The Oxidation of Fe₃O₄ on Iron and Steel Surfaces

Infrared and Raman spectroscopy were used to study the oxidation of Fe₃O₄ on surfaces of weathering steel, carbon steel, and pure iron. Two sets of samples were polished and coated with an Fe₃O₄ paste. One set was moistened daily with distilled water and allowed to freely dry in air. The second set was treated in a similar manner except that every other day, a 0.1M Na₂SO₄ solution was used in place of the distilled water solution. In the set of samples treated only with distilled water, Fe₃O₄ was oxidized to γ-FeOOH on both the weathering and carbon steel surface, but oxidation of Fe₃O₄ was not observed on the pure iron surface. On all of the samples treated with 0.1M Na₂SO₄, Fe₃O₄ was oxidized initially to γ-FeOOH which converted to α-FeOOH after several weeks. The initial oxidation of Fe₃O₄ is proposed to occur by a reaction with H₂O₂ produced from the reduction of O₂.