Simulating study of atmospheric corrosion of Ni-advanced weathering steels in salinity environment: Formation and structure of magnetite rust particles prepared from FeCl2 solutions containing Ni2+ at neutral pH

Abstract

In order to elucidate the role of alloying Ni in Ni-advanced weathering steels on the formation of Fe₃O₄ (magnetite) rust particles by atmospheric corrosion in salinity environment, aqueous FeCl₂ solutions containing various amounts of NiCl₂ were aged under bubbling the air at 50 °C for 24 h. The atomic ratio Ni/Fe of the solution was 0 – 0.2 and the solution pH before aging was about 7 over the whole Ni/Fe ratios. Aging for 3 h generated the Green rust(Cl^-) ([Fe₃^IIFe^III(OH)₈]⁺[Cl·nH₂O]^-) as a precursor of Fe₃O₄. Added Ni²⁺ was incorporated into Green rust(Cl^-) to form Ni²⁺-substituted Green rust(Cl^-) ([Fe_3-x^IINi_x^IIFe^III(OH)₈]⁺[Cl·nH₂O]^-]), resulting in enhancement of crystallization of this material. After aging for 24 h, the Ni²⁺-substituted Green rust(Cl^-) formed at Ni/Fe = 0 – 0.08 was mainly transformed into spherical Fe₃O₄ particles. The crystallization and particle growth of Fe₃O₄ were promoted on elevating Ni/Fe ratio. At Ni/Fe ≥ 0.12, Fe₃O₄ formation was suddenly impeded to generate rod-shaped α-FeOOH particles, of which the material possesses more stable crystal structure than Fe₃O₄. These results suggest that alloying Ni in Ni-advanced weathering steels accelerates the formation of stable rust layer composed of Fe₃O₄ and/or α-FeOOH particles by atmospheric corrosion in salinity environment such as coastal and marine zones to contribute to the formation of the protective rust particle layer.