Surface-Modified MoS<sub>2</sub> Nanoparticles as Tribological Additives in a Glycerol Solution
Xiaozhen Wang, Chencan Li, Kuiliang Gong, Xinhu Wu
Abstract
High Resolution Image Download MS PowerPoint Slide There is an urgent need to prepare high-performance tribological additives for water-based lubricants by a sustainable approach. Herein, we fabricated dextran-modified molybdenum sulfide nanoparticles (MoS 2 -dex NPs) by ball-milling in a nitrogen atmosphere. In addition to the exceptional water dispersion stability of MoS 2 -dex, substantial reductions in both the friction coefficient and wear were observed by adding MoS 2 -dex in a glycerol solution. Moreover, the tribological performance of a MoS 2 -dex and graphene oxide (GO) mixture outperformed that of individual MoS 2 -dex in a glycerol solution due to their synergy. The lubrication mechanism was investigated by a focused ion beam-aided cross-sectional scanning transmission electron microscopy/energy dispersive spectroscopy (FIB-STEM/EDS) and X-ray photoelectron spectroscopy (XPS). FIB-STEM/EDS results demonstrate that GO with a large surface area in a glycerol solution tends to enter frictional contact and fill the concaves on wear scars to generate a thick adsorbed film under the superficial top layer of the steel substrate. The top layer, mainly containing adsorbed MoS 2 -dex, is thinner but much dense and more compact than the bottom layer. In addition, XPS measurement indicates that a tribofilm containing MoS 2, GO, FeS 2, FeS, FeO, Fe 3 O 4, Fe 2 O 3, FeOOH, and FeSO 4 was also formed on the steel substrate. Both the adsorbed film and the tribofilm underpin the excellent friction reduction and antiwear (AW) performances of MoS 2 -dex and GO in a glycerol solution.