Thermal radiative properties of ceramic of cubic $\mathrm{ZrO}_2$ stabilized with $\mathrm{Y}_2\mathrm{O}_3$ at high temperatures

The results are given of the investigation of the normally hemispherical reflectivity of ceramic of cubic zirconia stabilized with $8$ mol $\%$ yttria for the wavelengths of $0.488$, $0.6328$, $1.15$, and $1.39\mu$m both in the process of its rapid heating in air by $\mathrm{CO}_2$-laser radiation from room temperature to $3200$ K and in the process of subsequent cooling after the heating radiation is discontinued. It is demonstrated that, in the entire investigated spectral range under conditions of a layer of melt $250$–$500\mu$m thick on the surface, an optically infinite layer is realized in the melt, and the reflection is largely defined by the refractive index. This latter layer remains optically infinite even immediately after solidification; however, by the end of the solidification process, its reflectivity somewhat increases due to cracks and pores. Measurements of the reflection under conditions of continuous stepwise heating by fluxes of relatively low intensity and in the course of subsequent cooling have produced data on the reflectivity of the layer under close-to-isothermal conditions. Some estimates are made of the values of the absorption coefficient of the melt.