Characterization Of High Temperature Optical Spectra Of Glass Melts And Modeling Of Thermal Radiation Conductivity

Two innovative experimental techniques for measuring the high temperature near infrared optical spectra of glass melts are compared. The critical experimental features of both techniques, one based on transmission and the other based on emittance measurements, are reviewed. Typical results of both techniques, including high temperature spectra and values for the Rosseland mean absorption coefficient and thermal radiation conductivity versus temperature for similar glass melts, are compared. The study is focused on sulfate fined soda lime silicate glass melts colored with iron oxide and chromium oxide and on the effect of the glass redox state on the thermal radiation conductivity. It is shown that essentially different measuring principles provide consistent results for similar glass melt types, that is, colors. Using the high temperature spectra of a large variety of (colored) glasses, a new semi-empirical model is developed for predicting the Rosseland radiation conductivity of arbitrary sulfate fined soda lime silicate glass melts, colored with iron oxide and chromium oxide. By separating the effects of (a) the temperature-dependent redox state, (b) the high temperature changes in ligand field strengths and (c) the glass matrix, the model reliably predicts the Rosseland radiation conductivity, with a chemical analysis of the glass as input only.