New insights into detonation synthesis and properties of nanodiamonds

Abstract

The paper presents mainly new or previously unanalysed data from the most important published papers of the last five years. Several possible mechanisms for the synthesis of detonation nanodiamonds (DND) are considered. A simple predictive estimate of the DND yield based on the content of elements in the explosive molecule is proposed. It is shown that nitrogen is not an inert element in the nanodiamond synthesis process. It is possible to form a fractal carbon lattice with simultaneous fluctuations of carbon density in the chemical reaction zone (CRZ) with the formation of a three-dimensional ordered core in the nodes of the lattice. The time of formation of such a carbon structure is close to 50 ns. For DND formation, the time of chemical reactions is 0.1–0.3 μs, and the width of the CRZ is 0.4 to 1.4 mm. The electrical conductivity of the 'plasma' in the CRZ is determined by the carbon content of the explosives, which forms extended conducting structures. It is shown that the region with the highest DND yield (up to 8.5 wt. %) is limited by the pressure in the Chapman-Jouguet plane of 23–29 GPa and the temperature of 3850–4350 K, the optimum oxygen balance of the explosive is in the range of –42÷–53 %, and the detonation velocity is in the range of 7250–8000 m⋅s –1. In general, DNDs from different explosives have close crystallographic parameters (except for nanodiamonds from benzotrifuroxane). To increase the yield of DNDs, it is necessary to use an aqueous charge shell, which is a solution of urotropine, urea or hydrazine. For the first time, the process of DND production from Tetryl and its binary and ternary charges was developed and recommended for industry, with a DND yield of ~7 wt. %. Experience with the industrial production of DND has shown that it is realistic to obtain nanodiamonds with a yield of 8.5 wt. % at their content in the diamond containing blend of 72 % and non-combustible impurities of 1.6 wt. %.