Shock compression and flash heating of graphite/metal mixtures at temperatures up to 3200 K and pressures up to 25 GPa

Abstract

Different aspects of phase-transition processes in carbon in dynamic conditions were studied. Samples of graphite/metal mixtures have been recovered and analyzed after exposure to the combined action of high temperature and pressure pulses generated by a unique flash-heating hemispherical implosion system. Transmission electron microscopy together with x-ray and electron diffraction examinations proved the existence of diamond, different forms of graphite, and carbynes in the samples. A mechanism of formation of diamond is proposed which relies on a solid-vapor-liquid-solid (SVLS) sequence of phase transformations. The experimental results were found to be in reasonable agreement with the proposed SVLS model. A tetragonally crystallized diamondlike carbon phase ( p-diamond) was identified in the course of the work as well as a new linear carbon polymorph (Carbon-XIV).