A comparative study between graphene oxide and diamond nanoparticles as water-based lubricating additives

The tribological properties of graphene oxide (GO) nanosheets and modified diamond (MD) nanoparticles with excellent water-solubility were investigated. GO nanosheets were synthesized using carbon fibers with a regular and uniform size, the lateral size being around 30 nm and the thickness being 2 or 3 nm, while MD nanoparticles were about 30 nm in the three dimensions. The friction properties of ceramics were improved by GO nanosheets or MD nanoparticles used as additives in water-based lubrication, though the effects of two nanoparticles were quite different. For GO nanosheets, the friction coefficient at the beginning decreased sharply from 0.6 to 0.1, as compared with the dionized water lubrication. At the same time, the running-in period was shortened from 2000 s to 250 s. A steady state characterized by ultralow friction (friction coefficient=0.01) was obtained after the running-in period. In the case of MD nanoparticles, the friction coefficient stayed at 0.1 without further decrease during the whole experiment. Based on the observation of wear scar and characterization of remains on the wear track, the positive effect of GO nanosheets was attributed to their lamellar structure and geometric size. MD nanoparticles reduced friction by forming the regularly grained surface on the mating surfaces, and prevented further reduction in steady-state friction coefficient owing to their larger size and hardness. In conclusion, GO nanosheets exhibited favorable potential as an effective additive for water-based lubrication.