Eliminate Friction with Graphite Lubricant

Published: 13 May 2003
High Tech Materials, By Aninditta Savitry
Graphite is known to be a good lubricant and therefore it is widely used in various practical applications. Material engineers have studied the material extensively and concluded that graphite's low-friction behavior is ascribed to the low resistance to shear between its neighboring atomic layers.
Martin Dienwiebel, a Dutch scientist, recently revealed a previously unknown effect in graphite. The discovery was made accidentally when he was testing a highly sensitive friction force microscope that he had developed. The microscope, called Tribolever, is a raster microscope that can measure frictional forces of just a few picoNewtons in three spatial dimensions.
Using the microscope, Dienwiebel measured atomic-scaled fiction as a function of the rotational angle between two contacting bodies. His experiment showed that the origin of the ultra-low friction of graphite lies in the incommensurability between rotated graphite layers.
Graphite consists of carbon atoms arranged in layers one above another. The carbon atoms in a graphite layers form a sort of undulating landscape, which is similar to an egg box. The different layers can slide over each other. However, the resistance can occur during the sliding process if the hills of one layer fit exactly into the valleys of another layer.
If the two layers are rotated with respect to each other, there are always points within the contact surface where the hills touch each other. As a result of this, the two layers cannot collapse into each other and the resistance is overcome. Dienwiebel called this phenomenon superlubrication. This effect probably explains why graphite is such a good lubricant.

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