Viscosity Measurement of SiO₂–Na₂O Melts with Addition of NaF

Abstract

The viscosity of SiO₂–Na₂O–NaF melts was measured by using a rotating crucible viscometer developed by the authors. The basicity (= C_Na2O/C_SiO2 in mol%) of the melts was 0.67, 0.82, and 1.00. The concentrations of NaF were 5, 10, and 15 mol%. As a result, the viscosity of the melts showed a good Arrhenius type linearity in any melts. It was found that the sample loss occurred in highly basic composition region due to a prolonged measurement at high temperature. The viscosity of the melts decreased with increasing the concentration of NaF, and the composition dependence is similar to that for SiO₂–CaO–CaF₂ melts. Viscosity decreasing ability of NaF is higher than that of Na₂O within the composition region investigated in this study. Transitions of activation energy of viscous flow are different between Na₂O addition and NaF addition. This implies that the mechanism of enhancement of fluidity is different between Na₂O and NaF.