The chemical reaction in shock-condensed liquid high explosives (HE) has a thermal character, and initial rate of reaction is a strong function of activation energy. It can change in a wide range by addition of diluents to HE. Definition of the initial rate value gives an important information for prediction of HE detonation due to its influence on the detonation wave structure and propagation limits. In this work, the reaction zone structure, stability of detonation waves and limits of detonation propagation in the mixtures of tetranitromethane/methanol (TNM/M) and TNM/nitrobenzene (TNM/NB), depending on the diluent concentration, were studied by a VISAR laser interferometer with nanosecond time resolution.

In the experiments, TNM with 1.64 g/cc initial density and 6.4 km/s detonation velocity, methanol and nitrobenzene with 0.79 g/cc and 1.20 g/cc initial densities were used. On the dependence of particle velocity on time, in the neat TNM behind the shock jump the velocity decreases smoothly and the maximum velocity gradient is realized directly behind the shock wave front. At the addition of diluents to TNM, the amplitude of von Neumann spike begins to decrease, whereas detonation parameters increase. At the methanol concentration of 15-35% and NB concentration of 15-40%, there is a sharp change in the character of the reaction zone – after the initial shock jump, the particle velocity continues to increase, for approximately 10 ns, reaches maximum, and then drops. At further increase of methanol concentration to the critical concentration of detonation (60%), the detonation parameters decrease and oscillations appear on the particle velocity profiles. It means that detonation front becomes unstable. In the mixture of TNM/NB, the loss of stability is observed near the critical concentration of nitrobenzene (76%), above which the detonation in the TNM/NB mixture does not propagate. The dependences of detonation velocity of the mixture on diluent concentration are non-monotonically. The highest value of detonation velocity is observed at a small negative oxygen balance (25-27% of diluent). It was found that in the mixture of TNM/NB, the detonation parameters continue to increase at the NB concentration of 26-30%, whereas detonation velocity decreases.

This work was supported by Russian Foundation for Basic Research (project No.16-29-01002).