Non-toxic Corrosion Inhibitor Research Articles

Electrochemical study of corrosion inhibition of steel reinforcement in alkaline solutions containing phosphates based components

The aim of this study is to investigate the viability of use of sodium phosphate (Na3PO4: SP), tetrasodium pyrophosphate (Na4P2O7: TSPP) and hydroxyethylidene-diphosphonic acid (C2H8O7P2: HEDP) as a non-toxic corrosion inhibitors of steel bars in alkaline media which simulate the electrolyte in the concrete pores. The effectiveness of these phosphate compounds as corrosion inhibitors was investigated by measuring the corrosion potentials, the polarization curves, the corrosion current densities, and the electrochemical impedance spectroscopy of steel bars immersed for 30 days in saturated Ca(OH)2 solutions with and without chlorides. At the completion of the tests, the mass losses were determined in order to verify the reliability of the electrochemical results. The results showed that phosphate compounds form a protective layer on the steel surface when immersed in alkaline solution without chlorides. In the presence of chloride ions, the SP acts as an anodic inhibitor and reduces the corrosion activity on steel. The HEDP shows lower efficiency, probably due to the decrease of the pH and to the high [Cl−]/[inh] ratio used. Results obtained by electrochemical and gravimetric methods are in quite reasonable agreement.

Evaluation of cysteine as environmentally friendly corrosion inhibitor for copper in neutral and acidic chloride solutions

The efficiency of cysteine as a non-toxic corrosion inhibitor for copper metal in 0.6 M NaCl and 1.0 M HCl has been investigated by electrochemical studies. Potentiodynamic polarization measurements and electrochemical impedance spectroscopy “EIS” were used to study the effect of cysteine on the corrosion inhibition of copper. Inhibition efficiency of about 84% could be achieved in chloride solutions. The presence of Cu 2+ ions increases the inhibition efficiency to 90%. Potentiodynamic polarization measurements showed that the presence of cysteine in acidic and neutral chloride solutions affects mainly the cathodic process and decreases the corrosion current to a great extent and shifts the corrosion potential towards more negative values. The experimental impedance data were analyzed according to a proposed equivalent circuit model for the electrode/electrolyte interface. Results obtained from potentiodynamic polarization and impedance measurements are in good agreement. Adsorption of cysteine on the surface of Cu, in neutral and acidic chloride solutions, follows the Langmuir adsorption isotherm. The adsorption free energy of cysteine on Cu (∼−25 kJ mol −1) reveals a strong physical adsorption of the inhibitor on the metal surface.

Caffeine as non-toxic corrosion inhibitor for copper in aqueous solutions of potassium nitrate

Different electrochemical methods were employed in order to confirm the ability of caffeine (1,3,7-trimethylxanthine) to inhibit the corrosion processes of copper in aqueous potassium nitrate solutions in the absence and in the presence of chloride. Some experiments were repeated in potassium perchlorate in order to compare the influence of the medium. The interaction between the organic compound and the electrode surface occurs independently of the electrode potential. However, maximum interaction was observed at 0.0V (Ag/AgCl) in aerated solutions, and at −0.25V (Ag/AgCl) in deaerated solutions.The presence of the organic compound adsorbed on the electrode surface was confirmed by comparing the voltammograms of copper electrode in the absence and presence of 1.5mmolL−1 of dissolved caffeine. The same results were observed by comparing polarization curves in the absence and in the presence of caffeine.Anodic currents decrease noticeably in the presence of the organic compound. Chronoamperometric experiments were conclusive to prove the inhibitor capability of caffeine to decrease the corrosion dissolution processes of copper under anodic polarization.

Effect of non-toxic corrosion inhibitors on steel in chloride solution

The effect of certain non-toxic inhibitors on the corrosion resistance of ordinary steel in chloride solution (2 × 10−2 M NaCl) at pH 8 was studied by polarisation curves, Raman spectroscopy and the electrochemical quartz crystal microbalance (EQCM).

Evaluation of non-toxic corrosion inhibitors for copper in sulphuric acid

The aim of this paper is to study influence of the molecular structure on the inhibiting properties of organic compounds in corrosion processes in acid media. The inhibiting efficiency of non-toxic imidazole derivatives on copper corrosion in sulphuric acid is investigated. The investigation is performed using electrochemical methods of potentiodynamic polarisation as well as gravimetric measurements. The results of the investigation show that the inhibiting properties of substituted imidazoles depend on molecular structure. The best protection (93%) is obtained by adding a phenyl ring to the imidazole structure. The values of standard free energies of adsorption, as calculated from the Freundlich isotherm, indicate that in the presence of sulphuric acid imidazole derivatives adsorb on copper by a physisorption-based mechanism.