RESUMEN
Spray drying has recently gained interest in the high explosives (HE) community for the production of novel nanocomposites and well-controlled particle size distributions. However, there is a dearth of information on spray-dried, neat energetic materials. In this work, we correlate the spray drying production parameters to the resulting microstructure and handling sensitivity properties of neat RDX. We demonstrate the capability to fine-tune the particle size distributions for "nanopowder" spray-dried RDX, as well as larger particle size distributions by simply changing the spray dryer setup. We also investigate other physical and chemical changes that RDX undergoes after being processed with spray drying. We characterize these changes with scanning electron microscopy, X-ray diffraction, ultrahigh-performance liquid chromatography, and small-scale sensitivity tests. Interestingly, although the phase and chemical properties are similar before and after spray drying, small-scale sensitivity testing reveals that size reduction of RDX does not follow the typical HE desensitization trends, generally observed for other energetic materials.
RESUMEN
Microstructural characterization of composite high explosives (HEs) has become increasingly important over the last several decades in association with the development of high fidelity mesoscale modeling and an improved understanding of ignition and detonation processes. HE microstructure influences not only typical material properties (e.g., thermal, mechanical) but also reactive behavior (e.g., shock sensitivity, detonation wave shape). A detailed nondestructive 3D examination of the microstructure has generally been limited to custom-engineered samples or surrogates due to poor contrast between the composite constituents. Highly loaded (>90 wt%) HE composites such as plastic-bonded explosives (PBX) are especially difficult. Here, we present efforts to improve measurement quality by using single and dual-energy microcomputed X-ray tomography and state-of-the-art image processing techniques to study a broad set of HE materials. Some materials, such as PBX 9502, exhibit suitable contrast and resolution for an automatic segmentation of the HE from the polymer binder and the voids. Other composite HEs had varying levels of success in segmentation. Post-processing techniques that used commercially available algorithms to improve the segmentation quality of PBX 9501 as well as zero-density defects such as cracks and voids could be easily segmented for all samples. Aspects of the materials that lend themselves well to this type of measurement are discussed.
RESUMEN
Graphene nanoribbons (GNR), can be prepared in bulk quantities for large-area applications by reducing the product from the lengthwise oxidative unzipping of multiwalled carbon nanotubes (MWNT). Recently, the biomaterials application of GNR has been explored, for example, in the pore to be used for DNA sequencing. Therefore, understanding the polymer behavior of GNR in solution is essential in predicting GNR interaction with biomaterials. Here, we report experimental studies of the solution-based mechanical properties of GNR and their parent products, graphene oxide nanoribbons (GONR). We used atomic force microscopy (AFM) to study their mechanical properties in solution and showed that GNR and GONR have similar force-extension behavior as in biopolymers such as proteins and DNA. The rigidity increases with reducing chemical functionalities. The similarities in rigidity and tunability between nanoribbons and biomolecules might enable the design and fabrication of GNR-biomimetic interfaces.