Abstract
The Cr 2O 3Cr composite coating has been produced on stainless steel and nickel plated mild steel substrate by the ebonizing process. Various immersion times have been tried and the solar absorptance, α s, and thermal emittance, ϵ T, are measured for each condition. For stainless steel samples, the maximum solar absorptance is found to be in the range of 0.92–0.93, with a corresponding thermal emittance of 0.32. However, for nickel plated mild steel samples, the emittance values, corresponding to solar absorptance of 0.90, are found to be in the range of 0.50 to 0.70. The coating is found to have poor adhesion to copper substrates. X-ray diffraction analysis has shown the coatings to be composed of Cr 2O 3 and chromium particles, thereby establishing the composite nature of the coatings. Scanning electron micrographs show that the microstructure consists of preferentially oriented disc-shaped particles. These coatings are characterised by rough surface morphology as compared to electro-deposited black chrome coatings reported earlier. Elevated temperature (≈250°C) testing and humidity exposure test have proved the excellent long term durability of the coatings on stainless steel substrates.
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