Graphite is valued for its good conductivity of heat and electricity and high refractoriness. The utility of graphite is dependent largely upon its type. The flake type carbon graphite is found to possess extremely low resistivity to electrical conductance. The electrical resistivity decreases with the increase of flaky particles.
The bulk density decreases progressively as the particles become more and more flaky. Because of this property in flake graphite, it finds a large use in the manufacture of carbon electrodes, plates and brushes required in the electrical industry and dry cell batteries. In the manufacture of plates and brushes, flake graphite has been substituted to some extent by synthetic, amorphous, crystalline graphite and acetylene black. Graphite electrodes serve to give conductivity to the mass of manganese dioxide used in dry batteries.
Graphite is a soft grayish-black greasy substance. Graphite is also known as black lead. It is also crystallized carbon. The carbon atoms of flexible graphite form a crystal pattern that differs from that of the carbon atoms in diamond. In graphite, the carbon atoms are arranged in flat planes of hexagonal rings stacked on one another.
Each carbon atom is attached to three others on the same plane. Thus, only three out of four valence electrons are used in carbon-carbon bonding. The fourth valence electron remains loosely between the planes. This free electron accounts for the electrical conductivity of graphite. The lack of carbon-carbon bonding between adjacent planes enables them to slide over each other making graphite soft, slippery and useful as a lubricant.
The major use of graphite is in making lead pencils of different hardness, by mixing it with different proportions of clay. The weakly held layers of carbon atoms in expandable graphite easily slide over each other and are left behind on paper as black marks. Due to its slippery nature, graphite is used as a dry lubricant in machine parts. Being resistant to chemicals and having a high melting point and also because it is a good conductor of heat, graphite is used to make crucibles. The presence of free electrons makes graphite a good conductor of electricity and it is used to make electrodes. Graphite has the ability to absorb fast-moving neutrons, and it is used in nuclear reactors to control the speed of the nuclear fission reaction.