Structural Defect Evolution of TATB‐Based Compounds Induced by Processing Operations and Thermal Treatments

Abstract

1IntroductionSolid explosives displays trongly heterogeneous microstructures, which are known to evolveu nderp rocessing, thermal treatments, and mechanical loads. In turn, microstructure evolutions may affect macroscopic properties, such as shock and impact sensitivity,o rt hermo-mechanicalb ehavior.T herefore, it is of crucial importancet oc haracterizee xplosives microstructures and their evolutions. The subject can still be considered to be in its infancy,b ut has grown significantly in recent years.G iven the complexity of the considered microstructures and the variety of spatial scales involved, having recourse to various techniques of investigation is the only way of improving the current level of knowledge in this domain.Opticala nd scanning electron microscopy are almost routinelyu sed nowadays, eithert oc haracterize microstructures and the influence of processingp arameters on them (see, for example,R ef. [1]), or to perform microstructure level simulations (see, for example, Refs. [2,3]). Besides, ag rowing number of modern techniques mayp rovide useful data related to differenta spectsa nd scales of explosives microstructures and their evolutionu nder variousa pplied thermal or mechanical loads. This is the case of X-ray or neutron small-angle scattering and of X-ray microtomography,u sed to investigate the role of pressing parameters and of thermalt reatmento nt he porosity of explosives [4] or to locate the binder [5].T his is also the case of X-ray diffraction, where the intensities of diffractionp eaks can be analyzed to characterize processing-induced texture. Schwarz et al. [6] studied samples taken at different locations of al arge part of PBX9502 (a plastic-bonded pressed explosive) manufactured by semi-isostaticp ressing.T hey showed that the shear component of the stresses applied duringt he pressingo peration causes crystals rotation such that their [0 02]p lanesc ome preferentially parallel to shear planes, thus inducing as trong texture. Such texture measurements could be correlated to the anisotropy of irreversible thermal expansion, known as "ratchet growth" for this family of materials [7].The width of diffraction peaks can also be analyzed, through the so-called Rietveld analysis, to derive information about the crystallographic structure and structural defects of constitutivec rystals of explosives, namely average crystallite size and microstrain. The crystallite size L,o rc oherent diffraction domain, is the size of the perfect crystal. It can be viewed as an average length between two structural defects in agiven plane family.The microstrain e corresponds to lattice distortion due tos light displacements of atoms and molecules from theirp ositioni na ni deal crystal. These two parameters are considered to represents tructural defects of the material [8] and induce broadeningo fXray diffraction peaks.Afew papers have been published about structural defects andt heir evolutioni ns everal explosives. Herrmann and Fietzek [9]s tudied cyclotrimethylenetrinitramine( RDX) and cyclotetram...

Syntheses and characterization of isotopically labeled 1,3,5‐triamino‐2,4,6‐trinitrobenzene (TATB)**

“…Unlabeled TATB (blue) exhibits the typical PXRD pattern for production level TATB [27,[38][39][40]. The (0 0 2) reflectance dominates the pattern at ~30°2Θ.…”

Using a fiber Bragg grating technique to investigate temperature cycling strain of pressed TATB‐based polymer‐bonded explosives

“…With advancing detection technologies such as optical microscopy (OM), scanning electron microscopy (SEM), neutron diffraction (NRD), small-angle neutron scattering (SANS), and small-angle X-ray scattering (SAXS), it is possible to study the multiphase interfaces, TATB crystals, binders, and holes inside PBX in complex environments, as well as the distribution characterization of molding powder and porosity testing, to gradually obtain a large amount of microstructure information of pressed TATB PBXs. Watkins, Tang, and others [7,19,[24][25][26][27][28][29][30][31][32] studied the crystal orientation, crystal fragmentation, porosity, and binder behavior during the expansion process of PBX pressed under different conditions. They demonstrated that the temperature is an important pressing parameter during PBX pressing, because high temperatures improve the flowability of polymer binders, leading to better bonding with explosive particles and reducing cracks and fragmentation in the explosive.…”

Investigation of precision, accuracy and confidence of X-ray diffraction for determining crystallite size in nanopowders

“…An accurate model that allows the calculation of a joint parameter distribution is necessary to understand fully the quantitative capability of XRD in determining crystallite size. However, for certain samples of consistent crystallite shape measured equivalently, it has been shown that these methods are useful for the determination of crystal strain, for example in tracking the evolution of single samples subjected to stress (Brown et al, 2014;Zotov et al, 2017), or to compare the effects of processing on the properties of materials (Scorticati et al, 2015;Schimpf et al, 2013;Leineweber, 2011;Guerain et al, 2016). For these ideal samples, XRD methods are preferred over image-based techniques for relatively high throughput crystallographic size information and are uniquely able to provide certain data such as lattice strain.…”