Cyclotetramethylene Tetranitramine Research Articles

Taming of Triazole, Tetrazole, and Azido Groups: Nitrogen-Rich Energetic Materials with High Thermal Stabilities.

Nitrogen-rich energetic materials are of interest due to their potential use as high-energy-density materials in various applications. However, most compounds with a high nitrogen content show poor thermal stabilities, which may limit their use in certain applications. In pursuit of nitrogen-rich energetic materials, this study presents the synthesis and characterization of two nitrogen rich energetic compounds, namely 3-azido-1-(1H-tetrazol-5-yl)-1H-1,2,4-triazol-5-amine (3, C3H3N11, N%: 79.78) and (E)-1,2-bis(3-azido-1-(1H-tetrazol-5-yl)-1H-1,2,4-triazol-5-yl) diazene (7, C6H2N22, N%: 80.62). Compounds 3 and 7 have high thermal stabilities of 216 and 221 °C, respectively, making them the most thermally stable among metal-free primary explosives. Additionally, they show good energetic performance (vD: 8345 m s-1; P: 25.17 GPa; vD: 8275 m s-1; P: 25.57 GPa), making them potential candidates for metal-free high energy primary explosive. The energetic salts of 3 and 7 were also investigated. Among them, hydrazinium salt 11 displays better energetic performance (vD: 9089 m s-1; P: 30.55 GPa), which was on par with those of cyclotetramethylene tetranitramine (HMX). This research contributes to the exploration of nitrogen-rich energetic materials with potential applications in various fields.

Preparation and performance studies on organic-inorganic phase change composites based on zeolitic imidazolate and paraffin for reducing gun barrel erosion

With the increasing requirements of tank guns for higher muzzle velocity and faster firing rate, some high energetic additives, such as cyclotrimethylene trinitramine (RDX) and cyclotetramethylene tetranitramine (HMX), have been widely used in high energy gun propellants. Consequently, the gun barrel erosion induced by the burning of high energy gun propellants has been an important issue that affects the lifespan of gun barrels. In order to address this problem, erosion reducing additives, including TiO2, paraffin, polyurethane or a combination of these, were introduced into the gun propellant or propellant charge system to alleviate the gun barrel erosion. In this study, a novel organic-inorganic phase change composite paraffin/ZIF-67 with solid paraffin (SP) as the phase change component and zeolitic imidazolate framework-67 (ZIF-67) as the matrix was designed and prepared as anti-erosion additives. The designed composite has a high thermal storage capacity of 93.88 J/g when the ZIF-67 content is 5 wt%. The erosion reducing effect of paraffin/ZIF-67 was determined by erosion tube test. The results show that the introduction of paraffin/ZIF-67 can improve the erosion-reducing efficiency of gun propellants. Compared with the control sample, the erosion-reducing efficiency of paraffin/ZIF-67 exhibited a faster increase with the increase of their contents, having the maximum erosion-reducing efficiency of 39.2 % when the addition of paraffin/ZIF-67 is 3.2 wt%. The incorporation of paraffin/ZIF-67 in the composites has a cooperative effect of each component on reducing gun barrel erosion. The developed organic-inorganic phase change composites exhibit great potential in the application of reducing gun barrel erosion, providing a new way for the development of erosion reducing additives.

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.

Shock-induced nanoscale pore collapse and hotspot in cyclotetramethylene tetranitramine (HMX)

Pore collapse induced hotspot formation is a key mechanism for initiating detonation of shocked high explosives. Accurate continuum models that faithfully capture the pore collapse dynamics and resulting hotspot temperatures for multiscale initiation of high explosive are still lacking. Here, an atomistically informed dislocation plasticity model is developed for cyclotetramethylene tetranitramine (HMX), which includes nonlinear thermoelasticity, pressure-dependent and temperature-dependent dislocation motion and homogeneous dislocation nucleation, and new melting criteria. Nanoscale pore collapse simulations based on the proposed model could well reproduce the pore collapse transition from a strength-dominated regime to a hydrodynamic regime observed in molecular dynamics results. During the pore collapse transition, dislocation motion and dislocation generation induced plasticity is decoupled and evaluated. It indicates that the homogeneous dislocation nucleation suppresses the dislocation motion. Through linkage analysis of dislocation physical quantity histories of tracer particles, this work clarifies the interplay between physical dependences and dislocation mechanisms on pore collapse behaviors for the first time. The results reveal that the transition of pore collapse regime emerges from the strong pressure-dependent homogeneous dislocation nucleation. In addition, the pore collapse responses and energy localizations of the proposed model are further compared with different strength models to prove the importance of pressure dependence and homogeneous dislocation nucleation on pore collapse behaviors. Based on the simulations of pore collapse, the potential heat sources are quantified to provide a physical understanding of hotspot formation mechanisms. The present work demonstrates a key step in multiscale modeling of high explosive initiation in that atomistic simulation results are directly used to guide and refine the mesoscale model of energetic crystal used in the continuum.

Rapid modulation of electrostatic sensitivity and explosive performance by X‐ray radiation

AbstractIt is highly desirable to actively modulate the explosive performance and sensitivity of traditional explosives, such as RDX (hexahydro‐1,3,5‐trinitro‐1,3,5‐triazine), and HMX (cyclotetramethylene tetranitramine), especially to reduce their explosive power and electrostatic sensitivity. Herein, a new avenue is found to effectively modulate the explosive performance and electrostatic sensitivity by direct irradiation of high‐density X‐ray from synchrotron radiation. RDX as a kind of popular and high‐performance explosive, is chosen to demonstrate the modulated effectiveness. After X‐ray irradiation with different irradiation time, the detonation velocity (DV), detonation pressure (DP), heat of detonation (HoD), and electrostatic sensitivity of RDX are determined. Compared with the electrostatic sensitivity and explosive parameters of original high‐quality RDX, the maximum electrostatic sensitivity value is increased to 1061 mJ after irradiation, which is an enhancement ratio of 39.61 %. The lowest DV is 7.57 km/s (−14.27 %), the lowest DP is 16.23 GPa (−53.20 %), and the lowest HoD is 5.15 kJ/g (−9.65 %). These changes mainly originate from the changes in the structure and crystal structure of RDX molecules after irradiation, as evaluated by Scanning Electron Microscope (SEM), X‐ray Diffraction (XRD), and X‐ray Photoelectron Spectroscopy (XPS). The mechanism of RDX modulation by X‐ray is due to denitrification, which always accompanies lots of energy releases, thus impacting the electrostatic sensitivity and explosive power of RDX. Therefore, this study not only provides a new method for reducing electrostatic sensitivity to improve the safety of storage, transportation, and application of RDX, but also holds great potential to reduce explosive performance by non‐contact means.

Enhancing combustion performance of solid propellants using synergistic effect of energetic metal–organic framework with cage-like [Bi6(µ3-O)3(µ3-OH)5] clusters and copper-iron hetero-metallic compound

This study explores the potential of energetic metal–organic frameworks (E-MOFs) to enhance the combustion performance of solid propellants. A {[Bi6O3(tza)5(NO3)2(OH)5]·H2O}n (Bi-MOF) incorporating the energetic ligand tetrazole-1-acetic acid (Htza) was synthesized and evaluated for structural characteristics and properties. The catalytic thermal decomposition of cyclotrimethylene trinitramine (RDX) and cyclotetramethylene tetranitramine (HMX) by mixed systems was investigated. These systems consisted of Bi-MOF and copper-iron hetero-metallic compound ({[CuFe3O(tza)6(H2O)3]·Cl·(NO3)2·4H2O}n, CuFe-MOF), previously reported by our group in different ratios. The effect of the mixed system with the highest synergy index on the combustion performance of composite modified double-base propellant (RDX-CMDB) and nitrate ester plasticized polyether propellant (HMX-NEPE) was investigated. The impact of varying carbon black (CB) contents on the catalytic performance of the mixed system was also examined. The results showed that Bi-MOF exhibits good thermal stability (Tdec = 226.9 °C) and insensitivity (IS>40 J, FS>360 J). The mixed system, comprising Bi-MOF and CuFe-MOF in a 2:1 ratio (M2), exhibited the highest synergistic indices (3.35 and 3.24) on thermal decomposition for RDX and HMX. RDX-CMDB and HMX-NEPE propellant formulations containing M2 and a small amount of CB exhibited significant improvements in combustion performance. RDX-CMDB propellant exhibited up to an 80.6 % increase in burning rate and up to a 59.6 % reduction in pressure index. The pressure indices of NEPE without and with aluminum were reduced from 0.65 and 0.50 to 0.38 and 0.40, respectively (10–20 MPa, 1–20 MPa). These findings highlight the promise of the mixed system, formed by Bi-MOF and CuFe-MOF, as a potential combustion catalyst for RDX-CMDB and HMX-NEPE propellants.

Micro-scale crystallization thermodynamics study of typical energetic compounds integrating optofluidics and machine learning

With the aim of investigating the changing law of crystallization driving force of typical energetic compounds under micro-scale crystallization conditions, a thermodynamic parameter determination method based on optofluidics was proposed. Aimed at nitro, nitramine and nitrate explosives in energetic compounds, hexanitrostilbene (HNS), cyclotetramethylene tetranitramine (HMX) and pentaerythritol tetranitrate (PETN) were selected as representatives, the solubility of the three kinds of energetic compounds in their respective commonly used solvents (HNS: in DMF, DMSO, NMP; HMX: in DMF, DMSO, CYC; PETN: in DMF, DMSO, EAc) at different temperatures were determined. Furthermore, microfluidics and machine learning were combined, the solubility data of the explosives were processed using BP neural network. Moreover, the metastable zone widths of HNS, HMX and PETN in each solvent were determined using on-line Raman technique. Additionally, crystalline thermodynamic parameters such as solid–liquid interfacial tension, crystal surface entropy factor, enthalpy of dissolution and etc. were calculated for each system.

Study of energy dissipation mechanisms and hotspot formation patterns during impact process in octogen explosives with circular cavities

Considerable focus has been given to hotspot generation and ignition phenomena in impact-induced explosives. Hotspot formation in explosives is typically attributed to internal dissipation and heat transfer occurring within them. This study refines the momentum and energy equations to illustrate the entire process of particle collision, temperature-rise evolution, and hotspot formation in octogen explosive bed under impact. By octogen, we mean the substance known as cyclotetramethylene tetranitramine, which is also commonly referred to as HMX. Dense particles are considered to have pseudo-fluid properties. During the impact of the explosive, we captured the propagation of the stress wave and compared its similarities and differences with the shock wave. The collision force model incorporates a combination of Hertz–Mindlin elastic and Thornton elastoplastic contact theories. The temperature-governing equation includes sliding friction, rolling resistance, and plastic dissipations as energy sources, taking into account the heat transfer processes between particles. Temperature evolution is a spatiotemporally correlated phenomenon divided into three processes: high-temperature bands formation, cavity collapse, and particle bed dispersion, all of which lead to hotspot formation near the cavity and near the wall. Plastic dissipation is the primary source for particle temperature-rise and hotspot formation. Furthermore, the effect of cavity size, impact velocity, and particle size on temperature evolution and hotspot formation patterns is analyzed. It was found that higher impact velocities and smaller cavity sizes are associated with increased hotspot temperatures near the wall, but the hotspot temperature near the cavity does not consistently vary with impact velocity and cavity size. This is attributed to the relationship between energy dissipation rate and void collapse time.

Reduction of agglomeration effect by aluminum trihydride in solid propellant combustion

AbstractAluminum trihydride (AlH3) has gained considerable attention as a substitute fuel for aluminum in solid propellants. In this study, we conducted a systematic investigation to evaluate the effects of AlH3 content, ranging from 0 % to 18 %, on propellant ignition, combustion, and agglomeration. Experimental methods such as thermogravimetry−differential scanning calorimetry (TG‐DSC), laser ignition, high‐speed photography, and collecting condensed combustion products (CCPs) were employed. The results indicate that AlH3 significantly promotes the high‐temperature decomposition of ammonium perchlorate (AP). Meanwhile, the addition of cyclotetramethylene tetranitramine (HMX) in propellant does not affect the hydrogen release reaction of AlH3. As the AlH3 content increases from 0 % to 18 %, the spectral emission intensity of the propellants decreases, and the ignition delay time initially increases from 253 ms to 321 ms, and then decreases to 258 ms. Furthermore, the burning rate increases with increasing the AlH3 content, while the pressure exponent is reduced from 0.551 to 0.460. The inclusion of AlH3 in propellants significantly inhibits aluminum agglomeration near the burning surface. Additionally, as the AlH3 content increases, the mean particle size D43 of the CCPs decreases from 50.95 μm to 8.28 μm at 1 MPa. The agglomeration degree of aluminum is very weak at 7 MPa, especially when the AlH3 content exceeds 9 %. The conclusions drawn from this study can serve as valuable guidance for optimizing propellant formulations.

Investigation on unsteady thermal process of NEPE propellant based on an refined chemical kinetic model

This study presents a sophisticated investigation into the intricate heat and mass transfer mechanisms of NEPE composite propellant under realistic rocket motor conditions, with particular emphasis on the rapid depressurization effects. To accomplish this, we have developed an innovative particle packing algorithm coupled with a novel semi-global kinetics model. By integrating detailed chemical kinetics models for Ammonium perchlorate (AP) oxidizing powders, Cyclotetramethylene tetranitramine (HMX) oxidizing powders, and Nitroglycerin/1,2,4-Butane triol trinitrate (NG/BTTN) fuel-binder, we have constructed a meso-scale model of NEPE propellant based on comprehensive experimental data. Furthermore, a refined 9-step kinetic mechanism has been incorporated into the meso-scale model, along with a pressure drop model that accurately captures the intricate gas reaction domain. The predicted parameters of NEPE propellant have been meticulously compared with experimental results, demonstrating a remarkable level of agreement. Moreover, meticulous analyses have been carried out to investigate the complex thermal processes exhibited by this composite propellant under the challenging conditions of rapid depressurization combustion. These analyses primarily focus on unraveling the dynamic evolution of the gas-solid phase and the underlying thermal regression mechanism of the solid phase. Notably, our findings reveal intriguing temporal changes in local heat flux feedback spikes throughout the entire depressurization process, owing to the intricate topology structure of NEPE propellant, which comprises multiscale oxidizing micro-particles embedded within a fuel-binder matrix. This research significantly enhances our understanding of the thermal behavior and performance characteristics of NEPE composite propellant, thereby paving the way for future advancements in rocket propulsion technology.

Mechanism-informed constitutive modeling of molecular crystal cyclotetramethylene tetranitramine (β-HMX)

Molecular crystals are of importance in many applications including energetic materials and pharmaceuticals. Here we focus on the energetic material cyclotetramethylene tetranitramine (β-HMX) whose plastic deformation plays an important role in reaction initiation and detonation. While constitutive modeling of monatomic crystals is well established, the development of models for molecular crystals is less advanced. We present a mechanism-based constitutive formulation for β-HMX crystals, and an equivalent Reuss averaged homogenized model, which are based on a wealth of information about the physics of plastic deformation collected from the literature and developed in this work. We use atomistic models to evaluate the dislocation velocity vs. resolved shear stress relation in multiple slip systems and at various pressures up to 20 GPa, while accounting for slip asymmetry. We use this data to evaluate the strain rate sensitivity on the crystal scale and calibrate all constitutive parameters of the thermally activated and dislocation drag regimes. The resulting crystal plasticity model is then Reuss averaged to produce a homogenized version. The model is perfectly plastic, strongly pressure-dependent and rate sensitive. Further, we observe that strain localization takes place at large enough strain rates and propose a criterion for the occurrence of localization. The formulation can be used to advance the state of the art of continuum modeling of microstructure-dependent initiation in HMX.

Effects of crystallographic orientation and strain‐hardening on nanoindentation response of cyclotetramethylene tetranitramine (‐HMX) single crystals

AbstractMechanical behavior of cyclotetramethylene tetranitramine (HMX) is complex and insufficiently understood, but it is imperative as it affects the initiation of the decomposition reaction though hot spots formation. We present a single‐crystal plasticity model for ‐HMX which accounts for pressure dependence of both the elastic constants and the yield surface. We evaluate the relative importance of pressure sensitivity of the elastic constants and plasticity, and of strain hardening, to the quasi‐static mechanical behavior of HMX, in general, and to indentation, in particular. Further, we study the effect of the in‐plane crystallographic orientations of the substrate with respect to the Berkovich indenter tip on the indentation force‐displacement curve. We conclude that pressure sensitivity of plasticity makes the largest contribution to defining the response to indentation, followed by strain‐hardening, sensitivity of which depends on hardening modulus, while the pressure sensitivity of elastic constants play a smaller role. Both the indentation plane normal orientation and the in‐plane indenter tip rotation may influence properties determined from nanoindentation test (e. g. hardness).

Solubility study and selective purification of HMX explosive in organic electrolyte solution of zinc acetate/diethylene glycol

In this study, an organic electrolyte solution based on zinc acetate/diethylene glycol (ZA/DEG) is introduced for the selective purification of cyclotetramethylene tetranitramine (HMX) high explosive from its identical homologue cyclotrimethylene trinitramine (RDX). The dielectric constant of various organic solutions were investigated through Electrochemical Impedance Spectroscopy (EIS) in the range of 1.0 Hz–30 MHz. and some quantum-chemical descriptors of RDX and HMX dissolutions in the ZA cosolvent were analyzed using Density Functional Theory (DFT). The results show dielectric constant and solubility of RDX is higher than that of HMX, and by increasing of ZA concentration in DEG solvent, the values of dielectric constants were enhanced. Furthermore, the presence of ZA cosolvent on the solubility of two explosives was statistically investigated by Central Composite Design (CCD) of experiment, and some solubility parameters including activity coefficient, dissolving enthalpy, and mixing enthalpies were determined. The experimental results indicate that the weight ratio of RDX to HMX solubility in the proposed organic electrolyte changes up to 30 times, which provides a selective and sequential separation method to separate two materials with similar chemical properties with a separation efficiency >98% and HMX purity> 99.8%. The X-Ray Diffraction (XRD) analysis, High-Performance Liquid Chromatography (HPLC), Laser-Induced Breakdown Spectroscopy (LIBS), and Fourier Transform Infrared Spectroscopy (FT-IR) approves the acceptable quality of the separated materials. The proposed method makes the efficient and safe purification of high-quality HMX for application in oil and gas well perforating gun charges, using a nonvolatile and inflammable organic electrolyte.

The role of HMX particle size in the combustion and agglomeration of HTPB-based propellant

Cyclotetramethylene tetranitramine (HMX) is usually added to solid propellants, but the inclusion of HMX significantly affects the propellant combustion characteristics, especially by yielding more condensed combustion products (CCPs). The effect of HMX size on aluminum agglomeration and CCPs of hydroxyl-terminated polybutadiene (HTPB)-based propellant is evaluated experimentally in this paper. Using a thermogravimetry–differential scanning calorimeter, laser ignition setup, and high-pressure combustion bomb, we have examined the propellants' thermal reactivity, ignition behavior, combustion characteristics, agglomeration, and CCPs with 10–200 μm virgin HMX particles. The results indicate that HMX in propellant suppresses the pyrolysis reaction of ammonium perchlorate. Meanwhile, the exothermic peak temperature of 200 μm HMX increases by 17.8°C compared to 10 μm HMX. With the increase of HMX size from 10 μm to 200 μm, the combustion intensity of the propellant increases, and the ignition delay time of aluminum particles decreases from 580.6 ms to 498.3 ms. Increasing HMX size leads to an increased burning rate, while the pressure exponent decreases from 0.34 to 0.23. Including HMX in propellants also promotes aluminum agglomeration during propellant combustion. With HMX size expanding from 10 μm to 200 μm, the mean agglomerate size in the CCPs decreases from 221.9 μm to 124.5 μm, and the fraction of aluminum involved in agglomeration decreases from 0.206 to 0.104. The unburned aluminum content in agglomerated particles increases monotonically with increasing agglomerates size. Overall, HMX size has a significant impact on the ignition, combustion, and agglomeration characteristics of aluminized propellant. The conclusions of the paper can be used as a guidance for optimizing the propellant formulation

Theoretical study on the interaction between 3,4-dinitropyrazole and cyclotetramethylene tetranitramine

Theoretical study on the interaction between 3,4-dinitropyrazole and cyclotetramethylene tetranitramine

Mechanical Characterisation and Cohesive Law Calibration for a Nitrocellulose Based–Cyclotetramethylene Tetranitramine (HMX) Polymer Bonded Explosive

BackgroundMechanical characterisation of polymer bonded explosives (PBXs) is crucial for their safe handling during storage and transportation. At temperatures higher than the binder's glass transition temperature, fracture is caused predominantly by interface debonding between the binder and explosive crystals. Interfacial friction between debonded crystals can lead to accidental detonation of the PBX material, even under a very small external load. Cohesive zone laws can describe this interfacial debonding.ObjectiveThis study aims to experimentally calibrate the interfacial cohesive zone parameters of a nitrocellulose based–cyclotetramethylene tetranitramine (HMX) PBX, a particulate composite with an 88% volume fraction of crystals.MethodsCompact tension fracture tests, coupled with Digital Image Correlation (DIC) were used to capture the strain fields around the crack tip. The experimental data were used in conjunction with an extended Mori–Tanaka method considering the effect of interfacial debonding.ResultsThe cohesive zone parameters were successfully calibrated and were found to be crosshead rate independent. The values of the critical traction {sigma }_{int}^{max} and interfacial energy release rate, {gamma }_{if}, dropped significantly with increasing temperature. The experimental method followed in this study is generic, and it can be employed to extract the cohesive zone parameters characterising the interface behaviour between the filler and matrix in other particulate filled, polymer composite materials.ConclusionsCohesive zone properties can be experimentally determined to provide inputs in micromechanical simulations linking the microstructure of the PBX composite to its macroscopic response as well as enabling the estimation of hot spot formation at debonded crystal interfaces.

Crystal-scale modelling of pore collapse in cyclotetramethylene tetranitramine (HMX) under different shock strengths

A physically-based anisotropic thermal-mechanical-chemical crystal model is developed for cyclotetramethylene tetranitramine (HMX), which includes nonlinear thermoelasticity, inelasticity due to both dislocation-based plasticity and shear cracking damage, melting, and single step chemical reaction. Based on the proposed model, thermal-mechanical-chemical responses and related physics of shock induced pore collapse in HMX single crystal under low to high strengths were investigated. Under low shock strength (3.4 GPa), obvious orientation dependency of pore collapse is shown for (011) and (110) orientations, where dislocation slip and shear cracking are the dominant mechanisms. The collapsing pore morphologies of the two orientations are distinctly different. Under medium shock strength (8.8 GPa), adiabatic shear bands around the pore area become prominent and they develop along ∼45° relative to the shock direction. Under strong shock strength (23.8 GPa), significant adiabatic shear bands are formed, and the hydrodynamic jetting and impingement afterwards directly lead to the formation of hot spot and eventually the ignition. For the first time, this work clarifies the pore collapse behaviors under various loading strengths with the crystal-scale mechanisms in a unifying framework, which automatically transits from a strength-dominated regime to a hydrodynamic regime. Moreover, in this work, all of potential deformation mechanisms are decoupled and evaluated, which could provide insights into the understanding of ignition mechanism and the development of microstructure-aware predictive models at the macroscale.

Solution structures and ultrafast vibrational energy dissipation dynamics in cyclotetramethylene tetranitramine.

Steady-state and time-resolved infrared (IR) studies of cyclotetramethylene tetranitramine (HMX) were carried out, using the asymmetric nitro-stretch as probe, to investigate its solution structures and vibrational energy transfer processes in pure dimethyl sulfoxide (DMSO) and in a DMSO/water mixture. A linear IR spectrum in the nitro-stretching mode region shows two major bands and one minor band in DMSO but changes to the two major bands mainly picture when adding water as an antisolvent of HMX, suggesting a transition from well-solvated and less perfect β-conformation to a less-solvated and close-to-perfect β-conformation. The latter bears a similar asymmetric nitro-stretch vibration profile to the β-polymorph in the crystal form. Density functional theory computations of the nitro-stretching vibrations suggest that HMX in DMSO may be in a NO2 group rotated β-conformation. Two-dimensional IR cross-peak intensity reveals intramolecular energy transfer between the axial and equatorial nitro-groups in the β-HMX on the ps time scale, which is slightly faster in the mixed solvent case. The importance of water as an antisolvent in influencing the equilibrium solvation structure, as well as the vibrational and orientational relaxation dynamics of HMX, is discussed.

Crystal plasticity including a phase-field deformation twinning model for the high-rate deformation of cyclotetramethylene tetranitramine

A new finite strain thermomechanical model for the high-rate deformation of the β-polymorph of cyclotetramethylene tetranitramine (β-HMX) has been developed and applied to simulations of plate impact experiments. The crystal plasticity model is based on a model developed previously for RDX (Luscher et al. 2017), which is extended to incorporate deformation twinning. Twinning during normal plate impacts is simulated with a phase-field twin model. First, material parameters governing the kinetics of dislocation slip are calibrated on the subset of simulations which had negative Schmid factors for the twin system. Second, a parametric study of the twin material parameters was performed to find suitable values. The results of the simulations with the phase-field twinning model are reported for impacts on several crystal orientations. We find that the twin growth decreases with increasing distance from the impact surface because of dissipation of the shock front via dislocation-mediated plasticity, and that the simulated interface velocity with and without phase-field twinning do not show appreciable differences. These modeling results suggest that the significance of twinning in β-HMX cannot be determined with traditional loading configurations and diagnostics.

Thermal interactions between hybrid HMX/ANPyO cocrystals and commonly used propellant ingredients

Nitramine-based composite propellants (N-CPs) are receiving significant attention in the field of solid rocket propulsion. Cyclotetramethylene tetranitramine (HMX)/2,6-diamino-3,5-dinitropyridine-1-oxide (ANPyO) cocrystals are a novel insensitive energetic material that may replace the high-energy component HMX in insensitive formulations. This study used the DSC-TG coupling technique and the in-situ FTIR technique to investigate the effects of propellant ingredients (AP, n-Al, and nano-Fe2O3) on the thermal decomposition of hybrid HMX/ANPyO. The results show that there are strong interactions among the components of these mixtures. In particular, the peak thermal decomposition temperatures of HMX/ANPyO/AP decreased by about 38.1–42.6 ​°C. In addition, the activation energy (Ea) of hybrid HMX/ANPyO cocrystals was reduced under the effects of Al and nano-Fe2O3. The hybrid HMX/ANPyO cocrystals have different flame propagation speeds, whereas the two typical binary mixtures of HMX/ANPyO/nano-Fe2O3 each have the lowest flame propagation speeds of 0.9 ​mm·s−1 and 1.0 ​mm·s−1 at ambient conditions. The flame propagation speed of HMX/ANPyO/n-Al was barely dependent on pressure, but those of HMX/ANPyO/AP and HMX/ANPyO/nano-Fe2O3 decreased with an increase in pressure.