Thick cobalt coatings obtained by electrodeposition

Thick cobalt coatings (10-40 μm) with a range of morphology and structure were obtained by electrodeposition on both vitreous carbon and copper electrodes. There is a direct relation between the morphology, structure and magnetic properties of cobalt deposits. A chloride medium at pH 4 and low deposition rates favoured the formation of black, ridge-like deposits of hexagonal close packed (h.c.p.) structure with mixed (100) + (110) preferred orientations. In CoCl2 at pH 4 at current densities in excess of -80 mA cm-2 and in CoSO4, dull grey deposits of h.c.p. (110) structure formed. Sulfate + citrate and chloride + citrate baths at pH 1.5 and very negative current densities promoted the formation of metallic grey deposits with face centred cubic (f.c.c.) structure. Constant saturation magnetization (Ms) was obtained for cobalt deposits independently of their structure (Ms = 160 emu g-1) although the coercive field (Hc) of the material varied: h.c.p. (100) > h.c.p. (110) > f.c.c.