Characterization of the physical and chemical properties of the surface of cavities of porous materials

This study concerns the characterization of the surface cavities of porous materials as ceramics foams used in high temperature volumetric solar absorbers. These ceramics materials must reach high efficiency at high temperature. Several foam samples currently available in the industry were characterized by XRD (Aluminium oxide: Al2O3, Zirconium oxide: ZrO2 and silicon carbide: SiC). However, Al2O3 and white ZrO2 compounds revealed low solar absorptivity efficiency for thermo solar conversion. Experimental results obtained for SiC foams (measured absorptivity = 0.7-0.8, IR-TF SOC 100), considered to be the reference material for volumetric absorber. New selective foam (Zirconium diboride, ZrB2) with spectral selectivity i.e. high solar absorptivity (0.7 to 0.8) and low infra-red emissivity was first investigated by XRD. Experimental methods for XPS were optimized in order to characterize the wall of the pores. XPS could become one of the most appropriate techniques to analyze oxidized foams (surface and bulk). After a heating treatment with solar energy, the microstructure (crystalline phases, chemical bonds and environments, chemical composition…) and the oxidation behavior of the ZrB2 and SiC foams were determined.