Non-ideal Explosives Research Articles

Thermal Hazard Analysis of Two Non-Ideal Explosives Based on Ammonium Perchlorate/Ammonium Nitrate and Aluminium Powder.

In recent years, various kinds of civil explosive detonation accidents have occurred frequently around the world, resulting in substantial human casualties and significant property losses. It is generally believed that thermal stimulation plays a critical role in triggering the detonation of explosives; consequently, the study of the thermal hazards of explosives is of great significance to many aspects of safety emergency management practices in the production, transportation, storage, and use of explosives. It is known that the thermal stability of the ammonium perchlorate-aluminium system and the ammonium nitrate-aluminium system has been extensively investigated previously in the literature. However, there is a paucity of research on the thermal hazard characteristics of non-ideal explosives under varying oxygen balance conditions within the academic sphere. Therefore, this research focused on the study of the thermal hazards of non-ideal explosives based on thermokinetic analysis. The thermal hazards of non-ideal explosive mixtures of ammonium perchlorate and aluminium and of ammonium nitrate and aluminium were studied by thermal analysis kinetics. The thermokinetic parameters were meticulously studied through differential scanning calorimetry (DSC) analysis. The results showed that the peak reaction temperature and activation energy of the ammonium perchlorate-aluminium system were significantly higher than those of the ammonium nitrate-aluminium system. Under the condition of zero oxygen balance, the peak reaction temperature of the ammonium nitrate-aluminium system was 259 °C (heating rate 5 °C/min), and the activation energy was 84.7 kJ/mol. Under the same conditions, the peak reaction temperature and activation energy of the ammonium perchlorate-aluminium system were 292 °C (heating rate 5 °C/min) and 94.9 kJ/mol, respectively. These results indicate that the ammonium perchlorate-aluminium system has higher safety under the same thermal stimulation conditions. Furthermore, research on both non-ideal explosive systems reveals that the activation energy is at its peak under negative oxygen balance conditions, recorded at 104.2 kJ/mol (ammonium perchlorate-aluminium) and 86.2 kJ/mol (ammonium nitrate-aluminium), which indicates a higher degree of safety. Therefore, the investigation into the thermal hazards of non-ideal explosive systems under different oxygen balance conditions is of utmost importance for the enhancement and improvement of safety emergency management practices.

Revisiting the Becker-Kistiakowsky-Wilson equation of state

The Jones-Wilkins-Lee (JWL) equation of state (EOS) is the most popular equation of state used in hydrocodes to model detonation products thermodynamics resulting from high explosives. However, the JWL EOS presents several major difficulties. Namely, its range of validity and convexity is limited as its parameters are adjusted on a given reference curve. When used in conditions where the thermodynamic state varies significantly, computational failure may happen. It occurs frequently in multiphase flow computations when heat and mass transfers with other phases are present, as the resulting thermodynamic state is far from the reference curve used for adjustment. Moreover, the detonation products composition is absent in the JWL formulation. This is another important limitation when additional physics are involved, such as post-combustion, phase transition, or when dealing with non-ideal explosives. In this work, the Becker-Kistiakowsky-Wilson (BKW) EOS is considered instead. The BKW EOS is widely used in thermochemical codes, as parent EOS to provide the reference data used to fit JWL EOS parameters. The BKW EOS present several advantages. Its formulation considers variable gas species in the detonation products. No specific adjustment is needed for a given explosive, and only the detonation products composition requires computational efforts. Its range of validity is large, as the various parameters have been adjusted for each gas species separately. However, the BKW EOS also present difficulties which limit its application in hydrocodes. These difficulties are the aim of the present work. The BKW EOS is currently restricted to thermochemical codes as its mathematical formulation is computationally expensive. It also requires the gas chemical composition to be computed via an appropriate chemical equilibrium solver. In the present work, the computational cost of the BKW EOS is reduced thanks to the thermodynamic relaxation method of Neron et al. (2023). The variable composition of the detonation products is accounted for through specific relaxation terms computed once, with the help of conventional thermochemical codes. The condensed species, such as solid carbon, are modelled with the Cochran-Chan (CC) EOS, having a simpler thermodynamic formulation and being thermodynamically consistent compared to usual EOSs used for condensed species. This multiphase formulation made of BKW gas mixture with variable composition and condensed phases is considered in temperature and pressure equilibrium. It is embedded in a multiphase flow formulation, with the help of the thermodynamic relaxation method mentioned above. It shows comparable computational cost as the JWL formulation, with significantly enhanced physics capabilities and improved robustness.

Numerical Analysis of Blast Behavior for Non-ideal Explosive ANFO in Shock-Tube Test

In an explosion test using a shock tube, the behavior of pressure waves can be reproduced with high reliability. However, the explosion in a shock tube occurs in a confined space. It is difficult to predict the behavior of pressure waves and its effect on various concrete specimens by using the research findings related to free-field explosions. Moreover, few studies have focused on explosive-driven shock tubes. In this study, the behavior of pressure waves in a shock tube was numerically analyzed using a finite-element analysis program. The explosive used to generate the pressure waves was an ammonium nitrate fuel oil (ANFO), which exhibits non-ideal explosion characteristics. The Jones–Wilkins–Lee (JWL) and ignition-and-growth (I&G) equations of state were used for blast-pressure calculation. The analysis results were affected by factors such as the release rate of explosive energy and the development of the pressure waves in the confined explosion. The blast behaviors, such as the low release rate of explosive energy and the resulting increase in the impulse, were analyzed using the ignition-and-growth equation. The impulse produced during the development of waves reflected by the block installed at the tube inlet exceeded that produced by the tube wall. Such behaviors that occurred at the beginning of a blast affected the process of wave propagation along the shock tube and the wave reflection due to the test specimen at the outlet of the shock tube. In this study, the blast behavior in the shock tube, which could be referenced for the analysis of blast overpressure and its effect on concrete specimens, was numerically analyzed. Further research on the structural behaviors of concrete specimens due to blast overpressure is needed.

INFLUENCE OF CONFINING MATERIALS ON DETONATION PARAMETERS OF ANFO EXPLOSIVE

Due to the low manufacturing cost and ease of handling, ammonium nitrate-fuel oil (ANFO) is one of the most popular mining explosives. ANFO explosive is a typical representative of non-ideal explosives, which means that its detonation properties are strongly dependent on the charge diameter and the existence and properties of the confinement. In this work, the effect of different confining materials on the detonation properties of ANFO explosive is studied experimentally, and by hydrocode simulation by varying charge diameter, and the type and thickness of the confining materials. The results show that, along with the diameter of the charge, density and thickness of the confining material have a key impact on the detonation properties. An empirical confinement model, applicable in the range 0.3 < mC/mE < 15, is proposed. The model enables the estimation of detonation velocity of confined ANFO charges with a mean absolute percentage error (MAPE) of 14.25%.

Non-ideal explosive underwater explosion shockwave model

The non-ideal behavior of aluminized explosives significantly affects the characteristics of underwater explosion shockwaves, rendering the classical model for underwater explosion shockwaves difficult to apply. In this paper, we analyze the underwater explosion shockwave characteristics of a new generation of aluminized explosives and propose a non-ideal explosive underwater explosion shockwave model incorporating a non-ideal explosive shockwave parameter correction function controlled by the Al/O ratio. First, we conducted underwater explosion tank experiments to obtain four groups of Al/O ratios of shockwave parameters of underwater explosion with aluminized explosives and analyzed the effect of the Al/O ratio on them. Subsequently, we calculated the equation of state of aluminized explosives and established a one-dimensional simulation model of underwater explosion. We verified the reliability of the mesh quality and equation of state using the experimental data. Finally, we used the model to calculate the underwater explosion shockwave parameters of aluminized explosives with Al/O ratios of 0.1–1.3. Based on data analysis, we established a calculation model of the pressure peak and energy flow density of the underwater explosion shockwave of aluminized explosives containing non-ideality correction functions. Our results demonstrate that shockwave pressure peak and energy increase and then decrease with an increase in the Al/O ratio, and the non-ideal behavior of aluminized explosives makes the shockwave energy of underwater explosion more sensitive to the Al/O ratio. The proposed model can better predict the experimental results and can be of high practical value as a general structure for underwater explosion shockwave models of other aluminized or metalized explosives.

Study on explosion reaction mechanism and energy release characteristics of HMX-based explosives containing B-Al

To explore the application of the micro-sized B-Al (boron-aluminum) compound powder in enhanced blast explosive(EBX) and thermobaric explosive(TBX), three HMX-based explosives containing B-Al (PF-1, PF-2 and PF-3)were designed and prepared. The ignition and combustion characteristics of various samples (micro- and nano-sized B, B-Al compound powders without and with HMX) under different pressures and atmospheres were studied by a laser ignition and combustion experimental system, and the flame evolution images and emission spectral characteristic parameters of the ignition and combustion process were obtained. The structures of detonation reaction zone of ideal and non-ideal explosives were studied by PDV (photonic doppler velocimeter), and the characteristic parameters and explosion reaction mechanism of wave profile were obtained. The energy output characteristics of explosives containing B-Al were evaluated by air blast and underwater explosion test. The results show that nano-sized B has better ignition and combustion characteristics than micro-sized B; the ignition and combustion property of B-Al compound powder with HMX is obviously superior to that of B-Al compound powder. PBX-1 is an ideal explosive, and the reaction zone width is 44ns, whilePF-1 and PF-3 are typical non-ideal explosives, the reaction zone widths are 112ns and 102ns, respectively. In the air blast and underwater explosion test, under the detonation of HMX, the combustion of micro-Al can promote the afterburning effect of micro-B, which releases a great amount of combustion heat, then generates expansible products with higher temperature and pressure, and finally increases the duration of fireball and total energy in underwater explosion.

Shock Initiation and Propagation of Detonation in ANFO

The ammonium nitrate (AN) and fuel oil (FO) mixture known as ANFO is a typical representative of non-ideal explosives. In contrast to ideal explosives, the detonation behavior of ANFO exhibits a strong dependence on charge diameter, existence, and properties of confinement, with a large failure diameter and long distance required to establish steady-state detonation. In this study shock initiation and propagation of detonation in ANFO were studied experimentally by determining the detonation velocity at different distances from the initiation point, as well as by numerical modeling using AUTODYN hydrodynamics code and a Wood–Kirkwood detonation model incorporated into EXPLO5 thermochemical code. The run-to-steady-state detonation velocity distance was determined as a function of charge diameter, booster charge mass, and confinement. It was demonstrated that a Lee–Tarver ignition and growth reactive flow model with properly calibrated rate constants was capable of correctly ascertaining experimentally observed shock initiation behavior and propagation of detonation in ANFO, as well as the effects of charge diameter, booster mass, and confinement.

Effect of Confinement on Detonation Velocity and Plate Dent Test Results for ANFO Explosive

The detonation properties of nonideal explosives are highly dependent on charge diameter and existence and properties of confinement. In this study, the effect of different confinements on the detonation velocity of ANFO explosives was experimentally determined along with the results of the plate dent test. ANFO explosive was selected as one of the most commonly used nonideal explosives. Following the measurement results, we found that the detonation velocity increased with increasing wall thickness, and the velocity increase was different for different confinement materials. A strong correlation existed between the ratio of the mass of confiner and explosive (M/C) and the detonation velocity (R = 0.995), and between (M/C) and the depth of the dent (δ) (R = 0.975). The data presented in this paper represent preliminary findings in developing a confinement model required for reliable numerical modeling of nonideal explosives.

Effect of Al–Mg–Mn Alloy on the Ignition Performance of RDX, HMX and CL-20

Aluminized explosives are known as non-ideal explosives due to their incomplete energy release. In order to improve its energy release, Al–Mg–Mn was used to replace aluminum. In this article, Thermogravimetric (TG) and Differential scanning calorimetry (DSC) techniques were used to study the ignition performance of three explosives (RDX, HMX and CL-20) with different mass fractions (0%, 10 wt.%, 20 wt.%, 30 wt.%) of Al–Mg–Mn alloy powder. The results were compared with those of the formulations with the addition of aluminum. The results suggested that the effect of the addition of Al–Mg–Mn on the extrapolated ignition temperature and exothermic peak temperature of the ignition reaction of aluminized explosives is basically similar to that of Al. However, the addition of Al–Mg–Mn increased the exothermic enthalpy. Explosives with the addition of Al–Mg–Mn alloy powder could release 1.7–17.4% more energy, depending on the mass fraction. On the other hand, unlike aluminum which reacts only during the ignition of CL-20, Al–Mg–Mn was involved in the exothermic reaction of all three explosives. During the exothermic decomposition of explosives, the more active magnesium in Al–Mg–Mn will be oxidized, and magnesium vapor will overflow along the grooves and crevices on the surface of the particles, thus destroying the surface oxidation shell and prompting the active ingredients inside to participate in the reaction.

Modelling non-ideal detonations in commercial explosives

Highly non-ideal explosives usually react expressively below their ideal velocities of detonation. In these cases, dimensional effects and product heterogeneities become important to proper model their respective detonation state. Although Direct Numerical Simulation (DNS) techniques can provide a complete and exact solution for this problem, their actual computation cost are still not practical for industrial applications. In order to minimize these constrains, a simplified two-dimensional steady non-ideal detonation model for cylindrical stick explosives is presented. Based on an ellipsoidal shock shape approach (ESSA), the proposed model combines the quasione-dimensional theory for the axial flow solution with the unconfined sonic post-flow conditions at the edge of the explosive. Once calibrated, the model offers the possibility to predict the non-ideal detonation state for any charge diameter, resulting in a full mapping of the diameter-effect curve of the explosive. In addition, the effect of the inert confiner on the detonation flow is calculated by coupling a mechanistic confinement approach with the ESSA model. Thus, the proposed engineering approach is used to model the main properties of one of the most common ammonium nitrate-based explosive used in mining and quarrying industries, including the complete axial flow solution.

DETERMINATION OF DETONATION FRONT CURVATURE RADIUS OF ANFO EXPLOSIVES AND ITS IMPORTANCE IN NUMERICAL MODELLING OF DETONATION WITH THE WOOD-KIRKWOOD MODEL

Nitratebased commercial explosives, such as ANFO (ammonium nitrate/fuel oil mixture) and emulsion explosives, are characterized by a curved detonation front. The curvature is directly related to the rate of radial expansion of detonation products in the detonation driving zone and the rate of chemical reactions, and it is one of the characteristics of nonideal explosives. The detonation theories used to model the nonideal behaviour of explosives require both reaction rate and rate of radial expansion to be known/specified as input data. Unfortunately, neither can be measured and what is mostly used is a link between these rates and parameters which can be more easily measured. In this paper, the Wood-Kirkwood approach of determination of radial expansion through the radius of detonation front curvature and the electro-optical technique for experimental determination of detonation front curvature of ANFO explosives is applied. It was shown that an experimentally determined radius of detonation front curvature vs charge diameter, incorporated in the Wood-Kirkwood detonation theory, can satisfactorily reproduce experimental detonation velocity-charge diameter data for ANFO explosives, especially when the pressure-based reaction rate law is also calibrated (D=1.3 and k=0.06 1/(μs/GPaD)).

The Influence of Microstructured Charcoal Additive on ANFO’s Properties

The verification of the blasting parameters of Ammonium Nitrate Fuel Oil (ANFO) with the addition of microstructured charcoal (MC) produced by destructive wood distillation was performed. Additional investigation of specific surface and pore distribution by the nitrogen adsorption of the two granulations of MC was also carried out. High-resolution scanning electron microscopy was used for morphology evaluation and revealed smoothening of the initially developed external surface of carbon with intensive milling. In addition, the analysis of the thermal properties of the studied samples (TG/DSC) indicated that the size of the microstructured charcoal additives influenced the decomposition temperature of the prepared materials. The explosives containing microstructured charcoal grains of −90 μm underwent decomposition at lower temperatures in comparison with those containing higher sizes of microstructure charcoal grains (−1.18 mm), for which the decomposition temperature reached 292 °C. The obtained results of blasting parameters compared to the results derived from thermodynamic simulation showed the non-ideal character of the explosives (much lower values of blasting parameters than in established thermodynamic models). It was indicated that higher velocities of detonations (VOD) were obtained for non-ideal explosives where finer MC grains were added. Blasting tests confirmed that the studied type of MC can be applied as an additive to the ANFO.

Application of Silicon Dioxide as the Inert Component or Oxide Component Enhancer in ANFO

Non-ideal explosives with differing contents of silicon dioxide (silica or dioxosilane) added in the form of powder and gel were tested. Measurements of structure, crystallinity and morphology were performed by means of infrared spectroscopy (IR), X-ray diffraction (XRD) and scanning electron microscopy (SEM). IR and XRD analysis revealed a lack of SiO2 influence on the non-ideal explosive structure. SEM analysis indicated that all the surface deformations of ammonium nitrate(V) prill were filled by a thin fuel film layer on which SiO2 was present. The additional calculations of selected theoretical properties of non-ideal compositions were made using ZMWCyw software. Based on this, it was established that the optimum semimetal content was 1.0 wt.%. Blasting tests confirmed that the addition of 1.0 wt.% SiO2 to the Ammonium Nitrate Fuel Oil (ANFO) resulted in the lowest volume of post-blast fumes. Moreover, it was established that finer SiO2 powder cannot be used as the oxide component enhancer due to the inhibition of detonation reaction. SiO2 should be used only as an inert component.

The characteristics of shock wave ignition about nonideal explosives

The ignition and detonation process of non-ideal explosives is orders of magnitude different from that of ideal explosives on the time scale, which makes non-ideal explosives have a longer growth distance when subjected to shock stimulation, and the ignition growth process of non-ideal explosives is strongly dependent on external conditions, and the process involves complex physical and chemical changes of explosive materials, and today's technology cannot accurately characterize it. In order to study the ignition growth characteristics of non-ideal explosives below the critical initiation pressure, by measuring the pressure change process in the explosive inside the sample tube during the deformation stage of the shock wave sensitivity, it is found that the internal pressure of the explosive first increases and then decays. Therefore, it is judged that when the critical initiation pressure of the explosive is lower than the critical ignition pressure, the non-ideal explosive still has the next critical ignition pressure. This lower pressure can cause the ignition reaction in the non-ideal explosive to occur locally and form a pressure increase phenomenon in the explosive.

Numerical modelling of non-ideal detonation in ANFO explosives applying Wood-Kirkwood theory coupled with EXPLO5 thermochemical code

Ammonium nitrate and fuel oil (ANFO) based explosive is a classic example of non-ideal high explosives. Its detonation is characterized by a strong dependence of detonation parameters on explosive charge diameter, presence and characteristics of confinement, as well as incomplete consumption of explosive at the sonic point.In this work we propose a detonation model based on the Wood-Kirkwood (WK) theory coupled with the thermochemical code EXPLO5 and supplemented with reaction rate models. Our objective is to analyze the validity of the model for highly non-ideal ANFO explosives, with emphasis on effect of reaction rate models.It was found that both single-step and two-step pressure-based models can be calibrated to reproduce experimental detonation velocity-charge radius data of ANFO at radii significantly above the failure radius (i.e. for D/Did > ∼0.6). Single-step pressure-based model, with the pressure exponent equal to 1.4, proved to be the most accurate, even in the vicinity of the failure radius. The impact of the rate models is most evident on temporal (and spatial) distribution of flow parameters in detonation driving zone, especially when it comes to the conversion and width of detonation driving zone.

Investigation of the effect of ammonium nitrate fragmentation on the development of ammonal detonation

Despite many years devoted to the study of the mixture of ammonium nitrate and aluminium, the composition is still very popular among others because of manufacture simplicity. Ammonals belong to nonideal explosives whose experimental results deviate from the theoretical ones. This thesis discusses the impact of fragmentation of the main component – ammonium nitrate – on the investigated detonation parameter. With a constant amount of aluminium dust, a series of detonation velocity measurements were carried out. The thesis was based on a continuous method using short-circuit sensors placed in the middle of the load. The methodology for determining the detonation velocity from the obtained voltage-time relationships was developed. Discussions of the obtained measurement results were carried out. Conclusions resulting from research on the development of the detonation process were formulated.

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

ABSTRACTThe 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.

An inverse method for the equation of state of detonation products from underwater explosion tests

Since the information of detonation product is transmitted outward in the form of compression wave during underwater explosion, the purpose of this paper is to explore how to determine the equation of state (EOS) of detonation products using underwater explosion tests. Compared with conventional cylinder test, underwater explosion test has the advantages of simpler equipment, lower cost, less limited charge size, and wider range of calibration pressures, which makes it more suitable for the on-site testing of large or non-ideal explosives. Based on the measurable shock wave trajectory and post-shock pressure history in general underwater explosion test, an inverse method of characteristics (inverse MOC) is proposed to recover the gas-water interface from the shock and post-shock data, and a genetic algorithm is developed to determine the EOS of detonation products by the gas-water interface. Compared with virtual experimental data extracted from underwater explosion simulations, it is found that the inverse MOC can properly reproduce the position and pressure of gas-water interface. The lower limit of pressure range is close to 2 MPa, which is far lower than that of 0.1 GPa in cylinder test. Based on the inversed results of gas-water interface, it is also confirmed that the genetic algorithm can also stably optimize the parameters of JWL equation because the isentrope pressure error of eight commonly used explosives is less than 3% in the range of detonation pressure 0.01 GPa. The results show that it is by the inverse MOC and genetic algorithm that the EOS of detonation products can be properly and stably determined by the underwater explosion test data.

The dependence of Ammonal detonation performance on cylinder test scale

For a detonation to propagate steadily, the lead shock must be supported by energy release from the chemical reaction zone. Flow divergence cools the flow behind the compression shock, slowing chemical reactions and reducing the available energy to drive the detonation forward. This results in the diameter effect and eventually detonation failure as charge size is reduced. Similarly, the energy available to perform work on adjacent materials in the product flow tends to decrease with charge size. The performance of non-ideal explosives such as ammonium nitrate blended with aluminum powder (Ammonal) are particularly sensitive to flow divergence. In this study, the effect of flow divergence on Ammonal performance is investigated through application of an analytic method to analyze cylinder expansion (CYLEX) test wall velocity profiles for tests with inner diameters of 12.7 mm up to 76.2 mm. For these tests, the detonation velocity, detonation product isentropes, and heat of detonation are reported. In addition, analysis of the velocity profiles is shown to reveal an experimental measurement of the Rayleigh line, which agrees well with the theoretical Rayleigh line for all experiments. Reaction zone times are inferred using this feature.

Enhancement of Underwater Blast Wave Directed from of a Metallized Explosive to a Bubble Channel in Continuous Water

The results of the experimental studies of underwater explosions of ideal and nonideal detonating charges in continuous water and water-containing air bubbles are presented. Charges weighing up to 50 g are exploded in a metal reservoir filled with water. The parameters of the compression waves in the water are recorded. The effect of the directional propagation of the shock wave in the water along the channel filled with air bubbles is shown. The mechanism of nonideal explosions of highly metallized compositions in water, including explosions in a bubble medium, is also discussed.