INTEMA   05428
INSTITUTO DE INVESTIGACIONES EN CIENCIA Y TECNOLOGIA DE MATERIALES
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
The effect of citrate ions on the stability of passive film on carbon steel in alkaline solution contaminated with chloride ions
Autor/es:
M.B. VALCARCE; S. TOUJAS; M. VÁZQUEZ
Lugar:
La Haya
Reunión:
Congreso; 67th Annual Meeting of the International Society of Electrochemistry; 2016
Institución organizadora:
International Society of Electrochemistry
Resumen:
Citrate ions have been presented [1] as good candidates for green, low cost inhibitor of carbon steel corrosion in alkaline media contaminated with chloride ions. It has been proposed that citrate ions could avoid chloride ions adsorption, preventing the disruption of the protective passive film naturally grown at high pH values. However, citrate can form soluble iron (II) complexes, favoring the generalized passive layer dissolution. In addition, the competitive adsorption between citrate and chloride ions, could be affected by the presence of a superficial passive layer [2]. The purpose of this work is to evaluate the influence of citrate ions on the stability of the passive film in alkaline solutions simulating a good quality concrete contaminated with chloride ions.All the tests are carried out in a solution that simulates the composition of the pores in chloride-contaminated concrete (PSS). The inhibitor concentration being tested (C6H5O7Na3.2H2O) is 0.3 mol L-1 and the pH of the synthetic medium that simulates concrete is 13, while the citrate/chloride ratio (Cit/Cl-) is kept at 1.Anodic polarization curves and weight loss test were employed to evaluate the effects of citrate ions on the stability of the passive films. The composition of corrosion products after anodic polarization and weight loss were analyzed by Raman spectroscopy. The polarization curves were obtained under two different conditions: bare metal vs. carbon steel kept 24 h at corrosion potential (ECORR). When anodic polarization curves were carried out on bare carbon steel, the passive layer is formed during the anodic scan. Under this condition, citrate ions delayed the pitting attack with an increment in the pitting potential (Epit). However, when the passive layer is previously grown, the Epit decreases while the passivity current increases which indicates a poor protective effect when the oxide layer is present. Citrate ions adsorption on Fe0 avoids chloride ions adsorption. However, iron oxides inhibit the citrate adsorption on the passive film. Weight loss coupons were weighted after 90 days of exposure. Coupons immersed in PSS + Cit + Cl- ions presented pitting attack with the highest loss weight (3.7 times higher than in the absence of Cit). The Raman spectra of corrosion products show no participation of iron(III) compounds when citrate ions are present, probably due to the formation of soluble citrate-Fe(II) compounds. Unexpectedly, the presence of citrate ions ends up favouring the dissolution of the passive film, increasing the porosity and decreasing the corrosion resistance.PSS pH=13ECORR / mVHg/HgOEPIT / mVHg/HgOipas / µA cm-2Weight loss/ mg Type of attacksCl--229 ± 516 ± 645.4 ± 2.6110PittingCit + Cl--250 ± 82-16 ± 427.9 ± 7.8412Pitting[1] M. Ormellese, L. Lazzari, S. Goidanich, G. Fumagalli and A. Brenna. Corros. Sci. 51, 2959-2968 (2009).[2] P. Kern, D. Landolt. Electocim. Acta. 47, 589-598 (2201).