Study of Plastic Explosives based on Attractive Cyclic Nitramines,Part II. Detonation Characteristics of Explosives with Polyfluorinated Binders

A series of plastic bonded explosives (PBXs) based on Viton A and Fluorel binders were prepared using four nitramines, namely RDX (1,3,5‐trinitro‐1,3,5‐triazinane), β‐HMX (β‐1,3,5,7‐tetranitro‐1,3,5,7‐tetrazocane), BCHMX (cis‐1,3,4,6‐tetranitro‐octahydroimidazo‐[4,5‐d]imidazole), and ε‐HNIW (ε‐2,4,6,8,10,12‐hexanitro‐2,4,6,8,10,12‐hexaazaisowurtzitane). The detonation velocities, D, were determined. Detonation parameters were also calculated by means of modified Kamlet & Jacobs method, CHEETAH and EXPLO5 codes. In accordance with our expectations BCHMX based PBXs performed better than RDX based ones. The Urizar coefficient for Fuorel binder was also calculated.     

Detonation Velocity of Emulsion Explosives Containing Cenospheres

The detonation velocity of an emulsion explosive containing hollow alumosilicate microspheres (cenospheres) as the sensitizer is measured. The size of the microspheres is 50–250 μm. The relations between the detonation velocity and the charge density and diameter are compared for emulsion explosives containing cenospheres or glass microballoons as the sensitizer. It is shown that for a 55 mm diameter charge, the maximum detonation velocity of the composition with cenospheres of size 70–100 μm is 5.5–5.6 km/sec, as well as for 3M glass microballoons. The critical diameter for the emulsion explosive with cenosphere is 1.5–2 times larger than that for the emulsion explosive with glass microballoons and is 35–40 mm. __________ Translated from Fizika Goreniya i Vzryva, Vol. 41, No. 5, pp. 119–127, September–October, 2005.     

Predicting the Detonation Velocity of CHNO Explosives by a Simple Method

A simplified method is shown, based on a semi‐empirical procedure, to estimate the detonation velocities of CHNO explosives at various loading densities. It is assumed that the product composition consists almost of CO, CO₂, H₂O and N₂ for oxygen‐rich explosives. In addition solid carbon and H₂ are also counted for an oxygen‐lean explosive. The approximate detonation temperature, as a second needed parameter, can be calculated from the total heat capacity of the detonation products and the heat of formation of the explosive by PM3 procedure. The detonation velocities of some well‐known CHNO explosives, calculated by the simple procedure, fit well with measured detonation velocities and the results from the well‐established BKW‐EOS computer code.     

工业炸药的爆轰性能研究

用有机玻璃法测定了岩石膨化、煤矿膨化、铵梯以及乳化炸药的爆速和爆压，同时用VLWR爆轰程序对岩11石膨化硝铵和铵梯炸药的爆轰参数及C—J产物的平衡组成进行了计算。结果表明，工业炸药具有低爆速和低爆压的非理想爆轰特征，而理论计算值和实验值比较接近，获得了较好的结果。     

Effect of Mixing Methods on the Thermal Stability and Detonation Characteristics of Ammonium Nitrate and Sodium Chloride Mixtures

A study has examined the effect of mixing methods on the thermal stability and detonation characteristics of ammonium nitrate (AN) and sodium chloride (NaCl) mixtures. NaCl was mixed with AN by two methods. The thermal stability, detonation velocity and structural properties were investigated by differential scanning calorimetry (DSC), measurement of detonation velocity and X‐ray diffraction (XRD). For the mechanical mixing method, in all tested scope of proportions of NaCl in the mixtures, activation energies increase when the proportion of NaCl increases; for solution mixing method, the activation energies decrease first and then start to increase as the proportion of NaCl increases. The detonation velocity of AN‐NaCl mixtures prepared by two mixing methods also showed different results. The results indicate that the mixing methods significantly affect the thermal stability and detonation characteristics of AN.     

Predicting Detonation Performance of CHNOFCl and Aluminized Explosives

A new “hand‐calculated” method is introduced for prediction of detonation pressure of explosive and mixture of explosives with general formula CHNOFClAl. Suitable decomposition paths are used to estimate heat of detonation and detonation pressure. These decomposition paths are based on the distribution of oxygen atoms between carbon and hydrogen atoms as well as the degree of oxidation of aluminum. For CHNOFCl explosives, it is shown that the predicted detonation pressures with the new method are more reliable with respect to one of the best available empirical methods for loading densities greater than or equal 0.8 g cm⁻³. Since aluminized explosives have non‐ideal behavior, the new method does not require using full or partial oxidation of aluminum, which is usually required by a computer code. The predicted results of the new model also provide more reliable results than outputs of complex computer code with the BKWS equation of state.     

Study of the Effect of Covolumes in BKW Equation of State on Detonation Properties of CHNO Explosives

Due to its simplicity, the Becker‐Kistiakowsky‐Wilson (BKW) equation of state has been used in many thermochemical codes in the calculation of detonation properties. Much work has been done in the calibration of the BKW EOS parameters to achieve agreement with experimental detonation velocities and pressures thus resulting in many different sets of BKW constants (α, β, κ and θ) and covolumes of detonation products, with varying levels of accuracy over broad density limits, i.e. broad pressure limits. The covolumes of the product gases in BKW EOS may be regarded as measures of intermolecular interactions, and their values should affect the predicted detonation properties, particularly at higher explosives densities. This work aims to study the effect of covolumes on calculated values of detonation parameters. Several sets of covolumes available from literature and derived by different methods (matching experimental Hugoniots of individual products, by stochastic optimization, and calculated from van der Waals radii), were studied. In addition, the covolumes of the product gases were also calculated by ab initio methods. The effect of covolumes is studied comparing detonation properties calculated using different sets of covolumes, and experimental data for a series of standard CHNO explosives. It was found that it is possible to reproduce experimental detonation velocities and pressures within reasonable accuracy (root mean square error of less than 5 % for all tested sets) using different set of covolumes, and simultaneously optimizing constants in BKW EOS. However, different values of covolumes strongly affect the composition of detonation products at the Chapman‐Jouguet state. It particularly applies to oxygen‐deficient explosives and at higher densities, where formic acid appears to be an important detonation product.     

Sensitivity and Detonation Characteristics of Selected Nitramines Bonded by Sylgard Binder

Four plastic explosives based on cyclic nitramines and polymeric matrix were prepared and studied. The nitramines were RDX (1,3,5‐trinitro‐1,3,5‐triazinane), HMX (1,3,5,7‐tetranitro‐1,3,5,7‐tetrazocane), BCHMX (cis‐1,3,4,6‐tetranitro‐octahydroimidazo‐[4,5‐d]imidazole), and ϵ‐CL20 (ϵ‐2,4,6,8,10,12‐hexanitro‐2,4,6,8,10,12‐hexaazaisowurtzitane, ϵ‐HNIW). Sylgard 184 was used in the all PBXs prepared samples as a binder. The sensitivities to different mechanical stimuli were determined. The detonation velocities were experimentally measured. Detonation characteristics were calculated by EXPLO5 thermodynamic code. For comparison, standard plastic explosives, Composition C4, Semtex 10, and EPX‐1 were studied. Results showed that the experimental detonation velocities as well as the calculated detonation parameters decrease in the following order: CL20‐sylgard>HMX‐sylgard≥BCHMX‐sylgard>RDX‐sylgard. Calculations by EXPLO5 computer program resulted in detonation velocities close to the experimental ones with 3.1 % maximum difference. Urizar coefficient for the Sylgard binder was calculated from experimental data. An inverse linear relationship between friction sensitivity and heat of detonation of the studied samples was observed. Sylgard binder significantly decreased the sensitivity of all the studied nitramines. Among these prepared samples, the properties of BCHMX‐sylgard are similar to other ordinary plastic explosives.     

Partial Reparametrization of the BKW Equation of State for DNAN‐Based Melt‐Cast Explosives

DNAN‐based melt‐cast explosives are a type of new, insensitive munitions (IM) explosives. Quickly determining munitions’ explosive properties is extremely important during the formulation design stage. The aim of this study was to partially reparameterize BKW‐EOS (only β and κ were reparameterized on the basis of the parameters (α , β , κ , and θ ) of classical BKW‐RDX set and BKW‐TNT set) to more accurately predict the properties of DNAN‐based melt‐cast explosives. A new set of parameters β and κ was obtained (β =0.19, κ =9.81) according to measured detonation velocity and detonation pressure for ideal DNAN‐based melt‐cast formulations (DNAN/RDX and DNAN/HMX). For non‐ideal DNAN‐based melt‐cast formulations (DNAN/RDX/Al and DNAN/HMX/Al), aluminum oxidation degree was first determined according to the measured detonation heat; then, another new set of parameters β and κ was obtained in the same way as the ideal formulations (β =0.24, κ =8.5). The predicted detonation properties with BKW reparametrization for DNAN‐based melt‐cast explosives agreed with the measured data.     

Detonation Performance of TATP/AN‐Based Explosives

The detonation velocity and performance were determined for four mixtures of triacetone triperoxide (3,3,6,6,9,9‐hexamethyl‐1,2,4,5,7,8‐hexoxonane, TATP), ammonium nitrate (AN) and water (W) by cylinder expansion tests. The composition of these mixtures varied in the following ranges: 21–31% TATP, 37–54% AN and 19–32% W. The obtained results were compared with those of powdery 2,4,6‐trinitrotoluene (TNT), AN‐fuel oil explosive (ANFO) and emulsion explosive. It was found that the tested TATP/AN/W mixtures represent typical non‐ideal explosives with relatively low critical diameter and with high sensitivity to initiation despite the high content of water due to the presence of the primary explosive (TATP). The detonation velocity is comparable to that of powdery TNT (at similar density). However, the acceleration ability is significantly lower than that of powdery TNT.     

Influence of Ammonium Nitrate Prills' Properties on Detonation Velocity of ANFO

Prilled/granulated ammonium nitrate is commonly used as a fertilizer and a basic ingredient of industrial explosives, especially of ANFO. One of the most important factors that affect the explosive properties of ANFO is the porosity of the prills/granules. This paper describes an attempt to manufacture ammonium nitrate prills of determined porosity in order to investigate its influence on the ANFO detonation velocity. A method of manufacturing porous ammonium nitrate prills with a high‐level of oil absorption (up to 20% by volume) was developed. The relations between porosity and granulometric distribution of ammonium nitrate prills versus the detonation velocity of ANFO were examined. It has been proved that the detonation velocity of ANFO increases significantly with higher porosity and smaller size of ammonium nitrate prills/granules. The influence of ANFO oxygen balance (researched by changing the content of fuel oil in the mixture) on detonation velocity has been determined for two kinds of ammonium nitrate prills–one with a low and another one with a high level of porosity.     

Model Detonation of Solid Explosives by the Homogeneous Mechanism

A twophase detonation model of solid porous explosives, which takes into account the compression of solidstate particles and the presence of a solid component in detonation products, is developed. The homogeneous detonation mechanism based on the Arrheniustype reaction is studied. Detonation is initiated by the region of highpressure and hightemperature gases modeling the detonator explosion. A numerical experiment confirms that there exists an initiationpressure limit below which no homogeneous mechanism of detonation is active. The detonation wave has the leading front in which the explosive is precompacted and the gas in the porous volume is compressed up to a pressure of 100 GPa without any significant change in particle density. Then the gas compresses the particles themselves up to the pressure and temperature of the thermal explosion. As a result, the leading front is followed (after a certain delay) by a narrow reaction zone where detonation products are formed with a further increase in pressure.     

Empirical Correlation of Minimum Burning Pressures of Ammonium Nitrate Emulsions

Experimental minimum burning pressures (MBP) of emulsions with solution phase containing ammonium nitrate/water, ammonium nitrate/sodium nitrate/water, and ammonium nitrate/sodium nitrate/sodium perchlorate/water are investigated. A correlation is proposed to relate the MBP’s with the combustion temperatures. The formulations containing sodium nitrate or sodium perchlorate have much lower MBP’s and can be accounted for by an activation energy of 150.7 kJ mol⁻¹ obtained from literature for ingredients having catalyzing effects on the reaction of ammonium nitrate, e.g. sodium nitrate. The ammonium nitrate/water formulations have a higher activation energy of 173.4 kJ mol⁻¹ deduced from an analysis of the data. The MBP vs. combustion temperature plot is linearized by a multiplication factor to the MBP that includes the activation energy of the corresponding system. This allows the MBP to be predicted from combustion temperatures determined from the formulations and the corresponding activation energy.     

Predicting Maximum Attainable Detonation Velocity of CHNOF and Aluminized Explosives

This paper describes a simple method to predict the detonation velocity of pure and mixed CHNOF explosives as well as aluminized explosives at their maximum nominal density as one of the most important detonation properties. The new correlation uses the contribution of some structural parameters to apply for a wide range of ideal and non‐ideal explosives. Aluminized explosives have non‐ideal behavior and the Chapman Jouguet detonation velocities significantly differ from those expected from existing thermodynamic computer codes for equilibrium and steady state calculations. With the presented method, there is no need to use any assumed detonation products, heat of formation and experimental data. Detonation velocities at maximum nominal density of explosives predicted by this procedure show good agreement with respect to experimental values. They are more reliable compared to the calculated results of well‐known empirical methods and computed outputs using BKWS equation of state for CHNOF and aluminized explosives.     

Study of Plastic Explosives based on Attractive Cyclic Nitramines Part I. Detonation Characteristics of Explosives with PIB Binder

Four plastic explosives based on energetic nitramines and a non‐energetic binder were prepared and studied. The nitramines were RDX (1,3,5‐trinitro‐1,3,5‐triazine), HMX (1,3,5,7‐tetranitro‐1,3,5,7‐tetrazine), BCHMX (cis‐1,3,4,6‐tetranitro‐octahydroimidazo‐[4,5‐d]imidazole) and HNIW (ε‐2,4,6,8,10,12‐hexanitro‐2,4,6,8,10,12‐hexaazaisowurtzitane, ε‐CL‐20). The binder was in all cases polyisobutylene (PIB) as in the standard composition C‐4. These powerful plastic explosives were compared to standard PETN‐based commercially available explosives Semtex 1A and Sprängdeg m/46. The detonation velocities were experimentally measured and compared to the ones calculated by the Kamlet–Jacobs method, CHEETAH and EXPLO5 Codes. The experimental detonation velocities as well as the calculated detonation parameters decrease in the following order: HNIW‐PIB>HMX‐PIB≥BCHMX‐PIB>RDX‐PIB>Sprändeg m/46≥Semtex 1A. Urizar coefficients for the various binders were calculated from experimental data.     

Small‐Scale Thermal Studies of Volatile Homemade Explosives

Several homemade or improvised explosive mixtures that either contained volatile components or produced volatile products were examined using standard small‐scale safety and thermal (SSST) testing that employed differential scanning calorimetry (DSC) techniques (constant heating rate and standard sample holders). KClO₃ and KClO₄ mixtures with dodecane exhibited different enthalpy behavior when using a vented sample holder in contrast to a sealed sample holder. The standard configuration produced profiles that exhibited only endothermic transitions. The sealed system produced profiles that exhibited additional exothermic transitions absent in the standard configuration produced profiles. When H₂O₂/fuel mixtures were examined, the volatilization of the peroxide (endothermic) dominated the profiles. When a sealed sample holder was used, the energetic releases of the mixture could be clearly observed. For AN and AN mixtures, the high temperature decomposition appears as an intense endothermic event. Using a nominally sealed sample holder also did not adequately contain the system. Only when a high‐pressure rated sample holder was used the high temperature decomposition of the AN could be detected as an exothermic release. The testing was conducted during a proficiency (or round‐robin type) test that included three U.S. Department of Energy and two U.S. Department of Defense laboratories. In the course of this proficiency test, certain HMEs exhibited thermal behavior that was not adequately accounted for by standard techniques. Further examination of this atypical behavior highlighted issues that may have not been recognized previously because some of these materials are not routinely tested. More importantly, if not recognized, the SSST testing results could lead to inaccurate safety assessments. This study provides examples, where standard techniques can be applied, and results can be obtained, but these results may be misleading in establishing thermal properties.     

The Role of Aluminum in the Detonation and Post‐Detonation Expansion of Selected Cast HMX‐Based Explosives

In order to improve understanding of how aluminum contributes in non‐ideal explosive mixtures, cast‐cured formulations have been analyzed in a series of cylinder tests and plate‐pushing experiments. This study describes the contribution of 15 % aluminum (median size of 3.2 μm) vs. lithium fluoride (an inert substitute for aluminum; <5 μm) in cast‐cured HMX formulations in different temporal regimes. Small cylinder tests were performed to analyze the detonation and wall velocities (1–20 μs) for these formulations. Near‐field blast effects of 58 mm diameter spherical charges were measured at 152 mm and 254 mm using steel plate acceleration. Pressure measurements at 1.52 m gave information about free‐field pressure at several milliseconds. While the observed detonation velocities for all formulations were within uncertainty, significantly higher cylinder wall velocities, plate velocities, and pressures were observed for the aluminum formulations at ≥2 μs. Additionally, hydrocode calculations were performed to determine how non‐ideal behavior affected the plate test results. Collectively, this work gives a clearer picture of how aluminum contributes to detonation on timescales from 1 μs to about 2 ms, and how the post‐detonation energy release contributes to wall velocities and blast effects. The experiments indicate that significant aluminum reactions occur after the CJ plane, and continue to contribute to expansion at late times.     

Microwave‐Assisted Quick Synthesis of Some Potential High Explosives

This paper reports a novel microwave‐assisted method for the synthesis of potential high explosives (HEs) such as 3‐nitro‐1,2,4‐triazol‐5‐one (NTO), bis‐(2,2‐dinitropropyl) nitramine (BDNPN), 4‐nitroimidazole (4‐NI) and 2,4,6,8,10,12‐hexanitro‐2,4,6,8,10,12‐hexaazaisowurtzitane (CL‐20). The high temperature thermal rearrangement of 1,4‐dinitroimidazole to 2,4‐dinitroimidazole was also reported using microwave radiation as heating source. The synthesized compounds were characterized by spectroscopic techniques and the data obtained confirmed their structures.     

Calculation of Detonation Properties of Gaseous Explosives Using Generalized Reduced Gradient Nonlinear Optimization

In this paper, a study on the development of a numerical modeling of the detonation of C H N O‐based gaseous explosives is presented. In accordance with the numerical model, a FORTRAN computer code named GasPX has been developed to compute both the detonation point and the detonation properties on the basis of Chapman–Jouguet (C‐J) theory. The determination of the detonation properties in GasPX is performed in chemical equilibrium and steady‐state conditions. GasPX has two improvements over other thermodynamic equilibrium codes, which predict steady‐state detonation properties of gaseous explosives. First, GasPX employs a nonlinear optimization code based on Generalized Reduced Gradient (GRG) algorithm to compute the equilibrium composition of the detonation products. This optimization code provides a higher level of robustness of the solutions and global optimum determination efficiency. Second, GasPX can calculate the solid carbon formation in the products for gaseous explosives with high carbon content. Detonation properties such as detonation pressure, detonation temperature, detonation energy, mole fractions of species at the detonation point, etc. have been calculated by GasPX for many gaseous explosives. The comparison between the results from this study and those of CEA code by NASA and the experimental studies in the literature are in good agreement.     

粉状铵梯油炸药的配方设计

建立了粉状铵梯油炸药配方设计及最优化的数学模型，给出了不同原材料条件下数学模型的计算配方，将计算配方与国内主要粉状铵梯油炸药的配方进行了比较和分析。