Tribological characterization and rheology of hybrid calcium grease with graphene nanosheets and multi-walled carbon nanotubes as additives

Recently used nanoparticle additives are proposed to improve lubricant performance under different conditions because of their unique properties. The key objective of this exploration is to study the possibility to employ multi-walled carbon nanotubes (MWCNT) and graphene nanosheets (GNS) as additives for lubricants. Calcium grease (CG), without chemical modification, was selected for the study as the base. Hybrid calcium nano grease (HCNG) with different percentages of MWCNT/GNS (0.5, 1, 2, and 3 wt. %) in a ratio of 1:1 were prepared and their rheological and tribological properties were investigated. The microstructures of the prepared nano grease and nano additives were characterized using state-of-the-art equipment. The results showed that by adding MWCNT/GNS the CG exhibited a considerable reduction in friction and wear. As the nano additives were increased, the tribological performance and the rheological properties improved. A consistent NG was obtained with 2 wt.% additives. The shear stress, viscosity, and dropping point temperature increased with the amount of nano additives, while there was no effect on the work penetration. The COF and WSD exhibited a remarkable reduction, while the thermal conductivity exhibited almost linear improvement with the addition of nano additives.