Carbon

Carbon is the fourth most abundant element in the universe by mass after hydrogen, helium and oxygen.  It has an affinity for bonding with other small atoms including other carbon atoms and is capable of forming multiple stable covalent bonds with such atoms.  Carbon is known to form almost ten million different compounds and is the chemical basis of all known life.

On earth the amount of carbon is affectively constant and through a process referred to as “the carbon cycle” it is constantly being transformed from one ‘state’ to another.

There are several different forms of pure carbon.  However, the most well known ones are Diamond and Graphite.  Under very high pressure, Carbon crystallizes in the cubic system to form diamond.  Diamond is clear and transparent and is the hardest known mineral.  It is also a good abrasive and an excellent electrical insulator and thermal conductor.  At more ‘normal’ pressures, carbon crystallizes in the hexagonal system to form Graphite.  Unlike Diamond, Graphite is a black and opaque material.  Graphite is very soft, a good lubricant and a good conductor of electricity.  Graphite is also a good thermal insulator.  The reason for the huge difference in properties between the two forms of carbon is due to the difference in the bonding of carbon atoms in diamond and graphite.

Other forms of carbon include amorphous carbon which is completely isotropic and carbon nanotubes, which are among the most anisotropic materials ever produced.

Carbon fiber is made by the pyrolysis of synthetic polyacrylonitrile and other organic substances.  These fibers have a structure resembling narrow filaments of graphite.  Through thermal processing the structure is re-ordered into a continuous sheet.  The resultant fiber sheets have a higher specific tensile strength than steel.  The crystal alignment gives carbon fiber a high strength to weight ratio.  Carbon fiber also has a low thermal expansion.  These properties has lead to extensive use of carbon fiber in aerospace, civil engineering, military, motor sports and other competitive sports such as cycling.

Graphite is used in a wide range of applications ranging from being used as a lubricant, a pigment, as electrodes for dry batteries, in electroplating and electroforming and as a neutron moderator in nuclear reactors, amongst other things.