Ratchet growth experiments on TATB and PBX 9502

Abstract

TATB (triaminotrinitrobenzene) crystals are graphitic in structure. In compacted form, with or without binder, TATB undergoes irreversible volume changes upon thermal cycling. This "ratchet growth" (RG) can change geometry and reduce density by several percent, however, the mechanism responsible remains unknown. We have conducted independent studies to shed light on the nature of RG characteristics. Using thermal mechanical analysis and dilatometry, strain values are measured in real time as temperature cycling protocols are varied. Initial work on PBX 9502 (95 weight% TATB) has led to new studies on dry-pressed TATB cylinders, thus eliminating binder contributions to the thermal response. Our results clearly show that the magnitude of RG over two different temperature ranges depends on the thermal history of the specimen. In addition, we have shown that for dry-pressed TATB, the RG magnitude over a given temperature range may depend on the temperature at which the specimen was compacted from molding powder. A pressing temperature of 130°C led to specimens with significantly lower RG growth magnitude than specimens pressed at 30 or 80°C. These data and their insights are being used to inform RG models. LA-UR 11-04058.