The inhibition of corrosion in a copper-gold galvanic microreactor using CTAB surfactant

This thesis investigated the measurement and regulation of corrosion rates in a copper-gold galvanic microreactor. A novel optical microscope technique was developed to measure the spatiotemporal dissolution rates of the copper electrodes in the microreactor, and it was also used to detect changes in the dissolution rate of the electrode due to the presence of cetyltrimethylammonium bromide (CTAB) surfactant. It was determined that the amount of inhibition provided by the CTAB surfactant in the microreactor increased with the surfactant concentration until the critical micelle concentration (CMC) of the surfactant was reached, after which it unexpectedly decreased with further increments in concentration. Electrochemical techniques were employed to elucidate the cause of the changes in amount of inhibition with surfactant concentration and the results indicated that CTAB inhibited reactions taking place on the gold electrode and also promoted the dissolution of copper. The decrease in amount of inhibition at higher CTAB concentrations was attributed to the reactions taking place on the copper electrode.;The morphology of CTAB micelles adsorbed on copper and gold surfaces similar to those in the microreactor was also investigated and the far reaching goal of these studies was to determine whether the morphologies of the adsorbed surfactant may influence inhibition efficiency. AFM images of the gold electrode showed that micelles with a cylindrical or a spherical morphology formed on this surface. On the other hand, the images of CTAB adsorbed on copper surfaces were not conclusive because CTAB reacted with this surface which made it difficult to interpret the images because a distinction between adsorbed micelles and corrosion products could not be made. Nevertheless, it was possible to image micelles on cuprous oxide surfaces and the imaged micelles had a cylindrical morphology. These cylindrical micelles may form on cuprous oxide passivated copper surfaces. A success of the imaging studies was that CTAB micelles were imaged on surfaces that were not atomically smooth. Through this study it was established that shorter micelles or micelles with a higher degree of curvature than those observed on analogous atomically flat surfaces were obtained. More work still needs to be done to determine whether a correlation between the morphology of the aggregates, and the amount of inhibition CTAB provides exists.;Some properties of the corrosion products formed on copper electrodes in the microreactor were also investigated in this thesis; it was determined that this corrosion product had a plate-like or dendritic morphology and it was at least partly organic. The passivating properties of this corrosion product were studied and the results showed that this material did not provide any passivation under the conditions experienced in the microreactor. However, when copper electrodes were anodically polarized (electrochemically) in solutions containing CTAB, a passivating corrosion product was formed at higher (≥ 0.8 mM) surfactant concentrations.