Corrosion Inhibition Performance Of Amino Acids Corrosion Inhibition Investigated By Theoretical Methods

Corrosion prevention is of great importance for industrial application of materials. Among numerous corrosion prevention measures, corrosion inhibitor, bearing advantages of economy, high-efficiency, and wide-applicability, has been applied in various fields, such as petroleum extraction and refining, iron and steel, electric power, and construction, etc. In recent years, with the recognition of environmental protection, development of new effective and environmental friendly corrosion inhibitors has drawn more attention. Amino acid compounds are highly biodegradable, low cost and large scale source, and thus raise much concern. In this paper, the inhibition mechanism of systeine, valine and alanine amino acids was investigated by combination of weight loss measurement, quantum chemical method and molecular dynamics simulation method for carbon steel in hydrochloric acid. The experimental results showed that the inhibition efficiency of these three compounds followed the order of cysteine>valine>alanine. The quantum chemical method demonstrated that the highest occupied molecular orbital (HOMO) was mainly located on the amino group, while the lowest unoccupied molecular orbital (LUMO) was distributed on the carboxyl group. These orbital distributions indicated that amino acids would adsorb onto metal surface stably through forming coordinate bonds and feed-back bonds. Molecular dynamics simulation showed that three compounds indeed adsorbed on the metal surface, and the monolayer formed on the metal surface could inhibit the diffusion of corrosive species from liquid phase to metal surface, which followed the order of cysteine>valine>alanine. Based above study, the corrosion inhibitor theory for hydrochloric acid corrosion could be complemented, and the validity and operability could be confirmed to investigate inhibition mechanism by combination of experimental method and molecular modeling method.