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

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.