CVD black chrome coatings for high temperature photothermal energy conversion
ABSTRACT Black chrome absorber coatings have been developed by CVD-technique involving deposition of chrome hexacarbonyl. The deposition of the black chrome absorber films by CVD proceeds through pyrolysis of chrome hexacarbonyl at atmospheric pressure in the presence of oxygen. The black chrome absorber coatings demonstrate a significant solar absorptance (as deposited α > 0.95) coupled with a high infrared reflectance (as deposited ϵ < 0.1) which is necessary for efficient conversion of solar energy into heat. Coatings deposited on steel substrates have remained intact and substantially after 1000 h of lifetime testing in air at 600°C. The characterization of these selective absorber coatings has been carried out by measuring the thermal optical properties (α, ϵ), by X-ray examination and by surface analysis using SEM and AES. The deposition at atmospheric pressure offering the potential of large-scale continuous flow-through manufacture. Substrates of such long pipes can be easily coated for solar farm plants.
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ABSTRACT: Optimization of an industrial DC magnetron sputtering process for thin graded index coatings for solar thermal absorbers is reported. The optimization concerned the main processing parameters: sputtering power, argon flow, oxygen flow, and system set-up for graded control. The purpose of the optimization was to achieve a surface with efficient solar-thermal energy conversion based on the concept graded index coating, using a metal-dielectric composite coating of nickel–nickel oxide with a continuous change in composition through the film depth profile. It was found that the optimization of the materials composition could be controlled by one parameter related to the sputtering process, the relative oxygen flow RO, defined as the ratio of applied oxygen flow to the critical oxygen flow. For optimized sputtering conditions a solar absorptance of 0.92 was obtained for a single graded index coating on aluminum for RO value of 0.8. From the materials characterization it was found that this gave a graded index coating of two thick sub-layers, a top layer of nano-sized nickel oxide grains and a base layer of nano-size metallic nickel grains with a very thin interface of a mixture of nickel and nickel oxide that was almost amorphous.Solar Energy Materials and Solar Cells. 01/2006;