Preparation and Properties of 2,6‐Diamino‐3,5‐dinitropyrazine‐1‐oxide based Nanocomposites

With estane as binder, a new nanocomposite energetic material based on 2,6‐diamino‐3,5‐dinitropyrazine‐1‐oxide (LLM‐105) was successfully prepared by the spray drying method. Scanning Electron Microscope (SEM), Transmission Electron Microscope (TEM), and X‐ray diffraction (XRD) was employed to characterize the nanocomposite samples. The impact sensitivity and thermal decomposition properties of the nanocomposites were also measured and analyzed. The results show that the nanocomposite particles are spherical in shape and range from 1 μm to 10 μm in size. The composite is aggregated of many tiny granules with nucleus/shell structure, in which the shell thickness and crystal size of LLM‐105 are about 20 nm and 50–100 nm. The crystal type of LLM‐105 in the nanocomposite is similar to that of raw LLM‐105, however, the diffraction peaks become weaker and wider mainly due to decreasing of particle size. The nanocomposite has lower impact sensitivity and better thermal stability.     

Dependence of the Mechanical Sensitivity on the Fractal Characteristics of Octahydro‐1,3,5,7‐tetranitro‐1,3,5,7‐tetrazocine Particles

Three fabrication methods were used to synthesize HMX powders with different particle sizes and microscopic morphologies. All as‐prepared samples were characterized by laser granularity measurements and scanning electron microscopy (SEM). The mechanical sensitivity and thermal stability of the different HMX powders were characterized using mechanical sensitivity tests and differential scanning calorimetry (DSC). Size distribution data and SEM images were used to find the size fractal dimension (D) and surface fractal dimension (D_s) of HMX samples, which were calculated by the least‐squares method and fractal image processing software (FIPS), respectively. The parameters D and D_s quantize two important properties of HMX particles, namely the complexity of the particle size distribution and the irregularity of the particle surface, which affect the thermal conductivity of the particle group if it is exposed to stimuli such as impact, friction or heating. The fractal dimensions reveal the dependence of the mechanical sensitivity of HMX on the powder size, size distribution and microscopic morphology. The results indicate that the proportion of fine particles in HMX powder increases as the D value increases, which causes decreased impact sensitivity. This occurs because hot spot formation leading to an explosion is more difficult because of the improved thermal conductivity of the particle group. Similarly, the surface roughness of HMX particles increases with an increase in D_s, causing an increase in friction sensitivity because of the excessive accumulation of frictional heat. In addition, thermal analysis results indicate that the maximum thermal decomposition rate of HMX decreases with increasing D and D_s.     

Pressurized Nozzle‐Based Solvent/Anti‐Solvent Process for Making Ultrafine ϵ‐CL‐20 Explosive

CL‐20 explosive is one of the most recent and powerful explosives. It has very high potential in futuristic applications but at present it has limitations of sensitivity to mechanical stimuli. Among the four different polymorphs (α, β, γ, and ϵ), ϵ‐polymorph has better stability and shock/detonics properties. However, preparation of pure ϵ‐polymorph is a challenging task particularly in terms of repeatability and polymorphism. In our research work, pressurized nozzle based solvent/anti‐solvent process (PNSAP) was developed for the preparation of ultrafine ϵ‐CL‐20 explosives with high repeatability, purity, and yield. To get ultrafine particle size, shape, distribution and yield, various process parameters/ variables such as solvent type, anti‐solvent type, dosing rate, stirring rate, ultra‐sonication, and temperature were identified and prioritized using the weighted average method of Analytical Network Process (ANP) techniques. It was observed that ultrafine ϵ‐CL‐20 particle size in the range of 2 to 3 μm can be obtained using this process. The ϵ‐polymorph was confirmed by FT‐IR characterization. The main feature of this PNSAP process is that it is a laboratory scale table‐top pilot plant which is simple, cost‐effective, safe and repeatable for continuous batch production of ultrafine ϵ‐CL‐20 at the rate of 100 grams per hour.     

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.     

Catalytic Effect of Two Shapes of Nano‐Fe2O3 on Hexanitrohexaazaisowurtzitane Using a Non‐Isothermal Decomposition Kinetic Method

Nanosized Fe₂O₃ particles (nano‐Fe₂O₃) with two shapes (tetrakaidecahedral and grainy) were synthesized by hydrothermal methods. The morphologies and structures were characterized using a combination of experimental techniques including X‐ray diffraction (XRD) and scanning electron microscopy (SEM). Two composites containing CL‐20 (hexanitrohexaazaisowurtzitane, HNIW) and tetrakaidecahedral nano‐Fe₂O₃ [nmT‐Fe₂O₃/CL‐20] or grainy nano‐Fe₂O₃/CL‐20 (nmG‐Fe₂O₃/CL‐20) were prepared. The thermal behaviors of the two composites and pure CL‐20 were investigated using differential scanning calorimetry (DSC). Non‐isothermal decomposition kinetic parameters and the thermal decomposition mechanism of the two composites and CL‐20 were obtained. The apparent activation energy (E_a) of the main thermal decomposition reaction of CL‐20, nmT‐Fe₂O₃/CL‐20 and nmG‐Fe₂O₃/CL‐20 are 181.94, 179.17, and 176.18 kJ mol⁻¹, respectively. The thermal decomposition mechanism of CL‐20 as well as nmT‐Fe₂O₃/CL‐20 was controlled by the Avrami‐Erofeev equation (n=2/5) assumed as random nucleation and subsequent growth, while, the reaction mechanism of the composite nmG‐Fe₂O₃/CL‐20 was controlled by the Mample Power law (n=1/2). The reason for this difference may be due to the different morphology and particle size of the two nano‐Fe₂O₃ particles.     

Preparation and Properties of Submicrometer‐Sized LLM‐105 via Spray‐Crystallization Method

Submicrometer‐sized 2,6‐diamino‐3,5‐dinitropyrazine‐1‐oxide (LLM‐105) crystals were prepared by spray‐crystallization method with dimethyl sulfoxide (DMSO) and ultra‐pure water with surfactant as the solvent and anti solvent, respectively. Submicrometer‐sized LLM‐105 particles were characterized by scanning electron microscopy (SEM), X‐ray diffraction (XRD), and particle size analysis. The thermal stability and sensitivity properties of submicrometer‐sized LLM‐105 were also investigated. The results revealed that the submicrometer‐sized LLM‐105 particles are spherelike in morphology with a narrow particle size distribution at the range of 100–600 nm. The submicrometer‐sized LLM‐105 has a lower exothermic peak at about 343.7 °C compared with the synthesized material. Sensitivity tests showed that submicrometer‐sized LLM‐105 is more insensitive under impact stimulus with a drop height (H₅₀) of 102 cm. The submicrometer‐sized LLM‐105‐based PBX is more sensitive for short impulse shock wave that can be initiated at lower initiation current.     

Preparation and Performances of Castable HTPB/CL‐20 Booster Explosives

HTPB/CL‐20 castable booster explosives were prepared successfully by a cast‐cured process. Scanning electron microscope (SEM) and the charge density test were employed to characterize the molding effect of HTPB/CL‐20 explosives. The propagation reliability, detonation velocity, mechanical sensitivity, thermal decomposition characteristics and thermal stability of the HTPB/CL‐20 explosives were also measured and analyzed. The results show that, when CL‐20 content is less than 91 wt.‐%, the charges with better molding effect were obtained easily. The critical diameter of HTPB/CL‐20 explosives is less than 1 mm, which exhibits good propagation reliability. When the density of HTPB/CL‐20 charge with 91 wt.‐% CL‐20 is 1.73 g cm⁻³, its detonation velocity can reach 8273 m s⁻¹. Moreover, this kind of explosives has low mechanical sensitivity and good thermal stability.     

Nano Cyclotetramethylene Tetranitramine Particles Prepared by a Green Recrystallization Process

The solubility of cyclotetramethylene tetranitramine (HMX) in four ionic liquids (ILs): 1,3‐dimethylimidazolium dimethylphosphate ([Memim]DMP), 1‐butyl‐3‐methylimidazolium chloride ([Bmim]Cl), 1‐hexyl‐3‐methylimidazolium bromide ([Hmim]Br), and 1‐ethyl‐3‐methylimidazolium tetrafluoroborate ([Emim]BF₄) was investigated. Nano‐HMX were produced particles by spraying [Hmim]Br solution into purified ice water. Finally, the particle size, morphology, crystal phase, impact sensitivity, and thermal decomposition properties of nano‐HMX particles were tested and analyzed. All four ILs could dissolve HMX to a greater or lesser extent in the temperature range from 20 °C to 80 °C. The solubility of HMX in [Hmim]Br at 80 °C is up to 0.7 g mL⁻¹. Recrystallized HMX particles are of polyhedral or spherical shape and 40 to 130 nm in size. X‐ray diffraction indicated that nano‐HMX has a similar crystal structure as raw HMX (β‐form). Compared with raw HMX, the nano‐HMX particles have much lower impact sensitivity. However, they are easier to explode than raw HMX under thermal stimulus due to the lower peak temperature and activation energy.     

Preparation of temperature‐ and pH‐sensitive,stimuli‐responsive poly(N‐isopropylacrylamide‐co‐methacrylic acid) nanoparticles

The effects of the monomer ratio, surfactant, and crosslinker contents on the particle size and phase‐transition behavior of the copolymer poly(N‐isopropylacrylamide‐co‐methacrylic acid) (PNIPAAm–MAA) were investigated with Fourier transform infrared, differential scanning calorimetry, and dynamic laser scattering techniques. In addition to the thermoresponsive property of poly(N‐isopropylacrylamide), ionized methacrylic acid groups brought pH sensitivity to the PNIPAAm–MAA copolymer particles. The polymer particle size varied with the amounts of the monomer ratio, surfactant, and crosslinker. As the monomer ratio and crosslinker content increased and the amount of the surfactants decreased, the particle size increased. The influence of the crosslinker content on the particle size was less significant than the effect of the monomer ratio and surfactants. When the temperature increased, the particles tended to shrink and decreased in size to near or below 100 nm. Particle sizes at 20°C decreased to less than 100 nm with increased surfactant content. The control of the particle size within the 100‐nm range makes PNIPAAm–MAA copolymer particles useful for biomedical and heavy‐metal‐ion adsorption applications. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

The Synthesis and Energetic Properties of 5,7‐Dinitrobenzo‐1,2,3,4‐tetrazine‐1,3‐dioxide (DNBTDO)

Energetic tetrazine‐1,3‐dioxide, 5,7‐dinitrobenzo‐1,2,3,4‐tetrazine‐1,3‐dioxide ( DNBTDO ), was synthesized in 45 % yield. DNBTDO was characterized as an energetic material in terms of performance (V_det 8411 m s⁻¹; p_{C J} 3.3×10¹⁰ Pa at a density of 1.868 g cm⁻³), mechanical sensitivity (impact and friction as a function of grain size), and thermal stability (T_dec 204 °C). DNBTDO exhibits a sensitivity slightly higher than that of RDX , and a performance slightly lower (96 % of RDX ).     

Electrochemical Deposition of 58SiO2‐33CaO‐9P2O5 Nanobioactive Glass Particles on Ti‐6Al‐4V Alloy for Biomedical Applications

The nanobioactive glass (58SiO₂‐33CaO‐9P₂O₅) powders were synthesized by simple sol–gel method. The prepared samples reveal amorphous nature, agglomerated spherical morphology with particle size of 100–150 nm. The specific surface area of nanobioactive glass (NBG) particle is 147 m²/g. The NBG samples were coated on titanium (Ti‐6Al‐4V) alloy through electrochemical deposition method. The particle size of the NBG‐coated surface was in the order of 200–300 nm, and it was confirmed by atomic force microscopy (AFM) analysis. In vitro and AFM studies reveal the existence of higher bioactivity and uniform coating of NBG on implants at 80 V for 1 h.     

Preparation of Nano‐Structured RDX in a Silica Xerogel Matrix

RDX is preferred as explosive in munitions due to its balance of power and sensitivity that is known to be dependent on its particle size and size distribution. In this study, we prepared nano‐sized RDX in a silica xerogel matrix using a sol‐gel method and investigated its sensitivity for explosive properties. The presence of RDX in composite xerogel was confirmed by TG‐DSC and FTIR techniques. Microstructure and porosity were characterized by transmission electron microscopy (TEM), small angle X‐ray scattering, and N₂‐physisorption techniques. TEM results showed that the size of RDX particles in the RDX‐silica composites is in the range of 10–30 nm. The sensitivity to impact and friction was found to be higher for the composites compared to raw RDX. It was also found to be significantly dependent on the acetone/TMOS ratio used in the preparation.     

Thermal Decomposition of Energetic Materials 86. Cryogel Synthesis of Nanocrystalline CL‐20 Coated with Cured Nitrocellulose

An unusual energetic composite, in which spherical nano‐dimensional particles of CL‐20 were uniformly coated with HDI‐cross‐linked nitrocellulose, was synthesized by the sol‐gel to cryogel method. Up to 90% solid loading was achieved. The particle size of CL‐20 was determined to be in the range of 20–200 nm by transmission electron microscopy, atomic force microscopy, and X‐ray powder diffraction. The decomposition characteristics of the composite were investigated by DSC and T‐jump/FTIR spectroscopy. The decomposition properties were controlled mostly by nitrocellulose until the percentage of CL‐20 was well above 50%. The drop weight impact sensitivity of the cryogels was essentially independent of the composition.     

Novel methods for synthesis of high‐impact polystyrene with bimodal distribution of rubber particle size

By using in situ prepolymerization and radiation curing, high‐impact polystyrene (HIPS) with a bimodal distribution of the size of the rubber particles (bimodal HIPS) was synthesized in the presence of ultrafine full‐vulcanized powdered styrene–butadiene rubber (UFPSBR) and polybutadiene rubber (BR). TEM photographs indicated that UFPSBR was dispersed uniformly as a single particle with a diameter of about 100 nm. On the other hand, bimodal HIPS with different rubber particle size distributions could also be obtained by blending HIPS and UFPSBR grafting styrene (UFPSBR‐g‐St) with different grafting yields. The bimodal HIPS with the smallest rubber particle size, at about 100 nm, could be prepared by blending the monomodal HIPS containing big rubber particles with polystyrene/UFPSBR. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

非溶剂制备细化HMX及其性能表征

以二甲基亚砜为溶剂,用喷雾重结晶细化法制备了HMX,研究了非溶剂(水、乙醇、氯代烷烃)的种类、溶剂与非溶剂的体积比以及非溶剂的温度对HMX晶体形貌的影响并分析了其影响机理。采用扫描电子显微镜(SEM)、激光粒度分析仪、X射线衍射仪(XRD)、差示扫描热量法(DSC)对其进行了表征和热分析。测试了细化HMX和原料HMX的撞击感度。结果表明,HMX细化最佳工艺条件是以35℃乙醇为非溶剂,溶剂与非溶剂体积比为1∶40,此时可获得中值粒径为616nm、粒径分布均匀、趋于球形且表面光滑的亚微米HMX;亚微米HMX表观活化能比原料HMX降低了13.75kJ/mol,与原料HMX相比具有更好的热安定性,特性落高从34.05cm升至79.10cm,撞击感度显著降低。     

Comparative Investigation of Thermal Decomposition of Various Modifications of Hexanitrohexaazaisowurtzitane (CL‐20)

The thermal decomposition kinetics of different polymorphs of CL‐20 (α, γ and ε) has been investigated by thermogravimetry, IR spectroscopy and optical and electronic microscopy. The reactions proceed with self‐acceleration and can be described by a kinetic law of first order with autocatalysis. Already at the earliest stages of decomposition (≤1%) phase transitions take place from αγ and from εγ. For this reason the observed decomposition is related to the decomposition of γ‐CL‐20. On the other hand, the kinetics of decomposition depends on the initial polymorphic state, so that the thermal decomposition increases in the series: α<γ<ε. Experiments with different samples of α‐CL‐20 demonstrate that different rates of decomposition are observed for the same polymorph depending on the mean size and the size distribution of the crystals and their morphological features. In some cases the thermal stability of α‐CL‐20 can be increased by previous annealing. It is concluded that the thermal decomposition of CL‐20 is purely a solid‐state process. Microscopical and spectroscopical analysis of the condensed CL‐20 decomposition product (formed after prolonged heating at high temperature) show that it has a network structure and consists mainly of carbon and nitrogen.     

Properties of high‐temperature drilling fluids incorporating disodium itaconate/acrylamide/sodium 2‐acrylamido‐2‐methylpropanesulfonate terpolymers as fluid‐loss reducers

The terpolymer of disodium itaconate (DIA), acrylamide (AM) and sodium 2‐acrylamido‐2‐methyl‐1‐propane sulfonate (SAMPS) was synthesized through free‐radical polymerization, and characterized using FTIR and TGA methods. The IR spectra of DIA‐AM‐SAMPS terpolymer confirmed that there was no olefinic band at 1635–1620 cm^?1, while the TGA results revealed that the terpolymer was of higher thermal stability than the SAMPS homopolymer. The filtrate volume reduced with increase of the terpolymer concentration before or after the aging test. The rheology properties of both fresh‐water mud and salt‐water mud were improved by DIA‐AM‐SAMPS terpolymer, and apparent viscosity (η_a); plastic viscosity (η_b) and yield point (τ₀) of salt‐water mud reached the smallest values at 1.2% of the terpolymer concentration after the aging test. The particle size data demonstrated that only a small change of the clay particle size occurred before and after the aging test at 220°C. This further confirmed the thermal stability of the terpolymer–clay dispersion from another point of view. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 3068–3075, 2002; DOI 10.1002/app.2335     

CL‐20 Evaporative Crystallization under Reduced Pressure

The effect of parameters of the CL‐20 crystallization process carried out by solvent removal by evaporation in vacuo on shape, polymorph type, crystal size, and on their shock sensitivity was studied. The CL‐20 crystallization process by this technique was shown to allow a precise control of the crystallization process parameters and of the process run. The o‐xylene/ ethyl acetate system proved to be highly effective. Selecting suitable values of the parameters such as: pressure, process time, temperature, stirring rate, CL‐20 crystals were obtained in the ε form (even with no need for inoculation of the crystallization system with polymorph ε seeds) and of the shape close to a spherical one. The crystal growth modifiers added allowed to additionally control the shape and size of the CL‐20 crystals formed and to produce crystals of reduced impact and friction sensitivity.     

Role of acrylic acid in the synthesis of core‐shell fluorine‐containing polyacrylate latex with spherical and plum blossom‐like morphology

The core‐shell fluorine‐containing polyacrylate latex was successfully synthesized by two‐stage semicontinuous emulsion copolymerization of methyl methacrylate (MMA), butylacrylate (BA), acrylic acid (AA), and dodecafluoroheptyl methacrylate (DFMA). The fluorine‐containing polyacrylate latex was characterized by Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), dynamic light scattering (DLS), zeta potential, thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC). The effects of AA content on monomer conversion, polymerization stability, particle size, corsslinking degree, carboxyl groups distributions (latex surface, aqueous phase or buried in latex), as well as mechanical properties and water absorption rate of latex film were investigated. The obtained fluorine‐containing polyacrylate latex exhibited core‐shell structure with a particle size of 120–150 nm. The introduction of AA was beneficial for the increase of monomer conversion and the polymerization stability, and had little effects on the mechanical property of latex film. However, the hydrophilicity of AA made the water resistance of latex film get bad. With the increase of AA content, the carboxyl groups preferred to distribute on aqueous phase, and the possibility of homogeneous nucleation increased and more oligomers particles were formed. Moreover, the oligomers would distribute to the latex and continued to grow up, making the latex morphology changed from spherical to plum blossom‐like. The core‐shell latex had two T_g corresponding to the rubber polyacrylate core and hard fluorine‐containing polyacrylate shell, and the latex film possessed excellent thermal stability. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42527.     

Voids and Density Distributions in 2,4,6,8,10,12‐Hexanitro‐2,4,6,8,10,12‐Hexaazaisowurtzitane (CL‐20) Prepared Under Various Conditions

The density distributions of six samples of CL‐20 were measured using the density gradient technique. This technique was used to determine which preparation procedure produced the highest average CL‐20 density. Assuming crystals with fewer flaws result in reduced sensitivity to shock initiation, higher average crystal density (closest to the theoretical maximum density) would imply the least number of voids or inclusions. Based on hot‐spot theory, better crystals, i.e., smaller number of flaws will reduce the shock sensitivity and perhaps other impact initiation mechanisms as well. Six samples from different synthesis and crystallization procedures gave average densities from 2.042 to 2.0230 g/cm³ as measured by density gradient. Assuming the voids have no density, the crystals were between 99.90 to 98.98% of the theoretical maximum density (TMD for ε‐CL‐20 is 2.044 g/cm³). An attempt was made to account for the density difference by identifying voids in the crystals using polarized light microscopy. This method also gave some insight into the different morphologies produced by different crystallization techniques. In 3 cases voids on the order of several micrometers could be resolved in large CL‐20 crystals.