Smokeless GAP‐RDX Composite Rocket Propellants Containing Diaminodinitroethylene (FOX‐7)

Composite rocket propellants prepared from nitramine fillers (RDX or HMX), glycidyl azide polymer (GAP) binder and energetic plasticizers are potential substitutes for smokeless double‐base propellants in some rocket motors. In this work, we report GAP‐RDX propellants, wherein the nitramine filler has been partly or wholly replaced by 1,1‐diamino‐2,2‐dinitroethylene (FOX‐7). These smokeless propellants, containing 60% energetic solids and 15% N‐butyl‐2‐nitratoethylnitramine (BuNENA) energetic plasticizer, exhibited markedly reduced shock sensitivity with increasing content of FOX‐7. Conversely, addition of FOX‐7 reduced the thermochemical performance of the propellants, and samples without nitramine underwent unsteady combustion at lower pressures (no burn rate catalyst was added). The mechanical characteristics were quite modest for all propellant samples, and binder‐filler interactions improved slightly with increasing content of FOX‐7. Overall, FOX‐7 remains an attractive, but less than ideal, substitute for nitramines in smokeless GAP propellants.     

High‐Temperature Structural Transformations of 1,1‐Diamino‐2,2‐dinitroethene (FOX‐7)

Stuctural transformations of 1,1‐diamino‐2,2‐dinitroethene (FOX‐7) were investigated in the temperature range 298–513 K by means of DSC, TG, isothermal calorimetry, PXRD, IR spectroscopy, and electron microscopy. The data obtained confirm the existence of the high‐temperature δ‐FOX‐7 polymorph stable above 480 K. The heat effect of the γ→δ transformation is − 4.6 J g⁻¹ (−680 J mol⁻¹). Metastable γ‐phase formed in the reverse process δ→γ has a perfect crystal structure and is stable towards thermal decomposition. Possible mechanisms of sharp deceleration of thermal decomposition of FOX‐7 at the 40 % conversion are discussed.     

FOX-7晶体形貌对感度的影响

通过在DMSO/H2O、冰醋酸、环己酮、乙腈、DMF/H2O溶剂中重结晶得到FOX-7晶体,采用扫描电子显微镜(SEM)、傅里叶变换红外光谱法(FTIR)、差示扫描量热法(DSC)对其进行了表征,测试了不同晶体的机械感度。结果表明,在不同溶剂中重结晶得到的FOX-7晶体形貌与粒径变化较大,在DMF/H2O中重结晶的FOX-7晶体形貌较好,接近于对称的球体;5种溶剂中得到的FOX-7晶体未发生晶型转变,均为α晶型;在DMSO/H2O和DMF/H2O中重结晶得到的FOX-7晶体的感度最低(撞击感度为4%,摩擦感度为4%),在环己酮中重结晶FOX-7晶体的感度最高(撞击感度为8%,摩擦感度为48%)。     

Application of Thin Layer Chromatography for Monitoring of FOX‐7 Synthesis

In this paper, results of the research on the application of thin layer chromatography (TLC) for the determination of 1,1‐diamino‐2,2‐dinitroethene (FOX‐7, DADNE) and its precursors produced in the synthetic path starting from 2‐methylpyrimidine‐4,6(1H,5H)‐dione are presented. Analytical parameters of the substances and methodology of their quantitative analysis were determined, and the results obtained were used for monitoring the FOX‐7 synthesis process.     

Partial Reparametrization of the BKW Equation of State for DNAN‐Based Melt‐Cast Explosives

DNAN‐based melt‐cast explosives are a type of new, insensitive munitions (IM) explosives. Quickly determining munitions’ explosive properties is extremely important during the formulation design stage. The aim of this study was to partially reparameterize BKW‐EOS (only β and κ were reparameterized on the basis of the parameters (α , β , κ , and θ ) of classical BKW‐RDX set and BKW‐TNT set) to more accurately predict the properties of DNAN‐based melt‐cast explosives. A new set of parameters β and κ was obtained (β =0.19, κ =9.81) according to measured detonation velocity and detonation pressure for ideal DNAN‐based melt‐cast formulations (DNAN/RDX and DNAN/HMX). For non‐ideal DNAN‐based melt‐cast formulations (DNAN/RDX/Al and DNAN/HMX/Al), aluminum oxidation degree was first determined according to the measured detonation heat; then, another new set of parameters β and κ was obtained in the same way as the ideal formulations (β =0.24, κ =8.5). The predicted detonation properties with BKW reparametrization for DNAN‐based melt‐cast explosives agreed with the measured data.     

Facile Preparation of Self‐Sensitized FOX‐7 with Uniform Pores by Heat Treatment

Self‐sensitized FOX‐7 (1,1‐diamino‐2,2‐dinitroethylene) was prepared by a facile heat treatment process near the decomposition temperature. Field emission scanning electron microscopy (FE‐SEM) shows the self‐sensitized FOX‐7 becomes multiple layers and porous after heat treatment. N₂ adsorbance measurements revealed that its specific surface area (6.754 m² g⁻¹) is 20 times of the area of expanded ammonium nitrate. The SAXS tests further indicate the existence of a large amount of voids in self‐sensitized FOX‐7 and the pore size is about 30 nm, belonging to mesopore (2.0–50 nm). Based on the analysis of X‐ray powder diffraction (XRD), the self‐sensitized porous FOX‐7 consists of α‐phase and a spot of γ‐phase. The TG‐DSC results show that the self‐sensitized FOX‐7 exhibits excellent thermal stability. The impact, frication and electrostatic spark sensitivities of self‐sensitized FOX‐7 also have considerable enhancement. This new method provides a promising route for exploring new green primary explosive replacements.     

Review on the Reactivity of 1,1‐Diamino‐2,2‐dinitroethylene (FOX‐7)

1,1‐Diamino‐2,2‐dinitroethylene (FOX‐7) is a novel high‐energy insensitive material with good thermal stability and low sensitivity, and exhibits excellent application performance in the field of insensitive ammunitions and solid propellant. Although FOX‐7 is simple in molecular composition and structure, its chemical reactivity is abundant and surprising, including salification reaction, coordination reaction, nucleophilic substitution reaction, acetylate reaction, oxidizing reaction, reduction reaction, electrophilic addition reaction, among other reactions. These reactions are systemically summarized and some reaction mechanisms are analyzed in this review.     

Directional Interactions of α‐Particles with FOX‐7. A DFT Study

FOX‐7 is exposed to the effects of α‐particles from selected directions of approach. Various energies and properties of these composite FOX‐7 systems (FOX‐7+α‐particle) are obtained. The effect of α‐particles on FOX‐7 is drastic. The CC double bond turns into a single bond and one of the C NO₂ bonds highly elongates. The approach from the side of amino groups results more stable composite system compared to the approach from the side of nitro groups.     

A First Principles Density Functional Study of Crystalline FOX‐7 Chemical Decomposition Process under External Pressure

We report on a first principles analysis of chemical decomposition reaction in a crystalline FOX‐7 (1,1‐diamino‐2,2‐dinitroethylene) molecule, which is a good candidate for insensitive energetic materials. Our calculations are based on variable‐cell shape methods under pressure, density functional theory with localized numerical orbital and pseudopotential, together with ab initio biasing molecular dynamics. The calculated crystal structure and equation of state (pressure vs. volume) up to 8 GPa agrees well with the corresponding experimental data. A chemical decomposition by intermolecular hydrogen transfer is found at higher pressure. This decomposition appears to be driven by a weakening in the chemical hardness. This suggests that the molecular HOMO and LUMO orbital energy difference is decreased when intermolecular hydrogen transfers occur, and for the FOX‐7 crystal the band gap is narrowed with increasing external pressure.     

γ‐FOX‐7: Structure of a High Energy Density Material Immediately Prior to Decomposition

1,1‐Diamino‐2,2‐dinitroethene, C₂H₄N₄O₄ (FOX‐7), is a novel high energy density material with low friction and impact sensitivity and a high activation barrier to detonation. In this study, the previously unknown crystal structure of the γ‐polymorph of trimorphic FOX‐7 is reported. γ‐FOX‐7 is stable from ∼435 K until the compound decomposes just above 504 K. A single crystal of α‐FOX‐7 (P2₁/n, Z=4, a=694.67(7) pm, b=668.87(9) pm, c=1135.1(1) pm, β=90.14(1)°, T=373 K) was first transformed into a single crystal of β‐FOX‐7 (P2₁2₁2₁, Z=4, a=698.6(1) pm, b=668.6(2) pm, c=1168.7(3) pm, T=423 K) and then into a single crystal of γ‐FOX‐7 at 450 K. The γ‐FOX‐7 crystal was then subsequently quenched to 200 K. The structure of γ‐FOX‐7 (P2₁/n, Z=8, a=1335.4(3) pm, b=689.5(1) pm, c=1205.0(2) pm, β=111.102(8)°, T=200 K) consists of four planar layers, each containing two crystallographically independent FOX‐7 molecules found in the asymmetric unit.     

Thermal and Sensitivity Study of Dihydroxyl Ammonium 5,5′‐Bistetrazole‐1,1′‐diolate (TKX‐50)‐based Melt Cast Explosive Formulations

Dihydroxyl ammonium 5,5′‐bistetrazole‐1,1′‐diolate (TKX‐50) is a promising energetic material with predicted performance similar to RDX as well as to CL‐20. In the present study, TKX‐50 was evaluated as a possible replacement for RDX in TNT‐based, aluminized as well as non‐aluminized melt cast formulations. Thermal analysis reveals the compatibility of TKX‐50 with benchmark explosives like RDX and TNT in explosive formulations. This paper describes the thermal and sensitivity study of TKX‐50 with RDX and TNT‐based melt cast explosives. The result indicated that TKX‐50 can be effectively used as a RDX replacement in melt cast explosive formulations. TKX‐50/TNT‐based aluminized composition shows more thermal stability than RDX/TNT based composition, which clearly indicated the usefulness of TKX‐50 in melt cast explosive formulations.     

Synthesis and Characterization of 1‐Nitroguanyl‐3‐nitro‐5‐amino‐1,2,4‐triazole

The synthesis of 1‐nitroguanyl‐3‐nitro‐5‐amino‐1,2,4‐triazole (ANTA‐NQ) ( 1 ) with good yield and high purity is described. DSC analysis showed that the material displays good thermal stability. An X‐ray crystallographic analysis confirms the structure of this material, as well as displays intramolecular hydrogen bonding. A gas pycnometry density for this material was measured to be 1.79 g cm⁻³. The heat of formation of this material was also measured. These data, along with the molecular formula were used as inputs to calculate the detonation velocity and detonation pressure using the Cheetah thermochemical code. The sensitivity of this material towards impact, spark and friction was also measured, as well as its vacuum thermal stability. The 3‐azido derivative 2 was also prepared and its properties are described as well. The above data show that (ANTA‐NQ) may be a high performing material with low sensitivity and good thermal stability.     

Effects of Additives on ε‐HNIW Crystal Morphology and Impact Sensitivity

Crystals of γ‐HNIW were transformed into crystals of ε‐HNIW by application of a drowning‐out process in the presence of different additives, namely ethylene glycol, triacetin, and aminoacetic acid. They show different effects on the crystal morphology of ε‐HNIW and cause less angular and more regular structures. Investigation of the sensitivities of the different ε‐HNIW crystals shows that their angles and regularity have an influence on the impact sensitivity. Aminoacetic acid selectively inhibits the growth of individual ε‐HNIW crystal faces to modify the morphology into spherical shape, these ε‐HNIW crystals are of much lower sensitivity, even compared with general RDX and HMX explosives.     

反相高效液相色谱法测定FOX-7的纯度

采用十八烷基非极性键合固定相色谱柱,以甲醇、水、乙酸为流动相,在流速1.0 ml/min,检测波长252 nm,柱温为室温的条件下测定FOX-7的纯度.结果表明,FOX-7与可能的副产物有很好的分离（分离度分别为1.04和1.96）,当浓度为6.6～66 μg/ml时,色谱峰高（H）与FOX-7浓度（C）呈线性关系：H=1.5047C＋0.7857,相关系数为r=0.9998;采用校正因子归一化法,测得 FOX-7样品纯度为99.70%,RSD为0.22%（n=3）.     

FOX-7和RDX基含铝炸药的冲击起爆特性

为研究FOX-7和RDX基含铝炸药的冲击起爆特性,对其进行了冲击波感度试验和冲击起爆试验,结合冲击波在铝隔板中的衰减特性,确定了FOX-7和RDX基含铝炸药的临界隔板值和临界起爆压力,并通过锰铜压阻传感器记录了起爆至稳定爆轰过程压力历程的变化。结果表明,以Φ40mm×50mm的JH-14为主发装药时,FOX-7和RDX基含铝炸药临界隔板值分别为37.51和34.51mm,对应的临界起爆压力为10.91和11.94GPa;起爆压力为11.58GPa时,FOX-7炸药的到爆轰距离为25.49~30.46mm,稳定爆轰后的爆轰压力为27.68GPa,爆轰速度为8 063m/s;起爆压力为14.18GPa时,RDX基含铝炸药的到爆轰距离为17.27~23.53mm,稳定爆轰后的爆轰压力为17.16GPa,爆轰速度为6 261m/s。     

Simultaneous Determination of Multiple Mechanical Parameters for a DNAN/HMX Melt‐Cast Explosive by Brazilian Disc Test Combined with Digital Image Correlation Method

Tensile strength, tensile modulus, compressive modulus, and Poisson's ratio are important mechanical parameters for brittle explosives. Generally, these parameters are separately measured by several different tests in which the homogeneity of specimens cannot be guaranteed, thus requiring a simultaneous determination of these mechanical parameters by one test. In this paper, simultaneous determination of multiple mechanical parameters of a DNAN/HMX melt‐cast explosive using Brazilian disc test combined with digital image correlation (DIC) method is described. The method would allow tensile strength, tensile modulus, compressive modulus, and Poisson′s ratio to be obtained simultaneously by one test, when the influences of rigid body motion have been effectively removed. The method principle was introduced in detail in this paper. The effect of temperature on the mechanical properties and the difference between the tensile modulus and compressive modulus of the DNAN/HMX melt‐cast explosive were investigated. The elastic constants and tensile strength were quantitatively analyzed and are qualitatively correct, which demonstrates the effectiveness of the presented method.     

Covalent and Ionic Insensitive High‐Explosives

Ongoing research into new insensitive energetic materials with low sensitivity toward accidental stimuli, high thermal stability and high performance characteristics is undertaken in many research groups worldwide. In order to obtain promising compounds, which fulfil the sensitivity, stability, and performance requirements, researchers use many different strategies. One of the most promising approaches is the synthesis of novel explosives with tailored physico‐chemical properties. In this review the synthesis and properties of some both covalent (NTO, TEX, FOX‐7, ADNP, DNPPs) and ionic (salts of ANDP and DNPP) insensitive explosives are presented, which are of high interest to this field of research.