Thermal Aging Characteristics of Electrodeposited Black Chrome Solar Coatings

摘要

By reducing the trivalent chromium concentration of Harshaw's Chromonyx black chrome plating bath, coatings with improved thermal stability characteristics are obtained. For trivalent chromium concentrations as low as 8 g/l, solar absorptance values have decreased only a few percent from initial values of approx. 0.97 after heating in air at 400 exp 0 C for over 3600 hours. Coating composition and structure have been studied using transmission electron microscopy, scanning electron microscopy, and sputter Auger-profiling. Initial results indicate that the coatings from the nominal bath composition are composed of small particles, with diameters in the range 65 to 90 nm. When the trivalent chromium concentration is reduced, these particles agglomerate into larger clusters that are 150 to 250 nm in size. Upon heating in air, all coatings experience a substantial amount of oxidation, but the stable coatings maintain a significantly higher metallic chromium content. The lower oxidation in the stable films is related to the larger average particle size. (ERA citation 04:046230)