Publications

On June 30, 2020, an inadvertent reaction occurred during pressing of the energetic material pentaerythritol tetranitrate (PETN). The location of the event was the energetic component Rapid Prototype Facility (RPF), where similar operations performed on a variety of energetic materials are routinely provided for customers throughout Sandia National Laboratories (SNL). A background on pressing of energetic materials is provided to enhance clarity in the description of the event. This background includes a description of the equipment, materials, and tooling present during the event.

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Chemiluminescence (CL) has been applied as a condition monitoring technique to assess aging related changes in a hydroxyl-terminated-polybutadiene based polyurethane elastomer. Initial thermal aging of this polymer was conducted between 110 and 50 °C. Two CL methods were applied to examine the degradative changes that had occurred in these aged samples: isothermal "wear-out" experiments under oxygen yielding initial CL intensity and "wear-out" time data, and temperature ramp experiments under inert conditions as a measure of previously accumulated hydroperoxides or other reactive species. The sensitivities of these CL features to prior aging exposure of the polymer were evaluated on the basis of qualifying this method as a quick screening technique for quantification of degradation levels. Both the techniques yielded data representing the aging trends in this material via correlation with mechanical property changes. Initial CL rates from the isothermal experiments are the most sensitive and suitable approach for documenting material changes during the early part of thermal aging. © 2006 Elsevier Ltd. All rights reserved.

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A study to characterize the low-temperature reactive processes for o-AP and an AP/HTPB-based propellant (class 1.3) is being conducted in the laboratory using the techniques of simultaneous thermogravimetric modulated beam mass spectrometry (STMBMS) and scanning electron microscopy (SEM). The results presented in this paper are a follow up of the previous work that showed the overall decomposition to be complex and controlled by both physical and chemical processes. The decomposition is characterized by the occurrence of one major event that consumes up to {approx}35% of the AP, depending upon particle size, and leaves behind a porous agglomerate of AP. The major gaseous products released during this event include H{sub 2}O, O{sub 2}, Cl{sub 2}, N{sub 2}O and HCl. The recent efforts provide further insight into the decomposition processes for o-AP. The temporal behaviors of the gas formation rates (GFRs) for the products indicate that the major decomposition event consists of three chemical channels. The first and third channels are affected by the pressure in the reaction cell and occur at the surface or in the gas phase above the surface of the AP particles. The second channel is not affected by pressure and accounts for the solid-phase reactions characteristic of o-AP. The third channel involves the interactions of the decomposition products with the surface of the AP. SEM images of partially decomposed o-AP provide insight to how the morphology changes as the decomposition progresses. A conceptual model has been developed, based upon the STMBMS and SEM results, that provides a basic description of the processes. The thermal decomposition characteristics of the propellant are evaluated from the identities of the products and the temporal behaviors of their GFRs. First, the volatile components in the propellant evolve from the propellant as it is heated. Second, the hot AP (and HClO{sub 4}) at the AP-binder interface oxidize the binder through reactions that preferentially strip the hydrogen from the binder and yield HCl and H{sub 2}O with some oxidation of the carbon from the binder. Third, the o-AP in the propellant decomposes in the same manner as in neat o-AP. Finally, AP-derived gaseous products interact with other ingredients in the propellant.

Preliminary STMBMS and SEM results of the thermal decomposition of AP in the orthorhombic phase are presented. The overall decomposition is shown to be complex and controlled by both physical and chemical processes. The data show that the physical and chemical processes can be probed and characterized utilizing SEM and STMBMS. The overall decomposition is characterized by three distinguishing features: an induction period, and accelerator period and a deceleratory period. The major decomposition event occurs in the subsurface of the AP particles and propagates towards the center of the particle with time. The amount of total decomposition is dependent upon particle size and increases from 23% for {approximately}50{micro}m-diameter AP to 33% for {approximately}200{micro}m-diameter AP. A conceptual model of the physical processes is presented. Insight into the chemical processes is provided by the gas formation rates that are measured for the gaseous products. To our knowledge, this is the first presentation of data showing that the chemical and physical decomposition processes can be identified from one another, probed and characterized at the level that is required to better understand the thermal decomposition behavior of AP. Future work is planned with the goal of obtaining data that can be used to develop a mathematical description for the thermal decomposition of o-AP.