Combination of nano-particles of graphite and PTFE in the right amount for synergism as anti-wear and extreme pressure additive in oil

Abstract

Solid lubricants (SLs) are known to enhance the tribo-performance of oils significantly. Polytetrafluoroethylene (PTFE) particles have proved as an excellent extreme-pressure additive (EPA) but not as so good anti-wear additive (AWA). In contrast, the graphite nano-particles (NPs) are known as very good AWA but not so promising EPA. In this context, graphite and PTFE particles with different shapes (graphite-laminar and PTFE- spherical) and sizes (graphite- 60–120 nm and PTFE- 11–13 μm) were used in combination in different amounts for exploring possible synergism as AWA and EPA. A series of oils based on Group III (Gr III) with polyisobutylene succinimide (PIBSI) dispersant (1 wt%) along with an increasing amount of graphite NPs (0%–4%) and a simultaneous decrease in PTFE NPs (4%–0%) was prepared. The tribo-performance of oils was evaluated on Four ball tester for EP (weld-load) and anti-wear performance. Formulations were characterized for density, viscosity, and viscosity index. Also, the stability of oils was monitored through visual observation, and it was more than two months. Combo-oils showed improvement in anti-wear (AW) performance up to 54% for the concentration of 2 wt% each. For AW, synergism was observed, while for extreme pressure (EP) property, PTFE particles in isolation proved best, showing almost 350% improvement for group III oil. The inclusion of graphite particles step by step deteriorated the performance. The SEM (Scanning electron microscopy) and EDAX (Energy-dispersive X-ray) were used to analyze worn surfaces of ball and film formation mechanism.