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).

Carbon isotope fractionation between graphite and diamond during shock experiments

“…Several possible mechanisms for the shock transformation from graphite to diamond have been proposed, including martensitic transformation of graphite (e.g., DeCarli and Jamieson 1961; Erskine and Nellis 1991) and nucleation and growth (diffusive reconstruction) from a glasslike structure (e.g., Pujols and Boisard 1970) or through a liquid phase (e.g., DeCarli 1979; Kleiman et al 1984;Burkhard et al 1994). The mechanism controlling diamond formation depends on shock conditions and starting materials.…”

Shock-Induced Growth of Superhard Materials

“…A pad of high-velocity explosive (1) in contact with a driver plate (2) is ignited at one end by a detonator (3). The detonation wave propagates down the pad with velocity, Udet, and the high pressure of the detonation gases accelerates the driver plate to velocity, V. If the driving explosive (1) with the attached plate (2) are inclined at an angle a = sin-1 (VNdet) to the explosive surface (4) to be detonated, the plate (2) will strike every point of surface (4) simultaneously and, if its velocity is high enough, will initiate a planar detonation wave which, in turn, will accelerate the driver plate (5). If angle a satisfies the condition discussed above, the third pad of high-explosive (6) will be stricken simultaneously by the driver plate (5) and a planar shock-wave will be transmitted into the sample (7).…”

Laser-induced versus shock wave induced transformation of highly ordered pyrolytic graphite

“…Techniques to chemically isolate nano-diamonds [23] might allow their detection. However, according to a suggested weak spots mechanism for diamond formation [25,26], the transition from graphite to diamond occurs through a diffusional reconstructive process where both pressure and temperature play major roles.…”