Some new phospho-zwitterionic Gemini surfactants as corrosion inhibitors for carbon steel in 1.0 M HCl solution

Abstract Three anionic-cationic phospho-surfactant candidates were prepared and tested as corrosion inhibitors against carbon steel corrosion in 1.0 M aggressive HCl medium. They having a different carbon chain tails ZGO (8 carbons), ZGD (12 carbons) and ZGH (16 carbons). This studying consider the first that handle these new surfactant category as corrosion inhibitors. The corrosion process has been studied gravimetrically & electrochemically. The atomic force microscope (AFM) & X-ray photoelectron spectroscopy (XPS) clarified the adsorption of the prepared anionic-cationic phospho-zwitterionic surfactant on the steel surface. The surfactant tail showed a significant impact on the corrosion protection process. Increasing the surfactant tail length led to improving the corrosion inhibition efficiency, which mainly ascribed to the higher adsorption affinity of longer chain surfactant. The ZGH surfactant showed highest inhibition efficiency 91.1% compared to other candidates with shorter chain length. The results confirmed enhancing the inhibition efficiency as function of increasing the temperature up to 70 °C, implying the preferably induced chemical adsorption by theses phospho-based surfactants. The maximum inhibition efficiency has been achieved at 70 °C, for all synthesized phospho-surfactants following Langmuir adsorption isotherm with chemical adsorption predication as the adsorption free energy ranges from -63.4 to -75.2 kJ/mol. The electrochemical Tafel clarified that the ZGO, ZGD, & ZGH behave as mixed-type inhibitors.