A kinetic study has been made of the effect of oxygen pressure (10−6 to 60 Torr) on the oxidation of Ferrovac E iron at 350° and 400°C. The initial rate of oxidation is found to increase with increasing oxygen pressure, while after 180 min the weight gain is independent of pressure (for pressures greater than 10−5 Torr). Initially forms on the surface, and once this is covered by a continuous layer of the oxidation rate is markedly reduced. The lower the oxygen pressure, the longer the time before starts to nucleate, and no is observed after oxidation at very low pressures . An induction period is observed for the oxidation at .