The Anodic Passivation of Zinc in Alkaline Solutions

Galvanostatic studies have been made on the anodic passivation of zinc in alkaline solutions. The influence of the current density, concentration of the alkali saturated with zinc oxide and the purity of the electrode metal on the behaviour of anodic passivation have been studied. Pure zinc (pronanalyse, Merck) electrode does not show the passivation tendency up to very high current densities, contrary to commercial pure zinc electrode which exhibits the changes in its potential in positive direction even at  very low current densities. Potential versus time, potential versus passivating current density curves were obtained.

The results obtained on the passivat ion of zinc in alkaline solutions have been discussed here. Equation relating the limiting current densities of accessary to passiviue the metal is found to be directly proportional to the square of the concentration of hydroxyl ions. The experimental results indicate that the passivation tendency of zinc is least within a concentration range of 6N to ION KOH. From the potential-passivation current curve it has been pointed out that the commercially pure Line pouivares in three discrete stages which correspond to the local cell action, anodic dissolution of the meta] and the pas evolution of the electrode followed by the evolution of oxygen. The nature of the deep blue colour film obtained on the surface of pare zinc electrode when the later is being subjected to the anodic treatment has been discussed.