Tomography-based radiative transfer analysis of an open-cell foam made of semitransparent alumina ceramics

This study aims to fully investigate the radiative characterization of ceramic foams in terms of local scale (single strut) and macro scale (foam sheet). A radiative transfer model was established in the limit of geometric optics for a porous structure obtained from real alumina ceramic foams by computed tomography technique. The model considers the reflection and refraction at solid-void interface and the volumetric transmission, absorption and scattering process inside semitransparent ceramic solids. It is found that at local scale, neglecting the real hollowness may bring considerable errors to the local radiative behavior of ceramic struts (maximum errors up to 20.4-39.3% for the cases investigated). The cross-sectional thickness of the strut increases from the middle to the extremities, which causes a significant variation of the local radiative behavior. At macro scale, a peak in transmittivity of foam sheet can be observed at the wavelength around 4.4 mu m. The scattering albedos obtained from the predictive model indicate that alumina ceramic foams behave strongly scattering within the wavelength 4 mu m but very absorbing over 6 mu m. The asymmetry factors obtained show a turning point at the wavelength around 1.8 mu m, suggesting a transition of the scattered radiation from backward predominance to forward predominance.