Abstract:
The paper presents the results of a study of a number of key optical characteristics of some highly porous thermal protection materials based on amorphous SiO$_2$ fibers in the near and mid IR ranges. In the optical part of the statistical simulation model of such materials, based on the rigorous Mie theory, its application requires the introduction of cooperative corrections to the results of interaction with electromagnetic radiation of individual fragments. These corrections are introduced into the model in the form of an additional multiplier $(C_s)$ of the scattering and absorption Mie efficiencies, which was usually used as a model tuning parameter when interpreting the experimental results of thermophysical studies. In this work, using the example of TZM-23M materials (Russia), made of a relatively thick ($\sim$ 9 $\mu$m) silica fiber PS-23 (Belarus), for the first time, data were obtained that make it possible to study the $C_s$ parameter as a spectral quantity. The study is based on the results of experimental determination of the spectral hemispherical reflectivity of layers of material of two or more optical thicknesses in the wavelength range 0.83–16.65 $\mu$m. These data and Zege's asymptotic formulas were used to estimate the values of the absorption and scattering coefficients. The spectral parameter $C_s$ is determined from the value of the scattering coefficient in the process of solving the inverse optical problem. The data obtained are compared with the results calculated on the basis of classical approximations of the optical constants. The results of this work can be useful for specialists in the field of radiation heat transfer and the interaction of electromagnetic radiation with complex partially transparent media with high spectral albedo scattering values.
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