Abstract
Synergistic inhibition of corrosion of carbon steel in low chloride environment using ascorbate as a synergist along with 2βphosphonobutaneβ1,2,4βtricarboxylic acid (PBTC) and Zn^2+^ is presented. The synergistic effect of ascorbate has been established from the present studies. In the presence of ascorbate, lower concentrations of PBTC and Zn^2+^ 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 24βh is necessary for the formation of the protective film, with a very high charge transfer resistance. The film is stable even at 60βΒ°C in the presence of the inhibitor in the corrosive environment. The surface analysis by Xβray 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)βPBTCβascorbate] 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.