A complete understanding of the mechanisms by which high explosives (HEs) are shock initiated, especially at the particle scale, is still in demand. One approach to explain shock initiation phenomenon is hot spot theory, which suggests that distributed energy in energetic material is localized due to shock or impact to generate the high temperatures for ignition. This study focuses on the impact response of a HE polycrystalline particle, specifically HMX, in a polymer matrix. This represents a simplified analog of a traditional polymer‐bonded explosive (PBX) formulation. A light gas gun, together with high‐speed x‐ray phase contrast imaging (PCI), was used to study the impact response of a single particle of production‐grade HMX in a Sylgard‐184® matrix. The high‐speed x‐ray PCI allows for real‐time visualization of HE particle behavior. The experiments revealed that, at impact velocities of ∼200 m s−1, the energetic particle was cracked and crushed. When the impact velocity was increased to 445 m s−1, a significant volume expansion of the particle was observed. This volume expansion is considered to be the result of chemical reaction within the HE particle. 相似文献
This paper reviews the production, synthesis, crystallography, particle morphology and spectroscopy of the insensitive high explosive nitroguanidine, (NGu, CH4N4O2), CAS‐No: [556‐88‐7] and its isotopologues [2D4]‐NGu and [15N4]‐NGu]. When compared with standard insensitive high explosives such as 1,3,5‐triamino‐2,4,6‐trinitrobenzene (TATB), 1,1‐diamino‐2,2‐dinitroethylene (FOX‐7) and N‐guanylurea dinitramide (FOX‐12), Nitroguanidine proves to be the least sensitive. The review gives 170 references to the public domain. For Part II see ref. [1]. 相似文献
ABSTRACTThe AKUFVE techniques were developed by Rydberg and co-workers in the 1960s. The main aim was to be able to perform a series of liquid-liquid extraction data varying one or more parameters and at the same time achieve very pure phases. As such, this technique was later used for short-lived isotope studies in the SISAK system, but also as a standalone unit for a large number of thermodynamic studies of extraction systems both for fundamental understanding as well as more applied investigations. In this paper, the apparatus with modifications made over the decades is described. In addition, studies with stability constant determinations for the zirconium-water-acetylacetone system as well as lanthanide extraction using bromodecanoic acid are exemplified to demonstrate the potential use of the technique. The results shown clearly demonstrate the versatility and ability of the AKUFVE system. 相似文献
Here, a novel melt electrospinning method to produce few‐micron and nanometer thick fibers is presented, in which a polymer‐coated wire with a sharp tip is used as the polymer source. The polymer coating is melted via Joule heating of the source wire and extracted toward the target via electrostatic forces. The high viscosity and low charge density of polymer melts lower their stretchability in melt. The method relies on confining the Taylor cone and reducing initial jet diameter via concentrated electrostatic fields as a means to reduce the diameter of fibers. As a result, the initial jet diameter and the final fiber diameter are reduced by an order of magnitude of three to ten times, respectively, using wire melt electrospinning compared to syringe‐ and edge‐based electrospinning. The fiber diameter melt electrospun via this novel method is 1.0 ± 0.9 µm, considerably thinner than conventional melt electrospinning techniques. The generation of thin fibers are explained in terms of the electrostatic field around the wire tip, as obtained from finite element analysis (FEA), which controls the size and shape of the melt electrospun jet. 相似文献
The selective incorporation of fluorinated motifs, in particular CF2FG (FG=a functional group) and CF2H groups, into organic compounds has attrracted increasing attention since organofluorine molecules are of the utmost importance in the areas of nuclear imaging, pharmaceutical, agrochemical, and material sciences. A variety of synthetic approaches has been employed in late‐stage difluoroalkylation reactions. Visible light photoredox catalysis for the production of CF2FG and CF2H radicals has provided a more sustainable alternative to other conventional radical‐triggered reactions from the viewpoint of safety, cost, availability, and “green” chemistry. A wide range of difluoroalkylating reagents has been successfully implemented in these organic transformations in the presence of transition metal complexes or organic photocatalysts. In most cases, upon excitation via visible light irradiation with fluorescent light bulbs or blue light‐emitting diode (LED) lamps, these photocatalysts can act as both reductive and oxidative quenchers, thus enabling the application of electron‐donor or electron‐acceptor difluoroalkylating reagents for the generation of CF2FG and CF2H radicals. Subsequent radical addition to substrates and additional organic transformations afford the corresponding difluoroalkylated derivatives. The present review describes the distinct strategies for the transition metal‐ and organic‐photocatalyzed difluoroalkylation of a broad range of organic substrates by visible light irradiation reported in the literature since 2014.
Aspergillus niger Monoamine Oxidase (MAO‐N) is a homodimeric enzyme responsible for the oxidation of amines into the corresponding imine. Laboratory evolved variants of MAO‐N in combination with a non‐selective chemical reductant represents a powerful strategy for the deracemisation of chiral amine mixtures and, thus, is of interest for obtaining chiral amine building blocks. As we reported recently, MAO‐N presents a rich conformational dynamics with a flexible β‐hairpin region that can adopt closed, partially closed and open states. Despite the β‐hairpin conformational dynamics is altered along the laboratory evolutionary pathway of MAO‐N, the connection between the β‐hairpin conformational dynamics and how this affects active site catalysis still remains unclear. In this work, we use accelerated molecular dynamics to elucidate the potential interplay between the β‐hairpin conformational dynamics and catalytic activity in MAO‐N wild type (WT) and its evolved D5 variant. Our study reveals a delicate communication between both MAO‐N monomers that impacts the active site architecture, and thus its catalytic efficiency. In both MAO‐N WT and the laboratory evolved D5 variant, the β‐hairpin conformation in one of the monomers affects the productive binding of the substrate in the active site of the other subunit. However, both MAO‐N WT and D5 variants show a quite different behaviour due to the impact of distal mutations introduced experimentally with Directed Evolution on the conformational dynamics of the enzyme.
Rhodium acetate effectively promotes the carboxylate‐directed ortho‐arylation of (hetero)aromatic carboxylates with aryl bromides. The main advantage of this phosphine‐free, redox‐neutral method arises from its efficiency in assembling biologically meaningful electron‐rich arylpyridines, which are problematic substrates in known C−H arylations using Pd, Ru, and Ir catalysts.
