In situ high temperature 27Al NMR study of structure and dynamics in a calcium aluminosilicate glass and melt

The temperature dependence (25–1400 °C) of 27Al NMR spectra and spin–lattice relaxation time constants T1 have been studied for a calcium aluminosilicate (43.1CaO–12.5Al2O3–44.4SiO2) glass and melt using an in situ high temperature probe, and the glass has been characterized by ambient temperature, high field MAS NMR. The peak positions and the line widths show a consistent behavior as motional averaging of the quadrupolar satellites increases with increasing temperature. The rate of decrease with temperature of T1 drastically increases near the glass transition temperature Tg, which suggests a change in NMR relaxation process from vibrational to translational motions. Above the T1 minimum (≈1200 °C), NMR correlation times obtained from T1 are in good agreement with shear relaxation times estimated from viscosity, suggesting that microscopic nuclear spin relaxation is controlled by the same dynamics as macroscopic structural relaxation, and thus that atomic-scale motion is closely related to macroscopic viscous flow.