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How does graphite’s crystal structure make it useful as a lubricant?

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A rough, translucent yellow crystal of elemental sulfur displayed against a solid black background. — crystal A crystal form of elemental sulfur. Sulfur has an atomic weight of about 32.06 atomic mass units (amu), which means that its molar mass is 32.06 grams.

Graphite’s effectiveness as a lubricant is a direct consequence of its unique crystal structure, which consists of parallel layers of carbon atoms arranged in fused hexagonal rings.1

Within each layer, the carbon atoms are held together by strong covalent bonds. However, the distance between these layers is relatively large, resulting in weak van der Waals interactions between them. Because the bonds between the layers are significantly weaker than those within the layers, the sheets can easily slide over one another. This ability of the layers to glide past each other provides the material with its characteristic softness and lubricity.12

It is important to note that graphite’s lubricating performance is also influenced by environmental factors; its low friction is largely dependent on the presence of adsorbed films, such as water vapor. In the absence of such vapors, graphite loses its lubricating properties and can become abrasive.2