HIGH-EFFICIENCY MO-AL2O3 CERMET SELECTIVE SURFACES FOR HIGH-TEMPERATURE APPLICATION

Highly efficient Mo-AL(2)O(3) cermet solar absorbers have been designe d with a numerical model and deposited experimentally. The typical fil m structure is an Al2O3 anti-reflection layer on a double Mo-Al2O3 cer met layer on a Mo or Cu metal thermal reflector. In numerical calculat ions of the thermal emittance at high temperature for these selective surfaces, the temperature dependencies of the complex refractive indic es of the metal reflector and cermet in the infrared region have been considered, and the dielectric functions of the cermet materials are e valuated using Sheng's approximation. An optimization calculation yiel ds a photothermal conversion efficiency as high as 0.914 at 350 degree s C for a concentration factor of 26 for the film structure consisting of a double cermet layer on a Mo metal thermal reflector with an Al2O 3 anti-reflection coating. The corresponding normal absorptance and he mispherical emittance at 350 degrees C are 0.96 and 0.11, respectively . Mo-Al2O3 cermet selective surfaces using the double cermet layer str ucture were deposited by vacuum co-evaporation, and an absorptance of 0.955 and near normal emittance of 0.032 at room temperature have been achieved. An emittance of 0.08 at 350 degrees C is estimated based up on room temperature experimental data for the film structure of a doub le cermet layer on a Cu metal thermal reflector with an Al2O3 anti-ref lection coating.