Nanoenergetic Materials Research Articles

Analysis on thermite reactions of CuO nanowires and nanopowders coated with Al

A thermite reaction between the CuO nanowires and the deposited nano-Al was studied. The heat energy obtained from the reaction was compared with that of CuO and Al nanopowders mixture. CuO nanowires were grown and patterned on glass substrate and nano-Al was deposited on top of it to produce nanoenergetic materials. The released heat energy of the reaction was approximately 1186 J/g, which was higher than that of mixed CuO and Al nanopowders. The higher heat formation mechanism could be explained by the intimate contact and reactivity between the CuO nanowires and the nano-Al.

Gas-Phase Synthesis of Bimetallic Oxide Nanoparticles with Designed Elemental Compositions for Controlling the Explosive Reactivity of Nanoenergetic Materials

We demonstrate a simple and viable method for controlling the energy release rate and pressurization rate of nanoenergetic materials by controlling the relative elemental compositions of oxidizers. First, bimetallic oxide nanoparticles (NPs) with a homogeneous distribution of two different oxidizer components (CuO and Fe2O3) were generated by a conventional spray pyrolysis method. Next, the Al NPs employed as a fuel were mixed with CuO-Fe2O3bimetallic oxide NPs by an ultrasonication process in ethanol solution. Finally, after the removal of ethanol by a drying process, the NPs were converted into energetic materials (EMs). The effects of the mass fraction of CuO in the CuO-Fe2O3bimetallic oxide NPs on the explosive reactivity of the resulting EMs were examined by using a differential scanning calorimeter and pressure cell tester (PCT) systems. The results clearly indicate that the energy release rate and pressurization rate of EMs increased linearly as the mass fraction of CuO in the CuO-Fe2O3bimetallic oxide NPs increased. This suggests that the precise control of the stoichiometric proportions of the strong oxidizer (CuO) and mild oxidizer (Fe2O3) components in the bimetallic oxide NPs is a key factor in tuning the explosive reactivity of EMs.

Nanoenergetic Gas-Generators: principles and applications

Metastable Intermolecular Composites or so-called Nanoenergetic Materials have been widely touted for their potential to fulfill dreams in high density energetic materials and nanotechnology. They are likely to become the next-generation explosives, propellants and primes as they enable flexibility in energy density and power release through control of particle size, tunable stoichiometry and choice of fuel and oxidizer. Despite intense examination by scientists and engineers worldwide the temperature progress and velocity of the thermal front propagation on the nanostructured formulations, however, gas pressure evolution and rate of gas release are not well investigated and understood. This issue has seriously impeded realization of various potential emerging applications envisioned in rocket solid fuels and explosives, which require a high pressure discharge in a short period of time as well as in bio-defeat systems. This highlight describes principles and development of Nanoenergetic Gas-Generators (NGG) systems comprising high PV (pressure × volume) values and energy densities (up to 25.7 kJ cm−3) that may have several potential civil and military applications. Our recent study revealed that Al/Bi2O3 and Al/I2O5 nanocomposites can generate a transient pressure pulse more than three times larger than that during the explosion of traditional thermite reactive mixtures.

Thermite Reaction Between CuO Nanowires and Al for the Crystallization of a-Si

Nanoenergetic materials were synthesized and the thermite reaction between the CuO nanowires and the deposited nano-Al by Joule heating was studied. CuO nanowires were grown by thermal annealing on a glass substrate. To produce nanoenergetic materials, nano-Al was deposited on the top surface of CuO nanowires. The temperature of the first exothermic reaction peak occurred at approximately <TEX>$600^{\circ}C$</TEX>. The released heat energy calculated from the first exothermic reaction peak in differential scanning calorimetry, was approximately 1,178 J/g. The combustion of the nanoenergetic materials resulted in a bright flash of light with an adiabatic frame temperature potentially greater than <TEX>$2,000^{\circ}C$</TEX>. This thermite reaction might be utilized to achieve a highly reliable selective area crystallization of amorphous silicon films.

Multilayered Al/CuO thermite formation by reactive magnetron sputtering: Nano versus micro

Multilayered Al/CuO thermite was deposited by a dc reactive magnetron sputtering method. Pure Al and Cu targets were used in argon–oxygen gas mixture plasma and with an oxygen partial pressure of 0.13 Pa. The process was designed to produce low stress (&amp;lt;50 MPa) multilayered nanoenergetic material, each layer being in the range of tens nanometer to one micron. The reaction temperature and heat of reaction were measured using differential scanning calorimetry and thermal analysis to compare nanostructured layered materials to microstructured materials. For the nanostructured multilayers, all the energy is released before the Al melting point. In the case of the microstructured samples at least 2/3 of the energy is released at higher temperatures, between 1036 and 1356 K.

Ultrafast Condensed-Phase Emission from Energetic Composites of Teflon and Nanoaluminum

Time and wavelength-resolved spectroscopy was used to monitor optical emission from picosecond flash-heated nanoenergetic materials consisting of 50 nm diameter Al/Al(2)O(3) core-shell nanoparticles in a matrix of Teflon(AF) oxidizer. The Al/Teflon was confined between optical windows to emphasize condensed-phase emission rather than emission from gas-phase reaction products. The Al/Teflon emission is compared to control samples of bare Al nanoparticles or nanoparticles in a nominally inert polybutadiene matrix (Al/PB). In all three materials just two types of emission were observed, a broadband (BB) emission peaked at 320 nm stretching out past 700 nm, and a narrowband (NB) emission with approximately 30 nm wide bands at 310 and 400 nm, coincident with the most intense Al atomic emission lines. The BB emission is attributed to a laser-generated Al plasma and the NB emission to excited-state Al atoms in a dense medium. Compared to Al/PB, the plasma in Al/Teflon emits with higher intensity and longer duration. The Al/Teflon excited-state NB emission was also more intense. The energy release characterizing ignition in Al/Teflon could be monitored via the increased emission intensity of the BB and NB species. We find the ignition process can be described with a global time constant of 100 ps, about twice the approximately 50 ps time constant for the initiation process seen in earlier work (Zamkov, M. A.; Conner, R. W.; Dlott, D. D., J. Phys. Chem. C 2007, 111, 10278), where infrared spectroscopy was used to monitor the disappearance of C-F stretch transitions.

Crystallization of amorphous Si thin films by the reaction of MoO 3/Al nanoengineered thermite

In this work, we investigated a new crystallization method for amorphous silicon (a-Si) using a mixture of nano-energetic materials: molybdenum oxide and aluminum (MoO 3/Al). The purpose of using nano-energetic materials is to improve the performance of a-Si films with a self-propagating exothermic reaction over a period of microseconds without any substrate damage. The mixture of MoO 3/Al nanopowders was used for a thermite reaction for crystallization of a-Si thin films. Characterization results showed that a-Si thin films were successfully crystallized to poly-Si as evidenced by a Raman peak near 519 cm − 1 . The crystalline volume fraction of poly-Si after the nanoengineered thermite reaction was about 94.7% and poly-Si grains was uniformly distributed with an average grain size of around 40–50 nm. These results indicate that high quality poly-Si thin films were successfully prepared on the substrate.

Micro/Nano Functional Manufacturing: From Microthruster to Nano Energetic Material to Micro/Nano Initiator

Functional manufacturing technologies are becoming more and more important to the manufacturing industry and research. As promising categories of functional manufacturing, micro and nano manufacturing have received steadily growing interests in recent years. In this paper, as typical examples to demonstrate micro and nano manufacturing, our work on microthruster, nano energetic material, and micro/nano initiator is presented. Microspacecraft is one application of microsystem in space. In a microspacecraft, a micropropulsion system is required for station keeping, attitude control, and orbit adjust. New silicon and ceramic microthrusters are described. Energetic materials including propellants, explosives, and pyrotechnics have found diverse applications. Nano energetic materials (nEMs) have improved performances in energy release, ignition, and mechanical properties compared to their bulk/micro counterparts. A novel nano Al and CuO nanowire based nEM is discussed. Electro-explosive devices (EEDs) activated by electrical energy are used to initiate an explosive, burning, electrical, or mechanical train. EEDs have found numerous applications in triggering the inflation of airbags in automobiles, micropropulsion, and arm fire/safe devices for ordnance systems. An innovative EED is developed by integrating Al/CuO based nEM with a Au/Pt/Cr micro heater on a substrate.

Fabrication of Metal Oxide Nanoparticles by Highly Exothermic Reactions

AbstractThe development of two methods using highly exothermic oxidation reactions to synthesize nanostructured oxide particles is described. The first method uses solution combustion to produce a high temperature front that moves through the sample and produces the nanoparticles. For example, Bi2O3 nanoparticles are produced using a solution of molten metal nitrates and glycine. The glycine (fuel) is completely combusted during the thermal decomposition of the (oxidizer) nitrates and generates a temperature front that propagates through the sample. The second method produces nanoparticles by a self‐propagating high‐temperature reaction from stoichiometric powder mixtures of metal oxides (or carbonates) and carbon. The exothermic oxidation of the carbon generates a propagating high‐temperature front at a velocity in the range of 0.1–2.5 mm/s that converts the reactants to products. In both cases, the synthesis was completed within a few seconds. In both methods, a higher maximum combustion temperature and larger oxide particle size were obtained following an increase in the fuel concentration. The main advantages of these synthesis methods technologies are simplicity, short reaction time, low reactant costs, and no external energy consumption. The methods can be used to synthesize nanoparticles for various applications including nanoenergetic materials, catalysts and electronic components.

Synthesis of high nitrogen doping of carbon nanotubes and modeling the stabilization of filled DAATO@CNTs (10,10) for nanoenergetic materials

In this work, we have performed synthesis of nitrogen-doped carbon nanotubes using chemical vapor deposition method. Morphology, structure and composition of the carbon nanotubes (CNTs), as well as concentration and distribution of nitrogen inside CNTs are characterized by scanning electron microscopy, transmission electron microscopy, X-ray dispersive spectroscopy and X-ray photoelectron spectroscopy techniques. A bamboo-like structure of the nitrogen-doped CNTs has been observed. Temperature dependency on the synthesis of nitrogen-doped carbon nanotubes has been investigated and discussed. Diameter and growth rate of these hybrid materials are obviously temperature dependent. Nitrogen concentration inside the CNTs increases with declining synthesis temperature. Nitrogen-doped CNTs with nitrogen content up to 10.4 at% can be achieved at a low temperature of 800 oC. Synthesis of the high nitrogen CNTs proposes a feasible way to develop novel nanoenergetic materials. Besides the experimental study, we have carried out Density Functional Theory calculations on five energetic molecules named n-oxides of 3,3′-azo-bis(6-amino-1,2,4,5-tetrazine) (DAATO), where n=1–5 refer to oxygen atoms, encapsulated in CNTs (10,10), in order to investigate the chemical stabilization of filled DAATO_n inside CNTs (10,10). In fact, the predicted adsorption energy values confirmed the chemical stability of the hybrid systems DAATO_n@CNTs (10,10) under normal conditions.

Experimental flame speed in multi-layered nano-energetic materials

This paper deals with the reaction of dense Metastable Intermolecular Composite (MIC) materials, which have a higher density than conventional energetic materials. The reaction of a multilayer thin film of aluminum and copper oxide has been studied by varying the substrate material and thicknesses. The in-plane speed of propagation of the reaction was experimentally determined using a time of- flight technique. The experiment shows that the reaction is completely quenched for a silicon substrate having an intervening silica layer of less than 200 nm. The speed of reaction seems to be constant at 40 m/s for silica layers with a thickness greater than 1 μm. Different substrate materials such as glass and photoresist were also used.

Rapid initiation of reactions in Al/Ni multilayers with nanoscale layering

Research into nanoenergetic materials is enabling new capabilities for controlling exothermic reaction rates and energy output, as well as new methods for integrating these materials with conventional electronics fabrication techniques. Many reactions produce primarily heat, and in some cases it is desirable to increase the rate of heat release beyond what is typically observed. Here we investigate the Al–Ni intermetallic reaction, which normally propagates across films or foils at rates lower than 10 m/s. However, models and experiments indicate that local heating rates can be very high (10 7 K/s), and uniform heating of such a multilayer film can lead to a rapid, thermally explosive type of reaction. With the hopes of using a device to transduce electrical energy to kinetic energy of a flyer plate in the timescale of 100's of nanoseconds, we have incorporated a Ni/Al nanolayer film that locally heats upon application of a large electrical current. We observed flyer plate velocities in the 2–6 km/s range, corresponding to 4–36 kJ/g in terms of specific kinetic energy. Several samples containing Ni/Al films with different bilayer thicknesses were tested, and many produced additional kinetic energy in the 1.1–2.3 kJ/g range, as would be expected from the Ni–Al intermetallic reaction. These results provide evidence that nanoscale Ni/Al layers reacted in the timescale necessary to contribute to device output.

A mesoscopic model of the intermixing during nanoenergetic materials processing

A general mesoscopic model for the simulation of thin-film vapor deposition applied to energetic materials, specifically bimetallic multilayers, is presented. We describe the setup of this mesoscopic simulator developed in the frame of a multiscale study by implementing ab initio data into a set of differential equations. We present numerical results relative to the formation of barrier layers as a result of interdiffusion between successive bimetallic AlNi multilayers. The key role of the vacancies species created during deposition is highlighted.

Enhanced reactivity of nanoenergetic materials: A first-principles molecular dynamics study based on divide-and-conquer density functional theory

Integration of nanowires and nanoparticles of energetic materials into semiconducting structures is giving birth to “nanoenergetics-on-a-chip” technology. Understanding and controlling the reactions of nanoenergetic materials pose a theoretical challenge for combining quantum-mechanical accuracy with large scales to capture nanostructural effects. Recent developments in linear-scaling density functional theory have set a stage for first-principles molecular dynamics simulation of thermite reaction at an Al∕Fe2O3 interface. Here, we report the finding of a concerted metal-oxygen flip mechanism that enhances mass diffusion and reaction rate at the interface. This mechanism leads to two-stage reactions, which may explain recent experimental observation in thermite nanowire arrays.

CuO Nanowires Grown from Cu Film Heated Under a N&lt;SUB&gt;2&lt;/SUB&gt;/O&lt;SUB&gt;2&lt;/SUB&gt; Flow

Pure, large-area, and aligned CuO nanowires are realized from copper thin film deposited onto silicon substrate by thermal annealing under a N2/O2 gas flow. The as-prepared pure and vertically aligned CuO nanowires along silicon substrate have several advantages over previous approaches such as easier integration into silicon based micro systems, more convenience for subsequent elements deposition, and higher heat of reaction for realization of CuO/Al based nano energetic materials. It is found that long and aligned nanowires can only be formed within a narrow temperature range from 400 to 500 degrees C. A N2/O2 gas flow rate of 400/100 sccm is moderate for realizing long and aligned CuO nanowires. The synthesized nanowires and thin film beneath the nanowires are confirmed to be pure CuO using X-ray diffraction. The CuO nanowires are found to be bicrystal by high resolution transmission electron microscopy.

Nanoenergetic materials: boron nanoparticles from the pyrolysis of decaborane and their functionalisation

The surfaces of boron nanoparticles 10-150 nm in diameter, prepared by gas phase pyrolysis of decaborane vapour at 1 atm and 700-900 degrees C, can be halogenated by treatment with Br2 or XeF2; the surface halogenation somewhat increases the onset temperature for the oxidation of the particles under O2.

Crystallization of amorphous silicon thin films using nanoenergetic intermolecular materials with buffer layers

Optimization of the crystallization of amorphous silicon (a-Si) using a mixture of nanoenergetic materials of iron oxide/aluminum (Fe 2O 3/Al) was studied. To achieve high-quality polycrystalline Si (poly-Si) thin films, silicon oxide (SiO 2) and silver (Ag) layer were deposited on the a-Si as buffer layers to prevent the metal diffusion in a-Si during thermite reaction and to transport the thermal energy released from nanoenergetic materials, respectively. Raman measurement was used to define the crystallinity of poly-Si. For molar ratio of Al and Fe of 2 with 100-nm-thick-SiO 2, Raman measurement showed the 519.59 cm −1 of peak position and the 5.08 cm −1 of full width at half maximum with 353 MPa of low tensile stress indicating high quality poly-Si thin film. These results showed that optimized thermite reaction could be used successfully in crystallization of a-Si to high -quality poly-Si thin films.

Integrating Al with NiO nano honeycomb to realize an energetic material on silicon substrate

Nano energetic materials offer improved performance in energy release, ignition, and mechanical properties compared to their bulk or micro counterparts. In this study, the authors propose an approach to synthesize an Al/NiO based nano energetic material which is fully compatible with a microsystem. A two-dimensional NiO nano honeycomb is first realized by thermal oxidation of a Ni thin film deposited onto a silicon substrate by thermal evaporation. Then the NiO nano honeycomb is integrated with an Al that is deposited by thermal evaporation to realize an Al/NiO based nano energetic material. This approach has several advantages over previous investigations, such as lower ignition temperature, enhanced interfacial contact area, reduced impurities and Al oxidation, tailored dimensions, and easier integration into a microsystem to realize functional devices. The synthesized Al/NiO based nano energetic material is characterized by scanning electron microscopy, X-ray diffraction, differential thermal analysis, and differential scanning calorimetry.

Understanding the high energetic behavior of nano-energetic porous silicon

Nano-energetic materials have recently become a subject of intense interest due to improved performance in terms of energy release, ignition, and mechanical properties. Here we report the mechanism of highly energetic behavior of nano-crystalline porous silicon. We show that the nanocomposite reacts at lower temperatures than that required for the dehydration of NaClO 4·1H 2O by itself. Using time-resolved emission during energetic reaction and infrared absorption analysis after explosion, we demonstrated the formation of O and OH radicals during the explosion. A detailed chemical mechanism for the formation of O and OH radicals is presented based on QRRK estimates.

Theoretical investigation on near-infrared and visible absorption spectra of nanometallic aluminium with oxide coating in nanoenergetic materials: size and shape effects

The effects of metal core dimension, oxide shell thickness and ellipsoid aspect ratio of Al—AI2 O3 core-shell nanopar-ticles on the near-infrared and visible absorption spectra of nanocomposite Al—Al2O3/nitrocellulose(NC) film are investigated by numerical calculations. Both the size-dependent interband transitions and frequency-dependent free electron damping of the nanometallic aluminium are taken into account in the calculations. Oxidation effect of nanoaluminium is also analysed. It is shown that oxidation may enhance but may also reduce the optical absorption, depending on the excited light energy and initial dimension of nanoparticle. Metal core size and excited light energy dominate the absorption characteristic. The absorption ability of ellipsoidal nanoparticles is larger than that of spheroidal nanopar-ticles and increases by the square index as the aspect ratio increases. These calculations will provide some significant theoretical guidance for the preparation and laser ignition of nanoenergetic materials.