Degradation study of black cobalt coating

Black cobalt coatings were electrodeposited on 304 stainless steel substrat es. In older to study the thermal stability of the films, they were subject ed to several cycles of heating in ail at a fixed temperature of 400 degree s C. The phase compositions of fresh samples and of heat treated films were identified using X-ray diffraction. Values of solar absorptance were calcu lated from the measured reflectance values before and after heat treatment. The studies revealed that the fresh samples of black cobalt were composed of (002) reflection phase (5-727 JCPDS), which suggests that the cobalt gro ws epitaxially along the [002] direction of the gamma(002) phase of the sub strate. The high absorptance of fresh samples and their deep black appearan ce can be explained in terms of the multiple reflection model, owing to the intrinsic absorption and roughness of the surface. This has a direct beari ng on the electrodeposition method, because it is also possible to prepare cobalt with metallic appearance. The thermal oxidation behaviour and morpho logical changes of the black cobalt were identified as the main causes of t he elevated temperature degradation of the coatings.