Thick cobalt coatings obtained by electrodeposition

Abstract

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 (M _s) was obtained for cobalt deposits independently of their structure (M _s = 160 emu g⁻¹) although the coercive field (H _c) of the material varied: h.c.p. (100) > h.c.p. (110) > f.c.c.