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The inhibitive effect and some quantum chemical parameters of cationic surfactants on the corrosion of carbon steel in 1M HCl

O.H.Abdelraheem, M.I.Nessim, M.M.Osman

The inhibitive effect of two cationic gemini surfactants,with different spacer lengths (12-2-12, 12-5-12), and their conventional form(DOTAB) on carbon steel corrosion in 1MHCl solution was studied. The chemical structures of synthesized surfactantswere characterized by the methodologies 1H-NMR, elemental analysis and XRD. Corrosion inhibition efficiency was investigated by weight loss and Potentiodynamic polarization techniques. The studied surfactants showed good inhibitive characteristics. The obtained data elucidated that the efficiencies vary with concentration, and increases in the following order: 12-2-12 >12-5-12 >DOTAB.Adsorption of the tested surfactants on carbon steel surface in the acid medium obeyed Langmuir isotherm. Adsorption isotherm parameters (Kads, ÄGads) were determined. The morphology of carbon steel surfaces was examined by scanning electronmicroscopy (SEM). Quantumchemical calculations were further applied to reveal the molecular structure and explain its effect on the inhibition efficiency. The molecule structural parameters such as highest occupied molecular orbital (HOMO), lowest unoccupied molecular orbital (LUMO) energy levels, energy gap (EHOMO-ELUMO), the dipole moment and charge densities were calculated.