MoS₂/WS₂ Quantum Dots as High‐Performance Lubricant Additive in Polyalkylene Glycol for Steel/Steel Contact at Elevated Temperature

Abstract

Herein, molybdenum disulfide (MoS2) and tungsten disulfide (WS2) quantum dots (QDs) are prepared by a facile and green technique, and characterized by microscopy and spectroscopy. The resulting products display exceptional stability in polyalkylene glycol (PAG) base oil, and are used for the first time as friction reducing and antiwear additives in PAG for steel/steel contact. Tribological measurements indicate that the stable dispersion consisting of PAG mixed with MoS2/WS2 QDs exhibits significant tribological properties compared with pure PAG and PAG containing MoS2/WS2 QDs nanosheets under different loads at elevated temperatures. The excellent tribological behaviors of MoS2/WS2 QDs are attributed to the formation of a boundary lubrication film, which can be generated not only by the physical entrapment of MoS2/WS2 QDs at the ball‐disk contact surfaces, but also by tribochemical reaction between MoS2/WS2 and the iron atoms/iron oxide species.

Investigation on tribological behaviors of MoS2 and WS2 quantum dots as lubricant additives in ionic liquids under severe conditions

“…5(a), the addition of MoS 2 and WS 2 QDs has no effect on the friction reduction and AW behaviors of the IL at a temperature below 50 °C , whereas the two NPs can significantly reduce the friction coefficients and wear volumes of the base oil when the temperature increases from 100 to 250 °C . This conclusion is in accordance with the result of addition of MoS 2 and WS 2 QDs to PAG base oil at different temperatures [22], and the possible mechanism for the lubrication action has been reported previously. In brief, high temperature plays an active role in the viscosity of nanofluids, the free movement of NPs in ILs, and the tribochemical reaction of the lubricant during friction and wear processes, which benefits the formation of a boundary protective film.…”

“…The Mo 3d XPS spectrum ( Fig. 2(a)) collected for the MoS 2 QDs contained peaks at 227.0 eV, 229.6 eV, and 232.8 eV, assigned to the 2s electrons of S 2− , Mo 4+ 3d5/2, and Mo 4+ 3d3/2, respectively [22]. The S 2p signal in the XPS spectrum ( Fig.…”

“…8(b) and 8(c)), corresponding to FePO 4 and FeF 2 [28], respectively. The signals of S 2p of the worn scars lubricated by the dispersions of the IL with 1% MoS 2 and WS 2 QDs are located at 168.6 eV, which are assigned to FeSO 4 [22,28]. The XPS spectra of Mo 3d shown in Fig.…”

“…The XPS spectra of Fe 2p ( Fig. 8(a)) can be deconvoluted into six peaks corresponding to FeS 2 (708.9 eV), FeO (709.7 eV), Fe 3 O 4 (710.7 eV), FeOOH (711.8 eV), FePO 4 (712.8 eV), and FeSO 4 (713.6 eV) [22,28], and the Fe 2p signals of the worn surfaces lubricated with the neat IL (a) and the IL additized with 1% MoS 2 QDs (b) and 1% WS 2 QDs (c) are similar to each other at 500 N and 150 °C , which might be attributed to the similar tribochemical reactions of the IL with the steel/steel contact surfaces. Similarly, the peaks of P 2p and F 1s of the worn surfaces under lubrication of the three types of lubricants appear at 133.7 eV and 684.9 eV ( Figs.…”

“…MoS 2 with different morphologies and sizes was fabricated and could be dispersed in different oils for a few weeks [19][20][21]. In particular, MoS 2 and WS 2 quantum dots (QDs, with particle size less than 10 nm) can form a homogeneous and stable dispersion in polyalkylene glycol (PAG) base oil, and can significantly enhance the friction-reducing and AW properties of neat PAG base oil at elevated temperatures [22]. Notably, the small size effect, high surface effect, and quantum size effect of MoS 2 and WS 2 QDs might play an important role in the formation of a stable dispersion of PAG base oil additized with solid NPs.…”