Investigation of the initial reaction of the alloy Co86Cr14 and its constituent metals with oxygen using secondary ion mass spectrometry

Abstract

The initial oxidation of Co86Cr14 and its constituent metals is investigated using an in situ dynamic secondary ion mass spectrometry (SIMS) technique. Simultaneous analysis and controlled formation of oxidation products, rather than just analysis, allows the oxidation to be studied at the very early stages of the process, i.e. when the oxidation product is of submonolayer extent. The technique, initiated by Hultquist5-7 for the study of pure metals in various in situ environments, involves exposing a sputter-cleaned sample to various partial pressures of oxygen in the SIMS chamber and achieving an equilibrium between the formation and removal of the reaction products under the normal dynamic SIMS conditions. Here, the study is extended to give some insight into the interpretation of the SIMS data obtained by this method, and to determine a model for the oxidation of materials. An empirical model is derived for the oxidation of cobalt. A theoretical model is also derived based on the Langmuir model, but allowing for the more energetic nature of ion bombardment and oxide removal. The theoretical and empirical models are indistinguishable at low oxygen pressures. The cobalt component in the alloy Co86Cr14 behaves in a similar way to that of the pure metal, which suggests that the cobalt oxidizes independently of the chromium in the alloy.