Preparation of selective surfaces of black cobalt by the sol-gel process

Black cobalt, Co-3 O-4, thin solid coatings on stainless steel and glass substrates have been prepared by the dip coating technique via the sol-gel route using a CoCl2 precursor. The coatings produced on substrates exhibit a blue to black colours as a function of the film thickness. Sols have been made from a cobalt acetate precursor 0.1 M, and for such conditions, the dip coating process gives 0.08-0.25 mu m thick uniform films per dipping depending on the viscocity of the sol.