Investigation of Rust Formed on Steel Surfaces and Related Oxyhydroxides

In order to indentity the corrosion products formed on steel surfaces from 57Fe Moessbauer spectroscopy, detailed Moessbauer parameters have been determined for various kinds of iron-oxyhydroxides: α-FeOOH, β-FeOOH, γ-FeOOH and δ'-FeOOH. 57Fe Moessbauer measurements of the iron oxyhydroxides indicate the following results. Fe occupies a single site in α-FeOOH, but below the Neel temperature as at e.g., 300 K the Moessbauer spectrum is always broad, showing a distribution of the strength of the magnetic exchange interactions. Its shape depends on the grain-size and synthetic methods of the specimen. Fe occupies 3 sites in β-FeOOH. High-purity reagents of γ-FeOOH always contain small amounts of α-FeOOH and their Neel temperatures depend on the synthetic methods of the specimen. Moessbauer spectroscopy of the synthetic δ'-FeOOH shows very broad distribution of the hyperfine magnetic fields.