On the Mechanism of Low-Temperature Oxidation (23°–450°C) of Polycrystalline Nickel

Abstract

The oxidation of “clean” nickel has been investigated from 24° to 450°C at oxygen pressures of . Ultra‐high vacuum techniques made it possible to start oxidation on specimens free of oxide and surface impurities such as C, Si, and S. Oxygen uptake was measured manometrically with a capacitance gauge of submonolayer sensitivity. Initial rapid oxygen adsorption (and place exchange) on nickel was followed by slower oxidation obeying a logarithmic rate law over the thickness range 8–30Aå. Growth of thicker films was in accord with a parabolic rate law, transport through the oxide occurring predominantly via easy diffusion paths. The value of 41 kcal·mole⁻¹ calculated from an Arrhenius plot of the parabolic rate constants from 300° to 450°C is an approximate measure of the activation energy for growth via leakage paths. A p ^1/6 dependence of the parabolic growth rate on oxygen pressure was found at 450°C.