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Résumé :
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Synergistic inhibition of corrosion of carbon steel in low chloride environment using ascorbate as a synergist along with 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTC) and Zn2+ is presented. The synergistic effect of ascorbate has been established from the present studies. In the presence of ascorbate, lower concentrations of PBTC and Zn2+ are sufficient in order to obtain good inhibition, thus making this formulation more environmentally friendly. Potentiodynamic polarisation studies inferred that this mixture functions as a mixed inhibitor, predominantly cathodic. Impedance studies revealed that an immersion period of 24 h is necessary for the formation of the protective film, with a very high charge transfer resistance. The film is stable even at 60 °C in the presence of the inhibitor in the corrosive environment. The surface analysis by X-ray photoelectron spectroscopy (XPS) showed the presence of iron, oxygen, phosphorus, carbon and zinc in the protective film. The XPS spectra inferred the presence of oxides/hydroxides of iron(III), Zn(OH)2 and [Zn(II)–PBTC–ascorbate] complex in the surface film. This inference was further supported by the reflection absorption Fourier transform infrared spectrum of the surface film. A plausible mechanism of corrosion inhibition has been proposed.
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