Investigation of the microstructure of energetic crystals by means of X-ray powder diffraction

Abstract

Mechanical sensitivity of energetic materials is discussed as a function of particle size and lattice defects. Therefore an approach is made to quantify and characterize lattice defects of the energetic powders RDX and HMX using X-ray diffraction. The mechanical properties of these cyclic nitramines are supposed to be dominated by different defect mechanisms-deformation twinning and dislocation slip. The energetic powders and the line-shape standard SRM 660a ͑NIST͒ were measured on a Bragg-Brentano diffractometer D5000 ͑Bruker-AXS͒, and the diffraction patterns were evaluated by Rietveld-and peak-profile analysis using Williamson-Hall plots. Additionally, preparing samples as thin powder layers was tested in order to reduce line broadening due to low absorption. The investigations reveal interesting details. Characteristic line broadening was found for RDX and HMX pointing to a comparably higher microstrain in HMX. Anisotropic line broadening was found for RDX and discussed in terms of strain fields of dislocations. © 2005 International Centre for Diffraction Data.

Microstructure of Energetic Particles Investigated by X‐ray Powder Diffraction

“…The data were evaluated according to Williamson and Hall [3] by plotting reciprocal peak widths versus reciprocal lattice distances, and the root mean square strains were estimated from slopes of regression lines. Figure 1 yields different levels and runs of curves, and a bend of the HMX curve around the reciprocal lattice distance 0.3 1/Å, so far confirming previous results [10]. Linear regression lines b* = a d*+b fitted to selected regions of the curves are plotted in Figures 2 and 3 and results of the fits are summarized in Table 1.…”

“…As the investigations revealed significant line broadening caused by low absorption of the nitramines, penetration depths have been confined by preparing thin particle layers. Thus, characteristic line broadening was found to distinguish HMX from RDX, and results have been discussed in terms of dislocations and twins [10]. The makeshift preparation technique, however, limited the accuracy and the method was successful only if powders provide sufficient orientation statistics, which is not the case for many crystallized powders.…”

Microscopic characterization of defect structure in RDX crystals

“…For a 3 days storage of the RDX samples in ultrahigh vacuum, this leads to a total mass of sublimed RDX of 17 ng. For an area of 100 × 100 μm 2 , this corresponds to a sublimation of a layer of ∼1-μm thickness (density of RDX is 1.82 g cm −3 , thickness of one molecular layer ∼1 nm; this latter value is an approximate value based on the lattice constants of the orthorhombic crystal structure of RDX: a = 13.182, b = 11.574 and c = 10.709Å; Herrmann & Fietzek, 2005). The estimated value for the sublimed layer thickness of ∼1 μm appears to be in the same range as the surface features that can be observed in Figure 11, indicating that sublimation of the RDX in ultrahigh vacuum can be a realistic explanation.…”

Acceleration of δ- to β-HMX-D8 Phase Retransformation with D2O and Intergranular Strain Evolution in a HMX-Based Polymer-Bonded Explosive

“…Mechanical tests revealed the twinning, cleavage, and defect structure of single-crystal HMX. , Microcosmic detection methods such as X-ray diffraction (XRD) were also applied to study the microstructure in HMX. Enhanced peak broadening of XRD patterns is found in HMX compared to other nitramines such as RDX because of twinning. , However, the mechanism of crystal fracture for the HMX-based polymer-bonded explosive (PBX) is still puzzling.…”