Sensitivity Of Energetic Materials Research Articles

Theoretically Revealing the Response of Intermolecular Vibration Energy Transfer and Decomposition Process of the DNTF System to Electric Fields Using Two-Dimensional Infrared Spectra.

The external electric field (E-field), which is an important stimulus, can change the decomposition mechanism and sensitivity of energetic materials. As a result, understanding the response of energetic materials to external E-fields is critical for their safe use. Motivated by recent experiments and theories, the two-dimensional infrared (2D IR) spectra of 3,4-bis (3-nitrofurazan-4-yl) furoxan (DNTF), which has a high energy, a low melting point, and comprehensive properties, were theoretically investigated. Cross-peaks were observed in 2D IR spectra under different E-fields, which demonstrated an intermolecular vibration energy transfer; the furazan ring vibration was found to play an important role in the analysis of vibration energy distribution and was extended over several DNTF molecules. Measurements of the non-covalent interactions, with the support of the 2D IR spectra, indicated that there were obvious non-covalent interactions among different DNTF molecules, which resulted from the conjugation of the furoxan ring and the furazan ring; the direction of the E-field also had a significant influence on the strength of the weak interactions. Furthermore, the calculation of the Laplacian bond order, which characterized the C-NO2 bonds as trigger bonds, predicted that the E-fields could change the thermal decomposition process of DNTF while the positive E-field facilitates the breakdown of the C-NO2 in DNTFⅣ molecules. Our work provides new insights into the relationship between the E-field and the intermolecular vibration energy transfer and decomposition mechanism of the DNTF system.

Theoretical study on the correlation between the structure, excess energy, surface energy, electronic structure, nitro charge, and friction sensitivity of N,N'-dinitroethylenediamine (EDNA).

The sensitivity of energetic materials along different crystal directions is not the same and is anisotropic. In order to explore the difference in friction sensitivity of different surfaces, we calculated the structure, excess energy, surface energy, electronic structure, and the nitro group along (1 1 1), (1 1 0), (1 0 1), (0 1 1), (0 0 1), (0 1 0), and (1 0 0) surfaces of EDNA based on density functional theory. The analysis results showed that relative to other surfaces, the (0 0 1) surface has the shortest N-N average bond length, largest N-N average bond population, smallest excess energy and surface energy, widest band gap, and the largest nitro group charge value, which indicates that the (0 0 1) surface has the lowest friction sensitivity compared to other surfaces. Furthermore, the conclusions obtained by analyzing the excess energy are consistent with the results of the N-N bond length and bond population, band gap, and nitro charge. Therefore, we conclude that the friction sensitivity of different surfaces of EDNA can be evaluated using excess energy.

Sensitivity of energetic materials: Evidence of thermodynamic factor on a large array of CHNOFCl compounds

• Impact, friction, and thermal sensitivity data for 150 CHNOFCl species is reported. • Impact testing of high-melting and low-sensitive compounds is most challenging. • Mechanical sensitivity generally increases with the energy content of compound. • Increasing of detonation performance without compromising sensitivity is possible. Mechanical and thermal hazards are critical for chemical compounds. Foremost, the design of novel energetic materials that are stable, insensitive, but have a detonation performance superior to in-service materials is of great interest. However, a single source of safety data for hazardous materials with explosophoric functionalities is still missing. Herein, an experimental database on thermal stability, impact, and friction sensitivity for 150 CHNOFCl compounds is presented. Mechanical sensitivity is discussed in detail: particle size and shape effects, instrument design, and experimental protocol are considered. The entire dataset was analyzed using the simple descriptors of molecular structure. Mechanical sensitivity was found to be linearly correlated with the maximal heat of explosion for certain classes of compounds (nitrobenzenes, furazans, pyrazoles, etc.). Consideration of all species shows that previously proposed sensitivity increase with an energy content rise is relevant, although it is not strict line, as was assumed, but rather a widened “strip”. A new parameter, safety factor, is proposed to combine two types of sensitivity data. With this factor, the limiting values of mechanical sensitivity at a given energy content are provided that represent the state-of-art development of energetic materials and may be used for screening and design of novel compounds.

Molecular Dynamics Simulation of the Influence of RDX Internal Defects on Sensitivity

The internal defect is an important factor that could influence the energy and safety properties of energetic materials. RDX samples of two qualities were characterized and simulated to reveal the influence of different defects on sensitivity. The internal defects were characterized with optical microscopy, Raman spectroscopy and microfocus X-ray computed tomography technology. The results show that high-density RDX has fewer defects and a more uniform distribution. Based on the characterization results, defect models with different defect rates and distribution were established. The simulation results show that the models with fewer internal defects lead to shorter N-NO2 maximum bond lengths and greater cohesive energy density (CED). The maximum bond length and CED can be used as the criterion for the relative sensitivity of RDX, and therefore defect models doped with different solvents are established. The results show that the models doped with propylene carbonate and acetone lead to higher sensitivity. This may help to select the solvent to prepare low-sensitivity RDX. The results reported in this paper are aiming at the development of a more convenient and low-cost method for studying the influence of internal defects on the sensitivity of energetic materials.

Professor Dr. Thomas M. Klapötke

Professor Dr. Thomas M. Klapötke

Can the sensitivity of energetic materials be tuned by using hydrogen bonds? Another look at the role of hydrogen bonding in the design of high energetic compounds.

Strongly positive electrostatic potential in the central areas of molecules of energetic materials is one of the most important factors that determines the sensitivity of these molecules towards detonation. Quantum chemical and density functional theory calculations were used to reveal the influence of hydrogen bonding on the values of electrostatic potential above the central areas of molecules of three conventional explosives: 1,3,5-trinitrobenzene, 2,4,6-trinitrophenol, and 2,4,6-trinitrotoluene. Both the case when energetic molecules act as hydrogen atom donors and when they act as hydrogen atom acceptors were considered. Results of the calculations performed using the M06/cc-PVDZ level of theory showed that there are significant differences in the influence of hydrogen bonding on the electrostatic potential of energetic molecules acting as hydrogen atom donors and hydrogen atom acceptors. In the case when energetic molecules act as hydrogen acceptors, an increase of 10% in the strength of positive electrostatic potential was identified. In the case when energetic molecules act as hydrogen atom donors, a significant decrease (20-25%) in the strength of the positive potential on the molecular surface was calculated. These differences give an opportunity for fine-tuning the impact sensitivities of energetic compounds and provide new guidelines for the design of explosives with desirable characteristics.

Sensitivity of Energetic Materials: Theoretical Relationships to Detonation Performance and Molecular Structure

It has been known for decades that high performances for explosives (as characterized by detonation velocity D, detonation pressure P, or Gurney energy EG) are connected with high impact sensitivities, i.e., low values of the drop weight impact height h50. This trade-off is theoretically substantiated for the first time. It stems from the primary role of the amount of chemical energy evolved per atom for both performance and sensitivity. Under realistic assumptions, log(h50) increases linearly with D–4 or equivalently with P–2 or EG–1. This prediction proves consistent with experimental data for nonaromatic nitro compounds. The occurrence of different explosophores on the same molecule is suggested as a factor influencing the performance-sensitivity trade-off. Finally, it is shown that a large body of data may be explained by the present approach, which naturally integrates thermodynamic (energy content) as well as kinetic (activation energies) aspects. This model should help in designing powerful high en...

Computational Study of the Decomposition of Cyclotetramethylenetetranitramine under Impact, Friction, and Electric Fields

Organic CHNO-containing high energy density materials have been widely used for storing large amounts of the chemical energies which can be rapidly transformed into heat upon various external perturbations during detonation. The sensitivity of the energetic materials is subjected to considerable concern for safety and maintenance. Periodic density functional theory with the all-electron basis sets were employed in this work to unravel the impact, friction, and electric-fields induced decomposition of HMX. The minimum energy paths for the N−NO2homolysis reactions of HMX in the bulk and gas phases were obtained. The surface-enhanced effect on the decomposition of HMX were calculated for both (010) and (100) surfaces. A general theoretical scheme has been proposed to assess the intrinsic mechanic and electrostatic sensitivities of the pure energetic materials.

Study on the Thermal Sensitivity of Energetic Materials Characterized by Accelerating Rate Calorimeter (ARC)

Liquid energetic materials were not tested through traditional test methods for thermal sensitivity. Accelerating Rate Calorimeter (ARC) was scientific to test thermal sensitivity of energetic materials. The decompositions of Hexogen (RDX), Octogen (HMX), 2,4,6-Trinitrotoluene (TNT), Nitromethane (NM), Iso-propyl Nitrate (IPN) were studied by ARC. Kinetic and thermodynamics parameters were calculated and analyzed. Temperature corresponding different time to maximum rate under adiabatic condition (θ) was calculated. The results show that the thermal sensitivity of energetic materials is NM>IPN>RDX>HMX>TNT, which suggests ARC could be used in the test of thermal sensitivity of liquid energetic materials.

A Fractal Approach to Assess the Risks of Nitroamine Explosives

To the best of our knowledge, this work represents the first thermal conductivity theory for fractal energetic particle groups to combine fractal and hot-spot theories. We considered the influence of the fractal dimensions of particles on their thermal conductivity and even on the sensitivity of the explosive. Based on this theory, two types of nitroamine explosives (hexahydro-1,3,5-trinitro-1,3,5-triazine [RDX] and hexanitrohexaazaisowurtzitane [HNIW]) with different sizes, size distributions, and microscale morphologies were prepared using wet milling, solvent/nonsolvent, and ridding methods. The dependence of the explosive sensitivity on the fractal characteristics of the particles was investigated. Specifically, the size distributions and scanning electron microscopy (SEM) images of the samples were used to obtain the fractal dimension (D) and surface fractal dimension (Ds), respectively, by using a least-squares method and fractal image processing software (FIPS). The mechanical sensitivity and thermal stability of the samples were characterized using mechanical sensitivity tests and differential scanning calorimetry (DSC) and were further compared with the previous results upon the investigation about HMX (octahydro-1.3.5.7-tetranitro-1,3,5,7-tetrazocine). The results indicate that the sensitivity of nitroamine explosives largely depends on the fractal dimensions of the particles. Specifically, the sample with a higher D value is more insensitive to impact action, whereas the sample with a higher Ds value is more sensitive to friction action. In addition, the sample with both higher D and Ds values has less heat release and a slower rate of thermal decomposition. All of the above observations can be attributed to the alternation of the formation of hot spots that was controlled by heat mass and thermal conductivity due to the increase of D and Ds values caused by changes in parameters such as fine particle content, specific surface area, porosity content, surface protruding points, and surface roughness. Therefore, the data in these studies were used to develop a thermal conductivity theory for fractal energetic particle groups that could be applied to the prediction of the sensitivity of energetic materials.

Modeling High Rate Impact Sensitivity of Perfect RDX and HMX Crystals by ReaxFF Reactive Dynamics

We report a methodology for rapid assessment of impact sensitivity of energetic materials which uses the ReaxFF reactive force field in reactive dynamics (RD) simulations of the high rate compression/expansion of a perfect energetic crystal. This approach is validated here to study the high rate impact sensitivity of 1,3,5-trinitrohexahydro-s-triazine (RDX) crystal and octahydro-1,3,5,7-tetrazocine (HMX) crystal at different phases (α, β, γ, and δ). These simulations found that for a compression rate of ∼8.76 km/s along the [100] direction, RDX crystals at lower volume compression ratios (x = 30, 35, 38%) led only to a few RDX molecules decomposing and only into primary products. However, at higher compression ratios (x ≥ 40%), all RDX molecules in the crystal decompose very quickly, leading to both primary and secondary decomposition reactions, including various intermediates such as NO2, NO, HONO, and OH and final products such as H2O, N2, CO, and CO2. For the various phases of HMX, these ReaxFF RD simulations found noticeably higher impact sensitivity for the δ-phase than for other three phases (α, β, and γ). At the same compression ratio x = 40%, all HMX molecules in δ-phase decompose leading to both primary and secondary reaction. However, at 40%, only few HMX molecules in α-, β-, and γ-phases decompose. For a higher compression ratio (x = 42%), increased HMX decomposition is observed for all four phases. These simulation results for both RDX and HMX crystals agree qualitatively with experiment observations. We also observe a variation of the strain energy in different HMX phases induced by the high rate compression, which could be related to the sensitivity difference of HMX phases. These simulations typically took less than 18 h to run on a single 3.0-GHz processor, demonstrating that the fast compression approach by MD simulations with the ReaxFF force field can be used for a quick evaluation of the sensitivity of energetic materials.

Product design of particulate energetic materials

The quality and internal microstructure of crystals have a great influence on the sensitivity of energetic materials. Moreover, their particle size and particle size distribution are of great importance to processing technology. Particle properties can especially be influenced by applying different crystallisation techniques, such as cooling crystallisation, membrane crystallisation, emulsion crystallisation, etc. The goal of the investigation reported was to determine the interrelationship between the properties of grown crystals and process parameters. Special attention was directed to the qualitative and quantitative examination of crystal defects and their dependence on the experimental conditions. The morphology and structure of crystals were calculated by molecular modelling. The effect of crystal defects on the sensitivity of the material was tested on different collectives of particles with varying amount of crystal defects.

Effect of radiation treatment on silver azide sensitivity

A novel technique is proposed for studying the effect of radiation treatment on sensitivity of energetic materials, based on irradiation of specimens by a series of pulses on an electron accelerator. Data obtained in experiments with silver azide crystals are reported. The explosion probability in irradiated specimens is shown to be a nonmonotonic function of the radiation dose, exhibiting a rise for low doses and a fall for high doses. The experimental data obtained agree with the divacancy model for heavy metal azide initiation.

Effectiveness of Phlegmatizers in Explosive Compositions under Mechanical Loading

The mechanism of the effect of phlegmatizers in phlegmatized nitramines under mechanical loading is studied. Current concepts regarding the effect of phlegmatizers on the sensitivity of energetic materials to impact, friction, and vibration are considered; insufficiency of experimental data of this effect is noted. Experimental estimates of the phlegmatizing effect of various phlegmatizers on HMX are given.

Acid‐Base Interactions in Energetic Materials: I. The Hard and Soft Acids and Bases (HSAB) Principle–Insights to Reactivity and Sensitivity of Energetic Materials

Acid‐Base Interactions in Energetic Materials: I. The Hard and Soft Acids and Bases (HSAB) Principle–Insights to Reactivity and Sensitivity of Energetic Materials

Acid-Base Interactions in Energetic Materials: I. The Hard and Soft Acids and Bases (HSAB) Principle-Insights to Reactivity and Sensitivity of Energetic Materials

The chemistry of energetic materials can be described applying acid-base reaction formalism. Addressing the HSAB concept, the number of electrons transferred, ΔN, in an acid-base reaction, allows for description and prediction of properties of composite and homogeneous materials. At first ΔN helps in estimating the rate of reaction of binary systems with either given fuel or oxidizer. Nevertheless ΔN is only a relative number thus the range of comparability remains narrow. At second ΔN can be used as a measure for the sensitivity of homogeneous explosives. The increased reactivity of hypothetical fragments to recombine in a reaction such as R3C.+.NO2=R3C−NO2 given by ΔN correlates very well with experimentally determined reduced impact sensitivity of 1,3,5-trinitrobenzene compounds. On the contrary the rising impact sensitivity of metal azides correlates with rising values of ΔN of Mn+/N3− reaction because increased reactivity, that is increased electron transfer from the azide anion to the metal cation triggers formation of the azide radical (.N3). The latter then decomposes rapidly to give dinitrogen. This increased reactivity/sensitivity of metral azides coincides with covalent bonding whereas ionic azides are relatively insensitive.

Interpreting Drop-Weight Impact Results in Terms of Deformation Dependent Initiation Criteria

AbstractThe impact sensitivity of energetic materials is frequently measured in small-scale drop-weight tests. Plastic deformation of the sample leads to heating, the onset of chemical reaction, and eventual ignition. An analytic model provides deformation dependent estimates of the energy delivered to the sample, its stress state, and its temperature distribution. Results for hydoxy-terminated polybutadiene (HTPB/AP) propellants are interpreted in terms of two initiation criteria: critical decomposition temperature and critical thickness for shear banding. The influence of friction, impact velocity, and sample size on initiation give possible explanations of experimental results. Sample material properties variations are studied for both initiation criteria. The model includes energy localization by varying the thickness of shear layers at the sample/machine interface.

Overview: High Speed Dynamics and Modelling as It Applies to Energetic Solids

AbstractThis paper discusses experimental techniques and modelling tools used to characterize energetic solids subjected to dynamic deformation and shock. Critical experiments have been designed to study shock response and impact sensitivity of energetic materials. For example, a simplified two dimensional experiment has been developed to study the critical phenomena involved in delayed detonation reactions (XDT). In addition, wedge tests are used to obtain equation-of-state data. Coupled with hydrocodes, these experiments give us an in-depth understanding of the response of energetic materials subjected to shock loading. A coupled methodology using both experimental and modelling tools is presented. Consisting of three parts, it addresses all possible responses to fragment impact. The three parts are: (1) Fragment impact modelling (hydrocodes and empirically based codes); (2) Experiments to obtain accurate data for predicting prompt detonation; and (3) Tests with planar rocket motor models to explore mechanisms related to bum reaction thresholds and degree of violence. This methodology is currently being used in weapon design and munitions hazard assessments.