Surface Analysis of Adsorbed Carbon Dioxide Corrosion Inhibitors

Surface analysis techniques have been used to study the adsorption behavior of corrosion inhibitors on mild steel in carbon dioxide (CO₂)-saturated brine media. In particular, polarized grazing angle Fourier transform infrared spectroscopy (PGA-FTIR) and x-ray photoelectron spectroscopy (XPS) have been used to investigate the adsorption mechanisms of corrosion inhibitors on mild steel surfaces. A number of compounds were analyzed by using PGA-FTIR, and a few selected ones were also examined by XPS. It was shown in this study that n-alkyl/alkenylsuccinic anhydrides, in particular n-hexadecylsuccinic anhydride, were chemisorbed at the surface of mild steel through the formation of an iron carboxylate salt. Adsorption of other carboxylic acid-based and nitrogenous inhibitor compounds could not be detected by using ex-situ surface analyses of washed samples. The PGA-FTIR results showed that several commercially available batch treatment inhibitors were chemisorbed at the surface of mild steel electrodes. These findings are consistent with the observation that batch treatment inhibitors display good persistence at mild steel electrodes when used to control CO₂ corrosion.