Ethylenediamine Catalyzes Nitromethane Shock-to-Detonation in Two Distinct Ways

Abstract

Adding amines to liquid nitromethane (NM) is known to lower the threshold for the shock-to-detonation transition because amines catalyze proton transfer reactions that are the initial steps in the energy release process. We studied NM with 1 wt % ethylenediamine (NM/EDA) with 4 ns input shocks using time and space resolved diagnostics: photon Doppler velocimetry (PDV), optical pyrometry, and nanosecond video imaging. The 4 ns shocks are fast enough to time-resolve the reaction kinetics and the shock-to-detonation transition. We find that it is possible to shock ignite the NM/EDA without producing a detonation, so there is more to amine sensitization of the shock-to-detonation process than simply lowering the barrier to initial reactions. We find that although 1 wt % EDA has little effect on the ambient properties of NM, it dramatically alters the Hugoniot. The shock speed in NM/EDA is reduced, indicating that shocked NM/EDA is significantly more compressible than NM. Higher compressibility is associated with greater adiabatic heating, so EDA both lowers the barrier to proton transfer reactions and increases shock energy absorption. To explain the enhanced compressibility, we propose that shocking NM/EDA produces a reactive flow that has a much higher ionic strength than in NM. The sudden transformation from a molecular liquid to an ionic liquid with stronger intermolecular interactions is responsible for enhanced compressibility and shock heating.

Laser pulses into bullets: tabletop shock experiments

“…To better understand detonations, researchers study the dynamics of the shock-to-detonation transition, typically using input shocks longer in duration than the exothermic stages of the complex chemistries. For detonation on a tabletop, 41,61,62 we design shocks to minimize the detonation build up time. That lets us use the smallest possible charges and time resolve some of the exothermic processes.…”

“…64 We studied NM with 1% added ethylenediamine catalyst (NM/EDA). 62 In Fig. 13(a), we plot the energy difference between the (time-integrated) outgoing and incoming shocks in NM and NM/EDA, in units of the shock energy fluence (kJ m À2 ), versus the imparted fluid velocity U p .…”

“…13(a) shows that the EDA catalyst lowers the velocity needed to trigger both shock absorption and energy release. 62 Fig. 13(b) shows the Hugoniot equations of state, a plot of shock velocity versus fluid velocity.…”

“…The sudden transformation from a molecular liquid to an ionic liquid with stronger intermolecular interactions is responsible for enhanced compressibility and shock heating. 62 Thus, the catalyst lowers the threshold for shock ignition in two ways, the usual barrier lowering plus a physical transformation that enhances the amount of shock energy absorbed by the fluid.…”

“…13(a) shows that the EDA catalyst lowers the velocity needed to trigger both shock absorption and energy release. 62…”