The electroplating of iridium with cobalt from an electrolyte containing 26 mmol dm-3 sodium hexabromoiridate(III) and 85 mmol dm-3 cobalt(II) sulphate was examined. The codeposition of cobalt with iridium was observed in the electrolyte containing iridium ion at more positive potential than the deposition potential of cobalt alone. The composition ratio of iridium and cobalt in the codeposit can be changed by controlling the current density or the electrode potential. The deposit seems to be alloyed because the oxidation behaviour was different from those of the deposits of either iridium or cobalt plated alone. The oxidation potential of the codeposit changes with the hydrogen adsorption. The increase in the cobalt content of the codeposited coating reduced deposit cracking.
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