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.     

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.     

Calculation of the Detonation Velocities and Detonation Pressures of Dinitrobiuret (DNB) and Diaminotetrazolium Nitrate (HDAT‐NO3)

The enthalpies of combustion (Δ_combH) of dinitrobiuret (DNB) and diaminotetrazolium nitrate (HDAT‐NO₃) were determined experimentally using oxygen bomb calorimetry: Δ_combH(DNB)=5195±200 kJ kg⁻¹, Δ_combH(HDAT‐NO₃)=7900±300 kJ kg⁻¹. The standard enthalpies of formation (Δ_fH°) of DNB and HDAT‐NO₃ were obtained on the basis of quantum chemical computations at the electron‐correlated ab initio MP2 (second order Møller‐Plesset perturbation theory) level of theory using a correlation consistent double‐zeta basis set (cc‐pVTZ): Δ_fH°(DNB)=−353 kJ mol⁻¹, −1 829 kJ kg⁻¹; Δ_fH°(HDAT‐NO₃)=+254 kJ mol⁻¹, +1 558 kJ kg⁻¹. The detonation velocities (D) and detonation pressures (P) of DNB and HDAT‐NO₃ were calculated using the empirical equations by Kamlet and Jacobs: D(DNB)=8.66 mm μs⁻¹, P(DNB)=33.9 GPa, D(HDAT‐NO₃)=8.77 mm μs⁻¹, P(HDAT‐NO₃)=33.3 GPa.     

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.     

Evidence for a High‐Pressure Phase Transition of ε‐2,4,6,8,10,12‐Hexanitrohexaazaisowurtzitane (CL‐20) Using Vibrational Spectroscopy

The high‐pressure response of ε‐2,4,6,8,10,12‐hexanitrohexaazaisowurtizane (CL‐20) has been examined to 27 GPa in diamond anvil cells using vibrational spectroscopy. The results reveal evidence of an ε→γ pressure‐induced phase transition between 4.1 and 6.4 GPa and suggest the existence of a γ→ζ transition near 18.7 GPa. Several Raman and infrared frequencies were found to decrease in intensity as the phase boundaries are approached. An anomalous intensity increase was noted in the C N C infrared mode that is believed to result from an increase in the Raman cross‐section due to a stronger interlayer coupling under pressure.     

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.     

High‐Pressure Vibrational Spectroscopy of Hexahydro‐ 1,3,5‐Trinitro‐1,3,5‐Triazine (RDX)

The molecular‐level response of RDX to hydrostatic compression was examined in a diamond anvil cell using Raman spectroscopy. The pressure‐induced alterations in spectral profiles of the C N stretching mode (886 cm⁻¹) were studied up to 8.3 GPa. At pressures near 4.4 GPa, several changes of the C N stretching mode become immediately apparent in Raman spectrum, such as large frequency shifts, line broadening, mode splitting, and intensity changes, which are associated with the α–γ phase transition and rearrangement between the RDX molecules. The high pressure Raman spectra changes of the C N stretching mode are indicative of an α–γ phase transition, and also suggest the lowering of molecular symmetry and crystal symmetry, which are expected to provide some insight into RDX molecular stability and decomposition.     

Investigation of Hydrodynamics of High‐Temperature Fluidized Beds by Pressure Fluctuations

Hydrodynamics of a gas‐solid fluidized bed at elevated temperatures was investigated by analyzing pressure fluctuations in time and frequency domains. Sand particles were fluidized with air at various bed temperatures. At a constant gas velocity, the standard deviation, power spectrum density function, and wide‐band energy of pressure fluctuations reach a maximum at 300 °C. Increasing the temperature to this value causes larger bubble sizes and after the bubbles reach their maximum size, they break into smaller bubbles. The Archimedes number decreases with higher temperature and the type of fluidization becomes closer to that of Geldart A boundary at this maximum temperature. Based on estimation of the drag force acting on the emulsion phase, it was concluded that 300 °C was a transition temperature at which the drag force reaches a minimum due to a significant change of interparticle and hydrodynamic forces.     

静态与动态高压对含能材料热分解的影响

利用常压和高压差示扫描量热仪（DSC、PDSC）在动态和静态状下研究了CL-20、HMX、RDX、NC、NG、NG NC等几种含能材料的热分解,探讨了常压与高压条件下,静态与动态对这些含能材料热分解的影响。结果显示含能材料热分解受压力和动态气氛的影响有三种情况：1、热分解同时受到压力和动态气氛的影响;2、热分解既不受压力也不受动态气氛的影响;3、热分解只受压力的影响而不受动态气氛的影响。     

The Facile Synthesis and Energetic Properties of an Energetic Furoxan Lacking Traditional “Explosophore” Moieties: (E,E)‐3,4‐bis(oximomethyl)furoxan (DPX1)

Energetic furoxan (E,E)‐3,4‐bis(oximomethyl)furoxan (DPX1) was synthesized in 75 % yield, using a literature procedure, from a precursor readily available in one step from nitromethane. DPX1 was characterized for the first time as an energetic material in terms of calculated performance (V_det = 8245 m s⁻¹; p_C‐J = 29.0 GPa) and measured sensitivity (impact: 10 J; friction: 192 N; T_dec: 168 °C). DPX1 exhibits a sensitivity less than that of RDX, and a performance significantly higher than 2,4,6‐trinitrotoluene (TNT).     

Synthesis and Characterization of 3,3′‐Bisazidomethyl Oxetane‐3‐Azidomethyl‐3′‐Methyl Oxetane Alternative Block Energetic Thermoplastic Elastomer

3,3′‐Bisazidomethyl oxetane‐3‐azidomethyl‐3′‐methyl oxetane (BAMO‐AMMO) tri‐block copolymer was successfully synthesized by azidation of a polymeric substrate containing bromo leaving groups, and an alternative block energetic thermoplastic elastomer (ETPE) was prepared by chain extension reaction. The tri‐block copolymer was characterized by Fourier transform infrared (FTIR), ¹H NMR, and ¹³C NMR spectroscopy, X‐ray diffraction (XRD), and thermogravimetric analysis (TGA). It was found that the composition of the copolymer is nearly 1 : 1; crystallinity of the copolymer (71.81 %) is less than that of PBAMO (78.30 %). This is due to a partly mixture between soft and hard segments. Kinetic result shows that a crosslinking network is formed after the decomposition of azide group. Tensile strength of alternative block ETPE is 150 % of traditionally synthesized BAMO‐AMMO ETPE.     

The Insensitive Energetic Material Trifurazano‐oxacycloheptatriene (TFO): Synthesis and Detonation Properties

The high‐energy insensitive compound trifurazano‐oxacycloheptatriene (TFO) was first by synthesized through special etherification. The reaction mechanism and reaction conditions were discussed. TFO has a low melting point (78.6 °C) and good compatibility. TFO is insensitive to impact and friction and has similar detonation velocity (7.7 km s⁻¹) and detonation pressure (35.6 GPa) to RDX.     

1,4‐Bis‐[1‐Methyltetrazol‐5‐yl]‐1,4‐Dimethyl‐2‐Tetrazene: A Stable,Highly Energetic Hexamer of Diazomethane (CH2N2)6

1,4‐bis‐[1‐methyltetrazol‐5‐yl]‐1,4‐dimethyl‐2‐tetrazene a formal hexamer of diazomethane can be viewed as a new stable high energy density material (HEDM) with the properties necessary for a potential green chemistry gas generator. The physical properties of the new tetrazene were determined by drop hammer and combined IR and MS pyrolysis experiments. The structure and bonding are discussed on the basis of X‐ray, MO and NBO analysis.     

Synthesis,Characterization, and Energetic Properties of N‐Rich Salts of the 4,5‐Dicyano‐2H‐1,2,3‐triazole Anion

The synthesis and characterization of the 4,5‐dicyano‐2H‐1,2,3‐triazole anion in its 5‐aminotetrazole, 1,5‐diaminotetrazole, and 1,5‐diamino‐4‐methyl‐tetrazole salts are reported. All compounds were characterized by IR, ¹H NMR, and ¹³C NMR spectroscopy, as well as elemental analyses. Their thermal decompositions were investigated by TG‐DSC. The densities, combustion heats, and sensitivity properties were tested. Additionally, enthalpies of formation, detonation pressures, detonation velocities, and heats of detonation were calculated. The compounds have potential application in the energetic materials field.     

Investigation of an N‐Butyl‐N‐(2‐Nitroxyethyl)Nitramine (BuNENA) Process: Identification of Process Intermediates,By‐Products and Reaction Pathways

A process for N‐butyl‐N‐(2‐nitroxyethyl)nitramine (BuNENA) was investigated: Step 1 involves N‐butyl‐ethanolamine addition to 98% HNO₃ to form a salt mixture; Step 2 is addition of acetic anhydride/acetyl chloride catalyst to the salt mixture. A number of potential intermediates, by‐products, and decomposition products from this process were identified/synthesized for use as analytical standards. BuNENA process reaction pathways/mechanisms were elucidated, including the nature of the amine salt solution formed in Step 1. In addition, potential pathways that could account for by‐product formation were elaborated. A study of the consumption of acetyl nitrate in Step 2 was undertaken to prevent its build‐up.     

Synthesis and Characterization of Poly(3‐azidomethyl‐3‐methyl oxetane) by the Azidation of Poly(3‐mesyloxymethyl‐3‐methyl oxetane)

Poly(3‐azidomethyl‐3‐methyl oxetane) (PAMMO) was prepared by the azidation reaction of poly(3‐mesyloxymethyl‐3‐methyl oxetane) (PMMMO), which was synthesized by cationic ring‐opening polymerization of MMMO for the first time. Two azidation reaction methods of PMMMO were considered to obtain PAMMO securely and efficiently. The thermal decomposition performance of PAMMO was studied by TG/FTIR/MS. The result of TG showed that the thermal decomposition of PAMMO involved two steps. Combined with FT‐IR and MS of the escaping gases to investigate the decomposition products of PAMMO, it is found that the first step was mainly corresponding to the thermal decomposition of azide group ( N₃), and the second step was mainly corresponding to the thermal decomposition of the polyether backbone.     

High‐temperature piezoelectric properties of 0‐3 type CaBi4Ti4O15:x wt%BiFeO3 composites

The 0‐3 type CaBi₄Ti₄O₁₅:30 wt%BiFeO₃ composite shows much better high‐temperature piezoelectric properties than the single‐phase CaBi₄Ti₄O₁₅ or BiFeO₃ ceramics. The composite with 0‐3 type connectivity exhibits a high density of 7.01 g/cm³, a saturated polarization of 21.5 μC/cm² and an enhanced piezoelectric d₃₃ of 25 pC/N. After the poled composite was annealed at 600°C, its d₃₃ is 21 pC/N at room temperature. Resistance of the composite decreases slowly from 10⁹ ohm at 20°C to ~10⁵ ohm at 500°C. Furthermore, the poled composite shows strong radial and thickness dielectric resonances at 20°C‐500°C.     

Synthesis and Characterization of Poly(glycidyl nitrate‐block‐caprolactone‐block‐glycidyl nitrate) (PGN‐PCL‐PGN) Tri‐Block Copolymer as a Novel Energetic Binder

An energetic binder was synthesized through ring opening copolymerization of glycidyl nitrate (GLYN) with polycaprolactone (PCL) as a macroinitiator to form tri‐block copolymer PGN‐PCL‐PGN. Effect of monomer concentration, catalyst, reaction time and solvent was investigated in polymerization. Resulting tri‐block copolymer was characterized by Fourier transform infrared spectroscopy (FT‐IR), nuclear magnetic resonance spectroscopy (NMR), gel permeation chromatography (GPC), differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA). The DSC result shows that glass transition temperature of tri‐block copolymer (T_g=−56.2 °C) is lower than PGN (T_g=−35 °C). In optimal condition, the M_w of this polymer was obtained 2900 g/mol.