Numerical and experimental determination of the temperature dependence of the spectral and integral emissivities of quartz ceramics of various porosity

The optical parameters of quartz ceramics (absorption and scattering indices) are determined by solving the inverse problem of radiation transfer based on the total-reflection spectra of two layers with different thicknesses measured in the wavelength range of $0.5$–$18$ $\mu$m. The spectra of hemispherical emissivities and integral thermal emissivities are calculated in the temperature range of $20$–$1400^{\circ}$C. The influence of porosity on the optical parameters and emissivities is analyzed in the range of $7$–$11\%$.