SHOCK METAMORPHISM OF THE GRAPHITE QUASIMONOCRYSTAL

Micro structure examination of graphite quasimonocrystal recovered aft er dynamic loading to pressure of 35-45 GPa was carried out. Only a sm all amount of cubic diamond and recrystalized graphite was detected. M ost of the graphite ( similar to 80 vol.%) remained in initial high or ientation, but transformed to fine, grained phase with crystalite size 0.1-1 microns. Relaxation time of the transformation ( similar to 10 ns) and the degree of the transformation ( similar to 70-80 vol.%) wer e determined by means of measurements of the electrical resistivity du ring loading up to 26 GPa and following computer simulation of the res ults. We proposed that two simultaneous processes take place at pressu res higher than 20 GPa: i) relatively slow diffusive graphite to diamo nd transformation localized in the zones with defect structure: ii) hi ghly oriented graphite transforms to a diamond like phase with density of about 3.2 g/cm(3) at zero pressure. This, transformation has fast, martensitic kinetics and is reversible.