The effect of type of self-assembled system and pH on the efficiency of corrosion inhibition of carbon-steel surfaces

In this work, three surfactants were used in the preparation of self-assembled systems to inhibit acidic corrosion on API5LX Gr X52 carbon-steel surfaces: CTAB (a cationic surfactant), SDS (an anionic surfactant), and C12E9 (a non-ionic surfactant). These surfactants were used in the form of aqueous solutions and in microemulsions. Pseudoternary diagrams were constructed using aqueous phases consisting of 0.5 M NaCl at pH = 2, 4 and 7, butan-1-ol as co-surfactant and kerosene as oil phase. The values of c.m.c., maximum surface excess, minimum surfactant cross-sectional area and free energy of micellization were determined using surface tensiometry. The distinct effects of pH and type of self-assembled system on the efficiency of corrosion inhibition have been elucidated by electrochemical techniques (polarization and Tafel curves). It has been demonstrated that these parameters can significantly affect the results, which depend largely on the mechanism of aggregate adsorption on the metal surface and droplet stability. By establishing the optimal conditions, excellent corrosion efficiencies were found for these systems, even at low surfactant concentrations.