Corrosion of Pure and Amalgamated Zinc in Concentrated Alkali Hydroxide Solutions

Abstract

Corrosion of pure and amalgamated zinc in pure concentrated KOH solutions was investigated using two methods: (a) galvanostatic measurements of the kinetics of hydrogen evolution with electrodic assessment of corrosion properties of the system, and (b) volumetric measurement of the hydrogen evolution reflecting directly the rate of corrosion. The latter was followed as a function of time during 150 hr. It was found that the corrosion rate varies considerably with time and was suggested that different factors control the initial and the steady-state corrosion. The initial corrosion rate increases with increasing KOH concentration which is indicative of the chemical mechanism of hydrogen evolution. The change of the corrosion rate with time and the steady-state corrosion rate can be explained in terms of formation of an impermeable ZnO film at the surface. In such a case the concentration dependence of the corrosion rate is inverse with time, which explains some results reported in literature. The amalgamated zinc surface gives complex galvanostatic transients which indicate a new phase formation in the process of initiation of hydrogen evolution, which could pertain to some solid potassium-zinc-mercury alloy.