Graphite in brake pads and other friction materials

Description

Graphite in brake pads and other friction materials

These properties result from the characteristic crystal structure of graphite.

Graphite has a layered crystal structure; within each layer (X direction) the carbon atoms are held together by strong covalent bonding.

On the other hand, atoms in different layers (Y direction) are held together by weak van der Waals forces.

Because of this crystal structure, the electrical resistance within each layer (X direction) of graphite is close to that of metals, while the bonding force between layers (Y direction) is very weak. Thanks to this property, graphite layers separate easily under external force, resulting in a low coefficient of friction.

In our everyday life, graphite is found inside pencils: writing is possible because graphite layers separate and adhere to the paper; because each graphite layer separates without much friction, the paper does not tear.

Carbon brushes must be built from materials that can receive and deliver large amounts of electric current to and from objects rotating (moving) at high speed using low friction force, and that can withstand heating and oxidation. Graphite, whose material properties are ideally matched to such requirements, is the natural choice for carbon brushes.

Graphite production involves the thermal decomposition of organic substances under airtight conditions to obtain a substance with a high carbon content. This process is called carbonization, and the resulting substance is called char. The substance is then further processed by subjecting it to high temperatures (above 2500 degrees Celsius), also under airtight conditions, to develop the crystal structure; the result of this process, called graphitization, is graphite. Graphite obtained artificially this way is called synthetic graphite, while graphite formed naturally is called natural graphite.

There are many different substances composed of the carbon element; it is a special element that forms an important part of all organic matter and plays an essential role in life on Earth. Because of these special properties, carbon is often referred to as the “black art”. News of the carbon nanotube, along with other carbon-related discoveries in recent years, has confirmed the almost magical power of this very special element.