Experimental and theoretical investigation into the high pressure deflagration products of 2,6-diamino-3,5-dinitropyrazine-1-oxide (LLM-105)

Diamond anvil cell (DAC) laser ignition experiments and reactive ab initio molecular dynamics (AIMD) simulations were performed on the high explosive (HE) LLM-105 to investigate its high pressure (HP) deflagration chemistry. Raman and optical spectroscopy measurements reveal LLM-105 reacts into an opaque carbonaceous product at 4–25 GPa. At pressures $>\sim$ 27 GPa, the reaction product consists of an amorphous optically transparent solid and nitrogen (N${}_2$) in the solid phase. While not a one-to-one comparison due to the small time and length scales, the HP AIMD simulations show that some of the product is molecular N${}_2$, in qualitative agreement with experiment, while above 20 GPa most of the product consists of large amorphous C${}_x$H${}_y$N${}_z$O${}_k$ clusters. Clustering is enhanced with pressure and reduces with temperature. In the experiments with initial sample pressure $>\sim$ 25 GPa, the pressure within the DAC decreases with minimal change in DAC cavity area. At initial sample pressures of 43.9 GPa, when quenched to 0 K, simulations predict a product experiencing a lower pressure consistent with the experimental measurement at lower load pressures. The results are important for understanding the HP deflagration chemistry of LLM-105.

Novelty and Significance Statement

It is typically difficult to identify the high-pressure reaction products of HEs such as LLM-105. Here, we have performed laser ignition DAC experiments on LLM-105 and successfully observed N${}_2$ in the Raman spectrum of the product for the first time. Above $>\sim$ 27 GPa, the recovered product is also transparent, and the pressure is lower than the initial pressure with minimal change in DAC cavity area. One of the largest scale reactive ab initio MD simulations was performed to help understand the chemistry. Qualitative consistency between the simulated and experimental products, changes in pressure, and changes in optical properties are reported. This allows for a less-ambiguous comparison of MD simulations to experiment. Most importantly, this is the first time evidence is presented for a pressure-reducing reaction in a high-explosive. This is significant because a pressure-reducing reaction cannot sustain a steady detonation.