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, 0t— 0\ = k0 In (1 4-/), 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.