Salts of Tetrazolone – Synthesis and Properties of Insensitive Energetic Materials

Tetrazolone (5‐oxotetrazole, 1 ) is formed by diazotization of 5‐aminotetrazole in the presence of CuSO₄. Nitrogen‐rich salts such as guanidinium ( 2 ), 1‐aminoguanidinium ( 3 ), 1,3‐diamino‐guanidinium ( 4 ), 1,3,5‐triamino‐guanidinium ( 5 ), ammonium ( 6 ), hydrazinium ( 7 ) and the hydroxylammonium ( 8 ) salts of tetrazolone were prepared by facile deprotonation or metathesis reactions. All compounds were characterized by single‐crystal X‐ray diffraction, vibrational spectroscopy (IR and Raman), multinuclear NMR spectroscopy, elemental analysis and DSC measurements. The heats of formation of 2–8 were calculated using the atomization method based on CBS‐4M enthalpies. With these values and the experimental (X‐ray) densities several detonation parameters such as the detonation pressure, velocity, energy and temperature were computed using the EXPLO5 code (V.5.04). In addition, the sensitivities towards impact, friction and electrical discharge were tested using the BAM drop hammer and friction tester as well as a small scale electrical discharge device.     

Estimated Detonation Velocities for TKX‐50, MAD‐X1, BDNAPM,BTNPM, TKX‐55, and DAAF using the Laser–induced Air Shock from Energetic Materials Technique

Since new energetic materials are initially produced in very small quantities for both safety and cost reasons, laboratory‐scale methods for characterizing their performance are essential for determining the most promising candidates for scale‐up. Laser‐induced air shock from energetic materials (LASEM) is a promising new method for estimating the detonation velocity of novel explosives using milligram amounts of material, while simultaneously investigating their high temperature chemical reactions. LASEM has been applied to 6 new explosives for the first time: TKX‐50, MAD−X1, BDNAPM, BTNPM, TKX‐55, and DAAF. Emission spectroscopy of the laser excited materials revealed the formation of the high pressure bands of C₂ during the ensuing exothermic reactions. The low thermal sensitivity of the materials also led to unusual laser‐material interactions, visualized with high‐speed video. The estimated detonation velocities for the 6 explosives were compared to predicted values from EXPLO5 and CHEETAH. The LASEM results suggest that TKX‐55, BDNAPM, and BTNPM have higher detonation velocities than predicted by the thermochemical codes, while the estimated detonation velocities for MAD−X1 and TKX‐50 are slightly lower than those predicted.     

Dinitromethyltetrazole and its Salts – A Comprehensive Study

Dinitromethyltetrazole is an easily accessible and highly energetic compound which – due to its acidity – gives rise to a wide range of energetic salts. The present study investigates dinitromethyltetrazole and several of its salts. The compounds were characterized using multinuclear NMR as well as vibrational spectroscopy and X‐ray diffraction. The energetic properties were estimated using the EXPLO5 code and the sensitivities of the compounds were measured.     

Energetic Derivatives of 2‐Nitrimino‐5,6‐dinitro‐benzimidazole

2‐Nitrimino‐5,6‐dinitrobenzimidazole ( 1 ) was synthesized by nitration of 2‐aminobenzimidazole at ambient temperature in good yield. In order to explore new insensitive explosives four energetic nitrogen‐rich 1 : 1 salts such as the guanidinium ( 1a ), aminoguanidinium ( 1b ), triaminoguanidinium ( 1c ) and hydroxylammonium ( 1d ) were synthesized either by facile acid/base or in situ metathesis reaction. In addition 2‐nitrobenzimidazole ( 2 ) was synthesized by the reaction of 2‐aminobenzimidazole using potassium hyperoxide in THF. Different nitration methods were tested to obtain a theoretically 2,4,5,6,7‐pentanitrobenzimidazole but only the already known 4,5,6,7‐tetranitrobenzimidazol‐2‐one ( 3 ) could be isolated. All synthesized compounds were characterized especially by low temperature X‐ray diffraction, CHN elemental analysis and ¹H and ¹³C NMR spectroscopy. The heat of formation of all new synthesized compounds was calculated using CBS‐4M electronic enthalpies in combination with the atomization method to calculate their detonation parameters with the EXPLO 5 V5.05 computer code.     

Changes in Pore Size Distribution upon Thermal Cycling of TATB‐based Explosives Measured by Ultra‐Small Angle X‐Ray Scattering

Hot‐spot models of initiation and detonation show that voids or porosity ranging from nanometer to micrometer in size within highly insensitive energetic materials affect initiability and detonation properties. Thus, the knowledge of the void size distribution, and how it changes with the volume expansion seen with temperature cycling, are important to understanding the properties of the insensitive explosive 1,3,5‐triamino‐2,4,6‐trinitrobenzene (TATB). In this paper, void size distributions in the 2 nm to 2 μm regime, obtained from small‐angle X‐ray scattering measurements, are presented for LX‐17‐1, PBX‐9502, and ultra‐fine TATB formulations, both as processed and after thermal cycling. Two peaks were observed in the void size distribution: a narrow peak between 7–10 nm and a broad peak between 20 nm and about 1 mm. The first peak was attributed to porosity intrinsic to the TATB crystallites. The larger pores were believed to be intercrystalline, a result of incomplete consolidation during processing and pressing. After thermal cycling, these specimens showed an increase in both the number and size of these larger pores. These results illuminate the nature of the void distributions in these TATB‐based explosives from 2 nm to 2 μm and provide empirical experimental input for computational models of initiation and detonation.     

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.     

Synthesis and Characterization of a New Class of Energetic Compounds – Ammonium Nitriminotetrazolates

1‐Methyl‐5‐nitriminotetrazole ( 1 ) and 2‐methyl‐5‐nitraminotetrazole ( 2 ) obtained by nitration of 1‐methyl‐5‐aminotetrazole ( 3 ) and 2‐methyl‐5‐aminotetrazole ( 4 ) were deprotonated using aqueous ammonia solution yielding the energetic compounds, ammonium 1‐methyl‐5‐nitriminotetrazolate ( 5 ) and ammonium 2‐methyl‐5‐nitriminotetrazolate ( 6 ). The nitrogen‐rich salts were tested and characterized comprehensively using vibrational spectroscopy (Infrared (IR) and Raman), multinuclear (¹H, ¹³C, ¹⁴N, and ¹⁵N) NMR spectroscopy, and elemental analysis. The molecular structures in the crystalline state were determined using low temperature single crystal X‐ray diffraction. The thermal behavior and the decompositions were investigated using differential scanning calorimetry (DSC) and gas IR spectroscopy. The heats of formation were calculated using bomb calorimetric measurements. In addition, the relevant detonation parameters, like the detonation pressure and velocity of detonation were calculated using the software EXPLO5 outperforming the values of TNT. Last but not least the sensitivities were determined using BAM methods showing moderate values against impact and friction (drophammer and friction tester) and the long‐term stabilities were tested using Flexy Thermal safety calorimetry (TSC). X‐ray crystallography: 5 : monoclinic, P2₁/c, a=370.06(2) pm, b=2079.06(9) pm, c=859.69(5) pm, β=99.120(5)°, V=65306(6) pm³, Z=4, ρ_calc=1.639 g cm⁻³; 6 : monoclinic, P2₁, a=365.39(2) pm, b= 788.82(5) pm, c=1124.95(7) pm, β=91.818(6), V=32408(3) pm³, Z=2, ρ_calc=1.651 g cm⁻³.     

The Synthesis of Energetic Compound on 4,4′‐((2,4,6‐trinitro‐1,3‐phenylene)bis(oxy)) bis(1,3‐dinitrobenzene)(ZXC‐5): Thermally Stable Explosive with Outstanding Properties

The novel, thermally stable explosive 4,4′‐((2,4,6‐trinitro‐1,3‐phenylene)bis(oxy))bis(1,3‐dinitrobenzene) (Be referred to as ZXC‐ 5 in our laboratory) has been reported. ZXC‐5 can be synthesized by a simple synthetic method (The total synthesis of ZXC‐ 5 requires only two steps and the total yield of ZXC‐ 5 is more than 89 %) and shows the superior detonation performances (detonation pressure, detonation velocity, sensitivity toward mechanical stimuli, and temperature of decomposition). The structure of ZXC‐5 was characterized by multinuclear (¹H, ¹³C) NMR and mass spectrometry. The structure in the crystalline state was confirmed by low‐temperature single‐crystal X‐ray diffraction. From the calculated standard molar enthalpy of formation and the measured densities, the detonation properties were predicted by using the EXPLO5 V6.01 thermochemical computer code. The sensitivity of ZXC‐ 5 towards impact, electrostatic discharge, and friction were also measured.     

Structural Defect Evolution of TATB‐Based Compounds Induced by Processing Operations and Thermal Treatments

2,4,6‐Triamino‐1,3,5‐trinitrobenzene (TATB) compounds are commonly used in high performance explosives because of their thermal stability and high detonation velocities compared to other materials. The insensitivity and mechanical properties are related to the stability of their crystalline structure. Crystallographic structure and structural defects evolution of TATB and TATB‐based compounds were studied by X‐ray diffraction for powders, molding powders, and pressed compounds, using Rietveld refinement. The effects of synthesis conditions, thermal treatments, coating and pressing operations on the structure of TATB compounds were evaluated. The results show that the pressing operation results in anisotropic crystallite size, leading to an increase of the structural defects density. It could be due to the anisotropic mechanical response of the TATB crystal under pressure, possibly plasticity. Finally, it is shown that increasing thermal treatment temperature on TATB powders decreases the structural defects density.     

An investigation on structure characterization of thermally stabilized polyacrylonitrile precursor fibers pretreated with guanidine carbonate prior to carbonization

Thermal stabilization of polyacrylonitrile (PAN) precursor fiber was performed with a pretreatment of an aqueous guanidine carbonate solution and its structure was thoroughly characterized using a combination of infrared spectroscopy (IR), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), density, elemental analysis, and X‐ray diffraction measurements. The use of guanidine carbonate pretreatment of polyacrylonitrile precursor fiber was found to be very useful for the acceleration of thermal stabilization of polyacrylonitrile precursor fiber prior to the carbonization stage. The results obtained from density, thermal analysis (TGA and DSC), infrared‐spectroscopy and X‐ray diffraction methods suggested an accelerated thermally stable aromatic ladder structure formation resulting in much reduced thermal stabilization time. X‐ray observations showed the transformation of the original structure from a highly ordered phase to a totally disordered amorphous phase which seemed to be a direct consequence of the crosslinked and cyclized structure present in the stabilized fibers. The results obtained from the infrared spectra of thermally stabilized samples showed a rapid and simultaneous cyclization and dehydrogenation reactions aided by the oxygen uptake in the form of oxygen containing functional groups. Guanidine carbonate pretreated and thermally stabilized PAN precursor fibers showed a carbon yield of 52.5% at 1100°C obtained from TGA measurements. The use of guanidine carbonate pretreatment is expected to significantly increase the productivity of carbon fiber manufacturing at a substantially reduced cost by significantly reducing the time necessary for thermal stabilization of polyacryonitrile fiber. POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers     

A New Energetic Salt Semicarbazide 5‐Dinitromethyltetrazolate: A Promising Explosive Alternative

The design and synthesis of new environmentally friendly energetic materials with excellent performance and reliable safety have received considerable attention. A new energetic salt of semicarbazide 5‐dinitromethyltetrazolate (SCZ ⋅ DNMZ) was synthesized by using semicarbazide and 5‐dinitromethyltetrazolate (DNMZ) as raw materials, and fully characterized by using elemental analysis, FT‐IR spectroscopy, ¹H, ¹³C, and ¹⁵N nmR and mass spectrometry. The monocrystal of the salt was obtained and the structure was determined by X‐ray single‐crystal diffractometer. Results show that it belongs to monoclinic space group P 2₁/c with a high density of 1.867 g cm⁻³. The thermal decomposition behavior was tested by DSC and TG‐DTG technologies; the non‐isothermal kinetic parameters for the salt were calculated. The enthalpy of formation for the salt is directly dependent on the combustion heats data with a result of 341.5 kJ mol⁻¹, which is about three times higher than that of RDX. The detonation pressure (P ) and detonation velocitiy (D ) of the salt were determined as 8931 m s⁻¹ and 36.2 GPa, which are also higher than that of RDX. The impact sensitivity was tested with a result of 10.8 J. We can draw a safe conclusion that the salt has provided a promising future by using as a kind of explosive alternative. The discovery also contributes significantly to the expansion and application of the N‐heterocyclic compounds applied as energetic materials.     

Development of ZrO2‐MgO nanocomposite powders by the modified sol‐gel method

The ZrO₂‐MgO nanocomposites were synthesized using a new sol‐gel method with sucrose and tartaric acid as a gel agent. The samples were characterized by thermal analysis (TG/DTA), X‐ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FESEM), energy‐dispersive X‐ray mapping (EDX mapping), and Ultraviolet‐visible spectroscopy (UV‐vis). The results showed that the cubic phase of ZrO₂‐MgO was formed in the presence of both gel agents. The average particle size of the samples synthesized with sucrose was lower (30 nm) than that of tartaric acid (50 nm). Finally, the formation mechanism and the optical properties of zirconia‐magnesia have been discussed.     

Synthesis of 5‐(1H‐Tetrazolyl)‐1‐hydroxy‐tetrazole and Energetically Relevant Nitrogen‐Rich Ionic Derivatives

Sodium 5‐cyanotetrazolate sesquihydrate ( 1 ) was prepared from sodium azide and two equivalents of sodium cyanide under acidic conditions. Sodium 5‐cyanotetrazolate sesquihydrate ( 1 ) reacts with hydroxylammonium chloride to form 5‐aminohydroximoyl tetrazole ( 2 ). 5‐Aminohydroximoyl tetrazole ( 2 ) is treated with sodium nitrite and hydrochloric acid to form 5‐chlorohydroximoyl‐tetrazole ( 3 ). The chloride azide exchange yields 5‐azidohydroximoyl‐tetrazole monohydrate ( 4 ). When compound 4 is treated with hydrochloric acid, 5‐(1H‐tetrazolyl)‐1‐hydroxytetrazole ( 5 ) is obtained in good yield. Compound 5 can be deprotonated twice by various bases. Different ionic derivatives such as bis(hydroxylammonium) ( 6 ), bis(hydrazinium) ( 7 ), bis(guanidinium) ( 8 ), bis(aminoguanidinium) ( 9 ), bis(ammonium) ( 10 ), and diaminouronium ( 11 ) 5‐(1‐oxidotetrazolyl)‐tetrazolate were synthesized and characterized. With respect to energetic use salts 6 and 7 are most relevant. Compounds 3 – 9 and 11 were characterized using low temperature single‐crystal X‐ray diffraction. All compounds were investigated by NMR and vibrational (IR, Raman) spectroscopy, mass spectrometry and elemental analysis. The thermal properties were determined by differential scanning calorimetry (DSC). The sensitivities towards impact ( 4 : 4 J, 5 : 40 J, 6 : 12 J, 7 : 40 J), friction: ( 4 : 60 N, 5 : 240 N, 6 : 216 N, 7 : 240 N), and electrical discharge ( 5 : 0.40 J, 6 : 0.75 J, 7 : 0.75 J), were investigated using BAM standards and a small scale electrostatic discharge tester. The detonation parameters of 5 – 7 were calculated using the EXPLO5.06 code and calculated (CBS‐4 M) enthalpy of formation values.     

Synthesis,Structure, and Explosive Properties of a New Trinitrate Derivative of an Unexpected Condensation Product of Nitromethane with Glyoxal

In the condensation reaction of nitromethane with glyoxal carried out in an aqueous solution of sodium hydroxide, 3,6‐dinitro‐cyclohexane‐1,2,4,5‐tetraol was obtained (the expected product, described in the literature) and, unexpectedly, also tricyclic nitro‐triol (6b‐nitrohexahydro‐2H‐1,3,5‐trioxacyclopenta[cd]‐pentalene‐2,4,6‐triol), which has been unknown until now, was obtained as the main product. The structure of the compound was confirmed with ¹H NMR and ¹³C NMR spectroscopy, LR, and HR‐MS techniques and with single‐crystal X‐ray diffractometry. The tricyclic triol (formally a hemiacetal) was transformed into 6b‐nitrohexahydro‐2H‐1,3,5‐trioxacyclopenta[cd]‐pentalene‐2,4,6‐triyl trinitrate by reaction with 98 % HNO₃. Some explosive properties of this compound were determined including: friction and impact sensitivity, activation energy, detonation velocity, heat of combustion in an oxygen atmosphere and enthalpy of formation. The nitrate ester is a powerful explosive with performance close to that of pentaerythritol tetranitrate (PETN).     

Preparation and Properties Study of Core‐Shell CL‐20/TATB Composites

The insensitive high explosive 1,3,5‐triamino‐2,4,6‐trinitrobenzene (TATB) was selected for coating and desensitization of hexanitrohexaazaisowurtzitane (CL‐20), another high explosive, after surface modification. About 2 wt‐% polymer binder was adopted in the preparation process to further maintain the coating strength and fill the voids among energetic particles. The structure, sensitivity, polymorph properties, and thermal behavior of CL‐20/TATB by coating and physical mixing were studied. Scanning electron microscopy (SEM) and X‐ray photoelectron spectroscopy (XPS) results indicate that submicrometer‐sized TATB was compactly coated onto the CL‐20 surface with coverage close to 100 %. The core‐shell structure of CL‐20/TATB was confirmed by observation of hollow TATB shell from the CL‐20 core dissolved sample. X‐ray diffraction (XRD) analysis revealed that the polymorph of CL‐20 maintained ε form during the whole preparing process. Thermal properties were studied by thermogravimetry (TG) and differential scanning calorimeter (DSC), showing effects of TATB coating on the polymorph thermal stability and exothermic decomposition of CL‐20. Both the impact and friction sensitivities were markedly reduced due to the cushioning and lubricating effects of TATB shell. The preparation of explosive composites with core‐shell structure provides an efficient route for the desensitization of high explosives, such as CL‐20 in this study.     

Explosives Based on Diaminourea

Diaminourea (DAU, 1 ) is synthesized by the reaction of dimethylcarbonate with hydrazine hydrate. DAU was protonated using nitric as well as perchloric acid yielding diaminouronium nitrate ( 2 ), diaminouronium dinitrate monohydrate ( 3 ) and diaminouronium perchlorate ( 4 ). The bis‐perchlorate salt could not be isolated due to its high hygroscopicity. Explosives 2 – 4 were fully characterized using X‐ray diffraction, NMR and vibrational spectroscopy, mass spectrometry and elemental analysis. The thermal properties were determined by differential scanning calorimetry (DSC). The sensitivities towards impact ( 2 : 9 J, 3 : >40 J, 4 : 2 J), friction ( 2 : 288 N, 3 : >360 N, 4 : 5 N) and electrical discharge ( 2 : 0.60 J, 3 : 0.50 J, 4 : 0.30 J) were investigated using Bundesanstalt für Materialforschung (BAM) methods and a small scale electrostatic discharge device. The detonation parameters of 2 and 3 were computed using the EXPLO5.04 code with the X‐ray densities as well as calculated (CBS‐4 M) energies of formation as input values.     

Preparation and Performance of Nano HMX/TNT Cocrystals

Cocrystals of 1,3,5,7‐tetranitro‐1,3,5,7‐tetraazacyclooctane (HMX) and 2,4,6‐trinitrotoluene (TNT) with high energy and low sensitivity were obtained by a spray drying method. Scanning electron microscopy (SEM), X‐ray diffraction (XRD), and Fourier Transform Raman spectroscopy (FT‐Raman) were used to characterize the raw materials and cocrystals. Impact sensitivity and thermal decomposition properties of the cocrystals were tested and analyzed. The results show that microparticles prepared by the spray drying method are spherical in shape and 1–10 μm in size. The particles are aggregates of many tiny cocrystals, ranging from 50 nm to 200 nm. The formation of cocrystals originates from the N O ⋅⋅⋅ H hydrogen bonding between  NO₂ (HMX) and  CH₃ (TNT). Compared with raw HMX, the impact sensitivity of the cocrystals reduces obviously and it is much harder to decompose the cocrystal thermally.     

4H,8H-双呋咱并[3,4-b:3′,4′-e]吡嗪(DFP)有机双胺盐的合成及性能研究

为改善4H,8H-双呋咱并[3,4-b:3′,4′-e]吡嗪(DFP)结构存在的酸性问题,以DFP和有机胺为原料,合成了DFP的氨基胍盐(DAGDFP)、氨基脲盐(DSDFP)、1,3-二氨基胍盐(DBAGDFP)、脒基脲盐(DGUDFP)、胍盐(DGDFP)、缩二胍盐(DBGDFP)、三氨基胍盐(DTAGDFP)等7种有机双胺盐化合物;通过核磁共振谱、红外光谱和元素分析对其结构进行了表征;采用DSC和TG法分析了目标化合物的热性能;采用BAM标准方法测试了机械感度;通过Kamlet-Jacobs方程和最小自由能法分别计算了DFP双胺盐的爆轰参数和单元推进剂的燃烧性能。结果表明,DFP双胺盐热稳定性良好,撞击感度均大于40J,摩擦感度均大于360N,为钝感含能离子盐;DSDFP热分解温度为273.4℃,理论爆速为7891m/s,爆压为27.07GPa,比冲为2352N·s/kg,特征速度为1462.9m/s,爆轰性能优于TNT,比冲和特征速度较偶氮四唑胍盐(GZT)大幅提高,有望应用于气体发生剂和固体推进剂等。     

Thermal Conductivity in Nanocrystalline Ceria Thin Films

The thermal conductivity of nanocrystalline ceria films grown by unbalanced magnetron sputtering is determined as a function of temperature using laser‐based modulated thermoreflectance. The films exhibit significantly reduced conductivity compared with stoichiometric bulk CeO₂. A variety of microstructure imaging techniques including X‐ray diffraction, scanning and transmission electron microscopy, X‐ray photoelectron analysis, and electron energy loss spectroscopy indicate that the thermal conductivity is influenced by grain boundaries, dislocations, and oxygen vacancies. The temperature dependence of the thermal conductivity is analyzed using an analytical solution of the Boltzmann transport equation. The conclusion of this study is that oxygen vacancies pose a smaller impediment to thermal transport when they segregate along grain boundaries.     

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.