Preparation and Modification of Graphite-based and Coal-based Graphene and its Tribological Properties in Lubricants

Abstract

Graphite-based graphene oxide (GO) and coal-based graphene oxide (GO/SiO2, which we call graphene oxide/SiO2 because the surface of the resulting coal-based GO is linked with SiO2 from the coal structure) were prepared by the conventional Hummers oxidation method and ultrasound-assisted Hummers oxidation method, respectively, using natural graphite powder and Xinjiang Wucaiwan coal as carbon sources. Furthermore, the structures of the two were studied comparatively. Afterwards, the two lamellar structure products were hydrophilically modified with octadecylamine and dicyclohexylcarbodiimide by a hydrothermal method. And then, added these products (graphite-based GO-ODA and coal-based GO/SiO2-ODA) to No.32 cycloalkyl base oils in order to comparatively investigated their tribological properties as lubricant additives. The results showed that the dispersion stability of coal-based GO/SiO2 in the lubricant was significantly better than that of graphite-based GO; meanwhile, the tribological performance of GO/SiO2-ODA in the lubricant better than that of graphite-based GO-ODA due to the surface linkage of coal-based GO/SiO2 with SiO2 particles. After 1 h - long grinding in a four-ball friction test, the lubricant friction coefficient of 0.03 wt% coal-based GO/SiO2-ODA oil reached a minimum of 0.118, which reduced 58.1% compared to pure base oil and reduced 2.8 times compared to the counterpart using graphite-based GO-ODA under the same experimental conditions.