Silica nanoparticles as copper corrosion inhibitors

Nanoparticle suspensions (or 'nanofluids') employed as heat transfer fluids (HTF) enhanced the thermal conductivity and the effectiveness of the heat exchangers as well as efficacy of thermal energy storage (TES) platforms by augmenting the effective specific heat capacity of various solvents. In prior studies, molten salt nanofluids also reduced corrosion by 50% (compared to that of neat molten salts and pure molten salt eutectics). Here, we demonstrate that silica nanoparticle suspension could be beneficial not only from the point of higher rates of heat transfer and thermal energy storage but also as corrosion inhibitors of copper substrates, that are typically used for thermal systems (e.g., HTF and TES). Combined use of Quartz Crystal Microbalance (QCM) technique and atomic force microscopy indicate a significant lowering of the corrosion rates (up to 4 times) when only 10% of the surface is covered by silica nanoparticles with a nominal diameter of 10 nm. These results are attributed to the negative surface potential of silica nanoparticles. As a result when the nanoparticles precipitate on the copper surface and form surface 'nano-fins'—they preferentially prevent negatively charged ions (such as chlorine ions) from approaching the metal surface and thereby serve as an impediment from increasing the metal dissolution rate. This counter-intuitive behavior occurs even when the nanofins are formed randomly (i.e., without forming a uniform coating) and are sparsely dispersed on the copper substrate. This phenomenon of reduced corrosion is attributed to be another manifestation of the 'nano-Fin Effect (nFE)'.