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

Using an emittance technique with a fast CO₂ laser heating of glass samples, the high-temperature absorption spectra in the near-infrared region of ultrapure and colored (Co-, Cu-, Mn-, and Ni-doped) glasses are measured. The effects of higher glass temperatures on these absorption spectra are explained in the framework of the ligand field theory. Thus, the temperature-dependent absorption bands of the previous transition metal ions are assigned to electronic transitions among the ligand field energy levels of these ions. In particular, spectral shifts, spectral broadening, and changes in absorption strength are ascribed to changes in the structural symmetry of the ionic sites in the glass matrix and to changes of the ligand field strength at increasing temperatures.

Besides, the temperature-dependent Rosseland mean absorptions of the sulfate fined soda lime silicate glass melts, colored with the previous transition metal ions, are derived from the absorption spectra. Combining all the data, semiempirical correlations are derived, which predict the Rosseland thermal radiation properties as a function of glass temperature and of glass redox chemistry. The latter property involves the temperature-dependent concentration of the specific valency of the coloring ions, determined independently, e.g. by a Gibbs minimization redox calculation tool.