Pressure and temperature dependence of the viscosity of NaAlSi₂O₆ melt

Abstract

The viscosity of silicate melt of NaAlSi₂O₆ composition was measured at pressures from 1.6 to 5.5 GPa and at temperatures from 1350 to 1880°C. We employed in situ falling sphere viscometry by using X-ray radiography. We found that the viscosity of NaAlSi₂O₆ melt decreased with increasing pressure up to 3.6 GPa at 1780±10°C. By using the relationship between the logarithm of viscosity and the reciprocal temperature, the activation energies for viscous flow were calculated to be 3.7±0.5 * 10^2 and 3.6±0.5 * 10^2 kJ/mol at 2.2 and 2.9 GPa, respectively.