PERFORMANCE AND STABILITY OF SOME NEW HIGH-TEMPERATURE SELECTIVE ABSORBER SYSTEMS BASED ON METAL/DIELECTRIC MULTILAYERS

Two systems of solar selective absorber surfaces based on metal/dielectric multilayers were examined. Al2O3/Pt and Al2O3/MoSi2 multilayer films were optimized by computer-simulations and prepared by rf-magnetron sputtering. Subsequent annealing was necessary for the Al2O3/MoSi2 system to obtain various modifications of MoSi2. Coatings of various thicknesses were deposited on different substrates. Their solar absorptances and IR emittances were measured to evaluate their use as spectrally selective surfaces. Absorptances up to alpha = 0.95 and emittances epsilon of approximately epsilon = 0.08 to epsilon = 0.2 (calculated for T = 1100 K) for Pt/Al2O3 and alpha = 0.92 and epsilon = 0.14 for tetragonal MoSi2/Al2O3 could be achieved. The thermal stability in air of these coatings was investigated. They are stable in air up to a temperature higher than 600 degrees C for more than 300 h. Aging experiments show a slight degradation of the optical properties of these films above this temperature, but the stability is dependent on the used substrates.