IN-SITU HIGH-TEMPERATURE RAMAN-SPECTROSCOPIC STUDIES OF ALUMINOSILICATE LIQUIDS

We have measured in-situ Raman spectra of aluminosilicate glasses and liquids with albite (NaAl-Si3O8) and anorthite (CaAl2Si2O8) compositio ns at high temperatures, through their glass transition range up to 17 00 and 2000 K, respectively. For these experiments, we have used a wir e-loop heating device coupled with micro-Raman spectroscopy, in order to achieve effective spatial filtering of the extraneous thermal radia tion. A major concern in this work is the development of methodology f or reliably extracting the first and second order contributions to the Raman scattering spectra of aluminosilicate glasses and liquids from the high temperature experimental data, and analyzing these in terms o f vibrational (anharmonic) and configurational changes. The changes in the first order Raman spectra with temperature are subtle. The princi pal low frequency band remains nearly constant with increasing tempera ture, indicating little change in the T-O-T angle, and that the angle bending vibration is quite harmonic. This is in contrast to vitreous S iO2, studied previously. Above Tg, intensity changes in the 560-590 cm (-1) regions of both sets of spectra indicate configurational changes in the supercooled liquids, associated with formation of additional Al -O-Al linkages, or 3-membered (Al, Si)-containing rings. Additional in tensity at 800 cm(-1) reflects also some rearrangement of the Si-O-Al network.