Influence of halide ions on the inhibitive effect of congo red dye on the corrosion of mild steel in sulphuric acid solution

The inhibitive effect of congo red dye (CR) on mild steel corrosion in sulphuric acid solution was studied at different temperatures using gravimetric techniques. The influence of halide additives namely: KCl, KBr and KI on the inhibition efficiency of CR was also investigated. Inhibition efficiency increased with CR concentration but decreased with rise in temperature. Corrosion activation energies of 82.98 and 96.92 U mol(-1) were observed in the absence and presence of CR, respectively. The observed corrosion data suggest that inhibition of mild steel corrosion is due to physical adsorption of the CR molecules on the metal surface, which follow Flory-Huggins isotherm. Inhibition antagonism and synergism were respectively observed at 30 and 60 degreesC on addition of halide salts to inhibited systems containing CR. The inhibition efficiency of CR in the presence of halides increased with rise in temperature and corrosion activation energy in these systems decreased to 40.63 kJ mol(-1). These observations indicate a chemical adsorption mechanism, thus suggesting that the halide ions reversed the mechanism of CR adsorption within the concentration range studied. The calculated values of heat of adsorption confirm physisorption and chernisorption mechanisms respectively for CR adsorption in the absence and presence of halides. (C) 2004 Elsevier B.V. All rights reserved.