Soret coefficient of a sodium germanate glass melt: Experiment, theory, and molecular dynamics simulation

Abstract

The Soret effect is a diffusion phenomenon driven by a temperature gradient in a multicomponent system. This effect in condensed systems is not fully understood. Previously, we reported a theoretical model called “adjusted Kempers model” to predict the Soret coefficient in glass melts, and compared the experimental value to the theoretical value for 11Na2O‐89B2O3 (mol%) melts. Here, molecular dynamics calculations, as well as theoretical and experimental values, are quantitatively compared in 10Na2O‐90GeO2 melts. We used a vertical tubular furnace to cause a temperature gradient and heated the sample from top side to reduce the natural convection. We measured the composition of 10Na2O‐90GeO2 glass samples after 45, 90, and 180 hours of heat treatment under a temperature gradient, and estimated the steady‐state Soret coefficient near 1373 K to be 1.09 × 10−3 K−1. In addition, we calculated Soret coefficients to be 3.65 × 10−3 K−1 and 1.85 × 10−3 K−1 in theory and molecular dynamics calculation, respectively. The ratios between the experimental and theoretical Soret coefficients were 1.2 and 3.3 for 11Na2O‐89B2O3 melts and 10Na2O‐90GeO2 melts, respectively. The difference in ratios may be attributed to the mass and size of diffusion species in the glass melts.