Lactobionic Acid as a New Synergist in Combination with Phosphonate-Zn(II) System for Corrosion Inhibition of Carbon Steel

Studies on lactobionic acid introduced as a synergist in the presence of phosphonobutane-1,2,4-tricarboxylic acid (PBTC) and zinc ions for corrosion control of carbon steel in aqueous environment are presented. The investigations revealed that lactobionic acid (LBA) acts as an excellent synergist in corrosion inhibition. Optimum concentrations of all the three components of the ternary formulation are established by gravimetric studies. Potentiodynamic polarization studies indicate that the new ternary system is a mixed inhibitor. Impedance studies show that a protective film is formed on the metal surface in the presence of the inhibitor formulation. The film is found to exhibit its protective nature even at higher temperatures up to 60 °C. Analysis of the protective film by X-ray photoelectron spectroscopy (XPS) and reflection absorption Fourier transform infrared (FTIR) spectroscopy infers the presence of Zn(OH)2, oxides and hydroxides of iron and the inhibitor molecules in the surface film probably in the form of a complex, [Zn(II)-PBTC-LBA]. The morphological studies by scanning electron microscopy (SEM) and the topographical studies by atomic force microscopy (AFM) also indicate the presence of protective film on the metal surface. A plausible mechanism of corrosion inhibition is proposed.