Influence of Side Chain on the Inhibition of Aluminium Corrosion in HCl by α-Amino Acids

Abstract

Aside from functional groups, aromatic rings have mostly been regarded as zones via which certain inhibitors can protect etching metal parts. Substituent groups generally can be aromatic or non-aromatic, comparison of which is scanty in literature. Among these, amino acids exhibit side substituent chain in addition to amino- and carboxylic carbonyl- functional groups, hence may show unique behaviours in corrosive environment. The side chains of amino acids can vary from to H- to alkyl and then to aromatic. This study is devoted to the investigation of the influence of non-polar, hydrophobic side chain of amino acid homologues (glycine, alanine and phenylalanine) on the inhibition of aluminium corrosion in 0.3 M HCl. Corrosion properties and inhibition mechanism were analysed using mass loss, solid-state characterisation and quantum chemical methods. Potentiodynamic polarisation results confirmed cathodic inhibition, which was relatively less efficient with glycine and phenylalanine. The adsorption of these inhibitors was consistent with Langmuir isotherm and physical mechanism. Activation parameters, topography, electropotential shifts quantum studies and mass loss confirmed the superiority of the inhibiting effect of alanine. It is therefore argued herein that the aromatic carbocyclic moiety of phenylalanine does not dictate its anti-corrosion effect in acidic media, but preferentially, properties such as the adsorption type, corrosion medium, interfacial behaviour of adsorbates and temperature.