Tribological performance of silicon nitride and carbon black Ionanofluids based on 1-ethyl-3-methylimidazolium methanesulfonate

Abstract

Development of nano-lubricants by the dispersion of nano-particles in current lubricants has contributed to improving energy efficiency reducing wear and friction. During the last two decades, ionic liquids have evolved as novel lubricants or lubricant additives, especially for high vacuum and high temperature. Nevertheless, the number of experimental studies regarding the tribological properties of Ionanofluids, defined as dispersions of nano-particles in ionic liquids, is limited. 1-Ethyl-3-methylimidazolium methanesulfonate, [EMIM][MS], is a promising candidate for lubrication applications due to its wide liquid range, high thermal conductivity, low friction coefficients and low compressibility in comparison with commercial mineral and synthetic hydrocarbon based lubricants. In this work, Ionanofluid lubricants based on dispersions of nano-additives (silicon nitride and carbon black) at mass concentration between 0.10 and 1.0 wt% in [EMIM][MS] were designed. The nearly spherical morphology of the nano-additives, silicon nitride and carbon black, was described by using scanning electron microscopy. The stabilities of the resulting nano-particle dispersions in the ionic liquid were analyzed by dynamic light scattering measurements of size for one month. Tribological characterization was performed by a rotational rheometer coupled with a tribology cell with ball-on-three-pins configuration (100Cr6 steel) in sliding conditions at 298.15 and 353.15 K. Afterwards, the wear track morphology of the worn pins was analyzed by a 3D optical profiler and Raman spectroscopy. The dispersions at the optimal nano-additive concentrations for lubrication reached friction coefficient decreases of up to 16% and wear tracks with a volume 28 times lower. Additionally, the density and dynamic viscosity of [EMIM][MS] and the optimal Ionanofluids for lubrication applications measured with a rotational Stabinger visco-densimeter in the 278.15 to 373.15 K temperature range showed small increases with almost no dependence on temperature.