Synthesis of a Hybrid Organic/Inorganic Pigment Based on Lignosulfonate/Zinc for Improving Corrosion Resistance of Mild Steel in 3.5 wt.% NaCl Solution

In this paper, organic/inorganic hybrid pigment based on sodium lignosulfonate and zinc acetate was synthesized for reducing the corrosion rate of St12 steel immersed in 3.5 wt.% NaCl solution. To evaluate the anti-corrosion protection performance of steel substrate immersed in solution in the presence and absence of synthesized pigment, electrochemical impedance spectroscopy, potentiodynamic polarization and open circuit potential tests were performed. Scanning electron microscope equipped with energy dispersive spectroscopy and X-ray diffraction tests were also used to evaluate the inhibition mechanism of pigment. The results of the electrochemical impedance spectroscopy test showed that the charge transfer resistance of steel sample increased from 2958 Ω.cm2 to 7500 Ω.cm2 after 120 h of immersion in the saline solution with pigment. The formation of an inhibitive film consisting of zinc and lignosulfonate complexes on the surface of the steel substrate is the main reason for enhancing of the charge transfer resistance of the steel substrate in the presence of the synthesized pigment.