Electrochemical Behavior of Zn-Ni Alloys in Borate Buffer Solutions

Abstract

The Electrochemical behavior of Zn-Ni alloys was studied in borate solutions using cyclic voltammetry, potentiodynamic anodic polarization, and current transient techniques under the effect of alloy composition, stepwise increasing potential, scan rate, and electrolyte concentration. The voltammogram consists of two potential regions separated by the critical potential . The first potential region involves the selective dissolution of the less noble metal, zinc, and the appearance of two anodic peaks and . Peak is due to the formation of Zn(OH)2 and to the formation of ZnO on the alloy surface. The second potential region relates to the simultaneous dissolution of nickel. This region was characterized by the appearance of three anodic peaks , , and prior to the oxygen evolution reaction. These peaks are assigned to the formation of Ni(OH)2, NiOOH, and Ni2O3, respectively. The anodic voltammetric profiles of the alloys lies below those of the pure metals indicating decreased rates of dissolution of the two metals, zinc and nickel, from the alloys. On alloying with nickel, the rate of zinc dissolution was decreased which increases its protective life as sacrificial anode for automobile body against corrosion. X-ray diffraction analysis confirmed the existence of Zn(OH)2, ZnO, Ni(OH)2, and Ni2O3 with preferred orientations (008), (101), (002), and (202) of the alloy surface polarized to noble potentials. Potentiostatic current/time transients showed that the formation of Zn(OH)2, ZnO, Ni(OH)2, NiOOH, and Ni2O3 layers involves a nucleation and growth mechanism under diffusion control.