Decomposition Of HMX Research Articles

Control of burning rate pressure sensitivity for solid propellants by changing the interfacial contact of Al/HMX/AP with precisely located graphene-based energetic catalysts

The control of burning rate pressure sensitivity is essential for stable and reliable combustion of solid propellants. It has been proved that the combustion behavior of propellants can be effectively tuned by interfacial control of Al/oxidizers. In this work, core-shell Al-based composites, using oxidizers such as ammonium perchlorate (AP) and cyclotetramethylene tetranitramine (HMX) as the shell layer, have been prepared with a well-controlled location of graphene-based carbohydrazide complexes (GO-CHZ-M, M = Co2+ or Ni2+) as the catalysts. The catalysts can be located inside HMX or embedded on the surface of AP particles. The decomposition of AP and HMX could be greatly promoted with a trace amount of catalyst. Under the synergistic effects of Al/oxidizer interfacial control and GO-CHZ-M, the ignition delay time is shortened by >48 % with increased in flame radiation. More importantly, the burning rate (r) and pressure exponent (n) of the solid propellants are effectively regulated in a wide range. In particular, the use of Al@HMX/Co results in a lowered n of 0.29 within 1∼20 MPa compared to 0.79 for the blank reference sample. The agglomeration of Al particles during combustion was also inhibited due to the micro-explosion effect of Al@HMX composites. Novelty and Significance statementThe innovative approaches of integrating Al/HMX/AP composites and precise catalysis of graphene-based energetic catalysts in solid propellants have successfully achieved, regarding the modulation of the burning rates and pressure sensitivity. Moreover, the effect of catalyst location on the ignition delay and burning rates has also been studied thoroughly and clarified. This paper provides new insight into the regulation of combustion performance of solid propellants, with improved reaction efficiency and maintained energy density.

Fabrication and performance characterization of NTO/HMX spherical composite explosives with improved safety performance.

AbstractImproving the energy density and safety of explosives are crucial for developing composite energetic materials. In this study, a facile and continuous spray drying granulation technique was used to obtain NTO/HMX composite explosives with insensitive NTO as coating material. The micro‐morphology, particle size, crystallographic structure, exothermic decomposition, impact sensitivity, and detonation performance of NTO/HMX composite explosives with different NTO contents were investigated by various experimental methods. The test results indicate that the higher the NTO content, the better the crystal integrity of HMX and the lower the mechanical sensitivity of NTO/HMX composite explosives. When the mass ratio of NTO and HMX is 25 : 75, NTO/HMX composite explosives have a good spherical density structure formed by the aggregation of nanoparticles, small particle sizes with a median size of 1.22 μm, and a uniform distribution of particle sizes in the range of 0.3–2.8 μm. The addition of NTO not only enhances the thermal decomposition of HMX but also significantly decreases mechanical sensitivity. The composite explosives had not altered the raw NTO and HMX crystallographic structures (β‐type). With the same ratio (25 : 75), NTO/HMX composite explosives (25 : 75) possess higher impact energy and friction force, better safety, and better thermal stability than physical mixtures. Additionally, the high‐energy insensitive composite microspheres preserve the important high‐energy properties of HMX while effectively enhancing its safety characteristics, which have the advantages of controllable crystallographic micromorphology, high energy, and excellent impact sensibility and could be broadly applicable in the field of munitions.

A comprehensive experimental and theoretical study of thermal response mechanisms of TKX-50 and HMX

TKX-50 and HMX, as two highly promising energetic materials, are widely used in rocket propellants. TKX-50/HMX cocrystal can also improve the defects of TKX-50 and HMX and vastly expand their application scope. Their response mechanisms to the same thermal stimulation, including reactivity and decomposition and combustion behavior, are important in understanding their combustion characteristics and engine performance. This study systematically investigates the thermal response mechanisms of TKX-50 and HMX under the same thermal stimulations based on experimental measurements and theoretical analysis. Ignition delay times and burn times of TKX-50 and HMX with different particle sizes at various temperatures and pressures are measured in shock tube experiments. ReaxFF MD simulations are performed to analyze the thermal decomposition of TKX-50 and HMX in terms of potential energy evolution, intermediate and final products, and possible reaction pathways. Ab initio kinetics of hydrogen atom abstraction reactions of TKX-50 and HMX with three highly active species, Ḣ, ȮH, and NO2, are studied. The barrier heights, reaction enthalpies and rate coefficients for all reactions are further analyzed. The results show that: (1) the ignition delay time and burn time of TKX-50 (128, 138, and 55 µm) are measured to be 200–600 µs and 40–400 µs respectively, which are almost the same as those of HMX (6 and 0.8 µm) in the same temperature range; (2) the burn time of TKX-50 is less affected by pressure but more affected by particle size, whereas both pressure and particle size have a significant effect on the burn time of HMX; (3) TKX-50 is shown to be readily decomposed and less affected by temperature changes than HMX under the same conditions; (4) ȮH is generated more rapidly in the TKX-50 system, but more persistently in the HMX system; (5) H atom abstraction reactions from TKX-50 by all species are less endothermic but more exothermic than those from HMX.

Thermal decomposition mechanism of HMX/HTPB hybrid explosives studied by reactive molecular dynamics.

The thermal decomposition process of octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine/hydroxyl-terminated polybutadiene (HMX/HTPB) hybrid explosives and pure HMX explosives at different temperatures (2000 ~ 3500 K) was investigated using the reactive molecular dynamics method. This study aimed to analyze the effect of binders on the thermal decomposition of HMX at the atomic scale and reveal the thermal decomposition mechanism of HMX/HTPB. The results showed that the thermal decomposition process of the HMX molecule in the HMX/HTPB hybrid system involves a continuous denitration followed by the disintegration of the main ring. The HTPB chain will experience dehydrogenation, dehydroxylation, and chain fragmentation. Including HTPB in the hybrid system significantly increased the presence of H and OH radicals. These radicals then interacted with HMX and its decomposition products and produced more of the final products H2O and H2 in the HMX/HTPB hybrid system compared to pure HMX. Additionally, it was observed that the HTPB chain fragments attached to the HMX decomposition products prevented the formation of N2 and CO2. Furthermore, the activation energies (Ea) of the initial and intermediate decomposition stages of the HMX/HTPB hybrid system were 98.45 kJmol-1 and 90.69 kJmol-1, respectively. The results showed that the activation energies of the HMX/HTPB hybrid system are lower than the pure HMX system in these two stages. Consequently, HTPB will enhance HMX's thermal decomposition and decreased the system's insensitivity to heat stimuli. The molecular dynamics simulation of the HMX/HTPB hybrid system was performed using the ReaxFF module in the LAMMPS software, and the ReaxFF/lg force field was used to describe the interatomic interactions as well as the chemical reactions.

Kinetic models of HMX decomposition via chemical reaction neural network

1,3,5,7-Tetranitro-1,3,5,7-tetrazocane (HMX) is commonly used in solid propellants and explosives as energetic materials. The study of its kinetics and decomposition mechanism is of great significance to its application in the aerospace industries. This work investigates the thermal decomposition of HMX based on the combined thermogravimetric (TG) measurements and chemical reaction neural network (CRNN). Two compact kinetic models for HMX are introduced, with one consisting of four substances and a single global reaction (4–1 model) and the other consisting of four substances and four reactions (4–4 model). In the 4–1 model, the calculated activation energy is 328.44 kJ·mol−1, which agrees with the experimental value. As for the 4–4 model, the substances and reactions are assigned based on a skeleton mechanism involving reactions of N-N and C-N bond cleavage and HONO elimination. Moreover, the catalytic effects of TiO2 and Al2O3 on HMX are well simulated using the aforementioned kinetic models. The CRNN models can reproduce the peak temperature with a reduced activation energy, but the initial decomposition temperature is overestimated owing to the complex nature of catalytic impact. This work presents the application of the CRNN model to obtain a decomposition mechanism of HMX, highlighting its efficacy in accurately capturing the thermal decomposition behavior. The potential extension of CRNN to kinetic modeling of other energetic materials is anticipated in future studies.

Thermal decomposition of fluorinated polymers used in plasticized explosives and munitions

AbstractA number of military explosives and munitions employ fluorinated polymers as binders or components, e. g., PBXN‐5. To determine potential environmental releases during disposal operations, the thermal decomposition of the fluorinated polymers Viton A, Kel‐F, and Teflon were examined alone and in combination with the explosive HMX. Although PBXN‐5 only contains 5 % by weight Viton A, laboratory prepared analogs were made with 5 % polymer as well as with 50 % polymer to ensure polymer decomposition products could be detected. Under air and under nitrogen decomposition was examined by SDT [simultaneous differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA)], TGA‐infrared (IR) spectrometry, and pyrolysis gas chromatography with mass spectrometric analysis (GC‐MS). All three techniques, SDT, TGA‐IR, and pyrolysis GC‐MS, suggest that decomposition of HMX could be completed at low temperature before polymer decomposition ensues. To confirm this observation, pyrolysis GC‐MS was performed at temperatures below 350 °C since above this temperature all three polymers exhibited some fluorinated decomposition products.

Reaction mechanism and kinetic modeling of gas-phase thermal decomposition of prototype nitramine compound HMX

The combustion, detonation, and explosion chemistry of energetic materials is regulated by the formation and decay of critical intermediates that are generated during the process. In this study, the pyrolysis mechanism of a commonly used cyclic nitramine explosive called octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine, also known as HMX or octogen, has been investigated by performing ab initio based RRKM/master equation analysis coupled with kinetic modeling simulations. The potential energy profiles of reaction network were constructed at the DLPNO-CCSD(T)/cc-pV[T,Q]Z level based on B3LYPD3/6-311+G(d,p) optimized geometries. The master equation calculations and kinetic modeling simulations indicated that the N-NO2 bond fission, leading to the formation of HMXR (the radical formed after NO2 loss) and nitro radicals, is the most important channel during the initial decomposition of HMX. The C-N and C-H β-scissions play an important role in the subsequent decomposition of the HMXR radical, with the C-H β-scission to form INT249 being the more favored consumption channel. Furthermore, this study also provided a preliminary exploration into the contribution of bimolecular reactions between HMX and H/OH/NO/NO2 radicals. The kinetic simulation results demonstrated that decomposition through these bimolecular reactions is of negligible importance under the investigated conditions.

Silver/polydopamine/HMX nanocomposite: novel functionalized catalyzed energetic matrix with superior decomposition kinetics

Surface engineering of energetic materials can secure novel decomposition characteristics. Nature can inspire novel solutions. Polydopamine, with strong adhesion power of mussel proteins, can open new venues for the facile development of functionalized energetic materials. HMX, one of the most powerful energetic materials in use, was surface modified with PDA. The reactive amine groups of PDA surfactant were employed for noble metal catalyst deposition. Silver nanocatalyst was deposited on HMX surface. Uniform deposition of silver nanocatalyst was assessed using EDAX detector. Decomposition kinetics was investigated via isoconversional (model free) and model fitting. Kissinger, Kissinger–Akahira–Sunose (KAS), integral isoconversional method of Ozawa, Flynn, and Wall (FWO), and differential isoconversional method of Friedman. Silver nanocatalyst offered an increase in HMX decomposition enthalpy by 32.4%. In the meantime, HMX activation energy was decreased from 350 ± 2.53 to 284.9 ± 1.5 kJ mol−1 by Friedman method. Silver nanocatalyst could combust exothermically; it could induce condensed phase reactions that could boost HMX decomposition. Silver nanocatalyst experienced change in HMX decomposition model from diffusion reaction (D1) to (A3) known as three-dimensional random nucleation and growth. Surface modification with PDA secured enhanced HMX sensitivity to falling mass impact by 40%.

Reactivity of high active aluminum powder with RDX and HMX mixtures

In order to reveal the interaction law of high active aluminum powder with RDX and HMX mixture, the thermal decomposition behavior of highly active Al powder and its interaction with typical nitramine explosive RDX and HMX were studied by differential scanning calorimetry (DSC), thermogravimetry (TG), thermo-mass spectrometry (TG-DTG-DSC-MS) and CO2 laser ignition technology. Results show that when the nanometer aluminum powder and RDX and HMX respectively, two typical nitramine explosive mixing action is of little influence on the mixing action to respond to the thermal decomposition of HMX, depress RDX points liberation degree of temperature, both the thermal decomposition process of mixed system for random nucleation and subsequent growth process, the ignition delay time decreases with the increase of laser ignition power density. The ignition delay time and ignition energy of the mixture of high active aluminum powder and RDX are greater than that of the mixture of high active aluminum powder and HMX and the high active aluminum powder.

Study on Thermal Decomposition and Thermal Safety of Mixtures of Highly Active Aluminum Powder and Nitramine Explosive

The newly prepared and stored highly active aluminum powder were mixed with common nitramine explosives HMX and CL-20 at a mass ratio of 1:1, respectively. The effects of the two kinds of high active aluminum powder on the thermal decomposition properties of HMX and CL-20 were investigated by differential scanning calorimetry (DSC). The thermal explosion critical temperature of the mixture of high active aluminum powder and nitramine explosive was calculated. The result shows that after joining highly active aluminium powder, highly active aluminium/nitramine explosive mixture, moderate and apparent activation energy decrease thermal decomposition peak suggests that highly active aluminium can contribute to the thermal decomposition of HMX and CL-20, compared with highly active aluminium stored after a certain period of time, the new system is highly active aluminum powder with a mixture of nitramine explosives with lower apparent activation energy, At the same time, the critical temperature of thermal explosion also decreased significantly, which indicated that the newly prepared high-activity aluminum powder had higher chemical reactivity, but its thermal safety was reduced.

Atomic insights into the thermal decomposition mechanism and cluster growth law of nanoscale HMX and LLM-126 mixture: A ReaxFF-lg molecular dynamics study

In this paper, the thermal decomposition process and cluster growth law of the HMX/LLM-126 nanoscale mixture system were studied by ReaxFF-lg combined with DFT, and the thermostability of the mixture system with a molar ratio of 1:1 was investigated. The results show that clusters can be formed between HMX and LLM-126 in the mixture system, which effectively delays the cracking speed of the HMX structure. Meanwhile, NO2 generated from the initial decomposition of HMX will accelerate the denitration process of LLM-126. The decomposition process of HMX is mainly a continuous denitration until the structural ring-opening disintegration, the initial decomposition step is C4H8O8N8 => C4H8O6N7 + NO2. In contrast, the initial decomposition of LLM-126 is dominated by intramolecular hydrogen transfer reactions and the generation of dimer clusters, followed by the detachment of nitro and bitter amino groups, and finally the cleavage of the pyridine ring. The intramolecular hydrogen transfer process of LLM-126 is the transfer of H on -NH- to the adjacent nitro group. After LLM-126 was added to the HMX system, the oxygen balance of the system increased, and the N content, exothermic rate, and the number of final products decreased significantly compared with the HMX pure component system. Also, the number of clusters generated, and the maximum cluster weight increased significantly. These phenomena are important reasons for the improved thermostability of the mixture system compared to the pure HMX system. This work can provide a theoretical basis for the design and application of nanoscale high-energy thermostable mixed explosives.

Using microfluidic technology to prepare octogen high-energy microspheres containing copper–aluminum composite particles with enhanced combustion performance

Aluminized explosives are widely used in military applications. However, the easy agglomeration of aluminum (Al) powder and its high ignition temperature greatly hinder the reaction of nano aluminum (n-Al) in the process of explosion, thus affecting the combustion and explosion of aluminum-containing explosives. In the present study, copper (Cu) coated n-Al composite particles were introduced into aluminized explosives, and Cu coated n-Al composite particles and ball-milled octogen (HMX) energetic microspheres were prepared via droplet microfluidic technology using binder. The morphology, crystal form, thermal properties, combustion, and mechanical sensitivity of the microspheres were studied using a variety of techniques. The prepared microspheres had regular spherical morphology and uniform particle size, with an even distribution of particles. Using microfluidic technology will not destroy the crystal form of each particle. The introduction of Cu promoted the thermal decomposition of HMX. The mechanical sensitivity of the prepared Cu/Al microspheres was lower than that of the microspheres only containing n-Al. The Cu/Al microsphere samples exhibited excellent and stable combustion performance, and that the addition of Cu increased the combustion speed compared to the microspheres only containing n-Al. This technology represents an inexpensive and simple way to improve on existing aluminized explosives.

Establishing TA-Pb/Cu and SA-Pb/Cu interface catalyst shells on HMX surfaces via in situ coprecipitation to ameliorate the performances of HMX

Lead/copper tannate (TA-Pb/Cu) and lead/copper salicylate (SA-Pb/Cu) interface catalyst shells are established on the surface of 1,3,5,7-tetranitro-1,3,5,7-tetrazacyclooctane (HMX) via in situ coprecipitation to prepare HMX@TA-Pb/Cu and HMX@SA-Pb/Cu composites. The structures and properties of the obtained HMX@TA-Pb/Cu and HMX@SA-Pb/Cu composites are characterized in detail. Molecular dynamics simulations are performed to study the adsorption mechanism of TA-Pb/Cu and SA-Pb/Cu on HMX surface. The residues after HMX@TA-Pb/Cu and HMX@SA-Pb/Cu combusted in air are collected and characterized to study the catalytic effect of TA-Pb/Cu and SA-Pb/Cu on combustion. The study results show that TA-Pb/Cu shells are coated on HMX surface due to the excellent membrane-forming properties of TA, while SA-Pb/Cu shells are embedded in the gullies and holes of HMX surface. TA-Pb/Cu and SA-Pb/Cu shells can decrease the mechanical sensitivities and catalyze the decomposition and combustion of HMX, and the catalytic effects of in situ coprecipitation are better than that of physical mixing. In addition, the phase transition temperature of HMX in HMX@TA-Pb/Cu is increased while that of HMX@SA-Pb/Cu is decreased, illustrating that TA-Pb/Cu can enhance the thermal stability of HMX while SA-Pb/Cu can catalyze the phase transition of HMX.

The unusual effect of paraffin wax on the thermal decomposition of cyclotetramethylenetetranitramine.

The practical application of paraffin wax (PW) in cyclotetramethylenetetranitramine (HMX)-based polymer-bonded explosive (PBX) requires an understanding of its effect on the thermal decomposition of HMX. In this work, by comparing the thermal decomposition of HMX and a HMX/PW mixture, combined with crystal morphology analysis, molecular dynamics simulation, kinetic analysis, and gas product analysis, the unusual phenomenon and mechanism of the PW effect on the thermal decomposition of HMX were evaluated. During the initial decomposition, PW infiltrates the crystal surface of HMX, reduces the energy barrier for chemical bond dissociation, and induces the decomposition of molecules on HMX crystals, resulting in a lower initial decomposition temperature. PW consumes the active gas produced by HMX with further thermal decomposition and inhibits the dramatic increase of the HMX thermal decomposition rate. In decomposition kinetics, this effect is manifested as PW inhibits transition from an n-order reaction to an autocatalytic reaction.

Tunning Combustion Behaviors of Composite Modified Double-Based Propellants with a Novel Energetic Burn Rate Modifier

ABSTRACT The flexible control in burning rate and stable combustion of solid propellants over a broad range of pressures essentially determine the performance of solid rocket motors. The nanoscale metals and their oxides are usually utilized as the traditional burn rate modifiers in adjusting the combustion behaviors of solid propellants, but the energy characteristics of propellants are greatly compromised owing to the inert nature of additives used. In this paper, a series of metal complexes of triaminoguanidine-glyoxal polymer (TAGP-Ms) with high nitrogen content were synthesized and employed as energetic burn rate inhibitors in tunning the combustion properties of composite modified double-based (CMDB) propellants. The influences of prepared TAGP-Ms on the thermal decomposition and combustion of CMDB propellants were comprehensively investigated based on thermal analysis technique and combustion characterization methods. It was found that the peak temperatures of the second exotherm displayed for the propellants containing TAGP-Ms inhibitors were significantly increased by more than 30°C (except for TAGP-Cu), indicating the TAGP-Ms is capable of suppressing the thermal decomposition of CMDB propellants. More importantly, the heat releases of CMDB propellants were substantially enhanced by 16%~34% determined by DSC analysis. In comparison to the blank reference, the energetic TAGP-Ms inhibitors could promote the heat of combustion for the involved CMDB propellants by 5%~9%. The burning rates of CMDB propellants were notably reduced over a wide range of pressures by adding TAGP-Ms, whereas the calculated pressure exponents at pressures ranging from 10 to ~ 22 MPa appear to be relatively high due to the accelerated HMX decomposition. The measured combustion wave temperatures suggest that the CMDB propellants with TAGP-Ms undergo a three-stage combustion process with the highest temperatures in the range of 2160 ~ 2230°C.

3D Electron-Rich ZIF-67 Coordination Compounds Based on 2-Methylimidazole: Synthesis, Characterization and Effect on Thermal Decomposition of RDX, HMX, CL-20, DAP-4 and AP

ZIF-67 is a three-dimensional zeolite imidazole ester framework material with a porous rhombic dodecahedral structure, a large specific surface area and excellent thermal stability. In this paper, the catalytic effect of ZIF-67 on five kinds of energetic materials, including RDX, HMX, CL-20, AP and the new heat-resistant energetic compound DAP-4, was investigated. It was found that when the mass fraction of ZIF-67 was 2%, it showed excellent performance in catalyzing the said compounds. Specifically, ZIF-67 reduced the thermal decomposition peak temperatures of RDX, HMX, CL-20 and DAP-4 by 22.3 °C, 18.8 °C, 4.7 °C and 10.5 °C, respectively. In addition, ZIF-67 lowered the low-temperature and high-temperature thermal decomposition peak temperatures of AP by 27.1 °C and 82.3 °C, respectively. Excitingly, after the addition of ZIF-67, the thermal decomposition temperature of the new heat-resistant high explosive DAP-4 declined by approximately 10.5 °C. In addition, the kinetic parameters of the RDX+ZIF-67, HMX+ZIF-67, CL-20+ZIF-67 and DAP-4+ZIF-67 compounds were analyzed. After the addition of the ZIF-67 catalyst, the activation energy of the four energetic materials decreased, especially HMX+ZIF-67, whose activation energy was approximately 190 kJ·mol-1 lower than that reported previously for HMX. Finally, the catalytic mechanism of ZIF-67 was summarized. ZIF-67 is a potential lead-free, green, insensitive and universal EMOFs-based energetic burning rate catalyst with a bright prospect for application in solid propellants in the future.

Effects of Two Common Binders on Decomposition Mechanism of HMX Molecule Under Linear Temperature Rise

ABSTRACT The effects of two common binders (BR and F binder) on the thermal decomposition of HMX molecules during linear heating were studied by molecular dynamics simulation. It was found that both binders can induce the decomposition reaction of HMX molecules earlier, promote the conversion of intermediate products to stable products, and reduce the activation energy and potential energy barrier of the system. The induction of the binder in the composite system makes the initial decomposition of HMX molecules appear at the interface between the binder and the HMX molecules, and the binder’s higher heat absorption rate absorbs a large amount of energy released by the hot spots. The promoting effect of binder on the conversion of intermediate products to stable products and the interaction between binder and HMX intermediate products consume excessive active particles, which inhibits the further decomposition of macromolecular intermediate products. The results show that both BR and F binders prolonged the decomposition duration of HMX, and F rubber with better thermal stability has the longest HMX decomposition duration in the composite system. Our simulation revealed the action mechanism of BR and F rubber in HMX thermal decomposition, which provided a new idea for studying the action mechanism of binders on the thermal properties of high explosives.

Bis(5-nitroimino-1,2,4-triazole-3-yl) methane-based energetic salts: Synthesis, crystal structure, thermal behavior and catalytic activity

Four energetic ionic salts of bis(5-nitroimino-1,2,4-triazole-3-yl) methane (BNTM) potassium (KBNTM), ammonium (A2BNTM), hydroxylamine ((HA)2BNTM), 1,3-diaminoguanidine ((DAG)2BNTM) have been synthesized and characterized by Elemental analysis(EA), Fourier infrared(FI) and Nuclearmagnetic resonance(NMR). Fortunately, the single crystals available for determination of KBNTM was acquired by slow evaporation of solvent method and its structure was discussed. The thermal behaviors of them were explored by Differential Scanning Calorimetry(DSC) and Thermogravimetry/ Derivative Thermogravimetry (TG/DTG) technique, and the result displayed that all of them had good thermal stability. The most possible mechanism function of main exothermic decomposition process were obtained (No.35 for KBNTM, No.6 for A2BNTM, No.24 for (HA)2BNTM, No.14 for (DAG)2BNTM). In addition, (HA)2BNTM has the best thermal safety, followed by KBNTM and A2BNTM according to the calculated value of self-accelerating decomposition temperature (TSADT) and critical temperature of thermal explosion (Tb). Moreover, the catalytic effects of four ionic salts on Cyclotrimethylenetrinitramine(RDX) and Octogen(HMX) were investigated respectively. The consequent showed that (HA)2BNTM accelerated the thermal decomposition of RDX and HMX, and reduced the decomposition temperature and apparent activation energy of RDX and HMX by 6.94 °C, 17.37 kJ·mol−1 and 4.17 °C, 2.77 kJ·mol−1, respectively. Surely, the thermal decomposition mechanism function of (HA)2BNTM/RDX was different from that of RDX (No.5, f(α)=6(1-α)2/3 [1-(1-α)1/3]1/2). In summary, (HA)2BNTM can be regarded as a potential energetic combustion catalyst with insensitive to physical impact (IS=16 J).

Temperature and Pressure Effects on HMX/Graphene via ReaxFF Molecular Dynamics Simulations

Studying the thermal decomposition of energetic materials at high temperatures can provide detailed reaction and mechanistic information, which is critical for understanding the reactivity of energetic materials, designing mixed explosives, and achieving improved safety. In this work, the effects of temperature and pressure on graphene (Gr)-based HMX crystals were investigated using ReaxFF molecular dynamics simulations. The thermal decomposition processes of perfect HMX crystals, HMX crystals with (001), (010), or (100) crystal planes, and HMX/Gr mixed systems were studied at high temperatures and pressures. In the mixed systems, different configurations of HMX molecules adsorbed on the Gr surface were confirmed by theoretical calculation methods. With the pressure ranging from atmospheric pressure to 31 GPa, 3, 5, and 3 configurations of HMX adsorbed on the Gr surface were identified for the (001)/Gr, (010)/Gr, and (100)/Gr systems, respectively. The time-dependent curves for the evolution of fragments, intermediates, and pyrolysis products were analyzed. The rate constant for the thermal decomposition of HMX was found to be significantly affected by the addition of Gr. In particular, the thermal decomposition reaction was strongly inhibited in the (010)/Gr system. This result indicates that Gr promotes an anisotropic thermal effect, resulting from the steric hindrance of the NO2 functional groups and the interaction between Gr and HMX molecules. Gr also affected the initial reaction pathway of homolytic N–NO2 bond cleavage, with C=O, C–OH, and C–OC bonds on the Gr surface participating in the formation of nitro radicals and HONO.

A study of the pore size effect on the formation of hot spot in a 1,3,5,7-tetranitro-1,3,5,7-tetrazocane crystal under a low-to-medium shock velocity

ABSTRACT It is rather difficult to observe, record and analyze the pore-collapse-induced initiation of a 1,3,5,7-tetranitro-1,3,5,7-tetrazocane or HMX crystal via experiment because it is an extreme phenomenon involving multiphysics (such as shock, phase change of HMX) and chemical reactions (thermal decomposition of HMX) occurring in microseconds or even nanoseconds. Herein, a mechanical-thermal-chemical coupled finite element model is proposed to simulate the pore collapse in a HMX crystal under a shock loading at velocities under 500 m/s. A viscoplastic constitutive model and a Birch-Murnaghan equation of state (EoS) are employed to predict the mechanical response of the HMX crystal. The melting of the HMX crystal is also considered. A multi-step thermal-decomposition model is employed to simulate the chemical reaction of the HMX. Firstly, numerical simulations were implemented for a few plane shock experiments and it is demonstrated that the material model of HMX have reasonable accuracy. Then, the pore collapse in a HMX crystal under a shock at 500 m/s was simulated. It is shown that severe plastic deformation and high-velocity impact of HMX jet both contribute to the temperature rise of local materials. Finally, the influence of pore size on the calculated maximum temperature of the HMX crystal was simulated under various shock velocities ranging from 100 m/s to 500 m/s. It seems that there exists an “optimal” pore size for the HMX crystal to obtain the highest temperature under a shock, which is explained with simulation results.