The Substituted Diphenyl-1,4-Diazepan-5-One - A New Class of Corrosion Inhibitor on Aluminium in Hydrochloric Acid

The effect of new class of corrosion inhibitors 1,4-diazepan-5-one viz., t-3-methyl- r-2, c-7-diphenyl-1,4-diazepan-5-one (3MHD), t-3-ethyl-r-2,c-7-diphenyl-1,4 diazepan-5-one (3EHD), and t-3-isopropyl-r-2,c-7-diphenyl-1,4-diazepan-5-one (3IPHD), on the corrosion of aluminium (Al) in 1N HCl medium has been investigated by weight loss measurements, electrochemical impedance spectroscopy and potentiodynamic polarization technique.    The results so obtained reveal that all the 1,4-diazepan-5-one derivatives are excellent corrosion inhibitors for Al in 1N HCl. The weight loss is found to be concentration and temperature dependent. The effect of temperature has been examined in the absence and presence of 1,4-diazepan-5-ones in 1N HCl solution in the range of 303K - 333K. Thermodynamic parameters like ΔH#, ΔS# and ΔGºads and activation parametes Ea were evaluated for both dissolution and inhibition processes. Potentiodynamic polarisation studies have shown that all these compounds suppress both the anodic and cathodic processes and behave as mixed type inhibitors. The ac impedance studies indicate that the adsorption mechanism is involved in corrosion inhibition. The adsorption of these compounds on Al surface is found to obey Temkin adsorption isotherm. The surface morphology was studied by scanning electron microscopy (SEM) as well as energy dispersive spectroscopy (EDS)