Dissolution and inhibition of Monel (400) alloy in aqueous formic and acetic acid solutions

75-82The corrosion behaviour of Monel (400) in different concentrations of formic and acetic acid solutions has been studied by potentiostatic technique, at different temperatures (30, 37 and 44°C). The maximum corrosion is observed in aqueous 20 mol/O formic and acetic acid solution. It was found that the extent of corrosion of the alloy is a function of acid concentration. The anodic polarisation curves show active corrosion behaviour of the alloy over the whole range of potential at each concentration of both the acids, individually. The cathodic polarisation curves are almost identical irrespective of the concentration of either acid. The inhibitive effect of some organotin compounds viz. Bu2SnCl2, PhSnCl3, Ph2SnCl2 and Ph3SnCl on the corrosion of monel (400) has been studied in aqueous solution mixture (20 mol/O) of either acid. The results have been discussed in the light of molecular structures of the organotin compound and their adsorption on the surface of the corroding metal. Among the inhibitors used Ph3SnCl functions as a better inhibitor in both the acids. SEM studies also show that the inhibitors act as passivator type inhibitor in acetic acid