Cyclotrimethylenetrinitramine Research Articles

A nonequilibrium kinetic model of high-resolution vibrational energy transfer in RDX from selective IR excitation.

In this paper, we develop a model based on a second quantization-with anharmonic phonon scattering and the phonon Boltzmann transport equation-to study precise high-resolution nonequilibrium vibrational energy transfer (VET) under selective phonon excitation in cyclotrimethylene trinitramine. We simulate mid-infrared pump-probe spectroscopy and observe a prompt appearance (<1ps) of broad-spectrum intensity, which agrees well with experimental data in the literature. The selective excitation of phonons at different frequencies reveals distinct VET pathways and the kinetic evolution of mode occupations as the system reaches a new equilibrium temperature. Three types of transition mechanisms are found to play outsized roles in terms of the amount of energy transferred and the transfer rate: (1) vibrational modes close to the excited frequencies typically respond faster and reach higher temperatures regardless of the excitation frequency; (2) the overtone pathway connecting the modes near 550 and 1150cm-1 is an important bridge between far- and mid-IR; and (3) fast aggregation of energy at 2800cm-1 mediates transfer to/from high frequencies through a second overtone pathway involving modes near 1400cm-1. In addition, by monitoring the temperature of the N-N/N-O stretching modes, strong coupling between those modes and the C-H stretching modes is found. The coupling likely draws the vibrational modes close to both the proton transfer transition state for HONO elimination and the N-N stretching for bond cleavage. The high-resolution understanding of the nonequilibrium kinetics of phonons provides important insight into the energy transfer and initiation mechanisms of molecular solids due to external stimuli.

Effects of aging on mechanical sensitivity threshold and thermal decomposition characteristic of RDX/HMX

In order to analyze the influences of storage aging on the safety of typical elemental explosives, the aged cyclotrimethylene trinitramine (RDX) and cyclotetramethylene tetranitramine (HMX) were prepared by isothermal aging tests. The reaction thresholds of aged RDX and HMX under any ignition probability were studied by Langlie-Optimal D method. The thermal decomposition characteristics of RDX and HMX after aging were analyzed by DSC and ARC. Experimental results showed that compared with unaged RDX and HMX, on the one hand, the critical impact energy and critical friction of RDX and HMX aged for 14, 28 and 56 days are significantly reduced at an explosion probability of 50%, 0.01% and 0.0001%, respectively. With the increase of aging time, the mechanical sensitivity of RDX and HMX increases obviously. On the other hand, the initial decomposition temperature of RDX and HMX after 56 days of aging decreases, the decomposition heat decreases, the activation energy increases, and the reaction difficulty increases.

Discrimination of Explosive Residues by Standoff Sensing Using Anodic Aluminum Oxide Microcantilever Laser Absorption Spectroscopy with Kernel-Based Machine Learning.

Standoff laser absorption spectroscopy (LAS) has attracted considerable interest across many applications for environmental safety. Herein, we propose an anodic aluminum oxide (AAO) microcantilever LAS combined with machine learning (ML) for sensitive and selective standoff discrimination of explosive residues. A nanoporous AAO microcantilever with a thickness of <1 μm was fabricated using a micromachining process; its spring constant (18.95 mN/m) was approximately one-third of that of a typical Si microcantilever (53.41 mN/m) with the same dimensions. The standoff infrared (IR) spectra of pentaerythritol tetranitrate, cyclotrimethylene trinitramine, and trinitrotoluene were measured using our AAO microcantilever LAS over a wide range of wavelengths, and they closely matched the spectra obtained using standard Fourier transform infrared spectroscopy. The standoff IR spectra were fed into ML models, such as kernel extreme learning machines (KELMs), support vector machines (SVMs), random forest (RF), and backpropagation neural networks (BPNNs). Among these four ML models, the kernel-based ML models (KELM and SVM) were found to be efficient learning models able to satisfy both a high prediction accuracy (KELM: 94.4%, SVM: 95.8%) and short hyperparameter optimization time (KELM: 5.9 s, SVM: 7.6 s). Thus, the AAO microcantilever LAS with kernel-based learners could emerge as an efficient sensing method for safety monitoring.

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.

Many-Body Expansion-Based Quantum Mechanical Force Field for Cyclotrimethylene Trinitramine under High Pressure.

RDX undergoes pressures of approximately 30-50 GPa during detonation, leading to significant changes in intermolecular interactions. Accurately describing these interactions is crucial for understanding the energy transfer in the detonation process. To address this, this work introduces a many-body expansion-based quantum mechanical force field (MB-QMFF) to accurately describe RDX's intermolecular interactions under high pressures. Using MB-QMFF, we evaluated various density functionals and found that the M062X functional with GD3 dispersion correction provided the highest accuracy. Regarding intermolecular forces, two-body interactions were the most significant, with three-body interactions being negligible. Additionally, we investigated intermolecular energy variations at different densities (or pressures). The results clearly demonstrate an accurate description of intermolecular interactions by the MB-QMFF scheme. Therefore, we believe that the MB-QMFF scheme can serve as a foundation for the development of RDX-specific force fields and pave the way for future studies on the detonation process of RDX.

Ag-deposited nanostructured Boehmite substrates for the detection of explosives with surface enhanced Raman spectroscopy

We propose aluminum oxide (Boehmite) sputter-deposited with Ag substrates for Surface-Enhanced Raman Spectroscopy (SERS). These substrates are cost-effective and easily fabricated by heating aluminum in an aqueous environment to create Boehmite, followed by Ag sputtering. The metal deposition is optimized, resulting in random arrays of Ag nanostructures with a diameter of ∼100 nm and a spacing of <100 nm leading to significant enhancement of the Raman signal. The performance and sensitivity of the substrates are initially tested with the use of Crystal Violet analyte which results in limits of detection close to 10−10M. These substrates are used for the rapid detection of four different explosive compounds: Nitroglycerin (NG), Picric Acid (PA), Cyclotrimethylene trinitramine (RDX) and 2,4,6-Trinitrophenylmethylnitramine (Tetryl). A series of Raman spectra are collected for these four selected explosives on the fabricated substrates and principal component analysis (PCA) was used for proper evaluation and identification of the corresponding measured spectra.

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.

First-principles study of structural, hydrogen bonds and mechanical properties of α-RDX under hydrostatic compression

The mechanical response of cyclotrimethylene trinitramine (RDX) under pressure loading is closely correlated with the structural deformation and chemical decomposition. The structural, hydrogen bonds (HBs) and mechanical properties of α-RDX under hydrostatic compression between 0 and 4 GPa have been studied using dispersion corrected density functional theory (DFT-D). The oxygen atoms in the E branch (AAE configuration) form important intermolecular HBs with pressure increasing, wherein the bond order of the HB marked as O3∙∙∙H5-C3 reaches up to 0.0716 (∼1.8 times of the intramolecular bonds) at 4 GPa. This HB directly prompts the pressure-dependent increase of Young’s modulus in y direction. α-RDX keeps mechanically stable below 4 GPa, while it shows a pressure-induced ductility owing to deformation tendency in (010) plane (i.e., ac plane). Finally, the pressure-dependent anisotropy, sound velocities and Debye temperature are also discussed based on the calculated mechanical moduli.

Physiological response mechanism of alfalfa seedlings roots to typical explosive cyclotrimethylene trinitramine (RDX)

This study explored the physiological response mechanism of alfalfa seedlings roots to a typical explosive, cyclotrimethylenetrinitramine (RDX), so as to improve the efficiency of phytoremediation. The response of plants to different levels of RDX were analyzed from the perspectives of mineral nutrition and metabolic networks. Exposure to RDX at 10–40 mg L−1 had no significant effect on root morphology, but the plant roots significantly accumulated RDX in solution (17.6–40.9%). A 40 mg L−1 RDX exposure induced cell gap expansion and disrupted root mineral metabolism, The key response elements, P, Cu, and Mg, were significantly increased by 1.60–1.66, 1.74–1.90, and 1.85–2.50 times, respectively. The 40 mg L−1 RDX exposure also significantly disturbed root basal metabolism, resulting in a total of 197 differentially expressed metabolites (DEMs). The main response metabolites were lipids and lipid-like molecules, and the key physiological response pathways were arginine biosynthesis and aminoacyl-tRNA biosynthesis. A total of 19 DEMs in root metabolic pathways, including L-arginine, L-asparagine, and ornithine, were significantly responsive to RDX exposure. The physiological response mechanism of roots to RDX therefore involve mineral nutrition and metabolic networks and are of great significance for improving phytoremediation efficiency.

Molecular Dynamics Simulations of the Thermal Decomposition of RDX/HTPB Explosives.

The addition of binders to energetic materials is known to complicate the thermal decomposition process of such materials. To assess this effect, the present work studied the thermal decomposition of cyclotrimethylene trinitramine (RDX)/hydroxy-terminated polybutadiene (HTPB) mixtures and of pure RDX over the temperature range of 2000-3500 K by combining the classical reaction and first-principles molecular dynamics methods. The incorporation of HTPB as a binder was found to significantly reduce the decomposition rate of RDX. At 3500 K, the decay rate constant of RDX in the RDX/HTPB system is 2.0141 × 1012 s-1, while it is 2.7723 × 1012 s-1 in the pure RDX system. However, the binder HTPB had little effect on the initial decomposition mechanism, which involved the rupture of N-NO2 bonds to produce NO2. The HTPB was predicted to undergo dehydrogenation and chain breaking. The free H resulting from these processes was predicted to react with low-molecular-weight intermediates generated by the RDX, resulting in greater equilibrium quantities of the final products H2O and H2 being obtained from the mixed system compared with pure RDX. HTPB-chain fragments were also found to combine with the primary RDX decomposition product NO2 to inhibit the formation of N2 and CO2.

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.

Low frequency lattice mode dynamics of cyclotrimethylene trinitramine (RDX) crystal studied by femtosecond time-resolved impulsive stimulated Raman scattering

The femtosecond time-resolved impulsive stimulated Raman scattering (fs-ISRS) has been performed to study the low frequency lattice mode dynamics of the RDX crystal. Through Fourier filtering, four lattice mode dynamics is distinguished from the time-resolved spectrum. And the wavenumbers and time constants of these four lattice modes are determined by fitting their dynamic curves. The energy dispersion paths of these four lattice modes are deduced from these fitting parameters. Compared with the other three lattice modes, the lattice mode with wavenumber 30 cm−1 has a very longer life time. We consider that the excitation of this lattice mode more likely to cause the damage of the intermolecular interaction under the strong external stimulation.

Constructing hotspots through star-shaped gold-copper alloy nanocrystals for laser initiation of explosives

Laser initiation technology is an effective way to detonate high energy materials safely and reliably, which has broad application prospect in military blasting. However, there are many obstacles in high-power laser propagating through optical fiber, which directly affect the initiation of high-energy explosives under low-power conditions. Photosensitizer is a necessary substance for initiating low energy and low sensitivity explosives. Herein we developed gold-copper alloys nanocrystals as free-standing laser energy converter material to reduce the laser initiation threshold and delay time. By controlling the nanocrystals morphology, more hotspots were created in the nanocrystals and the ultraviolet–visible-near infrared (UV–VIS-NIR) absorption peak of nanocrystals was regulated to around 808 nm. The laser irradiation result showed that the temperature of the gold-copper alloys nanocrystals was close to 280 ℃ within 10 s (808 nm, 1 W·cm−2). In the practical applications, the cyclotrimethy lenetrinitramine (RDX) initiation threshold can be reduced by 83.47% and B/KNO3 delay time by 43.95% by using gold-copper alloy nanocrystals as laser energy absorber. This result indicates that the gold-copper alloy as an independent laser absorbing material can effectively initiate low-sensitive explosives under low-power conditions.

Reshaping the microenvironment and bacterial community of TNT- and RDX-contaminated soil by combined remediation with vetiver grass (Vetiveria ziznioides) and effective microorganism (EM) flora

Explosive pollutants remaining in global soils are serious threats to human health and ecological safety. Soils contaminated by trinitrotoluene (TNT) and cyclotrimethylene trinitramine (RDX) are simulated in this study and remediated using vetiver grass and effective microorganism (EM) flora to determine the efficacy of combined remediation in reshaping the microenvironment and bacterial community of soils contaminated by explosives. The degradation rates of TNT and RDX after 60 days of combined remediation were 95.66% and 84.37%, respectively. Soil microbial activity and enzyme activities related to the nitrogen cycle were upregulated. The content of soil elements in the remediation group changed significantly. Vetiver remediation increased the diversity and significantly changed the structure of the microbial community. Notably, bacteria, such as Sphingomonadaceae and Actinobacteriota, which can degrade explosives, occupied the soil niche, and the Proteobacteria and Bacteroidota, which are involved in sugar metabolism, showed particularly increased abundance. The metabolism of soil carbohydrates, fatty acids, and amino acids was upregulated in the vetiver, EM flora, and combined vetiver+EM flora remediation groups, and the most significantly upregulated pathway was galactose metabolism. The combined vetiver and EM flora treatment of soil contaminated by explosives greatly improved the ecology of the soil microenvironment.

Temperature-Dependent Far-Infrared Absorption in Cyclotrimethylene Trinitramine Single Crystals Using Broadband Time-Domain Terahertz Spectroscopy

We investigate the absorption properties of cyclotrimethylene trinitramine (RDX) single crystals from ∼15 to 150cm−1 using the terahertz time-domain spectroscopy. We observe that all the absorption modes exhibit strong anisotropic behavior in terms of the crystal orientations. We demonstrate that the anharmonic phonon model can well describe the temperature-dependent behaviors of these absorption modes. These results indicate that the intermolecular interaction plays a major role in the collective motion of large number of RDX molecules. Our findings provide important information for understanding and controlling the dynamic properties in the explosive materials.

Improvement of Composite Propellants Energy Using Explosive Materials

Composite propellants are energetic materials have ability to ignite, burn fast and cause several simultaneous exothermic chemical reactions which produce huge amounts of gases under high pressures and temperatures which can spread spontaneously. 1n the present study, the explosive material hexogen (Cyclo tri-methylene tri-nitramine) was used to improve the performance properties of composite propellants, especially the specific impulse. For several formulations of hexogen at different added percentages, the specific impulse was calculated using thermodynamic calculations program of composite propellants. The results given were compared with those formulations not including hexogen. It was seen that; hexogen caused a significant positive effect in the specific impulse. Accordingly, the energy of composite propellant was improved positively in the samples containing hexogen till 40% of the oxidizer ratio. Also, it was noticed that the specific impulse began to decrease gradually for the oxidizers containing more than 40% of hexogen which caused in a decreasing of composite propellant energy. Finally, it was concluded that, the use of some amount of explosive materials like hexogen can improve composite propellants energy successfully.

Study on laser ignition characteristics of graphene Oxide/Cyclotrimethylene trinitramine composite films

The laser ignition has been proposed for the realization of safe and reliable ignition of explosives. However, the high energy of laser ignition has seriously hindered its practical application. Therefore, it is of great significance to the wide application of laser ignition for developing a photosensitizer with good laser ignition performance under low laser energy. Herein, a free-standing graphene oxide (GO)/cyclotrimethylene trinitramine (RDX) composite film, known as GxRy (x: the mass of GO, y: the mass of RDX) composite film, was obtained to investigate the laser ignition performance. The results showed that the laser photothermal properties of GxRy composite films could be significantly improved by mixing GO with RDX. The temperature of G20R5 composite film could raise from 25 to 1040 °C under the pulsed laser irradiation (450 nm, 0.7 W), showing excellent photothermal properties. The high temperature rise of G20R5 film under laser irradiation might be due to the decomposition and combustion of RDX in the G20R5 film. The G20R5 composite film would be a promising laser photothermal conversion device for low initial energy photothermal ignition and provide a new idea for the preparation of photosensitizers with high laser photothermal properties.

A unified model of anisotropy, thermoelasticity, inelasticity, phase transition and reaction for high-pressure ramp-loaded RDX single crystal

A unified thermomechanical consistent model integrating multiple mechanisms, including material anisotropy, nonlinear thermoelasticity, inelasticity, phase transition , and chemical reaction, is developed for cyclotrimethylene trinitramine (RDX) crystal under high-pressure ramp-loading. (i) The nonlinear thermoelasticity of material is described by pressure-temperature-dependent elasticity tensor and a free-energy based complete equation of state. (ii) The cracking-mediated brittle damage on eleven cleavage planes and dislocation-mediated ductile plasticity on thirteen slip systems are considered in inelastic deformation. (iii) The phase transition kinetics is dependent on a thermodynamic consistent driving force. (iv) The chemical reaction is described by a reactive flow model integrating equations of state for solid reactants and gaseous products, Arrhenius-type reaction rate model and mixed rule. The proposed model is utilized to simulate the mechanical-thermal-chemical responses of (100) and (010) oriented ramp-loaded RDX crystals at pressure up to ~33GPa. The simulated results are well in agreement with the experimental data and reveal a four-wave structure (elastic-inelastic-phase transition-reaction wave) hidden behind the pressure wave profiles. Crack and dislocation activities on (110) and (1-10) crystal planes play a dominant role in macroscopic inelasticity of (100) oriented RDX. Compared to (100) oriented RDX, the (010) oriented RDX exhibits a higher α→γ phase transition criterion and a faster chemical reaction, which is associated with the different overall heating rate and thermomechanical state.

Microbial community structure and metabolome profiling characteristics of soil contaminated by TNT, RDX, and HMX

This experiment was conducted to evaluate the ecotoxicity of typical explosives and their mechanisms in the soil microenvironment. Here, TNT (trinitrotoluene), RDX (cyclotrimethylene trinitramine), and HMX (cyclotetramethylene tetranitramine) were used to simulate the soil pollution of single explosives and their combination. The changes in soil enzyme activity and microbial community structure and function were analyzed in soil, and the effects of explosives exposure on the soil metabolic spectrum were revealed by non-targeted metabonomics. TNT, RDX, and HMX exposure significantly inhibited soil microbial respiration and urease and dehydrogenase activities. Explosives treatment reduced the diversity and richness of the soil microbial community structure, and the microorganisms able to degrade explosives began to occupy the soil niche, with the Sphingomonadaceae, Actinobacteria, and Gammaproteobacteria showing significantly increased relative abundances. Non-targeted metabonomics analysis showed that the main soil differential metabolites under explosives stress were lipids and lipid-like molecules, organic acids and derivatives, with the phosphotransferase system (PTS) pathway the most enriched pathway. The metabolic pathways for carbohydrates, lipids, and amino acids in soil were specifically inhibited. Therefore, residues of TNT, RDX, and HMX in the soil could inhibit soil metabolic processes and change the structure of the soil microbial community.

Comparison of the effects of several binders on the combination properties of cyclotrimethylene trinitramine (RDX)

Comparison of the effects of several binders on the combination properties of cyclotrimethylene trinitramine (RDX)