Graphitization of amorphous carbon at high pressures to 15 GPa

Abstract

Graphitization of amorphous carbon has been studied at high static pressures up to 15 GPa and high temperatures up to 1300 °C, primarily under diamond-stable conditions. Upon heating at 2 GPa, amorphous carbon turns into graphite at ∼900 °C. The temperature for the graphitization decreases with increasing pressure and approaches 600 °C at 10 GPa or higher. The graphitization process at 15 GPa comprises two stages over a temperature range 600–1300 °C. In the first stage, below 900 °C, graphite layers develop and the interlayer spacing decreases markedly. The second stage, above 1000 °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 °C isotherm, the structure and texture of graphite exhibit appreciable changes across the graphite-diamond equilibrium line and also across 11 GPa.