Impact Sensitivity Research Articles

Fabrication of micro/nano spherulitic hierarchical energetic materials via noncrystallographic branching induced by polymer additives: A case study of 2,2′,4,4′,6,6′-hexanitrostilbene (HNS)

In this work, the micro/nano spherulitic hierarchical 2,2′,4,4′,6,6′-hexanitrostilbene (HNS) with the excellent specific surface area was prepared for the first time, which was expected to overcome the agglomeration problems of nanoscale HNS. In detail, poly(N-isopropyl acrylamide) (PNIPAM), polysuccinimide (PSI), and polyvinylpyrrolidone (PVP) were selected as additives to induce forming spherulitic HNS. Leaflike crystals were obtained in the presence of PNIPAM, while spherulitic HNS could be fabricated in the presence of PSI or PVP. And the prepared spherulitic HNS owned nearly 6 times the specific surface area of the raw HNS, with decreased impact sensitivity and advanced melting and decomposition temperatures, demonstrating a good desensitization effect, and a favorable energy release of the hierarchical structure. Moreover, morphological changes under the effect of the molecular weight and concentration of PVP were explored. The approximated morphological evolution of spherulitic HNS was consistent with the classical spherulitic growth by noncrystallographic branching. Furthermore, it was verified that preferential adsorption of PVP and PSI on the HNS inhibits the growth steps of the (200) face and introduces stress to generate crystal defects, which triggers noncrystallographic branching and further spherulitic growth. Overall, the strategy of fabricating micro/nano spherulitic hierarchical energetic materials via polymer-additive induced noncrystallographic branching is promising to solve the problems of nanoscale energetic materials in agglomeration and microscale bulk crystals in low activity.

To explore the relationship between energy transfer rate and impact sensitivity by the first-principle calculation method

To investigate the relationship between impact sensitivity and energy transfer rate, the energy transfer behaviors of seven energetic materials were estimated. We divide energy transfer in molecules into two parts, which are the intramolecular energy transfer and the outward energy dissipation between the molecules, respectively. We use new defined parameter T to reflect the rate of energy transfer within the molecule. The sound velocity is used to reflect the rate at which energy is dissipated out of the molecule. The results show that the faster the energy transfer and the slower the intermolecular dissipation, the more sensitive the energetic material is.

A new CL‐20/1,4‐DNP cocrystal explosive with good comprehensive performance

AbstractA new energetic cocrystal of 2,4,6,8,10,12‐hexanitrohexaazaisowurtzitane (CL‐20) and 1,4‐dinitropyrazole (1,4‐DNP) with a 1 : 1 molar ratio was prepared by slow solvent evaporation. This cocrystal belongs to monoclinic system with P21/c space group formed mainly by the CH−O, CH−N, and NO2−π interactions through analyzing the structures and interactions. CL‐20/1,4‐DNP cocrystal has a melting point of 132 °C with a decomposition temperature of 253 °C, showing an excellent stability. Moreover, the impact sensitivity of the cocrystal (13.5 J) is similar to that of 1,1‐diamino‐2,2‐dinitroethene (FOX‐7, 14 J), a typical insensitive energetic material, indicating a favorable low sensitivity. Furthermore, the detonation performances of the cocrystal (8954 m/s, 35.90 GPa) are slightly superior to that of 1,3,5‐trinitro‐1,3,5‐ triazacyclohexane (RDX, 8877 m/s, 34.94 GPa), suggesting that CL‐20/1,4‐DNP cocrystal has an excellent detonation property. Therefore, the CL‐20/1,4‐DNP cocrystal may be an attractive new explosive with a good comprehensive performance and thus, may be used as a promising candidate instead of RDX for safety ammunitions in future.

Insensitive High-Energy Density Materials Based on Azazole-Rich Rings: 1,2,4-Triazole N-Oxide Derivatives Containing Isomerized Nitro and Amino Groups.

It is an arduous and meaningful challenge to design and develop new energetic materials with lower sensitivity and higher energy. How to skillfully combine the characteristics of low sensitivity and high energy is the key problem in designing new insensitive high-energy materials. Taking a triazole ring as a framework, a strategy of N-oxide derivatives containing isomerized nitro and amino groups was proposed to answer this question. Based on this strategy, some 1,2,4-triazole N-oxide derivatives (NATNOs) were designed and explored. The electronic structure calculation showed that the stable existence of these triazole derivatives was due to the intramolecular hydrogen bond and other interactions. The impact sensitivity and the dissociation enthalpy of trigger bonds directly indicated that some compounds could exist stably. The crystal densities of all NATNOs were larger than 1.80 g/cm3, which met the requirement of high-energetic materials for crystal density. Some NATNOs (9748 m/s for NATNO, 9841 m/s for NATNO-1, 9818 m/s for NATNO-2, 9906 m/s for NATNO-3, and 9592 m/s for NATNO-4) were potential high detonation velocity energy materials. These study results not only indicate that the NATNOs have relatively stable properties and excellent detonation properties but also prove that the strategy of nitro amino position isomerization coupled with N-oxide is an effective means to develop new energetic materials.

Experiment and Molecular Dynamic Simulation on Performance of 3,4-Bis(3-nitrofurazan-4-yl)furoxan (DNTF) Crystals Coated with Energetic Binder GAP

To investigate the crystallization of DNTF in modified double-base propellants, glycidyl azide polymer (GAP) was used as the coating material for the in situ coating of DNTF, and the performance of the coating was investigated to inhibit the crystallization. The results show that GAP can form a white gel on the surface of DNTF crystals and has a good coating effect which can significantly reduce the impact sensitivity and friction sensitivity of DNTF. Molecular dynamics was used to construct a bilayer interface model of GAP and DNTF with different growth crystal surfaces, and Molecular dynamics calculations of the binding energy and mechanical properties of the composite system were carried out. The results showed that GAP could effectively improve the mechanical properties of DNTF. The values of K/G, γ and ν are higher than those of DNTF crystals, and the values of C12-C44 are positive, indicating that GAP can improve DNTF ductility while also improving toughness. Combining the experimental results with the simulation calculations, energetic binder GAP can be referred to as a better cladding layer for DNTF, which is feasible for inhibiting the DNTF crystallization problem in propellants.

Theoretical exploration of polynitrogen compounds N6, N8, N10, and N6 ions based on N3 − and cyclo-N5 −

ABSTRACT Polynitrogen energetic materials have become an important branch of high-energy-density materials. In this work, a thorough theoretical exploration of polynitrogen compounds N6, N8, N10, and N6 ions was conducted based on N3 − and pentazolate anion (cyclo-N5 −). Based on quantum chemistry calculations and wavefunction analyses, the equilibrium geometry, bond orders, atoms-in-molecules analysis, atomic charges, electrostatic potential distribution, frontier molecular orbitals, and many indices to represent aromaticity were determined and represented. In addition, their densities, heat of formation, detonation properties, and impact sensitivities were calculated using thermodynamics methods. These polynitrogen compounds could exhibit good density (1.578–1.814 g cm−3); high heat of formation (7.45–8.05 kJ g−1); excellent detonation performance (D: 9206–10413 m s−1, P: 34.8–44.7 GPa). The detonation performance demonstrates that polynitrogen compounds are promising energetic materials.

Understanding the alkyl effect of geminal dinitropropyl ester energetic plasticizers on hydroxyl terminated polybutadiene (HTPB): Simultaneous tuning on low temperature behavior and processability

Geminal dinitropropyl ester plasticizers (DNPEPs) possess excellent energetic performances which provide good potentials as insensitive plasticizer. In this study, we design and synthesize DNPEPs with different alkane chain parts, and systematically investigate their structure-property relationships. Results show that DNPEPs have impact sensitivities all higher than 25.2 J, thermal decomposition temperatures all higher than 254 °C, and glass transition temperatures ( T g ) lower than −90 °C. Furthermore, the effects of DNPEPs as plasticizer are studied on hydroxyl terminated polybutadiene (HTPB) in detail, including the viscosity, glass transition temperatures and others. It is noteworthy that 2,2-dinitropropyl nonanoate (DNPNc) among these DNPEPs exhibits the most expected simultaneous tuning effects on both viscosity and T g of HTPB systems, providing favorable potentials to replace the conventional plastizers as dioctyl sebacate (DOS) in the HTPB based propellants and explosives.

Impact and Friction Sensitivities of PETN: II. Sensitivities of the Acidic Material During Manufacturing

AbstractIn this second part of our work on the sensitivity of pentaerythritol tetranitrate (PETN) the investigations focus on the manufacturing process. Literature about the explosive during production is very rare and optimization or changes in the process demand more in‐depth knowledge of the safety parameters. Therefore, the industrial process is imitated in a small‐scale laboratory reactor. Then impact and friction sensitivities of emergency drowned, spent acid wet and acid washed PETN are investigated. In advance, PETN samples were taken from the filter of the SSE production and measured in the same manner. It becomes clear at which point a sensitive material is expected in the process. The data will improve handling safety and plant design.

New cage super insensitive high energy materials constructed by the Diels-Alder reaction based on nitroazoles: A DFT study

In this work, seven series of new advanced cage insensitive high energy materials were constructed by one step of Diels-Alder reactions, using nitroazoles and aminoethylenes as dienes and dienophiles, respectively. The detailed reaction direction, reaction type and reaction barrier of Diels-Alder reactions were investigated by DFT computations, and found that most of dienes are most possibly to react with tetraaminoethylene though the inverse Diels-Alder reaction with low energy barrier, while this is the neutral one for the rest dienes. Then, based on selected dienes and dienophiles, seven series of new cage energetic compounds were constructed. Their structures, detonation properties and impact sensitivity were studied by DFT and ESP methods. The results showed that there are 8 optimal compounds (PA2, PB2, PC1, PC2, PD1, PD2, PE1, PF1) have both higher energy and lower sensitivity than one famous and widely used insensitive energetic compound trinitrotoluene, and may be used as potential advanced insensitive energetic compounds. In addition, the NO2 group was found to obviously reduce the reaction energy barrier and promote the Diels-Alder reaction. It increased the density and oxygen balance to improve the detonation properties significantly, but it also increased the impact sensitivity by increasing the positive ESP value and centralizing positive ESP in less regions. This study may be helpful for developing new advanced insensitive high energy materials from new design and synthesis perspectives.

Chemical Descriptors for a Large-Scale Study on Drop-Weight Impact Sensitivity of High Explosives.

The drop-weight impact test is an experiment that has been used for nearly 80 years to evaluate handling sensitivity of high explosives. Although the results of this test are known to have large statistical uncertainties, it is one of the most common tests due to its accessibility and modest material requirements. In this paper, we compile a large data set of drop-weight impact sensitivity test results (mainly performed at Los Alamos National Laboratory), along with a compendium of molecular and chemical descriptors for the explosives under test. These data consist of over 500 unique explosives, over 1000 repeat tests, and over 100 descriptors, for a total of about 1500 observations. We use random forest methods to estimate a model of explosive handling sensitivity as a function of chemical and molecular properties of the explosives under test. Our model predicts well across a wide range of explosive types, spanning a broad range of explosive performance and sensitivity. We find that properties related to explosive performance, such as heat of explosion, oxygen balance, and functional group, are highly predictive of explosive handling sensitivity. Yet, models that omit many of these properties still perform well. Our results suggest that there is not one or even several factors that explain explosive handling sensitivity, but that there are many complex, interrelated effects at play.

RDX crystals with high sphericity prepared by resonance acoustic mixing assisted solvent etching technology

In order to obtain high-quality spherical RDX crystal particles, the RDX crystals were suspended in a mixed solvent of cyclohexanone and cyclohexane, subsequently a solvent etching study was carried out under the action of vibration/acoustic flow coupled flow field, which generated by resonance acoustic mixing. The effects of solvent ratio, temperature, acceleration and experiment time on morphology as well as particle size of RDX crystals were studied. Not only were the morphology, particle size distribution and crystal form of RDX crystals determined, but also the thermal decomposition performance and mechanical sensitivity of spherical RDX were examined and discussed. Results indicated that under the process of solvent/non-solvent volume ratio at 1:2, temperature of 40°C, acceleration of 40 g and experiment time of 4 h, α-type RDX crystal with sphericity of 0.92 can be obtained. Furthermore, the median particle size (D50) of spherical RDX crystals is 215.8 μm with a unimodal particle size distribution (size span 1.34). For one thing, the thermal decomposition peak temperature of spherical RDX is about 2.5°C higher than that of raw RDX, and apparent activation energy reaches 444.68 kJ/mol. For another thing, impact sensitivity and friction sensitivity of spherical RDX are 18.18% and 33.33% lower than that of raw RDX, respectively. It demonstrates that safety of spherical RDX under thermal, impact and friction stimuli has been improved.

Bicyclic High-Energy and Low-Sensitivity Regioisomeric Energetic Compounds Based on Polynitrobenzene and Pyrazoles

With the development of synthetic methodology and crystallography of energetic materials, regiochemistry is becoming popular and vital in the design of versatile energetic compounds as well as in the thorough research on the relationship between structure and property. In this study, two regioisomeric bicyclic energetic compounds based on pyrazole and polynitrobenzene were synthesized simultaneously by a simple synthetic route, and the regioisomers could be purified by a facile approach. It is interesting to note that the ratio of the two compounds changed with temperature. From 80 to 110 °C, the proportion of compound 2 gradually enhanced with the increase in temperature. In addition, the nitramine product of compound 1 was also synthesized. The structural data of compounds 1, 2, and 3 were confirmed by X-ray single-crystal diffraction. The detonation velocities of the new compounds are in the range of 8436–8788 m s–1 and impact sensitivities are between 15 and 27.5 J, of which compounds 2 and 3 not only present superior sensitivities to those of the classical high-energy explosive RDX (7.5 J) but also exhibit comparable detonation velocities to the measured RDX powder (VD = 8796 m s–1), calculated by EXPLO5 as 8788 and 8526 m s–1, respectively. Moreover, compounds 1 and 2 show good thermal stability with decomposition temperatures up to 263 and 287 °C, which is higher than that of RDX (Tdec: 204 °C). All of the above information indicates that these compounds are high-energy, low-sensitivity energetic materials featuring prospective applications.

Fabricate hexanitrohexaazaisopentane@tannic acid core-shell energetic composites with reduced sensitivity and enhanced thermal stability

To improve the safety performance of hexanitrohexaazaisopentane (CL-20), a new type of CL-20@tannic acid core-shell energetic composites was prepared with tannic acid (TA) as the shell and CL-20 as the core. The structure and safety performance of CL-20@TA were analyzed by a series of characterization techniques. The results indicated that TA was tightly coated on the surface of CL-20, which not only protected CL-20 from external stimulation, but also improved its thermal stability and reduced its impact sensitivity.

IMPACT SENSITIVITY OF NITROMETHANE-BASED GREEN-PROPELLANT PRECURSOR MIXTURES

Nitromethane is a promising green propellant candidate. However, one potential issue for industrial use may be its high sensitivity to mechanical impact. In this paper, we assess the effect of adding several phlegmatizing substances (or inhibitors as we call them), on the impact sensitivity and the potential propulsive performance of the resulting mixtures. The impact sensitivity of the nitromethane mixtures was characterized using a BAM Fallhammer impact tester. The theoretical rocket performance of the mixtures was calculated utilizing the NASA CEA program. This study resulted in the identification of several nitromethane-inhibitor mixtures, which lack the high impact sensitivity of pure nitromethane but still retain much of its propulsive performance. The most promising approach was the addition of 6 wt.% of dimethyl sulfoxide: the theoretical specific impulse was only decreased by 3%, while the impact sensitivity was significantly lowered (> 10 J vs. < 5 J, as in pure nitromethane).

Which molecular properties determine the impact sensitivity of an explosive? A machine learning quantitative investigation of nitroaromatic explosives.

We decomposed density functional theory charge densities of 53 nitroaromatic molecules into atom-centered electric multipoles using the distributed multipole analysis that provides a detailed picture of the molecular electronic structure. Three electric multipoles, (the charge of the nitro groups), (the total dipole, i.e., polarization, of the nitro groups), (the total electron delocalization of the C ring atoms), and the number of explosophore groups (#NO2) were selected as features for a comprehensive machine learning (ML) investigation. The target property was the impact sensitivity h50 (cm) values quantified by drop-weight measurements, with a large h50 (e.g., 150 cm) indicating that an explosive is insensitive and vice versa. After a preliminary screening of 42 ML algorithms, four were selected based on the lowest root mean square errors: Extra Trees, Random Forests, Gradient Boosting, and AdaBoost. Compared to experimental data, the predicted h50 values of molecules having very different sensitivities for the four algorithms have differences in the range 19-28%. The most important properties for predicting h50 are the electron delocalization in the ring atoms and the polarization of the nitro groups with averaged weights of 39% and 35%, followed by the charge (16%) and number (10%) of nitro groups. A significant result is how the contribution of these properties to h50 depends on their actual sensitivities: for the most sensitive explosives (h50 up to ∼50 cm), the four properties contribute to reducing h50, and for intermediate ones (∼50 cm ≲ h50 ≲ 100 cm) #NO2 and contribute to increasing it and the other two properties to reducing it. For highly insensitive explosives (h50 ≳ 200 cm), all four properties essentially contribute to increasing it. These results furnish a consistent molecular basis of the sensitivities of known explosives that also can be used for developing safer new ones.

Enhanced thermal, safety and anti-hygroscopicity performance of core-shell ammonium perchlorate with a double coating layer.

A new core-shell structure AP/Cu-DABT/Cu(Pa)2 (10 wt% each) (AP = ammonium perchlorate, DABT = 3,3'-diamino-5,5'-bis(1H-1,2,4-triazole), Pa = palmitic acid) with two coating layers was synthesized through two self-assembly reactions to improve the thermal decomposition performance, safety performance and moisture absorption resistance of AP. The results show that the surface of AP particles is uniformly and densely covered by Cu-DABT and Cu(Pa)2 coatings successively. Compared with pure AP, the HTD (high-temperature decomposition) peak temperature and activation energy of the AP/Cu-DABT/Cu(Pa)2 (10 wt% each) composite material were reduced by 74.7 °C and 117.67 kJ mol-1, respectively, and the heat release increased by 1421.02 J g-1. In addition, the burning rate and maximum flame temperature of the propellant containing the AP/Cu-DABT/Cu(Pa)2 (10 wt% each) composite were increased by 8.7 mm s-1 and 815.8 °C, respectively, compared with the propellant containing pure AP. Moreover, compared with pure AP, the contact angle of the AP/Cu-DABT/Cu(Pa)2 (10 wt% each) composite with water increased by 89.15°, and the water content decreased by 0.38 wt%. The impact sensitivity and friction sensitivity of the composite material were reduced by 16.9 cm and 96%, respectively. Analysis shows that the Cu-DABT coating plays a major role in improving the thermal properties of the composite material, the burning rate and flame temperature of the propellant, while the Cu(Pa)2 coating plays a major role in improving the hygroscopic performance and safety performance of the composite material. The composite material has good thermal decomposition properties, anti-hygroscopic properties and safety properties, so the composite material is very promising as a potential additive for solid propellants.

Regulation of stability and density of energetic materials via isomerism.

Selective regulation of stability and density via isomerism is a promising strategy for developing energetic materials. In this work, we selectively introduced dinitromethyl groups at different positions of 4-nitro-1,2,3-triazole. The regional heterogeneity endows a high crystal density by virtue of the dense packing; on the other hand, it changes the charge distribution in the molecule, and reinforces the hydrogen bonding interactions, all of which stabilize the material. The resulting compounds exhibit excellent detonation properties and impact sensitivity that are comparable to those of HMX (Dv = 9250 m s-1 and IS = 10 J).

Constructing a graphene-like structure to lower friction sensitivity: Ag(i) complexes based on furan-2,5-dicarbohydrazide

Using furan-2,5-dicarbohydrazide (FDCA) as a ligand, we prepared [Ag(FDCA)(ClO4)]n (ECP-1) with a graphene-like structure, which successfully shows a low friction sensitivity (FS = 84 N), in sharp contrast with its high impact sensitivity (IS = 4 J).

Halogenated PETN derivatives: interplay between physical and chemical factors in explosive sensitivity.

Determining the factors that influence and can help predict energetic material sensitivity has long been a challenge in the explosives community. Decades of literature reports identify a multitude of factors both chemical and physical that influence explosive sensitivity; however no unifying theory has been observed. Recent work by our team has demonstrated that the kinetics of "trigger linkages" (i.e., the weakest bonds in the energetic material) showed strong correlations with experimental drop hammer impact sensitivity. These correlations suggest that the simple kinetics of the first bonds to break are good indicators for the reactivity observed in simple handling sensitivity tests. Herein we report the synthesis of derivatives of the explosive pentaerythritol tetranitrate (PETN) in which one, two or three of the nitrate ester functional groups are substituted with an inert group. Experimental and computational studies show that explosive sensitivity correlates well with Q (heat of explosion), due to the change in the number of trigger linkages removed from the starting material. In addition, this correlation appears more significant than other observed chemical or physical effects imparted on the material by different inert functional groups, such as heat of formation, heat of explosion, heat capacity, oxygen balance, and the crystal structure of the material.

Impact sensitivities of energetic materials derived from easy-to-compute ab initio rate constants.

New procedures to estimate the impact sensitivity of energetic materials are derived from an earlier semiempirical model correlating the drop weight impact height h50 to the rate constant k for the propagation of the decomposition process, assumed to be the limiting step. The new models are obtained by removing step by step the empiricism in the evaluation of k. We end up with a full ab initio expression for this constant in terms of theoretical activation energies and prefactors. The resulting model casts doubt on a previously introduced assumption regarding the temperature at the reaction front. Moreover, it questions possible interpretations of semiempirical estimates. A systematic comparison against alternative methods shows that although somewhat less accurate than its earlier semiempirical version, this ab initio model shows a predictive value similar to heavily parameterized approaches. The results imply that the decomposition kinetics accounts for at least 50% of the variation in the logarithms of drop height data.