Stripping Voltammetric, Conductance and Anodic Linear Polarization Analysis on Dissolution of Electrodeposited Zinc-Cobalt Alloy

The electrodeposition of zinc-cobalt alloys from sulfate bath was studied on steel substrate. In order to elucidate the deposition mechanism a complementary approach was used based on the combination of various electrochemical techniques. Under the studied experimental conditions, the electrodeposition of the alloys was of anomalous type. The dissolution rate of electrodeposited Zn-Co, from sulfate bath, in hydrochloric acid was investigated. Two techniques, the stripping voltammetry and the conductance measurements, were used for the first time in this concern. The anodic linear polarization measurements used to study the dissolution process and to confirm the others techniques results. A comparison was carried out between those newly suggested methods and the previously used method. This comparison shows of the reliability of these methods. X-ray diffraction measurements revealed that the alloy consisted of the two kinds of deposits have been formed, pure Zn and g-phase (Co5Zn21). The comparison between Co deposition and Zn-Co codeposition showed that the remarkable inhibition of Co deposition takes place due to the presence of Zn2+ in the plating bath. The Co deposition starts at -0.87 V in the bath of Co deposition only, but its deposition starts at more negative potentials in the codeposition bath although the concentration of Co2+ is the same in the both baths.