Technical note Influence of quarternary amine alkyl chain length on corrosion inhibition of mild steel in CO 2 saturated 5%NaCl solution at pH 6·5

Abstract

Experiments were conducted with initially clean and with precorroded mild steel surfaces to investigate the influence of alkyl chain length of three quarternary amines on corrosion inhibition in 5%NaCl. The aim was to discover which molecules could produce inhibition efficiencies greater than 900% within the first few hours. Results obtained indicate that although inhibition increased with increasing alkyl chain length, in no case did the required increase in efficiency, to greater than 90% within 2h, occur. When thiourea, a small molecule with a significantly different structure, was tested on a precorroded surface, the required rise in efficiency was achieved. Thus, it is suggested that the failure of the smaller amines was not simply related to their short alkyl chain lengths, and that other factors, such as localised differences in charge over the structure of the molecule, need to be taken into consideration. Furthermore, results showed that the small quarternary amine molecules, which were able to produce some inhibition, may have done so as a consequence of producing a change in the surface morphology of the corrosion product. This could help in the development of better and more appropriate inhibitors.