VISCOSITY, STRUCTURE AND MIXING IN (CA, NA) SILICATE MELTS

Abstract

Configurational entropy has been linked with the structure of Na2O-CaO-SiO2 melts, based on combined viscosimetry and Raman spectroscopic investigations. From viscosity measurements at low and high temperatures, we have obtained the configurational entropy, Sconf (using log η = Ae + Be / TSconf, where η is the viscosity, T the temperature and Ae, Be two constants). Using Raman spectroscopy, we obtained structural information from the Q speciation and from the variation of the boson peak with chemical composition. A rapid decrease in the viscosity at low temperature was observed in Ca-silicate melts with addition of Na2O. At high temperature, the viscosity is almost the same for the Ca- and Na-silicate liquids. The configurational entropy calculated from the viscosity measurements for Ca/Na mixing shows a non-ideal variation, which can be interpreted in term of non-random distribution of Na and Ca in the silicate network. The addition of Na2O to the Ca-silicate melts produces a decrease of the fragility of the liquid and an increase of the Q3/Q2 ratio observed with Raman spectroscopy. © 2006 Elsevier B.V. All rights reserved.