Growth kinetics of SiO2 nanofilm on MoSi2 in anodic polarization

Abstract

The anodic oxidation of MoSi2 ceramics in 3% NaCl solution is shown to be a multistage process. Auger electron spectroscopy established that only silica forms on the MoSi2 surface between 1.5 and 2.0 V, while molybdenum passes completely into solution. The growth kinetics of silica is studied using chronoamperometry under controlled potential conditions. The resulting kinetic curves show two stages. At the first stage, the reaction rate (current density) falls by one order for the first few minutes when SiO2 nanofilm begins to form. Then the diffusion-limited process, which fits parabolic kinetics, is established. On the whole, the model describing the electrochemical formation of oxide nanofilm on molybdenum disilicide agrees with the Mott-Cabrera theory, which was earlier proposed for high-temperature oxidation processes.