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24 September 1986 Nickel-Phosphorus Selective Coatings For Photothermal Absorption Of Solar Energy
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The creation of a rough surface state allows a modification of optical properties. Deposits of electroless layers of Ni-P have been realized on metallic (steel, aluminium), plastic and glass substrates. The layers are obtained by electroless process using the reduction of nickel ions by the hypophosphite ions. The non metallic surfaces must undergo pretraitment by chemical activation before plating. The layers have a rough surface state formed by juxtaposed nodules. When dipped in a nitric acid solution, the surface presents a blackening resulting from hole formation visible first on the boundaries between the nodules and then, on the whole deposit surface. During etching, absorptance as increases with etching time, and reaches values higher than 95%. Emittance ε remains weak and near 20%. We follow the evolution of optical, thermal, physical and chemical properties after aging. Several analytical methods have been employed like XPS, Auger spectroscopy, electron microprobe, EDAX, electron microscopies, etc. We show that the selectivity results from the creation of a rough surface state and that the effect of the acid etching on the optical properties is bound to the initial structure of the alloy. The optical properties are simulated by the utilization of a statistical model of roughness. An interpretation of the attack phenomenon is given that takes into account kinetics with two reaction rates depending on the microstructure of the as-prepared material.
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Marie Papini and Francois Papini "Nickel-Phosphorus Selective Coatings For Photothermal Absorption Of Solar Energy", Proc. SPIE 0653, Optical Materials Technology for Energy Efficiency and Solar Energy Conversion V, (24 September 1986);

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