Corrosion Inhibition: Synergistic Influence of Gluconates on Mild Steel in Different Corrosive Environments. Synergetic Interactions of Corrosion Inhibition Tendency of Two Different Gluconates on Mild Steel in Different Corrosive Environments

Susceptibility of mild steel to corrosion attack has restricted its industrial applications, despite its numerous advantageous characteristics. Comparison of the inhibitive tendency of a mixture of zinc gluconate (ZG) and ferrous gluconate (FG) on the corrosion behavior of mild steel in acid and saline media was investigated using electrochemical and weight loss techniques. The FG:ZG ratio was dosed from 0.5:0.5 to 2.0:2.0 g/v at an interval of 0.5:0.5. The surface morphology of the corroded mild steel samples was evaluated by high resolution scanning electron microscope equipped with energy dispersive spectroscopy (HR-SEM/EDS). Experimental results indicated that the combined inhibitor significantly reduced the corrosion rates of mild steel, with the maximum inhibition efficiency (IE) of 100% and 48% at 28 oC in the presence of 1.5:1.5 g/v concentrations in 3.5 % NaCl and 0.5 M H2SO4 solutions, respectively. The SEM micrographs of the inhibited samples show a clearly reduced surface degradation as opposed to the surface morphology without inhibitor. Potentiodynamic polarization curves studies showed that the combined inhibitor is a mixed type inhibitor for mild steel corrosion in 3.5 % sodium chloride and 0.5 molar sulphuric acid solutions. From the set of experimental data it was found that the combined inhibitor reduced the corrosion rate through an adsorption process and obeyed Langmuir’s adsorption isotherm in chloride medium and Freundlich adsorption isotherm in sulphuric acid medium at all concentrations and temperature studied. Good synergism exists between FG and ZG. The results obtained from potentiodynamic polarization are consistent with the results of the weight loss method. Synergistic performance of inhibitors was perfect in saline medium. From the analysis of grey relational grade model, the significant concentration ratios were indentified. The results showed the influence of synergistic FG:ZG at a concentration of 1.5 g/v on the corrosion rate of mild steel. Predicted results were found to be in good agreement with experimental results.