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The effect of lignitic humic acid in 0.1 M NaCl at pH 7 on low carbon steel was investigated using potentiodynamic polarization and immersion test. The morphology and elemental composition of the corrosion products were characterized using scanning electron microscopy with energy dispersive spectroscopy. The results showed that humic acid accelerated the corrosion of low carbon steel in 0.1 M NaCl. The negative effect of humic acid was attributed to the complexation of the molecules with iron ions. After seven days, immersion tests revealed that steel in 0.1 M NaCl was covered with the discontinuous black corrosion products, whereas humic acid in 0,1 M NaCl induced the formation of a continuous layer of brown corrosion products with low adhesion to the surface. The elemental composition of the black and brown corrosion products corresponded to Fe3O4 and FeOOH, respectively.
Keywords: Humic acid, low carbon steel, corrosion, corrosion product© This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.