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The purpose of this paper is to investigate the tribological properties of MoS₂ nano‐sized hollow spheres in liquid paraffin (LP) and the corresponding action mechanism. Morever, its feasibity of industrial application as an oil additive in the industrial lubrication field is also explored.

The tribological properties of MoS₂ nano‐sized hollow spheres (NH‐MoS₂) modified by Cyanex 301(di‐(2,4,4‐trimethylpentyl) dithiophosphinic acid) with size of 200 ∼ 300 nm in LP are studied and compared with those of the commercial colloidal MoS₂ (CC‐MoS₂) on a four‐ball tester and an Optimol SRV Oscillating friction and wear tester in a ball‐on disk configuration. The worn surfaces of the lower flat disc are examined with a scanning electron microscopy and an X‐ray photoelectron spectroscopy, respectively.

Results show that NH‐MoS₂ is a better extreme‐pressure additive and anti‐wear (AW) and friction‐reducing additive in LP than CC‐MoS₂. Under the optimum concentration of 0.5 per cent for both NH‐MoS₂ and CC‐MoS₂ and the load of 400 N, the friction coefficient of NH‐MoS₂ + LP and CC‐MoS₂ + LP decreases about 43.8 and 6.3 per cent, and the wear volume loss decreases about 60.3 and 12.0 per cent compared with the pure LP. The boundary lubrication mechanism for NH‐MoS₂ + LP can be deduced as the effective chemical adsorption protective film formed by the long chain alkyls R and active elements (S and P) in the modification layer and tribochemical reaction film containing the tribochemical products of the additive. Moreover, sliding and rolling frictions co‐exist in NH‐MoS₂ + LP, doing contributions to the good tribological properties as well.

In this paper, the Cyanex 301‐modified MoS₂ nano‐sized hollow spheres with diameter of 200 ∼ 300 nm are firstly added into LP to investigate its tribological properties. The excellent AW and friction‐reducing properties indicate that this MoS₂ hollow spheres product is a good oil additive, and the fundamental data presented here will be useful for its further industrial application in the future.