Detonation properties of ammonium nitrate/nitramine-based composite propellants

ABSTRACT

Ammonium nitrate (AN) propellants have attracted attention because of their low cost and ecofriendliness despite certain major disadvantages such as low burning rate, poor ignitability, low energy, and volume change due to phase transition of AN. The addition of nitramine to AN propellants is one of the approaches to overcome these disadvantages. However, AN/nitramine propellants are characterized by easy initiation, high sensitivity, and high detonation velocity because of the high energy of nitramine. The detonation properties of AN/nitramine propellants were investigated in this study. It was observed that the AN/nitramine propellant required a booster to detonate the propellants, as detonation did not occur while using only a commercial electric blasting cap. It was further observed that the detonation velocity (D) increased linearly as the mass of nitramine per unit propellant volume was increased, and AN had a negligible effect on the detonation properties. An approximate equation was derived from the relationship between D and the mass per unit propellant volume of nitramine. The dominant factors that can be used to estimate the detonation/no-detonation boundaries of the propellants were identified, and the experimental boundary equations were determined using these factors.     

Novel Energetic Compounds Based on 3-Methyl-1,2,5-Oxadiazole 2-Oxide

Two derivatives of 3-methyl-1,2,5-oxadiazole 2-oxide, (E) 4-methyl-1,2,5-oxadiazole-3-carboxaldehyde 5-oxide (2,4,6-trinitrophenyl)hydrazone (1) and 2,2,2-trinitroethyl 4-methyl-1,2,5-oxadiazole-3-carboxylate 5-oxide (2), were designed, synthesized, and fully characterized. The structures of the new compounds were confirmed by single-crystal X-ray analysis. Physicochemical and energetic properties including density, thermal stability, and sensitivity were investigated, and energetic properties (e.g., detonation velocities and detonation pressures) were calculated using EXPLO5 code. The results indicated that compound 1 exhibits positive heat of formation of 448.0 kJ mol^?1 and acceptable sensitivities (IS: 20 J, FS: 280 N). In addition, compound 2 possesses low melting point (99.92°C), moderate decomposition temperature (183.67°C), good detonation performances (D: 8430 m s^?1; P: 31.5 GPa), and lower sensitivities (IS: 18 J; FS: 220 N), which suggest 2 has the potential to be melt-cast explosive.     

Polynitroaliphatic explosives containing the pentafluorosulfanyl (SF5) group: The selection and study of a model compound

Abstract

An investigation concerning the effect of the pentafluoro-sulfanyl (SF₅) group on the properties of explosive nitro compounds is described. The investigation includes: (a) the preparation of several polynitro SF₅ model compounds; (b) the selection of the best model compound (based on overall properties such as melting point, stability, ease of synthesis, etc.); (c) the subjection of this compound to calorimetric determination of the heat and products of detonation. The initial results from the investigation support the hypothesis that the SF₅ group can provide explosives with improved properties (increased density, decreased sensitivity and good thermal stability) as well as produce energy in the detonation.     

Modelling of the underwater shock sensitivity of polyurethane FOAM / PETN explosives

Abstract

The underwater shock sensitivity of a Polyurethane Foam / PETN explosive system was investigated using the Forest Fire model. Pop plots for the explosive were determined by conducting calibrated gap tests. Wedge tests were used but proved extremely difficult to control due to the inhomogeneity of the explosive, its low detonation performance and its high sensitivity. Numerical modelling of calibrated gap tests and underwater gap sensitivity experiments yielded results very close to the experimental ones indicating that the technique is applicable to the low density - low impact pressure regimes.     

AN IMPROVED INHIBITION OF PARAFFIN DEPOSITION FROM WAXY CRUDES

ABSTRACT

A series of cold spot tests of progressively increasing complexity was employed to evaluate the potential of several chemical additives for inhibiting paraffin deposition from waxy crudes. Test data revealed that trichloroethylene-xylene (TEX) binary system has a unique ability to effect substantial pour point depression and improved transport properties for a wide range of waxy crudes. This led to improved inhibition of paraffin deposition by TEX additive in comparison with the perfonnance of some tested, commercial anti-paraffin chemical products.     

A New Synthetic Route for 3,3′-Bis(fluorodinitromethyl)difurazanyl Ether (FOF-13) and Its Energetic Properties

A new protocol for preparation of 3,3-bis(fluorodinitromethyl)difurazanyl ether (FOF-13) was developed. It involves (i) nitration of 3,3’-bis(chlorohydroxyminomethyl)difurazanyl ether with N₂O₅/MeCN to give 3,3-bis(chlorodinitromethyl)difurazanyl ether (4), (ii) reduction of 4 with KI/MeOH to obtain potassium salt of 3,3’-bis(dinitromethyl)difurazanyl ether (6) and (iii) fluorination of 6 with XeF₂ in anhydrous acetonitrile to form the desired FOF-13. FOF-13 was fully characterized by IR, ¹³C NMR, ¹⁹F NMR, and elemental analysis. FOF-13 exhibits excellent physicochemical and detonation properties, such as high density (1.91 g cm^?3), good thermal stability, reasonable impact sensitivity (14 J) and friction sensitivity (64%), high measured detonation velocity (8497 m s^?1 at 1.69 g cm^?3). Furthermore, the precursors 4 and 6 were developed for the first time.     

Investigation on the thermal decomposition performance and long-term storage performance of HNIW-based PBXs through accelerated aging tests

ABSTRACT

2,4,6,8,10,12-Hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (HNIW)-based polymer-bonded explosives (PBXs) were prepared through an aqueous suspension method using cellulose acetate butyrate (CAB) or fluorine rubber F₂₃₁₁ as a binder. Then the variation rules of mass, surface micro-topography, mechanical properties, thermal decomposition performance, detonation velocity and mechanical sensitivity of the samples before and after accelerated aging tests for different durations were measured. Then the variables of the samples that before and after accelerated aging tests for different durations, will be measured, these variables including the variation rules of mass, surface micro-topography, mechanical properties, thermal decomposition performance, detonation velocity, and mechanical sensitivity. The PBX columns showed an acceptable mass loss of less than 1%, after accelerated aging tests. The surface of the PBX samples became more and more uneven as the aging duration prolonged, which was in a good agreement with the order of mass loss. Moreover, the tensile strength, the thermal stability, the detonation velocity and the mechanical sensitivity of the samples were not significantly affected by the aging process, suggesting that the PBXs remained valid after an accelerated aging test at 60°C for 60 days. A further estimation using the modified Arrhenius equation revealed that the storage life at ambient temperature (20°C) of the HNIW-based PBXs was over 10 years, which satisfies the application demands for explosives.     

A molecular dynamics study and detonation parameters calculation of 5,5’-dinitramino-3,3’-bi[1,2,4-triazolate] carbohydrazide salt (CBNT) and its PBXs

ABSTRACT

Molecular dynamics (MD) simulation has been used to investigate the new explosive 5,5?-dinitramino-3,3?-bi[1,2,4-triazolate] carbohydrazide salt (CBNT) and its polymer-bonded explosives (PBXs) with polymethyl methacrylate (PMMA), polyisobutylene (PIB), cellulose acetate butyrate (CAB) and polyurethane (Estane 5703). The binding energy, isotropic mechanical properties (tensile modulus, bulk modulus, shear modulus, and Poisson’s ratio) and moldability are reported for CBNT and its based PBXs. Moreover, the detonation parameters (detonation velocity, detonation pressure, detonation temperature, and detonation heat) of CBNT and CBNT-based PBXs are calculated using EXPLO5. The binding energy between each of the crystalline surfaces and each polymer is different, of which the descending order is CBNT/CAB > CBNT/Estane5703 > CBNT/PMMA > CBNT/PIB. The obtained mechanical properties results indicate that the mechanical properties of the CBNT can be effectively improved by adding a tiny amount of polymer binders and the ability of different polymer binders improving the plasticity and moldability of CBNT in the descending order of Estane 5703 > CAB > PMMA > PIB. The calculated detonation performances show that when 5% binders are added, the detonation velocity and detonation pressure of PBXs are lower than those of pure CBNT, of which the detonation velocity is higher than 8500 m/s and the detonation pressure is higher than 26 GPa. Due to the high enthalpy of formation, the detonation temperature and detonation heat of CBNT/CAB are larger than those of pure CBNT.     

Evaluation of the Detonation Performance of Insensitive Explosive Formulations Based on 3,3ʹ Diamino-4,4ʹ-Azoxyfurazan (DAAF) and 3-Nitro-1,2,4-Triazol-5-One (NTO)

Two energetic materials identified for relatively high energy, but little to no response to impact, spark or friction stimuli are 3-nitro-1,2,4-triazole-5-one (NTO), and 3,3? diamino-4,4?-azoxyfurazan (DAAF). More of an outlier in performance versus sensitivity, DAAF illustrates insensitivity by small-scale sensitivity tests, yet has a failure diameter estimated to be 1.25 mm and a short run length to detonation. Because of this unusual behavior, DAAF is an ideal material to formulate with NTO to obtain tailored shock sensitivity and critical diameter, with detonation velocities and pressures higher than PBX 9502. Here, we present detonation properties of Kel-F^® bonded formulations with ratios of 20–70 wt.-% DAAF added to NTO. All formulations were evaluated for detonation velocity, aluminum flyer acceleration at jump-off, and via the cylinder expansion test.     

Evaluation studies on partial replacement of RDX by spherical NTO in HTPB-based insensitive sheet explosive formulation

ABSTRACT

Hydroxyl terminated polybutadiene (HTPB)-based sheet explosive incorporating spherical 3-nitro-1,2,4-triazol-5-one (NTO) as a partial replacement of 1,3,5-trinitro-1,3,5-triazinane (RDX) was investigated. The effect of incorporation of NTO on mechanical properties, sensitivity behavior, and velocity of detonation (VOD) was studied in comparison with a sheet explosive formulation containing 82 wt% RDX, both based on an HTPB-binder system. The replacement of 22 wt% of RDX by spherical NTO resulted in reduced vulnerability to shock as well as impact stimuli. The data demonstrated that the NTO-added formulation was found to be higher shock insensitive compared to the RDX-only formulation. However, ~5% decrease in VOD was observed on incorporation of NTO. Further, the sheet explosive formulations were found insensitive toward friction up to 360 N. Also, molecular dynamics simulations were performed to predict the elastic constants of RDX and NTO and the results revealed that the predicted trend correlated with the experimentally obtained mechanical properties of the formulations.     

The study of chemical micromechanism governing detonation initiation of some m-dinitrobenzopolyazaarenes

Abstract

Electronic charges, q, at nitrogen atoms of twelve m-dinitrobezopolyazaarenes were calculated by means of ab initio HF/6–31G?? and semi-empirical AM1 methods. The relationships have been confirmed between squares of the detonation velocities or, as the case may be, the detonation heats of the azaarenes and q-values for primarily split off nitro groups. These relationships were considered as an analogue of modified Evans-Polanyi-Semenov equation and so they directly specify the most reactive nitro groups of m-dinitrobenzopolyazaarene molecules in the detonation.     

Binary eutectics formed between ammonium nitrate and amine salts of 5-nitrotetrazole I. preparation and initial characterization

Abstract

We have found that both the ammonium salt of 5-nitrotetrazole (ANT) and the ethylenediamine salt of 5-nitrotetrazole (ENT) form eutectics with ammonium nitrate (AN). Initial characterization and small-scale sensitivity tests of CO₂-balanced AN/ANT and AN/ENT formulations were performed; it was found that both eutectics were less sensitive in all tests than pure ANT or ENT, respectively. The phase diagrams of both mixtures were also determined. ANT forms a eutectic with AN that melts at 121°C; the eutectic composition of the AN/ANT system is 78.5 mol% AN. The eutectic temperature and composition of the AN/ENT system were found to be 110.5°C and 87.8 mol% AN, respectively. Thermal stability studies of the eutectics indicate that they are stable below 160°C and that thermal decomposition occurs slowly over a long period of time.

The detonation velocities of both eutectics, measured unconfined at 2.54-cm diameter, were found to be within 95% of those predicted by the Kamlet-Jacobs method assuming ideal behavior.     

A rapid method for the assessment of the axial output performance of booster charges

Abstract

An experimental method involving the determination of the shock induced in PMMA by a test explosive is described which allows an assessment of the relative output performance of a booster composition in a geometry and size which could be reasonably expected to appear in a weapon design. By applying the same analytical treatment of the experimental results to data generated by the 2-D Eulerian Hydrodynamic Code, HULL, estimates of the detonation pressure and the adiabatic exponent, γ, are obtained. The results indicate that the ordering of performance determined experimentally by this method agrees well with that deduced from velocity of detonation data using a simple γ-law equation of state and with a subsequent experimental verification where the run distance to detonation in a main charge explosive is observed when the booster is separated from the acceptor by a standard attenuator. Further, it is deduced that in the geometry considered using the initiation system described, the booster charges have probably reached steady-state detonation in 25mm lengths.     

Theoretical Studies on Amino- and Methyl-Substituted Trinitrodiazoles

Different amino- and methyl-trinitrodiazoles have been considered as potential candidates for high explosives by quantum chemical treatment. Geometric and electronic structures, band gap, thermodynamic properties, crystal density, and detonation properties have been studied using density functional theory (DFT) at the B3LYP/aug-cc-pVDZ level. Presumably the relative positions of methyl or amino group and nitro groups in the trinitrodiazole determines the stability, sensitivity, and crystal density and thus detonation performance. The chemical energy of explosion (1.35 to 1.47 kcal/g), density (1.93 g/cm³), detonation velocity (9.0 to 9.30 km/s), and detonation pressure (38 to 40.10 GPa) of aminotrinitrodiazoles are comparable to 1,3,5-trinitro-1,3,5-triazinane (RDX) and 1,3,5,7-tetranitro-1,3,5,7-tetrazocane (HMX).     

Thermodynamic analysis of afterburning of detonation products in confined explosions

Abstract

In the paper, an attempt is undertaken to apply the thermodynamic theory of closed combustion, proposed by A. K. Oppenheim and co-workers, to analyse the process of afterburning of the detonation products of condensed explosives in a chamber filled with air. The principal assumptions of the theory are presented and the problem of combustion of fuel in a closed volume is formulated. The relations between thermodynamic parameters and fuel consumption are determined from the laws of conservation of volume, mass and energy. These relations are used to estimate the rate and heat effect of afterburning of the detonation products of some explosives in a steel chamber of 150 dm³ volume. The influence of assumed degree of mixing of the combustion products and air on the mean pressure in the chamber is discussed.     

Fabrication of three-dimensional TKX-50 network-like nanostructures by liquid nitrogen-assisted spray freeze-drying method

ABSTRACT

Design and fabrication of micro- and nanostructures for energetic materials have attracted more attention recently to improve safety properties and enhance detonation performance. Exploring and developing dihydroxylammonium 5,5′-bistetrazole-1,1′-diolate (TKX-50) with unique microstructures, an emerging high-energy-density material with superior comprehensive properties, is of great significance for the potential applications. In this work, we reported that three-dimensional (3D) TKX-50 network-like nanostructures were designed and fabricated successfully via the liquid nitrogen-assisted spray freeze-drying method. Characterization results suggested 3D TKX-50 network-like nanostructures were constructed by self-assembly of small nanoparticles. Furthermore, a nucleation-and-growth self-assembly formation mechanism of the network-like nanostructures depended on the different concentrations of the aqueous solution of TKX-50 was proposed in detail based on the experimental results. More interestingly, thermal analysis results demonstrated these novel 3D TKX-50 network-like nanostructures are much easier to be activated and have a lower decomposition temperature than the raw material, due to decrease in particle sizes, and the impact sensitivity of 3D TKX-50 network-like nanostructures become more sensitive than that of raw TKX-50. Their friction sensitivity of as-prepared samples is similar to the raw materials. Therefore, this work could provide a new prospect for fabrication and application of TKX-50 nanostructures.     

Numerical modeling of the effect of temperature and particle size on shock initiation properties of HMX and TATB

Abstract

The three-dimensional Eulerian reactive hydrodynamic code 3DE has been used to investigate the effects of particle size (and the remaining void or hole size) and of initial temperature on the shock initiation of heterogeneous explosive charges of HMX and TATB.

Shocks interacting with HMX and TATB containing various hole sizes have been modeled. The void fraction was held at 0.5% while the spherical hole sizes were varied from 5.0- to 0.00005 mm radius. The shock pressure was also varied.

As the hole size in TATB was varied from 5.0 to 0.5 mm, the explosive became more sensitive to shock. Decreasing the hole size to 0.0005 mm resulted in failure of the shock wave to build toward a propagating detonation. This is similar to the results previously reported for TNT.

HMX became more sensitive to shock as the hole size was varied from 0.5 to 0.005 mm. The hole size had to be decreased to 0.0005 mm before the explosive became less shock sensitive. Smaller hole sizes (0.00005 mm) resulted in failure of the shock wave to build to detonation.

At the same density, the most shock-sensitive explosive is the one with particle sizes between coarse and fine material. The shock sensitivity of HMX continues to increase with decreasing hole sizes for hole sizes where TNT or TATB fail.

The shock sensitivity of TATB, TNT, and HMX increases with initial temperature. TATB at 250°C is as shock-sensitive as HMX at 25°C. This is in agreement with experimental observations. The shock sensitivity of HMX is less dependent on temperature than TATB or TNT.     

Theoretical Studies on 4-amino-3,5-dinitropyrazole and Its Analogues

Seven analogues of a new high-energetic material, 4-amino-3,5-dinitropyrazole (LLM-116), were designed through changing NH₂ or NO₂ groups on the pyrazole ring of LLM-116. Density functional theory studies on LLM-116 and its analogues were performed at the B3LYP/6-31G(d) level. The geometric and electronic structures, natural bond orbital, charge on the nitro group (-Q_NO2 ), density, detonation properties, and bond dissociation energies (BDEs) of these molecules were investigated and compared with LLM-116. The results showed that molecules E , F , and G had comparable performance with better insensitivity characteristics and might be potential candidates of powerful energetic materials.     

Synthesis of 3,6-bis(3-azido-1,2,4-triazol-1-yl)-1,2,4,5-tetrazine

The synthesis of 3,6-bis(3-azido-1,2,4-triazol-1-yl)-1,2,4,5-tetrazine (3) (BATTz) is described. The physical and explosive sensitivity properties of this material were determined. The heat of formation was measured to be 1376 kJ/mol by combustion calorimetry. Additionally, X-ray crystallography confirmed the structure of this high-nitrogen primary explosive.