Thermal expansion characteristics of high energy insensitive explosive α-NTO

Thermal expansion is an important structural parameter to evaluate the structural stability and performance reliability of energetic materials. In order to further understand the thermal expansion characteristics and mechanism of high-energy insensitive explosive 3-nitro-1, 2, 4-triazol-5-one (NTO), the thermal expansion characteristics of α-NTO were studied by in-situ X-ray diffraction (XRD) technique. Based on the Rietveld full-spectrum fitting structure refinement principle, the thermal expansion coefficient of α-NTO was obtained. The results show that α-NTO exhibits obvious reversible anisotropic thermal expansion under the action of thermal field. Based on infrared and Raman spectroscopy combined with theoretical calculation methods, the crystal packing structure of α-NTO at different temperatures and its correlation with thermal expansion characteristics were studied. It is believed that the functional groups that produce hydrogen bonds and hydrogen bond receptors in the crystal structure of α-NTO under thermal stimulation play a leading role. At the same time, compared with the thermal expansion characteristics of other explosive crystals, the influence of crystal packing on the thermal stability of explosive crystal structure was analyzed. The results show that the thermal expansion anisotropy of layered packing explosive crystals with strong hydrogen bonding is more obvious.</p

The Temperature-Dependent Thermal Expansion of 2,6-Diamino-3,5-dinitropyrazine-1-oxide Effected by Hydrogen Bond Network Relaxation

<div><p>The temperature-dependent thermal expansion of 2,6-diamino-3,5-dinitropyrazine-1-oxide (LLM-105) was investigated by using powder X-ray diffraction (PXRD) together with Rietveld refinement to estimate the dimension at a crystal lattice level. In the temperature range of 30–200°C, the coefficient of thermal expansion (CTE) of LLM-105 is temperature dependent, which is different from other explosives, such as hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), 2,2′,4,4′,6,6′-hexanitrostilbene (HNS) and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX), with constant CTEs. The results of temperature-dependent infrared (IR) spectra indicated that the intermolecular hydrogen bond network relaxes with increasing temperature, which results in temperature-dependent thermal expansion. In this work, more accurate CTEs for LLM-105 crystals are obtained and the effects of the hydrogen bond network on the thermal expansion are further clarified. These results are beneficial to the design of materials with structural peculiarities and as-expected thermal expansion to satisfy different application requirements.</p></div

High-Yielding and Continuous Fabrication of Nanosized CL-20-Based Energetic Cocrystals via Electrospraying Deposition

Energetic cocrystals, especially CL-20-based cocrystals, have attracted a wide range of attention due to their low sensitivity and impressive detonation performance. In this study, a series of nanosized CL-20-based energetic cocrystals were successfully fabricated by electrospray deposition. For CL-20/TNT nanococrystals, the influence of different solvents on the morphology and crystal structure of as-prepared cocrystals were investigated. The results showed that all the electrosprayed CL-20/TNT samples were partial formation of cocrystals and particles obtained from ketone had smaller size than those obtained from ethyl solvents. In contrast, electrosprayed CL-20/DNB nanococrystals had completely formed the cocrystal structure proved by DSC and PXRD. Moreover, the terahertz (THz) result confirmed the formation of intermolecular hydrogen bonds. Additionally, we have fabricated the CL-20/TNB cocrystals for the first time by using electrospray method. The PXRD and DSC results confirmed the formation of this novel energetic cocrystal. Expectedly, all the electrosprayed nanosized CL-20-based cocrystals exhibited visible reduced impact sensitivity compared with raw CL-20. The electrospray can thus offer a flexible and versatile approach for continuous and high-yielding synthesis of nanosized energetic cocrystals with preferable safety performance, and provide an efficient screening to quickly distinguish whether two energetic materials can form a cocrystal

Occupancy Model for Predicting the Crystal Morphologies Influenced by Solvents and Temperature, and Its Application to Nitroamine Explosives

A new occupancy model for predicting the crystal morphologies influenced by solvent and temperature is proposed. In the model, the attachment energy is corrected by a relative occupancy, which is the occupancy of a solute molecule relative to the total ones of a solute molecule and a solvent molecule. The occupancy is defined proportional to the averaged interaction energy between a solute or solvent molecule and a crystal surface. The validity of the model is confirmed by its successful applications to predict the crystal morphologies of a class of well-known nitroamino explosives hexahydro-1,3,5-trinitro-1,3,5- triazine, octahydro-1,3,5,7-tertranitro-1,3,5,7-tetrazocine and 2,4,6,8,10,12-hexanitrohexaaz-aisowurtzitane grown in solution. Furthermore, the applications of this model regarding concentration, molecular diffusion ability in solution, and mixed solvents are prospected

Growth of 2D Plate-Like HMX Crystals on Hydrophilic Substrate

Two-dimensional (2D) plate-like HMX crystals have been grown first on hydrophilic substrate using an evaporation/solvent–nonsolvent crystallization technique. As-grown crystals have been investigated by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectra, scanning electron microscopy (SEM), confocal laser scanning microscope (CLSM), and atomic force microscopy (AFM). The results unambiguously indicate that the plate-like crystals with large (011) faces are β-HMX, and the fluctuations in the smooth area of (011) face are monomolecular or bimolecular HMX, which suggests the mechanism of monomolecular stacking pattern and layer-by-layer growth. Furthermore, the distinct recess consisting of hexagons parallel to each other is observed on the center of the (011) face. The special growth morphology, which is markedly different from that by the classical spiral growth, is attributed mainly to the negative concentration gradient in the constrained condition

From a Novel Energetic Coordination Polymer Precursor to Diverse Mn₂O₃ Nanostructures: Control of Pyrolysis Products Morphology Achieved by Changing the Calcination Atmosphere

A novel strategy to fabricate diverse α-Mn₂O₃ nanostructures from the nitrogen-rich energetic coordination polymer (ECP) [Mn­(BTO)­(H₂O)₂]_<i>n</i> (BTO = 1<i>H</i>,1′<i>H</i>-[5,5′-bitetrazole]-1,1′-bis­(olate)) has been developed by changing the pyrolysis atmosphere. The results show that the energetic constituent and calcination environment are vital factors to get quite different morphologies of pyrolysis products. When the calcination reaction occurs under N₂ or O₂, rod-shaped mesoporous α-Mn₂O₃ with a large specific surface of 50.2 m²·g^–1 and monodispersed α-Mn₂O₃ with a size of 10–20 nm can be obtained, respectively, which provides a new platform to prepare specific shapes and sizes of manganese oxides. Inspired by the transformation of <b>1</b> under O₂ atmosphere, we applied an in situ generated ultrafine α-Mn₂O₃ catalyst in the decomposition of ammonium perchlorate (AP) using ECP <b>1</b> as a precursor. The catalytic process of AP shows a remarkable decreased decomposition temperature (271 °C) and a narrower decomposition interval (from 253 to 275 °C). To our best knowledge, with such a low metal loading (0.65 wt %), the catalytic performance of in situ generated monodispersed ultrafine α-Mn₂O₃ is by far the best, which suggests that this ultraefficient catalyst has great potential in AP-based propellants

Evident Hydrogen Bonded Chains Building CL-20-Based Cocrystals

We report two kinds of evident hydrogen bonded chains constructing two binary cocrystals of 2,4,6,8,10,12-hexanitrohexaazaisowurtzitane (CL-20) with <i>para</i>-benzoquinone (<b>1</b>) and 1,4-naphthoquinone (<b>2</b>): one kind is the CL-20 molecule chains linked by <i>R</i>₂²(6) hydrogen bonds, and the other is connected by CL-20 and coformer (<b>1</b> or <b>2</b>) molecules alternately through <i>R</i>₂¹(5) hydrogen bonds. All chains extend to the entire cocrystals CL-20/<b>1</b> and CL-20/<b>2</b> with crossing points of CL-20 molecules. In contrast to the unremarkable intermolecular interactions in observed CL-20 polymorphs and cocrystals, these two kinds of chains in CL-20/<b>1</b> and CL-20/<b>2</b> are evident and can be readily understood using the definition of supramolecular synthons. Moreover, the thermal behaviors, impact sensitivity, and detonation properties of these two energetic cocrystals are reported

Three Energetic 2,2′,4,4′,6,6′-Hexanitrostilbene Cocrystals Regularly Constructed by H‑bonding, π‑Stacking, and van der Waals Interactions

Three new energetic 2,2′,4,4′,6,6′-hexanitrostilbene (HNS) cocrystals, HNS/4,4′-bipyridine, HNS/<i>trans</i>-1,2-bis­(4-pyridyl)­ethylene, and HNS/1,2-bis­(4-pyridyl)­ethane have been synthesized. A good geometric match and rich H-bonds have been observed between the selected coformer and HNS molecules in all three cocrystals. According to similar configuration and arrangement of HNS–coformer H-bonds, coformer–coformer π-stacking, and HNS–HNS H-bonding interactions, the three cocrystals have a common cocrystal architecture and show high thermal stability and improved sensitivity. This study is helpful for understanding the formation mechanism of energetic cocrystals and the design of new energetic cocrystals

Five Energetic Cocrystals of BTF by Intermolecular Hydrogen Bond and π‑Stacking Interactions

Five novel BTF (benzotrifuroxan) cocrystals, possessing a similar density to RDX (1,3,5-trinitrohexahydro-1,3,5-triazine), have been prepared and reported first. Their single-crystal structures are presented and discussed. Interactions between cocrystal formers are discussed with shifts in the IR spectra providing additional support for the presence of various interactions. Hydrogen-bonding and π-stacking interactions are found to be the most prominent. Especially, the interactions between electron-poor π-systems of BTF and electron-rich groups of other cocrystal formers such as nitro groups of TNB exist commonly in all five novel cocrystals. This kind of interaction can be a more potential driving force for energetic cocrystals, since explosives with poor active hydrogen bonds are usually hard to form cocrystals with other explosives for the lack of strong intermolecular interactions. Because of the changes in structure, the physicochemical characteristics including density and melting point together with energetic properties of BTF altered after cocrystallization. All of the densities are between both of the cocrystal formers. Cocrystals of BTF with TNT and TNB have impact sensitivities between those of both cocrystal formers, while the remaining three cocrystals (BTF/TNA, BTF/MATNB, and BTF/TNAZ) all are more sensitive than either cocrystal former. It indicates that a cocrystal with TNT or TNB can reduce the shock sensitivity of BTF; especially, the cocrystal BTF/TNB not only has a lower sensitivity than RDX but also equal energetic properties, which potentially improve the viability of BTF in explosive applications. This paper owns an important consideration in the design of future BTF and other explosive cocrystals, and the result provides some feasibility to improve the application of the high explosive BTF