Inhibition of aluminium corrosion in alkaline solutions using natural compound

Inhibition of aluminium corrosion in 2M sodium hydroxide solution in the presence and absence of 0.5 M NaCl using damsissa (Ambrosia maritime, L.) extract has been studied employing different chemical and electrochemical techniques. Chemical gasometry technique showed that addition of chloride ions or damsissa extract to sodium hydroxide solution decreases the volume of the hydrogen gas evolved. Potentiodynamic results manifested that chloride ion retard the anodic dissolution of aluminium, below the pitting potential, in sodium hydroxide solution. Damsissa extract, in presence or absence of chloride ion, influenced both the anodic dissolution of aluminium and the generated hydrogen gas at the cathode indicating that the extract behaved as mixed-type inhibitor. The decrease in the observed limiting current with increasing damsissa extract concentration indicated that the anodic process is controlled by diffusion. Nyquist plots present two capacitive semicircles at higher and lower frequencies separated by an inductive loop at intermediate frequencies. The inductive loops were clarified by the occurrence of adsorbed intermediates on the surface. A proposed equivalent circuit was used to analyze the impedance spectra for aluminium in alkaline solutions. The results showed that the damsissa extract could serve as an effective inhibitor for the corrosion of aluminium in alkaline solutions. The impedance measurements verified the remarkable stability of the extracts during storage up to 35 days. Damsissa extract was found more effective in presence of chloride ions than in its absence. Inhibition was found to increase with increasing concentration of the extract but decreases with increasing temperature. The associated activation parameters were determined and discussed. (C) 2007 Elsevier B.V. All rights reserved.