Microstructure of a Black Chrome Solar Selective Absorber

摘要

The structure of Harshaw Chemicals' CHROM-ONYX type of black chrome/metal selective absorber was studied to gain a better understanding of its influence upon the mechanism of wavelength selectivity. Spectral reflectance measurements were performed on seven samples. In this study, the best selectivity was found by these measurements to be 1.0 micron of black chrome on copper and 0.7 micron of black chrome on nickel. Both transmission and scanning electron microscopy were employed to study microstructure and chemical composition. As a result of the combined studies, some effects of black chrome thickness and the metallic substrate were determined. It was found that black chrome consisted of a very fine metallic distribution of particles of chromium, possibly suspended within a matrix of an oxide of chromium. This combination was, in turn, agglomerated into larger particles within the 0.05--0.3 micron size range. These larger particles formed a network which constituted the surface coating. (ERA citation 04:022353)