Tribological properties of polyalphaolefin oil modified with nanocarbon additives

Abstract

Enhancing the tribological properties and performance of lubricants with nanoparticle additives is an active area of research. Results of block-on-ring experiments examining tribological properties of polyalphaolefin (PAO) oil containing small amount of nanocarbon additives are reported in this study. Comparative analysis of coefficient of friction (COF) and wear was performed for PAO oil containing nanodiamond particles, onion-like carbon (OLC), single/multiwall carbon nanotubes (SWNT/MWNT) or nanographene platelets (NGPs). The performance of PAO oil samples containing nanodiamond additives was considerably different from those containing sp2 nanocarbon additives. The presence of sp2 nanocarbons reduced the COF of PAO by ~8–12 times. This effect on the COF was accompanied by a reduction in wear with the addition of carbon nanotubes and NGP; however, the wear was slightly increased in the presence of OLC. The presence of nanodiamond reduced the COF by ~70×, and the wear was significantly increased. The performance of nanocarbon particles in PAO in combination with molybdenum dialkyldithiophosphate (MoDDP) was also investigated. The combination of polishing capability of nanodiamonds with the protective action of MoDDP resulted in the reduction of both wear and COF as compared to pure PAO. In contrast, the combination of sp2 nanocarbons with MoDDP caused degradation of the PAO lubrication performance.