Relaxation Mechanisms and Effects of Motion in Albite (NaA1Si308) Liquid and Glass: A High Temperature NMR Study

The nuclear magnetic relaxation of 23Na and z9Si in albite glass and liquid has been studied from 800 K to 1400 K. The dominant spin-lattice relaxation mechanism for 23Na is found to be nuclear quadrupole interaction arising from the Na + diffusion. The activation energy of the Na diffusion is found to be 71 _+ 3 kJ/mol, in close agreement with the results on electrical conductivity and on Na self-diffusion from radio-tracer experiments. The correlation time of the Na motion is estimated to be about 8.5 x 10 11 s near the melting point (~1390 K). Both nuclear dipole-dipole interaction and chemical shift anisotropy interaction are large enough to contribute to the 298i relaxation. However, calculations based on a simplified model which employ single correlation time and exponential correlation function, with interactions typical of crystalline silicates, cannot completely account for the experimental data. N M R relaxation data also reveal that the Si motion is correlated to the Na motion and that the Si is relatively immobile. Several possible motions of SiO 4 tetrahedra that can cause 298i relaxation are suggested. The motion responsible for 29Si relaxation differs from that which is responsible for viscosity: the apparent activation energy for the former is much lower. Measurements of spin-spin relaxation times and linewidths are also presented and the significance of their temperature dependence is discussed.