LX‐17 Corner‐Turning

We have performed a series of highly‐instrumented experiments examining corner‐turning of detonation. A TATB booster is inset 15 mm into LX‐17 (92.5% TATB, 7.5% kel‐F) so that the detonation must turn a right angle around an air well. An optical pin located at the edge of the TATB gives the start time of the corner‐turn. The breakout time on the side and back edges is measured with streak cameras. Three high‐resolution X‐ray images were taken on each experiment to examine the details of the detonation. We have concluded that the detonation cannot turn the corner and subsequently fails, but the shock wave continues to propagate in the unreacted explosive, leaving behind a dead zone. The detonation front farther out from the corner slowly turns and eventually reaches the air well edge 180° from its original direction. The dead zone is stable and persists 7.7 μs after the corner‐turn, although it has drifted into the original air well area. Our regular reactive flow computer models sometimes show temporary failure but they recover quickly and are unable to model the dead zones. We present a failure model that cuts off the reaction rate below certain detonation velocities and reproduces the qualitative features of the corner‐turning failure.     

Detonation Properties of 1,3,5-Triamino-2,4,6-Trinitrobenzene when impacted by hypervelocity projectiles

This investigation analyzes the reaction of an insensitive high explosive with binder to hypervelocity impact by four projectiles of two types: rod and plate. The insensitive high explosive is composed of 92.5% 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) and 7.5% Kel-F 800 binder, a vinylidene fluoride-chlorotrifluoroethylene copolymer. In this paper, for simplicity, we refer to this composition as “TATB”. Of the the impacting projectiles, three are steel-rod assemblies ranging in weight from 32.6 g to 34.6 g, and are composed of a steel rod 8 mm in diameter and 19 mm in length, of which 9 mm protrudes from a Polyzelux plastic holder. The fourth is a tantalum-plate assembly, weighing 23.9 grams and composed of a tantalum plate 24.2 mm in diameter and 1.5 mm in thickness mounted on a Polyzelux holder. The tantalum-plate experiment provides a highly efficient diverging detonation profile as predicted by similar previous investigations with flyer plates and TATB. The steel-rod experiments are compared to the tantalum-plate experiment to determine if detonation has occurred with the steel-rod impacts. The projectiles are accelerated by a two-stage, light-gas gun to velocities in the range of 3.1 km/s to 6.5 km/s (10,171 ft/s to 21,325 ft/s) and have bracketed the detonation threshold of the impacted TATB target. Comparisons of the TATB reaction data to a computer modeling of the experiment show that at 3.06 km/s, the computer model correctly predicts no initiation of detonation; at 4.75 km/s, the computer model correctly predicts a partial detonation; and at 5.67 km/s and 6.53 km/s, both the computer analyses and the experiments give divergent detonations.     

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).     

Predicted Anisotropic Thermal Conductivity for Crystalline 1,3,5‐Triamino‐2,4,6‐trinitobenzene (TATB): Temperature and Pressure Dependence and Sensitivity to Intramolecular Force Field Terms

The anisotropic thermal conductivity of the layered molecular crystal 1,3,5‐triamino‐2,4,6‐trinitrobenzene (TATB), an insensitive secondary high explosive, is determined using classical molecular dynamics on the P=0.0 GPa isobar for temperatures 200 K≤T≤700 K and on the T=300 K isotherm for pressures 0.0 GPa≤P≤2.5 GPa. Sensitivity of the predicted (300 K, 0.0 GPa) conductivity to intramolecular terms in the force field is investigated. Two conduction directions are considered, one nominally within and the other exactly perpendicular to the stacked planar single‐molecule‐thick layers comprising the TATB crystal. The thermal conductivity λ(T,P) along both directions is found to decrease approximately as λ∝1/T with increasing temperature and increase approximately linearly λ ∝ T with increasing pressure. The temperature dependence is found to be highly anisotropic with nearly twice as large a reduction in absolute conductivity within the molecular layers (Δλ=−0.67 W m⁻¹ K⁻¹) compared to between them (Δλ=−0.35 W m⁻¹ K⁻¹). Anisotropy in the conductivity is predicted to decrease with increasing temperature; the P=0.0 GPa conductivity is 68 % greater within the layers than between them at 200 K, but only 49 % greater at 700 K. The pressure dependence is also anisotropic, with a 51 % and 76 % increase in conductivity within and between the layers, respectively. Predicted values for the conductivity are found to differ by less than 12 % for several instructive modifications to the intramolecular force field. Completely eliminating high‐frequency N H bond vibrations using the SHAKE algorithm leads to an isotropic reduction in the conductivity that scales as the corresponding reduction in the classical heat capacity, indicating that optical phonons are likely significant contributors to the total conductivity. Replacing harmonic bond potential energy functions with anharmonic Morse functions results in an isotropic ≈6 % reduction that is likely due to stronger phonon‐phonon coupling and corresponding reduction in the phonon mean free path.     

Shock Initiation of PBX-9404 by electrically driven flyer plates

The shock initiation threshold of PBX-9404 has been studied over the pressure range 3.1 GPa-28 GPa with pulse lengths ranging from 0.007 μs-0.63 μs. The short-duration, high pressure pulses were produced by the impact of thin plastic flyer plates accelerated by electrically exploded metal foils. We performed the experiments on explosive pellets 25.4 mm in diameter with thicknesses of 6.0 mm, 10.1 mm and 19.1 mm. No dependence of the initiation threshold on pellet thickness was observed. The data are represented reasonably well by either the critical initiation energy or by the constant P²τ initiation criteria.     

Hydrostatic Compression Curve for Triamino‐Trinitrobenzene Determined to 13.0 GPa with Powder X‐Ray Diffraction

Using powder X‐ray diffraction in conjunction with a diamond anvil cell (DAC), the unit cell volume of triamino‐trinitrobenzene (TATB) has been measured from ambient pressure to 13 GPa. The resultant isotherm is compared with previous theoretical (Byrd and Rice and Pastine and Bernecker) and experimental (Olinger and Cady) works. While all reports are consistent to approximately 2 GPa, our measurements reveal a slightly stiffer TATB material than reported by Olinger and Cady and an intermediate compressibility compared with the isotherms predicted by the two theoretical works. Analysis of the room temperature isotherm using the semi‐empirical, Murnaghan, Birch–Murnaghan, and Vinet equations of state (EOS) provided a determination of the isothermal bulk modulus (K_o) and its pressure‐derivative (K_o′) for TATB. From these fits to our P–V isotherm, from ambient pressure to 8 GPa, the average results for the zero‐pressure bulk modulus and its pressure derivative were found to be 14.7 GPa and 10.1, respectively. For comparison to shock experiments on pressed TATB powder and its plastic‐bonded formulation PBX 9502 (95% TATB, 5% Kel‐F 800), the isotherm was transformed to the pseudo‐velocity U_s–u_p plane using the Rankine–Hugoniot jump conditions. This analysis provides an extrapolated bulk sound speed, c_o=1.70 km s⁻¹, for TATB and its agreement with a previous determination (c_o=1.43 km s⁻¹) is discussed. Furthermore, our P–V and corresponding U_s–u_p curves reveal a subtle cusp at approximately 8 GPa. This cusp is discussed in relation to similar observations made for the aromatic hydrocarbons anthracene, benzene and toluene, graphite, and trinitrotoluene (TNT).     

Air Gaps,Size Effect,and Corner‐Turning in Ambient LX‐17

Various measurements under ambient conditions are presented for LX‐17. The size (diameter) effect has been measured with copper and Lucite confinement, where the failure radii are 4.0 and 6.5 mm, respectively. The air well corner‐turning has been measured with an LX‐07 booster, and the dead‐zone results are comparable to the previous TATB‐boosted work. Four double cylinders have been fired, and dead zones appear in all cases. The steel‐backed samples are faster than the Lucite‐backed samples by 0.6 μs. Bare LX‐07 and LX‐17 charges of 12.7 mm radius were fired with air gaps. Long acceptor regions were used to truly determine if detonation occurred or not. The LX‐07 booster crossed a 10 mm gap with a slight time delay. Steady‐state LX‐17 crossed a 3.5 mm gap but failed to cross a 4.0 mm gap. LX‐17 charge with a 12.7 mm radius run after the booster crossed a 1.5 mm gap but failed to cross a 2.5 mm gap. Timing delays were measured where the detonation crossed the gaps. The Tarantula model is introduced as embedded in reactive flow JWL++and Linked Cheetah V4, mostly at 4 zones mm⁻¹. Tarantula has four pressure regions: off, initiation, failure, and detonation. The physical basis of the input parameters is considered.     

A Miniature Device for Shock Initiation of Hexanitrostilbene by High‐Speed Flyer

A miniature device for shock initiation of the hexanitrostilbene (HNS) through micro‐charge detonation‐driven flyer was fabricated. This device consisted of the substrate, micro‐charge, flyer, and barrel. Four types of flyer (titanium of 28 μm, aluminum of 22 μm, copper of 22 μm and polyimide (PI) of 55 μm in thickness) were studied and the effect of micro‐charge thickness, diameter, and barrel length were investigated by measuring the average flyer velocities using polyvinylidene fluoride (PVDF) films. The results show that the titanium flyer is more proper for such initiation device compared to aluminum, copper, and polyimide flyer. The average velocity of the flyer increased with the thickness of micro‐charge and the increment was larger when the thickness increases from 0.3 mm to 0.4 mm than when the thickness increases from 0.4 mm to 0.6 mm. The flyer velocity significantly increased with the increase in the diameter of micro‐charge until a plateau appeared at 0.8 mm. The flyer velocity increased first and then decreased sharply with the increase in barrel length. The average velocity for a 28 μm thick titanium flyer was measured to be as high as 2468 m s⁻¹ when the thickness, micro‐charge diameter and the length of barrel were 0.6 mm, 0.8 mm and 659 μm, respectively. The HNS‐IV explosive with density 1.57 g cm⁻³ was initiated by this miniature device.     

Nanothermite/RDX‐Based Miniature Device for Impact Ignition of High Explosives

A miniature rocket device integrating nanothermite and RDX is presented for shock initiation of high explosive application. This Ø 2.5 mm device consists in several assembled and screwed parts: a pyroMEMS chip with a Al/CuO multilayers on it to ignite within less than 100 μs a few milligrams of nanothermite, which reacts violently and ignites within 150 μs a RDX charge compacted in the closed combustion chamber. The gases generated by the RDX combustion rapidly expand, cut and propel a Ø 2.5 mm by 1 mm thick stainless steel flyer in the barrel. After the presentation of the rocket design, fabrication and assembly, by measuring the pressure‐time evolution in the chamber we demonstrate the advantage to ignite the RDX with Al/Bi₂O₃ nanothermite to optimize the pressure impulse. We show that the stainless steel flyer of 40 mg is properly cut and propelled at velocities calculated from 665 to 1083 m s⁻¹ as a function of the RDX extent of compaction and ignition charge. As expected, the average flyer velocity increases with the mass of loaded RDX and flyer's shear thickness. We finally prove that the impact of the flyer can initiate directly in detonation a RDX explosive, which is very promising to remove primary explosives in detonator.     

Growth of 1,3,5-Triamino-2,4,6-trinitrobenzene (TATB) I. Anisotropic thermal expansion

Expansion of TATB is studied on a molecular level by means of x-ray crystallography. Continuous monitoring of the cell constants of TATB between 214 K and 377 K allows calculation of a volume change of +5.1% for this molecular system. Expansion of the pure material is almost exclusively a function of a 4% linear increase in the c axis (the perpendicular distance between sheets of hydrogen-bonded TATB). Calculated from these data, the volume coefficient of thermal expansion for crystalline TATB is 30.4 × 10⁻⁵ K⁻¹. The structural features of crystalline TATB and its anisotropic thermal-expansion behaviour are compared with those of graphite and boron nitride. Two other crystalline products in the bulk TATB are either actual polymorphs of TATB or impurities.     

Oxidative dehydrogenation of butenes over Bi‐Mo and Mo‐V based catalysts in a two‐zone fluidized bed reactor

The oxidative dehydrogenation of a 1‐butene/trans‐butene (1:1) mixture to 1,3‐butadiene was carried out in a two‐zone fluidized bed reactor using a Mo‐V‐MgO and a γ‐Bi₂MoO₆ catalyst. The significant operating conditions temperature, oxygen/butene molar ratio, butene inlet height, and flow velocity were varied to gain high 1,3‐butadiene selectivity and yield. Furthermore, axial concentration profiles were measured inside the fluidized bed to gain insight into the reaction network in the two zones. For optimized conditions and with a suitable catalyst, the two‐zone fluidized bed reactor makes catalyst regeneration and catalytic reaction possible in a single vessel. In the lower part of the fluidized bed, the oxidation of coke deposits on the catalyst as well as the filling of oxygen vacancies in the lattice can occur. The oxidative dehydrogenation reaction takes place in the upper zone. Thorough particle mixing inside fluidized beds causes permanent particle exchange between both zones. © 2016 American Institute of Chemical Engineers AIChE J, 63: 43–50, 2017     

Initiation Pressure Thresholds from Three Sources

Pressure thresholds are minimum pressures needed to start explosive initiation that ends in detonation. We obtain pressure thresholds from three sources. Run‐to‐detonation times are the poorest source but the fitting of a function gives rough results. Flyer‐induced initiation gives the best results because the initial conditions are the best known. However, very thick flyers are needed to give the lowest, asymptotic pressure thresholds used in modern models and this kind of data is rarely available. Gap test data are in much larger supply but the various test sizes and materials are confusing. We find that explosive pressures are almost the same if the distance in the gap test spacers are in units of donor explosive radius. Calculated half‐width time pulses in the spacers may be used to create a pressure‐time curve similar to that of the flyers. The very‐large Eglin gap tests give asymptotic thresholds comparable to extrapolated flyer results. The three sources are assembled into a much‐expanded set of near‐asymptotic pressure thresholds. These thresholds vary greatly with density: for TATB/LX‐17/PBX 9502, we find values of 4.9 and 8.7 GPa at 1.80 and 1.90 g/cm³, respectively.     

Preparation and Characterization of Nano‐TATB Explosive

Nano‐TATB was prepared by solvent/nonsolvent recrystallization with concentrated sulfuric acid as solvent and water as nonsolvent. Transmission Electron Microscopy (TEM) and Atomic Force Microscopy (AFM) were used to characterize the appearance and the size of the particles. The results revealed that nano‐TATB particles have the shape of spheres or ellipsoids with a size of about 60 nm. Due to their small diameter and high surface energy, the particles tended to agglomerate. By using X‐ray powder diffraction (XRD), broadening of diffraction peaks and decreasing intensity were observed, when the particle sizes decreases to the nanometer size range. The corrected average particle size of nano‐TATB was estimated using the Scherrer equation and the size ranged from 27 nm to 41 nm. Furthermore, the specific surface area and pore diameter of nano‐TATB were determined by BET method. The values were 22 m²/g and 1.7 nm respectively. Thermogravimetric (TG) and Differential Scanning Calorimetric (DSC) curves revealed that thermal decomposition of nano‐TATB occurs in the range of 356.5 °C–376.5 °C and its weight loss takes place at about 230 °C. Furthermore, a slight increase in the weight loss was observed for nano‐TATB in comparison with micro‐TATB.     

Investigation of shock detonation of TATB using proton radiography

The initiation of detonation of plasticized TATB by shock loading using an initiator pressure charge of an HMX based explosive was studied by radiography. In the experiments, the size of the initiator and the initial density of the TATB charge were varied. During initiation of TATB detonation, part of the material did not react, forming so-called dark zones. As the process goes on, the detonation wave bends around the dark zones, without initiating the material within them. The evolution of the area of dark zones was compared for samples of different initial density and initiators of different sizes. The characteristic boundaries and X−t diagrams of detonation front propagation under different loading conditions were constructed from images of the explosive process. Density distributions behind a divergent detonation wave front at different times were obtained and analyzed.     

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.     

Crosslinking reaction and properties of two‐component waterborne polyurethane from terpene‐maleic ester type epoxy resin

A two‐component waterborne polyurethane (2K‐WPU) is prepared with the terpene‐maleic ester type epoxy resin‐based polyol dispersion and a hydrophilically modified hexamethylene diisocyanate tripolymer. Laser particle size analyzer and transmission electron microscopy are used to characterize the particle size distribution and the micromorphology of the 2K‐WPU. Crosslinking reaction kinetics of the 2K‐WPU is examined by fourier transform infrared spectrometry (FTIR) spectra. In the preliminary stage of the crosslinking reaction, it shows a very good fit with a second order reaction kinetics, and the apparent activation energy is 94.61 kJ mol^?1. It is also shown from the FTIR spectra that the complete crosslinking reaction of the 2K‐WPU needs 7 h at 70°C. The crosslinked products of the 2K‐WPU have good thermal resistant properties, with glass‐transition temperatures (T_g) in the range of 35–40°C and 10% weight loss temperatures (T_d) in the range of 275–287°C. The films obtained from the crosslinked products have good water‐resistance, antifouling, blocking resistance properties and impact strength of >50 cm, flexibility of 0.5 mm, adhesion of 1 grade, pencil hardness of HB‐2H. The pencil hardness and thermal‐resistant properties of the crosslinked products increase with the molar ratio of isocyanate (? NCO) group to hydroxyl (? OH) group. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Fracture behaviour of a rubber nano-modified structural epoxy adhesive: Bond gap effects and fracture damage zone

This paper critically examined the fracture behaviour of a rubber-modified, structural epoxy adhesive with various bond gap thicknesses ranging from 0.05 mm to 6 mm. The main and very novel contribution is direct measurement of the fracture process zone, plastic deformation zone and intrinsic fracture energy dissipated in the fracture process zone. The shape and size of the fracture process zone and plastic deformation zone were identified using scanning electron microscopy, transmission electron microscope and transmission optical microscope. As the bond gap thickness increased, the fracture energy increased steadily from 2365 J/m² for 0.05 mm bond gap thickness to 6289 J/m² of 1.6 mm bond gap thickness, and then plateaued. The thickness and failure strain of the fracture process zone remained essentially constant, being approximately 0.052 mm and 0.55 respectively, for different bond gap thicknesses. The intrinsic fracture energy (dissipated in the fracture process zone) appeared to be a material property, which remained approximately 2738 J/m². The plastic deformation zone extended through the entire bond gap in thickness and occupied a significant length for all bond gap thicknesses. The effect of bond gap thickness on the fracture energy of the adhesive joints is hence directly attributed to the variation of the plastic deformation energy (dissipated in the plastic deformation zone) with bond gap thickness.     

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.     

Selective and Practical Oxidation of Sulfides to Diastereopure Sulfoxides: A Combined Experimental and Computational Investigation

We describe an effective oxidation of diltiazem (DTZ)‐like molecules (a class of prochiral sulfides with potential pharmacological properties) using m‐chloroperbenzoic acid (MCPBA) as oxidant either in dichloromethane or methanol. An excellent diastereomeric excess of one sulfoxide has been observed “in the absence of any chiral auxiliary”. The stereochemistry of the two diastereomeric sulfoxides has been determined by TDDFT simulations of the experimental electronic circular dichroism (ECD) spectra. A computational DFT study of the reaction mechanism shows that the attack of MCPBA on the two sulfide enantiotopic faces affords two preliminary complexes M1 and M1′. M1 is more stable than M1′ by 3.3 and 3.5 kcal mol⁻¹ in dichloromethane and methanol, respectively, and after equilibration its population must be dominant. Two diastereomeric pathways originate from M1 and M1′ and give two diastereomeric sulfoxides with R and S configurations at the new chiral sulfur, respectively. Since TS (the transition state originating from M1 ) is more stable than TS′ (the energy gap is 0.7 kcal mol⁻¹ in dichloromethane or methanol), following the Curtin–Hammett principle, the favoured path is the pro‐R channel ( M1 → TS→M2 ) affording the (R_c,R_s)‐ 2a′ product species in agreement with the observed diastereoselectivity. The M1 – M1′ and TS – TS′ energy gaps are actually determined by the difference in the hydrogen bond network that features the two species even if the approaching orientation of the two molecules is governed by the interactions between the π systems of oxidant and substrate aromatic rings. The diastereomeric ratio computed on the basis of the energy difference between TS and TS′ (0.7 kcal mol⁻¹) is 63:37, which must be compared to the experimental value 9:1. When we consider free energy differences (2.4 kcal mol⁻¹ in vacuum and 2.9 kcal mol⁻¹ in solution) this theoretical ratio becomes 85:15 and 89:11, respectively, in excellent agreement with the experimental value 9:1.     

Investigation of the reaction zone in heterogeneous explosives substances using an electrical conductivity method

A technique for measuring the electrical conductivity profile behind a detonation wave front with a resolution of about 0.1 mm was used to analyze the reaction zone in heterogeneous explosives. TNT-RDX mixtures, RDX with additives of water, NaCl, and a saturated aqueous solution of NaCl, and pure RDX of low density were studied. It was shown that the particle size of the explosive can have a significant effect on the structure of the reaction zone. The most narrow conducting zone (0.22 mm) was observed in fine RDX of density 1.2 g/cm³. __________ Translated from Fizika Goreniya i Vzryva, Vol. 45, No. 2, pp. 109–115, March–April, 2008.