The Oxidation of Iron Single Crystals around 200°C

Abstract

The oxidation of electropolished iron in the temperature region of 200~ is highly dependent on the surface orientation in respect to both the total thickness and phase composition of the oxide. In general, surface orientations close to the (001), (011), and (111) planes oxidize to give films with a large proportion of Fe304. The thick oxide formed on the (001) surface has a thin outer layer containing a high percentage of ~-Fe203. Specimens with orienta-tions remote from the above low index planes oxidize to form films containing a smaller percentage of Fe304. On the (112) surface, ~-Fe203 develops in the outer layer of the oxide at an earlier stage than on the (001). No discrete phase boundaries exist between the oxide phases. These trends are also shown at higher temperatures. Thin films of Fe304 (up to about 100A) on the (001) and (112) surfaces behave differently with regard to cathodic reduction, with mainly formation of Fe + + from magnetite on the (001) surface, and a mixed reaction with a large amount of reduction to metallic iron on the (112) surface. A change in surface preparation can change the distribution of phases in the oxide.