Thermal Radiation Characteristics of Transparent Semi-Transparent and Translucent Materials under Non-Isothermal Conditions

摘要

Over the range of wavelengths from one to six microns where oxide ceramics are partially transparent, radiant energy emission must be treated as a volume rather than a surface phenomena. As a result the absorption coefficient (mainly determined by microstructure) are important variables. In addition, temperature gradients affect radiant energy emission so that the effective 'emissivity' under non-isothermal conditions is neither a material constant nor a sample constant. Analytical relationships were derived for spectral radiant energy emission as a function of absorption coefficient, scattering coefficient, surface temperature and temperature gradient. Experimental measurements of non-isothermal radiant energy emission of Al2O3 and SrTiO3 samples are in agreement with these calculations. Analytical relations and experimental measurements for diffuse and parallel light transmission are reported. Comparison of the Hamaker approximation with an exact solution show that the approximation is suitable for these materials and conditions. (Author)