Thermal resistance of solar volumetric absorbers made of mullite, brown alumina and ceria foams under concentrated solar radiation

Three semi-closed open cell ceramic foams, namely mullite, brown alumina and ceria-based materials, were subjected to thermal cycles by direct concentrated solar irradiation to study their thermal resistance in view of their potential application as photothermal devices, such as volumetric solar absorbers. After cycling, the extent of the damage in the samples was determined by measuring the retained crushing (compressive) strength. The extent of the damage was found to depend on the composition, the applied surface temperature difference (Delta T) of thermal cycling and the temperature gradient across the foams. It was found that the retained crushing strength gradually decreased with an increase in Delta T and was independent of the number of thermal cycles in the range investigated. The ceria foams displayed the poorest thermal shock resistance. Experimental data fit the Gibson-Ashby model for the thermal shock resistance of ceramic foams, for a constant C = 0.65.