Effect of size and structure of carbon particles on the threshold pressure of diamond formation behind a detonation wave

Detonation velocity of RDX mixtures with 25 wt% of coarse crystalline graphite, colloid graphite, and carbon black is measured as a function of the initial charge density. The detonation velocity versus initial density in charges with graphite additives shows two kinks corresponding to the beginning and completion of graphite conversion into diamond in the reaction zone behind detonation waves. The peak pressures at the kink points are 11.6 and 16.2 GPa in mixtures with colloid graphite and 12.3 and 13.4 GPa in mixtures with coarse crystalline graphite. In charges with carbon black additives the detonation velocity is a linear function of density. A comparative analysis of the electric conductivity profiles in the detonation products in RDX and its mixtures with carbon black, colloid graphite, and boron nitride suggest that diamond formation from carbon black starts at a density which is lower than that used in the present experiments and reaches the maximum at a pressure which is lower than the pressure corresponding to beginning of diamond formation from graphite in detonation of its mixtures with RDX. The initial state of carbon particles (their size and crystallinity) are shown to affect the mechanism, parameters, and rate of diamond formation in detonation waves.