Properties of Goethite Grown under the Presence of Cr3+, Cu2+ and Mn2+ Ions

This study is focused on properties of goethite related to the inhibition of the corrosion process in low alloy, weathering steels. These steels are characterized by the presence of small amounts of Cr3+, Cu2+ and Mn2+ ions, which drive their protecting behavior in mild atmospheres. Several goethite samples with 5 mole % content of the alloying elements in nominal composition are synthesized by a hydrolysis route. Additionally, Cl-, SO42- are used as precursor ions in order to simulate the presence of atmospheric pollutants. All samples are analyzed by X-ray diffraction and 57Fe transmission Moessbauer spectroscopy (MS). The presence of the alloying elements and pollutant ions reduces the overall magnetic interactions in goethite, which is reflected in the lowering of the hyperfine field of maximum probability at 77 K, in comparison to that of pure goethites. However, the mechanisms of the magnetic interaction reductions are different for each combination of alloying element and pollutant ions. Finally the combined effect of anions and cations produces a wider distribution of particle sizes.