Interaction of oxygen with zinc surfaces

Abstract

The interaction of oxygen with clean zinc surfaces has been investigated in the temperature range 78–493 K. Oxygen incorporation occurs extensively at 78 K, the limiting uptake being equivalent to ∼ 6 monolayers of oxygen. Above 340 K a further prolonged uptake of oxygen occurs. Isothermal and temperature programmed kinetic studies of this process show that the oxidation of zinc within the temperature range 340–493 K takes place according to a pressure independent logarithmic relationship, θ_t–θ_i=k₀ ln (1 +t), that appears to be related to the surface regeneration which is observed in vacuo at these temperatures. The temperature dependence of k₀ gives an initial energy of activation of 28 ± 2 kJ mol^–1 for the logarithmic process, increasing linearly with the increasing thickness by 5 kJ mol^–1 monolayer^–1.

Illumination of the oxidised surface with ultraviolet light provides evidence which strongly suggests that electron transfer is the rate determining step at all temperatures. At the higher temperatures (340–493 K) the dark thermal reaction seems to be limited by an electron transfer involving a zinc atom at the surface.