Obtention and characterisation of cobalt plus copper electrodeposits from a citrate bath

The electrodeposition of cobalt + copper alloy on vitreous carbon, copper a nd nickel electrodes in a citrate bath at pH ca. 5 has been studied for two [Co(II)]/[Cu(II)] ratios in solution. Voltammetric and stripping results o n vitreous carbon show that co-deposition of the two metals takes place und er these conditions. Electrodeposition leads to the formation of a solid so lution of cobalt in copper, detected by only one oxidation peak that shifts from the copper to the cobalt position as the applied current density-appl ied potential is made more negative. Structural XRD analysis and compositio nal analyses, confirm the formation of a cobalt-copper solid solution of fa ce-centred-cubic (fcc) structure. Diffractograms show peaks that appear at diffraction angles between the lines corresponding to copper and fee cobalt . The value of the fee lattice constant a of the alloy decreases linearly w ith the increase in the cobalt percentage in the deposits, following Vegard 's law. Deposits obtained at the same charge and current density from the s ame bath on different substrates have similar morphology: nodular-grained d eposits at low deposition current densities-applied potentials, which evolv e gradually to more fine-grained and structured deposits as the cobalt perc entage in the deposits is increased. (C) 2000 Elsevier Science B.V. All rig hts reserved.