Achieving ultra-low friction in commercial oils by serpentine modification of sliding surfaces

摘要

The growing concerns over energy and environmental security lead to increase in global demand for energy efficiency and reduced emission in transportation systems. Nanoadditives are proven to have a positive impact on a lifespan of moving mechanical components used in transportation and other industrial systems. Certain carbonaceous materials, such as carbon nano-onions, nano-tubes, and graphitic particles, offer improved tribological properties when used on sliding tribological surfaces. Likewise, a serpentinite (a cheap, safe and abundant mineral) whose main constituent is 1:1 stratified magnesium hydrosilicate has also been proven to offer dramatic friction reduction and anti-wear properties when used as a lubricant additive due to formation of tribofilms. We envision that serpentinites can be a cost-efficient component of lubricating formulations that dramatically improves energy efficiency when used systemwide, especially in already deployed systems as a drop-in replacement. In this paper, we report ultra-low friction behavior of tribofilms formed in-situ from commercial oils, including fully formulated gear and hydraulic oils, blended with serpentine powders which facilitate frictional transition from boundary lubrication to a mixed or hydrodynamic lubrication regime. Experimental studies were performed using a block-on-ring test machine on three oil carriers including 46 hydraulic oils (HO), fully formulated mineral gear oil (FFMGO) and fully formulated synthetic gear oil (FFSGO). The material of the block and the ring was 12Cr. Natural Serpentine with, set of catalysts and surfactants, was added to these oils at optimized concentrations to promote mixed or hydrodynamic like frictional behavior under conditions that typically result in boundary-like frictional behavior. The results (Figure 1), show that with the use of a serpentinite, the coefficient of friction (COF) declined in all oils, but the magnitude of reduction and the time needed to trigger a step-like transition from high to low friction were different. Under the maximum contact pressure of 0.33GPa and a speed of 0.83m/s, the COF of 12Cr stainless steel block and 12Cr stainless steel ring lubricated with HO declined gradually from 0.12 to 0.01 after 280 minutes and for FFMGO the COF declined from 0.11 to 0.02 in 360 minutes. For FFSGO the COF declined from 0.07 to 0.055. Both curves 3 and 5 show that without a serpentine the friction coefficient didn't decline as dramatically. From the width of the wear scars shown in Figure 2a we can observe that serpentinite reduced the block wear compared with Figure 2b that obtained without the powder.