Graphitization and preparation of diamond in an amorphous carbon material at high pressures and temperatures

Structural transformations of a carbynoid amorphous carbon material after high-temperature, high-pressure processing at different rates of isobaric heating have been studied by scanning electron microscopy and Raman spectroscopy. Using the 6 GPa data as an example, we demonstrate that slow heating leads to gradual graphitization of the material at temperatures above 600°C, in perfect agreement with previous measurements, in which graphitization was observed up to 8 GPa. At the same time, increasing the heating rate to 50°C/s at a sufficiently high pressure (8 GPa) leads to significant changes in the nature of the transformations. Whereas heating to temperatures from 1100 to 1200°C also leads to the formation of graphite-like phases, rapid heating to 1300°C ensures the formation of considerable amount of diamond in the absence of catalysts.