how does graphite act as lubricant

When we hold a pencil in our hand, we can feel the black substance that lies within. It’s called graphite, and it’s the strongest natural substance known. It’s a form of carbon that comes in sheets and is held together by weak van der Waals forces, like those found on smooth glass surfaces.

Graphite is one of three allotropic forms of carbon; the other two are diamond and buckyballs (fullerenes). It is an opaque gray to black material that is soft but not elastic, and has a metallic luster. It is naturally occurring in metamorphic rocks and is mainly used for refractory materials, high-temperature lubricants, brushes for electrical motors, friction materials, and batteries and fuel cells.

how does graphite act as lubricant

In graphite, each carbon atom is bonded to 3 other carbon atoms in hexagonal rings. These sheets are held together by weak Van der Waals forces, the same forces that gecko feet use to climb smooth glass surfaces.

These forces make the layers of graphite slippery, and they can slide over each other. This makes graphite a good lubricant, and it is often mixed with a solvent to help lubricate tight spots where graphite can’t reach.

Several mechanisms have been proposed to explain the lubricity of graphite. A common explanation is that the flakes of graphite move around each other and create friction between them, causing frictional heat. An alternative theory is that water molecules adsorbed on top of the flakes form boundary lubrication films, passivating defects and protecting graphite from wear and corrosion.