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→γFe2O3a-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→Fe3O4a-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.