Thermal degradation of black chrome coatings

Black Chrome coatings were prepared on Ni, Fe, Cu and stainless-steel substrates by an electroplating technique. The changes in the physical properties of the sample due to thermal degradation were characterized by Auger electron spectroscopy and spectrophotometry. The optimum black chrome coating was made on Ni substrates using newly synthesized electrolyte at a current density of 0.3–0.4 A/cm2 for 20–30 s. Its optical properties were absorptance (α) of 0.90–0.96 and emittance (ε) of 0.25–0.30. From the surface analysis, it was found that thermal degradation occurred primarily by oxidation of metallic Cr particles with an increase of the annealing temperature. It was also found that stainless steel #304 suffered less optical degradation of the black chrome coating by the selective oxidation process than other pure substrate materials for temperatures up to 450°C.