Spectral reflectance properties of black chrome for use as a solar selective coating

Abstract

The NASA-Lewis Research Center has determined that a widely available, commercially electroplated decorative finish known as black chrome has desirable solar selective properties. Black chrome electroplated coating has high absorbence in the solar spectrum and low emissivity in the 250°F blackbody thermal spectrum. The discovery of the solar selective properties of black chrome adds another high-efficiency coating to the older, previously known coatings. Additionally, the black chrome is significant as a solar selective coating because the current extensive use of black chrome in the electroplating industry as a durable, decorative finish makes black chrome widely available and potentially lower cost as a solar selective coating. The spectral reflectance properties of a commercially prepared black chrome on steel have been measured. Values are presented for reflectance of the black chrome. These are compared with the reflectance of black paint (Nextel) and with two available samples of black nickel which had been prepared for solar selective properties. The reflectance of black chrome, the two black nickels, and black paint integrated over the solar spectrum for air mass 2 were 0·132, 0·123, 0·133 and 0·033, respectively. The reflectance of the black chrome, two black nickels, and black paint integrated over the blackbody spectrum for 250°F from 3 to 15 μm are 0·912, 0·934, 0·891 and 0·033, respectively. These reflectance measurements indicate absorptivity-to-emissivity ( α ϵ ) values of 9·8, 13·8, 8·0 and 1·00, respectively.