Corrosion Protection of Cupronickel Alloy by Fatty Acid Film Formed by Various Methods

Cupronickel alloys (CuNi), especially 70Cu- Ni30, are frequently used in marine applications as a construction material because of their good corrosion resistance in seawater. However, corrosion protection of cupronickel is often required to ensure its longevity. Many commercial corrosion inhibitors are ecologically unsuitable for seawater application due to their toxic impact on the marine ecosystem. The application of self- assembled monolayers (SAMs) presents potential ecologically suitable solution for increasing a corrosion resistance of cupronickel alloy. SAMs are thin assemblies of dense and well defined structure that block the active spots on the metal surface and present a barrier to electron transfer and ion penetration. They are formed spontaneously by chemical adsorption and self- organization on the surface of the metal/metal oxide. Up to date, studies of SAMs on cupronickel alloy have mainly been performed with the dip-coating method, which is time consuming, requires higher amounts of working solution and is not always practical for application in industry. The aim of this work is to investigate the possibility of cupronickel alloy protection by self-assembled monolayers of stearic acid (SA) prepared by different techniques: dip-coating, electrochemical method and spraying. Each one of these techniques has some advantages: dip- coating method is simple, electrochemical method is less time consuming, but spraying is more practical than the above mentioned methods. The protective properties of such formed monolayers are examined in artificial seawater by electrochemical polarization methods and electrochemical impedance spectroscopy while the structure of the film is determined by contact angle measurements and Fourier transform infrared spectroscopy. The results of electrochemical investigations show that by using an adequate preparation method and conditions (temperature, time, concentration, applied potential etc.) it is possible to form protective layer of carboxylic acid that significantly reduces cupronickel corrosion rate in artificial seawater. Acknowledgments: The research leading to these results has received funding from Croatian Science Foundation under grant agreement 9.01/253.