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Integrating Al with NiO nano honeycomb to realize an energetic material on silicon substrate
Abstract
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.
... The Al/NiO thermite was already prepared by physical mixing [15,16], sputtering deposition [1,17], vacuum filtration [18], thermal evaporation [19], and electrophoretic deposition [10]. In recent years, some theoretical calculations were performed to study the reaction of the Al/NiO nanothermite. ...
... Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) are widely used to characterize the thermal reaction properties of the nanothermites. Some experiments have revealed that the reaction of the Al/NiO nanothermite presents a twice heat release phenomenon [1,15,17,19]. However, few researchers have studied the formation mechanism of the twice exothermic peaks during the Al/NiO thermite reaction, especially for these thermites with nanomultilayer morphology. ...
... Furthermore, some Ni atoms penetrate the aluminum oxide film to enter the Al layers and interact with Al to form Al-Ni phase. This phenomenon is consistent with the experimental and theoretical results [13,[16][17][18][19]49]. Finally, NiO is reduced to Ni and tends to aggregate, while some interfacial Ni atoms penetrate into the Al layers where the Al atoms are oxidized to aluminum oxide. ...
Ab initio molecular dynamics was used to simulate the ignition and combustion reaction process of the Al/NiO nanothermite. The exothermic characteristics and the role of oxygen migration in the whole reaction were disclosed. The results suggest that the primary and secondary heat release are mainly caused by the interfacial and bulk thermite reaction, respectively. The interfacial oxygen migration and the breaking of Ni–O bonds cause the initial ignition. The destruction of the bulk NiO lattice is the precursor process of the secondary heat release and retards the rapid thermite reaction. The 18O isotope leads to a lower oxygen mass transport rate, having a great influence on the ignition delay time and reaction progress. The metal–oxygen flip mechanism ensures the continuous propagation of the thermite reaction. Our work may be helpful for understanding the reaction mechanisms of the metal/metal oxide thermites and optimizing the formulation design and performance of the nanothermites.
... [4] Consequently, a great many novel methods to prepare nanothermites were put forward, such as sol-gel, [5][6][7] physical mixing with sonication, [8][9][10] ar-rested reactive milling, [11] sputtering synthesis, [12,13] and so on. On the other hand, a new series of nanostructured oxidizers (nanowires, [14,15] nanorods, [16] nanotubes, [17] and nano honeycomb [18] ) were fabricated and participated in nanothermites as a result of its high specific surface area. ...
... The NiO honeycomb nanostructure has been realized by thermal oxidation of a Ni thin film deposited on a silicon substrate. [18,39] The results found that the interfacial contact area of Al/NiO nanothermite had been enhanced by a wide margin. These experimental results indicated that the release energy of the reaction process of Al/NiO nanothermite is increased up to 2.2 kJ/g. ...
... Film-honeycomb nanostructure of Al/NiO nanothermite is specifically selected on the ground that the filmhoneycomb Al/NiO nanocomposite has several advantages over previously investigated nanocomposite in some aspects such as lower ignition, enhanced interfacial contact area, reduced impurities and Al oxidation, tailored dimensions, and easier integration into a microsystem to realize functional devices. [18,39] Molecular dynamics simulation in combination with the ReaxFF is performed in this work. In the past decade, the ReaxFF has already been adopted and applied to the various types of reaction system covering combustion [44] and catalyst. ...
The diffusion and thermite reaction process of Al/NiO nanothermite composed of Al nanofilm and NiO nano honeycomb are investigated by molecular dynamics simulations in combination with the ReaxFF. The diffusion and thermite reaction are characterized by measuring energy release, adiabatic reaction temperature, and activation energy. Based on time evolution of atomic configuration and mean square displacement, the initialization of the thermite reaction process of Al/NiO nanothermite results from the diffusion of Al atoms. Under the microcanonical ensemble, it is found that the adiabatic reaction temperature of the thermite reaction process of Al/NiO nanothermite reaches over 5500 K, and activation energy is 8.43 kJ/mol. The release energy of the thermite reaction process of Al/NiO nanothermite is 2.2 kJ/g, which is in accordance with the available experimental value. With the same initial temperature, the adiabatic reaction temperature of the thermite reaction process of Al/NiO nanothermite has a tendency to decrease dramatically as the equivalence ratio increases. On the basis of chemical bond analysis, the initial temperature and equivalence ratio have great effects on the thermite reaction process, but do not significantly affect the average length of Al–Ni nor Al–O bond. Overall, the thermite reaction of film-honeycomb Al/NiO nanothermite is a complicated process instead of a theoretical equation.
... Theoretically, the gas product from the NiO/Al thermite is 10 −4 mol·g −1 , which is only 7.7% of those from Fe 2 O 3 /Al system and 2.0% from CuO/Al system [17]. Moreover, NiO/Al possesses a lower onset temperature than Fe 2 O 3 /Al [21] and CuO/Al [22,23], which is a valuable advantage to reduce ignition delay. There- fore, it is important to carry out intense investigations on the NiO/Al thermite system. ...
... Recently, there were some investigations on the preparation and properties of NiO/Al nanothermite [18,19,22]. In the literature, the com- posite of Al nanoparticles (Al-NPs) and NiO nanowires have been syn- thesized through ultrasonic mixing method, and the influence of NiO mass ratio over Al-NPs are widely discussed [19]. ...
... The study on a two-di- mensional NiO/Al nano energetic material synthesized on a silicon substrate is another approach. The NiO nano honeycomb is produced by thermal oxidation of a Ni thin film and Al is directly deposited via thermal evaporation [22]. This approach favors reducing ignition tem- perature, increasing interfacial contact area and compatibility with microsystems. ...
The performances of nanothermites largely rely on a meticulous design of nanoarchitectures and the close assembly of components. Three-dimensionally ordered macroporous (3DOM) NiO/Al nanothermite film has been successfully fabricated by integrating colloidal crystal template (CCT) method and controllable magnetron sputtering. The as-prepared NiO/Al film shows uniform structure and homogeneous dispersity, with greatly improved interfacial contact between fuel and oxidizer at the nanoscale. The total heat output of 3DOM NiO/Al nanothermite has reached 2461.27 J·g− 1 at optimal deposition time of 20 min, which is significantly more than the values of other NiO/Al structural systems that have been reported before. Intrinsic reduced ignition temperature (onset temperature) and less gas production render the wide applications of 3DOM NiO/Al nanothermite. Moreover, this design strategy can also be readily generalized to realize diverse 3DOM structured nanothermites.
... The fluorine-aluminum reaction has been widely concerned because of its high heat yield and a large number of gas products, which has important application prospects in pyrotechnics, solid rocket propellants, solid fuels, and so on. Al is present as fuel and fluoropolymers as the oxidants in most of the fluorine-aluminum reactions studied so far [1][2][3][4][5][6]. And at present, the fluoropolymers used in fluoroaluminate reactions mainly include such fluoropolymers as polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), perfluorinated polyethylene (PFPE), and fluorinated rubbers (F26, F23, etc.) [7][8][9][10]. ...
Aluminum (Al) fluoropolymer composites are widely used in the field of energetic materials. At present, it is a research hotspot to improve the agglomeration of nano-aluminum powder in fluoropolymer and make micro-nano-Al/fluorine rubber (F2601) composites. In this study, it was the first step to modify the surface of nano-aluminum (n-Al) powders, and then Al/F2601 composite microspheres were prepared by Pickering emulsion. The effects of oil–water ratio, solid content and fluorine–aluminum ratio on the stability of the emulsion were investigated. Al/F2601 microspheres with particle sizes of about ≤ 50 μm and different surface pores were prepared by controlling various conditions, which appeared the thermal decomposition peak between 485.5 °C and 524.9 °C. The combustion process of samples in the air was recorded by a high-speed camera, the composites with different F2601 contents burn stably and show a clear pattern of combustion velocity, and the maximum linear combustion velocity is up to 30.7 cm s⁻¹.
... Another common method is using thermal evaporation to fabricate tEMs with outstanding properties. For example, Al/NiO EMs based on silicon substrates have been fabricated by the thermal evaporation technique, showing the advantages of enhanced interfacial contact area, lowered ignition temperature (~400° C), reduced impurities, tailored dimensions, and strong heat capacity (~2.2 kJ/g) [93]. The sequence of steps to prepare Al/Fe2O3 EMs via this method (Figure 7a) was proposed by L. Menon et al. [94]. ...
As a promising kind of functional material, highly reactive thermite energetic materials (tEMs) with outstanding reactive activation can release heat quickly at a high reaction rate after low-energy stimulation, which is widely used in sensors, triggers, mining, propellants, demolition, ordnance or weapons, and space technology. Thus, this review aims to provide a holistic view of the recent progress in the development of multifunctional highly reactive tEMs with controllable micro/nano-structures for various engineering applications via different fabricated techniques, including the mechanical mixing method, vapor deposition method, assembly method, sol-gel method, electrospinning method, and so on. The systematic classification of novel structured tEMs in terms of nano-structural superiority and exothermic performance are clarified, based on which, suggestions regarding possible future research directions are proposed. Their potential applications within these rapidly expanding areas are further highlighted. Notably, the prospects or challenges of current works, as well as possible innovative research ideas, are discussed in detail, providing further valuable guidelines for future study.
... The traditional charging technology is therefore not suitable for MEMS. Although a series of light metal/transition metal films (Al/Ni, Al/Ti, etc. [12][13][14][15]) and light metal/metal oxide films (Al/CuO, Al/MoO 3 , Al/Fe 2 O 3 , Al/NiO, Al/Co 3 O 4 , etc. [16][17][18][19][20]) compatible with MEMS have been prepared by magnetron sputtering and electron beam evaporation, these integrated technologies will no longer be applicable if sensitive explosives are introduced. In addition, the low gas generation of these reported light metal/transition metal films and light metal/ metal oxide films caused by the lack of gas elements (such as C, H, and N) limits their applications in industrial pneumatic devices, micro-initiator devices, and actuation in lab-on-a-chip devices [21,22]. ...
Integrating energetic materials with microelectromechanical systems (MEMS) to realize miniaturized energetic chips has shown broad application prospects in micro-spacecraft, micro-satellites, ballistic correction munitions, and smart munitions. In this work, a new type of MEMS compatible Cu/ICM-101 energetic film was successfully fabricated on copper substrates by in-situ electrochemical synthesis, the morphology and ignition property of which can be effectively controlled by adjusting the voltage and electrochemical deposition time. The morphology, composition, thermal properties, and ignition performance of as-prepared Cu/ICM-101 films were characterized by scanning electron microscopy, X-ray diffraction, differential scanning calorimetry, and pulsed laser. The results show that the as-prepared Cu/ICM-101 films possesses nano porous framework structure with an exothermic heat of 1800.9 J·g⁻¹ and a thermal decomposition peak temperature of 256.4 °C. In addition, the flame height and ignition duration of which reach 10 mm and 300 μs, respectively. This work provides a reference for the integration and application of energetic materials in MEMS systems.
... e activation energies of the two exothermic peaks corresponded to the solid-solid and solid-liquid chemical reactions at two temperature stages, respectively, and also corresponded to the difficulty of the two reactions. e first solid-solid reaction between 300°C and 450°C was relatively easy to occur, while the second exothermic reaction required molten Al to break through the Al 2 O 3 barrier layer; thus, two kinds of reaction mechanisms have been speculated for the TiO 2 /Al film [20,[24][25][26][27]. e solid-solid reaction was condensed state of free molecular oxygen reaction process equation (1), in which free oxygen firstly reacted with Al and then produced the Al 2 O 3 barrier in the interface. ...
The laser-driven flyer plate is an important loading technology in high energy physics, shock wave physics, and explosive initiation application. How to generate a high-velocity and intact flyer plate by using the laser is a matter of concern for laser driving. In this study, the multilayer flyer plates (MFPs) of Al/Al2O3/Al and TiO2/Al/Al2O3/Al with adjustable performance were designed and fabricated by magnetron sputtering and analyzed by scanning electron microscopy (SEM), laser reflectance spectrometer, and differential thermal analysis (DTA). The effects of the structure and material on the output performance of MFPs were analyzed by photon Doppler velocimetry (PDV) and ultrahigh-speed video. The morphology results showed that the structure of MFPs had uniform and clear boundaries between side-by-side layers. The MFP velocity was controlled in the range of 4.0–6.0 km/s by adjusting the film thickness, structure, and thermite material with 43.1 J/cm² laser ablation. Among them, the energetic flyers with the thermite ablation layer had the highest final velocity of 5.38 km/s due to the prestored energy of TiO2/Al. By appropriately increasing the thickness of Al2O3 from 0.4 μm to 0.8 μm, the complete flight of the flyer plate to 3.72 mm can be realized. In addition, TiO2/Al thermite film had characteristics of reaction heat release and lower laser reflectivity (72.13%) than the Al layer (80.55%), which explained the velocity enhancement effect of energetic flyer plates. This work provides facile strategy to enhance the output performance of MFPs, which may facilitate the practical applications of laser driving technology.
... Nano aluminum (Al) powder has become the most commonly used metallic fuel in the MIC system due to its high energy release and low cost [5,6]. The performances of binary MIC systems composed of Al and metallic oxides (such as iron oxide (Fe 2 O 3 ), copper oxide (CuO), tungsten trioxide (WO 3 ), nickel oxide (NiO), molybdenum trioxide (MoO 3 ), cobalt oxide (Co 3 O 4 ), and bismuth trioxide (Bi 2 O 3 )) have been prepared through different methods and studied by many scholars at home and abroad [7][8][9][10][11][12][13][14][15][16][17]. ...
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.
... Up to now, there has been little research performed on this topic. In relevant literatures, magnetron sputtering, cold spray and thermal evaporation have been employed to fabricate thermite materials into micro devices [23,[30][31][32][33][34]. Nevertheless, the cost of experimental equipments is expensive and the fabrication efficiency is relatively low. ...
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 oC) and successful ignition of B/KNO3 propellent, 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.
... After Fig. 7 The reflectivity of various RMFs Fig. 8 a, b DTA plots of RMFs with two different modulation periods at heating rate of 20°C min −1 melting of Al film, the melted Al reacted with a MnO 2 beneath the MnO 2 nano-films at an onset temperature of about 830°C. This exothermal reaction occurred by a liquid-solid diffusion mechanism [32,33]. The heat releases of MnO 2 /Al-132 nm and MnO 2 /Al-400 nm at a heating rate of 20°C min −1 were 1241.0 and 1659.0 ...
Three types of reactive multilayer films (RMFs) were integrated to the energetic flyer plates (EFPs) by depositing TiO2, MnO2, and CuO onto aluminum films with different modulation periods using magnetron sputtering technology in this study. The effects of the laser ignition property and laser reflectivity on the RMFs and the thermal behavior of the RMFs were analyzed and compared with those of a single-layer Al film. A high-speed video, photonic Doppler velocimetry (PDV), and a thermal analysis were utilized to characterize the flame morphology, EFP velocity, and chemical thermal behavior, respectively. The surface reflectivities of the TiO2/Al, MnO2/Al, and CuO/Al layers were measured using laser reflectivity spectrometers. The results showed that RMFs with smaller modulation periods exhibited excellent laser ignition performances, and EFP with MnO2/Al had the best performance. These RMFs achieved flame durations of 120-220 μs, maximum flame areas of 7.523-11.476 mm2, and reaction areas of 0.153-0.434 mm2 (laser-induced with 32.20 J/cm2). Flyer velocities of 3972-5522 m/s were obtained in the EFPs by changing the material and modulation period of the RMFs. Furthermore, the rate of the chemical reaction and laser energy utilization were also enhanced by reducing the modulation period and using different material. This behavior was consistent with a one-dimensional nanosecond-laser-induced plasma model. The RMFs of MnO2/Al exhibited the highest level of energy release and promoted laser energy utilization, which could better improve the performance of laser ignition for practical application.
... In order to improve the ignition ability of SCB, multilayered metastable intermolecular composites (MICs), which usually comprised the nanoscale fuels and reductants, such as Al/CuO [12][13][14][15], Al/ MoO 3 [16,17] and Al/NiO [18][19][20], have been introduced into the SCB. The multilayer reactive films have been adopted as heat sources in many areas, such as micro-actuators and micro-ignitions. ...
In order to enhance the ignition ability and reliability of traditional electronic initiators, a novel electronic initiator has been designed to integrate with a nanothermite multilayer film and an electrode plug. The Al/CuOx nanothermite multilayer film with different thickness is deposited on the surface of the electrode plug by magnetron sputtering which uses Pt-W wire as electronic resistance. The exothermicity of Al/CuOx nanothermite multilayer film is so favourable that the ignition ability of electronic initiator is significantly improved. The full firing-voltage sensitivity of the electronic initiator is 10.8 V. The thickness of Al/CuOx multilayer film has negligible effects on the ignition time and ignition energy, but leads to great impacts on the function time, the maximum length of combustion flame and ignition ability. The electrical ignition experiments have exhibited outstanding ignition ability, since the electronic initiator can easily fire the insensitive ignition composition of boron-potassium nitrate (B-KNO3) tablet in a gap of 20.35 mm. It proves that this novel proposal of remoulding the traditional electronic ignition devices will distinctly improve the ignition ability and reliability of electronic initiator.
... In the past few years, a variety of energetic films have been prepared by physical and chemical methods [6,7]. Among them, metastable intermolecular composite, composed of nano Al and metal oxides such as Fe 2 O 3 [8], CuO [9], MoO 3 [10], NiO [11] and Co 3 O 4 [12], has been the mainly studied energetic films for NOC, although other energetic films such as Al/metal film [13,14] and organic energetic film [15] were also researched. However, with the rapid development of novel highenergy-density materials (HEDMs), synthesis of energetic coordination polymers, especially energetic metal-organic frameworks (EMOFs), provides a feasible strategy to fabricate energetic films. ...
Energetic thin films have been widely used in the field of microscale energy-demanding systems. In this work, a novel energetic metal–organic frameworks [Cd5(Mtta)9]n film is fabricated on the copper substrate through an in situ synthesis method for the first time. A 5-methyl tetrazole/copper complex is deposited to modify the copper substrate through an electrochemical-assisted strategy. The [Cd5(Mtta)9]n film is then integrated on the surface of modified copper substrate by an in situ reaction of acetonitrile with sodium azide and cadmium nitrate. The morphological, structural and compositional information of the [Cd5(Mtta)9]n film is characterized by field emission scanning electron microscopy, X-ray diffraction and infrared spectrum. The thermostabilities of the [Cd5(Mtta)9]n film are studied by differential scanning calorimetry and thermogravimetry. In addition, the preliminary laser ignition test is conducted by using pulsed Nd:YAG laser. The results show that the as-prepared [Cd5(Mtta)9]n film possesses a rod-like topography. The flame height and ignition duration of [Cd5(Mtta)9]n film reach 9.0 mm and 220 µs, respectively, revealing that [Cd5(Mtta)9]n film is an excellent ignition material. This research opens up a new avenue for the preparation of novel energetic films, which provides potential applications on microelectromechanical systems to achieve functional nanoenergetics-on-a-chip.
... The two dimensional (2-D) nanostructures such as nanoplates offer large surface area with remarkable active sites for adsorption of gas molecules and good electron transport properties [15]. Among various synthesis methods for NiO nanostructures such as electrodeposition (ED) [16], laser deposition [17], thermal oxidation [18], sputter deposition [19], microwave-assisted chemical synthesis [20], and so on but hydrothermal synthesis method has potential to produce nanostructures with high quality materials [21][22][23]. NiO nanostructures such as nanowires, nanoparticles, nanoflower, nanorods, nanotubes, have been explored for gas sensor application [24][25][26][27][28], however nanoplates like morphology of NiO has not been investigated for hydrogen gas sensor application as per our best of the knowledge. ...
High quality nanocrystalline NiO nanoplates were synthesized using surfactant and template free hydrothermal route. The gas sensing properties of NiO nanoplates were investigated. The nanoplates morphology of NiO with average thickness ~ 20 nm and diameter ~ 100 nm has been confirmed by FE-SEM and TEM. Crystalline quality of NiO has been studied using HRTEM and SAED techniques. Structural properties and elemental compositions have been analyzed by XRD and energy dispersive spectrometer (EDS) respectively. The detailed investigation of structural parameters has been carried out. The optical properties of NiO were analyzed from UV–Visible and photoluminescence spectra. NiO nanoplates have good selectivity towards hydrogen (H2) gas. The lowest H2 response of 3% was observed at 2 ppm, whereas 90% response was noted for 100 ppm at optimized temperature of 200 °C with response time 180 s. The H2 responses as functions of different operating temperature as well as gas concentrations have been studied along with sensor stability. The hydrogen sensing mechanism was also elucidated.
... Among various metals such as aluminum, magnesium, titanium, zinc, silicon and boron, aluminum is the most commonly used fuel in thermites due to its high affinity for oxygen, easy handling, high reactivity, the abundance, and high boiling temperature [23]. Many of the metal oxides including Fe 2 O 3 [24][25][26], CuO [27][28][29], MoO 3 [30,31], WO 3 [32] Bi 2 O 3 [33,34], NiO [35][36][37], etc. can be used as a oxidizer in the thermite reactions. ...
In this work, the thermal reaction of aluminum (Al) and nickel oxide (NiO) was investigated by molecular dynamics simulations. Some
effective features of reaction such as reaction temperature, reaction mechanism, and diffusion rate of oxygen into aluminum structure were
studied. ReaxFF force field was performed to study the Al/NiO thermite reaction behavior at five different temperatures (500, 900, 1100,
1200 and 1400 K). The results obtained from the molecular dynamics simulation predict that the reaction temperature for aluminum metal
and nickel oxide mixture would be 1141 K, which is in a good agreement with that of the experimental value (i.e. 1148.8 K). In addition,
the mean square displacement analysis suggests that the movement of aluminum atoms is less than that of oxygen and nickel atoms. The
estimated diffusion coefficient of oxygen in the aluminum/nickel oxide thermite mixtures was 4.53 10-8 m2 s-1. The results show that the
diffusion coefficients significantly increase with increasing temperature.
... Therefore, it implies that the thermite reaction between Al and Mn 2 O 3 can be divided into two steps. First reaction is based on solid-solid diffusion mechanism, and second reaction triggers by liquid-solid diffusion mechanism after Al is melted, which is similar to NiO/Al system that has been reported before 37 . In comparison, the DSC curve of Mn 2 O 3 /Al NPC under the same test conditions is shown in Fig. 8d. ...
Mn2O3 has been selected to realize nanothermite membrane for the first time in the literature. Mn2O3/Al nanothermite has been synthesized by magnetron sputtering a layer of Al film onto three-dimensionally ordered macroporous (3DOM) Mn2O3 skeleton. The energy release is significantly enhanced owing to the unusual 3DOM structure, which ensures Al and Mn2O3 to integrate compactly in nanoscale and greatly increase effective contact area. The morphology and DSC curve of the nanothermite membrane have been investigated at various aluminizing times. At the optimized aluminizing time of 30 min, energy release reaches a maximum of 2.09 kJ∙g−1, where the Al layer thickness plays a decisive role in the total energy release. This method possesses advantages of high compatibility with MEMS and can be applied to other nanothermite systems easily, which will make great contribution to little-known nanothermite research.
... According to the literature [17], the amount of reaction heat released in redox reaction such as Al/CuO, Al/MoO x , and Al/NiO is almost two times than that of intermetallic reaction. In addition, Al/NiO nanomultilayer redox reaction shows its advantage among the vast range of Al/metallic oxide reactions, which have been confirmed by the investigation of Al/metallic oxide nanocomposites such as nanowire [18,19] and nanohoneycomb [20]. The various oxidation state of nickel in nickel oxides is an important parameter for released reaction heat. ...
The redox reaction between Al and metallic oxide has its advantage compared with intermetallic reaction and Al/NiO nanomutlilayers are a promising candidate for enhancing the performance of energetic igniter. Al/NiO nanomutlilayers with different modulation periods are prepared on alumina substrate by direct current (DC) magnetron sputtering. The thicknesses of each period are 250 nm, 500 nm, 750 nm, 1000 nm, and 1500 nm, respectively, and the total thickness is 3
μ
m. The X-ray diffraction (XRD) and scanning electron microscope (SEM) results of the as-deposited Al/NiO nanomutlilayers show that the NiO films are amorphous and the layered structures are clearly distinguished. The X-ray photoelectron spectroscopy (XPS) demonstrates that the thickness of Al
2
O
3
increases on the side of Al monolayer after annealing at 450°C. The thermal diffusion time becomes greater significantly as the amount of thermal boundary conductance across the interfaces increases with relatively smaller modulation period. Differential scanning calorimeter (DSC) curve suggests that the energy release per unit mass is below the theoretical heat of the reaction due to the nonstoichiometric ratio between Al and NiO and the presence of impurities.
... Fig. 3a and b shows the optical microstructure of the stainless steel in the as polished and electro etched using KOH (56 g KOH+ 100 ml H 2 O) etchant with 3 V DC current for 5 min, respectively. This etchant makes delta ferrite bluish and Sigma phase brownish while has no effect on the austenite phase [15,20]. It is observed that there is a uniform distribution of black particles in the microstructure of the stainless steel in Fig. 3a. ...
304 austenitic stainless steel reinforced by Al2O3 particles was prepared by microwave assisted self-propagating high temperature synthesis process using the Fe2O3Cr2O3NiOAlFe reaction system. Furthermore, effects of mechanical activation of the reactants and the addition of 21.2 wt.% extra Al to the chemical composition of the reactants on the chemical composition of the produced stainless steel was investigated. Atomic absorption spectroscopy analysis results indicated that by the addition of extra Al to the reactant mixture and using 30 minute mechanical activation, stainless steel containing 17.27 wt.% Cr and 7.73 wt.% Ni could be produced with its chemical composition very close to the chemical composition of 304 stainless steel. X-ray diffraction analysis showed that the stainless steel contains nanostructured austenite and ferrite phases. Also microstructural characterizations indicated that there is a uniformdistribution of black particles in the steel matrix. Energy dispersive spectroscopy analysis showed that these particles are composed of Al and O elements while the matrix contains Fe, Cr and Ni elements. The presence of Al2O3 particles and nanostructure matrix improved the hardness and therefore the wear properties of the composite in comparison with the wrought 304 stainless steel plate.
Integrating energetic materials with microelectromechanical systems (MEMS) to achieve miniaturized integrated smart energetic microchips has broad application prospects in miniaturized aerospace systems and civil explosive systems. In this work, MEMS compatible [Cu(BODN)·5H2O]n arrays and [Cu(BODN)·5H2O]n@nano-Al composite energetic films were successfully fabricated on copper substrates by the in situ reaction method and drop-coating method. Single crystal X-ray diffraction, powder X-ray diffraction, scanning electron microscopy, infrared spectroscopy, differential thermal analyses, and pulsed laser ignition were employed to characterize the prepared samples. The results show that [Cu(BODN)·5H2O]n arrays formed by the coordination reaction between the Cu(OH)2 template and the BODN ligand exhibit a porous supramolecular structure with excellent thermal and energy properties. Their morphology and composition on a copper substrate can be effectively regulated by adjusting the reaction time and solution concentration. In addition, adjustable energetic properties of [Cu(BODN)·5H2O]n@nano-Al composite films can be achieved after the encapsulation of nano-Al. Their heat release, flame height and ignition duration can reach as much as 1987.5 J g-1, 13.2 mm, and 5900 μs, respectively, indicating that [Cu(BODN)·5H2O]n@nano-Al can be used as an excellent pyrotechnic agent in MEMS ignition chips. Overall, this work provides a reference for the integration and application of energetic materials in MEMS systems.
Nanothermite NiO-Al is a promising material system for low gas emission heat sources, yet its reactive properties are highly dependent on material processing conditions. In the current study, sputter deposition is used to fabricate highly controlled nanolaminates comprised of alternating NiO and Al layers. Films having an overall stoichiometry of 2Al to 3NiO were produced with different bilayer thicknesses to investigate how ignition and self-sustained, high temperature reactions vary with changes to nanometer-scale periodicity and pre-heat conditions. Ignition studies were carried out with both hot plate and laser irradiation and compared to slow heating studies in hot-stage X-ray diffraction. Ignition behavior has bilayer thickness and heating rate dependencies. The 2Al/3NiO with λ < 300 nm ignited via solid/solid diffusion mixing (activation energy, Ea = 49 ± 3 kJ/mole). Multilayers having λ > 500 nm required the more favorable mixing kinetics of solid/liquid dissolution into molten Al (Ea = 30 ± 4 kJ/mole). This solid/liquid dissolution Ea is a factor of 5 lower than that of previously reported powder compacts due to the elimination of a passivating Al oxide layer present on powder. The reactant mixing mechanism between 300 nm and 500 nm bilayer thicknesses was dependent on the ignition source's heating rate. The self-propagating reaction velocities of 2Al/3NiO multilayers varied from 0.4-2.5 m/s. Pre-heating nanolaminates to temperatures below the onset reaction temperatures associated with forming intermediate nickel aluminides at multilayer interfaces led to increased propagation velocities, whereas pre-heating samples above the onset temperatures inhibited subsequent attempts at laser ignition.
To explore the effect of potassium perchlorate (KClO4) on Al nanoparticles/MnO2-nanorods nanothermite systems, in this paper, Al/MnO2 nanothermites with different mass fraction of KClO4 were prepared by electrospray. The samples were characterized by XRD, SEM, TG-DSC analysis. According to the results of TG-DSC, the addition of KClO4 seemed to cause no direct improvement on their exothermic reactions. But the results of activation energy calculations showed that KClO4 could remarkably reduce the activation energy of nanothermite systems by up to 48.8%. The XRD results indicated that residues consisted mainly of Mn3O4. The reasons why KClO4 has little effect on thermal properties but makes a great difference on kinetics were analyzed and discussed. Finally, onset combustion tests were carried out. The results and findings provide a useful approach to decrease the activation energy and combustion rate of nanothermites, which may facilitate practical and combustible applications.
Development of the structural, anti-wetting and exothermic stability of composite metal based-energetic composite is still a great challenge, especially used in complex environments (e.g. moisture circumstances). Thus, this paper firstly proposed electrophoretic controlled assembly (ECA) technique and facile modification process to construct the multifunctional nano-Al based NiO/perfluorosilane energetic composite films with even distribution of nanoscale particles and triple (a: microstructure, b: anti-wetting and c: exothermic performance) stability of for three years. The ECA dynamics study of Al/NiO particles was deeply explored as a “controlled bridge” to adjusting the reaction ratio of Al to NiO in product. The target film displays an outstanding high water contact angle of 171±1° with an almost perfect sphere of droplet placed on that surface, and shows a small fluctuation of anti-wetting ability after immersed and exposure tests. In addition, the total heat output (Q) of product can reach up to ~2.5 kJ/g with a low activation energy of 247.624 kJ/mol, and shows ultra-long exothermic stability for three years. The realization of target film highly compatible with microelectromechanical systems (MEMS) here will largely improve the safety level of propellant or detonator system.
Thermite films are typical energetic materials (EMs) and have great value in initiating explosive devices. However, research in thermite film preparation is far behind that of research in thermite powders. Electrophoretic deposition (EPD) is an emerging, rapid coating method for film fabrication, including of energetic composite films. In this work, a polytetrafluoroethylene (PTFE)/Al/CuO organic-inorganic hybrid energetic film was successfully obtained using the above method for the first time. The addition of lithocholic acid as a surfactant into the electroplating suspension enabled PTFE to be charged. The combustion and energy release were analyzed by means of a high-speed camera and differential scanning calorimetery (DSC). It was found that the combustion process and energy release of PTFE/Al/CuO were much better than that of Al/CuO. The main reason for the excellent combustion performance of the hybrid PTFE/Al/CuO system was that the oxidability of PTFE accelerated the redox reaction between Al and CuO. The prepared PTFE/Al/CuO film was also employed as ignition material to fire a B–KNO3 explosive successfully, indicating considerable potential for use as an ignition material in micro-ignitors. This study sheds light on the preparation of fluoropolymer-containing organic-inorganic hybrid energetic films by one-step electrophoretic deposition.
As the most important component for MEMS-based pyrotechnics, the micrometer should generate enough energy to successfully ignite the next explosive. An enhanced reactive igniter was designed and fabricated through sputtering the Al/CuO nanolaminates onto the NiCr micro-heater to enhance the output energy of the NiCr micro-heater. The average thickness of the Al/CuO nanolaminate is 6.84 [Formula: see text]m, and the designed thickness is 6 [Formula: see text]m. The grain sizes of Al/CuO nanolaminates are not uniform, and the particle grains of the Al/CuO nanolaminates at the top are smaller than those at the bottom. When the applied currents passed through the igniter, the resistance of the igniter changed dynamically, leading to the igniter experiencing three stages. Compared to the bare NiCr micro-heater without depositing Al/CuO nanolaminates, the enhanced reactive igniter can successfully ignite Zr/KClO 4 explosive, indicating that the Al/CuO nanolaminates could enhance the output capability of the NiCr micro-heater. It is of vital importance to guide the design of MEMS-based pyrotechnics.
Remarkable progress has been established in the field of nanoenergetic materials (mixture of nanoscale fuel and oxidizer) since the advent of nanotechnology. Combustion of nanoenergetic materials depends on many key factors like synthesis route, equivalence ratio, morphology of constituents, and arrangements and handling of materials. For tailoring and tuning of the combustion properties of nanoenergetics, sound knowledge of the reaction mechanism is needed; in this review article a schematic study on the reaction mechanism is presented. By employing various routes and strategies in synthesizing and nanoengineering of the fuel or/and oxidizer to realize a significant evolution from normal physical mixing of nanopowders to the formulation of core/shell nanostructures, the nanoenergetic materials achieved the best ever combustion properties in terms of combustion reactivity, ignition sensitivity, energy density, etc. Overall, in this article, a critical state-of-the-art review of the existing literatures has been conducted to feature the main developments in the molecular combustion modeling of melting, oxidation, and core–shell reaction/diffusion of nanoaluminum and the molecular modeling of combustion reactivity and ignition sensitivity of nanoenergetic materials.
Nanothermites refer to the mixtures of metal fuels and oxidizers, at least one component of which is nanoscale. In the past few decades, nanothermites have attracted much attention as a kind of highly reactive nanoenergetic materials (nEMs). Since nanothermites are mixtures rather than single compounds, the mass-transport efficiency between the reactants dominates their reaction kinetics, thus many efforts have been made to increase the number of contact sites between fuels and oxidizers. Building core–shell structured nanothermites is an effective way to overcome the uneven distribution of fuels and oxidizers and increase the contact area between the reactants. According to the construction sequence of fuel and oxidizer, the core–shell nanothermite can be divided into two main categories, including fuel–oxidizer and oxidizer–fuel. Their exothermic properties, combustion, and pressure performance have been preciously controlled by adjusting composition, size, and structure. In this chapter, the preparation strategies and energetic properties of core–shell nanothermites are introduced and summarized. In particular, the advantages of core–shell structured nanothermites in terms of energy density and combustion efficiency are clarified, based on which suggestions regarding the possible future research directions are proposed.
Energetic materials, including explosives, pyrotechnics, and propellants, are widely used in mining, demolition, automobile airbags, fireworks, ordnance, and space technology. Nanoenergetic materials (nEMs) have a high reaction rate and high energy density, which are both adjustable to a large extent. Structural control over nEMs to achieve improved performance and multifunctionality leads to a fascinating research area, namely, nanostructured energetic materials. Among them, core–shell structured nEMs have gained considerable attention due to their improved material properties and combined multiple functionalities. Various nEMs with core–shell structures have been developed through diverse synthesis routes, among which core–shell structured nEMs associated with explosives and metastable intermolecular composites (MICs) are extensively studied due to their good tunability and wide applications, as well as excellent energetic (e.g., enhanced heat release and combustion) and/or mechanical properties. Herein, the preparation methods and fundamental properties of the abovementioned kinds of core–shell structured nEMs are summarized and the reasons behind the satisfactory performance clarified, based on which suggestions regarding possible future research directions are proposed. The “shell” of core–shell structured explosives is like a protective “coat” on the sensitive explosive, making them more resistant to external stimuli. The fuel and oxidizer in core–shell structured metastable intermolecular composites (MICs) are like a well‐matched “gear,” they have large and close contact with each other, so that the thermite reaction exhibits increased heat output and improved reactivity.
Here, we have fabricated a highly performed asymmetric supercapacitor (ASC) device comprising of a honeycomb-like nickel‒copper‒carbonate‒hydroxide (NC) coated stainless steel (SS) as positive and an iron oxide nanoparticles (Fe2O3 NPs) coated SS as negative electrodes, separated by poly(vinyl alcohol)‒potassium hydroxide (PVA–KOH) based gel membrane. Both the component electroactive materials was synthesised via substrate-free polyvinylpyrrolidone (PVP) assisted facile hydrothermal protocols. The as-synthesised NC with numerous interconnected nanoflakes and mesoporous Fe2O3 NPs exhibits superior electrochemical properties. As an outcome, NC and Fe2O3 display specific capacitance (Csp) values of ~ 1706.2 and 221.5 F g‒1 (at 1 A g–1 current density), respectively, accompanied by an improved retention of their inherent Csp (~ 94.4 % for NC and ~ 95.7 % for Fe2O3) after 3000 galvanostatic charge-discharge (GCD) cycles at 1 A g‒1. Finally, our assembled ASC device reveals an energy density value of ~ 40.03 Wh kg‒1 with a power density of ~ 325.4 W kg‒1 at 1 A g–1. Noticeably, the ASC retains an energy density of ~ 27.2 Wh kg‒1 (with a power density ~ 3250 W kg‒1) even at 10 A g–1. Moreover, the ASC retains ~88.1 % of its original Csp after 10000 successive GCD cycles. Thus, the ASC device with adequate electrochemical performances is highly promising for portable and flexible electronics.
We examined the effect of polymer encapsulation on the insensitivity and thermal reactions of Al and CuO-based nanoenergetic materials (nEMs). The nEMs were encapsulated by nitrocellulose (NC) polymer using aerosol and solution drying processes for comparison. Severe aggregation and precipitation of Al/CuO reactants in the NC matrix were made in the liquid phase during the drying process so that the thermal reactions of the resulting Al/CuO/NC composites was unstable. However, the rapid aerosol drying process in the gas phase resulted in the formation of uniformly mixed NC-encapsulated Al/CuO composites. The NC content in the Al/CuO composites fabricated in the gas phase strongly affected the thermal reactions by perturbing thermochemical interactions between the Al and CuO reactants. Meanwhile, the insensitivity of Al/CuO composites gradually increased with increasing NC content. Therefore, the aerosol drying process in the gas phase is suggested as a viable and effective method to generate polymer-encapsulated homogeneously mixed nEMs with enhanced insensitivity and thermal reaction properties.
Herein, the roles of an Al/Fe2O3 energetic composites as a heat energy source and a bonding medium for interfacially bonding dissimilar Al/Cu metallic substrates are systematically investigated. Energetic material (EM)/solder material (SM) bilayer pellets are assembled and ignited between the interfacial Al/Cu substrates for bonding. The upper EM layer comprising an Al microparticle (MP)/Al nanoparticle (NP)/Fe2O3 NP composite serves as a heat source for melting the lower SM layer comprising SAC305 MP for strongly bonding the Cu substrate with the melted SM layer. The intermetallic compounds (AlxFey) formed during the aluminothermic reactions of the ignited EM layer play an important role as a bonding medium between the Al substrate and the melted EM layer. The dissimilar Al/Cu substrates are interfacially bonded using an EM layer with a fuel-to-oxidizer ratio of 1.97–4.44. The maximum mechanical strength of the bonded Al/Cu substrates increases with the increase in the fuel-to-oxidizer ratio owing to the supply of sufficient heat energy under fuel-rich conditions. The EM layer acts as an effective heat energy source and mechanical bonding medium. The proposed interfacial bonding technique is simple, easy, and versatile for welding and joining dissimilar metallic substrates for industrial applications.
Single walled carbon nanotubes (CNTs) were added into layered Al/NiO nano-thermite composites, to tune their energetic and reaction properties. Scanning Electron Microscopy (SEM) images showed a direct contact between the Al and NiO layers, where the presence of CNTs in a designated layer was clearly visible. Thermal-chemical data obtained from Differential Scanning Calorimetry (DSC) demonstrated these composites, although modified with CNTs in either the Al or the NiO layer, exhibited a nearly constant onset temperature, implying comparable reaction initiation mechanisms. However, different amounts of energy release, accompanied with formation of distinct layer composition and microstructures of their products, was produced. It was further revealed that, by means of mass spectrometry, SEM and X-ray Diffraction (XRD) analysis, upon the initiation of the thermite reaction between Al and NiO at the interface layer, the reaction between CNTs and NiO nanoparticles produced CO and CO2, which promoted the gas-solid chemistry and gas diffusion within the microstructure of the composite. Both increased the energy release and resulted in less agglomerated reaction products. In comparison, adding CNTs into the Al layer did not bring a significant change to the condensed-phase reaction mechanism which was proposed previously for the Al/NiO composite.
The mechanisms of metal phase transition process during electrical explosion are experimentally and theoretically investigated. Past experiments of investigation are single metal foil, such as gold, aluminum, and copper. The characteristics of aluminum‐nickel (Al/Ni) multilayer foil were investigated, which means electrical behavior and energy output. The foil was fabricated by magnetron sputtering based on ceramic substrate, and lithographically patterned into bow‐tie bridge regions. Scanning electron microscopy characterization revealed the layer structure of the Al/Ni multilayer. X‐ray diffraction characterization was employed to ascertain the composition of Al/Ni. The probing of voltage‐current waveforms reveals that Al/Ni multilayer foils exhibit high voltage, short burst time and high absorbing energy in electrically heated in comparison with copper or nickel alone. We also measured the energy output of foils through velocity measurements of encapsulation layers ejected from bridge region by Photonic Doppler velocimetry. We observed flyer velocities from Al/Ni multilayer foil in the 1.6–2.9 km/s range, which is much higher than copper foil. Combined with the 1‐D non‐stationary acceleration model calculation, it is found that the chemical energy and increased electrical absorbing energy contributed to additional kinetic energy in the 40–80 mJ range.
Highly reactive metastable intermixed composites (MICs) have attracted much attention in the past decades. The MIC family of materials mainly includes traditional metal‐based nanothermites, novel core–shell‐structured, 3D ordered macroporous‐structured, and ternary nanocomposites. By applying special fabrication approaches, highly reactive MICs with uniformly dispersed reactants, “layer‐by‐layer” or “core–shell” structures, can be prepared. Thus, the combustion performance can be greatly improved, and the ignition characteristics and safety can be precisely controlled by using a certain preparation strategy. Here, the preparation and characterization of the MICs that have been developed during the past few decades are summarized. Traditional preparation methods for MICs generally include physical mixing, high‐energy ball milling, sol–gel synthesis, and vapor deposition, while the novel methods include self‐assembly, electrophoretic deposition, and electrospinning. Various preparation procedures and the ignition and combustion performance of different MIC reactive systems are compared and discussed. In particular, the advantages of novel structured MICs in terms of safety and combustion efficiency are clarified, based on which suggestions regarding the possible future research directions are proposed.
NiO films were fabricated by reactive direct current magnetron sputtering on glass and alumina substrates for the application in energetic nano-multilayers. The structural and thermal properties of the films were investigated with the volume ratio of oxygen to argon ranging from 1:9 to 3:2, and the optimized ratio value is obtained as 1:3, which was confirmed by X-ray diffraction (XRD), atomic force microscopy and ultrafast measurement system. The effect of the film thickness, varying from 150 to 900 nm, on the structural properties was characterized by XRD and scanning electron microscopy (SEM). XRD analysis reveals that the (111) lattice plane is the preferred orientation. The intensities of preferential peaks and the grain sizes increase as the film thicknesses increase.
The reaction mechanisms and microstructures of various layered nano-thermite composites are investigated through characterization of their energetic properties. Migration of reactive components across the reaction zone is analyzed, which plays an important role in determining the process initiation, reaction propagation, and chemical stability at low temperatures. Distinct types of nanoparticles are deposited onto filter paper in a sequence, using the vacuum filtration method, which promotes intimate contact between neighboring reactive layers. Scanning Electron Microscopy (SEM) images demonstrate a well-defined contact region between the two layers in the Al/CuO or Al/NiO composites. Differential Scanning Calorimetry (DSC) data shows that the thermite reaction occurs below the melting temperature of Al, resulting in rapid heat release, and improves reaction initiation. Elemental mapping results reveal the migration of Al, Ni/Cu, and oxygen before and after the thermite reaction, which is arranged during thermogravimetric analysis (TGA). This analysis indicates the dominant pathway of the thermite reaction in each composite, through either decomposition of the CuO nanoparticles in the Al/CuO composite or through direct migration of reactive components across the conducting surface within the Al/NiO composite.
Nanocomposites consisting of iron oxide (Fe2O3) and nano-sized aluminum (Al), possessing outstanding exothermic redox reaction characteristics, are highly promising nanothermite materials. However, the reactant diffusion inhibited in the solid state system makes the fast and complete energy release very challenging. In this work, Al nanoparticles anchored on graphene oxide (GO/Al) was initially prepared by a solution assembly approach. Fe2O3 was deposited on GO/Al substrates by atomic layer deposition (ALD). Simultaneously thermal reduction of GO occurs, resulting in rGO/Al@Fe2O3 energetic composites. Differential scanning calorimetry (DSC) analysis reveals that rGO/Al@Fe2O3 composite containing 4.8 wt% of rGO exhibits a 50% increase of the energy release compared to the Al@Fe2O3 nanothermite synthesized by ALD, and an increase of about 130% compared to a random mixture of rGO/Al/Fe2O3 nanoparticles. The enhanced energy release of rGO/Al@Fe2O3 is attributed to the improved spatial distribution as well as the increased interfacial intimacy between the oxidizer and the fuel. Moreover, the rGO/Al@Fe2O3 composite with an rGO content of 9.6 wt% exhibits significantly reduced electrostatic discharge sensitivity. These findings may inspire potential pathways for engineering energetic nanocomposites with enhanced energy release and improved safety characteristics.
One of the challenges for the application of energetic materials is their energy-retaining capabilities after long-term storage. In this study, we report a facile method to fabricate superhydrophobic Al/Fe2O3 nanothermite film by combining electrophoretic deposition and surface modification technologies. Different concentrations of dispersion solvents and additives are investigated to optimize the deposition parameters. Meanwhile, the dependence of deposition rates on nanoparticle concentrations is also studied. The surface morphology and chemical composition are characterized by field-emission scanning electron microscopy, X-ray diffraction, X-ray energy-dispersive spectroscopy, and X-ray photoelectron spectroscopy. A static contact angle as high as 156° shows the superhydrophobicity of the nanothermite film. Natural and accelerated aging tests are performed and the thermal behavior is analysed. Thermal analysis shows that the surface modification contributes to significantly improved energy-release characteristics for both fresh and aged samples, which is supposed to be attributed to the preignition reaction between Al2O3 shell and FAS-17. Superhydrophobic Al/Fe2O3 nanothermite film exhibits excellent long-time storage stability with 83.4% of energy left in natural aging test and 60.5% in accelerated aging test. This study is instructive to the practical applications of nanothermites, especially in highly humid environment.
Ignition temperature is a simple and important parameter that pertains to both the practical aspects of thermite usage as well as a key to exploring reaction mechanisms. In this study, nine aluminum-fueled oxysalt-containing thermites including K2S2O8, K2SO4, KIO4, KIO3, KClO4, KClO3, KBrO3, KNO3 and K3PO4, were investigated. Results from combustion cell tests show that these thermites can be divided into two groups, with the reactive thermites (e.g., Al–K2S2O8) generating ∼10× higher of pressure and ∼10× shorter of burn time than the less reactive thermites in the aforementioned list (e.g., Al–K2SO4). Thermal decomposition analysis of these oxysalts at both slow and fast heating rates (0.17 K/s v.s. 10⁵ K/s) demonstrates that these oxysalts have a wide range of oxygen release and melting temperatures. On the other hand, the ignition temperatures of the reactive thermites (in Ar and air) are consistent with the temperature of polymorphic phase change of alumina (close to the melting point of Al), indicating that the limiting initiation step of these thermites is the acceleration of outward diffusion flux of Al. In addition, the ignition temperatures of these reactive thermites in vacuum are much higher than those in Ar, suggesting that ignition is based on the interaction between outwardly diffused Al, and generated gas phase O2. In contrast, the ignition temperatures of the two less reactive thermites are insensitive to pressure. They ignite at temperatures much higher than the melting point of Al, although lower than the decomposition temperature of the corresponding oxysalts, indicating a condensed phase reaction mechanism. Finally, by employing carbon as a non-melting, non-oxide coated fuel, we found an essentially direct correlation between the oxygen release temperature and the ignition temperature.
Three-dimensional ordered macroporous (3DOM) Al/NiFe2O4 nanothermite has been obtained by a colloidal crystal templating method combined with magnetron sputtering processing. Owing to the superior material properties and unique 3DOM structural characteristics of composite metal oxides, the heat output of the Al/NiFe2O4 nanothermite is up to 2921.7 J g⁻¹, which is more than the values of Al/NiO and Al/Fe2O3 nanothermites in literature. More importantly, by comparison with the other two nanothermites, the onset temperature of about 300 °C from Al/NiFe2O4 is remarkably low, which means it can be ignited more easily. Laser ignition experiments indicate that the synthesized Al/NiFe2O4 nanothermite can be easily ignited by a laser. In addition, the preparation process is highly compatible with the MEMS technology. These exciting achievements have great potential to expand the scope of nanothermite applications.
Extensive research of compact and reliable ignition method has extended the applicability of nano-energetic materials to various thermal engineering fields. In this paper, an integrated film initiator was designed and fabricated through combining B/Ti nano-multilayers with a Cu film bridge. Cu film bridge was initially wet-etched and B/Ti multilayers were deposited on the top of Cu film bridge with magnetron sputtering. The periodic layer structure of the B/Ti multilayers was verified by scanning electron microscopy. Self-propagation exothermic reaction of the B/Ti multilayers (2 μm thick) could be initiated by 60 V capacitor discharge, and the reaction temperature can be raised up to 2600 K. Different reaction temperature can be achieved by simply altering the thickness of B/Ti multilayers. The explosion processes of the Cu film bridge and the Cu/B/Ti integrated film bridge were explored by electric explosion tests. Compared to the Cu film bridge, integrated film bridge exhibits improved performances with higher explosion temperature, longer explosion duration time, more violent explosion phenomenon and larger quantities of ejected product particles. These results indicate that the electric explosion performances of micro-initiator could be improved evidently with combination of nano-energetic materials.
Based on magnetron sputtering deposition technology, Ti and B single thin films are deposited on a Si substrate while varying the sputtering power, the working pressure and the Ar flow conditions. The effect of varying these conditions on the deposition rate, the roughness and the microstructure of these materials is studied. The optimal parameters for preparing Ti and B single thin films are identified according to the experimental and analysis results. Thus, the deposition parameters are optimized to minimize the roughness of the thin films (i.e. sputtering power: 225 and 120 W; working pressure: 0.8 and 0.3 Pa; Ar flow: 100 and 50 sccm for Ti and B thin films, respectively). The compositions and crystal orientation of the Ti and B thin films deposited at these conditions are investigated by x-ray diffraction. These optimized parameters are used while depositing Ti-B thin films on a polyimide substrate. Scanning electron microscopy is used to observe the microstructure of the Ti-B multi-layer nanoenergetic films. Aclose contact between the Ti film and the substrate is observed along with a clear boundary between the B and Ti films. Finally, the results of an electrical explosion experiment over a Ti-B composite thin film are discussed.
Because of its high energy density, an Al–Co3O4 reactive nanocomposite (Al–Co3O4 RNC) has attracted vast attention. In this study, Al–Co3O4 RNC was successfully prepared as a coating by an electrophoretic deposition (EPD) method. An ethanol–acetylacetone (1:1 in volume) mixture containing 0.25 mM nitric acid was employed as a suitable dispersion medium for EPD. Differential scanning calorimetry revealed that the obtained Al–Co3O4 was a high-energy coating with a maximum heat release of 2638 J·g–1. Moreover, an attempt at assembling an electrophoretic Al–Co3O4 RNC coating onto an electrothermal copper bridge was also made. A successful ignition test indicated that this novel Al–Co3O4 RNC coating has great potential for application in the microignitor field.
The heating and low temperature thermite reactions of the Al/SiO2 sandwich nanostructure are investigated by molecular dynamics simulations in combination with the reactive force field, ReaxFF. In this paper, the initial atomistic processes, thermal stability and energetic reaction properties of Al and SiO2 are presented. The results show that the melting temperature of the Al/SiO2 sandwich structure is ∼1400 K. The thermite reaction self-heating rates are determined by the thickness of the interfacial diffusion barrier at the interface in the nanoparticle.
A three-dimensionally ordered macroporous(3DOM) alpha-Fe2O3 membrane was prepared by inversing polystyrene(PS) spheres colloidal crystal template, and nano aluminum was then introduced into the 3DOM alpha-Fe2O3 skeleton using magnetron sputtering method. Scanning electron microscope(SEM) images show that nano Al coats on surface of alpha-Fe2O3 skeleton uniformly, and pore structure converts into a kind of diamond from previously suborbicular after aluminizing with wall thickness increasing from 32 nm to 100 nm. Simultaneously, elemental analysis of the membrane is investigated via energy dispersive spectrum(EDS). Differential scanning calorimety(DSC) results indicate that onset temperature of the Fe2O3/Al nanothermite membrane is 490 degrees C, and thermite reaction between Al and Fe2O3 can be divided into solid-solid reaction and liquid-solid reaction. The total heat release is 1374.7 J/g. Ignition performance of the energetic membrane is investigated by laser ignition test. Sparks spatter outward with dazzling light can be observed for 2.6 ms, demonstrating that Fe2O3/Al nanothermite membrane can be ignited normally.
PTFE/Al (polytetrafluoroethylene/aluminum) reactive multilayer films with different thickness and alternating deposition were prepared by a radio frequency magnetron sputtering method using Al as combustible and PTFE as oxidant. The influence rules of sputtering power on the film surface morphology was investigated by atomic force microscope (AFM) and X-ray diffraction (XRD). The appropriate preparation technology of the films was obtained. The mechanical property of PTFE/Al reactive multilayer films was measured by a nano-indentation apparatus. Results show that when the radio frequency sputtering power is 50 W and 150 W, the mean roughness and RMS roughness of PTFE film and Al film obtained are low. When the total thickness of PTFE/Al reactive multilayer films is about 300 nm, in comparison with pure PTFE film and Al film, PTFE/Al reactive multilayer films have higher hardness and elastic modulus: 5.8 GPa and 120.0 GPa, respectively.
The composite semiconductor bridge (SCB) electrical-explosive device (EED) with excellent performances of low ignition energy, short ignition time, high security and high energy output in comparison with polycrystalline silicon semiconductor bridge, is a new type ignition product obtained by a reactive materials-semiconductor bridge combination, using a modern microelectronic technology. The research progress, advantages and weaknesses of the composite semiconductor bridge EED were reviewed. In order to increase the ignition energy of SCB to provide a viable basis and reference, the structure features, reactive materials, ignition conditions and output performance of the multi-layer composite film ignition bridge were comparatively analyzed. Considering that the multi-layer composite semiconductor bridge EED is ideal improvement products of polycrystalline silicon SCB, having a wider range of application and prospects.
A carbon nanotube energetic igniter was fabricated by integrating carbon nanotube composite energetic materials with a Cu layer realized onto a ceramics substrate. Carbon nanotube composite energetic materials were prepared by means of the wet chemical method, filling multiwalled carbon nanotubes with KNO 3. DSC curves show that the carbon nanotube composite energetic materials released chemical heat of 876.1 J·g -1 at the peak value of 386.8 °C. The electroexplosive performances of the carbon nanotube energetic igniter were investigated using a capacitor-discharger apparatus. The electro-explosive time decreased exponentially with increasing the charging voltage and approached a certain value of 39.3 μs. The electric explosion process of the carbon nanotube energetic igniter recorded by high speed photography shows that chemical reaction of carbon nanotube composite energetic materials was involved in the electric explosion process, accompanied by more heat release.
We prepare energetic nanocomposites, which undergo an exothermic reaction when ignited at moderate temperature. The nanocomposites are a mixture of Al fuel and Fe2O3 oxidizer where Fe2O3 is in the form of an array of nanowires embedded in the thin Al film. We achieve a very high packing density of the nanocomposites, precise control of oxidizer–fuel sizes at the nanoscale level, and direct contact between oxidizer and fuel. We find that the flame temperature does not depend on ignition temperature. © 2004 American Institute of Physics.
Nanothermite composites containing metallic fuel and inorganic oxidizer are gaining importance due to their outstanding combustion characteristics. In this paper, the combustion behaviors of copper oxide/aluminum nanothermites are discussed. CuO nanorods were synthesized using the surfactant-templating method, then mixed or self-assembled with Al nanoparticles. This nanoscale mixing resulted in a large interfacial contact area between fuel and oxidizer. As a result, the reaction of the low density nanothermite composite leads to a fast propagating combustion, generating shock waves with Mach numbers up to 3.
Combustion velocities were experimentally determined for nanocomposite thermite powders composed of aluminum (Al) fuel and molybdenum trioxide (MoO3) oxidizer under well-confined conditions. Pressures were also measured to provide detailed information about the reaction mechanism. Samples of three different fuel particle sizes (44, 80, and 121 nm) were analyzed to determine the influence of particle size on combustion velocity. Bulk powder density was varied from approximately 5% to 10% of the theoretical maximum density (TMD). The combustion velocities ranged from approximately 600 to 1000 m/s. Results indicate that combustion velocities increase with decreasing particle size. Pressure measurements indicate that strong convective mechanisms are integral in flame propagation. (c) 2005 American Institute of Physics.
A nano initiator is developed by integrating Al/CuO-based nanoenergetic materials with a Au/Pt/Cr thin-film microheater realized onto a glass substrate. It is fabricated by using standard microsystem techniques that allow batch fabrication and high level of integration and reliability. The nano initiator is characterized by open-air combustion testing with an ignition success rate of 98%. The ejected combustion flame is seen clearly with a potential exceeding 2000 . The ignition power, ignition delay, and ignition energy are 1.16 W, 0.1-0.6 ms, and 0.12-0.70 mJ, respectively. The energy output is calculated to be around 60 mJ.
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.
Sol-gel chemistry is used to prepare igniters comprising energetic multilayer structures coated with energetic booster materials. These igniters can be tailored to be stable to environmental aging, i.e., where the igniters are exposed to extremes of both hot and cold temperatures (-30 C to 150 C) and both low (0%) and high relative humidity (100%).
Self-propagating formation reactions have been studied in multilayer foils and they are currently being investigated for applications in joining and ignition. Here, we introduce a reactive multilayer foil which contains a reduction-oxidation thermite reaction between CuOx and Al. Typically in reactive multilayer foils, elemental layers react and form a single intermetallic product. In this thermite reaction, however, aluminum and copper oxide are, respectively, oxidized and reduced and form aluminum oxide and copper. The fully dense multilayer foils provide a well-defined geometry for studying the thermodynamics, kinetics, and intermediate phase formation in the CuOx/Al thermite reaction. Here, sputter deposition of CuOx/Al multilayer foils is demonstrated, and x-ray diffraction and transmission electron microscopy, including high resolution transmission electron microscopy and electron spectroscopic imaging, are used to characterize the as-deposited foil and the final products. The heat released in the reaction is quantified using differential thermal analysis, and the velocity of the self-propagating reaction is reported. © 2003 American Institute of Physics.
The enhancement of energy release from nanoenergetic materials by using electrostatically enhanced assembly was investigated. The nanoscale assembly of the reactant particles was dependent on the collision rate between fuel and metal oxide zer particles. The transmission electron microscope (TEM) was used to identify the effect of particle charge on morphology of the nanocomposite particles. It was found that the size distribution and the degree of intermixing of thermite reactants affects the burning rate of energetic materials.
The synthesis of super-reactive metastable intermolecular composite (MIC) formulation of AL/KMnO4 was described using nanoscale energetic materials. Reaction-rate measurements were performed in terms of pressurization rate under confined combustion of the MIC. The synthesis of KMnO4 nanopaticles was done by an aerosol-phase spray-drying method, and pressurization-rate performance of a MIC in the form of a loose powder composed of Al/KMnO4 nanoparticles. It was found that a strong correlation existed between the pressurization rates for several MIC combinations and the fraction of reactive oxygen present in the combustion product.
Nanoenergetic materials (nEMs) have improved performances compared to their bulk counterpart or microcounterpart. The authors propose an approach to synthesize an Al / Cu O based nEM that has several advantages over previous investigations such as enhanced contact, reduced impurities and Al oxidation, tailored dimensions, and easier integration into microsystem. CuO nanowires are synthesized by thermally annealing Cu film deposited onto silicon. Nano-Al is integrated with the nanowires to realize an Al / Cu O based nEM. The synthesized nEM is characterized by scanning electron microscopy, high resolution transmission electron microscopy, x-ray diffraction, differential thermal analysis, and differential scanning calorimetry.
We have utilized a sol–gel synthetic approach in preparing nano-sized transition metal oxide components for new energetic nanocomposites. Nanocomposites of Fe2O3/Al(s), are readily produced from a solution of Fe(III) salt by adding an organic epoxide and a powder of the fuel metal. These materials can be processed to aerogel or xerogel monolithic composite solids. High resolution transmission electron microscopy (HRTEM) of the dried energetic nanocomposites reveal that the metal oxide component consists of small (3–10 nm) clusters of Fe2O3 that are in intimate contact with ultra fine grain (UFG) ∼25 nm diameter Al metal particles. HRTEM results also indicate that the Al particles have an oxide coating ∼5 nm thick. This value agrees well with analysis of pristine UFG Al powder and indicates that the sol–gel synthetic method and processing does not significantly perturb the fuel metal. Both qualitative and quantitative characterization has shown that these materials are indeed energetic. The materials described here are relatively insensitive to standard impact, spark, and friction tests, results of which will be presented. Qualitatively, it does appear that these energetic nanocomposites burn faster and are more sensitive to thermal ignition than their conventional counterparts and that aerogel materials are more sensitive to ignition than xerogels. We believe that the sol–gel method will at the very least provide processing advantages over conventional methods in the areas of cost, purity, homogeneity, and safety and potentially yield energetic materials with interesting and special properties.
Thermite mixtures with improved contact between the fuel and oxidizer can provide increased reaction rates compared with traditional thermite mixtures. One technique to create thermite mixtures with improved contact is to deposit the oxidizer directly onto nanometer-sized fuel particles. This study investigates the atomic layer deposition (ALD) of SnO2 onto nanoparticles using SnCl4 and H2O2 reactants. The nanoparticle ALD was performed in a small, hot wall, vertical fluidized bed reactor. The SnO2 ALD was first demonstrated on ZrO2 nanoparticles. Auger electron spectroscopy, inductively coupled plasma-atomic emission spectroscopy (ICP-AES), transmission electron microscopy (TEM) and particle size distribution analysis were used to characterize the SnO2-coated ZrO2 nanoparticles. Subsequently, SnO2 ALD was performed on Al nanoparticles. The SnO2-coated Al nanoparticles were analyzed using ICP-AES and TEM. The SnO2-coated Al and the uncoated Al particles were also ignited and filmed with a digital video recorder. Although the SnO2-coated Al particles were far from stoichiometric thermite composites, the SnO2-coated Al particles reacted much more quickly and violently than the uncoated Al particles. The lower than expected Sn percent by mass observed on the SnO2-coated Al nanoparticles highlighted a major difficulty with coating nanoparticles. The nanoparticles have an extremely high surface area and the required reactant exposures are large even when assuming 100% reactant efficiency. These results illustrate the utility of ALD techniques to coat oxidizers on fuel nanoparticles to create enhanced thermite materials.
Combustion behavior of energetic composite materials was experimentally examined for the purpose of evaluating the unique properties of nano-scale compared with traditional micron-scale particulate media. Behavior of composite systems composed of aluminum (Al) and molybdenum trioxide (MoO3) were studied as a function of Al particle size, equivalence ratio and bulk density. Samples were prepared by mechanically mixing individual fuel and oxidizer particles and combustion experiments included measurements of ignition and flame propagation behavior. Ignition was achieved using a 50-W CO2 laser and combustion velocities were measured from photographic data. Reaction kinetics were studied with differential scanning calorimetry (DSC). Results indicate that the incorporation of nano-Al particles (1) significantly reduces ignition temperatures and (2) produces unique reaction behavior that can be attributed to a different chemical kinetic mechanism than observed with micron-Al particles.
Laser ignition experiments were performed to determine the ignition time of nanoscale particle diameter composites of aluminum (Al) and molybdenum trioxide (MoO3). Ignition time and burn rate were measured as a function of stoichiometry and also as a function of Al particle diameter, which ranged from 17.4 nm to 20 mum. Composites were pressed into solid cylindrical pellets with a 4.5-mm diameter and length and with a constant 38% theoretical maximum density (TMD). A 50-W CO2 laser provided the ignition source and high-speed digital images were used to determine ignition time and burn rates. Results indicate that nanoscale Al particle composites show significantly reduced ignition times that varied from 12 ms up to 6 s for nanometer compared with micrometer scale Al particle composites, respectively. (C) 2004 The Combustion Institute. Published by Elsevier Inc. All rights reserved.
Two-dimensional nanostructures have various interesting applications due to their large surface areas. In this study, we propose a simple approach to synthesize two-dimensional NiO nano honeycomb by thermal annealing of Ni thin film deposited onto silicon substrate by thermal evaporation. The effects on the nano honeycomb morphology of the annealing temperature and time are investigated. Because the NiO nano honeycomb is realized onto silicon substrate, a basic material for microelectronics and micro-system, this will probably open the door to integrate the nano honeycomb into micro-system, thus leading to nano based functional devices. The as-synthesized NiO nano honeycomb is characterized by SEM, XRD, and surface area measurement.
This article presents a novel method for tuning the reactivity of nanoenergetic materials by coating a strong oxidizer nanoparticle (potassium permanganate; approximately 150 nm) with a layer of a relatively mild oxidizer (iron oxide). The measured reactivity for a nano-Al/composite oxidizer could be varied by more than a factor of 10, as measured by the pressurization rate in a closed vessel (psl/micros), by changing the coating thickness of the iron oxide. The composite oxidizer nanoparticles were synthesized by a new aerosol approach in which the nonwetting interaction between iron oxide and molten potassium permanganate aids the phase segregation of a nanocomposite droplet into a core-shell structure.
Explosive composition and its use
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Tail-hades, C. Vahlas, Nano energetic materials for MEMS: a review
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C. Rossi, K. Zhang, D. Estève, P. Alphonse, J.Y.C. Ching, P. Tail-hades, C. Vahlas, Nano energetic materials for MEMS: a review. J. Microelectromech. Syst. 16(4), 919–931 (2007
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Nanolaminate-based ignitors. US Patent WO
- T W Barbee
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T.W. Barbee, R.L. Simpson, A.E. Gash, J.H. Satcher, Nanolaminate-based ignitors. US Patent WO 2005 016850 A2, Feb. 24,
2005