Abstract
To simulate the atmospheric corrosion of weathering steel, artificial Schwertmannite (Fe8O8(OH)6(SO4)) rust particles were synthesized by aerial oxidation of aqueous FeSO4 solution in the presence of metal ions such as Cr(III), Cu(II) and Ni(II), and the transformation behavior of metal-doped Schwertmannite into α-FeOOH was examined at different pH. No remarkable change in crystallinity of Schwertmannite was recognized by addition of Cr(III), Cu(II) and Ni(II). The Schwertmannite prepared without adding metal ions was needle-like particles with a length of ca. 265 nm. The added Cr(III) would be incorporated by substituting for Fe(III) in Schwertmannite crystal, leading to the reduction of particle size of this material. The Cu(II) and Ni(II) in the solution were less easily incorporated in the particles than Fe(III), although growth of the Schwertmannite particles was slightly suppressed by Cu(II). The Schwertmannite particles were transformed into α-FeOOH at pH=3－11. Incorporation of metal ions into Schwertmannite suppressed the transformation into α-FeOOH. Especially, added Cr(III) strongly inhibited the transformation over the whole pH ranges. These results allow us to infer that metals alloying with weathering steel strongly affect the formation of α-FeOOH rust from Schwertmannite and the effect is in order of Cr(III)＞＞Cu(II)＞Ni(II).
