Ignition experiments and models of a plastic bonded explosive (PBX 9502)

Area of Science:

• Energetic Materials Science
• Chemical Kinetics
• Combustion Science

Background:

• PBX 9502, a formulation of 95% triaminotrinitrobenzene (TATB) and a fluoropolymer binder, is a key insensitive high explosive.
• Understanding its ignition behavior under various conditions is critical for safety and performance assessments.
• Existing ignition models may not fully capture the pressure-dependent decomposition kinetics observed in experiments.

Purpose of the Study:

• To develop a simple, pressure-dependent ignition model for PBX 9502.
• To investigate the influence of density, venting, and ullage on the ignition characteristics of PBX 9502.
• To elucidate the decomposition mechanisms (open-pore vs. closed-pore) governing PBX 9502 ignition.

Main Methods:

• Ignition experiments were conducted on PBX 9502 samples with densities ranging from 38% to 98% of theoretical maximum density (TMD).
• Experiments included sealed and vented configurations with ullage percentages from 18% to 75%.
• A four-step kinetic model involving drying, mono-furazan formation, and decomposition of intermediates and TATB was developed.

Main Results:

• Ignition times decreased with increasing sample density.
• Ignition times increased with increased venting and increased ullage.
• Observed pressure-dependent decomposition, with open-pore behavior in low-density samples and closed-pore behavior in high-density samples.
• Multiple pre-ignition temperature excursions were observed in confined, high-density experiments.

Conclusions:

• PBX 9502 ignition is strongly pressure-dependent.
• The developed four-step model provides a simplified yet effective representation of PBX 9502 ignition.
• Density and confinement significantly influence the decomposition pathway and ignition behavior of PBX 9502.