Optimization and microstructural analysis of cobalt-sulfide-pigmented aluminum oxide

Porous anodic films formed on aluminum in a phosphoric acid electrolyte were used to develop selective solar coatings by double precipitation of cobalt acetate and ammonium sulfide indide the pores. The black coatings containing cobalt sulfide were then sealed in hot water and their optical, mechanical and thermal degradation properties were tested. Multiple linear regression routines were used to optimize the absorptance and emittance values and the coating formation conditions were accordingly adjusted. After optimization, the coatings were characterized by scanning and transmission electron microscopy, and thermal stability tests were performed to determine the long-term quality of the coatings. The coatings were found to have good thermal stability up to 150°C and high adhesion strength as well as absorptances of up to 0.965 at emittances ranging from 0.15 to 0.25.