Preparation And Tribological Properties Of Controllable Li-intercalated Molybdenum Disulfide

The controllable intercalated molybdenum disulfide (MoS₂) compounds were prepared by intercalating MoS₂ with lithium in a solution of n-butyl lithium in hexane.The effects of reaction temperature, mass ratio of the reactants, reaction times and mixing means were studied. The x value in the Li-intercalted MoS₂ (Li_xMoS₂) increased when the reacting time, temperature and molar ratio of reactants (n-butyl lithium:MoS₂) increased, and finally reached a relative stable level.The as prepared intercalated MoS₂ were characterized by means of powder X-ray diffraction (XRD). It was shown that the intensities of the diffraction peaks of the synthesized powders were smaller and the diffraction peaks became broaden when the x value increased, especially in case of bigger than 1.0. The suspension of MoS₂ could be obtained using different exfoliation solvents, like hydrochloric acid, LiOH solution, distilled water and ethanol. It was found that the exfoliated suspensions were more stable in both LiOH solution and ethanol. Using XRD and scanning electron microscopy (SEM) and transmission electron microscope (TEM), it was found that the diffraction peaks of the restacked MoS₂ became broader, compared with MoS₂. At the same time, the morphology of MoS₂ exfoliated looked loose, and had bigger spaces between layers.The effect of variation of x in Li_xMoS₂ on the stablility and lubricity of the aqueous suspension of Li_xMoS₂ exfolied was studied, it was found its stability increased with x increased, however, when the x was over 1.3, the stability of suspension became weak. When the 0.5 wt% MoS₂ stacked was suspensed in water, both friction reduction and wear scar diameter decreased initially with x, and then became increased according to the results from four-ball test. The reason may be attributed to the weak lubricity of water.The lubrication of the MoS₂ restacked under different conditions weres also examined by MQ-800 four-ball tribometer as additive in liquid paraffin (LP). The MoS₂ restacked from Li_xMoS₂, in which x was about 1.0, under acid conditions could not improve the tribological performance. The MoS₂ restacked from Li_xMoS₂, in which x was about 1.0, under the alkalescence condition could increase the abilities of antiwear and friction reduction. The best tribological performances were shown when the MoS₂ restacked was added at a concentration of 0.5 wt%. The improvement of the tribological performance was mainly ascribed to the formation of complex films of MoO₃, FeS and FeSO₄ on the rubbed surface via SEM and X-ray photoelectron Spectroscopy (XPS).