2275. MICHEL, A., BENARD, J., AND CHAUDRON, G. [Mechanism of the Superficial Oxidation of Iron.] Bull. soc. chim., vol. 1, 1944, pp. 175-179; Chem. Abs., vol. 40, 1946, p. 2370.
Specimens of electrolytic Fe were heated at temperatures from 250°-900° in air. The structure of the separated oxide scale was determined by use of the Debye-Scherrer method of X-ray diffraction and the thermomagnetic method of analysis. At 250°, the oxide consists largely of γ Fe2O3 and a small quantity of Fe3O4. The reaction mechanism is given by the equation Fe→Fe3O4→γ-Fe2O3. In the interval of 400°-600° variable mixtures of γ Fe2O3 and Fe3O4 are formed. The mechanism is given by the equation Fe→Fe3O4→γFe2O3→a-Fe2O3. Above 600° FeO is the major component. At 900° after 3 hr. of oxidation and a rapid cooling the oxide consists largely of FeO. A small quantity of Fe3O4 is found in the superficial layer and a film of a-Fe2O3 on the surface. The mechanism of oxidation is Fe→FeO→Fe3O4→a-Fe2O3. The FeO is assumed to decompose on cooling by the reaction 4FeO→Fe3O4+Fe. It is concluded that both Fe and O2 diffuse in the oxidation reaction. The distribution of reaction products is determined by the magnitude of each process.