Assessment of the efficiency of mixtures of sodium molybdate, thiourea, N-allylthiourea and N, N' diethylalthiourea in protecting CA-50 steel in a 1.0 M HCL solution

Silva, Djalma R.; Mirapalheta, Almir; Martinez-Huitle, Carlos A.; Tonholo, Josealdo
February 2014
International Journal of Engineering & Technology;Feb2014, Vol. 14 Issue 1, p113
Academic Journal
The present study assessed the effect of sodium molybdate combined with organic compounds as a corrosion inhibitor for CA-50 steel in a 1.0 M aqueous solution of HCl at a temperature of 27±1°C. The organic compounds used were thiourea, N-allylthiourea and N,N'- diethylthiourea. Electrochemical techniques such as potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) were applied to investigate the electrochemical behavior of steel. The action mechanism of inhibitors in protecting metallic surfaces was examined and respective Kads and ΔG°ads values for each electrolyte composition were estimated. Faradaic impedance spectra and Tafel voltammograms showed that the sodium molybdate / N,N' diethylthiourea mixture exhibited greater efficiency and the same behavior as a mixed inhibitor. Optical photomicrographs show improved conditions on the surface of the metal after addition of the mixture. There are prospective environmental benefits due to the reduced inhibitor levels of the mixtures, without compromising efficiency. It was found that the adsorption of inhibitor mixtures on the metallic surface obeys the Langmuir adsorption isotherm.


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