Nanocarbon Phase Diagram and Conditions for Detonation Nanodiamond Formation

Abstract

To analyse the process of detonation nanodiamond (UDD) synthesis, the positions of the melting and phase equilibrium curves in the carbon phase diagram were calculated for UDD particles of 1-10 nm in size. We also found the position of a set of triple points in the ranges of P = 13.5-16.5 GPa and T = 2210-4470K. This set of points indicates the area of liquid nanocarbon. The diamond area in the phase diagram was subdivided into three regions, depending on the nature of the nanoparticles: UDD and diamond, liquid nanocarbon, and amorphous nanoparticles. The C-J parameters of explosives used in the UDD synthesis are found to lie within the liquid nanocarbon region. Therefore, the reaction zone of the detonation wave is the site of formation of carbon nanodroplets, which then crystallize to form UDD particles along a segment of the isotropic line of the detonation product spreading through the UDD area at P = 16-10 GPa and T = 3400-2900K. The curve for the detonation rate vs. the density of the explosive charge exhibits breaks that can be interpreted as being due to the onset and termination of nanocarbon melting rather than to UDD formation in the reaction zone.