The Graphitization of Diamond

In experiments on diamond octahedra at temperatures of 1700 °C and above in high vacua, graphite has been observed to develop both internally and on the surfaces. The surface graphite that has been observed is different from that associated with etching, and is independent of the gaseous environment. Its development increases with time and rapidly increases with temperature. The internal graphite always has associated with it an intense strain in the surrounding diamond. It has varied in appearance from isolated particles to orientated distributions of crystallographic microscopic inclusions. Some diamonds have remained completely free from internal changes. For the diamonds which have developed inclusions the changes have occurred suddenly and discontinuously, the internal graphite generally not extending with time or increasing temperature. It is thought that both phenomena are due to a physical phase transformation, and that defects, of some particular kind which are present inside many but not all diamonds, initiate the transformation which has given rise to the internal changes that have been observed.