The effect of substrate surface preparation on the optical properties of a black chrome solar absorber coating

In this study, black chrome (ChromeOnyx) was electrodeposited onto mechanically roughened, mechanically polished and electrochemically polished copper plates in order to investigate the influence of substrate surface preparation on the optical properties of the coating. The spectral reflectances of the uncoated and coated surfaces were measured. In addition, the total normal emittance of the coated surfaces and the directional solar absorptance of the coated roughened surfaces are reported. The spectral reflectance of black chrome in the visible spectrum was found to be unaffected by the substrate surface preparations considered in this study. However, the near infrared reflectance was dependent upon the surface preparation. Black chrome on electropolished and mechanically polished substrates has higher near-infrared absorptance than black chrome on fine ground (rough) substrates. Scanning electron micrographs revealed that the average size of the surface particles of the coating was largest for the mechanically polished and smallest for the electrochemically polished substrates, with that of the mechanically roughened substrates falling in between. The results suggest that the variations in near-infrared absorptance are a consequence of differences in the structure and composition of the films resulting from substrate preparation.