Abstract
Influence of temperature on the passivation of zinc in a concentrated alkaline zincate solution has been studied using stationary and rotating disk electrode techniques. Passivation time increased as the bath temperature increased reaching a maximum at 45-55°C. Effect of rotation was larger at higher temperatures than at low temperatures. Limiting current density and value of constant K changed at 40-45°C. It was found that the dissolution process of zinc was kinetic-controlled in the low temperature range and was diffusion-controlled in the high temperature range. A gray film was formed on the anode at low temperatures, the color of which varied to blue, brown and white at temperatures above 40°C. The apparent activation energies for the formation of a passivated film onzinc anode were 3.80Kcal/mol and 2.19Kcal/mol in the bath temperature range of 15-45°C and 45-65°C respectively. From the results obtained, it could be seen that the anodic reaction of zinc changed radically when the solution temperature reached 50°C.
