| সংক্ষিপ্ত: | The entropies, enthalpies and free energies of mixing of melts in the system NaAlSiO4-KAlSiO4-SiO2 were determined by Knudsen cell mass spectrometry (KCMS). The enthalpies of mixing have an accuracy and precision (1 - sigma ) of approx 1.0 and 0.5 kJ/mol, respectively (M.A. 86M/0442) and are thus comparable to the best solution calorimetric data available for glasses. The mixing properties of the melts are related to the topology of the underlying liquidus surface, so that marked changes in the entropy, enthalpy and free energy of mixing of the melts accompany changes in the nature of the crystalline phase in equilibrium with the melt at lower T. These data and the results of XRD, NMR and Raman spectroscopic studies of glass of similar composition, indicate that clustering may occur in the melts to produce regions which differ in structure and composition on the 20 A scale. The equilibrium liquids are thus inhomogeneous on the micro-scale and may contain structures more closely related to the crystalline phase on the liquidus than to a mineral phase of the same composition as the liquid. (Authors' abstract)-J.M.H.
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