Graphite and Diamond

        Graphite and diamond are both stable forms of Carbon. Essentially, the difference

between the two lies in their bond structure (which changes the unit cell structure

obviously), and can be attributed to the temperature and pressure at which the lattice is

formed (Reynolds, 88). In this diagram we see the pure and intermediate forms of

the two structures and note that the two can independently and coexist under a large

range of conditions. In the transition from graphite to diamond, bonds in the graphite

lattice are broken and the lattice is compressed and reordered, resulting in strong bonds

in a tetrahedral formation involving bonding between sp³ orbitals (Reynolds, 1). The

following diagrams (Diamond, Graphite) are diamond and graphite stable structures.

        Usually in the manufacture of synthetic diamond, graphite is used under high

temperatures and pressures to form diamond. Relatively recent advancements have been

made in diamond thin film deposition as a way to coat with diamond, and use of

procedures involving basal cleaving and hot-filament assisted methods to convert a

graphite lattice to diamond under less strenuous circumstances (Dubray, 3136). Just as

diamond can be formed from graphite, films of graphite can be formed between

diamond-diamond surfaces.

        Previously, we discussed the effects of surface films in graphite. Diamond also has

surface films that give a diamond-diamond contact a very low coefficient of friction. By

the same methods mentioned before, the surface films can be removed in a heated

vacuum. Resulting coefficients of friction are of a much higher order, just as in the case of

graphite. If pressure is applied between the two diamonds and they are run against each

other, the interface path of contact can be observed to have a thin graphite film that has

evolved (Ubbelohde, 63).