Nanoscale Energetic Materials Research Articles

Additive Manufacturing and Combustion Characteristics of Polyethylene Oxide/Aluminum/Copper Oxide-Based Energetic Nanocomposites for Enhancing the Propulsion of Small Projectiles.

The application of nanoscale energetic materials (nEMs) composed of metal and oxidizer nanoparticles (NPs) in thermal engineering systems is limited by their relatively high sensitivity and complex three-dimensional (3D) formability. Polymers can be added to nEMs to lower the sensitivity and improve the formability of 3D structures. In this study, the effect of the addition of polyethylene oxide (PEO; polymer) on the combustion characteristics of aluminum (Al; fuel)/copper oxide (CuO; oxidizer)-based nEMs is investigated. With an increase in the PEO content, the resulting PEO/nEM composites are desensitized to relatively high electrical spark discharges. However, the maximum explosion-induced pressure decreases significantly, and the combustion flame fails to propagate when the PEO content exceeds 15 wt.%. Therefore, the optimal PEO content in a nEM matrix must be accurately determined to achieve a compromise between sensitivity and reactivity. To demonstrate their potential application as composite solid propellants (CSPs), 3D-printed disks composed of PEO/nEM composites were assembled using additive manufacturing. They were cross-stacked with conventional potassium nitrate (KNO3)/sucrose (C12H22O11)-based disk-shaped CSPs in a combustion chamber of small rocket motors. Propulsion tests indicated that the specific impulse of KNSU/PEO/nEM (nEMs: 3.4 wt.%)-based CSPs was at a maximum value, which is approximately three times higher than that of KNSU CSPs without nEMs. This suggests that the addition of an optimized amount of polymer to nEMs is beneficial for various CSPs with compromised sensitivity and reactivity and excellent 3D formability, which can significantly enhance the propulsion of small projectiles.

Fabrication of micro/nano spherulitic hierarchical energetic materials via noncrystallographic branching induced by polymer additives: A case study of 2,2′,4,4′,6,6′-hexanitrostilbene (HNS)

In this work, the micro/nano spherulitic hierarchical 2,2′,4,4′,6,6′-hexanitrostilbene (HNS) with the excellent specific surface area was prepared for the first time, which was expected to overcome the agglomeration problems of nanoscale HNS. In detail, poly(N-isopropyl acrylamide) (PNIPAM), polysuccinimide (PSI), and polyvinylpyrrolidone (PVP) were selected as additives to induce forming spherulitic HNS. Leaflike crystals were obtained in the presence of PNIPAM, while spherulitic HNS could be fabricated in the presence of PSI or PVP. And the prepared spherulitic HNS owned nearly 6 times the specific surface area of the raw HNS, with decreased impact sensitivity and advanced melting and decomposition temperatures, demonstrating a good desensitization effect, and a favorable energy release of the hierarchical structure. Moreover, morphological changes under the effect of the molecular weight and concentration of PVP were explored. The approximated morphological evolution of spherulitic HNS was consistent with the classical spherulitic growth by noncrystallographic branching. Furthermore, it was verified that preferential adsorption of PVP and PSI on the HNS inhibits the growth steps of the (200) face and introduces stress to generate crystal defects, which triggers noncrystallographic branching and further spherulitic growth. Overall, the strategy of fabricating micro/nano spherulitic hierarchical energetic materials via polymer-additive induced noncrystallographic branching is promising to solve the problems of nanoscale energetic materials in agglomeration and microscale bulk crystals in low activity.

Effect of Nano-Sized Energetic Materials (nEMs) on the Performance of Solid Propellants: A Review.

As a hot research topic, nano-scale energetic materials have recently attracted much attention in the fields of propellants and explosives. The preparation of different types of nano-sized energetic materials were carried out, and the effects of nano-sized energetic materials (nEMs) on the properties of solid propellants and explosives were investigated and compared with those of micro-sized ones, placing emphasis on the investigation of the hazardous properties, which could be useable for solid rocket nozzle motor applications. It was found that the nano-sized energetic materials can decrease the impact sensitivity and friction sensitivity of solid propellants and explosives compared with the corresponding micro-sized ones, and the mechanical sensitivities are lower than that of micro-sized particles formulation. Seventy-nine references were enclosed.

Fully packaged paper heater systems with remote and selective ignition capabilities for nanoscale energetic materials

Development of low-voltage driven multifunctional thermal igniters for nanoscale energetic materials (nEMs) is important for extending the application of nEMs to various thermal engineering fields. In this study, highly flexible heater chips capable of generating a sufficient amount of heat to ignite nEMs at a low voltage are demonstrated by incorporating a patterned aluminum-doped paper (AP) with polymeric substrates. A combination of automatic paper cutting and single-step ultraviolet polymer curing techniques helps in the fabrication of various designs of flexible AP heater chips in a simple and low-cost manner. Based on the AP heater chips, three models of flexible thermal igniters are designed to develop new functions such as selective ignition and sequential ignition in a single chip and successfully operated at low voltages. Two types of compact ignition systems are fabricated by fully integrating the arrayed AP igniters, circuit modules, and portable batteries in a three-dimensional printed single package and on a flexible circuit board. The systems are successfully demonstrated to ignite nEMs wirelessly and selectively with a smartphone.

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.

Tuning the ignition and combustion properties of nanoenergetic materials by incorporating with carbon black nanoparticles

In this study, the effect of carbon black nanoparticle (CB NP) additives on the ignition and combustion properties of Al/CuO NP-based nanoscale energetic materials (nEMs) has been systematically investigated. When an excessive amount of CB NPs (> 1 wt.%) was added to these nEMs, their pressurization and burn rates were considerably suppressed by a magnitude of about 50% due to the heat dissipation and thermochemical intervention in the self-propagating reactions of Al/CuO NPs. The ignition delay time of the studied energetic materials was monotonically reduced with increasing amount of added CB NPs because of the enhancement of their heat transfer properties. The total heat energy generated by the Al/CuO NP-based nEMs gradually decreased with increasing amount of CB NPs because of their thermochemical intervention in the exothermic reaction. Finally, the results of soil explosion testing revealed that the diameter of the produced crater could be controlled by varying the content of CB NPs in the nEM matrix. Therefore, the CB NP additives can be potentially used as a control medium, which affects the heat transfer process and thermochemical interactions between nEM components and is thus capable of precisely tuning their ignition, combustion, and explosion properties for various thermal engineering applications.

Influence of Stoichiometry on the Thrust and Heat Deposition of On‐Chip Nanothermites

AbstractCurrently, there is very little systematic work quantifying the thrust or heat applied to an electronic circuit or other substrate by a deposited layer of energetic material. A better understanding of the interactions between nanoscale energetic materials and electronic systems, as a function of stoichiometry, is needed. For this purpose, formulations of nAl‐CuO and nAl‐Bi2O3 nanothermites were prepared at different equivalence ratios and selectively deposited onto electronic circuit analogues (silicon wafers) and the amounts of thrust production and heat deposition were measured. Both nanothermite systems produced maximum thrust near stoichiometric ratios, accompanied by a shock wave, with minimal thermal effects due to large gas production, which ejects the hot products of the substrates. Conversely, more fuel‐rich mixtures led to significantly decreased thrust while increasing heat deposition due to the lower gas production, which allowed more heat to diffuse to the substrates. This shows that the energetic material response can be tuned between thrust or heat deposition by just varying the equivalence ratio. The conductive heat transfer within the silicon substrates from the nAl‐CuO system increased more than the nAl‐Bi2O3 system at fuel rich conditions due to its higher heat of combustion.

Nanoenergetic material-on-multiwalled carbon nanotubes paper chip as compact and flexible igniter

A compact and flexible multiwalled carbon nanotubes (MWCNTs)-coated paper electrode was fabricated in this study. The shape of the paper electrode could be varied simply by cutting it. Further, its electrical resistance did not change appreciably either when it was bent with different curvatures or when it was subjected to repeated bending and stretching. An nanoscale energetic material (nEM)-on-MWCNTs paper chip formed by depositing an nEM thin film on the MWCNTs-coated paper electrode could be stably ignited by applying voltages higher than ∼ 15 V. The ignition and explosion characteristics of the chip were investigated systematically. It was found that the explosion reactivity of the chip increased with an increase in the thickness of the nEM thin film. Finally, the remote ignition of the nEM-on-MWCNTs paper chip was successfully demonstrated by explosively breaching a door, suggesting that such nEM-on-MWCNTs paper chips can be used as compact, flexible, and versatile igniters in various civil and military applications.

Micro- and Nanoscale Energetic Materials as Effective Heat Energy Sources for Enhanced Gas Generators.

In this study, we systematically investigated the effect of micro- and nanoscale energetic materials in formulations of aluminum microparticles (Al MPs; heat source)/aluminum nanoparticles (Al NPs; heat source)/copper oxide nanoparticles (CuO NPs; oxidizer) on the combustion and gas-generating properties of sodium azide microparticles (NaN3 MPs; gas-generating agent) for potential applications in gas generators. The burn rate of the NaN3 MP/CuO NP composite powder was only ∼0.3 m/s. However, the addition of Al MPs and Al NPs to the NaN3 MP/CuO NP matrix caused the rates to reach ∼1.5 and ∼5.3 m/s, respectively. In addition, the N2 gas volume flow rate generated by the ignition of the NaN3 MP/CuO NP composite powder was only ∼0.6 L/s, which was significantly increased to ∼1.4 and ∼3.9 L/s by adding Al MPs and Al NPs, respectively, to the NaN3 MP/CuO NP composite powder. This suggested that the highly reactive Al MPs and NPs, with the assistance of CuO NPs, were effective heat-generating sources enabling the complete thermal decomposition of NaN3 MPs upon ignition. Al NPs were more effective than Al MPs in the gas generators because of the increased reactivity induced by the reduced particle size. Finally, we successfully demonstrated that a homemade airbag with a specific volume of ∼140 mL could be rapidly and fully inflated by the thermal activation of nanoscale energetic material-added gas-generating agents (i.e., NaN3 MP/Al NP/CuO NP composites) within the standard time of ∼50 ms for airbag inflation.

Ni-Al Nanoscale Energetic Materials: Phenomena Involved During the Manufacturing of Bulk Samples by Cold Spray

It has been shown that the cold-gas dynamic spraying process, or simply cold spray, is a suitable technique to manufacture nanoscale energetic materials with high reactivity and low porosity. The current study focuses on the Ni-Al system, for which the reactivity has been increased by an initial mechanical activation achieved by the ball-milling technique, leading to lamellar nanostructured composite particles. The consolidation of this nanoscale energetic material using the cold-gas dynamic spray technique permits to retain the feedstock powder nanoscale structure in the coatings, which in turn retain the high reactivity features of the powder. However, it has been noticed that the stagnation temperature during the spray can lead to partial reaction of the highly reactive feedstock powder, which directly influences the reactivity of the coatings. In this study, different stages of the spray process were investigated: (i) the in-flight behavior of the nanoscale energetic material (powder) at different stagnation temperatures (from 300 to 800 °C); (ii) the substrate-temperature evolution as the function of gas temperature; and (iii) the impact of the powder on the substrate, related to particle’s velocity and its influence on the nanostructure of the particles.

Enhanced reactivity of mechanically-activated nano-scale gasless reactive materials consolidated by coldspray

The present study presents a novel method to prepare nano-scale energetic materials with high reactivity, low porosity and controllable shape. The experiments have been focused on the Ni–Al system. To increase the reactivity, an initial mechanical activation was achieved by the ball milling technique. The consolidation of the materials was achieved via the use of the Cold Gas Dynamic Spray (also known as Cold Spray) technique, where the particles are accelerated to high speeds and consolidated via plastic deformation upon impact, forming activated nanocomposites in arbitrary shapes with porosity levels close to zero. This technique permits to retain the powder microstructure in the coatings and prevents any reactions during the consolidation phase. The material reactivity is addressed through the flame propagation velocity, which showed an increase in the flame speed of the cold sprayed samples by up to one order of magnitude compared to their cold pressed counterparts.

Effects of bimetallic catalysts on synthesis of nitrogen-doped carbon nanotubes as nanoscale energetic materials

Well aligned nitrogen-doped carbon nanotubes (CN x-NTs), as energetic materials, are synthesized on a silicon substrate by aerosol-assisted chemical vapor deposition. Tungsten (W) and molybdenum (Mo) metals are respectively introduced to combine with iron (Fe) to act as a bimetallic co-catalyst layer. Correlations between the composition and shape of the co-catalyst and morphology, size, growth rate and nitrogen doping amount of the synthesized CN x-NTs are investigated by secondary and backscattered electron imaging in a field emission scanning electron microscope (FESEM) and X-ray photoelectron spectrometer (XPS). Compared to pure iron catalyst, W–Fe co-catalyst can result in lower growth rate, larger diameter and wider size distribution of the CN x-NTs; while incorporation of molybdenum into the iron catalyst layer can reduce the diameter and size distribution of the nanotubes. Compared to the sole iron catalyst, Fe–W catalyst impedes nitrogen doping while Fe–Mo catalyst promotes the incorporation of nitrogen into the nanotubes. The present work indicates that CN x-NTs with modulated size, growth rate and nitrogen doping concentration are expected to be synthesized by tuning the size and composition of co-catalysts, which may find great potential in producing CN x-NTs with controlled structure and properties.

UNIFORM- AND HIGH-YIELD CARBON NANOTUBES WITH MODULATED NITROGEN CONCENTRATION FOR PROMISING NANOSCALE ENERGETIC MATERIALS

It is well known that pure polynitrogen systems are metastable. Recently, a theoretical study showed that when a polymeric nitrogen chain is encapsulated in a carbon nanotube, it will be stable at ambient pressure and room temperature, which makes carbon nanotubes now promising as nanoscale energetic materials. Here, we report a systematic study of multiwalled carbon nanotubes with different nitrogen-doping amounts produced by aerosol-assisted chemical vapor deposition, in which growth temperature, hydrogen flow rate, and aerosol amount have been varied. The morphological and compositional changes of nitrogen-doped carbon nanotubes were characterized by means of scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. The detailed investigation of nitrogen-doped carbon nanotubes will provide a route to obtain evidence of the above theoretical prediction, and will have potential applications in nanoscale energetic materials.

UNIFORM- AND HIGH-YIELD CARBON NANOTUBES WITH MODULATED NITROGEN CONCENTRATION FOR PROMISING NANOSCALE ENERGETIC MATERIALS

Uniform and High Yield Carbon Nanotubes with Modulated Nitrogen Concentration for Promising Nanoscale Energetic Materials Hao Liu, Yong Zhang, Ruying Li, Hakima Abou-Rachid, Louis-Simon Lussier and Xueliang Sun a Department of Mechanical and Materials Engineering, University of Western Ontario, London, ON. N6A 5B9, Canada b Defence Research & Development Canada – Valcartier, 2459 Boulevard PieXI Nord, Quebec, QC. G3J 1X5, Canada Abstract: It is well known that pure polynitrogen systems are metastable. Recently, a theoretical study showed that when polymeric nitrogen chain is encapsulated in a carbon nanotube, it will be stable at ambient pressure and room temperature, which makes carbon nanotubes new promising as nanoscale energetic materials. Here, we report a systematic study of multi-walled carbon nanotubes with different nitrogen-doping amounts produced by aerosol assisted chemical vapor deposition, in which growth temperature, hydrogen flow rate and aerosol amount have been varied. The morphological and compositional changes of N-doped carbon nanotubes were characterized by means of scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. The detailed investigation of N-doped carbon nanotubes will provide a route to obtain evidence of the above theoretical prediction and will have potential applications in nanoscale energetic materials.

Evaluation of nanoparticles in the performance of energetic materials

The addition of nanosized metal particles in propulsion systems such as solid and liquid propellants, hybrid propellant and ramjet motors has recently became a major focus of research. Significant increases in the burning velocity and in the specific impulse are some of the advantages of using nano-scale energetic materials in many different types of propulsion systems. Aluminum has been largely employed as a metallic additive in energetic materials, also in a recently new propulsion system (aluminum/ice propulsion, Alice), and some studies show that the advantages of using nanosized aluminum instead of microsized aluminum are facilitating the ignition of the systems and allowing better incorporation of the components in the formulations and improving its homogeneity. Some of the combustion processes that require high pressures and even higher temperatures can occur in moderate conditions due to the increase of the surface area of the reactants, in this case, the metallic additive. Keywords: Nanoparticles, Aluminum, Energetic materials. Avaliacao das nanoparticulas no desempenho de materiais energeticos

Nanoenergetic Materials for MEMS: A Review

New energetic materials (EMs) are the key to great advances in microscale energy-demanding systems as actuation part, igniter, propulsion unit, and power. Nanoscale EMs (nEMs) particularly offer the promise of much higher energy densities, faster rate of energy release, greater stability, and more security (sensitivity to unwanted initiation). nEMs could therefore give response to microenergetics challenges. This paper provides a comprehensive review of current research activities in nEMs for microenergetics application. While thermodynamic calculations of flame temperature and reaction enthalpies are tools to choose desirable EMs, they are not sufficient for the choice of good material for microscale application where thermal losses are very penalizing. A strategy to select nEM is therefore proposed based on an analysis of the material diffusivity and heat of reaction. Finally, after a description of the different nEMs synthesis approaches, some guidelines for future investigations are provided.

Reactivity of aluminum nanopowders with metal oxides

During the past few years, significant progress has been made in research of the formation of nanopowders and their application in both civilian and military sectors. One example of such an application is the development of nanoscale energetic materials. This paper presents the recent experimental studies of ultra-fast reactions between nanosized aluminum and various metal oxides, including WO 3, MoO 3, CuO, and Fe 2O 3 under unconfined conditions. Combustion front velocity in Al–CuO system is strongly affected by the presence of surface functional coating, which significantly improves dispersion and mixing of nanoreactants and, in low concentration, increases the combustion front velocity. Measurements of dynamic pressure responses in Al–CuO reacting system have shown that ignition delay time is a function of the amount and type of functional surface coating.

Preparation of Energetic Metastable Nano-Composite Materials by Arrested Reactive Milling

ABSTRACTHighly metastable, nano-scale energetic materials were prepared by Arrested Reactive Milling (ARM). When reactive milling is carried out with materials systems suitable for Self-Propagating High Temperature Synthesis (SHS), reaction between the components occurs spontaneously and violently after a certain period of milling. In this research, metastable nanocom-posites with high energy density, were prepared by arresting the milling process prior to the spontaneous reaction. Products thus obtained are powders with particle sizes in the 10–50 μm range. Individual particles are intimate mixtures of reactive components, comparable to Metast-able Intermolecular Composites (MIC), with near theoretical maximum density. The time of arrest determines the degree of grain refinement and therefore the sensitivity to mechanical, electrical, or thermal initiation. Particle sizes of the product powders can be adjusted by appropriate choice of milling parameters. This paper describes the application of ARM to the material systems Al-Fe2O3 and Al-MoO3. After empirical determination of optimum milling parameters, the reactive composites are structurally characterized by electron microscopy and x-ray diffraction. First results of combustion tests are presented.