Corrosion inhibition of carbon steel in alkaline chloride media by Na3PO4

The decrease of the pH of the concrete due to the interaction with the CO2 contained in the air creates an electrolyte in the pores with a pH < 8 that destroys the passive film. Also the presence of chloride ions at the rebar surface in alkaline media making susceptible to the aggression of the chlorides as pollutant in marine environment. The inhibiting efficiency of Na3PO4 against corrosion of carbon steel in alkaline medium simulating the interstitial solution of the concrete (pH 12.5) polluted with chloride ions were carried out. Two manners for adding the Na3PO4 were examined: one where the inhibitor was added into the pore solution also containing the aggressive solution, and other where the rebar was first pre-treated by immersion in the inhibitor solution. The protective effectiveness of these two procedures for the inhibitor addition was evaluated by means of several electrochemical techniques, EIS, polarisation curves and microbalance. The results allow concluding that: The pre-passivation procedure is more effective for the rebar protection. The impregnation duration of steel in phosphate solution and the electrode rotation speed influence considerably the phosphate-based film resistance against corrosion. (c) 2007 Elsevier Ltd. All rights reserved.