Characterization of high temperature optical spectra of glass melts and modeling of thermal radiation conductivity

Abstract

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. K E Y W O R D Scolor< optical properties, glass forming melts< properties, thermal conductivity< glass forming melts

High‐temperature near‐IR spectral properties and thermal radiation conductivity of (un)colored silicate glass melts

“…previously for the SLS container glass, see Ref. [8]. This is to be expected, as normal undoped container glass will contain more impurities than the undoped SLS glass sample in this study, which was made from chemically pure raw materials.…”

“…For the emittance measurements, the glass discs were mounted in an alumina ring as described in Ref. [8]. The device for measuring the emittance of solid and viscous materials in a broad spectral region from visible to far IR wavelengths at high temperatures is described in Refs.…”

“…The device for measuring the emittance of solid and viscous materials in a broad spectral region from visible to far IR wavelengths at high temperatures is described in Refs. [7,8]. These articles include a description of the CO 2 laser heating system for heating semitransparent samples, the blackbody reference furnace, the optics and the two spectrometers used, and the procedure to derive the spectral emittance of samples under study.…”

“…In the extended model, the effects of the other important coloring ions (Cu, Co, Mn, and Ni) on the Rosseland mean absorption coefficient α R (T) (m −1 ) are included as well, so the expression (4) in Ref. [8] is replaced by the following expression (5):…”

“…In a previous paper in this journal, 8 we reported on innovative measurement techniques of the high-temperature NIR optical spectra of sulfate fined, soda lime silicate (SLS) glasses, colored with Fe and/or Cr ions, which encompass more than 90% of the industrially produced glasses for containers, flat (float), and domestic glass products. Furthermore, a new semiempirical model was described for reliably predicting the temperature-and redox-dependent Rosseland thermal radiation conductivity of these glasses, with a chemical analysis of the glass as input only.…”