Nanothermite Research Articles

Facile preparation and energetic characteristics of core-shell Al/CuO metastable intermolecular composite thin film on a silicon substrate

Nanostructured energetic composites, in which the oxidizing component and the reducing component are uniformly distributed and intimately contacted, are attracting much attention in recent years. In this study, a new method is developed to facilely prepare CuO nanotubes and accordingly the core-shell structured Al/CuO metastable intermolecular composite (MIC) thin film on a silicon substrate. Cr and Cu thin films are sputter-deposited onto the silicon substrate sequentially, where Cr thin film functions as the adhesion layer. The silicon substrate is then immersed in a mixture of NaOH and (NH4)2S2O8 to form one-dimensional Cu(OH)2 nanostructures, which are then dehydrated at 180°C to form CuO nanotubes. Nano Al is then sputter-deposited around CuO to obtain core-shell Al/CuO MIC. The morphological, structural and compositional information of the core-shell Al/CuO MIC is characterized by field emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The energy-release characteristics of core-shell Al/CuO MIC are studied by differential scanning calorimetry and differential thermal analysis, and the preliminary laser ignition test is conducted by using pulsed Nd:YAG laser. The results show that the prepared Al/CuO MIC possesses a fine core-shell structure and is highly exothermic. The preparation method developed is suitable for the facile synthesis of non-cracking core-shell Al/CuO MIC thin film that can be integrated with microelectromechanical systems to realize functional energetic chips.

Metastable intermolecular composites of Al and CuO nanoparticles assembled with graphene quantum dots

Metastable intermolecular composites (MICs) have attracted great attention during the last two decades owing to their potential applications for both civilian and military purposes.

Thermo-chemical and energetic properties of layered nano-thermite composites

Thermochemical properties and microstructures of layered aluminum (Al) and iron oxide (Fe2O3) nano-thermite were investigated via thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and scanning electron microscopy (SEM) for developing a new type of metastable intermolecular composites (MIC). The nanoparticles of Al and Fe2O3 were dispersed in solution and deposited separately on stainless steel electrodes by means of the electrophoretic deposition (EPD) process. These nanoparticles were dispersed and deposited without any surfactant and additive, which eliminates potential contaminates in products. In order to produce layered structures, nanoparticles were deposited in a sequence which promotes effective bonding between two different types of nanoparticles. SEM images demonstrate a layered structure with the intimate contact between Al and Fe2O3. DSC data was collected to characterize the onset temperature and energy release per unit mass from the layered composites with different molar ratios of Al/Fe2O3. It is revealed, based on the consistent onset temperatures from different composites, that the ignition of Al and Fe2O3 layers is closely associated with oxygen which is produced from thermal decomposition of Fe2O3. In addition, the thickness of the reaction zone is restricted by the diffusion length of oxygen across the layer-to-layer interface, which results in a varying degree of reaction completion within the composite and subsequently the distinct energy release values per unit mass. The decomposition of Fe2O3 nanoparticles, diffusion path of oxygen and interfacial contact between Al and Fe2O3 layers are found to determine the energetic properties of layered thermite composites.

Application of Al/B/Fe2O3 Nano Thermite in Composite Solid Propellant

Hydroxyl-terminated polybutadiene (HTPB) propellant were prepared with different content of Al/B/Fe2O3 nano thermite, and the mechanical, thermal and energetic performances were studied. Al/B/Fe2O3 nano thermite exhibited good compatibility with HTPB and dioctyl sebacate (DOS) through differential scanning calorimetry (DSC) tests. Mechanical experiments show that the mechanical properties of HTPB propellant could be improved by the addition of a small quantity of Al/B/Fe2O3 nano thermite, compared with the absence of Al/B/Fe2O3 nano thermite. For example, with the addition of 3% Al/B/Fe2O3 nano thermite, the tensile strength and elongation of propellant had the increase of 15.3% and 32.1%, respectively. Thermal analysis indicated that the decomposition of ammonium perchlorate (AP) in HTPB propellant could be catalyzed by Al/B/Fe2O3 nano thermite, the high-temperature exothermic peak of AP was shifted to lower temperature by 70.8 °C when the content of Al/B/Fe2O3 nano thermite was 5%, and the heat released was enhanced by 70%. At the same time, the heat of explosion of HTPB propellant could also be enhanced by the addition of Al/B/Fe2O3 nano thermite.

Density functional theory study of high-energy metal (Al, Mg, Ti, and Zr)/CuO composites

We investigated the geometric and electronic structures and stability of high-energy metal metastable intermolecular composites (Al, Mg, Ti, and Zr)/CuO(111) between metal layers and a CuO(111) substrate by density functional theory.

Large‐Scale Synthesis of a Porous Co3O4 Nanostructure and Its Application in Metastable Intermolecular Composites

AbstractThree‐dimensional nanostructured porous Co3O4 was synthesized on a silicon substrate via a hydrothermal route in conjunction with annealing treatment. The structure and morphology of the obtained Co3O4 samples were systemically examined using field‐emission scanning electron microscopy and X‐ray diffraction. The Co3O4 structures were composed of nanosheets forming a pore‐network architecture that promoted Al penetration into its inner regions during deposition resulting in enhanced interfacial contact area, which significantly improve metastable intermolecular composites (MICs) burning rate and the release of energy. The successfully Co3O4 was used to synthesize Al/Co3O4 based MICs by integration with nano‐Al deposited via thermal evaporation. The heat of reaction of Al/Co3O4, particularly the exothermic reaction before Al melting, was greatly enhanced by the Co3O4 nanostructures. The Al/Co3O4 based MICs were fabricated on a silicon substrate, which is very convenient for integrating MICs with silicon‐based microelectromechanical systems to achieve functional nanoenergetics‐on‐a‐chip.

Fast deflagration to detonation transition of energetic material based on a quasi-core/shell structured nanothermite composite

Abstract Nanothermites (also called metastable intermolecular composites), composed of nanoscale metals and metal oxides, have drawn increasing interests as energetic materials over the past two decades. Nanothermites have twice the energy density of 2,4,6-trinitroluene, and their nanostructures, functions, energy release, and reaction performance are continuously being improved. However, these materials suffer from low pressure because of low gas expansion from the reaction and incapability of deflagration to detonation transition (DDT). Fast DDT is necessary to substantially improve the reaction velocity and output pressure not only of nanothermites but also of other monomolecular organic energetic materials, such as cyclotrimethylene trinitramine (RDX) and octogen. Accordingly, this study aims to produce energetic composites material that are safe, green, and free from heavy metals. A strategy of rapid DDT acceleration is proposed by fabricating quasi-core/shell structured materials of RDX@Fe2O3–Al based on Fe2O3–Al nanothermites. A surface modifying and ultrasonic synthesis technology is also demonstrated. Scanning electron microscopy and X-ray photoelectron spectroscopy characterizations prove that the material comprises an RDX core and an Fe2O3–Al nanothermite shell. Results of closed vessel combustion tests show that the RDX@Fe2O3–Al combustion velocity accelerates to an average pressurization rate of 2.527 MPa/μs. DDT tube tests further confirm that DDT accelerates to a primer explosive level in which the run-to-detonation distances of DDT is below the test-condition limitation (

Large-scale Synthesis of Aligned MoO<sub>3</sub> Nanobelt Arrays on Silicon Substrates for Nanoenergetics-on-a-chip

Aligned MoO3 nanobelts and tree-like arrays have been synthesized onto silicon substrates by an ordinary gas cooker. The synthesis method is simple, rapid, low-cost, safe, and also suitable for large-scale fabrication. A possible growth mechanism of the nanobelts is presented based on the experimental observations. Via integrating nano-Al with the MoO3 nanobelt arrays, metastable intermolecular composites (MICs) based on Al/MoO3 nanobelt arrays are achieved. The Al/MoO3 MIC arrays have high energy density and can combust continuously by themselves at small dimensions and low density, which makes the MIC arrays synthesized on the silicon substrate, have promising applications in nanoenergetics- on-a-chip based functional devices at the micro and nanoscale. Keywords: Flame synthesis, growth mechanism, MoO3 nanobelts and tree-like arrays, nanoenergetics-on-a-chip.

Pressure loss and compensation in the combustion process of Al–CuO nanoenergetics on a microheater chip

This study investigates pressure loss and compensation in the combustion process of Al–CuO metastable intermolecular composite (MIC) on a microheater chip. A ball cell model of pressure change in the combustion process is proposed to show the effects of pressure loss on the reaction rate and efficiency of energy output at microscale. An effective compensation method for pressure loss is then developed by integrating Al–CuO MIC with CL-20 (2,4,6,8,10,12-hexanitrohexaazaisowurtzitane) onto a SiO2/Cr/Pt/Au microheater chip. The combustion processes of Al–CuO MIC with different weight percentages of fine CL-20 particles on the microheater chips are observed by high-speed video recording. Results indicate that the reaction of Al–CuO MIC is a slow combustion process that turns into intense deflagration after adding fine CL-20 particles to Al–CuO MIC. The pressure–time characteristics indicate higher maximum pressure and pressurization rate for Al–CuO/CL-20 because the pressure loss at microscale is well compensated by the addition of fine CL-20. This study proves the importance of pressure loss in the combustion process of MIC at microscale and provides an efficient compensation strategy for pressure loss to improve the reaction rate and efficiency of energy output at microscale environment.

Pressure waves generated by metastable intermolecular composites in an aqueous environment

In the present study, pressure waves generated by a metastable intermolecular composite (MIC) have been measured experimentally in an aqueous environment and correlated with flame speed measurements. Underwater experiments were performed in a 1.0 L high-pressure chamber mounted with high-resolution pressure transducers and designed with optical access. Samples consisting of a stoichiometric mixture of aluminium and copper(II)-oxide particles were evaluated. Two types of samples were synthesized; a mixture of micron-sized raw powders, and ball-milled powders with a fine-scale nano-structure. A planetary mill was used to refine reactant powders from micron- to nano-scale dimensions. The dynamics of the pressure wave and high-pressure gas bubble were monitored via pressure histories and high-speed Schlieren visualization. The effect of reactant particle size has been evaluated quantitatively. The dynamics of the pressure wave were correlated with the rate of expansion of the high-pressure gas bubble.

Fabrication, Characterization, and Energetic Properties of Metallized Fibers

Polystyrene fibers loaded with an energetic blend of nanoaluminum (n-Al) and perfluoropolyether (PFPE) were successfully fabricated via electrospinning producing nanothermite fabrics. Fibers were generated with loadings up to 17 wt % n-Al/PFPE incorporated into the fiber. Microscopy analysis by SEM and TEM confirm a uniform dispersion of PFPE treated n-Al on the outside and inside of the fibers. Metallized fibers were thermally active upon immediate ignition from a controlled flame source. Thermal analysis by differential scanning calorimetry (DSC) found no change in glass transition temperature when comparing pure polystyrene fibers with fibers loaded up to 17 wt % n-Al/PFPE. Thermal gravimetric analysis (TGA) revealed a shift in decomposition temperatures to lower onsets upon increased loadings of n-Al/PFPE blends, consistent with previous studies. Flame propagation studies confirmed that the metallized fibers are pryolants. These metallized fibers are a recent development in metastable intermolecular composites (MICs) and details of their synthesis, characterization, and thermal properties are presented.

Effects of nano-Ag on the combustion process of Al–CuO metastable intermolecular composite

Effects of nano-Ag with high thermal conductivity on the combustion wave behavior of Al–CuO MIC (metastable intermolecular composite) are studied in this paper by incorporating Al–CuO MIC with nano-Ag particles in different weight proportions. The physical and chemical characteristics of Al–CuO MIC are determined using scanning electron microscope (SEM), X-ray diffraction (XRD) and differential scanning calorimeter (DSC). The combustion wave behavior is identified by high-speed video recording (HSVR). The experimental observations confirm that the presence of nano-Ag particles improves the heat transfer efficiency. With nano-Ag increasing from 1 wt% to 10 wt%, the first exothermic peak temperature decreases from 607.8 °C to 567.6 °C, and average combustion speed (ACS) increases at first and then reduces. The most suitable amount of nano-Ag is 2 wt% with the ACS and instantaneous combustion velocity on the order of 954.0 m/s, 1562.5 m/s. Moreover, heat transfer mechanisms in the combustion process of Al–CuO MIC are better understood, especially by distinguishing conduction from convection during the combustion propagation. Furthermore, three stages (ignition, acceleration and steady combustion) of reactive propagation are observed in the combustion process. And the corresponding dominative heat transfer mechanisms in the three stages are conduction, conduction to convection transition, and convection, respectively.

Microstructured Al/Fe2O3/Nitrocellulose Energetic Fibers Realized by Electrospinning

At present, metastable intermolecular composites (MICs) have been widely studied for their potential in high-density energetic materials and nanotechnology, but the relatively low-pressure discharge in a short period of time and the oxidation of Al powders have seriously impeded their applications in rocket solid fuels and explosives. In this work, the authors successfully fabricated microstructured Al/Fe2O3/nitrocellulose (Al/Fe2O3/NC) fibers via simple electrospinning, introducing nitrocellulose (NC), a gas generator to MICs. In view of previous reports, wrapping nAl in NC fibers might reduce their further oxidation during storage. In addition, the thermal properties and elastic modulus of NC fibers were measured before and after adding Al/Fe2O3.

Development of the ReaxFF reactive force field for aluminum–molybdenum alloy

Abstract

Oxidation Dynamics of Aluminum Nanorods

ABSTRACTUnderstanding of combustion of metastable intermolecular composites, including the burning of aluminum nanoparticles, is critical for broad applications such as propulsion, explosives and other pyrotechnics. Aluminum nanorods (Al-NR) with oxidized shells are good candidates for stable fuel-oxidizer combinations. We investigate the oxidation dynamics of Al-NRs of different diameters (26, 36 and 46 nm) but the same aspect ratio using molecular dynamics simulations. We heat one end of the Al-NR to 1100 K and then study the oxidation reaction at the interface of the alumina shell and the Al core. We find: (1) heat produced by oxidation causes the melting of nanorods; (2) heat release is accelerated due to Al-O reaction at outside-shell and core-shell interfaces; and (3) the larger surface-to-volume ratio causes faster burning of thinner nanorods. We present results for the oxidation speed of nanorods.

Preparation and characterisation of nanofibrous CuO/Al metastable intermolecular composite films

Metastable intermolecular composite (MIC) has been widely touted for their potential to fulfil the objectives of high energetic materials and nanotechnology. In this study, nanofibrous CuO/Al MIC films on the silicon substrate were successfully synthesised by evaporating and depositing Al on the surface of nanoporous CuO films, which were prepared by calcinating polyvinylpyrrolidone (PVP)/Cu(NO3)2 films obtained through the electrospinning process. The structures and energetic properties of the nanofibrous CuO/Al MIC films were characterised by a scanning electron microscope, X-ray diffraction, Fourier transform-infrared spectroscopy, TGA–DSC and open-air combustion experiments. The results revealed that the electrospinning process was an effective way to prepare energetic films. The optimised calcination temperature of the PVP/Cu(NO3)2 composite films was 500°C, and the starting reaction temperature of the nanoporous CuO/Al MIC film was 532°C.

Effect of metal oxide nanostructures on the explosive property of metastable intermolecular composite particles

The fineness of reactants, degree of intermixing and interfacial contact area between fuel and oxidizer comprising of metastable intermolecular composite (MIC) particles are important factors to determine their overall kinetics of burning process. Here, we demonstrate a viable method for enhancing the explosive property of MICs by tailoring the nanostructures of oxidizer located in close proximity to fuel nanoparticles. The measured pressurization rate for a specific sample of solid Al nanoparticle (fuel)-porous CuO nanowire (oxidizer) MICs exploded in a closed vessel was found to be increased by a factor of ~ 10 compared with that for solid Al nanoparticle-solid CuO nanoparticle MICs. In addition, with the assistance of intensive sonication energy, the fabricated porous oxidizer nanowires were disintegrated into oxidizer nanoparticles, which considerably reduced the pressurization rate when they were ignited with fuel nanoparticles. This suggests that the morphology of oxidizer nanostructures from solid nanoparticles (i.e. 0-D) to porous nanowires (i.e. 1-D) play a key role in significantly changing the interfacial contact area with fuel nanoparticles so that nascent oxygen can be produced effectively for promoting the explosive property of the fuel nanoparticles.

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.

Simultaneous Pressure and Optical Measurements of Nanoaluminum Thermites: Investigating the Reaction Mechanism

This work investigates the reaction mechanism of metastable intermolecular composites by collecting simultaneous pressure and optical signals during combustion in a constant-volume pressure cell. Nanoaluminum and three different oxidizers are studied: CuO, SnO2, and Fe2O3. In addition, these mixtures are blended with varying amounts of WO3 as a means to perturb the gas release in the system. The mixtures with CuO and SnO2 exhibit pressure signals that peak on timescales faster than the optical signal, whereas themixtures containingFe2O3 do not show this behavior. The burn time is found to be relatively constant for bothCuOandSnO2, evenwhen a large amount ofWO3 is added. For Fe2O3, the burn time decreases asWO3 is added, and the temperature increases. The results are consistent with the idea that oxidizers such as CuO and SnO2 decompose and release gaseous oxidizers fast, relative to the burning, and this is experimentally seen by an initial pressure rise followed by a prolonged optical emission. In this case, the burning is rate limited by the aluminum, and it is speculated to be similar to the burning of aluminum in a pressurized oxygenated environment. For the Fe2O3 system, the pressure and optical signals occur concurrently, indicating that the oxidizer decomposition is the rate-limiting step.

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.