Effect of nitrites as inhibitors for steel corrosion, examined in alkaline solutions with various degrees of HCO3-/CO3= contents

M.B. VALCARCE; C. LÓPEZ; M. VÁZQUEZ

Cancun, méxico

Congreso; XVII Internacional Materials Research Congress y VI NACE Mexican section Corrosion Congress.; 2008

NACE International Mexican Section

Nitrite ions are well-known corrosion inhibitors of wide application in the field of steel corrosion in concrete [1]. This investigation aims at investigating solutions that simulate carbonated concrete pore solutions representative of marine environments: slightly alkaline solutions (pH=9) contaminated with chloride ions ([Cl-]=0.1 mol l-1), containing NaNO3 0.2 mol/l as inhibiting agent. It has been suggested that the CO3= and HCO3- contents could influence the properties of the surface layer [2, 3].Thus, two HCO3-/CO3= ratios are tested in these simulating pore solution. One of them has a so-called low degree of carbonation (LDC) with Na2CO3 0.0015 mol l-1 and NaHCO3 0.03 mol l-1, while the other has a high degree of carbonation (HDC) with Na2CO3 0.015 mol l-1 and NaHCO3 0.3 mol l-1. Changes in key electrochemical parameters are investigated on steel electrodes, using electrochemical techniques such as polarization curves and electrochemical impedance spectra (EIS), together with weight loss evaluation. Nitrite ions are well-known corrosion inhibitors of wide application in the field of steel corrosion in concrete [1]. This investigation aims at investigating solutions that simulate carbonated concrete pore solutions representative of marine environments: slightly alkaline solutions (pH=9) contaminated with chloride ions ([Cl-]=0.1 mol l-1), containing NaNO3 0.2 mol/l as inhibiting agent. It has been suggested that the CO3= and HCO3- contents could influence the properties of the surface layer [2, 3].Thus, two HCO3-/CO3= ratios are tested in these simulating pore solution. One of them has a so-called low degree of carbonation (LDC) with Na2CO3 0.0015 mol l-1 and NaHCO3 0.03 mol l-1, while the other has a high degree of carbonation (HDC) with Na2CO3 0.015 mol l-1 and NaHCO3 0.3 mol l-1. Changes in key electrochemical parameters are investigated on steel electrodes, using electrochemical techniques such as polarization curves and electrochemical impedance spectra (EIS), together with weight loss evaluation. Nitrite ions are well-known corrosion inhibitors of wide application in the field of steel corrosion in concrete [1]. This investigation aims at investigating solutions that simulate carbonated concrete pore solutions representative of marine environments: slightly alkaline solutions (pH=9) contaminated with chloride ions ([Cl-]=0.1 mol l-1), containing NaNO3 0.2 mol/l as inhibiting agent. It has been suggested that the CO3= and HCO3- contents could influence the properties of the surface layer [2, 3].Thus, two HCO3-/CO3= ratios are tested in these simulating pore solution. One of them has a so-called low degree of carbonation (LDC) with Na2CO3 0.0015 mol l-1 and NaHCO3 0.03 mol l-1, while the other has a high degree of carbonation (HDC) with Na2CO3 0.015 mol l-1 and NaHCO3 0.3 mol l-1. Changes in key electrochemical parameters are investigated on steel electrodes, using electrochemical techniques such as polarization curves and electrochemical impedance spectra (EIS), together with weight loss evaluation. In LCD solutions the steel surface undergoes general corrosion. The presence of 0.2 mol/L nitrite ions restore the surface passivity, stabilizing an oxide film mainly composed of Fe3O4 and d-FeOOH. In the presence of nitrite and chloride ions a passive layer develops on the electrode surface. The composition of this layer is similar to that found in the absence of chloride ions but pitting attack is observed. The nitrite dosage used is effective in preventing surface repassivation after pitting attack In HCD solutions the steel surface remains passive. The presence of 0.1 mol/L chloride ions induces pitting. However, when nitrite and chloride ions are simultaneously present the pitting potential moves to much positive values comparing with LCD solutions. Nevertheless, after pitting attack no repassivation takes place. [1] C. L. Page, V. T. Ngala and M. M. Page, Magazine of Concrete Research 52 (2000) 25. [2] M. C. Alonso and M. C. Andrade, Corrosion Science 29 (9) (1989) 1129. [3] S. B. Farina and G. S. Duffó, Electrochimica Acta 52 (2007) 5131.