Measurement of Afterburning Effect of Underoxidized Explosives by Underwater Explosion Method

The afterburning effect of TNT and a desensitized hexogen RDX-Al explosive was studied in a defined gas volume under water. A double-layer container (DLC) filled with different gases (air, oxygen, and nitrogen) was used to control and distinguish the afterburning effect of explosives. After the charges in the DLC were initiated under water, the shock wave signals were collected and analyzed. It is shown that shock wave peak pressures are duly in compliance with explosion similarity law, pressure, and impulse histories for explosions in oxygen and air are greater than those recorded for explosions in nitrogen due to the afterburing reaction. Moreover, the afterburning energy was calculated. Results show that even though there is excess oxygen in the gas volume, the afterburning energy may not reach the theoretically maximum value. This result is different from that in confined explosion, where the presence of excess oxygen in the compressed gas filling a bomb leads to complete combustion of the detonation products.     

Calculation of thermodynamic parameters of combustion products of propellants under constant volume conditions using the virial equation of state. Influence of values of virial coefficients

Abstract

The thermodynamic aspects of the propellant combustion under constant volume conditions are considered. The combustion model and computer program named BOMBA8 for the calculation of the thermodynamic and interior ballistics parameters of combustion products are described.

The applicability of the presented combustion model and computer program is tested on several different types of propellants under different combustion conditions.

The equilibrium composition of combustion products is calculated by applying the Gibbs energy minimization method. The pressure and thermodynamic parameters of combustion products are calculated by applying the virile equation of state. The virile coefficients of individual species are calculated in different manners — applying equations derived from experimental measurements and using different potential equations.     

Jet initiation and penetration of explosives

Abstract

The two-dimensional Eulerian hydrodynamic code 2DE, with the shock initiation of heterogeneous explosive burn model called Forest Fire, is used to model numerically the interaction of jets of steel, copper, tantalum, aluminum, and water with steel, water, and explosive targets.

The calculated and experimental critical condition for propagating detonation may be described by the Held V² d expression (jet velocity squared times the jet diameter). In PBX 9502, jets initiate an overdriven detonation smaller than the critical diameter, which either fails or enlarges to greater than the critical diameter while the overdriven detonation decays to the C-J state. In PBX 9404, the jet initiates a detonation that propagates only if it is maintained by the jet for an interval sufficient to establish a stable curved detonation front.

The calculated penetration velocities into explosives, initiated by a low-velocity jet, are significantly less than for non-reactive solids of the same density. The detonation products near the jet tip have a pressure higher than that of nonreactive explosives, and thus slow the jet penetration. At high jet velocities, the calculated penetration velocities are similar for reactive and inert targets.     

Empirical estimate of detonation parameters in condensed explosives

Abstract

Based on the available data base on the detonation parameters of existing explosives, an observation was made that by proper normalization with the dynamic pressure - ρ_oD² the Chapman-Jouguet states of all explosives converge to a single generic point in the pressure-specific volume plane. With the exception of very few explosives, this point in P-V plane has a variance of less than 1 %. The pressure-particle velocity (P-Up) plot of all Chapman-Jouguet states revealed a simple quadratic relationship between P and Up which, together with the nondimensional identities of the generic point, led to a simple relationship between the initial density (ρ_o) of an explosive and its detonation velocity (D).

Thus, having the values of ρ_o and D of any explosive, one can easily estimate all of its detonation parameters (P_CJ, U_CJ, V_CJ, and Γ_CJ) with an accuracy of less than 3%. However, if the detonation velocity is also not known, it too can be estimated quite accurately, increasing the margin of uncertainty to about 10%.     

The influence of temperature on the detonation velocity of selected emulsion explosives

ABSTRACT

Many years of research on more effective and safer explosives led to the development of emulsion explosives. They are the second most commonly used group of explosives in the world, primarily due to the fact that they are a good alternative to ANFO explosives or dynamites. Their key advantage in underground applications is the lower content of toxic fumes in the detonation products. Emulsions are also characterized by high detonation velocity, high water resistance, low value of critical diameter and mechanical loading capacity. Multiple factors related to the applied mining method influence the detonation parameters of emulsion explosives. One such parameter is the time between the loading of the explosive into the blast hole and firing, which in the case of underground copper mines in Poland can even last up to 48 hours. This becomes a particularly significant issue due to the increasing depth of mining in Polish copper mines and the high virgin temperature of rock mass at these depths. Experiences related to the use of explosives and their efficiency under such conditions confirm the intuitive thesis that high ambient temperature has a negative impact on the explosives’ effectiveness. In this regard, research concerning the influence of temperature on the detonation velocity of selected emulsion explosives was carried out, including bulk and packaged explosives. The tests were performed for different conditioning temperatures, which are all locally observed in Polish copper mines. The obtained results confirmed the significant influence of temperature on the velocity of detonation of the considered explosives.     

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).     

Thermal Behaviors and Their Correlations of Mg(BH4)2-Contained Explosives

In order to explore the effect of metal hydride on energetic materials’ thermal behaviors and their correlations, we studied the heats of combustion and detonation of RDX, TNT, and Mg(BH₄)₂-containing explosives both theoretically and experimentally. The results showed that Mg(BH₄)₂ can significantly improve the energy of explosive. As the mass fraction of Mg(BH₄)₂ increases, the combustion heat of composite explosives increases gradually, while the combustion efficiency decreases. When its mass fraction is about 30%, the theoretical heats of detonation of RDX/Mg(BH₄)₂ and TNT/Mg(BH₄)₂ reach maximum, which are 7418.47 and 7032.46 kJ/kg, respectively. When we compared the errors between calculation and experimental values, we found that L-C method is more accurate in calculating oxygen-enriched and oxygen-balanced explosives, and that minimum free energy method is more suitable for seriously negative oxygen-balanced explosive. For single explosive, there are three kinds of relationships between heat of combustion and detonation according to the oxygen balance. For Mg(BH₄)₂-containing explosives, the relationship is in accordance with Boltzmann function.     

Simple method to calculate explosion temperature of ideal and non-ideal energetic compounds

ABSTRACT

The explosion (detonation) temperature of organic compounds containing energetic groups can be related to the study of the kinetics of chemical reactions in the reaction zone as well as the thermodynamic state of the detonation products. It can be predicted by a simple approach for ideal and less ideal energetic compounds as well as non-ideal composite explosives containing aluminum (Al) or ammonium nitrate (AN). A general correlation is introduced for calculation of the explosion temperature from the heat of detonation where it can be corrected for AN and liquid organic energetic compounds. For ideal and less ideal energetic compounds, the predicted results are compared with the outputs of complex thermochemical/hydrodynamic computer codes using two appropriate equations of state (BKWR-EOS and BKWS-EOS). The values of mean absolute percentage error (MAPE) in the explosion temperature for ideal and less ideal organic energetic compounds are 5.4, 5.5 and 12.5 for the new method, BKWS-EOS, and BKWR-EOS, respectively. The new method shows good agreement for non-ideal energetic compounds with respect to the outputs of BKWS-EOS using partial equilibrium where it provides good predictions for detonation performance.     

Study of continuous velocity probe method for the determination of the detonation pressure of commercial explosives

ABSTRACT

A novel velocity probe, which permits recording the continuous velocities of detonations and shock waves, has been developed based on the transition of operation principle from ionization to pressure-conduction. Using the new probe and the impedance matching method, a series of measuring devices were set up to obtain the shock wave velocities in different inert materials, i.e., water, Plexiglas and paraffin wax. Two test types of powder ammonium nitrate/fuel oil (ANFO), exposed on the ground and tamped in the blast hole, were performed, from which we calculated their detonation pressures, with a density of approximately 0.86 g·cm^?3, ranged from 3.52 GPa to 3.65 GPa, and the adiabatic exponents from 2.24 to 2.30. The results show that the present velocity probe-based method can be used to determine the detonation pressure of commercial explosives conveniently and reliably, which is an important supplement for the testing techniques of explosive performance.     

Comments on ‘‘a simple method for calculating detonation parameters of explosives'

Abstract

The present contribution deals with a modified method of estimating the detonation parameters starting with a general formulation of the adiabat for explosives as expressed using the adiabatic exponent γ_j = f(ρ₀) according to Wu Xiong¹. The author uses also the works of Russian authors.^2,7,8     

Nitro Derivatives of 1,3,5-Triazepine as Potential High-Energy Materials

Structure optimization and frequency calculation of six nitro derivatives of 1,3,5-triazepine were performed using a MP2(FULL)/6-311G(d,p) method. In order to obtain reliable energy data, single-point energy and subsequently thermodynamic properties of the species considered were calculated at a fairly high level of theory, CCSD(T)/6-311G(d,p). Solid-phase heats of formation and crystal density were determined using an electrostatic potential (ESP) method utilizing wave function analysis-surface analysis suite (WFA-SAS) code. The result shows that all nitro derivatives possess high positive heats of formation that increase with an increase in the number of nitro groups attached to the ring moiety. The crystal density was found to be in the range of 1.67–1.90 g/cm³. Detonation properties of the compounds were estimated using the Kamlet-Jacobs equation. The results showed that detonation velocity (D) and detonation pressure (P) increased with an increase in the number of nitro groups attached at the ring moiety. It was found that all six nitro derivatives of the title compound had better or comparable performance characteristics than the most widely used commercial explosives, such as TNT, research and development explosives (RDX), and 1,3,5,7-tetranitro-1,3,5,7-tetrazocane (HMX). The trinitro derivative (1,3,5-trinitro-1,3,5-triazepine, F) yielded detonation pressure (P) and detonation velocity (D) of 45.5 GPa and 9.23 km/s, respectively, at a loading density of 1.90 g/cm³, which are superior to the most powerful available explosive HMX (P = 39.00 GPa and D = 9.11 km/s). The results obtained during the present study show that the title compounds can be used as promising futuristic high-energy-density materials (HEDMs).     

Sensitivity and performance properties of tex explosives

Abstract

Some sensitivity and performance properties of TEX were studied experimentally and theoretically. The TEX sensitivity to electrostatic spark was determined and tests for transportation were performed. The detonation properties, like the critical diameter, detonation pressure and Gurney energy were determined. Moreover, the detonation velocities of TEX-based cast explosives were compared with those of similar NTO-based ones.     

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.     

On predicting properties of explosives – detonation velocity

Abstract

A systematic method of representing an explosive, based on its composition, is presented. This method is used to display performance data for existing explosives, and suggests an alternate definition for oxygen balance and determines compositions that might produce high-performance explosives. A new method for predicting the detonation velocity of a proposed explosive is also presented. This is a simple method that also yields insight into which factors are important in predicting performance.     

Computational Studies on Nitro Derivatives of 1-Hydroxy-1,2,4-triazole

Thermodynamic properties and energetics of the nitro derivatives of 1-hydroxy-1,2,4-triazole, viz. 1-hydroxy-3-nitro-1,2,4-triazole (A), 1-hydroxy-5-nitro-1,2,4-triazole (B), and 1-hydroxy-3,5-dinitro-1,2,4-triazole (C), are considered for a detailed computational study during the present investigation using a density functional theory B3LYP/6-311G(d,p) method as implemented in the Gaussian 03 suite of programs. Heats of formation and other thermodynamic properties for all of the compounds considered were determined. Studies revealed that these compounds possess the requisite properties for use as high-density energetic materials. Detonation velocity (D) and detonation pressure (P) of the title compounds were evaluated using the Kamlet-Jacobs method based on the crystal densities calculated at the DFT(B3LYP)/6-311G(d,p) level incorporating the electrostatic interaction. Calculation showed that these compounds yielded a detonation pressure and detonation velocity in the range of 27–35 GPa and ～8 km/s, respectively, at loading densities of 1.60–1.90 g/cm³. The calculated values are comparable to the values determined for powerful commercial explosives such as Research Department Explosive (RDX) (34.10 GPa, 8.75 km/s, 1.80 g/cm³), High Melting Explosive (HMX) (39.00 GPa, 9.11 km/s, 1.89 g/cm³), and Trinitrotoluene (TNT) (21.00 GPa, 6.93 km/s, 1.64 g/cm³).     

Preparation and thermal properties study of HNIW/FOX-7 based high energy polymer bonded explosive (PBX) with low vulnerability to thermal stimulations

ABSTRACT

For modern munitions, high energy explosives are expected to reduce vulnerability and improve safety. In this study, based on the formulation of PAX-11 (94 wt% HNIW, 2.4 wt% CAB, 3.6 wt% BDNPA/F), FOX-7 is used as a portion replacement for HNIW to decrease vulnerability. To further decrease mechanical sensitivities and prevent static electricity, 0.5 wt% graphite is added to the surface of PBXs. A series of HNIW/FOX-7 based polymer bonded explosives (PBXs) with different formulations are prepared and mechanical sensitivities, thermal stabilities, detonation velocities, and slow cook-offs are studied to evaluate the energy and hazard of these PBXs. Additionally, finite element numerical simulations are utilized to study the transient temperature distributions, ignition time and ignition locations of the PBX cylinders during slow cook-off. Based on the results of this study, we obtain a high energetic low vulnerable PBX formulation (54 wt% HNIW, 40 wt% FOX-7, 2.4 wt% CAB, 3.6 wt% BDNPA/F, 0.5 wt% additional graphite) that balances energy and vulnerability. This formulation passes the slow cook-off test and detonation velocity reaches 8776 m·s^?1, which can be used in the warhead of the high explosive anti-tank cartridge.     

Effect of RDX powders on detonation characteristics of emulsion explosives

ABSTRACT

To obtain an explosive suitable for the explosive welding of foils and produce a new way to reuse demilitarized explosives, RDX powders and high amounts of hollow glass microballoons (GMs) were introduced into an emulsion matrix to reduce detonation velocity and critical thickness. The effect of different percentages of RDX on the detonation performance of the mixtures was systematically investigated. The results showed that the critical thickness decreased significantly with increasing RDX contents, and the detonation velocity at the critical thickness was almost unchanged for the different RDX contents. Thus, the as-created mixtures were suitable for the explosive welding of foils due to their low detonation velocities and low critical thicknesses. The brisance test results indicated that the brisance of the composite explosives increased with increasing RDX contents, and this trend was more remarkable at low RDX contents. All the energy output parameters of the underwater explosions also increased with increasing RDX contents.     

Explosion Power and Pressure Desensitization Resisting Property of Emulsion Explosives Sensitized by MgH2

Due to low detonation power and pressure desensitization problems that traditional emulsion explosives encounter in utilization, a hydrogen-based emulsion explosives was devised. This type of emulsion explosives is sensitized by hydrogen-containing material MgH₂, and MgH₂ plays a double role as a sensitizer and an energetic material in emulsion explosives. Underwater explosion experiments and shock wave desensitization experiments show that an MgH₂ emulsion explosives has excellent detonation characteristics and is resistant to pressure desensitization. The pressure desensitization–resistant mechanism of MgH₂ emulsion explosives was investigated using scanning electron microscopy.     

Microstructure effects on the detonation velocity of a heterogeneous high-explosive

ABSTRACT

Although numerous methods exist for the theoretical calculation of detonation parameters of explosives, few thermodynamic-hydrodynamic-based theoretical codes take into account particle size. The basis for their computational analysis is primarily focused on the equation of state of the detonation products, heat of formation, and density of the explosive composition. This study utilized regression analysis to model the relationship between the microstructure characteristics and detonation velocity of a heterogeneous high-explosive composition containing cyclotrimethylene-trinitrmaine (RDX). The principal characteristics examined were the average particle size of RDX, amount of HMX impurity within the RDX particles, method of RDX manufacture, and compositional density. Statistical analysis demonstrated the relevancy of the microstructure influence on the detonation velocity of the developed experimental compositions of 73 wt. % solids and 27 wt. % polyurethane binder. An equation is developed that accurately predicts detonation velocity based on average particle size, density, and manufacturing process for RDX. The model underscores the significance of the relationship between the average particle size and detonation velocity. Compositions containing smaller average particle sizes of RDX generate higher detonation velocities. A 100 micron increase in the average particle size was shown to decrease detonation velocity by 161 m/s for the monomodal polyurethane compositions used in this study. The relevance of using statistical models for selecting characteristics that result in optimum explosive performance is addressed.     

OPERATION AND EFFICIENCY OF CYCLIC COAL BURNING ENGINES

ABSTRACT

A method of burning porous solid fuels in a fixed bed and in pellet or chunk form is described wherein compressing the fuel with air forces oxygen deep into the fuel pores where primary reaction occurs. Subsequent expansion brings the primary re action gases out of the fuel pores where secondary reaction with additional oxygen can occur. Useful mechanical work can be produced by carrying out this compression-reaction-expansion process within a piston engine or within a gas turbine engine. Maximum useable engine speeds are not limited by burning rates but by pressure drop due to gas flow into and out of the fuel pores. Approximate thermal efficiency relations are presented which show the piston engine process to be less efficient than the turbine engine process due to incomplete expansion in the piston engine. Engines using this cyclic porous burning are somewhat less efficient than engines using constant volume burning at minimum volume, as in Otto engines, or constant pressure burning at maximum pressure as in Brayton engines. This latter efficiency difference is due to the cyclic burning being distributed throughout the compression and expansion rather than occurring all at the end of compression.