Data_all.zipInfluence of Cr(III) on the formation and transformation of corrosion products of steel in marine environments

A fundamental approach is used to better understand the influence of Cr on the resistance of low alloy steel to marine corrosion. It focuses on the formation and transformation of corrosion products of steel in seawater-like electrolytes. Fe(OH)₂ precipitates are then prepared by mixing a solution of NaCl, Na₂SO₄·10H₂O, FeCl₂·4H₂O or FeCl₂·4H₂O + CrCl₃·6H₂O (so that Cr = 8% and Fe = 92%), with a solution of NaOH. In a first approach, the obtained aqueous suspension is stirred, at a controlled temperature of 25±0.5°C, to be oxidized by air. The resulting oxidation product is characterized by XRD and Raman spectroscopy. In a second approach, the Fe(OH)₂ precipitates are aged one week in suspension in anoxic conditions, filtered, mixed as a wet paste with glycerol and set as a thin compact layer on the sample holder of a X-ray diffraction system. The oxidation process of Fe(OH)₂is then monitored in situ during the acquisition of the X-ray diffractogram. The obtained results demonstrate that Cr(III) hinders the formation of green rust compounds, hence hindering the formation of gamma-FeOOH, i.e., the main oxidation product of green rust compounds. The other oxidation pathways of Fe(OH)₂, which lead to Fe₃O₄ or alpha-FeOOH, are thus favored. Nevertheless, Cr(III) favors mainly the solid state transformation pathway of Fe(OH)₂, thus promoting a-FeOOH via the formation of poorly ordered Fe(III) oxyhydroxides, namely feroxyhyte and ferrihydrite.