Synthesis of Ultrathin WS2 Nanosheets and Their Tribological Properties as Lubricant Additives

In this paper, ultrathin WS 2 nanosheets with thickness of about 5 nm were successfully prepared by a facile solid phase reaction method. The as-synthesized samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). On the basis of experimental results obtained under different reaction durations, a possible formation mechanism of WS 2 nanosheets is proposed. The tribological performance of ultrathin WS 2 nanosheets as additives in the 500SN base oil was tested by an UMT-2 ball-on-disc tribotester, and the worn surface of the steel disc was investigated by a non-contact optical profile testing instrument and SEM. The results showed that the friction coefficient and anti-wear property of base oil can be improved strikingly by adding ultrathin WS 2 nanosheets. Especially, when the concentration of WS 2 nanosheets was 1.0 wt.%, the corresponding lubricating oil exhibited the best tribological properties. Moreover, according to the investigation of the wear scar, an anti-friction and anti-wear mechanism is proposed. It is believed that the reduction of friction and wear must come from the addition of ultrathin WS 2 nanosheets which can penetrate and enter the friction interface and form a continuous tribofilm on the rubbing face.