Graphene Layers on Steel Surfaces Found to be Perfect Lubricant, Superior to Oil
Scientists discovered that one-atom-thick graphene layers work very well as lubricants on sliding steel surfaces, enabling a dramatic reduction in the amount of wear and friction over solutions like oil-based lubricants.
New studies led by Argonne materials scientists Anirudha Sumant and Ali Erdemir attributed the very low coefficient of friction (COF) to the low shear and highly protective nature of graphene, which also prevented oxidation of the steel surfaces when present at sliding contact interfaces.
The findings could have huge practical benefits, saving enormous amounts of costs and energy, since steel ball bearings alone form an integral part of most moving mechanical machines of today's vast technical infrastructure, ranging from computer fans over cars to giant wind turbines.
The researchers write their estimate is that the reduced loss of energy to friction offered by new materials could yield potential energy savings of 2.46 billion kilowatt-hours per year, equivalent to 420,000 barrels of oil.
Current lubricants reduce friction and wear either through the use of environmentally unfriendly additives, or in some cases, solid lubricants such as molybdenum disulfide or boric acid. The oil-based lubricants need to be consistently reapplied, producing additional waste. The cost of applying solid lubricant coatings is rather high and due to finite thickness, they do not last very long and must also be expensively reapplied.
On the other hand, coatings made of graphene flakes are not harmful to the environment and can last a considerable length of time due to the flakes' ability to reorient themselves during initial wear cycles, providing a low COF during sliding.
"Applying or reapplying the graphene coating does not require any additional processing steps other than just sprinkling a small amount of solution on the surface of interest, making this process simple, cost-effective, and environmentally friendly," said Diana Berman, a postdoctoral researcher at Argonne's Center for Nanoscale Materials (CNM).
"It is interesting to see how a one-atom-thick material affects the properties at a larger scale," Sumant said. "I believe that graphene has potential as a solid lubricant in the automotive industry and, once fully developed, it could have positive impacts on many mechanical applications that could lead to a tremendous savings of energy."
The team published their findings in two consecutive papers in the high impact journal Carbon:
D. Berman, A. Erdemir, A.V. Sumant: "Few layer graphene to reduce wear and friction on sliding steel surfaces". Carbon, 54, 454-459 (2013)