Texture and Porosity Effects on the Thermal Radiative Behavior of Alumina Ceramics

Thermal and optical properties of ceramics are dependent on radiation scattering and cannot be determined by a knowledge of their chemical composition alone, as for single crystals. In this paper, extrinsic effects, such as roughness, porosity, and texture, on the spectral emissivity of alumina ceramics are investigated. Roughness effects have an influence mainly in the opaque zone; an important porosity dependence and the presence of a critical porosity threshold were observed in the semitransparent zone. Furthermore, it was shown that two ceramics with similar total porosities, but with different textures, possess radically different emissivities, showing that grain size, pore size, and spatial repartition of the grains are also crucial for an understanding of the thermal properties of the ceramics.