HIGH-TEMPERATURE RAMAN SPECTROSCOPY OF ALKALI SILICATE GLASS MELTS

摘要

The structural investigation results of high-temperature Raman spectra of alkali silicate glass melts (alkali=Li, Na and K) are presented. High resolution high-temperature Raman spectra of alkali silicate glass melts were measured by the Raman spectrometer using a short pulse laser, and the changes of the vibration bands of Si-O-(NBO) in Q3 and Q2 units found at 1100 and 950 cm-1 were examined. Based on the comparison of the band intensity ratios with the [Qn] obtained by MSi-NMR for quenched glasses in the literature, the temperature and composition dependences of [Qn] were quantitatively investigated. From the analysis of alkali disilicate melts, alkali oxide species strongly affected the temperature dependences of [Qn] distribution. Lithium disilicate system had wide and temperature-independent [Qn] distribution. This showed that the [Qn]s in melt were held in glass. Sodium and potassium systems, on the other hand, strongly depended on temperature. The plots of [Qn] of these melts versus TITm crossed at the same point at T=Tm, where [Q2]=[Q4]=1/4[Q3] was held. Comparison with the structure of disilicate crystal (continuous sheet structure of 6-membered ring of Q3) revealed that melting process would requires the conversion of a couple of Q3 to a pair of Q2 and Q4 in 6 membered ring according to the equilibrium 2Q3<->Q2+Q4, and this was found to be the identity of the fusion entropy AS}; The large crystallization tendency of lithium disilicate was also explained; temperature independent and wide Qn distribution (=ΔSf) increases the driving force for crystallization AG=AS/Ar under the super-cooling ΔT(=Tm-T). The [Qn]s obtained from the examined glass melts were summarized in the Qn diagram and proposed its availability for the new representation of the structure of glass melts.