Spectrally selective copper oxide films

Copper oxide coatings have been produced on aluminium substrates by the spray pyrolysis technique. Studies have been carried out to observe the variations of solar absorptance ([alpha]S) and thermal emittance ([epsilon]T) with different concentrations of the spraying solution for different coating thicknesses. The effect of baking temperature on the optical properties of the coatings has also been studied. Under optimum conditions, with a baking temperature of 350°C and a spray concentration of 0·005m, a solar absorptance of 0·90 with a corresponding thermal emittance of 0·15 is obtained for a film 1·35 [mu]m thick. Structural studies carried out with X-ray diffraction and electron diffraction techniques have shown that the monovalent oxide CuO is the clear dominating constituent of the oxide layer with a small percentage of the divalent Cu2O. The stagnation temperature measurements give a maximum stagnation temperature of 120·8°C for the selective surface whereas, under identical conditions, it is 106·8°C for a non-selective black surface.