CaCO 3 nanoparticles with an average size of 45 nm were synthesized via the carbonation method. The tribological properties of the CaCO 3 nanoparticles as an additive in lithium grease were evaluated with a four-ball tester. The results show that these CaCO 3 nanoparticles exhibit good performance in anti-wear and friction-reduction, load-carrying capacity, and extreme pressure properties. The action mechanism was estimated through analysis of the worn surface with X-ray photoelectron spectroscopy (XPS) and scanning electron microscope (SEM). The results indicate that a boundary film mainly composed of CaCO 3 , CaO, iron oxide, and other organic compounds was formed on the worn surface during the friction process.

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The tribological behaviors of hydroquinone bis(diphenyl phosphate) (HDP) and tricresyl phosphate (TCP) for polyalkylene glycol (PAG) were evaluated at 200 °C. Results showed that HDP could effectively reduce the friction coefficient and prevent wear of sliding pairs during the test. The best tribological properties of HDP achieves at the concentration of 4 wt %. At this level, the wear volume of the lower disk can be reduced by a factor of 2.4 and the load-carrying capacity can increase from 500 N to 930 N, with respect to pure PAG. Furthermore, HDP exhibited better antiwear (AW) and extreme pressure (EP) properties than TCP, despite the fact that their friction-reducing performances were similar. Boundary lubrication films composed of FeOOH, Fe 2 O 3 , FePO 4 , and polyether compounds were formed on the worn surface, which resulted in excellent friction reduction and AW performance.

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.

Nano-calcium borate (NCB) with an average particle size of about 70 nm was synthesised via ethanol supercritical fluid drying technique, and the morphology and microstructures of as-prepared particles were characterised by means of scanning electron microscope (SEM, JEOL LTD., Tokyo, Japan) and X-ray powder diffraction. The friction and wear behaviour of the NCB as additive in lithium grease were evaluated with an Optimol-SRV IV (Optimol Instruments Prüftechnik GmbH, Munich, Germany) oscillating friction and wear tester (SRV tester). The morphology and surface composition of the worn surfaces of lower discs after SRV test were analysed by SEM and X-ray photoelectron spectroscopy (XPS, Physical Electronics, Inc., USA). The result demonstrated that the anti-wear and load-carrying capacities of the lithium grease were significantly improved, and the friction coefficient of the lithium grease decreased with the addition of NCB additive. The analytical results of XPS indicate that the good tribological performance of NCB is attributable to the formation of a boundary lubrication film composed of deposited NCB and the tribochemical reaction products such as B 2 O 3 , CaO and iron oxides on the rubbing surface. P m : mean contact pressure. P o : maximum contact pressure, with P o being 1.5 times P m . 45 NANO-CALCIUM BORATE AS GREASE ADDITIVE Figure 4. Wear scar width as a function of additive concentration. SRV tester; load, 200 N; frequency, 20 Hz; stroke, 1 mm; duration, 10 min; room temperature. 48 G. ZHAO ET AL.

Red phosphorus (P) was covalently attached to graphene nanosheets (Gr) using high-energy ball-milling under a nitrogen atmosphere.

Nanosized MoS2 on graphene was firstly investigated in the lubrication field and exhibited excellent tribological performance in perfluoroalkylpolyether under high vacuum.

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