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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. [ABSTRACT FROM AUTHOR]

The understanding of thermal explosions and burn propagation lags that of detonations and shock propagation. Diagnostics such as high energy radiography have been used to image shocks, but have been previously precluded from use in thermal explosions due to their stringent timing requirements: shock propagation can be synchronized to an external diagnostic while thermal explosion can not. This issue is solved by following the evolution of the ignition volume in a thermal explosion and using a laser pulse to provide a temperature jump in that central volume during the final thermal runaway leading to ignition. Thermal explosion experiments have been conducted at the Los Alamos Proton Radiography facility and have yielded images of the evolution of ignition, post-ignition burn propagation, and case failure in a radially confined cylinder of PBX 9501. This paper presents images taken during the hours long quasistatic heating, the final minutes of thermal runaway, and the post ignition burn propagation. [ABSTRACT FROM AUTHOR]

We have applied proton radiography to study the conversion of solid density to gaseous combustion products subsequent to ignition of a thermal explosion in PBX 9501. We apply a thermal boundary condition to the cylindrical walls of the case, ending with an induction period at 205 C. We then introduce a laser pulse that accelerates the thermal ignition and synchronizes the explosion with the proton accelerator. We then obtain fast, synchronized images of the evolution of density loss with few microsecond resolution during the approximately 100 microsecond duration of the explosion. We present images of the solid explosive during the explosion and discuss measured rates and assumed mechanisms of burning the role of pressure in this internal burning. [ABSTRACT FROM AUTHOR]

We have made spatially and temporally resolved temperature measurements internal to a thermal explosion in PBX9501, which is a plastic bonded explosive composed of 95% HMX and 2.5% estane mixed with 2.5% nitroplasticizer (BDNPA/F). In order to study the evolution of ignition in a thermally treated piece of explosive, we have pushed the time resolution of several different temperature diagnostics. In this paper, we will discuss the details of the time response of these diagnostics including temperature uncertainties. The temperature measurements are made both by thermocouples with corrections applied to compensate for the thermocouple response time and with optical pyrometry. An additional goal of adding high energy radiography diagnostics to future experiments has motivated an effort to synchronize thermal explosions to an external clock. In this paper, I discuss our current capabilities for controlling and measuring the development of an ignition within a piece of heated PBX9501. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]