Synthesis and Characteristics of Bis(nitrofurazano)furazan (BNFF), an Insensitive Material with High Energy‐Density

The insensitive compound bis(nitrofurazano)furazan (BNFF) with high energy‐density was synthesized by three‐step reactions and fully characterized. The key reduction reaction was discussed. BNFF has a high crystal density (1.839 g cm⁻³) and a low melting point (82.6 °C). BNFF is insensitive to impact and friction and has similar detonation velocity (8680 m s⁻¹) and detonation pressure (36.1 GPa) compared to RDX.     

A Novel Insensitive High Explosive 3,4‐Bis (Aminofurazano) Furoxan

A novel insensitive high explosive 3,4‐bis (aminofurazano) furoxan (BAFF) was prepared using 3‐amino‐4‐acylchloroximinofurazan (ACOF) as a precursor. The molecular and crystal structures of BAFF were characterized by IR, MS, ¹H NMR, ¹³C NMR, elemental analysis, and single crystal X‐ray diffraction. The single crystal structure of BAFF recrystallized from water is monoclinic, space group P 21/c, and ρ_c=1.745 g cm⁻³, and that recrystallized from ethanol is triclinic, space group P 1, and ρ_c=1.737 g cm⁻³. BAFF has multiple crystal forms. The calculated detonation velocity by BKW code is 8100 m s⁻¹ (ρ=1.795 g cm⁻³, theoretical density calculated by quantum chemistry) and the experimental value is 7177 m s⁻¹ (ρ=1.530 g cm⁻³, charge density). The tested values of impact, friction, and electrostatic spark sensitivity show that BAFF is insensitive.     

A DFT Study on the Structures and Energies of Isomers of 4‐Amino‐1,3‐dinitro‐1,2,4‐triazol‐5‐one‐2‐oxide: New High Energy Density Compounds

Isomers of 4‐amino‐1,3‐dinitrotriazol‐5‐one‐2‐oxide (ADNTONO) are of interest in the contest of insensitive explosives and were found to have true local energy minima at the DFT‐B3LYP/aug‐cc‐pVDZ level. The optimized structures, vibrational frequencies and thermodynamic values for triazol‐5‐one N‐oxides were obtained in their ground state. Kamlet‐Jacob equations were used to evaluate the performance properties. The detonation properties of ADNTONO (D=10.15 to 10.46 km s⁻¹, P=50.86 to 54.25 GPa) are higher compared with those of 1,1‐diamino‐2,2‐dinitroethylene (D=8.87 km s⁻¹, P=32.75 GPa), 5‐nitro‐1,2,4‐triazol‐3‐one (D=8.56 km s⁻¹, P=31.12 GPa), 1,2,4,5‐tetrazine‐3,6‐diamine‐1,4‐dioxide (D=8.78 km s⁻¹, P=31.0 GPa), 1‐amino‐3,4,5‐trinitropyrazole (D=9.31 km s⁻¹, P=40.13 GPa), 4,4′‐dinitro‐3,3′‐bifurazan (D=8.80 km s⁻¹, P=35.60 GPa) and 3,4‐bis(3‐nitrofurazan‐4‐yl)furoxan (D=9.25 km s⁻¹, P=39.54 GPa). The  NH₂ group(s) appears to be particularly promising area for investigation since it may lead to two desirable consequences of higher stability (insensitivity), higher density, and thus detonation velocity and pressure.     

Role of cold isostatic pressing in the formation of the properties of ZrO2-base ceramics obtained from ultradisperse powders

The physicomechanical properties of ceramics obtained from plasmachemical and sol-gel powders of partially stabilized (3% Y₂O₃) zirconia (PSZ) and its compositions with 20% Al₂O₃ by cold isostatic pressing (CIP) at a pressure of at most 2 GPa and sintering at 1300–1650°C are investigated. It is established that plasmachemical PSZ exhibits its best properties (K _lc=7.8 MPa · m^1/2, a strength of 650 MPa) only after complete disintegration at a CIP of 0.1 GPa and a sintering temperature of 1650°C, when the material is sintered to a density of 5.5 g/cm³. After partial stabilization and CIP at 0.1 GPa the plasmachemical composition of PSZ+20% Al₂O₃ is sintered at 1650°C to a density of 4.7 g/cm³, but hasK _lc=8.5 MPa · m^1/2 and a strength of 700 MPa. The deagglomerated sol-gel powder exhibits properties at a level ofK _lc=12.4 MPa · m^1/2 and a strength of 950 MPa at a density above 6.0 g/cm³ after CIP at 0.3 GPa and sintering at 1450°C. The latter obviously has the best mechanical properties of all the investigated materials.Translated from Ogneupory, No. 2, pp. 12 – 19, February, 1995.     

Supercritical CO2-assisted extrusion foaming: A suitable process to produce very lightweight acrylic polymer micro foams

A strategy of CO₂-assisted extrusion foaming of PMMA-based materials was established to minimize both foam density and porosities dimension. First a highly CO₂-philic block copolymer (MAM: PMMA-PBA-PMMA) was added in PMMA in order to improve CO₂ saturation before foaming. Then the extruding conditions were optimized to maximize CO₂ uptake and prevent coalescence. The extruding temperature reduction led to an increase of pressure in the barrel, favorable to cell size reduction. With the combination of material formulation and extruding strategy, very lightweight homogeneous foams with small porosities have been produced. Lightest PMMA micro foams (ρ = 0.06 g cm⁻³) are demonstrated with 7 wt% CO₂ at 130°C and lightest blend micro foams (ρ = 0.04 g cm⁻³) are obtained at lower temperature (110°C, 7.7 wt% CO₂). If MAM allows a reduction of T^foaming, it also allows a much better cell homogeneity, an increase in cell density (e.g., from 3.6 10⁷ cells cm⁻³ to 2 to 6 10⁸ cells cm⁻³) and an overall decrease in cell size (from 100 to 40 μm). These acrylic foams produced through scCO₂-assisted extrusion has a much lower density than those ever produced in batch (ρ ≥ 0.2 g cm⁻³).     

Explosive Properties and Thermal Stability of Urea‐Hydrogen Peroxide Adduct

The adduct of urea and hydrogen peroxide (UHP) is industrially produced material on a large scale. Although UHP is widely used as a bleaching and oxidizing agent, its properties as energetic material are generally overlooked. In this work we report comprehensive characterization of UHP explosive and thermal properties. We found that UHP is a compound with a negative value of standard enthalpy of formation (−565.1 kJ mol⁻¹). It is not sensitive to impact and friction. However, we demonstrated that UHP (ρ =0.93 g cm⁻³; packed into a steel pipe with inner diameter of 206 mm) detonates with experimental velocity of detonation (VOD) of 3780 m s⁻¹. Moreover, for UHP with maximal theoretical density (ρ =1.43 g cm⁻³), the calculated VOD reaches 5219 m s⁻¹. Based on our findings, we recommend that present regulations regarding the handling, storage and transportation of the UHP should be revised, especially in cases, where UHP is kept on a large scale, under confinement and at places where the temperature can reach above 60 °C.     

Triazidotrinitro Benzene: 1,3,5‐(N3)3‐2,4,6‐(NO2)3C6

Triazidotrinitro benzene, 1,3,5‐(N₃)₃‐2,4,6‐(NO₂)₃C₆ ( 1 ) was synthesized by nitration of triazidodinitro benzene, 1,3,5‐(N₃)₃‐2,4‐(NO₂)₂C₆H with either a mixture of fuming nitric and concentrated sulfuric acid (HNO₃/H₂SO₄) or with N₂O₅. Crystals were obtained by the slow evaporation of an acetone/acetic acid mixture at room temperature over a period of 2 weeks and characterized by single crystal X‐ray diffraction: monoclinic, P 2₁/c (no. 14), a=0.54256(4), b=1.8552(1), c=1.2129(1) nm, β=94.91(1)°, V=1.2163(2) nm³, Z=4, ϱ=1.836 g⋅cm⁻³, R_all =0.069. Triazidotrinitro benzene has a remarkably high density (1.84 g⋅cm⁻³). The standard heat of formation of compound 1 was computed at B3LYP/6‐31G(d, p) level of theory to be ΔH°_f=765.8 kJ⋅mol⁻¹ which translates to 2278.0 kJ⋅kg⁻¹. The expected detonation properties of compound 1 were calculated using the semi‐empirical equations suggested by Kamlet and Jacobs: detonation pressure, P=18.4 GPa and detonation velocity, D=8100 m⋅s⁻¹.     

Studies on Advanced RDX/TATB Based Low Vulnerable Sheet Explosives with HTPB Binder

Hydroxyl‐terminated polybutadiene (HTPB) based sheet explosives incorporating insensitive 1,3,5‐triamino‐2,4,6‐trinitrobenzene (TATB) as a part replacement of cyclotrimethylene trinitramine (RDX) have been prepared during this work. The effect of incorporation of TATB on physical, thermal, and sensitivity behavior as well as initiation by small and high caliber shaped charges has been determined. Composition containing 85% dioctyl phthalate (DOP) coated RDX and 15% HTPB binder was taken as control. The incorporation of 10–20% TATB at the cost of RDX led to a remarkable increase in density (1.43→1.49 g cm⁻³) and tensile strength (10→15 kg cm⁻²) compared to the control composition RDX/HTPB(85/15). RDX/TATB/HTPB based compositions were found less vulnerable to shock stimuli. Shock sensitivity was found to be of the order of 20.0–29.2 GPa as against 18.0 GPa for control composition whereas their energetics in terms of velocity of detonation (VOD) were altered marginally. Differential scanning calorimeter (DSC) and thermogravimetry (TG) studies brought out that compositions undergo major decomposition in the temperature region of 170–240 °C.     

Synthesis,Crystal Structure,and Thermal Behaviors of 3‐Nitro‐1,5‐bis(4,4′‐dimethylazide)‐1,2,3‐triazolyl‐3‐azapentane (NDTAP)

The energetic material, 3‐nitro‐1,5‐bis(4,4′‐dimethyl azide)‐1,2,3‐triazolyl‐3‐azapentane (NDTAP), was firstly synthesized by means of Click Chemistry using 1,5‐diazido‐3‐nitrazapentane as main material. The structure of NDTAP was confirmed by IR, ¹H NMR, and ¹³C NMR spectroscopy; mass spectrometry, and elemental analysis. The crystal structure of NDTAP was determined by X‐ray diffraction. It belongs to monoclinic system, space group C2/c with crystal parameters a=1.7285(8) nm, b=0.6061(3) nm, c=1.6712(8) nm, β=104.846(8)°, V=1.6924(13) nm³, Z=8, μ=0.109 mm⁻¹, F(000)=752, and D_c=1.422 g cm⁻³. The thermal behavior and non‐isothermal decomposition kinetics of NDTAP were studied with DSC and TG‐DTG methods. The self‐accelerating decomposition temperature and critical temperature of thermal explosion are 195.5 and 208.2 °C, respectively. NDTAP presents good thermal stability and is insensitive.     

Effect of Nitrogen‐Doping on Detonation and Stability Properties of CL‐20 Derivatives from a Theoretical Viewpoint

Six nitrogen‐doping CL‐20 derivatives were designed and investigated as energetic materials at B3LYP/6‐31G** level based on the density functional theory method. Results show that nitrogen‐doping derivatives exhibit high crystal densities (1.98∼2.18 g cm⁻³) and positive heats of formation (451.68∼949.68 kJ mol⁻¹). Among nitrogen‐doping derivatives, 2,4,6,8,10,12‐hexanitro‐2,4,6,8,9,10,12‐heptaazaisowurtzitane(A1), 2,4,6,8,10,12‐hexanitro‐2,3,4,6,8,9,10,12‐octaazaisowurtzitane(B1) and 2,4,6,8,10,12‐hexanitro‐1,2,3,4,6,8,9,10,12‐nonaazaisowurtzitane(C1) possess better detonation velocity and pressure than CL‐20, and A1 gives the best performance (D _K‐J•A1=9.6 km s⁻¹; P _K‐J•A1=43.07 GPa). Moreover, the specific impulse, brisance, and power of N‐doping CL‐20 derivatives are also higher than that of CL‐20. The thermal stability and sensitivity of nitrogen‐doping molecules were analyzed via the bond dissociation energy (BDE ), the characteristic height (h₅₀) and electrostatic sensitivity (E _ES). The results indicate that the stability of A1, B1 and 2,4,6,8,10,12‐hexanitro‐1,2,3,4,6,7,8,9,10,12‐decaazaisowurtzitane(D1) is comparable with that of CL‐20. Considering detonation performance and stability, A1 and B1 may be promising candidates as energetic materials with superior detonation performance and favorable stability.     

The Initiation Threshold Sensitivity of HNS Explosive as a Function of its Grain Size

The initiation threshold sensitivity of HNS versus explosive grain size has been measured, using an electric gun, with two flyer thicknesses. The initiation threshold, (kinetic energy of flyer plate), versus explosive grain size shows that the threshold curve increases dramatically at grain size over 5.4 m̈m (for flyer thickness 76.2 m̈m at explosive density 1.6 g/cm³). Minimum critical energies were calculated to be 12.15 ± 0.5 J/cm² and less than 7.0 J/cm², for flyer thicknesses 76.2 m̈m and 20.0 m̈m, respectively.     

Synthesis,Structure, Molecular Orbital and Valence Bond Calculations for Tetrazole Azide,CHN7

The synthesis, NMR spectroscopic characterization and structure determination of highly explosive tetrazole azide, a very nitrogen‐rich material (88.3% N) is reported. Tetrazole azide was prepared in high yield from the diazotation reaction of aminotetrazole, followed by treatment of the formed diazonium salt with sodium azide. Synthesis in diethylether/methanol and recrystallization from diethylether afforded colorless cubes: CHN₇ ( 1 ): monoclinic, P1 2₁/n₁, a=1346.6(5), b=499.6(2), c=1360.9(5) pm, β=105.14(1)⁰, V=0.884(2) nm³, Z=8, ϱ=1.670 g cm⁻³. The observed structural parameters (X‐ray) are in good accordance with the results from molecular orbital (MO) calculations. The computed electrostatic potential (B3LYP) suggests a pronounced shock and friction sensitivity which was confirmed experimentally. Quantitative valence bond (VB) calculations were performed for the most important 21 VB structures in order to obtain the structural weights and to obtain an assessment for the importance of the various individual VB structures considered.     

Natural gas storage in activated carbon pellets without a binder

Activated carbon pellets without a binder from cellulose microcrystals as a raw material were investigated. After compression of the raw materials, the thus obtained raw material pellets were slowly carbonized to 1073 K under nitrogen. To activate them, the carbon pellets were heated to 1173 K under carbon dioxide. The activated carbon pellet shape, after heat treatment, was columnar by using the previous employed compression of the raw material. The total surface area, pore volume, and average pore diameter for all the samples were evaluated from the analysis of N₂ adsorption isotherm data. The total surface area and the pore volume were decreased with an increase in compression pressure under the same heat treatment conditions. On the contrary, the bulk densities of the activated carbon pellets were increased. However, these properties can be easily controlled by changing the sintering temperature and time. The bulk density of sample pellet was 0.56 g/cm³. It is 2.3 times higher than activated carbon powder, which was made without the compression process. The total methane storage capacity at 298 K reached 164 cm³ in 1 cm³ volume of activated carbon pellets at 3.5 MPa.     

Mechanical properties and thermal conductivity of dense β-SiAlON ceramics fabricated by two-stage spark plasma sintering with Al2O3-AlN-Y2O3 additives

Fully dense β-SiAlON ceramics with excellent mechanical properties and good thermal conductivity were fabricated by two-stage spark plasma sintering (SPS) processes without and with applying pressure respectively, using α-Si₃N₄ powder and 6 Al₂O₃-3 AlN-6 Y₂O₃ (in wt.%, label with 636), 424 and 422 additives. In the first stage SPS process without pressure, the relative dense β-SiAlON ceramics with interlock microstructures of elongated grains and density of 3.14˜3.18 g cm⁻³, hardness of 14.00˜14.82 GPa and fracture toughness of 6.00˜6.63 MPa m^1/2 were obtained by sintering at about 1600 °C for 20 min. In the second stage SPS process at about 1425 °C for 5 min under pressure of 24 MPa, the fully dese β-SiAlON ceramics with density of 3.22˜3.24 g cm⁻³, high hardness of 15.68˜15.95 GPa, high fracture toughness of 6.38˜7.03 MPa m^1/2 and thermal conductivity of 13.5˜19.6 Wm^-1K^-1 were obtained. The reaction between the samples and the graphite mold can be avoided in this fabrication method.     

Density Distributions in TATB Prepared by Various Methods

The density distribution of two legacy types of 1,3,5‐triamino‐2,4,6‐trinitrobenzene (TATB) particles were compared with TATB synthesized by new routes and recrystallized in several different solvents using a density gradient technique. Legacy wet (WA) and dry aminated (DA) TATB crystalline aggregates gave average densities of 1.9157 and 1.9163 g cm⁻³, respectively. Since the theoretical maximum density (TMD) for a perfect crystal is 1.937 g cm⁻³, legacy TATB crystals averaged 99% of TMD or about 1% voids. TATB synthesized from phloroglucinol (P) had comparable particle size to legacy TATBs, but significantly lower density, 1.8340 g cm⁻³. TATB synthesized from 3,5 dibromoanisole (BA) was very difficult to measure because it contained extremely fine particles, but had an average density of 1.8043 g cm⁻³ over a very broad range. Density distributions of TATB recrystallized from dimethylsulfoxide (DMSO), sulfolane, and an 80/20 mixture of DMSO with the ionic liquid 1‐ethyl‐3‐methyl‐imidazolium acetate (EMImOAc), with some exceptions, gave average densities comparable or better than the legacy TATBs.     

Fractal Networks of Inter‐Granular Voids in Pressed TATB

Small‐angle neutron scattering techniques were used to study the evolution of void morphology with pressed density of the insensitive high explosive, TATB. Samples were studied as a loose powder and as pressed pellets, ranging in density from approx. 1 to 1.804 g cm⁻³. Inter‐granular voids in the loose powder were randomly arranged (non‐fractal) and had a surface defined mean size of 0.66 μm. Pressing was found to induce a fractal network of voids with fractally rough interfaces. The surface‐defined mean void size of the pressed samples was between 0.21–0.33 μm over the range of densities studied and was found to increase with pressed density up to 1.720 g cm⁻³, decreasing thereafter. The volume fractal dimension, indicative of the void arrangement, mirrored the changes in the mean void size. No systematic change in the surface fractal dimension was found. Surface area analysis allowed the average TATB grain size within the pressed samples to be quantified. An initial decrease of the mean grain size followed by an increase with pressed density suggests that the TATB grains behave in a brittle fashion at low densities and ductile at higher pressed densities.     

Tetrazolyl Triazolotriazine: A New Insensitive High Explosive

A triazolotriazine carbonitrile ( 1 ) was formed by diazotization of 3‐amino‐5‐cyano‐1,2,4‐triazole followed by treatment with nitroacetonitrile. Cyclization of the C≡N bond with sodium azide results in a tetrazolyl triazolotriazine ( 2 ). Formation of the sodium salt of 2 , followed by metathesis with [PPN][Cl] resulted in the organic salt 3 . Compounds 1 , 2 , and 3 were characterized by elemental analysis and infrared, ¹H, and ¹³C{¹H} NMR spectroscopy and 1 and 3 were characterized by single‐crystal X‐ray diffraction. Compound 2 has a density of 1.819 g cm⁻¹, is thermally stable up to 305 °C, and is insensitive to impact, friction, and electrical discharge. The detonation pressure and velocity of 2 are calculated to be 27.04 GPa and 8.312 km s⁻¹, respectively, making this a 1,3,5‐triamino‐2,4,6‐trinitrobenzene (TATB) replacement candidate.     

Effect of Quasi-Hydrostatic Compression on the Mechanical Properties of Ceramics in the ZrO2 + 3 MOL.% Y2O3 System

The effect of quasi-hydrostatic compression on the strength of ZrO₂ + 3 mol.% Y₂O₃ ceramic specimens of two series was studied. The series 1 ceramic was a powder commercially available from TOSOH Co. (Japan), with a density of 6.1 g/cm³, and the series 2 ceramic was a powder with a density of 5.9 g/cm³ prepared under laboratory conditions at the IPM Research Institute (National Academy of Sciences, Ukraine). The pressure range was up to 1.2 GPa, and the pressure-transmitting medium was a coarse-grained corundum powder. In the series 1 specimens, the strength increases with pressure over the entire pressure range (from 670 MPa to 1098 MPa at 1.2 GPa); in the series 2 specimens, the strength increases only to a pressure of 0.8 GPa (from 695 MPa to 828 MPa) and then, with further increase in pressure drops sharply to nearly zero (30 MPa at 1.2 GPa). It was proposed that the observed effect might be associated with a martensite transformation in the zone of structural imperfections (discontinuities). On reaching a critical value determined by the strength of the matrix, the martensite transformation becomes a cause of failure of the material.     

Measurement of Shock Initiation Threshold of HNAB by flyer plate impact

The shock initiation threshold of HNAB (Hexanitroazobenzene) explosive has been measured using pressure pulses generated by flyer plate impact. The flyer plates were accelerated by an electrically exploded metallic foil (electric gun) up to velocity of 2.5 mm/m̈s generating impact pressures, P, up to 7.3 GPa lasting between τ = 40 ns to 210 ns, where τ is the duration of the impact. One dimensional semi-empirical model was developed to describe the exploding foil process. We found a good agreement between the semi-empirical model and the experimental data. It was found that as the pressure duration gets longer, the initiation threshold curve swings away from the P²τ= constant. For long (200 ns) pulses, the initiation criterion becomes one of a constant pressure. This constant threshold pressure is 2.9 GPa at 1.6 g/cm³ (grain size is 5 m̈m). The effect of the explosive density and grain size on initiation threshold can be explained by hot spots and porous explosive concept. A critical energy for initiation threshold of 12 J/cm² was derived from our measurements (with flyer thickness 76 m̈m and grain size 5 m̈m).     

Dynamic Compressibility of Carbamide at Low Pressures

The shock adiabats of pressed carbamide samples with a density of 1.29 g/cm³ and carbamide samples with a bulk density of 0.78 g/cm³ were studied at pressures of 1–14 GPa using an electromagnetic method. In the coordinates D and U, the shock adiabat of pressed carbamide is linear and the shock adiabat of carbamide of bulk density at a pressure of 2.4 GPa is represented as two linear segments: D = 2U at 0.6 < U <1.3 km/sec and D = 0.6 + 1.55U at 1.3 <U < 2.8 km/sec. The possibility of a phase transition in carbamide under shock compression is discussed.