Surface modification of industrial alloys induced by long-term interaction with an ionic liquid

The surface modification of Inconel 600, Naval Brass and AISI 1018 carbon steel after immersion into the [C4mim][Tf2N] ionic liquid (IL) at 225 °C for 20 days has been studied using SIMS, XPS and by surface topography measurements. The trace concentration of alloys’ components in the IL solution after the immersion test was measured by inductively coupled plasma-optical emission spectroscopy (ICP-OES). Appreciable amounts of carbon, nitrogen, oxygen, sulphur and fluorine were detected on the surface of the alloys after the immersion test because of thermal decomposition of the IL. The corrosion layer formed onto the surface of Inconel was found to be rather thick (ca 400–500 nm) and rough (Ra ∝ 100–200 nm) due to the dominant adsorption of the IL decomposition products. At the same time, Inconel exhibited minor weight loss (2.5× 10−5 g× cm−2) after the immersion test. On the contrary, for Brass, the thickness (70–100 nm) and roughness (Ra ∝ 80–100 nm) of the corrosion layer were the smallest among the alloys studied, and the weight loss was the greatest (1.3× 10−2 g ×cm−2). It is assumed that IL decomposition might be catalysed by some metallic atoms, for instance Ni, that, in turn, could slow down the surface corrosion and migration of metal atoms into the ionic liquid.