Influence of Ni(II), Cu(II) and Cr(III) on the formation, morphology and molecular adsorption properties of α-FeOOH rust particles prepared by aerial oxidation of neutral Fe(II) solutions

Abstract

To elucidate the role of alloying metals such as Ni, Cu and Cr in weathering steels on the formation of α-FeOOH rust by atmospheric corrosion of the steels in industrial and urban districts, influence of alloying metal ions on the formation, morphology and adsorption properties of α-FeOOH particles synthesized by aerial oxidation of neutral FeSO4 solution was examined. The addition of Cu(II) and Cr(III) dramatically suppresses the crystal growth of α-FeOOH and turns the rod-shaped α-FeOOH particles into nano-sized irregular ones. Besides, increase of amount of added Cr(III) forms the iron oxyhydroxysulfate named as Schwertmannite (Fe8O8(SO4)(OH)6). Whereas, the Ni(II) addition shows no noticeable influence on the growth of α-FeOOH crystal and particles. These results imply that the inhibitory effect of crystal and particle growth of α-FeOOH is in order of Cr(III) > Cu(II) >> Ni(II). The adsorption of CO2 gas on the α-FeOOH particles is impeded by adding Cu(II) and Cr(III). Whereas, the formation of Schwertmannite by adding Cr(III) enhances the CO2 and SO2 adsorption. These results suggest that alloying Cu and Cr in weathering steels inhibit the crystal and particle growth of α-FeOOH to accelerate the formation of protective rust layer composed of fine α-FeOOH and/or Schwertmannite rust particles on the steels in urban and industrial atmosphere.