Spectroscopic study of anhydrous and hydrous silicate glasses under high pressure and high temperature

Modified confocal micro-Raman spectrometry was used in this study for measuring Raman spectra of anhydrous and hydrous silicate glasses at high temperature both at ambient and reducing atmosphere, and at high pressure and room temperature. Results from high temperature studies indicate that the structures of glasses are similar to that of respective high temperature melts, except some minor changes, e.g., the increase in bond length and bond angle, and occurrence of some disproportionation reactions at high temperatures. We suggest that the distinct differences in the physical properties, e.g., viscosity, are primarily from different behaviors of cations and anions in the melts relative to that in glasses. High temperature study of iron-bearing silicate glasses under reducing conditions demonstrated that in our samples Fe{dollar}sp{lcub}2+{rcub}{dollar} are basically octahedrally rather than tetrahedrally coordinated. The present study clearly indicates that a decrease in the degree of polymerization of structure is accompanied by the reduction from Fe{dollar}sp{lcub}3+{rcub}{dollar} to Fe{dollar}sp{lcub}2+{rcub}.{dollar} The presence of Fe{dollar}sp{lcub}2+{rcub}{dollar} in reduced quenched glasses is demonstrated using Mossbauer spectroscopy.; Our results from high pressure studies on K{dollar}sb2{dollar}Si{dollar}sb4{dollar}O{dollar}sb9{dollar} glass show that coordination number of Si increases from 4 to higher numbers (5 or 6) at pressures higher than {dollar}sim{dollar}6 GPa, which has important implications for the emplacement of natural magma in the deep earth. The decrease in the viscosity of highly polymerized compositions of silicate melts could result from the shrink in the Si-O-Si bond angle which weakens the interaction between neighboring TO{dollar}sb4{dollar} tetrahedra.; Our study of hydrous albite glass at pressure provide insight into the controversial assignments of Raman bands in both hydrous and anhydrous albite glasses. It demonstrates an intrinsic relationship between the distinct 900 cm{dollar}sp{lcub}-1{rcub}{dollar} band and other bands in the Raman spectrum of hydrous albite glass. Our study at high pressure also indicates that OH species have various structural environments when the pressure-induced structural changes occurs. Our results of high temperature studies demonstrate that the introduction of water preferentially affects the structural site of Al cations relative to Si. In addition, strength of hydrogen bonding is found weakened with increasing temperature.