut de Physique du Globe, et Départment des Sciences de la Terre, Universités Paris VI et VII, 75251 Paris Cedex 05, France |
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| Abstract: | With the configurational entropy theory of relaxation processes of Adam and Gibbs (1965), one predicts that the viscosity depends on temperature according to log , where Sconf is the configurational entropy of the liquid. Thermochemical calculations of Sconf performed for some mineral compositions show the importance of non-configurational contributions to the entropy differences between amorphous and crystalline phases. Except for the case of SiO2, the available thermodynamic data indicate that the above equation for viscosity accounts quantitatively for the experimentally determined temperature dependence of the viscosity of silicate melts. The Adam and Gibbs theory also provides a simple rationale for the non linear variation of the logarithmic viscosity with composition in mixed alkali silicate liquids at low temperatures, the minimum of viscosity resulting from the contribution of the entropy of mixing to Sconf. |
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