Inhibition mechanisms of organic compounds on copper and copper alloys

Abstract

Because of a series of predominant properties, copper and copper alloys are used nowadays in the production and manufacturing industries. Amongst all available copper alloys, brass, with a relative low cost, is one of the most common materials with a wide range of applications, such as heat exchangers and maritime industry. Corrosion is a common phenomenon for copper and brass in their various applications resulting in serious consequences and direct as well as indirect economic losses. Therefore, a high degree of attention should be paid to their corrosion control. The usage of corrosion inhibitors is one of the efficient approaches to retard corrosion of copper and brass.
This master thesis focused on three organic corrosion inhibitors, i.e. imidazole, 2-mercapto-benzimidazole (MBI) and 2-mercapto-1-methyl-benzimidazole (1H-HB-2T). Open Circuit Potential (OCP) measurement, Linear Polarization Resistance (LPR) measurement and Electrochemical Impedance Spectroscopy (EIS) were used together with Fourier Transform Infrared Spectroscopy (FTIR, both ex-situ FTIR and in-situ FTIR) to evaluate their inhibition efficiencies and interaction mechanisms, where the latter inhibitors were studied in more details.
The results collected in this master thesis show the following: (1) different organic inhibitors provided different inhibition effects on copper and brass; (2) One kind of inhibitor had different inhibition effects on copper and brass; (3) the inhibition effects of MBI and 1H-HB-2T on copper and brass were linked with an electrostatic interaction between their molecules and the surface of specimens; (4) during the physisorption process at the specimen/solution interface, interfacial bonds were formed and a thin but protective layer was produced on the surface of immersed specimens, but these interfacial bonds could break because of soluble aggressive species in the environment resulting in a diminished corrosion protection; (5) the time required for the interfacial bond to break depends on the inhibitor and specimen types.