Tribological characterization of graphene oxide by laser ablation as a grease additive

In this work, the structural and tribological behavior of graphene oxide samples as a grease addi-tive was studied. By Nd:YAG laser ablation system and using graphite target at two laser energy of 0.3 W and 0.6 W, graphene oxide (GO) samples were successfully prepared. GO samples were characterized using Raman spectroscopy, field emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FTIR) and energy dispersive X-ray spectroscopy (EDAX). Also, tribological behaviors of the lubricating grease, with and without the graphene oxide in grease, by the pin-on disc tribometer were determined. The Raman spectroscopy measurements showed D and G bound, which confirmed the successful synthesis of the graphene oxide sample and also the I-D/I-G, decreased by increasing laser power due to decreasing disorder in graphene oxide structure. FESEM images show that by ablating carbon atoms from graphite target in water, particles assemble to form a GO micro-cluster due to thermodynamically agglomeration with average size of about 3-4 mu m, which the size of them depends on the laser pulse energy. Based on FTIR and EDAX analysis, GO sample which prepared at lower laser energy possessed the highest content of oxygen and oxygen functional groups. In addition, the results of tribological behavior showed that the friction-reducing ability and antiwear property of the grease can be improved effectively with the addition of GO. However, it is revealed that the small size GO has a better lubricating performance and therefore cluster size appears to play a role in the degree of wear protection due to its impact on the physical and chemical properties. The results of this study indicate that the GO sample prepared at lower laser energy (0.3 W) has a smaller size and the higher the oxygen content therefore provide better friction-reducing and anti-wear effect. Also, additive of graphene oxide in lubricating grease decreases coefficient of friction as well as wear. Based on our results, the application of GO as an additive in grease leads to increased performance of the lubricated kinematic machine.