Studies on the corrosion inhibition behaviour of some amino acid surfactant additives

Abstract

Among the metals, mild steel is the most extensively investigated metals for corrosion studies due to its wide application in different corrosive environments. It is subjected to excessive corrosion attack when exposed to service in aqueous acidic environments. One of the important and practical methods of protecting steel from corrosion is the use of inhibitors. A number of organic compounds containing heteroatoms such as N, O, S and P in their aromatic ring or long carbon chain have been widely used as potential corrosion inhibitor in acid solutions. These compounds prevent corrosion by blocking the active corrosion sites either by getting adsorbed, or by forming a protective layer or an insoluble complex on the metal surface. The inhibitive action of these compounds depends on the structure of molecule, corrosion environment, the charge and nature of metal surface and organic molecule. However, most of the organic compounds used as inhibitor are synthetic chemicals, expensive and very hazardous to both human beings and the environments and needs to be replaced with nontoxic and environmental friendly compounds. In order to promote green chemistry electrochemists and corrosion engineers have been looking for naturally occurring organic substances or biodegradable organic materials that can be used as metal corrosion inhibitors. Amino acids represent a category of organic compounds that fulfills many of the aspects needed for such purpose. They are naturally occurring, relatively cheap and their structure and properties are long established. They contain carboxyl and amino functionalities bonded to the same carbon atom and are nontoxic, completely soluble in aqueous media and are easy to produce in purities greater than 99%. It has been shown that some amino acids can acts as corrosion inhibitors, which has generated an increasing interest in these compounds as substitute to conventional corrosion inhibitor that is usually toxic.