Influence of Direct Current Electric Field on the Formation, Composition and Microstructure of Corrosion Products Formed on the Steel in Simulated Marine Atmospheric Environment

X-ray diffraction, Raman spectroscopy and scanning electron microscopy were employed to investigate the effects of the DC electric field on the composition, formation and structure of corrosion products formed on the surface of the steel immersed in NaCl solution. The results show that goethite (alpha-FeOOH), akaganeite (beta-FeOOH), lepidocrocite (gamma-FeOOH) and magnetite (Fe3O4) are the major constituents among the corrosion products. The arrangement of different levels of the DC electric field intensity gives rise to the following results. The little higher DC electric field intensity (around 100-200 kV/m) promotes the crystallinity and growth of gamma-FeOOH; obviously, much higher DC electric field intensity (greater than 400 kV/m) prevents the growth of alpha-FeOOH and facilitates the generation of Fe3O4. Both the promotional growth of gamma-FeOOH and suppression of alpha-FeOOH growth indicated the weakness of the protectiveness of the rust layer. Consequently, the suppression of the transformation of alpha-FeOOH from gamma-FeOOH favors the yield of the Fe3O4, which works as a large cathode area and would be about to quicken the subsequent steel corrosion.