Note on the Temperature Stability of Wüstite in Surface Oxide Films on iron

Abstract

Davies et al. have shown that, when iron is oxidised at temperatures above 700°, the oxide film present on flat specimens contains mainly wüstite (FeO), in fact the three oxides FeO, Fe₂O₄ and Fe₂O₄ are all present, approximately in the ratio 95: 4: 1. Below 570°, FeO is not stable, as shown by the iron–oxygen equilibrium diagram₂ and Collongues & Chaudron₃ have shown that in vacuo wüstite decomposes to give iron and magnetite at temperatures below 570°. Wüstite formed as an oxide layer on iron oxidised at temperatures above 570° should also become unstable on cooling to room temperature. The following results show how the degree of wüstite breakdown can be easily estimated.