Energetic Composites Research Articles

Synthesis and structure of 6-azido-2,4-bis(2,2,2-trinitroethylamino)-1,3,5-triazine and its N-nitro derivatives

Methods were developed for the synthesis of 6-azido-2,4-bis(2,2,2-trinitroethylamino)- 1,3,5-triazine and its N-nitro derivatives (6-azido-2,4-bis(2,2,2-trinitroethyl)nitramino-1,3,5-triazine and 6-azido-2-(2,2,2-trinitroethylamino)-4-(2,2,2-trinitroethyl)nitramino-1,3,5-triazine) containing combinations of azido, trinitroethyl, and nitramine groups. These compounds are of interest as components of energetic composites. The molecular and crystal structures of 6-azido-2,4-bis(2,2,2-trinitroethylamino)-1,3,5-triazine and 6-azido-2,4-bis(2,2,2-trinitroethyl) nitramino-1,3,5-triazine were studied by X-ray diffraction and NMR spectroscopy.

Effect of aluminum micro- and nanoparticles on ignition and combustion properties of energetic composites for interfacial bonding of metallic substrates

In this study, the effect of micro- and nanoscale energetic materials in the formulation of aluminum microparticles (Al MPs)/aluminum nanoparticles (Al NPs)/iron oxide nanoparticles (Fe2O3 NPs) as a heat energy source for melting solder microparticles (SAC 305 MPs) on the interfacial bonding properties of Cu metallic substrates, is investigated. The optimized mixing ratio is Al MP:Al NP:Fe2O3 NP = 30:30:40 wt%, which generates a maximum total exothermic energy of ∼2.0 kJ g−1. The presence of Al NPs is essential to make stable ignition and initiation of Al MPs, which enable to attain relatively long combustion duration. The use of highly reactive Al NPs/Fe2O3 NPs can improve the aluminothermic reaction, while the addition of Al MPs to the Al NPs/ Fe2O3 NPs is also required to maintain their high thermal energy for a longer duration. An energetic material (EM) layer composed of Al MP/Al NP/Fe2O3 NP composites is employed as a heat source between solder material (SM) layers composed of SAC305 MPs. The SM/EM/SM multilayer pellets are assembled and ignited between interfacial Cu substrates for bonding. Thus, interfacial bonding between the Cu substrates is successfully achieved, and the resulting maximum mechanical strength for the bonded Cu substrates using the SM/EM/SM multilayer pellets increases by ∼40% compared to that when using a pure SM layer pellet. Hence, EM layers can act as both an effective heat energy generation source and a mechanical reinforcing medium, while the interfacial bonding process using SM/EM/SM multilayer pellets demonstrated herein provides an easy and versatile means of welding and jointing for industrial applications.

Nitrated Cross‐linked β‐Cyclodextrin Binders Exhibiting Low Glass Transition Temperatures

AbstractPolymeric binders such as β‐cyclodextrins (βCDs) are used to bind with other constituents of energetic formulations and to prevent accidental ignition. One of the advantages of βCDs is the ability to tune their properties by chemical modification. Here, we synthesised nitrated cross‐linked βCDs (βNCXCDs) to produce new binders for energetic formulations. The cross‐linking of βCD with non‐toxic triethylene glycol diglycidyl ether (TEGDGE, X=T) and poly(ethylene glycol) diglycidyl ethers (PEGDGE, X=P) yielded soft, water soluble oligomeric compounds (βCXCDs) which can improve the processability of energetic formulations and contribute to their desensitisation. When the PEGDGE cross‐linker was used, lower glass transition temperatures were achieved, which extended the operative range of the βCPCD binder to −20 °C. The analogous nitrated systems (βNCXCDs) were therefore synthesised using a 1 : 1 (v/v) ratio of 98 % sulfuric acid/100 % nitric acid or 100 % fuming nitric acid, increasing their solubility in acetone and tetrahydrofuran. The nitrated derivatives were characterised by decomposition temperatures (200 °C) and energies (up to 1750 J g−1) comparable to nitrocellulose. Moreover, the glass transition of the inert βCXCDs at low temperatures (<0 °C) was conserved in the corresponding nitrated βNCXCDs, ensuring the desensitisation of energetic compositions even at low temperatures. This is the first time that nitrated derivatives of βCD with glass transition temperatures below 0 °C have been reported, suggesting such derivatives could make suitable replacements for nitrocellulose and other binders in energetic formulations.

In situ preparation of explosive embedded CuO/Al/CL20 nanoenergetic composite with enhanced reactivity

Hybrid explosive-nanothermite energetic composite is synthesized on silicon substrate by embedding hexanitrohexaazaisowurtzitane (CL20) with CuO/Al core/shell nanothermite arrays. The CL20 is in situ integrated with CuO/Al through a facile dissolution-recrystallization process utilizing the core/shell array structure. The hybrid energetic composite is characterized by field-emission scanning electron microscope, X-ray diffraction, and Fourier transform infrared spectroscopy. The heat release characteristics are studied by differential scanning calorimetry and thermogravimetric analysis, and the combustion phenomenon is investigated through open burn experiments. It is found that CL20 is recrystallized within the CuO/Al arrays as a linker with a controllable loading amount. The integration of CL20 explosive not only improves the heat release properties with an increased total heat of reaction and an 18.2% decreased activation energy of integrated CL20, but more interestingly, causes an obvious two-step reaction. Each step is rate-limited by CuO decomposition and diffusion of reacting species through alumina, respectively. In addition, the embedded CL20 and CuO/Al nanothermite arrays jointly ensure a violent and stable combustion behavior, which are very promising for practical applications.

Performance characterization of Bi2O3/Al nanoenergetics blasted micro-forming system

Abstract This paper reports a novel micro-blast driven manufacturing process for micro-forming of Aluminum foils. The micro-blast is realized by using a nanoenergetic material system comprising of Bi2O3 micro-rods and aluminum particles. There is an enhanced need of forming of thin aluminum foil structures in small regions from point of view of drug packaging etc. The process developed caters to this need by using a single shot forming process using a micro-blast source. The micro-blast that is generated from an energetic composite system is made highly tunable by modulating the peak pressure generated through the blasting process and their impact in micro-forming of thin aluminum foils is observed through parametric studies. The engineering challenge involved in these experiments is to tune the blast pressure properties in order to address the forming of thin metal sheets with limiting boundary values as defined by the failure criteria. A variety of characterization techniques related to a thorough analysis of the synthesized material viz. X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) etc. are used to tune the functional properties like gauge blast pressure etc. of material system. We have found a material system that can generate a maximum peak pressure of 73.8 MPa with pressurization rate of 2460 GPa s−1 and that is able to accomplish micro-forming on thin metal foils (around 0.3 mm thickness). Experimental investigations demonstrate that tunabilty aspect of the energetic composites when exercised can enable variant processes such as embossing, coining, drilling etc. which may be of significant utility to drug packaging industries. A proper mathematical modeling of the forming process and critical process parameters therein have also been detailed.

Emulsion synthesis of CL-20/DNA composite with excellent superfine spherical improved sensitivity performance via a combined ultrasonic–microwave irradiation approach

An advanced emulsion method was developed via combined ultrasound-microwave irradiation and utilized for the crystallization of 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20) and 2,4-dinitroaniline (DNA) spherical composite, which had been successfully fabricated with molar ratio of 1:1, The morphology and structure of the products were fully characterized using field emission scanning electron microscopy, powder X-ray diffraction, Fourier transform infrared spectroscopy. The thermal stability of micro structure was closely investigated via differential scanning calorimetry, and sensitivity performance was tested. The results suggested that the surface of particle was glazed while particle with narrow size distribution were produced. Remarkably, the drop height of 50% explosion probability data showed insensitivity compared to the previously reported energetic composites, which data was up to 57.8 cm. Besides, some experimental conditions including the amount of surfactant gelatin (0–1.2 wt% of accounting for the mass of CL-20) and standing time were examined. It was found that the greater the concentration of surfactant, the more conducive to the formation of emulsion, and standing time had a dramatically significant effect on the particle size. Summarily, the present process involving an initial powder made it possible to obtain micro spherical composite with ideal impact sensitivity, compared to those produced by conventional methods.

Catalytic Reactivity of Graphene Oxide Stabilized Transition Metal Complexes of Triaminoguanidine on Thermolysis of RDX

In this paper, the graphene oxide (GO) doped transition metal (Cu, Co, and Ni) complexes of triaminoguanidine (TAG) have been prepared where the GO serves as the stabilizing agent. The catalytic reactivity of GO stabilized TAG-M (M = Cu, Co, Ni) energetic composites on thermolysis of 1,3,5-trinitro-1,3,5-triazinane (RDX) has been investigated by using DSC/TGA techniques. It has been found that these materials have strong catalytic effects on decomposition of RDX by decreasing the apparent activation energy. Meantime, GO would not only stabilize TAG-M energetic composites but also enhance the thermal stability of RDX due to its high thermal conductivity. The physical models that govern the decomposition processes were also studied, and it has been shown that different reaction processes are accomplished by varying transition metals or in cooperation with GO. The complex catalyst, with improved thermal stability, represents a unique class of catalyst of considerable value for catalytic combustion and safety...

Enhancing fracture toughness of polymer‐based functional energetic composites by filling nano‐graphene in matrix

With the emergence and commercialization of graphene, new opportunities have emerged for toughening polymer‐based functional energetic composites (e.g., polymer‐bonded explosives [PBX]) using nano‐graphene without sacrificing strength and glass transition temperature, as compared with conventional elastomeric tougheners. In this work, inorganic nano‐graphene is used to study the toughness enhancing effects and mechanical properties of 1,3,5,7‐tetranitro‐1,3,5,7‐tetrazocane (HMX)‐based PBX. Fabrication procedures of HMX‐based PBX with different content of graphene are presented, and well‐dispersion for graphene in binder matrix is obtained by ultrasonic processing. Experimental results indicated the addition of nano‐graphene can greatly increase the toughness, with the fracture energy enhanced from 32.5 to 64.9 J m−3 compared with normal HMX‐based PBX. Such improvement was obtained at a low graphene concentration (0.2–0.4 wt%). Strong interaction of the graphene and the binder matrix, combined with the inherent properties of well‐dispersed graphene are the decisive factors with respect to the outstanding toughening effect. POLYM. COMPOS., 40:E1151–E1161, 2019. © 2018 Society of Plastics Engineers

Hot Spot Interaction with Hydroxyl-Terminated Polybutadiene Binder in Energetic Composites

Binders play a pivotal role in solid propellants and polymer-bonded energetic composites by providing the means for safe transport, storage, and use. The fundamental role of binders is known qualitatively, but the exact role in the modification of chemistry and thermal transport is hard to quantify. Thermochemical response of a commonly used binder, hydroxyl-terminated polybutadiene (HTPB), in a model composite comprising of cyclotrimethylene trinitramine (RDX) in the presence of a thermal hot spot was studied using reactive molecular dynamics (RMD) simulations. The results from model interfaces between RDX and HTPB were analyzed to identify the unique role played by the binder phase. It was found that the binder phase provides a safety buffer by extending the time required for the hot spot to undergo ignition-to-deflagration transition. This delay is mainly due to the disparity in the heat capacities of HTPB and RDX. HTPB, which has a higher heat capacity than RDX, absorbs energy from the hot spot at a r...

A New Method for Measuring the Pressure Increase in Energetic Compositions in a Maximally Filled Container

A new method for direct measurement of the pressure increase in energetic compositions (propellants, powders, and explosives) upon thermal decay of energetic samples is described. This method is applicable to the control of the decay kinetics of elastic compositions during long-time storage. The testing of this method showed that the error in measuring the pressure increase in the systems under study during long-time storage at a constant temperature and the maximum filling of the reaction container did not exceed 4%.

The interaction mechanism of mechanical activated energetic composites

Herein, in order to study the interaction mechanism of mechanical activated energetic composites, molecular dynamics simulation was carried out to calculate the binding energy and the interaction mode of PTFE with different crystalline surfaces of Al and Al2O3. Then the mechanical activated energetic composites were prepared, the microscopic morphology and the surface element content of Al-PTFE composites before and after mechanical activation have been studied. At last, the reactivity was tested. The results show that the adsorption of PTFE on the (0 0 1), (0 1 0) and (1 0 0) surface of Al2O3 and Al is stable. PTFE interacts with Al2O3 mainly via electrostatic force, and PTFE interacts with Al mainly via Van der Waals’ force. After 40 min ball milling, Al and PTFE melt into a composite aggregate, the adsorption of PTFE on the surface of Al and Al2O3 is stable, the experimental results are in good agreement with the simulation results. Mechanical activation can remarkably reduce the diffusion distance, improve the reaction activity and the detonation velocity of Al-PTFE composites.

Dynamic fracture and hot-spot modeling in energetic composites

Defects such as cracks, pores, and particle-matrix interface debonding affect the sensitivity of energetic materials by reducing the time-to-ignition and the threshold pressure to initiate an explosion. Frictional sliding of preexisting cracks is considered to be one of the most important causes of localized heating. Therefore, understanding the dynamic fracture of crystalline energetic materials is of extreme importance to assess the reliability and safety of polymer-bonded explosives. Phase field damage model simulations, based on the regularization of the crack surface as a diffuse delta function, are used to describe crack propagation in cyclotetramethylene-tetranitramine crystals embedded in a Sylgard matrix. A thermal transport model that includes heat generation by friction at crack interfaces is coupled to the solution of crack propagation. 2D and 3D dynamic compression simulations are performed with different boundary velocities and initial distributions of cracks and interface defects to understand their effect on crack propagation and heat generation. It is found that, at an impact velocity of 400 m/s, localized damage at the particle-binder interface is of key importance and that the sample reaches temperatures high enough to create a hot-spot that will lead to ignition. At an impact velocity of 10 m/s, preexisting cracks advanced inside the particle, but the increase of temperature will not cause ignition.

Cross‐linking of Hydroxyl‐terminated Polyols with Triethyleneglycol Diglycidyl Ether: An Alternative to Toxic Isocyanates

AbstractIsocyanates are highly reactive and toxic substances with severe health effects. Certain diisocyanates are restricted under REACH – The European Regulation on Registration, Evaluation, Authorisation and Restriction of Chemicals. Triethyleneglycol diglycidyl ether (TEGDGE) was used as an alternative to toxic isocyanates for the cross‐linking of hydroxyl‐terminated pre‐polymers at 70 °C. The effect of three curing accelerators was determined while following the reaction kinetics by 1H‐NMR spectroscopy and differential scanning calorimetry (DSC). Polybutadiene (Poly BD R45HT‐LO) and acrylic ester (HyTemp 4454) successfully cross‐linked in 7–10 days to produce thermally stable networks with low glass transition temperatures, as observed by DSC. Pre‐aging the polybutadiene resin promoted cross‐linking with TEGDGE. Four energetic compositions were then prepared using cyclotrimethylenetrinitramine (RDX) and pentaerythritoltetranitrate (PETN) as fillers, and polybutadiene (Poly BD R45HT‐LO) and acrylic ester (HyTemp 4454) as binders. Both binders successfully cross‐linked with TEGDGE in the presence of RDX and PETN, but only PETN was found to be chemically compatible with the cross‐linked polymers. These results show that TEGDGE is suitable as a replacement for toxic isocyanates for the cross‐linking of hydroxyl‐terminated polyols.

Inkjet printing of energetic composites with high density.

To explore a new manufacturing method in preparing energetic composites, an inkjet printing device possessing the ability of high precision and flexibility was utilized to deposit six 3,4-dinitrofurazanofuroxan (DNTF) and hexogen (RDX) based explosive inks. The printed quality, inner structure, printed density and crystal morphology of energetic composites were tested, as well as their thermal decomposition properties and detonation properties. The results indicate that inkjet printing provides a good formation uniformity for explosive inks. Interestingly, all energetic composites exhibit excellent printed density with all values higher than 90% theoretical maximum density (TMD). Meanwhile, the composite DNTF/RDX/EC/GAP (54/36/5/5) performs best, reaching 96.88% TMD, which has reached a new height in the three-dimensional printing of energetic composites. Further study manifests that there is no appearance of new material, and the stacking manner of rodlike structures in multilayer manufacturing is the key to achieving such an amazing result. The particles in the energetic composites are spherical with the size ranging from 500 nm to 2 μm and connect with each other closely in the matrix of binders. Moreover, the energetic composites that were directly deposited into wedge channels display a good capability in steadily detonating above the size of 1 × 0.32 mm.

Microwave Excitation of Crystalline Energetic Composites

Hotspots produced by microwaves radiating into an energetic composite of RDX crystals and an estane binder are examined using transient electromagnetic (EM) and coupled EM-thermal analyses. Hotspots, localized regions where energetic activity is likely to initiate, manifest as regions of peak electric field or high temperature. Stress caused by these high fields and temperatures may result in molecular breakdown, creating a chain reaction leading to the release of chemical energy via deflagration (burning and melting) in the absence of a mechanical shock wave. High peak electric fields up to three times higher than the incident field result from subwavelength scattering and occur near crystalline surfaces while peak temperatures occur in the binder, with both generally coinciding at the binder-RDX interface. Abstractions enable materials to be modeled with crystals having an average characteristic dimension of 100 $\mu \text{m}$ . With an incident field of 1 MV/m the peak electric field in the composite was 2.9 MV/m and peak temperature increased by 75 K in the binder and 65 K in the RDX after 3.7 ms. The RDX fill factor of the composite was 37%, typical of an improvised explosive.

Highly stable functionalized aluminum nanoparticles for magneto-energetic composite fabrication

An effective coating strategy is employed to functionalize and protect the surfaces of aluminum (Al) nanoparticle (NPs) from oxidation and aggregation using silanization of the oxide surface with (3-aminopropyl) triethoxysilane (Al@APTES), followed by an amine/carboxylic exchange using glutaric anhydride (Al@APTES@GA). The stability of the two types of functionalized Al NPs in aqueous solution is studied using dynamic light scattering and x-ray diffraction phase/composition identification. It is found that Al@APTES NPs transform into bayerite (β-Al(OH)3) after storage for a short period of time, while Al@APTES@GA NPs exhibit long-term stability. Hydration of Al results in micro-sized aggregates and a large proportion of dead weight, which reduces the particles’ energetic properties. Al–Fe3O4 magnetic–energetic (Magnerg) composites are fabricated via the electrostatic interaction of oppositely charged NPs in an aqueous solution. The high dispersity and stability of Al@APTES@GA NPs assure their intimate arrangement with oxidizing Fe3O4 NPs that facilitates mass transport between reactants.

Energetic Compositions Application for the Reduction of the Environmental Pollution Because of Space Vehicle Launches

Technogeneous impact of rocket and space activities on the environment is one of the most actual problems of practical cosmonautics. This technogeneous impact is not only the pollution of near Earth space with space debris (worked-off stages of space launch vehicle (SLV)), but also the pollution of significant areas on the Earth surface with worked-off lower stages of SLV, which fall down after having accomplished their mission. In OmSTU and IPCP RAS it was suggested to apply different self-burning compositions, generating hot gases for the evaporation of the unused residues of liquid propellant in tanks of SLV. Then the mixture of the evaporated compounds together with the gaseous combustion products from gas-generating compositions is used as propellant mixture for the autonomous gas rocket engine. Such a solution would decrease considerably the level of the environment pollution and additionally it increases the energetic characteristics of SLV. For example, in the case of the second stage of SLV «Soyuz-2.1.v» it increases the total velocity by 5%. Also it is proposed to use firing the pyrotechnic compositions like (thermites) for the fairings heating up to the temperature when the fairing material can be ignited in air. It would reduce considerably the amount and the mass of the separating parts of SLV that fall to the Earth.

A parametric study of the dynamic failure of energetic composites

Heating by frictional sliding of cracks is often considered to be one of the most important causes of localized melting and ignition in solid explosives. Furthermore, recent high speed X-ray phase contrast experiments on energetic composites under dynamic compression [Parab et al., Appl. Phys. Lett. 109(13) (2016)] show that most fracture events appear inside the particles. Initial cracks develop in regions where particles are close, and widespread fragmentation is observed in the interior of the particles as the stress waves propagate through the sample. However, most simulations have focused on interface debonding of energetic composites and, in general, do not include fracture of the particles explicitly. A phase field damage approach is used to model the dynamic response of a system of cyclotetramethylene-tetranitramine particles embedded in a Sylgard matrix. The simulations show several damage mechanisms observed in the experiments. The effects of the energy release rate and the initial crack distribution on the energy dissipation due to fracture are studied. The numerical results confirm that initial cracks play an important role in the evolution of damage, energy dissipation and consequently, the formation of hot-spots.

Selection of solvent for the mechanical activation process: A molecular dynamics simulation and experiment study

Herein, molecular dynamics simulations and experiments were carried to select solvent for the mechanical activation process. The interaction between solvent and each component of the Al‐PTFE mechanical activated energy composites has been studied by means of molecular dynamics. Then, the status of Al and PTFE in solvent was analyzed, and the microstructure of the composite was also studied combined with experiment. At last, the mechanical activated energy composites were prepared with n‐hexane as the solvent. The results show that the adsorption of PTFE, toluene, and hexane on the (0 0 1), (0 1 0), and (100) surface of Al2O3 is stable. Al2O3 (0 0 1) surface and Al2O3 (0 1 0) surface interact with 3 substances mainly via the electrostatic force. Al2O3 (1 0 0) surface interacts with 3 substances mainly via the van der Waals force. The binding energies of toluene‐Al2O3 and hexane‐Al2O3 are larger than PTFE‐Al2O3. PTFE cannot adsorb on the surface of aluminum in the existence of n‐hexane and toluene. n‐Hexane can make PTFE disperse uniformly, and a considerable part of these PTFE will be coated on the surface of Al after n‐hexane is removed. The uniformity of Al/PTFE mechanical activated energetic composites prepared in n‐hexane is good, and it increases with the milling time.

Catalytic effect of lead oxide nano- and microparticles on thermal decomposition kinetics of energetic compositions containing TEGDN/NC/DAG

The catalytic effect of lead oxide nano- and microparticles (PbO) on the thermal behavior and decomposition kinetics of energetic formulations composed of nitrocellulose (NC), triethyleneglycol dinitrate (TEGDN) and diaminoglyoxime (DAG) was investigated by simultaneous thermogravimetric analysis and differential scanning calorimetry. The results show that lead oxide nano- and microparticles could significantly alter thermal pattern of the studied energetic compositions. The effect of lead oxide content on thermal behavior of energetic compositions was also studied, and the results revealed that addition of different amounts of lead oxide caused to shift in the DSC peaks. Moreover, the catalyst decreases activation energy of the decomposition stage of energetic composition at about 20–40 kJ mol−1. However, the catalyst enhances decomposition temperature of TEGDN/NC/DAG energetic compositions. By the aid of DSC data resulted by non-isothermal methods, the thermokinetic parameters such as activation energy (E a), frequency factor (A), the critical ignition temperature of thermal explosion, the self-accelerating decomposition temperature (T SADT) and also thermodynamic parameters of the studied energetic compositions were calculated and compared.