GRAPHITIZATION OF AMORPHOUS-CARBON AT HIGH-PRESSURES TO 15 GPA

Graphitization of amorphous carbon has been studied at high static pressures up to 15 GPa and high temperatures up to 1300-degrees-C, primarily under diamond-stable conditions. Upon heating at 2 GPa, amorphous carbon turns into graphite at approximately 900-degrees-C. The temperature for the graphitization decreases with increasing pressure and approaches 600-degrees-C at 10 GPa or higher. The graphitization process at 15 GPa comprises two stages over a temperature range 600-1300-degrees-C. In the first stage, below 900-degrees-C, graphite layers develop and the interlayer spacing decreases markedly. The second stage, above 1000-degrees-C, corresponds to in-layer arrangement and partial development of three-dimensional ordering. At temperatures approaching diamond formation under this pressure, the graphitization does not acquire completion. Along 1300-degrees-C isotherm, the structure and texture of graphite exhibit appreciable changes across the graphite-diamond equilibrium line and also across 11 GPa.