Efficient Sensitivity Reducing and Hygroscopicity Preventing of Ultra‐Fine Ammonium Perchlorate for High Burning‐Rate Propellants

In this research, several inert materials, including some functional carbon materials, paraffin wax and the well‐known insensitive energetic material 1,3,5‐triamino‐2,4,6‐trinitrobenzene (TATB) were selected to reduce the undesirable high sensitivity and hygroscopicity of ultra‐fine ammonium perchlorate (UF‐AP) via polymer modified coating. Structure, sensitivity, thermal and hygroscopicity performances of the UF‐AP based composites were systematically studied by scanning electron microscopy, sensitivity tests, thermal experiments, contact angle, and hygroscopicity analysis. The results showed that both the impact and friction sensitivity of UF‐AP can be remarkably reduced, respectively, with only a small amount of 2 % (in mass) desensitization agents. Meanwhile, improved thermal decomposition was gained, and the hygroscopicity can also be reduced to a large extent. Propellants containing 10 % coated UF‐AP in mass were processed and tested, the burning rate reached 45.7 mm s⁻¹, 50 % higher compared with that of normal AP, with remarkably reduced impact sensitivity from 11.5 J to 29.6 J and friction sensitivity from 76 % to 28 %.     

Laser‐Induced Deflagration of Unconfined HMX – The Effect of Energetic Binders

The effect of three energetic binders [poly(3‐methyl‐3‐nitratomethyloxetane (polyNIMMO), polyglycidyl nitrate (polyGLYN) and an energetic polyphosphazene (PPZ‐E) – all at 10%] on the unconfined laser‐induced deflagration of cyclotetramethylene tetranitramine, commonly known as High Melting point Explosive (HMX) by a near IR (NIR) diode laser (801 nm) has been examined. Hydroxyl terminated polybutadiene (HTPB) and PPZ (the precursor to PPZ‐E – before nitration) were used as reference materials. The formulations required the addition of an optical sensitizer – carbon black (CB) – for ignition. At the designated threshold flux density of 2.3 kW cm⁻², a minimum of ∼1 wt.‐% CB was needed for the reliable ignition of unbound HMX and its formulations with polyGLYN, PPZ‐E and PPZ. Under similar conditions HMX/polyNIMMO and HMX/HTPB required 3% CB. Ignition maps (ignition time versus laser flux density) have been constructed for the five formulations. Comparison of ignition times and ignition energy densities for HMX and HMX/polyGLYN showed this binder to have only a marginal effect. In contrast, HTPB, PPZ and PPZ‐E all retarded HMX ignition at the threshold flux density, but showed negligible effect at higher flux densities. As PPZ and PPZ‐E produced both similar delays in the ignition time and similar increases in the flame development times (10–90%) at the threshold flux density, the inhibition of the HMX ignition by these PPZs appears to be largely independent of the polymer energy content. Such characteristics could be useful for high performance and insensitive energetic formulations. PolyNIMMO (3% CB) increased the ignition time of HMX only slightly at 2.3 kW cm⁻². However, at this threshold flux level the HMX flame development times with polyNIMMO or HTPB were much longer than that for the unbound material; this effect is attributed to the enhanced CB content.     

Energetic Salts of 5‐(5‐Azido‐1H‐1,2,4‐triazol‐3‐yl)tetrazole

Several metal and nitrogen‐rich salts of the recently presented 5‐(5‐azido‐1H‐1,2,4‐triazol‐3‐yl)tetrazole (AzTT), including silver ( 1 ), copper(I) ( 2 ), potassium ( 3 ), cesium ( 4 ), copper(II) ( 7 ), ammonium ( 8 ), and guanidinium ( 9 ), as well as the respective double‐salts of 3 , 4 , 8 and 9 , were prepared and well characterized by IR and multinuclear (¹H, ¹³C, ¹⁴N) NMR spectroscopy, DSC, mass spectrometry, elemental analysis and one ( 4 ) additionally by single‐crystal X‐ray diffraction. The sensitivities towards impact, friction and electrostatic discharge were determined according to BAM standards, revealing most of the metal salts as highly sensitive and the nitrogen‐rich salts as insensitive. The metal salts were further tested for their ability of being primary explosives.     

Potential Energetic Plasticizers on the Basis of 2,2‐Dinitropropane‐1,3‐diol and 2,2‐Bis(azidomethyl)propane‐1,3‐diol

Different carboxylic acid derivatives of 2,2‐dinitropropane‐1,3‐diol (DNPD) and 2,2‐bis(azidomethyl)propane‐1,3‐diol (BAMP) were synthesized to investigate their suitability as energetic plasticizers. The syntheses were carried out using acyl chlorides of acetic, propionic, and butyric acid. The obtained products were characterized by elemental analysis, NMR, and IR spectroscopy. The energetic properties of the synthesized compounds were calculated on the basis of the computed heats of formation at the CBS‐4M level of theory using the EXPLO5 version 6.02 computer code. Investigations of physical stabilities were carried out using BAM drop hammer and friction tester. Low and high temperature behavior was determined by differential scanning calorimetry (DSC). The energetic and physical properties of the synthesized compounds were compared to the literature known energetic plasticizers N‐butyl nitratoethylnitramine (BuNENA) and diethylene glycol bis(azidoacetate) ester (DEGBAA). For analyzing the plasticizing abilities, mixtures of glycidyl azide polymer (GAP) and poly(3‐nitratomethyl‐3‐methyloxetan) (polyNIMMO) were prepared with both propionyl based compounds in different ratios and investigated regarding their glass transition temperatures and viscosity. Both compounds showed plasticizing effects in the range of BuNENA.     

Controllable Fabrication of CuO/Ammonium Perchlorate (AP) Nanocomposites through Ceramic Membrane Anti‐Solvent Recrystallization

To improve the dispersion of CuO nanoparticles in ammonium perchlorate (AP), CuO/AP nanocomposites are designed and the novel ceramic membrane anti‐solvent crystallization (CMASC) method is applied to the nanocomposites synthesis. Typical experimental results demonstrate that nanocomposites with a size of less than 20 μm exhibit well‐defined hexahedral‐like structure and that the CuO nanoparticles are physically coated by AP crystals. The well‐dispersion of CuO nanoparticles and preparation of superfine AP crystals can be achieved at one step. The nucleation and growth mechanism of nanocomposites is discussed. To explore the actual formation process of the nanocomposites, relevant experiments are designed and carried out. The results are well consistent with previous assumptions and verify that several parameters, including feeding rate, volume ratio of matched solvent and anti‐solvent, can be employed to manipulate the size and morphology of the nanocomposites. The catalytic activity of CuO nanoparticles in the nanocomposites exhibits superior performance.     

The High‐Pressure Characterization of Energetic Materials: 1,4‐Dimethyl‐5‐Aminotetrazolium 5‐Nitrotetrazolate

In‐situ high‐pressure room temperature synchrotron X‐ray diffraction and infrared microspectroscopy were used to examine the structural and vibrational properties and the equation of state of 1,4‐dimethyl‐5‐aminotetrazolium 5‐nitrotetrazolate (DMATNT). The X‐ray measurements show a smoothly varying pressure‐volume relationship to 20 GPa. However, the anisotropic ratios of the unit cell parameters reveal a discontinuity near 3.3 GPa, which can be attributed to an irreversible isostructural phase transition. A significant increase in the Infrared spectral intensity near this pressure coupled with Dayvdov splitting of the NO₂ bending and scissoring modes suggest the transition results in a skewing of the NO₂ groups and increasing asymmetry of the hydrogen bonding sublattice.     

Preparation and Characterization of Fe2O3/Ammonium Perchlorate (AP) Nanocomposites through Ceramic Membrane Anti‐Solvent Crystallization

A novel ceramic membrane anti‐solvent crystallization (CMASC) method was proposed to prepare Fe₂O₃/AP nanocomposites with core‐shell structure. For the preparation of Fe₂O₃/AP nanocomposites, several key advantages of the CMASC method are as follows. Firstly, both well‐dispersed Fe₂O₃ nanoparticles and the superfine AP preparation can be achieved at one step. Secondly, no non‐component of solid propellant was involved in this composite process. Thirdly, the size and morphology of Fe₂O₃/AP nanocomposites can be effectively controlled by using the ceramic membrane with regular pore structure as feeding template. The morphology and structure of Fe₂O₃/AP nanocomposites were characterized by inductively coupled plasma spectrophotometry (ICP), IR spectroscopy, SEM, and HRTEM. The results verified that the size and morphology of Fe₂O₃/AP nanocomposites are controllable, and the dispersion of Fe₂O₃ nanoparticles is greatly improved in Fe₂O₃/AP nanocomposites. Moreover, the thermal decomposition of the as‐prepared Fe₂O₃/AP nanocomposites was measured with TG‐DSC. The results showed that the Fe₂O₃ nanoparticles in Fe₂O₃/AP nanocomposites exhibit better catalytic activity on the thermal decomposition of AP. In addition, the mechanism was also discussed.     

Facile Preparation of AP/Cu(OH)2 Core‐Shell Nanocomposites and Its Thermal Decomposition Behavior

Ammonium perchlorate (AP)/Cu(OH)₂ core‐shell nanocomposites were successfully synthesized using a facile ultrasonic assisted‐coprecipitation synthesis route. The obtained AP/Cu(OH)₂ nanocomposites were characterized by means of powder X‐ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Its thermal decomposition was studied under the non‐isothermal conditions with thermogravimetric analysis and differential scanning calorimeter (TG‐DSC) techniques. In this procedure, SEM and TEM observations revealed that Cu(OH)₂ nanoparticles with an average size of 10–15 nm were uniformly deposited on the surface of AP particles. Detailed characterization results indicated that the existence of evidence of Cu(OH)₂. As expected, it was found that the AP/Cu(OH)₂ nanocomposites with mass fraction of 2 wt % Cu(OH)₂ remarkably decreased the peak temperature of high temperature decomposition of AP by 80.2 °C from approximately 441.3 °C to 361.1 °C. As compared with pure AP, the AP/Cu(OH)₂ nanocomposites show lower impact and friction sensitivity. These results may lead to potential applications of the AP/Cu(OH)₂ nanocomposites in the composite solid propellants for accelerating the thermal decomposition of AP.     

Thermal Stability Studies Comparing IMX‐101 (Dinitroanisole/Nitroguanidine/NTO) to Analogous Formulations Containing Dinitrotoluene

The 2,4,6‐trinitrotoluene (TNT) replacement, IMX‐101, containing 43.5 % 2,4‐dinitroanisole (DNAN), 19.7 % 3‐nitro‐1,2,4‐triazol‐5‐one (NTO) and 36.8 % nitro‐guanidine (NQ), has been certified for use as an insensitive munition. IMX‐101 has passed standardized performance, stability, and aging tests but in some categories was not necessarily an improvement over TNT or RDX. This study compared the thermal stability of DNAN and another low‐melting nitroarene, 2,4‐dinitrotoulene (DNT). When examined individually, DNAN was more stable; but formulated in IMX‐101 with NTO and NQ, the opposite was true. In two part mixtures, NQ had a similar acceleratory effect on the decomposition of both nitroarenes, while NTO had a greater impact on DNAN than on NTO. Ammonia, a reported decomposition product of both NQ and NTO, also accelerated the decomposition of both DNAN and DNT, with a larger impact on DNAN. The formation of dinitroaniline, potentially due to the interaction between the nitroarenes and ammonia, was detected by LC/MS as a decomposition product when either nitroarene was combined with NTO and/or NQ, indicating that this molecule may play a significant role in the decomposition mechanism. While not advocating the use of DNT in insensitive munitions formulations, this study addresses the importance of chemical compatibility as a criterion for selecting replacement components in formulations.     

Low Risk Synthesis of Energetic Poly(3‐Azidomethyl‐3‐Methyl Oxetane) from Tosylated Precursors

Azidated oxetanic polymers such as poly(3‐azidomethyl‐3‐methyl oxetane), are under investigation as “energetic” binder to be used as an alternative to polybutadiene in solid rocket propellants. The classic synthetic route for the production of the polymer is through an azidated monomer where the N₃⁻ functionality has been previously introduced by nucleophilic displacement of a suitable, usually a halogen, leaving group. However, this could involve critical steps with manipulation of a highly unstable liquid monomer. Here it is shown that the azidation can be performed as the final step of the preparation by substitution of the tosyl group in a preformed polymer. The procedure assures good yield and purity of the product and satisfactory rate of reaction, being the energetic functionality always kept in a safe form, which shows low shock and friction sensitivity. Poly(3‐azidomethyl‐3‐methyl oxetane) was prepared by azidation of poly(3‐tosyloxymethyl‐3‐methyl oxetane) in dimethylsulfoxide, testing several operating conditions. Moreover, hypothesizing a second order kinetics, the rate constant and the activation energy for the azidation step have been estimated.     

Investigation of the Solubility of 3,4‐Diaminofurazan (DAF) and 3,3′‐Diamino‐4,4′‐azoxyfurazan (DAAF) at Temperatures Between 293.15 K and 313.15 K

The solubilities of 3,4‐diaminofurazan (DAF) and 3,3′‐diamino‐4,4′‐azoxyfurazan (DAAF) were investigated in water, dichloromethane, acetonitrile, ethyl acetate, methanol, and acetone between 293.15 K and 313.15 K. The solubility was determined by high‐pressure liquid chromatography with ultraviolet detection. The solubilities of DAF and DAAF are increased with the increasing of temperature in all solvents studied. The enthalpy of solution in each solvent was calculated according to van't Hoff Equation.     

The High‐Pressure Characterization of Energetic Materials: 2‐Methyl‐5‐Nitramino‐2H‐Tetrazole

The isothermal structural properties, equation of state, and vibrational dynamics of 2MNT were studied under high‐pressure using synchrotron XRD and optical Raman and IR microspectroscopy. Analysis of the XRD patterns revealed no indication of a phase transition to near 15 GPa and the pressure‐volume isotherm remained smooth to 15 GPa. Near 15 GPa, significant sample damage was observed from the X‐ray beam which precluded the acquisition of patterns above this pressure. XRD and Raman spectroscopic measurements showed the monoclinic ambient condition phase of 2MNT remains the dominant phase to near 20 GPa, although a shift of the NO₂ IR active vibrational modes to lower frequencies suggested a subtle geometry modification not reflected in the XRD data.     

The High‐Pressure Characterization of Energetic Materials: 1‐Methyl‐5‐Nitramino‐1H‐Tetrazole

Pressure–volume relations and optical Raman and Infrared spectra of polycrystalline 1MNT have been obtained under quasi‐hydrostatic conditions up to 16 and 40 GPa, respectively, by using diamond anvil cell, synchrotron‐based angle‐resolved X‐ray diffraction, and microspectroscopy. The X‐ray measurements show that the pressure–volume relations remain smooth up to 16 GPa at room temperature, while vibrational measurements show no evidence of a phase transition to near 40 GPa. Anomalous increases of several vibrational intensities and bandwidths suggest that subtle molecular distortions and structural modifications occur in the crystal as pressure increases. Decompression experiments indicate the structural modifications are reversible.     

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.     

The Low‐Temperature High‐Pressure Phase Diagram of Energetic Materials: I. Hexahydro‐1,3,5‐Trinitro‐s‐Triazine

The reaction phase diagram of hexahydro‐1,3,5‐trinitro‐s‐triazine (RDX) has been studied as a function of temperature and pressure by Raman spectroscopy to 29 GPa and temperatures ranging from 4 to 298 K. Three stable phases (α, γ, and δ) have been found and their phase stabilities have been investigated. Phase boundaries were studied as a function of pressure and temperature, permitting a delineation of the various polymorph stability fields. A pressure–temperature reaction/phase diagram is constructed from the results of this study and compared to previous high temperature work.     

Measurement,Correlation and Thermodynamics of Solubility of 2,6‐Diamino‐3,5‐Dinitropyrazine‐1‐Oxide (LLM‐105) in Eight Solvents

The solubility of insensitive explosive 2,6‐diamino‐3,5‐dinitropyrazine‐1‐oxide (LLM‐105) in dimethyl sulphoxide (DMSO), N,N‐dimethylformamide (DMF), N‐methyl‐2‐pyrrolidone (NMP), N,N‐diethylformamide (DEF), 1,4‐dioxane, 1,4‐butyrolactone, ethyl acetate and 1‐butyl‐3‐methylimidazolium trifluoromethanesulfonate ([Bmim]CF₃SO₃), were measured by a polythermal method in the temperature range of 293.15 K to 375.15 K at the atmospheric pressure. The solubility of LLM‐105 decreased in the order of DMSO, NMP, DMF, DEF, 1,4‐butyrolactone, [Bmim]CF₃SO₃, 1,4‐dioxane, ethyl acetate. With higher temperature, the solubility of LLM‐105 increased in all solvents. The solubility data was correlated against temperature with the modified Apelblat equation and Ideal solution model. In addition, the dissolution enthalpy, entropy, and mole Gibbs free energy of LLM‐105 in each solvent were also calculated from the experimental solubility data by using van′t Hoff equation with the temperature dependence. The results show that the dissolution process of LLM‐105 in these solvents is endothermic and the mechanism is the entropy‐driving. DMSO is suggested as the appropriate solvent for the cooling crystallization or drowning‐out crystallization of LLM‐105.     

Preparation and Molecular Structure of {[Ca(CHZ)2(H2O)](NTO)2⋅3.5H2O}n

The title compound {[Ca(CHZ)₂(H₂O)](NTO)₂⋅3.5H₂O}_n was synthesized by using an aqueous solution of calcium 3‐nitro‐1,2,4‐triazol‐5‐onate and carbohydrazide (CHZ, NH₂NHCONHNH₂). Its molecular structure was determined by X‐ray diffraction and its crystals have monoclinic form, with space group C2/c, where a=2.4483(4) nm, b=1.2581(2) nm, c =1.6269(3) nm, β=121.168(12)°, V=4.2879(13) nm³, Z=8, d_c=1.727 g⋅cm⁻³, μ (Mo K_α)=3.9 cm⁻¹, M=557.47, F(000)=2312. The coordination polyhedron is a tricapped trigonal prism in a tetradecahedron with a coordination number of nine. The whole molecule has many long chains formed through the carbohydrazide bridges, and every long chain is unlimited along the c axis. The long chains are linked by hydrogen bonds to form the crystal structure.     

Synthesis of Poly(3,3‐Bis‐Azidomethyl Oxetane) via Direct Azidation of Poly(3,3‐Bis‐Bromo Oxetane)

In order to avoid using highly unstable and sensitive monomer 3,3‐bis‐azidomethyl oxetane, poly(3,3‐bis‐azidomethyl oxetane) (PBAMO) was successfully synthesized via azidation of poly(3,3‐bis‐bromo oxetane) (PBBrMO) in the aprotic and polar solvent cyclohexanone in the presence of a catalyst. It was found that the azidation proceeded very fast and almost completed in 6 h when the reaction temperature was up to 115 °C. PBAMO was characterized by gel permeation chromatography (GPC), Fourier transform infrared spectrometry (FTIR), hydrogen nuclear magnetic resonance (¹H NMR), and carbon nuclear magnetic resonance (¹³C NMR).     

Chemical Transformation of Octahydro‐1,3,5,7‐tetranitro‐1,3,5,7‐tetrazocine (HMX) Induced by Low Energy Electron Beam Irradiation

The effects of 8.0×10⁻¹⁷ J (500 eV) and 3.2×10⁻¹⁹ J (2 eV) electrons on chemical structure of octahydro‐1,3,5,7‐tetranitro‐1,3,5,7‐tetrazocine (HMX) were studied in situ, under ultra‐high vacuum conditions using a combination of X‐ray photoelectron spectroscopy (XPS) and quadrupole mass spectrometry. XPS data indicated that electrons impact by 8.0×10⁻¹⁷ J for 30 s caused a decrease in nitro group concentration, and a little shift in the binding energy of the nitrogen 1s peak. Such a phenomenon was found at very low kinetic energy (3.2×10⁻¹⁹ J) with time evolution. Quadrupole mass spectrometry detected gas desorption after electron irradiation included H₂O and H₂ mostly. Microscopy‐IR spectroscopic investigations also proved that the intensity of nitro groups of HMX after irradiation decreased compared with those of the pristine HMX. We attributed the structure changes obtained by XPS and IR spectroscopy result in a chemical transformation, which was associated with low‐energy dissociative electron attachment (DEA) of surface contaminants followed by deoxidization reactions to form the product molecules.     

Solubility Calculation of Oil‐Conta‐minated Drill Cuttings in Supercritical Carbon Dioxide Using Statistical Associating Fluid Theory (PC‐SAFT)

Supercritical fluid extraction is a new technology that could be effectively used to treat oil‐contaminated drill cuttings generated during drilling for oil and gas. In this work, the solubility of oil‐contaminated drill cuttings in supercritical carbon dioxide is obtained by an experimental flow type apparatus. The solubility was measured at 200 bar pressure, over a temperature range of 55–79.5 °C. The measured solubility and experimental data for oil in drill cuttings were correlated using the PC‐SAFT, PR and SRK EOS models, without any adjustable parameters. Average absolute derivations of less than 15.1 %, 98.7 %, and 99.3 % are achieved between predicted and experimental values for the PC‐SAFT, PR and SRK EOS models, respectively, over a wide range of temperatures.