Heat capacities and entropies of silicate liquids and glasses |
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| Authors: | J F Stebbins I S E Carmichael L K Moret |
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| Institution: | (1) Earth Sciences Division, Lawrence Berkeley Laboratory, 94720 Berkeley, CA, USA;(2) Department of Geology and Geophysics, University of California, 94720 Berkeley, CA, USA |
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| Abstract: | The heat capacities of several dozen silicate glasses and liquids composed of SiO2, TiO2, Al2O3, Fe2O3, FeO, MgO, CaO, BaO, Li2O, Na2O, K2O, and Rb2O have been measured by differential scanning and drop calorimetry. These results have been combined with data from the literature to fit C
pas a function of composition. A model assuming ideal mixing (linear combination) of partial molar heat capacities of oxide components (each of which is independent of composition), reproduces the glass data within error. The assumption of constancy of ¯C
p,iis less accurate for the liquids, but data are not sufficient to adequately constrain a more complex model. For liquids containing alkali metal and alkaline earth oxides, heat capacities are systematically greater in liquids with high  field strength network modifying cations. Entropies of fusion (per g-atom) and changes of configurational entropy with temperature, are similarly affected by composition. Both smaller cation size and greater charge are therefore inferred to lead to greater development of new structural configurations with increasing temperature in silicate liquids. |
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