- Conference date: 20-25 July 2003
- Location: Portland, Oregon (USA)
Plastic bonded explosives (PBX) generally consist of 85–95 % by weight energetic material, such as HMX, and 5–15 % polymeric binder. Understanding of the structure and morphology at elevated temperatures and pressures is important for predicting of PBX behavior in accident scenarios. The crystallographic behavior of pure HMX has been measured as functions of temperature and grain size. The investigation is extended to the high temperature behavior of PBX 9501 (95% HMX, 2.5 % Estane, 2.5 % BDNPA/F). The results show that the HMX β‐ to δ‐phase transition in PBX 9501 is similar to that in neat HMX. However, in the presence of the PBX 9501 binder, δ‐phase HMX readily converts back to β‐phase during cooling. Using the same temperature profile, the conversion rate decreases for each subsequent heating and cooling cycle. As observed in earlier experiments, no reverse conversion is observed without the polymer binder. It is proposed that the reversion of δ‐phase to β‐phase is due to changes in the surface molecular potential caused by the influence of the polymer binder on the δ‐phase. Upon thermal cycling, the polymer binder segregates from the HMX particles and thus reduces the influence of the binder on the surface molecules. This segregation increases the resistance for the δ‐phase to β‐phase transition, as demonstrated in an aged PBX 9501 material for which the reversion is not observed.
- Surface segregation
- Crystal structure
- Physics demonstrations
- Surface charge
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