Properties Of Energetic Materials Research Articles

Exploring the physical, chemical and thermal characteristics of a new potentially insensitive high explosive RX-55-AE-5

Current work at Lawrence Livermore National Laboratory (LLNL) includes both understanding properties of old explosives and measuring properties of new ones. The necessity to know and understand the properties of energetic materials is driven by the need to improve performance and enhance stability to various stimuli, such as thermal, friction and impact insult. This paper will concentrate on the physical properties of RX-55-AE-5, which is formulated from heterocyclic explosive, 2,6-diamino-3,5-dinitropyrazine-1-oxide, LLM-105, and 2.5% Viton A. Differential scanning calorimetry (DSC) was used to measure a specific heat capacity, C p, of≈0.950 J g−1 °C−1, and a thermal conductivity, κ, of≈0.475 W m−1 °C−1. The LLNL kinetics modeling code Kinetics05 and the Advanced Kinetics and Technology Solutions (AKTS) code thermokinetics were both used to calculate Arrhenius kinetics for decomposition of LLM-105. Both obtained an activation energy barrier E≈180 kJ mol−1 for mass loss in an open pan. Thermal mechanical analysis, TMA, was used to measure the coefficient of thermal expansion (CTE). The CTE for this formulation was calculated to be ≈61 μm m−1 °C−1. Impact, spark, friction are also reported.

Prediction of effective thermo-mechanical properties of particulate composites

A micromechanics-based model is developed to predict the effective thermo-mechanical properties of energetic materials, which are composite materials made from agglomeration of particles of a range of sizes. A random packing algorithm is implemented to construct a representative volume element for the heterogeneous material based on the experimentally determined particle diameter distribution. The effective mechanical properties of the material are then evaluated through finite element modeling, while its thermal properties are determined through a finite volume approach. The model is first carefully validated against results from the literature and is then used to estimate the thermo-mechanical properties of particular energetic materials. Good agreement is found between experimental results and predictions. The stress-bridging phenomenon in the particulate materials is captured by the model. Thermodynamic averaging is shown to be a poor representation for the estimation of thermo-mechanical properties of these heterogeneous materials.

DECOMPOSITION AND PERFORMANCEOFNEW HIGH NITROGEN PROPELLANTS AND EXPLOSIVES

As of late, molecules with high nitrogen content have received increased attention, due in large part to their novel energetic materials properties. At the Los Alamos National Laboratory, we continue to pursue the development and characterization of new high-nitrogen materials for applications in a wide variety of fields. In this work three molecules, triaminoguanidinium azotetrazolate (TAGzT), 3,6-bis-nitroguanyl-1,2,4,5-tetrazine and its corresponding bis-triaminoguanidinium salt, are studied all of which are high-nitrogen compounds with little or no oxygen, however, retain energetic material properties as a result of their high heats of formation. Because of this, the decomposition of this class of compounds have limited or no secondary oxidation reactions of carbon and hydrogen. Other materials discussed for comparison include 3,3'-azobis(6-amino-1,2,4,5-tetrazine)-mixed N-oxides (DAATO{sub 3.5}) and 3,6-bis(1H-1,2,3,4-tetrazol-5-ylamino)-s-tetrazine (BTATz) and the nitramine octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX). The fact that many of these molecules approach 80% nitrogen content makes them potentially useful as gas generants or energetic materials with low flame temperatures, while simultaneously increasing the impulse of gun or rocket propellants. The burning rate, flash pyrolysis (T-jump/FTIR spectroscopy), explosive sensitivity and performance properties were determined. Some examples of interesting behaviors include that TAGzT exhibits one of the fastest low pressure burning rates yet measured for an organic compound,more » and 3,6-bis-nitroguanyl-1,2,4,5-tetrazine has one of the lowest pressure exponents yet measured for a pure organic compound.« less

Theoretical chemical characterization of energetic materials

Our research is focused on developing computational capabilities for the prediction of properties of energetic materials associated with performance and sensitivity. Additionally, we want to identify and characterize the dynamic processes that influence conversion of an energetic material to products upon initiation. We are attempting to achieve these goals through the use of standard atomistic simulation methods. In this paper, various theoretical chemistry methods and applications to energetic materials will be described. Current capabilities in predicting structures, thermodynamic properties, and dynamic behavior of these materials will be demonstrated. These are presented to exemplify how information generated from atomistic simulations can be used in the design, development, and testing of new energetic materials. In addition to illustrating current capabilities, we will discuss limitations of the methodologies and needs for advancing the state of the art in this area.

Decomposition and Ignition of the High‐Nitrogen Compound Triaminoguanidinium Azotetrazolate (TAGzT)

AbstractThe high‐nitrogen compound triaminoguanidinium azotetrazolate (TAGzT) belongs to a class of C, H and N compounds that are free of both oxygen and metal, but retain energetic material properties as a result of their high heat of formation. Its decomposition thus lacks secondary oxidation reactions of carbon and hydrogen. The fact that TAGzT is over 80% nitrogen makes it potentially useful as a gas generant and energetic material with a low flame temperature to increase the impulse in gun or rocket propellants. The burning rate, laser ignition and flash pyrolysis (T‐jump/FTIR spectroscopy) characteristics were determined. It was found that TAGzT exhibits one of the fastest low‐pressure burning rates yet measured for an organic compound. Both the decomposition and ignition behavior of TAGzT are dominated by condensed phase reactions. T‐Jump/FTIR spectroscopy indicates that condensed phase reactions release about 65% of the energy, which helps to explain the high burning rate at low pressure.

Predicting the Impact Sensitivities of Polynitro Compounds Using Quantum Chemical Descriptors

ABSTRACT There has been considerable interest in predicting the stabilities of energetic materials to improve safety during manufacture, handling, storage, and transportation. Although a variety of experimental techniques are available to test the properties of energetic materials, computational screening techniques can harness the convenience of modern computers to reduce the cost of destructive tests. In this paper quantitative structure–property relationships (QSPRs) based on quantum mechanical calculations were employed to correlate the measured impact sensitivities from shock or impact tests with molecular properties. Molecular descriptors were evaluated using both the Hartree-Fock method with a STO-3G basis set and the semiempirical method PM3. Equations that correlate impact sensitivities to the energy of lowest unoccupied molecular orbital (ϵLUMO), energy of highest occupied molecular orbital (ϵHOMO), midpoint potential (MPP), ionization potential (IP), dipole moment (DM), and total energy (E) of the molecules were developed.

New High‐Nitrogen Materials Based on Nitroguanyl‐Tetrazines: Explosive Properties, Thermal Decomposition and Combustion Studies

AbstractThis paper describes the explosive sensitivity and performance properties of two novel high‐nitrogen materials, 3,6‐bis‐nitroguanyl‐1,2,4,5‐tetrazine (1, (NQ2Tz)) and its corresponding bis‐triaminoguanidinium salt (2, (TAG)2(NQ)2Tz)). These materials exhibit very low pressure dependence in burning rate. Flash pyrolysis/FTIR spectroscopy was performed, and insight into this interesting burning behavior was obtained. Our studies indicate that 1 and 2 exhibit highly promising energetic materials properties.

Shock Initiation of Energetic Materials at Different Initial Temperatures (Review)

Shock initiation is one of the most important properties of energetic materials, which must transition to detonation exactly as intended when intentionally shocked and not detonate when accidentally shocked. The development of Manganin pressure gauges that are placed inside the explosive charge and record the buildup of pressure upon shock impact has greatly increased the knowledge of these reactive flows. This experimental data, together with similar data from electromagnetic particle velocity gauges, has allowed us to formulate the Ignition and Growth model of shock initiation and detonation in hydrodynamic computer codes for predictions of shock initiation scenarios that cannot be tested experimentally. An important problem in shock initiation of solid explosives is the change in sensitivity that occurs upon heating (or cooling). Experimental Manganin pressure gauge records and the corresponding Ignition and Growth model calculations are presented for two solid explosives, LX-17 [92.5% triaminotrinitrobenzene (TATB) with 7.5% Kel-F binder] and LX-04 [85% octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazine (HMX) with 15% Viton binder] at several initial temperatures.

Theoretical Chemical Characterization of Energetic Materials

AbstractOur research is focused on developing computational capabilities for the prediction of properties of energetic materials associated with performance and sensitivity. Additionally, we want to identify and characterize the dynamic processes that influence conversion of an energetic material to products upon initiation. We are attempting to achieve these goals through the use of standard atomistic simulation methods. In this paper various theoretical chemistry methods and applications to energetic materials will be described. Current capabilities in predicting structures, thermodynamic properties, and dynamic behavior of these materials will be demonstrated. These are presented to exemplify how information generated from atomistic simulations can be used in the design, development, and testing of new energetic materials. In addition to illustrating current capabilities, we will discuss limitations of the methodologies and needs for advancing the state of the art in this area.

Computational studies on a kind of novel energetic materials tetrahedrane and nitro derivatives

The computational studies on a series of nitro derivatives of tetrahedrane are carried out at B3LYP/aug-cc-pvdz level. The molecular geometries are optimized and the vibrational frequencies are calculated. The electronic structures are analyzed using natural bond orbital theory and atoms in molecules theory. The results show that the skeleton, tetra-carbon cage, is subject to the large stress, C–C bonds of which are weaker than normal C–C bond. The introduction of nitro group reduces the stability of tetra-carbon cage and the C–N bond is weak. The more nitro groups are introduced, the weaker the C–N bonds are. Due to the charge transfer from lone pairs on oxygen to σ ∗(C–N), the C–N bond possesses some π-bonding characteristic and is activated. For C 4(NO 2) 4, the C–N bond is more readily broken than the C–C bond. Heats of formation (HOFs) of nitro derivatives are calculated by isodemic reactions. Values of obtained HOFs are all positive and large so they are belonging to endothermic materials. The HOFs increase with the increase on the number of nitro groups. The results show that these kind of compounds possess some properties of energetic materials and polynitrotetrahedrane may be the potential candidates of the powerful energetic material.

Influence of Pressing Intensity on the Microstructure of PBX 9501

Microstructural features, such as defects, crystal morphology, and crystal size distribution, can significantly affect the ignition sensitivity, performance, and mechanical properties of energetic materials. To evaluate the influence of pressing parameters on microstructure, three cylinders of PBX 9501 were pressed at 5,000, 15,000, and 30,000 psi, using a 100 ton heated steel die press. Polarized light microscopy images taken at 144 locations within each cylinder show differences in porosity, crystal size, and crystal size distribution between cylinders and at different locations within the same cylinder. Scanning electron microscopy further verifies increased fracture and pulverization of HMX crystals during pressing.

Changes in the Mechanical Properties of Energetic Materials With Aging

The mechanical properties of energetic materials were studied as a function of actual age and accelerated aging produced by heat treatment at elevated temperatures for several months. All measurements were made in uniaxial compression at one or more of three temperatures-- m 45, 25, and 65°C--at strain rates between 1 and 10/sec. For TNT that was in the stockpile for up to 40 years, no change in the compressive properties were found. Single-base nitrocellulose propellants that were subjected to 65°C for 18 months also gave no change in the compressive strength. In addition, the compressive strength of a plastic-bonded explosive, PAX 2A, was not changed after 6 months at 60°C and 12 months at 50°C. In contrast, after 6 months at 70°C the compressive strength and modulus of octol were reduced by up to about 40%. The compressive strengths of double- and triple-base nitrocellulose propellants were also decreased by 50-70% by the same heat treatment given to the single-base propellants. These changes for octol and the propellants are a function of measurement temperature. Other changes in most of these material were observed and are discussed. Probable reasons for the changes in mechanical properties are presented.

The Shock Initiation and High Strain Rate Mechanical Characterization of Ultrafine Energetic Powders and Compositions

ABSTRACTThis paper reviews the techniques that have been developed at the Cavendish Laboratory for the study of the mechanical and ignition properties of energetic materials.

Molecular Modeling of Energetic Materials: The Parameterization and Validation of Nitrate Esters in the COMPASS Force Field

To investigate the mechanical and other condensed phase properties of energetic materials using atomistic simulation techniques, the COMPASS force field has been expanded to include high-energy nitro functional groups. In this paper, the parameterization and validation of COMPASS for nitrate esters (−ONO2) is presented. The functional forms of this force field are of the consistent force field type. The parameters were derived with an emphasis on the nonbonded parameters, which include a Lennard-Jones 9−6 function for the van der Waals (vdW) term and a Coulombic term for an electrostatic interaction. To validate the force field, molecular mechanics calculations and molecular dynamics simulations have been made on a variety of molecules containing the nitrate ester functionality. Excellent agreement has been obtained between the calculated and experimental values for molecular structures, vibrational frequencies, liquid densities, heats of vaporization, crystal structure, mechanical properties, and lattice...

A study on dynamic compressive properties of energetic materials at low temperature

The mechanical response of explosives at low temperature was investigated and an experiment apparatus is presented which is available to conduct dynamic compression for explosives at low temperature. Measurements of Comp. B and TNT explosives have been made. The data obtained experimentally depend greatly on the strain rate employed. It is found that the strain ϵm (ϵm is the strain at compressive strength σm) increased with increasing strain rate for both explosives at low temperature. The mechanical properties of Comp. B are higher than those of TNT for all measuring conditions in the present study. The effect of inertia on experiment curves was reduced by introducing a factor of flexibility.

An experimental study on mechanical properties of energetic materials in triaxial compression due to impact

An experimental apparatus of triaxial compressionl which is available to measure the mechanical response of explosives at different temperatures and strain rates, is developed by authors. Dynamic and static compressive experiments of Comp. B and TNT are performed and the material properties) such as compressive modulus, Poisson's ratio and yield strength etc., are obtained. The results show that there exist clear effects of temperature and strain rate for TNT and Comp. B. It also can be found that compressive modulus and strength of Comp. B are larger than that of TNT. In addition, a new method to determine the yield strength in triaxial loading state is presented.

Optical Properties of Energetic Materials: RDX, HMX, AP, NC/NG, and HTPB

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Optical properties of energetic materials from infrared spectroscopy

Optical properties of energetic materials from infrared spectroscopy

Optical Properties of Energetic Materials from Infrared Spectroscopy

A method of determining infrared (2.5‐ 18 m) optical properties of dielectric, crystalline, particulate solids such as energetic materials was developed based on KBr ‐ FTIR (infrared) spectroscopy. Two techniques (spectral subtraction and baseline shifting ) were used to account for light scattering by the KBr matrix. An independent CO 2 laser‐ spatial e ltering measurement was also developed to check the spectral subtraction approach. The method is demonstrated here for the oxidizer ammonium perchlorate (AP). The Rayleigh ‐ Gans limit of light scattering theory was exploited to establish a relationship between the apparent KBr-pellet absorption coefe cient and the intrinsic AP absorption coefe cient. Dispersion theory was used to determine refractive index from the absorption index for AP. Conventional (nonscattering ) FTIR spectroscopy was also used to determine the absorption coefe cient for the common solid propellant binder hydroxyl-terminated polybutadiene. Nomenclature A = absorbance d = particle diameter fv = particle volume fraction It,0 = intensity, transmitted and incident, respectively n = real part of complex refractive index Ka = absorption coefe cient k = imaginary part of complex refractive index or absorption index

Compressive mechanical property tests for energetic material hazard sensitivity

Threat stimuli to propulsion systems lead to a broad range of responses depending on several factors, one being loading rate and its influence on energetic materials compressive behavior. This article reviews techniques for characterizing the mechanical properties of energetic materials and the significance of those properties to the material's hazards sensitivity. Small-scale hazards test devices and conventional mechanical properties testers would preferably simulate the loading conditions of the high-rate insensitve munitions (IM) tests but often fall short of this goal. The strain rate ranges of these tests are compared, and in cases where their strain rate capabilities do not adequately extend to IM ranges, low-temperature testing techniques are reviewed which expand their useful rates. Next, several newer compressive mechanical properties test devices are reviewed which have significantly higher strain rate range capabilities than the conventional test devices. By incorporating the low-temperature testing techniques, their capability to simulate higher rate IM regimes is shown. Finally, a comparison is presented of how material properties vary as a function of strain rate and temperature, using data obtained with these newer test devices.