ABSTRACT
Carbon, the sixth element in the atomic series, is the 19th most abundant on the surface of the earth. It has four valence electrons, all of which can enter into o-type or covalent bonds. The valence electrons of carbon can also form less energetic n-type or resonant bonds. This arrangement of valence electrons gives carbon the ability to form compounds with many other elements. Elemental carbon exists in two crystalline forms at room temperature, diamond and graphite. The key to the value of carbon as a self-lubricating solid lies in its laminar crystal structure, its ability to form strong chemical bonds with gases such as water vapor, and the fact that adsorbed gas weakens the interlayer bonding forces. Additives are widely used in manufactured carbon parts such as seals and bearings destined for use in applications where adsorbable gases may be in short supply. In most engineering applications the carbon part rubs against a smooth metal surface.
