Characterization of Al2O3-TiO2 nano porous solar absorbers derived via MAO/sol-gel hybrid process

Micro arc oxidation combined with sol-gel process was used to develop solar selective absorber systems for the first time. Phase structure and chemical composition of the layers were studied by XRD and XPS techniques. The layers consisted of anatase, rutile, α-alumina, γ-alumina, and Al2TiO5 phases with varying fractions with the growth conditions. SEM and AFM investigations revealed a porous structure (pore size: 60-550 nm) with a rough surface where pore size and surface roughness increased with the applied voltage. Solar absorption and emission coefficients were measured using UV-Vis-NIR and IR spectrophotometry. In spite of being so thin, the fabricated samples revealed a high solar absorptivity of α = 0.99 and low thermal emissivity of ε = 0.06. A formation mechanism was proposed based on the electrochemical foundations as well.