Corrosion inhibition of iron by amphoteric surfactants in hydrochloric acid solutions

In the present work the corrosion inhibition of iron in 2 M HCl solution by amphoteric surfactants was studied. The techniques of measurements were (i) weight loss, (ii) linear polarization and (iii) electrochemical impedance spectroscopy. The investigated surfactants have the structure:

where, R = –C₁₄H₂₉(I), –C₁₅H₃₁(II), –C₁₆H₃₃(III), –C₁₇H₃₅(IV), –C₁₈H₃₇(V). These surfactants have a high inhibitory effect on the corrosion of iron in HCl solution. The inhibiting effect of these surfactants may take place through the blocking effect resulting from their adsorption on the metallic surface and hydrophobic effect. The inhibition efficiency increases according to the order: I < II < III < IV < V. This is due to the increase of the length of the alkyl group (–R) in the surfactants. The adsorption of these surfactants via their adsorption centers on the metallic surface obeyed the Frumkin adsorption isotherm. The presence of these surfactants in the corrosive solution increases the activation energy of the corrosion process with that order of inhibition efficiency.