Theoretical and experimental studies of corrosion inhibitors of aluminum alloys

摘要

Aluminum alloys are used in industry for their low weight and good mechanical properties. They may be used in solutions containing corrosive agents inducing a degradation of the metal. A solution is the use of corrosion inhibitors. Several compounds have been reported but they are often expensive or present a risk for environment and humans [1, 2]. So, the research of green inhibitors is increasing [3], Quantum chemical calculation may be one solution to lead this research enabling to understand and predict the corrosion inhibition properties of molecules [4]. It has been shown that individual properties of molecules are not sufficient to predict their inhibitor behavior [5]. The properties of the self-assembled molecule and the molecule-metal interaction should be taken into account to define correct descriptors. For example, we recently showed that the electronic properties of aluminum functionalized by carboxylic acid can explain their corrosion inhibiting properties [6]. We present here a joined experimental and theoretical work based on the adsorption of two organic molecules with different corrosion inhibiting properties on aluminum and 2024-T3 aluminum alloy: 2-mercaptobenzothiazole (MBT) and 2-mercaptobenzimidazole (MBI). Molecular modeling is employed to define the most appropriate descriptors at the atomic scale in order to further distinguish a good inhibiting molecule from a bad one. Several model surfaces are envisaged, spanning from metallic, oxide, hydroxylated aluminum surfaces and metallic copper surface. The first set of results show that the orientation of the adsorbed molecule depends on the surface condition and the coverage ability of the molecule itself. For each surface, several modes of adsorption are studied. The most favorable mode on metallic and hydroxylated surfaces is the same for both molecules namely in parallel of the surface when the molecule is alone and on top during the formation of a self-assembled layer. On oxide, MBI seems to be adsorbed in bridge between two aluminum atoms and nitrogen and sulfur atoms while MBT seems to forma denser film thanks to an adsorption on top. From an experimental point of view, aluminum samples are put in contact with water solutions including each molecule, while surface analyzes are performed by means of X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectroscopy to characterize the metal-molecule interaction in terms of formation of organic layer(s), and composition/thickness of the oxide covering the metal. The experimental data allow us to build realistic models of molecule-surface interaction.