Graphite is the mineral form of carbon. Veins of graphite occur in limestone due the presence of organic materials. Graphite is a soft mineral and occurs in either lump or flake form. Graphite is the only non-metal element that is a good conductor of electricity. Crystal structures rarely occur and easily break down. This is the reason for the material’s greasy feeling despite being a dry lubricant.
When a crystal structure occurs in graphite, it is a rough six-sided crystal that easily breaks down into flakes. This process is known as basal cleavage. These flakes readily slide across each other. This is the cause of the greasy characteristic of graphite and results in its application as a lubricant. Since the material is a solid, graphite is considered a dry lubricant.
Both graphite and diamonds are carbon-based. Graphite is an excellent lubricant. Diamonds are the hardest abrasive. Diamonds are a good insulator of electricity. Graphite is a good conductor. Graphite is a stable form of carbon. Diamonds near the surface of the Earth are undergoing the change to graphite; however, the process is slow.
Graphite and diamonds both have strong bonds between the atoms of carbon. The difference lies in the structure of the atoms. In diamonds, the atoms are arranged in a three-dimensional structure. This results in stronger bonds above and below. Graphite atoms are in two-dimensional sheets with weak bonding above and below.
Graphite needs water vapor to lubricate. The bonding energy between the water and the graphite is lower than between the graphite and the surface to be lubricated. This means that graphite functions best in a regular atmosphere. Graphite is not suitable for lubrication in a vacuum.
Natural graphite is mined. Ore quality and processing will determine the grade of the graphite. High-grade natural graphite contains levels of carbon between 96 percent and 98 percent. The higher carbon content and high crystallization will increase the lubricating quality and resistance to chemically bond through oxidation. Synthetic graphite can be created with similar carbon levels to high-grade natural graphite. Where there are lower requirements for lubrication, amorphous graphite with 80 percent carbon content can be used.
High Temperature Applications
Graphite can be used in continuous temperatures of 450 degrees Celsius. Graphite can withstand even higher temperature peaks. Graphite conducts little heat itself and will provide some thermal insulation.
While graphite is a soft material and an excellent lubricant, it can be rolled into fibers. These fibers can be twisted into threads and held in place with a binder such as epoxy resin. This is the method of creating composites for uses in such items as airplanes, automobiles and golf clubs.