Super-reactive Nanoenergetic Gas Generators Based on Periodate Salts

Periodate-Based Perovskite Energetic Materials: A Strategy for High-Energy Primary Explosives

The requirements for high energy and green primary explosives are more and more stringent because of the rising demand in the application of micro initiation explosive devices. Four new energetic compounds with powerful initiation ability are reported and their performances are experimentally proven as designed, including non-perovskites ([H2 DABCO](H4 IO6 )2 ·2H2 O, named TDPI-0) and perovskitoid energetic materials (PEMs) ([H2 DABCO][M(IO4 )3 ]; DABCO=1,4-Diazabicyclo[2.2.2]octane, M=Na+ , K+ , and NH4 + for TDPI-1, -2, and -4, respectively). The tolerance factor is first introduced to guide the design of perovskitoid energetic materials (PEMs). In conjunction with [H2 DABCO](ClO4 )2 ·H2 O (DAP-0) and [H2 DABCO][M(ClO4 )3 ] (M=Na+ , K+ , and NH4 + for DAP-1, -2, and -4), the physiochemical properties of the two series are investigated between PEMs and non-perovskites (TDPI-0 and DAP-0). The experimental results show that PEMs have great advantages in improving the thermal stability, detonation performance, initiation capability, and regulating sensitivity. The influence of X-site replacement is illustrated by hard-soft-acid-base (HSAB) theory. Especially, TDPIs possess much stronger initiation capability than DAPs, which indicates that periodate salts are in favor of deflagration-to-detonation transition. Therefore, PEMs provide a simple and feasible method for designing advanced high energy materials with adjustable properties.

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.

Synergetic Effect of Potassium Oxysalts on Combustion and Ignition of Al/CuO Composites

In this study, we studied the synergetic effect of potassium oxysalts on combustion and ignition of nano aluminum (Al) and nano copper oxide (CuO) composites. Potassium periodate (KIO4) and potassium perchlorate (KClO4) are good oxidizers with high oxygen content and strong oxidizability. Different contents of KIO4 and KClO4 were added to nano Al/CuO and the composites were assembled by sonication. When the peak pressure of nano Al/CuO was increased ~5-13 times, the pressurization rate was improved by ~1-3 orders of magnitude, the ignition delay time was shortened by ~0.08 ms-0.52 ms and the reaction completeness was adjustable when 30-70% KIO4 and KClO4 were added into the composites. The reaction of Al/KIO4 and Al/KClO4 at a lower temperature was helpful to ignite the ternary composite. Meanwhile, CuO significantly reduced the peak temperature of oxygen released from the decomposition of KIO4 and KClO4. The synergetic effect of binary oxidizers made the combustion performance of the ternary composites better than that of the binary composites. The present work indicates that KIO4 and KClO4 are promising additives for nano Al/CuO to tune and promote the combustion performance. The ternary composites have potential application in energy devices and combustion apparatus.

New Promises from an Old Friend: Iodine-Rich Compounds as Prospective Energetic Biocidal Agents

For a very long time, frequent occurrences of biocrises have wreaked havoc on human beings, animals, and the environment. As a result, it is necessary to develop biocidal agents to destroy or neutralize active agents by releasing large amounts of strong biocides which are obtained upon detonation. Iodine is an efficient biocidal agent for bacteria, fungi, yeasts, viruses, spores, and protozoan parasites, and it is the sole element in the periodic table that can destroy microbes without contaminating the environment. Based on chemical biology, the mechanism of iodine as a bactericide may arise from oxidation and iodination reactions of cellular proteins and nucleic acids. However, because of the high vapor pressure causing elemental iodine to sublime readily at room temperature, it is inconvenient to use this material in its normal solid state directly as a biocidal agent under ambient conditions. Iodine-rich compounds where iodine is firmly bonded in molecules as a C-I or I-O moiety have been observed to be among the most promising energetic biocidal compounds. Gaseous products comprised of large amounts of iodine or iodine-containing components as strong biocides are released in the decomposition or explosion of iodine-rich compounds. Because of the detonation pressure, the iodine species are distributed over a large area greatly improving the efficacy of the system and requiring considerably less effort compared to traditional biocidal methods. The commercially available tetraiodomethane and tetraiodoethene, which possess superb iodine content also have the disadvantages of volatility, light sensitivity, and chemically reactivity, and therefore, are not suitable for use directly as biocidal agents. It is absolutely critical to synthesize new iodine-rich compounds with good thermal and chemical stabilities.In this Account, we describe our strategies for the syntheses of energetic iodine-rich compounds while maintaining the maximum iodine content with concomitant stability and routes for the synthesis of oxygen-containing iodine-rich compounds to improve the oxygen balance and achieve both high-energy and high-iodine content. In the other work, which involves cocrystals, iodine-containing polymers were also summarized. It is hoped that this Account will provide guidelines for the design and syntheses of new iodine-rich compounds and a route for the development of inexpensive, more efficient, and safer iodine-rich antibiological warfare agents of the future.

Effect of the Ni and NiO Interface Layer on the Energy Performance of Core/Shell CuO/Al Systems

The interface layer is responsible for the outward migration of oxygen atoms, which subsequently leads to an adjustment in the energetic performance of nanothermite films. In this study, sandwich-structured CuO@Ni/Al and CuO@NiO/Al nanowire thermite films were successfully prepared to investigate the effects of the interface layer on the heat-release, ignition, and combustion performance. The effects of the Ni and NiO interface layers are extremely different on the heat-release performance and combustion properties of the CuO/Al nanowire thermite film. Herein, the introduced Ni layer decreased the heat release (1979.7 J/g), reactivity (E_a = 177.3 kJ/mol), and maximum pressure (2.32 MPa) compared with the CuO/Al composite. Al/Ni alloys can be formed at the interface to prevent oxygen from diffusing between CuO and Al. Moreover, the incorporation of the Ni interface layer into the CuO/Al systems results in a heat drop due to its heat-absorption capability as well as its blockage of heat transfer from the thermite reaction. The deposition of the NiO layer between CuO and Al leads to an increase in the heat release (3014.2 J/g) and a decrease in the activation energy (E_a = 178.6 kJ/mol). The NiO layer endows the CuO/Al system with a high energy-release rate and chemical reactivity. NiO can participate in a thermite reaction, which promotes the reaction of CuO/Al and induces the condensed phase.

Highly Flexible and Patternable Multiwalled-Carbon Nanotube/Nitrocellulose Hybrid Conducting Paper Electrodes as Heating Platforms for Effective Ignition of Nanoenergetic Materials

In this study, a highly flexible, patternable multiwalled-carbon nanotube (MWCNT) paper electrode was specially designed and fabricated. The addition of a nitrocellulose (NC) polymer binder at less than the critical amount (≤2 wt %) was found to be effective for maintaining both the flexibility and electrical conductance of the resulting MWCNT paper electrode. The fabricated MWCNT paper electrode was then employed as a heating platform to ignite Al/CuO nanoparticle-based nanoenergetic materials (nEMs). The nEM layer was drop-cast on the surface of the MWCNT paper electrode with specially patterned shapes using a plotter, and its ignition was evaluated by applying various voltages through the MWCNT paper electrode. To increase the adhesion between the nEM layer and MWCNT paper electrode and to decrease the sparking sensitivity of the nEM layer, it was essential to incorporate NC in the nEM matrix. However, the combustion and explosion properties of nEM layers deteriorated with the addition of NC, enabling the estimation of the optimum amount of NC to be incorporated. The fabricated igniter can be employed in various thermal engineering applications, such as in the ignition of explosives and propellants, and in pyrotechnics. To demonstrate this, a compact, flexible, and patternable igniter composed of the NC/nEM layer (NC/nEM = 2:8 wt %) on an MWCNT paper electrode was used to successfully ignite solid propellants for launching a small rocket.

Constructing Strategies and Applications of Nitrogen-Rich Energetic Metal–Organic Framework Materials

The synthesis of energetic metal–organic frameworks (EMOFs) with one-dimensional, two-dimensional and three-dimensional structures is an effective strategy for developing new-generation high-energy-density and insensitive materials. The basic properties, models, synthetic strategies and applications of EMOF materials with nitrogen-rich energetic groups as ligands are reviewed. In contrast with traditional energetic materials, EMOFs exhibit some interesting characteristics, like tunable structure, diverse pores, high-density, high-detonation heat and so on. The traditional strategies to design EMOF materials with ideal properties are just to change the types and the size of energetic ligands and to select different metal ions. Recently, some new design concepts have come forth to produce more EMOFs materials with excellent properties, by modifying the energetic groups on the ligands and introducing highly energetic anion into skeleton, encapsulating metastable anions, introducing templates and so on. The paper points out that appropriate constructing strategy should be adopted according to the inherent characteristics of different EMOFs, by combining with functional requirements and considering the difficulties and the cost of production. To promote the development and application of EMOF materials, the more accurate and comprehensive synthesis, systematic performance measurement methods, theoretical calculation and structure simulation should be reinforced.

Controllable Electrically Guided Nano-Al/MoO3 Energetic-Film Formation on a Semiconductor Bridge with High Reactivity and Combustion Performance

Film-forming techniques and the control of heat release in micro-energetic chips or devices create challenges and bottlenecks for the utilization of energy. In this study, promising nano-Al/MoO3 metastable intermolecular composite (MIC) chips with an uniform distribution of particles were firstly designed via a convenient and high-efficiency electrophoretic deposition (EPD) technique at room temperature and under ambient pressure conditions. The mixture of isopropanol, polyethyleneimine, and benzoic acid proved to be an optimized dispersing agent for EPD. The kinetics of EPD for oxidants (Al) and reductants (MoO3) were systematically investigated, which contributed to adjusting the equivalence ratio of targeted energetic chips after changing the EPD dynamic behaviors of Al and MoO3 in suspension. In addition, the obtained nano-Al/MoO3 MIC energetic chips showed excellent heat-release performance with a high heat release of ca. 3340 J/g, and were successfully ignited with a dazzling flame recorded by a high-speed camera. Moreover, the fabrication method here is fully compatible with a micro-electromechanical system (MEMS), which suggests promising potential in designing and developing other MIC energetic chips or devices for micro-ignition/propulsion applications.

From nanoparticles to on-chip 3D nanothermite: electrospray deposition of reactive Al/CuO@NC onto semiconductor bridge and its application for rapid ignition

Nanothermites composed of nano-fuels and oxidants are attractive energetic materials, which have potential applications in microscale energy-demanding systems. Herein, nano-Al/CuO with nitrocellulose (NC) binder have been bottom-up assembled on semiconductor bridge (SCB) chip by electrospray, from nanoparticles to three-dimensional (3D) deposited structure. The morphological and compositional characterization confirms the constituents in Al/CuO@NC are homogeneously mixed at nano scale and the 3D structure at micro scale is tunable. The as-deposited Al/CuO@NC exhibits excellent energy output and superior chemical reactivity. Specifically, the heat release of Al/CuO@NC (1179.5 J g^-1) is higher than that of random mixed Al/CuO (730.9 J g^-1). Benefiting from outstanding exothermic properties, the material integrated with SCB initiator chip (Al/CuO@NC-SCB) for potential ignition application was investigated. The Al/CuO@NC-SCB micro energetic initiator can be functioned rapidly (with delay time of 2.8 μs) and exhibits superb ignition performances with violent explosion process, high combustion temperature (4636 °C) and successful ignition of B/KNO₃ propellant, in comparison to SCB initiator. The strategy provides promising route to introduce nano reactive particles into various functional energy-demanding systems for potential energetic applications.

Probing the reaction mechanism of Al/CuO nanocomposites doped with ammonium perchlorate

The oxide shell of Al nanoparticles (Al NPs) prevents further reaction of Al/CuO nanothermites which reduces Al utilization efficiency and the performance of the nanothermites. However, the performance of Al/CuO nanothermites can be improved by adding ammonium perchlorate (AP). In this work, in order to confirm and explain the enhancement mechanism of AP on Al/CuO nanothermites, Al/CuO/NC and Al/CuO/NC/AP composites were prepared using the electrospray method. The composites were characterized by differential scanning calorimetry/thermogravimetric, x-ray diffraction, scanning electron microscope and transmission electron microscopy. Meanwhile, the ignition temperature and the time-resolved analysis of the rapid pyrolysis chemistry of the composites were tested using T-jump and time-of-flight mass spectrometry, respectively. The results show that Al NPs of Al/CuO/NC/AP composite are hollow compared to Al/CuO/NC composite after reaction. Al NPs and CuO NPs reduce the decomposition temperature and facilitate the rapid decomposition of the AP, and the decomposition products of the AP can destroy the oxidation layer of Al NPs. This result facilitates the further conduct of the thermite reaction. A mutually reinforcing relationship exists between the Al/CuO/NC composites and AP.

Super-Efficient Synthesis of Mesh-like Superhydrophobic Nano-Aluminum/Iron (III) Oxide Energetic Films

In this study, a novel superhydrophobic nano-aluminum/iron (III) oxide composite has been prepared by a facile one-step process of electrophoretic deposition, with wide potential applications. The optimal suspension included ethanol, acetyl-acetone, and the additives of fluorotriphenylsilane and perfluorodecyltriethoxysilane. The microstructure, wettability, and exothermic performance were analyzed by field emission scanning electron microcopy (FESEM), X-ray diffraction (XRD), water contact angle measurements, and the differential scanning calorimetry (DSC) technique. The water contact angle and the heat-release of the target composites could reach to ~170° and 2.67 kJ/g, and could still keep stable, after exposure for six months, showing a great stability. These results provided an exquisite synthesis of ideas, for designing other superhydrophobic energetic materials with self-cleaning properties, for real industrial application.

What atomic properties of metal oxide control the reaction threshold of solid elemental fuels?

The redox reaction between fuel (metal, metalloid, etc.) and metal oxide is ubiquitous. On the other hand simple thermodynamic considerations do not seem to yield much insight into what makes for a vigorous oxidizer. In this study, two different systematically doped metal oxide systems: perovskites (9 compounds) and δ-Bi2O3 (12 compounds) were synthesized in a manner such that for each system the crystal structure and morphology were maintained. Four fuels (Al, B, Ta, C) with different physical properties, covering almost all fuel types, were included in this study. The initiation temperature and oxygen release temperature was measured by fast heating (>105 K s-1) temperature-jump/time-of-flight mass spectrometry coupled with high-speed imaging. These results were then correlated with the average metal-oxygen bond energy in the oxidizer, and overall metal-oxygen electronegativity. In general, within each systematic metal oxide, we found linear relationships between average bond energy and electronegativity of the metal oxides with initiation temperature for all four fuels, despite their very different physical/chemical properties. These results indicate that intrinsic atomic properties of metal oxide control fuel-metal oxide reaction initiation.

Core/shell CuO/Al nanorod thermite film based on electrochemical anodization

In this study, a new method was reported for the fabrication of the nanostructured CuO/Al thermite film on a Cu substrate. The CuO nanorod (NR) arrays grew vertically from the Cu surfaces by electrochemical anodization processes, followed by the deposition of an Al layer on the CuO NRs via magnetron sputtering to form a core/shell CuO/Al nanothermite film, whose component, structure and morphology were subsequently characterized. In addition, the energy-release characteristics of the obtained nanothermite film were investigated using thermal analyses and laser ignition tests. All evidence demonstrates that the obtained CuO/Al is of a uniform structure and has superb energy performance. Impressively, the resulting material is potentially useful in applications of functional energetic chips due to its easy integration with microelectromechanical systems (MEMS) technologies.

Mechanistic Studies of [AlCp*]4 Combustion

The combustion mechanism of [AlCp*]₄ (Cp* = pentamethylcyclopentadienyl), a ligated aluminum(I) cluster, was studied by a combination of experimental and theoretical methods. Two complementary experimental methods, temperature-programmed reaction and T-jump time-of-flight mass spectrometry, were used to investigate the decomposition behaviors of [AlCp*]₄ in both anaerobic and oxidative environments, revealing AlCp* and Al₂OCp* to be the major decomposition products. The observed product distribution and reaction pathways are consistent with the prediction from molecular dynamics simulations and static density functional theory calculations. These studies demonstrated that experiment and theory can indeed serve as complementary and predictive means to study the combustion behaviors of ligated aluminum clusters and may help in engineering stable compounds as candidates for rocket propellants.

Aluminum nanopowder: A substance to be handled with care

Aluminum nanopowders are increasingly used in various areas of research in materials and physical chemistry. Their unconventional properties are still little understood and make their handling sometimes quite hazardous. In this article, we report the case of apparently benign mixtures of Al with sulfuric acid (H₂SO₄), which violently explode when they are exposed to a flame. The explosions of 100mg samples were observed by high speed video (60000fr/s). These experiments have showed a three-step mechanism, in which the primary hydrogen combustion ignites and disperses the nano-Al/H₂SO₄ paste in clusters with high velocities (∼100m/s). The combustion of the paste increases the hydrogen release and initiates the explosion of the H₂/air mixture, which propagates at high velocities (760-1060m/s). This effect was not observed with micron-sized Al powders, and it is a good illustration of new hazards with nano-Al. Extreme caution is hence recommended to chemists who handle such materials.

Combustion Study of Different Transitional Metal Oxide based on AN/MgAl Composites Gas Generators

Ammonium nitrate (AN)-based composite gas generator have attracted a considerable amount of attention because of the clean burning nature of AN as an oxidizer. However, ammonium nitrate-based gas generator has several major problems, namely, poor ignitability, a low burning rate, low energy, and high hygroscopicity. The addition of different transitional metal oxides and MgAl mechanical alloyed proved to be effective in improving the burning characteristics of AN-based gas generator. In this research work, combustion study of different transition metal oxide based on AN/MgAl composites gas generators was studied. Gas generators were combusted at the pressure of 1 MPa, 3 MPa and 5 MPa in the combustion chamber and the burning rates were determined. It was stated that the addition of metal oxides into the composition of the gas generators improves ignition at low pressure and increases the burning rate. The use of the mechanical MgAl alloys as a fuel allowed the ignition of the gas generator at a lower temperature. The method of thermogravimetric/differential thermal analyzer (TG/DTA) was used to investigate the effect of metal oxides addition on the AN/MgAl-based gas generators thermal decomposition characteristics.

Nanothermite with Meringue-like Morphology: From Loose Powder to Ultra-porous Objects

The goal of the protocol described in this article is to prepare aluminothermic compositions (nanothermites) in the form of porous, monolithic objects. Nanothermites are combustible materials made up of inorganic fuel and an oxidizer. In nanothermite foams, aluminum is the fuel and aluminum phosphate and tungsten trioxide are the oxidizing moieties. The highest flame propagation velocities (FPVs) in nanothermites are observed in loose powders and FPVs are strongly decreased by pelletizing nanothermite powders. From a physical standpoint, nanothermite loose powders are metastable systems. Their properties can be altered by unintentional compaction induced by shocks or vibrations or by the segregation of particles over time by settling phenomena, which originates from the density differences of their components. Moving from a powder to an object is the challenge that must be overcome to integrate nanothermites in pyrotechnic systems. Nanothermite objects must have both a high open porosity and good mechanical strength. Nanothermite foams meet both of these criteria, and they are prepared by dispersing a nano-sized aluminothermic mixture (Al/WO3) in orthophosphoric acid. The reaction of aluminum with the acid solution gives the AlPO4 "cement" in which Al and WO3 nanoparticles are embedded. In nanothermite foams, aluminum phosphate plays the dual role of binder and oxidizer. This method can be used with tungsten trioxide, which is not altered by the preparation process. It could probably be extended to some oxides, which are commonly used for the preparation of high performance nanothermites. The WO3-based nanothermite foams described in this article are particularly insensitive to impact and friction, which makes them far safer to handle than loose Al/WO3 powder. The fast combustion of these materials has interesting applications in pyrotechnic igniters. Their use in detonators as primers would require the incorporation of a secondary explosive in their composition.

High-Performance Integrated Self-Package Flexible Li-O2 Battery Based on Stable Composite Anode and Flexible Gas Diffusion Layer

With the rising development of flexible and wearable electronics, corresponding flexible energy storage devices with high energy density are required to provide a sustainable energy supply. Theoretically, rechargeable flexible Li-O₂ batteries can provide high specific energy density; however, there are only a few reports on the construction of flexible Li-O₂ batteries. Conventional flexible Li-O₂ batteries possess a loose battery structure, which prevents flexibility and stability. The low mechanical strength of the gas diffusion layer and anode also lead to a flexible Li-O₂ battery with poor mechanical properties. All these attributes limit their practical applications. Herein, the authors develop an integrated flexible Li-O₂ battery based on a high-fatigue-resistance anode and a novel flexible stretchable gas diffusion layer. Owing to the synergistic effect of the stable electrocatalytic activity and hierarchical 3D interconnected network structure of the free-standing cathode, the obtained flexible Li-O₂ batteries exhibit superior electrochemical performance, including a high specific capacity, an excellent rate capability, and exceptional cycle stability. Furthermore, benefitting from the above advantages, the as-fabricated flexible batteries can realize excellent mechanical and electrochemical stability. Even after a thousand cycles of the bending process, the flexible Li-O₂ battery can still possess a stable open-circuit voltage, a high specific capacity, and a durable cycle performance.

Creation of energetic biothermite inks using ferritin liquid protein

Energetic liquids function mainly as fuels due to low energy densities and slow combustion kinetics. Consequently, these properties can be significantly increased through the addition of metal nanomaterials such as aluminium. Unfortunately, nanoparticle additives are restricted to low mass fractions in liquids because of increased viscosities and severe particle agglomeration. Nanoscale protein ionic liquids represent multifunctional solvent systems that are well suited to overcoming low mass fractions of nanoparticles, producing stable nanoparticle dispersions and simultaneously offering a source of oxidizing agents for combustion of reactive nanomaterials. Here, we use iron oxide-loaded ferritin proteins to create a stable and highly energetic liquid composed of aluminium nanoparticles and ferritin proteins for printing and forming 3D shapes and structures. In total, this bioenergetic liquid exhibits increased energy output and performance, enhanced dispersion and oxidation stability, lower activation temperatures, and greater processability and functionality.

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.

Highly reactive Al–Cr2O3 coating for electric-explosion applications

Electrophoretic deposition is a promising general strategy to design electric-explosion device with nanoenergetic material coatings (e.g. Al–Cr₂O₃).

Core-Shell Al-Polytetrafluoroethylene (PTFE) Configurations to Enhance Reaction Kinetics and Energy Performance for Nanoenergetic Materials

The energy performance of solid energetic materials (Al, Mg, etc.) is typically restricted by a natural passivation layer and the diffusion-limited kinetics between the oxidizer and the metal. In this work, we use polytetrafluoroethylene (PTFE) as the fluorine carrier and the shielding layer to construct a new type of nano-Al based fuels. The PTFE shell not only prevents nano-Al layers from oxidation, but also assists in enhancing the reaction kinetics, greatly improving the stability and reactivity of fuels. An in situ chemical vapor deposition combined with the electrical explosion of wires (EEW) method is used to fabricate core-shell nanostructures. Studies show that by controlling the stoichiometric ratio of the precursors, the morphology of the PTFE shell and the energy performance can be easily tuned. The resultant composites exhibit superior energy output characters than that of their physically mixed Al/PTFE counterparts. This synthetic strategy might provide a general approach to prepare other high-energy fuels (Mg, Si).

Nanocomposite of Fe2 O3 @C@MnO2 as an Efficient Cathode Catalyst for Rechargeable Lithium-Oxygen Batteries

A new design and synthesis of Fe2O3 @C@MnO2 nanocomposite via aerosol spray pyrolysis and electrodeposition is reported for application in rechargeable Li-O2 batteries. Owing to the superior oxygen reduction/evolution reaction bifunctional catalytic activities attributed to the combined function of Fe2O3 and MnO2 and facile charge transfer in the carbon matrix, the nanocomposite exhibits long life, large capacity, and a small overpotential in Li-O2 batteries.

Metal Iodate-Based Energetic Composites and Their Combustion and Biocidal Performance

The biological agents that can be weaponized, such as Bacillus anthracis, pose a considerable potential public threat. Bacterial spores, in particular, are highly stress resistant and cannot be completely neutralized by common bactericides. This paper reports on synthesis of metal iodate-based aluminized electrospray-assembled nanocomposites which neutralize spores through a combined thermal and chemical mechanism. Here metal iodates (Bi(IO3)3, Cu(IO3)2, and Fe(IO3)3) act as a strong oxidizer to nanoaluminum to yield a very exothermic and violent reaction, and simultaneously generate iodine as a long-lived bactericide. These microparticle-assembled nanocomposites when characterized in terms of reaction times and temporal pressure release show significantly improved reactivity. Furthermore, sporicidal performance superior to conventional metal-oxide-based thermites clearly shows the advantages of combining both a thermal and biocidal mechanism in spore neutralization.

Bioinspired High-Performance Energetic Materials Using Heme-Containing Crystals

Synthetic hemozoin crystals (β-hematin) are assembled with aluminium nanoparticles (nAl) to create a nanomaterial composite that is highly energetic and reactive. The results here demonstrate that hemozoin rapidly oxidizes the nAl fuel to release large amounts of energy (+12.5 ± 2.4 kJ g(-1) ).

A Carbon- and Binder-Free Nanostructured Cathode for High-Performance Nonaqueous Li-O2 Battery

Operation of the nonaqueous Li-O2 battery critically relies on the reversible oxygen reduction/evolution reactions in the porous cathode. Carbon and polymeric binder, widely used for the construction of Li-O2 cathode, have recently been shown to decompose in the O2 environment and thus cannot sustain the desired battery reactions. Identifying stable cathode materials is thus a major current challenge that has motivated extensive search for noncarbonaceous alternatives. Here, RuO x /titanium nitride nanotube arrays (RuO x /TiN NTA) containing neither carbon nor binder are used as the cathode for nonaqueous Li-O2 batteries. The free standing TiN NTA electrode is more stable than carbon electrode, and possesses enhanced electronic conductivity compared to TiN nanoparticle bound with polytetrafluoroethylene due to a direct contact between TiN and Ti mesh substrate. RuO x is electrodeposited into TiN NTA to form a coaxial nanostructure, which can further promote the oxygen evolution reaction. This optimized monolithic electrode can avoid the side reaction arising from carbon material, which exhibits low overpotential and excellent cycle stability over 300 cycles. These results presented here demonstrate a highly effective carbon-free cathode and further imply that the structure designing of cathode plays a critical role for improving the electrochemical performance of nonaqueous Li-O2 batteries.

Direct deposit laminate nanocomposites with enhanced propellent properties

One of the challenges in the use of energetic nanoparticles within a polymer matrix for propellant applications is obtaining high particle loading (high energy density) while maintaining mechanical integrity and reactivity. In this study, we explore a new strategy that utilizes laminate structures. Here, a laminate of alternating layers of aluminum nanoparticle (Al-NPs)/copper oxide nanoparticle (CuO-NPs) thermites in a polyvinylidene fluoride (PVDF) reactive binder, with a spacer layer of PVDF was fabricated by a electrospray layer-by-layer deposition method. The deposited layers containing up to 60 wt % Al-NPs/CuO-NPs thermite are found to be uniform and mechanically flexible. Both the reactive and mechanical properties of laminate significantly outperformed the single-layer structure with the same material composition. These results suggest that deploying a multilayer laminate structure enables the incorporation of high loadings of energetic materials and, in some cases, enhances the reactive properties over the corresponding homogeneous structure. These results imply that an additive manufacturing approach may yield significant advantages in developing a tailored architecture for advanced propulsion systems.