Interaction between ionic liquids and metal alloys for thermal application

Ionic liquids (ILs) are room temperature molten salts composed of many combinations of organic and/or inorganic ions. They are widely used as solvents for clean synthesis and catalytic processes. Recently ILs application as fluids for heat transfer and storage has been considered with encouraging results. Nevertheless, understanding of the interaction behaviour between ILs and materials employed in the construction of thermal storage and exchange devices as well in chemical reactors is still at a very early stage. In present work we report on the characterization of the corrosion layer formed onto the surface of the different metal alloys after the immersion test performed at 225C for 20 days. The tested materials were brass, Inconel and carbon steel (AISI1018), while the considered IL was the 1-butyl-3-butyl-imidazolium bis(trifluoromethane)sulfonimide. Such ionic liquid was selected for its extremely high thermal capacity, chemical stability and high decomposition temperature. Our focus is on the elemental identification and sputter depth profiling of the as-received and treated samples by SIMS. XPS technique was employed in our study for surface chemical analysis, and low-energy ion scattering with complementary mass separation of scattered ions (MARISS technique) was enlisted to determine the composition of the outer atomic layer of the samples. Surface roughness before and after the immersion test was measured by a stylus profiler. The experimental data indicate that the products of decomposition of the ionic liquid (C, N, O, F, S) are the principal components of all surfaces analysed. It is shown that the most corrosion resistant material is the copper alloy (brass). The essential features of corrosion behaviour of the samples are discussed.