Effect of temperature on adsorption and corrosion inhibition characteristics of gelatin on mild steel in hydrochloric acid medium

Adsorption characteristics of a water-soluble bio-polymer, gelatin, on mild steel in 1-M hydrochloric acid (HCl) together with its potential corrosion resistive property in the temperature range of 20-50 A degrees C have been evaluated. Electrochemical impedance spectroscopy reveals that when mild steel is exposed to HCl solution containing gelatin, a protective layer develops on its surface resulting in retardation of the rate of charge transfer reaction across the metal-solution interface. Potentiodynamic polarization and weight loss studies also exhibit substantial decrease in the rate of corrosion for mild steel in HCl in the presence of a low concentration of the polypeptide. Gelatin is seen to act as a mixed-type inhibitor towards corrosion of mild steel in HCl blocking both the cathodic and anodic reaction sites, and its adsorption characteristics are found to follow the Langmuir adsorption isotherm. Adsorption phenomenon may be explained involving a competitive model between physical and chemical adsorption modes. The corroded metal surface in the absence and presence of gelatin has been characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and Fourier transform-infrared (FTIR) methods. The backbone amide linkage of the polypeptide chain is thought to be responsible for the adsorption of gelatin on the mild steel surface.