ABSTRACT Iron-oxide layers formed on the surfaces of acicular iron particles and of magnetite are examined by means of Mössbauer spectroscopy. Our results indicate that thin iron-oxide layers formed on iron below 393 K consist of gamma-Fe2O3, where as Fe3O4 is formed on the surface of metallic iron if iron with thick iron-oxide layer is heated at 573 K in vacuum. Thickness of 2.1 and 3.5 nm of gamma-Fe2O3 is necessary to keep iron and Fe3O4 from air oxidation at room temperature, respectively.
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