Energetic Formulation Research Articles

Investigation of the Synthesis and Energetic Properties of an ANTA-Based Energetic Plasticizer.

Energetic plasticizers are being sought for their use in energetic formulations when combined with explosives. An energetic plasticizer based on the insensitive highly explosive 3-amino-5-nitro-l,2,4-triazole (ANTA) was synthesized and characterized by spectroscopy, X-ray crystallography, thermal analyses, and safety testing. Lastly, density functional theory calculations were employed to examine the observed selectivity among the three nucleophilic ring nitrogen atoms of ANTA toward electrophiles such as ANTA acrylate; this selectivity was found to be a combination of steric, electronic, and hydrogen bonding effects.

Nanoenergetic Materials: From Materials to Applications.

Both nanoscience and nanotechnology have undoubtedly contributed significantly to the development of thermite-based nanoenergetic materials (NEMs) with tunable and tailorable combustion performance and their subsequent integration into devices. Specifically, this review article reflects the immense paybacks in designing and fabricating ordered/disordered assembly of energetic materials over multiple length scales (from nano- to milli-scales) in terms of realization of desired reaction rates and sensitivity. Besides presenting a critical review of present advancements made in the synthesis of NEMs, this article touches upon aspects related to various applications concomitantly. The article concludes with the author's summary of the insurmountable challenges and the road ahead toward the deployment of nanoenergetic materials in practical applications. The real challenge lies in the ability to preserve the self-assembly of fuel and oxidizer nanoparticles achieved at the nanoscale while synthesizing macroscale energetic formulations using advanced fabrication techniques both in bulk and thin film forms. Most importantly, these self-assembled NEMs have to exhibit excellent combustion performance at reduced sensitivity to external stimuli such as electrostatic discharge (ESD), friction and impact.

NiCoCr2O4 as a potential catalyst for the thermal decomposition of ammonium nitrate: a kinetic investigation

The thermal decomposition of high energetic materials plays an important role in their thermal performance. Use of the catalyst is one of the efficient ways improve the thermal performance of the high energetic materials. Therefore, in this work nickel cobalt chromite (NiCoCr2O4) prepared using precipitation approach was utilized as a catalyst for decreasing the thermal decomposition temperature and activation energy of high energetic material ammonium nitrate (AN). The results suggest that AN/NiCoCr2O4 decomposes at lower temperature (240 °C) within a short temperature range (Thermo gravimetry decomposition curve = 180–250 °C). The kinetic study was investigated using Kissinger-Akahira-Sunose (KAS) and Kissinger method (5, 10, and 15 °C min−1 heating rates). The activation energy of AN was reduced from 158.0 to 141.5 kJ mol−1 and decrease in the pre-exponential factor was observed upon addition of NiCoCr2O4. The outcome of the present work can be used to design AN based high energetic formulations containing NiCoCr2O4 catalyst with better thermal decomposition performance.

Preparation, characterization, and investigation of thermal behavior of improved HMX and RDX through coating by TNT

ABSTRACT Simultaneous achievement of both low sensitivity and high energy is crucial in practical applications of high energetic materials such as HMX and RDX. In this work, TNT, a low-sensitive explosive, was used to improve sensitivity and thermal stability of HMX and RDX explosives. The method is based on coating HMX and RDX with TNT using solvent-anti-solvent technique. The characterization of samples was done by scanning electron microscopy (SEM), transmission electron microscope (TEM), and X-ray diffraction (XRD). The SEM and TEM images revealed that a layer of TNT was coated on the HMX and RDX surfaces. TG/DSC thermograms for HMX/TNT and RDX/TNT show that decomposition enthalpy change (ΔH) increased to 121.1 and 197.6 J/g compared to pure HMX and RDX, respectively. Fluidity test results showed that the fluidity of the samples improved from medium to good grade after coating. The impact sensitivity for HMX/TNT and RDX/TNT improved to 7.35 and 19.62 J, respectively. Also, friction sensitivity for coated HMX and RDX increased to 210.2 and 196.1 N. The electrostatic discharge experiments showed that HMX/TNT and RDX/TNT were safer than pure HMX and RDX. Therefore, the coated samples will be good candidates for energetic formulations.

Modified Arrhenius kinetics for double base propellant decomposition: Effect of water

Numerous studies have been conducted on the decomposition mechanisms of cellulose nitrate (NC), a polymer employed in double base (DB) rocket propellants. It is well known that storage temperature affects the lifetime of these energetic formulations. However, less studies have been published on the influence of water. This research examined the role of water on the stabiliser consumption rate during accelerated ageing of a DB rocket propellant, as well as the impact on the shelf life prediction of the energetic formulation. Different volumes of water (0.8, 1.6, 2 and 4 µl/g) were added to the propellant in sealed vials, which were then isothermally aged (70, 80, 90, 100 °C). Analyses of the stabiliser consumption showed a faster decomposition kinetics in presence of water which is indirectly linked to the shortening of the storage life of the NC based propellant by 35 %. For the conditions, an activation energy of 133 ± 4 kJ/mol was reported for the water catalytic decomposition mechanism. A numerical model that included water as a variable was reported to reduce the uncertainty in the determination of the service life of NC based propellant. International standards such as Allied Ordnance Publication 48 should not overlook the effect of water/moisture on the safety of ammunition containing NC and should implement a modified Arrhenius equation.

Phase-field model for 2D cohesive-frictional shear fracture: An energetic formulation

This paper presents a phase-field model for cohesive-frictional shear fracture. The model is derived based on two energetic principles: the energy conservation law and a variational inequality of virtual work that serves as a stability condition. We show that all the governing equations for frictional fracture can be obtained from the above two principles, including the equilibrium condition, the phase-field evolution law and, most importantly, the yield function and flow rule for the plasticity-like frictional slip. The information of crack direction is naturally included in the flow rule. Theoretical and numerical results show that the proposed model is faithfully consistent with the Mohr–Coulomb theory of frictional failure in terms of the crack nucleation stress and direction. In addition, the presented phase-field model has an explicit frictional cohesive law.

Characterization and calibration of a piezo-energetic composite film as a reactive gauge

The field of multifunctional energetics encompasses a range of materials including propellants, explosives, and pyrotechnics that possess the ability to be manipulated through various characteristics that can be switched between go and no-go, or those that have controllable energy release levels or have additional functions beyond energetic output. The development of multifunctional energetics harnessing electromechanical or piezoelectric properties of polymeric materials or binder systems has garnered increasing interest in recent years. Among polymers, fluoropolymers such as poly(vinylidene fluoride) (PVDF) and copolymers such as poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)], which are used as the binder and oxidizer in the energetic formulations, have demonstrated the highest piezoelectric coefficients. In this study, we fabricated piezo-energetic composite films using aluminum nanopowders (10 wt. % active content) as fuel and P(VDF-TrFE) (70/30) as an oxidizer and investigated the piezoelectric response using a small-scale drop weight setup. Additionally, we employed a shaker setup to investigate the response of the films to vibrations. Our findings demonstrate that these piezo-energetic films can replicate the behavior of a commercial PVDF gauge at relatively low-pressure impacts, indicating their potential use as shock or pressure sensors in various fields, as well as an accelerometer gauge. Additionally, aging studies of up to one year indicated minimal loss in the energetic content of the created films, enabling the use of energetic gauges for an extended period. Our findings support the effectiveness of piezo-energetic composite films as pressure sensors or accelerometers and highlight their potential for energetic applications.

Highly energetic formulations of boron and polytetrafluoroethylene for improved ignition and oxidative heat release

Boron (B) is desirable for energetic applications due to high gravimetric and volumetric energy densities. However, their use is limited because the native oxide shells on their surfaces limit oxidation and heat release by acting as a diffusion barrier and dead weight that does not contribute to heat release during oxidation. This paper reports a facile and efficient method of blending B with perfluoro additives to obtain materials with augmented heat release. We use polytetrafluoroethylene (PTFE) as a fluorine source that reacts with the oxide layer exothermally and use thermochemical analysis to identify the optimum composition of PTFE to extract high energy from B as a result of synergistic oxidation and fluorination reactions. The reduction in ignition temperatures of B is also observed due to its blending with PTFE. In this work, we determined B/PTFE blends with lower ignition temperature and higher oxidative heat release. These effects are due to the gasification of native surface oxide by fluorine via exothermic reactions that facilitate the enhanced reactions in the exposed metal core by eliminating the kinetic/thermodynamic barrier in the diffusion of the oxidizer to the B particle core. The study demonstrates the optimized formulation of highly energetic blends of B/PTFE for energetic applications.

Oxidation behavior and combustion characteristics of micro- and nano-sized titanium boride for energetic applications

This study explored the characteristics of TiB2 powders as an additive fuel of energetic materials. Results revealed that the whole oxidation of TiB2 was divided into two stages before and after the melting of B2O3. The effect of Ti on the onset oxidation temperature and low-temperature oxidation efficiency of TiB2 highlighted energy output features. The mass gain of the first stage, the combustion heat, the peak pressure, and the maximum pressurization rates of nano-sized TiB2 were larger than those of micro-sized TiB2. These properties of TiB2 provide evidence for the synergistic effect between Ti and B, which could promote its application in energetic formulations.

Synthesis, Characterization, and Energetic Properties of Nitrate Ester Acrylate Polymer.

An energetic nitrate ester acrylate monomer (4) was synthesized in a total yield of 68% and polymerized to form the energetic nitrate ester acrylate polymer (NEAP). Compound 4 is a liquid at room temperature with a melting point of -8.6 °C and NEAP is a solid with a glass-transition temperature of -8.8 °C. Intermediates leading to 4 and NEAP were characterized by high-resolution mass spectrometry, elemental analysis, Fourier transform infrared spectroscopy, and proton and carbon nuclear magnetic resonance spectroscopies (1H and 13C{1H} NMR). Both 4 and NEAP have electrostatic discharge, friction, and impact sensitivities comparable to those of trinitrotoluene, making NEAP a potential candidate for advanced energetic formulations.

Doping HTPB binder with cellulose nitrate: A promising strategy for advanced energetic material applications

This study explored the characteristics of hydroxyl-terminated polybutadiene (HTPB) supplemented with cellulose nitrate (NC), as a high-energy density binder. The effect of NC doping and its content on the chemical structure, morphology, energetic, and thermokinetic behavior of HTPB–NC binder highlighted attractive features such as good compatibility, improved density, homogeneity, and fiber dispersion. Additionally, HTPB–NC exhibited excellent thermal stability with significant energy release and notable chemical reactivity. These interesting properties of the HTPB–NC binder, provide evidence for the excellent synergistic effect between HTPB and NC, which could promote its application in the next generation of energetic propellant formulations.

Influence of humidity on the decomposition process of double base rocket propellant

The decomposition mechanisms of the polymer cellulose nitrate (NC) which is used in double base (DB) rocket propellants, have been extensively studied, and the influence of storage temperature on the lifetime of these energetic formulations is well known. However, the impact of humidity and water on the polymer decomposition process is poorly understood. This paper studies the influence of humidity on the decomposition chemistry of NC and its impact on shelf life. Stabiliser consumption was first analysed by ageing the propellant in sealed vials at different humidity levels for 7 days at an isothermal temperature of 90 °C. Samples were also analysed using heat flow calorimetry (HFC) at isothermal temperatures of 80 °C, 90 °C, and 100 °C. The results indicates that stabiliser depletion increases with increasing water content. Life assessment calculations (AOP 48 ed2) show that increasing the absolute humidity from 6 to 22 g m-3 will decrease the propellant life from 11 to 6 years (25 °C equivalents). The HFC results follow the same trend as the stabiliser depletion where greater absolute humidity increases the heat flow by up to 400 %. Unlike the pass/fail criteria for stabiliser depletion, the HFC samples passed the 10-year (25 °C equivalent) life criteria (STANAG 4582). A multi-temperature (80, 90, 100 °C) kinetic analysis of the initial heat flow showed that the heat flow rate increased with increasing humidity, but the activation energy for all humidity levels remained at 131 (± 3) kJ mol−1.

Evaluation of a sequential anaerobic-aerobic membrane bioreactor system for treatment of traditional and insensitive munitions constituents

New energetic formulations containing insensitive high explosives (IHE), such as 2,4-dinitroanisole (DNAN), 3-nitro-1,2,4-triazole-5-one (NTO), and nitroguanidine (NQ) are being developed to provide safer munitions. The addition of IHE to munitions formulations results in complex wastewaters from explosives manufacturing, load and pour operations and demilitarization activities. New technologies are required to treat those wastewaters. The core objective of this research effort was to develop and optimize a dual anaerobic-aerobic membrane bioreactor (MBR) system for treatment of wastewater containing variable mixtures of traditional energetics, IHE, and anions. The combined system proved highly effective for treatment of traditional explosives (TNT, RDX, HMX), IHE (DNAN, NTO, NQ) and anions commonly used as military oxidants (ClO4−, NO3−). The anaerobic MBR, which was operated for more than 500 d, was observed to completely degrade mg L−1 concentrations of TNT, DNAN, ClO4− and NO3− under all operational conditions, including at the lowest hydraulic residence time (HRT) tested (2.2 d). The combined system generally resulted in complete treatment of mg L−1 concentrations of RDX and HMX to <20 μg L−1, with most of the degradation occurring in the anaerobic MBR and polishing in the aerobic system. No common daughter products of DNAN, TNT, RDX, or HMX were detected in the effluent. NTO was completely transformed in the anaerobic MBR, but residual 3-amino-1,2,4-triazole-5-one (ATO) was detected in system effluent. The ATO rapidly decomposed when bleach solution was added to the final effluent. NQ was initially recalcitrant in the system, but microbial populations eventually developed that could degrade >90% of the ∼10 mg L−1 NQ entering the anaerobic MBR, with the remainder degraded to <50 μg L−1 in the aerobic system. The dual MBR system proved to be capable of complete degradation of a wide mixture of munitions constituents and was resilient to changing influent composition.

Development and Characterization of New Energetic Composites Based on HNTO/AN Co-Crystal and Nitro-Cellulosic Materials.

To develop advanced cellulose-based energetic composites, new types of high-energy-density formulations containing hydrazine 3-nitro-1,2,4-triazol-5-one (HNTO)/ammonium nitrate (AN) cocrystals combined with nitrocellulose or nanostructured cellulose nitrate (NC and NMCC) were experimentally characterized. The prepared energetic formulations were analyzed in terms of their physicochemical properties, mechanical sensitivities, structural features, and thermal behavior. Their heats of combustion and theoretical energetic performance were assessed as well. Experimental results exhibited the inherent characteristics of the designed NC@HNTO/AN and NMCC@HNTO/AN, including improved density, specific impulse, and impact sensitivity compared to their raw compounds. Besides that, thermo-kinetic findings revealed that the as-prepared insensitive and high-energy-density composites undergo two exothermic decomposition processes, and that NC@HNTO/AN has higher thermal activity. The present study demonstrated the outstanding characteristics of the new composites and could serve as a reference for developing more advanced cellulose-based energetic formulations.

Self‐Healing Polyurethane Binder with Catalytic Thermal Decomposition Property Based on Metal‐Ligand Interaction

AbstractHydroxyl Terminated Poly Butadiene (HTPB) based polyurethanes are widely used as polymeric binders in energetic formulations &amp; other applications. Hence, customization in structure of HTPB has been investigated to improve their mechanical and thermal properties. Herein, modification of HTPB polyurethane has been reported in this paper by incorporating 2‐hydroxy‐3, 5‐dinitropyridine (DNP) covalently into the HTPB polyurethane matrix in order to exhibit self‐healing properties. The functionalized polyurethane concurrently displays self‐healing capability via metal‐ligand interaction and also catalytic activity towards thermal decomposition of Ammonium Perchlorate (AP). The self‐healing ability was observed by Optical Microscope and up to 96 % healing efficiency was observed by UTM analysis. Further, the catalytic activity was observed with thermal decomposition of Ammonium Perchlorate performed by DSC shows lowering in decomposition temperature by 73 °C. By involving the self‐healing and catalytic activity through single moiety in the polymer chain, this two‐in‐one strategy allows to produce advance binders for energetic formulations.

Al/SnO2 Nanothermite ESD Desensitization by Means of the Elaboration of Tailored SnO2-Polypyrrole Composites.

Incidents can occur when handling energetic materials (EMs) due to their sensitivity to external stimuli. Mechanical (friction, impact) and electrical (electrostatic discharge (ESD)) stimuli can trigger involuntary ignition of EMs. Nanothermites, defined as highly reactive mixtures of a metal and a metal oxide, show interesting reactive properties (high temperature/amount of heat). However, their extreme sensitivity to ESD is a significant drawback in their development. With a sensitivity threshold of lower than a millijoule and considering the human body capacity discharge is a few tens of millijoules, the handling of such energetic mixtures is extremely hazardous. ESD desensitization is therefore of crucial importance for the use of these materials. To achieve this goal, polypyrrole (PPy) conductive polymer was used as an additive within an Al/SnO2 energetic formulation. This polymer is able to easily conduct the electrostatic charges, which is useful to avoid an ignition after a spark stimulus. PPy was added to the nanothermite through the elaboration of SnO2-PPy composites. Delaying the SnO2 introduction time during pyrrole's polymerization (t = 0, 1, 24 h) changed the microstructures of the composites. The various SnO2-PPy composites highlighted that the additive's distribution within the composite is a key component for the modulation of ESD sensitivity. For example, this threshold is higher for a nanothermite formulated with the composite elaborated at t = 0 h (96.5 mJ with 7.5 vol % of polymer) than a composition based on the composite at t = 24 h (16.9 mJ with 8.2 vol % of polymer). Meanwhile, the reactive properties are decreased. The loss of reactivity (e.g. combustion speed) was explained by the thermal insulating property of the additive. Overall, the aim of this study is to help in the understanding of ESD desensitization of nanothermites in order to make them safer for operators and adapted to the required applications.

Effect of Aromatic Chain Extenders on Polyurea and Polyurethane Coatings Designed for Defense Applications.

The present work describes the synthesis of new versatile polyurea (PU) and polyurethane (PUR) matrices, including different chain extenders, which facilitate the design of distinct, tunable properties, and high-performance derivatives. These polymers can be used for various defense and security applications, such as coatings for ballistic protection, CBRN protection, binders for energetic formulations, etc. Combining aliphatic and aromatic molecules in PU or PUR structures enables the synthesis of polymers with improved and controllable thermo-mechanical properties. Thus, for polyurea synthesis, we utilized two types of polymeric aliphatic diamines and three types of aromatic chain extenders (1,1'-biphenyl-4,4'-diamine, benzene-1,2-diamine, and 1,2-diphenylhydrazine). An analogous method was used to synthesize polyurethane films by employing one polymeric aliphatic polyol and three types of aromatic chain extenders (benzene-1,3-diol, benzene-1,4-diol, and benzene-1,2,3-triol). Subsequently, various analytic techniques (Fourier transform infrared spectroscopy-attenuated total reflectance (FTIR-ATR), single cantilever dynamic mechanical analysis (DMA), thermogravimetric analysis (TGA), frequency-dependent shear modulus survey, tensile tests, water contact angle measurements, and scanning electron microscopy (SEM) with energy-dispersive X-ray analysis (EDX)) have been utilized to characterize the synthesized materials and to evaluate the influence of each chain extender on their final properties.

The Influence of Potassium Salts Phase Stabilizers and Binder Matrix on the Properties of Novel Composite Rocket Propellants Based on Ammonium Nitrate.

The environmental impact and availability of ingredients are vital for the new generation of rocket propellants. In this context, several novel composite propellants were prepared based on the "greener" oxidizer phase-stabilized ammonium nitrate (PSAN), a micronized aluminum-magnesium alloy fuel, iron oxide powder burn rate modifier, triethylene glycol dinitrate (TEGDN) energetic plasticizer and a polyurethane (PU) binder. The novelty of this study is brought by the innovative procedure of synthesizing and combining the constituents of these heterogeneous compositions to obtain high-performance "eco-friendly" rocket propellants. The polymorphism shortcomings brought by ammonium nitrate in these energetic formulations have been solved by its co-crystallization with potassium salts (potassium nitrate, potassium chromate, potassium dichromate, potassium sulphate, potassium chlorate and potassium perchlorate). Polyester-polyol blends, resulting from recycled post-consumer polyethylene terephthalate (PET) glycolysis, were utilized for the synthesis of the polyurethane binder, especially designed for this type of application. To adjust the energetic output and tailor the mechanical properties of the propellant, the energetic plasticizer TEGDN was also involved. The performance and safety characteristics of the novel composites were evaluated through various analytical techniques (TGA, DTA, XRD) and specific tests (rate of combustion, heat of combustion, specific volume, chemical stability, sensitivity to thermal, impact and friction stimuli), according to NATO standards, providing promising preliminary results for further ballistics investigations.

Unraveling the Effect of MgAl/CuO Nanothermite on the Characteristics and Thermo-Catalytic Decomposition of Nanoenergetic Formulation Based on Nanostructured Nitrocellulose and Hydrazinium Nitro-Triazolone

The present study aims to develop new energetic composites containing nanostructured nitrocellulose (NNC) or nitrated cellulose (NC), hydrazinium nitro triazolone (HNTO), and MgAl-CuO nanothermite. The prepared energetic formulations (NC/HNTO/MgAl-CuO and NNC/HNTO/MgAl-CuO) were analyzed using various analytical techniques, such as Fourier-transform infrared (FTIR), scanning electron microscopy (SEM), thermogravimetry (TGA), and differential scanning calorimetry (DSC). The outstanding catalytic impact of MgAl-CuO on the thermal behavior of the developed energetic composites was elucidated by kinetic modeling, applied to the DSC data using isoconversional kinetic methods, for which a considerable drop in the activation energy was acquired for the prepared formulations, highlighting the catalytic influence of the introduced MgAl-CuO nanothermite. Overall, the obtained findings demonstrated that the newly elaborated NC/HNTO/MgAl-CuO and NNC/HNTO/MgAl-CuO composites could serve as promising candidates for application in the next generation of composite explosives and high-performance propellants.

TOWARDS COERCIVE BOUNDARY ELEMENT METHODS FOR THE WAVE EQUATION

In this note, we discuss the ellipticity of the single layer boundary integral operator for the wave equation in one space dimension. This result not only generalizes the well-known ellipticity of the energetic boundary integral formulation in $L^2$, but it also turns out to be a particular case of a recent result on the inf-sup stability of boundary integral operators for the wave equation. Instead of the time derivative in the energetic formulation, we use a modified Hilbert transformation, which allows us to stay in Sobolev spaces of the same order. This results in the applicability of standard boundary element error estimates, which are confirmed by numerical results.