ケイ酸塩メルトの圧力による構造および物性の変化

概要

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The structures of quenched melts in the system CaO-MgO-SiO2 have been studied using the Raman spectroscopic technique. Quenched melts along the joins Ca2SiO4-SiO2and Ca MgSiO4-SiO2consist principally of three different structural units; with increasing SiO2 along these joins the structural units change from monomer (SiO44-) +dimer (Si2 O76-) +chain (SiO32-) through monomer+chain+sheet (Si2O52-) to chain+sheet + 3-dimentional network (SiO2) . The ratios of these structural units change little with pressure in the compositional ranges studied. However, the structure of 3-dimentional network appears to change with pressure. The viscosity of melts enriched in the 3-dimentional network decreases with increasing pressure at constant temperature. Particularly NaAlSi2O6 (jadeite) melt shows a large decrease in viscosity. Glass quenched from the same melt shows an increase of density, a shift of AlKα radiation, and changes of both infrared absorption and Raman spectra with increasing preassure of quenching. These changes are due to the structural changes of melts probably caused by decrease in size of rings consisting of (Si, Al) O4tetrahedra. At higher pressures (>50 kbar) Al in the melts may shift from 4-fold to 6-fold coordination, resulting in further decrease in viscosity and increase in density.
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