Corrosion inhibition and adsorption behaviour for aluminuim by extract of Aningeria robusta in HCl solution: Synergistic effect of iodide ions

The corrosion inhibitive effects of Aningeria robusta extract for aluminium in 2 M HCl solution and the influence of potassium iodide additives on the inhibition efficiency was assessed using hydrogen evolution method at 30 and 60 oC. Inhibition efficiency was determined by comparing the corrosion rates in the absence and presence of additives. The trend of inhibition efficiency with temperature was used to propose the mechanism of inhibition. It was found that the Aningeria robusta extract acts as an inhibitor for acid-induced corrosion of aluminium. Inhibition efficiency (%I) of the extract increased with an increase in concentration of the Aningeria robusta extract and with increase in temperature. On the other hand, inhibition efficiency (%I) synergistically increased on addition of potassium iodide but decreased with increase in temperature. Inhibitor adsorption characteristics were approximated by Langmuir adsorption isotherm at all the concentrations and temperatures studied. The mechanism of chemical adsorption is proposed for the Aningeria robusta extract and physical adsorption for the extract-iodide mixture from the trend of inhibition efficiency with temperature and from the calculated values of activation energy and heat of adsorption.