Effect of SO₄²⁻ in aerobic/anaerobic environment and its interaction with HCO₃⁻ on corrosion behavior of carbon steel

The purpose of this research is to investigate the influence of SO₄²⁻ in aerobic/anaerobic environment and its interaction with HCO₃⁻ on the corrosion behavior of Q345 carbon steel using potentiodynamic polarization, X-ray diffraction, white-light interferometer, electrochemical impedance spectroscopy and scanning electron microscopy methods. It was found that the corrosion rates of Q345 carbon steel are faster in aerobic environment under the synergistic effects of SO₄²⁻ and dissolved oxygen compared to that in the absence of oxygen. In solutions containing SO₄²⁻ and HCO₃⁻ in anaerobic environment, a high proportion of HCO₃⁻/SO₄²⁻ leads to the passivation of Q345 carbon steel sample as a result of the competitive adsorption of HCO₃⁻ on substrate surface with smaller radius. As the ratio of HCO₃⁻/SO₄²⁻ decreases, the presence of SO₄²⁻ can enhance the dissolution of Fe matrix, thereby resulting in the corrosion of specimens. High concentration of HCO₃⁻ also exhibits the suppression on corrosion because of the formation of dense corrosion products.