Direct Conversion of Graphite to Diamond in Static Pressure Apparatus

Static pressure apparatus has been developed which is capable of pressures up to 200 kbar and transient temperatures up to about 5000°K, using an electric flash-heating technique. At pressures above about 125 kbar and temperatures in the 3000°K range it is found that graphite spontaneously collapses completely to polycrystalline diamond which may be retrieved quantitatively. The threshold temperature of the transformation is several hundred degrees lower than the melting temperature of graphite. The diamond/graphite/liquid triple point is found to be located at about 125 (+10, —0) kbar and 4100 (±200)°K. The shock compression results of DeCarli and Jamieson, and of Alder and Christian, are linked with the present results to construct a phase diagram of carbon extending to 5000°K and 800 kbar.