Oxidation of Magnesiowustite Single Crystals: II, Dependence on Temperature, Oxygen Pressure, and Crystal Composition

Publisher Website
Google Scholar
Abstract
Single crystals of magnesiowustite (Mg,Fe)O containing up to 79 at.% Fe were prepared, and the proportions of ferrous and ferric ions were determined by chemical analysis. The rate of oxidation of individual crystals was studied at temperatures from 1000° to 1100°C and oxygen partial pressures of 2 × 10−1 to 3 × 10−6 atm. The reaction follows an equation based on diffusion through a product layer. The rate constant varies with temperature according to the Arrhenius relation, and activation energies range from 52 kcal/mole with 13 at.% Fe to about 17 to 20 kcal/mole when Fe atoms occupy one third or more of the cation positions. The rate constant is independent of oxygen partial pressure within the pressure range studied. Spectrographic measurements show that Fe in magnesiowustite occupies mainly octahedral sites, but some tetra‐hedral positions appear to be occupied. The mechanism of the oxidation reaction is considered.