High pressure study of graphitization of diamond crystals

Graphitization of {100} and {111} faces of diamond crystals at pressures of 0.1 and 2 GPa and various temperatures was studied by Raman spectroscopy, x-ray single crystal diffractometry, and scanning electron microscopy. Different primary mechanisms of graphitization are discussed: (a) normal growth of graphite layer by detachment of single atoms from {100} and {111} diamond surfaces and (b) lateral growth of graphite on the {111} surface by breaking off groups of atoms followed by their rearrangement into planar graphitic structures. The growth of oriented graphite crystallites was observed only on the {111} diamond faces and at p=2 GPa. In the case of synthetic diamonds, internal graphitization was observed and explained in terms of catalytic effects on the metal inclusions.