Corrosion behaviour of electrodeposited Zn–Co–Fe alloy

Abstract

The anodic dissolution and passivation of Zn–Co–Fe alloy film; deposited galvanostatically on a steel rod from a sulfate bath, has been studied in 0.5 M NaOH. The study is carried out using electrochemical methods such as, galvanostatic measurements for electrodeposition, cyclic voltammetry (CV) for the anodic and cathodic behaviour of alloy to study the potential ranges at which the oxidation and reduction processes occur. Anodic linear sweep voltammetry (ALSV) technique is used for the phase structure determination. The values of parameters such as scan rate and the influence of concentration and temperature of NaOH solution have been varied to study their effect on the electrodeposited Zn–Co–Fe alloy. X-ray Diffraction (XRD) show that Zn–Co–Fe alloy coatings consist of a zinc solid solution and iron–cobalt intermetallic phase (FeCo). It is found that the anodic excursion exhibited two anodic dissolution peaks A1 and A2. The first anodic peak A1 related to the dissolution of Zn from pure zinc phase and the second A2 to the complex dissolution of the elements iron and cobalt from their homogeneous FeCo phase. Increasing the scan rate enhance the height of the anodic peak and shifts potentials to nobler values, which may be due to the selective dissolution of zinc increases. Increasing NaOH concentration and temperature, accelerates the diffusion rate of the diffusing species to or from the anode surface, results in increasing the height of the anodic peak and shift their potentials towards more negative values.