The effects of periodic current reversal on the electrodeposition of a black chrome selective solar absorber surface

Abstract

The effects of Periodic Current Reversal (PCR) during black chromium-oxide electrodeposition on the microstructure, and therefore the optical properties, of the selective solar absorber surface were investigated in this study. It was found that direct current (dc) versus PCR-mode deposits varied considerably in their optical responses, the dc coatings being decidedly superior. Thermal stability test results, based on a coating's solar absorptance/infrared emittance behavior following prolonged exposure to high temperature conditions, varied considerably; the dc coatings again out-performed the PCR coatings. A decrease in the chromium/chromium-oxide ratio, a decrease in the film thickness, and non-uniformity of the coating surface/subsurface microstructure were seen to occur in the PCR coatings. This study concludes that the current reversal associated with the PCR process of electrodeposition is responsible for the removal of all or most of the black chrome coating from the resulting deposits. While some black chrome coatings produced by the use of PCR (followed by dc deposition) exhibited good optical behavior, the total procedure would be uneconomical compared to the traditional dc deposition.