A COMPARATIVE-STUDY OF THE OPTICAL-PROPERTIES OF NICKEL PIGMENTED ALUMINA FILMS OF DIFFERENT THICKNESSES EXPOSED TO ELEVATED-TEMPERATURE AND HUMIDITY

Commercial solar absorbers of nickel pigmented anodized aluminium are composed of an inner nickel pigmented sublayer of about 0.3 mu m thick ness and a 0.4-0.5 mu m thick top layer of plain alumina. Thermal emit tance can be reduced from 0.17 to 0.12 if the top layer is made thinne r, to be about 0.1 mu m. The solar absorptance is 0.96 as for the thic ker coating. In this study degradation is analysed for samples with th in or thick alumina top layer after exposure to elevated temperature, 300-500 degrees C, or humidity. The results from these tests show that a thinner aluminium oxide top layer has the same durability as a thic ker top layer. The implication of making commercial nickel pigmented a nodized aluminium with an oxide half as thick as today is a reduction of the anodization time to about half the time and lower manufacturing costs. (C) 1998 Elsevier Science B.V. All rights reserved.