Origin of the synergistic effect between polysaccharide and thiourea towards adsorption and corrosion inhibition for mild steel in sulphuric acid

The origin of the synergistic effect between polysaccharides and thiourea towards adsorption on mild steel in 0.5 M H2SO4 and their effect on corrosion inhibition has been studied. Two different polysaccharides, gum arabic and agar agar are used for this purpose. Results obtained from potentiodynamic polarization and electrochemical impedance spectroscopic studies reveal that thiourea imparts a profound synergistic effect towards the corrosion inhibition of mild steel in H2SO4 by the polysaccharides. The polysaccharide-thiourea system acts essentially as a mixed type corrosion inhibitor and the phenomenon of adsorption mechanism on metal surface is proposed as physisorption. Detailed FTIR studies of the surface adsorbed layers of inhibitors have been done to elucidate the origin of the synergistic effect towards the coadsorption and subsequent corrosion inhibition of the metal.