SECTOR FOCUS: GREASES Fighting friction with

new material science The potential of graphene as a grease additive Chris Johnson, Managing Director, EZO Bearings; supplier SMB Bearings

In a study on the potential of graphene as a new emerging lubricant1

, researchers estimated that the

reduced loss of energy to friction offered by new materials would yield potential energy savings of 2.46 billion kilowatt-hours per year, equivalent to 1.5 million barrels of oil.

Friction’s most basic definition is the force that prevents smooth and easy movement of two moving surfaces in contact with each other. If not reduced or controlled effectively, a high level of friction often leads to higher wear and ultimately, poor reliability and equipment failure. Friction is a complicated problem for engineers — bearing friction is not constant and is addressed using certain tribological phenomena that occur in the lubricant film between the rolling elements, raceways and cages.

Whether a design engineer opts for a dry, silicon or mineral lubricant, an oil or grease, the aim will be to expertly match the lubricant to the application requirements to reduce friction between the internal surfaces of the bearing’s components by reducing or preventing metal-to-metal contact between rolling elements and raceways. While this is a good way of reducing wear and preventing corrosion, there are new materials that, when used on bearings, dramatically reduce friction compared to the lubrication and surface treatment options that are currently on the market.

On the macroscale, friction is the result of microscopic imperfections in surfaces. On the

1 article/pii/S1369702113004574

atomic scale, however, friction concerns the attractive forces between individual atoms. This opens up the phenomenon of super lubricity; where the atomic scale structural mismatch makes it impossible for multiple atoms in one surface to get close to atoms in the other, leading to extraordinarily low friction.

Since super lubricity was first proposed in 1990, several groups have observed the effect, but it has been difficult to scale because of the inconsistency between macroscopic surfaces. That is, until now.

Graphene as a grease additive

Graphene and its tribological potential as a lubricant remains relatively unexplored. Several studies have sought to investigate the sliding properties of graphene based dry lubricant, however few studies have explored the application of graphene as an oil or grease additive in rolling contacts.

Graphite was first used as an additive in early investigations due to its layered lattice-like properties. A 2014 study investigating multilayer graphene as a lubricating additive in bentone grease2

the solid graphene additive was well dispersed in the grease, therefore provided a lower friction coefficient and less wear compared to graphite and ionic liquids.

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