No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Nanostructured Energetic Composites: Synthesis, Ignition/Combustion Modeling, and Applications
Abstract
Nanotechnology has stimulated revolutionary advances in many scientific and industrial fields, particularly in energetic materials. Powder mixing is the simplest and most traditional method to prepare nanoenergetic composites, and preliminary findings have shown that these composites perform more effectively than their micro- or macro-sized counterparts in terms of energy release, ignition, and combustion. Powder mixing technology represents only the minimum capability of nanotechnology to boost the development of energetic material research, and it has intrinsic limitations, namely, random distribution of fuel and oxidizer particles, inevitable fuel pre-oxidation, and non-intimate contact between reactants. As an alternative, nanostructured energetic composites can be prepared through a delicately designed process. These composites outperform powder-mixed nanocomposites in numerous ways; therefore, we comprehensively discuss the preparation strategies adopted for nanostructured energetic composites and the research achievements thus far in this review. The latest ignition and reaction models are briefly introduced. Finally, the broad promising applications of nanostructured energetic composites are highlighted.
... Nanoenergetic composite films, whose total thickness is generally 0.1-300 µm [1], consisting of alternating layers of nano-aluminum and nano-metal oxide are a new type of nano-thermite [1][2][3]. Such energetic systems of metal and metal oxides at the nanoscale are known as metastable intermolecular composites (MICs) or super-thermite [2][3][4]. ...
... Nanoenergetic composite films, whose total thickness is generally 0.1-300 µm [1], consisting of alternating layers of nano-aluminum and nano-metal oxide are a new type of nano-thermite [1][2][3]. Such energetic systems of metal and metal oxides at the nanoscale are known as metastable intermolecular composites (MICs) or super-thermite [2][3][4]. MIC powder, MIC nanoenergetic composite films, MIC nanorods, and other forms are included. Composite films made of metals and metal oxides are reactive, so energetic films are called reactive multilayer films (RMFs) [5]. ...
... Composite films made of metals and metal oxides are reactive, so energetic films are called reactive multilayer films (RMFs) [5]. According to the types of chemical reactions, nanoenergetic composite films can be divided into two categories: one is metal/oxide nanoenergetic composite films that can undergo aluminothermic reactions, such as Al/CuO [3,4,6], Al/MoO 3 [7,8], Al/Fe 2 O 3 [9,10] , and Al/NiO [11,12], etc. The other is metal/metal nanoenergetic composite films, such as Al/Ni [13][14][15], Al/Ti [16,17], and B/Ti [18,19], which can be alloyed. ...
The effect of the interface layer on energy release in nanoenergetic composite films is important and challenging for the utilization of energy. Nano Al/CuO composite films with different modulation periods were prepared by magnetron sputtering and tested by differential scanning calorimetry. With the increase in the modulation period of the nano Al/CuO energetic composite films, the interface layer contained in the energetic composite film decreased meaningfully, increasing the total heat release meaningfully. Ab initio molecular dynamics (AIMD) simulation were carried out to study the preparation process changes and related properties of the nano Al/CuO energetic composite films under different configurations at 400 K. The results showed that the diffusion of oxygen atoms first occurred at the upper and lower interfaces of CuO and Al, forming AlOx and CuxAlyOz. The two-modulation-period structure changed more obviously than the one-modulation-period structure, and the reaction was faster. The propagation rate and reaction duration of the front end of the diffusion reaction fronts at the upper and lower interfaces were different. The Helmholtz free energy loss of the nano Al/CuO composite films with a two-modulation-period configuration was large, and the number of interfacial layers had a great influence on the Helmholtz free energy, which was consistent with the results of the thermal analysis. Current molecular dynamics studies may provide new insights into the nature and characteristics of fast thermite reactions in atomic detail.
... Nanotechnology emerges as an enthusiastically evolving field, with numerous applications in materials, energy, manufacturing, and medical diagnosis (Neto 2014;Safari and Zarnegar 2014). There are about 800 different types of nanomaterial goods on the market, which are the by-products of nanotechnology generated with NPs (Dutschk et al. 2014: Zhou et al. 2014. Nanotechnology holds good promises for solving the issues related to abiotic stresses ensuring sustainable agriculture. ...
... Carbon (C) NPs are widely used in bioimaging (Tao et al. 2012), chemical sensing (Sharma et al. 2020), biomedical applications (Chen et al. 2017), and diagnostics ). Therefore, various physical, chemical, and biological techniques are used for the synthesis of CNPs, such as electrochemical oxidation (Zhou et al. 2014), ultrasonic treatment (Wang et al. 2015), hydrothermal synthesis (Yang et al. 2011), microwave-aided synthesis (Zhai et al. 2012), and thermal decomposition (Wang et al. 2016a). Fluorescent CNPs were synthesized through C soot oxidation of nitric acid (Ray et al. 2009). ...
Nanoparticles (NPs) are one of the most innovative and promising tools for their tremendous applications in agriculture. On one hand, physicochemical and green strategies are applied for the synthesis of NPs for administration in various fields. On the other hand, plants are subjected to harsh climatic conditions that constrain plant growth and yield. Understanding the plant nano-interaction mechanism becomes essential to assess the possible role in stress ameliorations. NPs affect plant growth and seed yield by affecting the fundamental physiological processes either positively or negatively.
Combining the physiological understanding with proteomic information highlighted the impact of NPs on various hormones and antioxidant systems that serve as a key factor in finding improved tolerance. This review illustrates the NPs synthesis strategies along with uptake/accumulation mechanism of silver (Ag), aluminum (Al), copper (Cu), iron (Fe), and carbon (C). Moreover, the interaction of these NPs with important plants like Arabidopsis , rice, wheat, and soybean are discussed in detail. NPs regulate the oxidative homeostasis and energy metabolism of crop plant to tolerate unfavorable conditions. Although many studies are conducted to explain plant–NP interaction at the morphological level, the molecular basis of such interactions is still not clear. This chapter summarizes the interaction mechanisms of NPs with crop plants, specifically wheat and rice.
... Nanothermites, comprising oxidizer and metal fuel existing at the nanoscale, are quite important among energetic materials, on account of their high energy density and rapid energy release [1][2][3][4][5]. As a hot research topic in recent years, nanothermites have found uses in a multitude of applications. ...
... The duration of the induced assembly process was extended to 7 d to examine the effect of the PBS of Al/CuO on their reactivity. In ultrapure water, Al NPs gradually transformed to Al(OH) 3 ...
Biological self-assembly procedures, which are generally carried out in an aqueous solution, have been found to be the most promising method for directing the fabrication of diverse nanothermites, including Al/CuO nanothermite. However, the aqueous environment in which Al nanoparticles self-assemble has an impact on their stability. We show that using a peptide to self-assemble Al or CuO nanoparticles considerably improves their durability in phosphate buffer aqueous solution, with Al and CuO nanoparticles remaining intact in aqueous solution for over 2 weeks with minimal changes in the structure. When peptide-assembled Al/CuO nanothermite was compared with a physically mixed sample in phosphate buffer for 30 min, the energy release of the former was higher by 26%. Furthermore, the energy release of peptide-assembled Al/CuO nanocomposite in phosphate buffer showed a 6% reduction by Day 7, while that of the peptide-assembled Al/CuO nanocomposite in ultrapure water was reduced by 75%. Taken together, our study provides an easy method for keeping the thermal activity of Al/CuO nanothermite assembled in aqueous solution.
... Energetic materials (EMs), can typically be classified as propellants, explosives, and pyrotechnics based on their various compositions, properties, and application fields Zhou et al. 2014). Therein, propellants comprising fuels, oxidizers, binders, and functional additives are one significant research aspect of the weapon systems, which produce gases with high temperatures and pressures by controlled combustion behavior and have common applications in rockets and munitions Yan et al. 2016). ...
In energetic materials, high-energy propellants always encounter poor mechanical properties. Herein, a novel energetic binder nitrate glycerol ether cellulose (NGEC)/hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) composite was prepared by a facile, safe water suspension and freeze-drying technology, and integrated in gun propellant (GP) through semi-solvent manufacturing. A series of characterizations and tests were conducted to characterize the NGEC/RDX-GP. The findings revealed that the mechanical properties in terms of the impact strength of NGEC/RDX-GPs with different content of NGEC was improved by 15.3% ~ 117.1%, 3.9% ~ 34.6%, 6.9% ~ 31.1% under conditions of -40 °C, 20 °C and 50 °C; the compression strength was improved by 2.5% ~ 23.1%, 10.7% ~ 27.9%, 7.3% ~ 28.5%, while the tensile strength was improved by 15.4% ~ 35.0%, 10.4% ~ 33.0%, 11.8% ~ 35.5%, respectively. Besides, the thermal decomposition dynamics and thermodynamics were also investigated to probe the thermal properties of NGEC/RDX-GP. Moreover, the impact and electrostatic spark sensitivity have also been tested and present excepted results compared with neat propellant. In addition, the improved gunpowder impetus of NGEC/RDX-GP indicated that the energetic performance of propellant was further enhanced, and maintained stable combustion behavior. Finally, the enhancement mechanism of the propellant was discussed and proposed. Therefore, this construction strategy and application of NGEC/RDX composites in propellants can provide reliable fundamental theory and data support for the development of high performances propellant.
Graphical abstract
... In contrast, explosives are commonly characterized by the integration of fuel and oxidizer moieties into a single molecule. This categorization reflects the different nature of EMs and their distinct roles in different energetic applications (Zhou et al. 2014;Li et al. 2022;Dlott 2006). Nowadays, there is continuous advancement in the expanding applications of insensitive munitions (IM). ...
In response to the demands for elevated energy levels and enhanced homogeneity in propellant and explosive formulations, new energetic composites based on unmodified and modified nanostructured cellulose nitrate and 3-nitro-2,4-dihydro-3H-l,2,4-triazol-3-one (NTO) were fully scrutinized. Indeed, microcrystalline cellulose nitrate (MCCN)/NTO, and carbamated microcrystalline cellulose nitrate (M3CN)/NTO composites were elaborated using a solvent evaporation method and their characteristics were compared to those of nitrocellulose (NC)/NTO. Experimental findings highlighted that the newly developed energetic composites exhibit favorable features, including a density exceeding 1.775 g/cm³. Moreover, theoretical performance calculations using EXPLO5 version 6.02.06 indicated that the optimal composition resulted in excellent specific impulses and detonation velocities, which increased from 217.5 s and 7910 m/s for NC/NTO to 235.1 s and 8165 m/s for M3CN/NTO. Structural analyses revealed a homogeneous dispersion and embedding of NTO particles within the nitrated cellulosic matrix. In addition, thermo-kinetic results demonstrated that the activation energy of the three designed energetic composites is lower than that of pristine NTO explosive. Therefore, this investigation offers a potential fabrication approach and basic theory for the application of nanostructured cellulose nitrate in advanced high-performance energetic formulations.
... Research has focused on finding new energetic materials [22][23][24] with a high purity and a unique reticulate nanostructure [25,26] concerning nanocellulose [27][28][29] and, most notably, bacterial cellulose (BC) as the leader among the nanocelluloses [30-32], has presently reached its highest demand [33][34][35][36][37]. The broad application prospects and benefits of nanocellulose nitrate-based energetic materials were overviewed back in 2014 [38]. Nanocellulose nitrates have a high demand in the manufacture of ionizing radiation detectors, bioindicators, biosensors, chips, semipermeable membranes, selective sorbents, and adhesives for electronic applications [2,35,39,40]. ...
Cellulose nitrates (CNs)-blended composites based on celluloses of bacterial origin (bacterial cellulose (BC)) and plant origin (oat-hull cellulose (OHC)) were synthesized in this study for the first time. Novel CNs-blended composites made of bacterial and plant-based celluloses with different BC-to-OHC mass ratios of 70/30, 50/50, and 30/70 were developed and fully characterized, and two methods were employed to nitrate the initial BC and OHC, and the three cellulose blends: the first method involved the use of sulfuric–nitric mixed acids (MAs), while the second method utilized concentrated nitric acid in the presence of methylene chloride (NA + MC). The CNs obtained using these two nitration methods were found to differ between each other, most notably, in viscosity: the samples nitrated with NA + MC had an extremely high viscosity of 927 mPa·s through to the formation of an immobile transparent acetonogel. Irrespective of the nitration method, the CN from BC (CN BC) was found to exhibit a higher nitrogen content than the CN from OHC (CN OHC), 12.20–12.32% vs. 11.58–11.60%, respectively. For the starting BC itself, all the cellulose blends of the starting celluloses and their CNs were detected using the SEM technique to have a reticulate fiber nanostructure. The cellulose samples and their CNs were detected using the IR spectroscopy to have basic functional groups. TGA/DTA analyses of the starting cellulose samples and the CNs therefrom demonstrated that the synthesized CN samples were of high purity and had high specific heats of decomposition at 6.14–7.13 kJ/g, corroborating their energy density. The CN BC is an excellent component with in-demand energetic performance; in particular, it has a higher nitrogen content while having a stable nanostructure. The CN BC was discovered to have a positive impact on the stability, structure, and energetic characteristics of the composites. The presence of CN OHC can make CNs-blended composites cheaper. These new CNs-blended composites made of bacterial and plant celluloses are much-needed in advanced, high-performance energetic materials.
... The designed Al/Ni energy-containing thin film device consists of a silicon substrate, a SiO 2 insulating layer, and a bridge region with a modulation period of 400 nm (modulation ratio Al: Ni = 3:2). 22,23 In order to simplify the calculation, meshing is only very fine at the V-shaped corners, and the rest of the mesh is coarsened; the mesh view is shown in Fig. 1(a). The physical parameters involved in the simulation are shown in Table I. ...
In this paper, we designed double V-shaped Al/Ni multilayer energy-containing microdevices with different V-angles, and we performed finite element modeling and simulation of the heat transfer process of the designed energy-containing microdevice. Temperature-dependent resistivity was introduced to effectively simulate the phase change during ignition. We simulated the temperature and current density distribution in the central region of the Al/Ni multilayer energy-containing microdevice and predicted the ignition voltage threshold for the specific device structure. Al/Ni multilayer energy-containing microdevices with different V-angles were prepared by electron beam evaporation technology, and ignition experiments on the prepared devices under the excitation of 47 μF capacitance were conducted. The experimental results show that the critical voltage of ignition increases with the increase in the V-angle, which verifies the correctness of the proposed finite element model.
... The effects of (Nos) on different plant species can vary significantly with different plant shapes, methods and duration of exposure and depend on (Nos) shape, size, chemical composition, concentration, and solubility 10 . More studies are needed on the potential risks of using (Nos) and their potential adverse effects 11 . Research indicates that (Nos) are highly toxic to aquatic life, bacteria, and human cells at the nanoscale; according to particle physics and studies of micro-atmospheric pollutants, even usually benign substances may become dangerous. ...
Anatomical characteristics are essential in determining the stress that affects plants. In addition, they provided a piece of evidence for environmental pollution. The increasing use of nanomaterials (EnNos) in industries, medicine, agriculture, and all fields. Nanomaterials also have many uses as a new science; they have toxic effects that have not been studied well. Therefore, this research was interested in recording recent studies on (EnNos) and their impact on the anatomical characteristics of plants. Moreover, the possibility of using anatomical characteristics as evidence of nano contamination (nanotoxicity) in plants comprises a crucial living component of the ecosystem. Studies on the effect of EnNos (carbon) on plant anatomy indicated that excess EnNos content affects the anatomical structure of the plant from the vital structures of the root, stem and leaves. Toxicological effect on xylem and phylum vessels from toxicological studies to date, Toxicological effects on EnNos of various kinds can be toxic if they are not bound to a substrate or freely circulating in living systems. Different types of EnNos, behavior, and plant capacity generate different paths. Moreover, different, or even conflicting, conclusions have been drawn from most studies on the interactions of EnNos with plants. Therefore, this paper comprehensively reviews studies on different types of carbon EnNos and their interactions with different plant species at the anatomical responses. Keywords: Anatomical characteristics, nanomaterials, nanotoxicity, Fullerene and Carbon Nanotubes
... Metastable intermolecular composite (MIC), typified by nanothermite, is one kind of energetic material comprising solid fuel and oxidizer which two are composited at nanoscale [1][2][3]. Upon proper stimulus, MIC can undergo self-sustained reaction with huge amounts of heat and gases released, which characteristics are promising for a range of military and civilian fields, such as micro-ignitor, micro-thruster, gas generator, and security device [4][5][6][7][8]. Owing to the nature of intercomponental reaction which starts at the interface, the actual performance of MIC is highly dependent on the micro-structure, where the high specific interfacial area and the intimate contact between components are desirable to achieve high reactivity and fast reaction speed. ...
... The introduction of nanotechnology into the design of energetic materials has resulted in a new type of highly reactive material: metastable intermolecular composites (MICs) [1][2][3]. Accompanied by significant nano-scale effects, MICs have a more uniform spatial distribution as well as enhanced interfacial contacts, along with tunable energy release and combustion properties [4][5][6][7]. Therefore, MICs are full of promising applications in the fields of detonation [8], micro-propulsion [9], material processing and synthesis [10], etc. ...
In this study, mesoporous silicon nanoparticles (M-Si) were successfully prepared by a magnesiothermic reduction of mesoporous silica nanoparticles, which were synthesized by a templated sol-gel method and used as the precursors. M-Si exhibited a uniform size distribution with an average diameter of about 160 nm. The measured BET surface area was 93.0 m2 g−1, and the average pore size calculated by the BJH method was 16 nm. The large internal surface area provides rich reaction sites, resulting in unique interfacial properties and reduced mass diffusion limitations. The mechanism of the magnesiothermic reduction process was discussed. The reactivity of prepared M-Si was compared with that of commercially available non-porous Si nanopowder (with the average diameter of about 30 nm) by performing simultaneous thermogravimetry and differential scanning calorimetry in the air. The results showed that the reaction onset temperature indicated by weight gain was advanced from 772 °C to 468 °C, indicating the promising potential of M-Si as fuel for metastable intermolecular composites.
... Energetic materials (EMs) are one kind of compound or mixture that contain explosive groups, oxidants, and fuels, which can carry out chemical reactions quickly and independently with high energy releases [1] . EMs can be widely used in weapon systems, rocket propulsion, civil blasting, and so on. ...
Graphene-based carbohydrazide coordination polymers are beneficial for improving solid propellants’ energy level and safety, so the study of their thermal decomposition mechanism is promoted for their wide application. In this paper, graphene oxide (GO) intercalated transition metal (Cu²⁺, Co²⁺, and Ni²⁺) complexes of carbohydrazide (CHZ) have been evaluated by using DSC/TGA apparatus and the TG-FTIR technique. Both isoconversional and combined kinetic methods were employed to calculate the kinetic parameters. The components inside GO-CHZ-M would react with each other to cause a large mass loss rate and lead to a larger heat-releasing value than pure GO. The types of metal ions could affect their reaction model. Compared with GO, G-CHZ-Co shows a two-sided effect (stabilization and catalytic) on its decomposition. For G-CHZ-Co, the reaction model of each peak is close to the random 2d nucleation and nucleus growth model.
... In addition to the experiments, computational chemistry has also become a mature approach to complement and aid experimental studies for predicting and designing novel EMs [2,12,[16][17][18][19][20][21][22][23][24], such as the density functional theory (DFT) method [25,26]. Several empirical models have been developed to guide the EMs design, including the Kamlet-Jacobs equation and the nitro charge method [27,28]. ...
Energetic materials (EMs) are the core materials of weapons and equipment. Achieving precise molecular design and efficient green synthesis of EMs has long been one of the primary concerns of researchers around the world. Traditionally, advanced materials were discovered through a trial-and-error processes, which required long research and development (R&D) cycles and high costs. In recent years, the machine learning (ML) method has matured into a tool that compliments and aids experimental studies for predicting and designing advanced EMs. This paper reviews the critical process of ML methods to discover and predict EMs, including data preparation, feature extraction, model construction, and model performance evaluation. The main ideas and basic steps of applying ML methods are analyzed and outlined. The state-of-the-art research about ML applications in property prediction and inverse material design of EMs is further summarized. Finally, the existing challenges and the strategies for coping with challenges in the further applications of the ML methods are proposed.
... Metastable intermolecular composites (MICs) usually consist of nano-sized active fuels (e.g., Al) and oxidants as a system [1][2][3]. It has many applications in the water environment, including underwater propulsion, blasting, and welding [4][5][6]. However, the underwater application of MICs is mainly limited by the reaction environment [7,8]. ...
The rapid heat loss and corrosion of nano-aluminum limits the energy performance of metastable intermolecular composites (MICs) in aquatic conditions. In this work, superhydrophobic n-Al/PVDF films were fabricated by the cryogel-templated method. The underwater ignition performance of the energetic films was investigated. The preparation process of energetic materials is relatively simple, and avoids excessively high temperatures, ensuring the safety of the entire experimental process. The surface of the n-Al/PVDF energetic film exhibits super-hydrophobicity. Because the aluminum nanoparticles are uniformly encased in the hydrophobic energetic binder, the film is more waterproof and anti-aging. Laser-induced underwater ignition experiments show that the superhydrophobic modification can effectively induce the ignition of energetic films underwater. The results suggest that the cryogel-templated method provides a feasible route for underwater applications of energetic materials, especially nanoenergetics-on-a-chip in underwater micro-scale energy-demanding systems.
... Compared to CHNO-based energetic materials, they exhibit higher chemical energy density owing to the closer contact between solid particles with a short transport distance, hence presenting exceptional reaction characteristics such as higher combustion performance, significant energy release, and faster reaction rates [14]. They have been applied in various fields such as microelectrochemical systems (MEMS), microactuatio n/micropropulsion, reactive bonding, inactivation of biological agent /microorganisms [15], and gas generators [16]. Besides that, owing to their large surface area, small particle size, and high surface atom mobility, they can significantly enhance the thermocatalytic performance and thus improve not only thermal efficiency but also enhance the ignition, thermal conductivity, burning rate, and combustion performance of numerous pure energetic ingredients such as ammonium percolorate and NC, and their respective formulations like double base and composite solid propellants [17][18][19]. ...
Nanothermites have been widely employed as an additive in explosive and propellant formulations owing to their high energy release efficiency, fast reaction rate, and enhanced performance. Their properties are closely dependent on the chemical nature of the implemented fuel/oxidizer components as well as the method used for their fabrication. Despite binary nanothermites, which contain one fuel and one oxidizer, being extensively developed and exhibiting interesting results, the exploration of ternary nanothermite systems is still scarce. Herein, MgAl-CuO ternary nanothermite was successfully prepared by the arrested reactive milling method (ARM). The product was characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), and laser granu-lometry, revealing that the particle size distributions of the powder samples obtained with pre-milled ingredients tend to shift to smaller sizes. On the other hand, composite films based on cellulose nitrate (NC) at different ratios of the nanothermite (5 %, 10 %, 15 %, and 20 %) were accordingly prepared and were fully characterized using different analytical techniques such as Fourier transform infrared (FTIR) and Raman spectroscopies, XRD, SEM, oxygen bomb calorimeter, and differential scanning calorimetry (DSC). The thermal decomposition behavior of the obtained composites was further investigated using isoconversional kinetic analysis to assess the catalytic effect of the ternary nanothermite on the thermal behavior of cellulose nitrate (CN), whereas the energetic performances of the obtained nanocomposites were predicted by EXPLO5 V6.04 software. The obtained results have shown that MgAl-CuO nanothermite has a minor influence on the thermal decomposition temperature of the studied composites, while a noticeable decrease in the activation energy has been obtained for the different composites , demonstrating the catalytic effect of the nanothermite. It was revealed that NC composite supplemented with 5% MgAl-CuO displayed the greatest heat of reaction and better energetic performance.
... Although they have advantages such as clean and low cost, their applications are limited by the environment and they are only viable when available [11]. Nanostructured energetic composites (NECs) contain all reactants inside [12,13], and can break through the limits of environment on the applications. The nano reactants significantly reduces the atomic diffusion distances, resulting in the high reactivity and high energy density of the NECs [14]. ...
In this study, the nanostructured Al/Ni energetic composites were processed using the high-energy ball milling method. The milling conditions, i.e. the ball to powder ratio (BPR), ball sizes, and milling time, were varied to investigate their effect on the microstructures and reaction properties of the Al/Ni NECs. Results indicated that large BPR, appropriate size assortment of milling balls, and long milling time promoted the formation of nano lamellar structure and improved the reaction performance. When the BPR was 10 and the milling time was 100min, the Al/Ni NECs had a nano lamellar structure and a low ignition temperature of 619 K. The activation energy was calculated to be 54.49 kJ/mol using the Kissinger method, and 63.87 kJ/mol using the Ozawa method, respectively.
... A large number of reviews on Al have been published. Xiang Zhou [58] summarized the synthesis, ignition and combustion modeling, and applications of Al-based nanocomposites. Wei He [59] introduced the preparation and characterization of Al-based MICs. ...
Aluminum (Al) has been widely used in micro-electromechanical systems (MEMS), polymer bonded explosives (PBXs) and solid propellants. Its typical core-shell structure (the inside active Al core and the external alumina (Al2O3) shell) determines its oxidation process, which is mainly influenced by oxidant diffusion, Al2O3 crystal transformation and melt-dispersion of the inside active Al. Consequently, the properties of Al can be controlled by changing these factors. Metastable intermixed composites (MICs), flake Al and nano Al can improve the properties of Al by increasing the diffusion efficiency of the oxidant. Fluorine, Titanium carbide (TiC), and alloy can crack the Al2O3 shell to improve the properties of Al. Furthermore, those materials with good thermal conductivity can increase the heat transferred to the internal active Al, which can also improve the reactivity of Al. Now, the integration of different modification methods is employed to further improve the properties of Al. With the ever-increasing demands on the performance of MEMS, PBXs and solid propellants, Al-based composite materials with high stability during storage and transportation, and high reactivity for usage will become a new research focus in the future.
... Several ongoing pieces of research worldwide are made to develop new energetic materials (EMs), which may be defined as a type of compounds that store a significant quantity of chemical energy in their structure and are released easily under some stimuli in a very short laps of time [1,2]. Nowadays, the novel generation of EMs requires to be balanced among low sensitivity, high-energy content, eco-friendly, and favorable thermal stability [3]. ...
The catalytic activity of energetic coordination polymers of triaminoguanidine-transition iron, containing graphene oxide (GO-T-Fe-T) or not (T-Fe), on the thermolysis of an energetic co-crystal of hydrazinium 3-nitro-1,2,4-triazol-5-one and ammonium nitrate (HNTO/AN) has been investigated. DSC apparatus has been employed to investigate the thermal behavior of the different products. Four isoconversional integral kinetic approaches have been used to calculate the kinetics triplets. The achieved results showed that both of T-Fe and GO-T-Fe-T possess good catalytic activity. The decomposition temperature and the activation energy of the co-crystal were reduced by 31 kJ/mol and by 55 kJ/mol when T-Fe and GO-T-Fe-T are introduced, respectively. Furthermore, using iron as a metal in the catalysts increased the decomposition heat released from the co-crystal. This can be due to the better dispersion of Fe on the GO sheets, which enhanced the decomposition reaction.
... Nanothermites are characterized by their high reactivity and energetic density [6], and can be tailored to specific applications. As they undergo highly exothermic reactions, a dispersed group of core-shell structured nanothermites can result in self-sustaining combustion due to the thermal diffusion and convection of the heated products of combustion, which ignite the neighboring particles. ...
The group combustion characteristics of core–shell nanothermite particles differ from other dispersed solid or liquid fuels. In a core–shell structure, each discrete nanothermite particle can undergo an exothermic reaction as the oxygen atoms in the metal oxide shell undergo a solid state diffusion to oxidize the metal core. This feature allows the spherical core–shell nanothermites to react in the absence of gaseous oxygen, thus modifying their group combustion characteristics compared to char or liquid fuels. Using a number of simplifying assumptions, a theoretical framework was established—based on existing group combustion theory—to examine the characteristics of mass and heat diffusion in nanothermite combustion. First, a model for the quasi-steady state single-particle combustion, in quiescent air, was established. The isolated particle combustion theory serves as the basis for the combustion interaction and mass transfer in a spherical cloud of dispersed nanothermite particles. The type of group combustion is strongly dependent on the diffusion of vapour products, i.e., the interaction is more pronounced when the diffusion of vapour products is higher. The group combustion regimes in dispersed nanothermites were identified and delineated.
... These materials undergo a characteristic oxidation-reduction reaction involving aluminum (Al) and a metallic oxide (MO) leading to the formation of a stable product. These energetic nanomaterials are known to have better combustion efficiencies and better ignitability compared to the typical Fulminic acid isomers energetics, represented by a common molecular formula CHNO (including cyanic acid, isocyanic acid and isofulminic acid), and are relatively much safer [1][2][3][4][5][6]. In general, a reduction in the grain size of Al and metal oxide increases the effective surface area and henceforth reduces the reaction barrier and results in an increased overall homogeneity. ...
In this study we demonstrate the effect of change of the sputtering power and the deposition pressure on the ignition and the combustion properties of Al/CuO reactive thin films. A reduced sputtering power of Al along with the deposition carried out at a higher-pressure result in a high-quality thin film showing a 200% improvement in the burn rate and a 50% drop in the ignition energy. This highlights the direct implication of the change of the process parameters on the responsivity and the reactivity of the reactive film while maintaining the Al and CuO thin-film integrity both crystallographically and chemically. Atomically resolved structural and chemical analyzes enabled us to qualitatively determine how the microstructural differences at the interface (thickness, stress level, delamination at high temperatures and intermixing) facilitate the Al and O migrations and impact the overall nano-thermite reactivity. We found that the deposition of CuO under low pressure produces well-defined and similar Al-CuO and CuO-Al interfaces with the least expected intermixing. Our investigations also showed that the magnitude of residual stress induced during the deposition plays a decisive role in influencing the overall nano-thermite reactivity. Higher is the magnitude of the tensile residual stress induced, stronger is the presence of gaseous oxygen at the interface. By contrast, high compressive interfacial stress aids in preserving the Al atoms for the main reaction while not getting expended in the interface thickening. Overall, this analysis helped in understanding the effect of change of deposition conditions on the reactivity of Al/CuO nanolaminates and several handles that may be pulled to optimize the process better by means of physical engineering of the interfaces.
... Energetic materials (EM) hold unparalleled importance in space exploration, public security and national defense, also our lives, and thus drawing great attentions and being investigated extensively [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15]. Among them, fluoride-contained reactive materials [16,17], especially fluoropolymer/metal pyrolants, is the non-ideal energetic materials concerned due to their outstanding insensitiveness and huge chemical potential energy (even twice larger than that of the utmost molecular explosive) [18][19][20][21][22][23]. ...
Fluoropolymer based reactive materials (FRM) have huge potential in propellant, thermobaric ammunition and damage augmentation applications due to high reaction enthalpy, excellent insensitivity and robust mechanical properties. However, existing FRM do not achieve ideal properties due to the difficulties to achieve fluoropolymers that satisfy both high F (fluorine) content and good processability, new fluoropolymer/s with high F content and good processability is urgently desired. Perfluorosulfonic acid ionomer (PFSA) is unique water-soluble fluoropolymer with intrinsic advantage for fluorinated reactive materials by combing the processability of fluoroplastics/fluororubbers and high F ratio of PTFE (Polytetrafluoroethylene), but application in reactive materials is extremely rare. Herein, we report PFSA based nano reactive materials (nRM). The material can be prepared in a very simplified solution mixing process, benefiting mass production of FRM, but holds impressive energy release, with 3 times larger heat release than that of PTFE based nRM. Characterization and analysis demonstrated that PFSA promoted (1) intimacy and interaction between fluorinated macromolecules and nano Al particles, and thus causes good dispersion and material strength; (2) reactivity between fluorinated macromolecules and nano Al particles due to its lower stability compared to PTFE and intimacy to nAl. Our work supports a new choice for developing high performance reactive materials, devices, and ammunitions.
... Pressing the mixture between glass slides reduces the exposure of particles to ambient air and promotes close contact between Mg and B to facilitate effective atomic diffusion during heating. 12,13 The glass slides were then placed in a muffle furnace (model FB1415M, Thermolyne) at 25°C and were heated at a heating rate of 30°C/min to 500°C. Isothermal conditions were maintained at 500°C for 90 min, after which the furnace was turned off and the sample was left inside to cool for 3 h. ...
A major problem limiting boron (B) use as a fuel or fuel additive is the native oxide layer present at the surface, which acts as a diffusion barrier at the boron/oxidizer interface. A requirement for improving the reactivity and exothermicity during the oxidation of B particles is to reduce the thickness of the native oxide. This can be achieved by the addition of reactive metals with reasonable gravimetric energy density, such as Mg, in the form of a mechanical mixture or alloyed compounds, which can undergo an exothermic redox reaction to reduce native oxide and enrich metallic B. Herein, we develop an approach to synthesize Mg/B solid solutions through a self-propagating high-temperature synthesis (SHS) reaction at 500°C leading to the formation of an outer shell comprised of Mg, MgO, and MgB2 around a B core as demonstrated by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and high-angle annular dark-field - scanning transmission electron microscopy - energy dispersive spectroscopy (HAADF-STEM-EDS). Particle size analysis by dynamic light scattering (DLS) shows a size distribution with an average size of 550 nm. The low synthesis temperature minimizes sintering and is inherently free of organic contamination compared to other available methods. The core-shell architecture offers two advantages: extension of the shelf life of B particles by the formation of a passivation shell; and in addition to the exothermic oxidation of Mg, MgB2, and B, an exothermic redox reaction occurs between Mg and native B2O3 to produce additional B fuel, culminating in a synergistic interaction that leads to increased heat release. Thermal analysis shows the promotional effect of Mg on B oxidation with increased heat release (24% higher) and higher oxidative stability than Mg and B under identical conditions. Synthesized Mg/B solid solutions release 90% of the theoretical energy density of Mg/B and thus show promise as energetic materials.
KEYWORDS: boron, magnesium, energetic materials, solid solutions, core-shell, thermal oxidation, heat release, combustion
In this research, three distinct ternary-nanothermites were subsequently integrated into double base propellant formulated with nitrocellulose (NC) and diethylene glycol dinitrate (DEGDN). These nanothermites consisted of magnesium and aluminum alloy (MgAl) as fuel and metal oxides (CuO, NiO, and TiO2) acting as oxidizers. Experimental results demonstrated the uniform distribution of the three investigated nanothermites throughout the NC/DEGDN composite. DSC findings indicated a significant increase in the overall heat release of the NC/DEGDN double base propellant upon the addition of the three nanothermites. It is found that the type of oxidizer within the nanothermite composition played a crucial role in the thermo-kinetic proprieties of the NC/DEGDN propellant. Specifically, nanothermites incorporating CuO and TiO2 acted as catalysts, substantially enhancing the thermolysis of the propellant. In contrast, MgAl–NiO exhibited a stabilizing effect on the thermal decomposition of NC/DEGDN propellant. These findings offer appreciated insights into the tailoring properties of double-base propellant by selectively incorporating specific nanothermites based on their oxidizer content.
Reactive multilayer films (RMFs), a type of nanostructured energetic material, are recognized as an indispensable component for laser-driven flyer plate initiator systems. In this work, Al/Ti-RMF with three different modulation periods (600, 300, and 150 nm) were prepared and integrated into multilayer flyer plates, and energetic material with optimized performance for laser-driven flyers was obtained. Cross-sectional observations demonstrate that the modulation periods of the RMF are precisely regulated, with thickness errors falling within 3.4%. The velocity of the flyer plates was significantly higher with a modulation period of 150 nm, reaching 2174.16 m/s. Molecular dynamics simulation results show that as the modulation period decreases, the diffusion rate of atoms increases, enabling the reaction between the RMF to be completed in a shorter time span, which makes for higher velocity of the flyer. The energy coupling efficiency results indicate that the kinetic energy coupling efficiency of the RMF with a modulation period of 150 nm is 145.6% and 29.8% higher compared to those with modulation periods of 600 and 300 nm, respectively. It is proved that Al/Ti-RMF have high-energy output performance and can be a novel candidate for laser-driven flyer plates, which will play a critical role in complex electromagnetic interference environments in the future.
Micron-sized titanium particles have potential applications as energetic metal high-enthalpy fuel materials. The molecular perovskite energetic material DAP-4 (H2dabco)[NH4(ClO4)3] is a potential high-energy oxidizer in solid rocket propellants. To explore the combustion mechanism and energy output of DAP-4-based Ti composites, the combustion characteristics of DAP-4/Ti and F/DAP-4/Ti were studied by electrode ignition device. The results show that the burning rate of DAP-4 can be adjusted by controlling the mass ratio of DAP-4/Ti. After adding Ti into DAP-4, the heat release, self-sustaining combustion time and flame front propagation velocity are greatly increased to 9,113 J g−1, 265 ms and 0.225 mm ms−1, respectively, better than those of DAP-4. With Ti added, the decomposition peak temperature of F/DAP-4/Ti dropped from 381.5 to 360.4 ℃. The experimental results contribute to a better understanding of the chemical reaction mechanism and energy release characteristics of DAP-4-based propellants containing Ti.
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.
This study investigated the nitration of nanostructured bacterial cellulose (NBC). The NBC, obtained using symbiotic Medusomyces gisevii Sa-12 as the microbial producer and then freeze-dried, was nitrated herein by two methods, the first using mixed sulphuric–nitric acids (MA) and the second using concentrated nitric acid in the presence of methylene chloride (NA+MC). The synthesized samples of NBC nitrates (NBCNs) exhibited 11.77–12.27% nitrogen content, a viscosity of 1086 mPa·s or higher, 0.7–14.5% solubility in an alcohol–ester mixture, and 0.002% ash. Scanning electron microscopy showed that the nitration compacted the NBC structure, with the original reticulate pattern of the structure being preserved in full. Infrared spectroscopy for the presence of functional nitro groups at 1658–1659, 1280, 838–840, 749–751 and 693–694 cm−1 confirmed the synthesis of cellulose nitrates in particular. Thermogravimetric and differential thermal analyses showed the resultant NBCNs to have a high purity and high specific heats of decomposition of 6.94–7.08 kJ/g. The NBCN samples differ conceptually from plant-based cellulose nitrates by having a viscosity above 1086 mPa·s and a unique 3D reticulate structure that is retained during the nitration. The findings suggest that the NBCNs can be considered for use in novel high-tech materials and science-driven fields distinct from the application fields of plant-based cellulose nitrates. The NBCN sample obtained with NA+MC has the ability to generate an organogel when it is dissolved in acetone. Because of the said property, this NBCN sample can find use as a classical adhesive scaffold and an energetic gel matrix for creating promising energetic polymers.
The paper elucidates the main driving mechanisms at play during the early stage of the Ti/CuO thermite reaction using reactive forcefields in the frame of molecular dynamics calculations. Results show that TiO preferentially forms in immediate contact to pure Ti at temperatures as low as 200 K rather than TiO2. Increasing the temperature to 700 K, the 2 nm TiO2 in contact to Ti is found to be homogeneously depleted from half of its oxygen atoms. Also, the first signs of CuO decomposition are observed at 600 K, in correlation with the impoverishment in oxygen atom reaching the titanium oxide layer immediately in contact to CuO. Further quantification of the oxygen and titanium mass transport at temperatures above 700 K suggests that mostly oxygen atoms migrate from and across the titanium oxide interfacial layer to further react with the metallic titanium fuel reservoir. This scenario is opposed to the one of the Al/CuO system, for which the mass transport is dominated by the Al fuel diffusion across alumina. Further comparison of both thermites sheds light on the enhanced reactivity of the Ti-based thermite, for which CuO decomposition is promoted at lower temperature, and offers a novel understanding of thermite initiation at large.
Metastable intermixed composites (MICs) are a class of energetic materials that have found applications in both civilian and military fields due to their high volumetric energy density and attractive combustion performances. The reactivity of MICs is tunable that has been proven theoretically and experimentally by controlling their microstructures. The design of microstructures of nanocomposites becomes more freely with the aid of the advanced preparation methods. In this chapter, the properties of MICs that were fabricated into three typical structures, namely the randomly distributed structure, the multilayered structure, and the core–shell structure are mainly focused. The preparation and characterization of the MICs with various structures are briefly introduced. The reactivity and mechanisms that influence the ignition and combustion behaviors of different structured Al‐based nanocomposites are reviewed and compared. In addition, the effects of components and structures on the combustion properties of MICs are analyzed and discussed. Lastly, the advantages of MICs with novel structures in terms of the combustion efficiency are clarified, and the suggestions to the existing challenges associated particularly with the core–shell structured MICs are proposed.
Ternary nanothermites are considered promising energetic materials and a key option to meet the increasing demand in the field of energetic and propulsion systems. The first part of this chapter outlines the advantages of using nanothermites over microthermites. Traditional composites of nanothermites based on n‐Al and metallic oxides are described. Furthermore, efforts to improve the combustion characteristics of basic nanothermites mixtures are summarized. In the second part of the chapter, we introduce the benefits of using oxygenated salts as alternative oxidizers to metallic ones in enhancing the energetic properties of nanothermites. The impact of different carbon nanomaterials (graphene oxide, reduced graphene oxide, carbon nanotubes, and carbon nanofibers) on the combustion behavior of ternary nanothermites is discussed. Another focus is on the proper use of ternary nanothermites in micro‐energetic devices. For this purpose, tuning the proportion of the oxidizer and fuel in ternary nanothermites is an important issue. In addition, the combustion propagation process, pressure, and thrust generating characteristics of ternary nanothermite mixtures in small tubes are examined.
Metastable intermolecular complexes (MICs), which have exceptional energy density and reactivity, have drawn considerable attention in the field of energetic materials. In this work, a facile cryogel method is explored for fabricating n-Al/PVDF energetic films with the controllable tuning of reactivity and laser sensitivity. The microstructure of the films was transformed from dense packing to 3D cross-linking by adjusting the process parameters. With the formation of the porous structure, the energetic film exhibits a higher energy release rate (the flame propagation speed increases from 8.2 cm∙s⁻¹ to 13.5 cm∙s⁻¹) and a lower laser ignition delay (from 33.6 ms to 10.1 ms). The mechanisms underlying the altered reactivity are discussed in depth to provide insights into understanding changes in energy properties. This work provides an effective and facile strategy for realizing the tunability of the reactivity and sensitivity of n-Al/PVDF composites, which will aid to broaden their use in micro-transducers.
Al/MLG/Fe2O3 nanothermite mixture was successfully synthesised by the physical mixing and ultrasonication technique. The synthesised nanothermite samples were characterised by XRD, FESEM, EDS, TEM, Raman spectroscopy and DSC/TG. X-ray diffraction (XRD) analysis showed that the constituent phases remain chemical stable during the synthesis process. The surface morphology of samples was observed by field emission scanning electron microscopy (FESEM), besides this, elemental composition of the sample was checked by energy dispersive spectroscopy (EDS). The homogenous mixing between the constituents was observed by transmission electron microscopy (TEM). The structural stability of graphene sheets was examined by using Raman spectroscopy. The energy release of nanothermite powder was investigated by differential scanning calorimetry (DSC) at different heating rates i.e. 5, 10, 15, 20 and 25 °C/min. The loss of mass during the thermite reaction was observed by thermogravimetric analysis (TG). Results indicate that the overall energy released of Al/(MLG 12 wt%)/Fe2O3 was increased by increasing the heating rate upto 25 °C/min and reached the maximum energy release of 1860 J/g, which is 46.5% of its theoretical value i.e. 4000J/g. The model-free Starink method was used to calculate the activation energy of the nanothermite sample and the observed value is 76 kJ/g.
In this study, core‐shell structured Al@CuO energetic microspheres are prepared through the alcohol‐thermal method. CuO is grown in situ around superfine Al powder, and Cu(OH)2 powder is used directly as the precursor for CuO growth. The effects of reaction temperature and reaction time on the chemical transformation as well as coating quality are investigated by using scanning electron microscopy, transmission electron microscopy and X‐ray diffraction. More importantly, the transformation of Cu(OH)2 into CuO during alcohol‐thermal process is tentatively discussed. And the growth mechanisms of CuO are speculated, which mainly consist of the continuous dissolution of Cu(OH)2, the transformation of dissolved Cu(OH)2 to CuO which happens at a lower temperature than that of dry Cu(OH)2 powder, and the heterogeneous nucleation and growth of CuO. The prepared Al@CuO energetic microspheres are compared with physically mixed Al/CuO counterparts by using thermal analysis, electric ignition and constant‐volume combustion tests. Benefiting from the improved interfacial contact quality, Al@CuO energetic microspheres show overall enhanced reaction characteristics in terms of reaction onset temperature, heat release, apparent activation energy, ignition delay, burning time and pressurization rate.
The available oxygen repositories of metal oxide play vital role in aluminothermic reactions. The contact surface of an oxidizer to metal fuel (aluminum) in high density energetic materials especially nanothermites control its chemical reactivity and combustion performance. MnO2 exposed facets {310}, {110}, {100} are hydrothermally synthesized with different precursors, physical mixed with nano-aluminum and MnO2/nAl composite came into existence. So far, the metal oxides around aluminum are theoretically well explained but experimentally lack some information about oxygen activity at interface. The VB-XPS, TEM, DSC in cooperation with density functional theory (DFT) calculations were used to investigate the exposed facet activity. Crystal facets have different surface oxygen and bulk arrangements where oxygen and vacancy electrostatic balance at interface engulfed aluminum, start pinching the alumina layer just before the onset temperature and finally breach the alumina in to aluminum. The activity of exposed facets to aluminum directly controls the reaction temperature, heat release and combustion pressure. The coherence between experimental and theoretical calculations shown MnO2-310 facet with lowest surface energy 1.12 J/m² not only expedite O2 activation at interface but also increase Al2O3/nAl oxidation activity with more heat release due to more oxygen vacancy formation. The MnO2 facet effect in MnO2/nAl composite is obvious from onset temperature 542℃, 535℃,529℃ to peak temperature 586 ℃, 578 ℃, 560 ℃ with heat release 2368 J/g, 2297 J/g, 765.5 J/g for {310}, {110}, {100} facets respectively. This research is presenting significance of MnO2 surface chemistry, comprehension facet activity to nAl and strategy to explore facet engineering in nanothermite.
In this study, to solve the boron oxide (B2O3) formed on the boron (B) surface, which reduces the reactivity and energy release. The energetic composite films with mutual reactions of B as fuel and polyvinylidene fluoride (PVDF) as oxidant are designed, based on the mosaic structure. Then, samples with different contents of B are successfully prepared by the novel synergistic emulsification and transient freezing methods. The morphology and composition results show that B is embedded in PVDF films, which makes the energetic composite films have excellent hydrophobicity and oxidation resistance. Interesting, the thermal analysis results show that in the low-temperature stage, the addition of B advances the initial decomposition temperature of PVDF; in the high-temperature stage, the gas product hydrogen fluoride (HF) of PVDF decomposition has a pre-ignition reaction (PIR) with B2O3, which destroys the shell of B2O3 and accelerates the oxidation of internal active B. And the heat release of 50% B content is the highest (3845.4J/g). Furthermore, the ignition and combustion results show that all samples can be ignited smoothly and easily. But the combustion performance is greatly affected by the content of B. Finally, the reaction mechanism of samples is preliminarily obtained by molecular model through the characterization of combustion products. These results show that composite films with mutual reactions based on B/PVDF mosaic structure have an excellent prospect for application in thermite with fluoropolymer.
By integrating a coaxial spinneret with a tri-axial parallel spinneret, a distinctive monoaxis//coaxis//monoaxis parallel spinneret is firstly constructed. A novel flexible one-dimensional nanoribbon (abbreviated as NR), very like the tricolor and thus named as quasi-tricolor NR, is firstly designed and prepared via electrospun technique by the distinctive spinneret. As a case study, {[Tb(TTA)3(TPPO)2] (abbreviated as TbTT)/PMMA}//{[CoFe2O4/PMMA]@[polyaniline (PANI)/PMMA]}//{anthracene/rhodamine B/PMMA} quasi-tricolor NR and array (named as QNA for short) are prepared. Each quasi-tricolor NR is made up of left and right sides of green luminescent [TbTT/PMMA] NR and blue-red luminescent [anthracene/rhodamine B/PMMA] NR, respectively, and the middle of magnetic-conductive [CoFe2O4/PMMA]@[PANI/PMMA)] coaxial NR. The quasi-tricolor NR as the building unit with unique quadri-partitioned structure restricts the conductive polymer, luminescent materials and magnetic nanoparticles in their own spatial domains, which effectively avoid unfavorable effects among various functions and ensure strong luminescence and high conductive aeolotropy of the array. Luminescent-magnetic-conductive trifunctionality is highly integrated. Moreover, energy transfer among luminescent materials is regulated by the aid of special structure of NR and thus white light emission (abbreviated as WLE) is realized by the combination of terbium complexes with dyes. The conductive aeolotropy and magnetism of the QNA can be respectively modulated by varying the contents of PANI and CoFe2O4. The highest conductance ratio in two perpendicular directions can reach 10⁸ when PANI content is 70 %. The quasi-tricolor NR can be extended to assemble other functions to avoid adverse mutual interferences to achieve poly functions.
Green chemistry is considered as a significant device for achieving sustainability which includes the synthesis of chemical products with less or remediates the toxicity of hazardous substances. Green nanotechnology affords solutions to several global challenges. Green nanotechnology is being considered as an imperative tool in achieving sustainability in agriculture, food industries, and animal feed. In green nanotechnology, nanomaterials (NMs) are synthesized via biological methods and have numerous applications in the sustainable agriculture sector and allied sectors. Different tissues of plants such as leaf, stem, bark, seed, root, fruits, and flower have been used for nanoparticles (NPs) biosynthesis. A variety of NMs are being used to sustain the agricultural sectors. Since the potential of this newly emerged field of medicine and research is beyond the scope of this book chapter, we will be focusing on a brief overview of green nanotechnology and the research efforts on its potential applications in sustainable agriculture and allied sectors. Various engineered nanomaterials (ENMs) have different impacts, mechanisms, and behaviors on plants. Therefore, this book chapter also comprehensively reviews various ENM’s uptake, translocation, interactions mechanisms, and their phytotoxicity in plant species in order to develop systems for sustainable agriculture is provided in this chapter. The advantage and importance offered by NMs utilization are highlighted in this chapter, in concert with the main technological confronts prospect implementation of the systems for sustainable agriculture.
Aluminized composite propellants have long suffered from efficiency and thermal chal-lenges related to production of condensed phase slag droplets during operation. In an effort to mitigate the production of large droplets, a mechanically activated intermetallic forming nickel-aluminum compound was substituted for a portion of a propellant's aluminum fuel. The resulting agglomerate size and burning rate of this propellant was compared to a stan-dard aluminized AP/HTPB propellant. Addition of mechanically activated fuel particles increased the burning rate exponent of the propellant, while simultaneously decreasing condensed phase agglomerate size from 235 µm (for the control propellant) to 90 µm (for the propellant containing 75 wt.% Ni-Al fuel). As such, intermetallic forming fuels may provide a route for increasing efficiency in solid rocket motors by simultaneously reducing the need for burning rate catalysts and minimizing two-phase nozzle flow losses.
The paper considers the rules of formation, the structure and reactivity of aluminum based composites with the additives of graphite, BN, MoO3 and Teflon, prepared by mechanochemical method. Under mechanical treatment the following stages were separated: (i) independent grinding and mixing of reagents, (ii) formation of molecular-dense composites consisted from nanosized Al particles and matrix of second component, (iii) chemical interaction of components and (iv) crystallization of products. Formation of nanosizes Al/X composites (stage ii) leads to the great increase of reactivity. For example, for Al/C nanocomposites the depth and oxidation rate of reaction of Al with oxygen, nitrogen and water significantly increases, but temperature of solid - phase interaction Al + C decreases down to 850 °C; for system Al/MoO3 combustion rate increases from 1 to 400 m/s, for Al/Teflon was observed detonation-like regime with the velocity up to 1300 m/s, etc.
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.
The conditions for self-sustaining combustion synthesis in nanosized multilayer Ni/Al films deposited on a substrate are studied based on a 2D model. The model considers two conjugate processes, i.e. propagation of the synthesis wave in a multi-layer Ni/Al system and propagation of the accompanying thermal wave into the substrate. It is shown that the boundary between the regimes of self-sustaining reaction and annealing is determined by the number of binary layers of reactants (at a given heater temperature, stoichiometric ratio of the reactants and ration of film and substrate thermal diffusivities), but it does not depend on the bilayer thickness. The distinctive features of synthesis in the thermal explosion mode and in the annealing regime are studied as well.
The porous silicon (PS) film has gained increasing attention in recent years as advanced nanoenergetic materials (nEMs). A simple fabrication method to prepare uncracked PS thick films was successfully realized with precisely controlled electrochemical etching, and the relationship between the current density and the concentration of electrolytes was found in its fabrication. Additionally, the capillary stresses resulted from the liquids in nanopores of PS films was another factor resulted in its crack. The nanopores composed of uncracked PS thick films distributed regularly and their diameters ranged from 2 nm to 6 nm. Its Sa (average roughness) of PS film surface was 6.53 nm, and its thickness ranged from 102.41 μm to 205.75 μm. The specific surface area was 587 m2/g and the average diameter of nanopores was 4.3 nm. The PS film was found to be monocrystal and it was same as the substrate. The crack mechanism of PS films was discussed: the porous structure reduced the strength of PS films comparing the silicon bulk and the capillary effect hastened the crack of PS films. PS films filling with sodium percholorate in nanopores were ignited by laser and the stable combustion showed that they were advantageous to be applied as micro-electromechanical systems (MEMS) compatible devices, such as silicon-based chips of mircothruster and microigniter.
Ignition was studied experimentally for four nanocomposite materials prepared by Arrested Reactive Milling (2Al·3CuO, 2.35Al·Bi2O3, 4Al·Fe2O3, and 8Al·MoO3). Thin layers of the prepared powders were coated on an electrically heated Ni–Cr filament and ignited at heating rates between 200 and 17,000 K/s in a miniature vacuum chamber. The ignition was monitored based on both photodiode and pressure transducer signals recorded simultaneously. Ignition temperatures were found to be weakly dependent of the heating rate and similar for all thermites (in the range of ∼800–950 K) except for that using Bi2O3 as an oxidizer, which ignited at lower temperatures. Both maximum pressure and the rate of pressure rise (dP/dt) decreased with increasing heating rate. The onsets of pressure pulses produced by ignited thermites occurred prior to those of the respective emission pulses, with the effect increasing at higher heating rates. It was observed that 2.35Al·Bi2O3 did not ignite at heating rates above 5000 K/s in vacuum, while it readily ignited when heated in air. A qualitatively similar observation was made for 8Al·MoO3, which could not be ignited in vacuum when heating rates reached 13,000 K/s. The results are interpreted to suggest that the low-temperature redox reactions occurring prior to ignition modify the oxidizers, making them less stable and prone to rapid decomposition upon further heating. Ignition, triggered by a change in transport properties of the growing interfacial Al2O3 layer is not directly affected by the oxygen release from the decomposing oxides. Both oxygen release and growth of the interfacial Al2O3 layer are directly affected by the rates of low-temperature redox reactions preceding ignition.
A multi-step reaction model is developed to describe heterogeneous processes occurring upon heating of an Al-CuO nanocomposite material prepared by arrested reactive milling. The reaction model couples a previously derived Cabrera-Mott oxidation mechanism describing initial, low temperature processes and an aluminium oxidation model including formation of different alumina polymorphs at increased film thicknesses and higher temperatures. The reaction model is tuned using traces measured by differential scanning calorimetry. Ignition is studied for thin powder layers and individual particles using respectively the heated filament (heating rates of 10–10 K s) and laser ignition (heating rate ∼10 K s) experiments. The developed heterogeneous reaction model predicts a sharp temperature increase, which can be associated with ignition when the laser power approaches the experimental ignition threshold. In experiments, particles ignited by the laser beam are observed to explode, indicating a substantial gas release accompanying ignition. For the heated filament experiments, the model predicts exothermic reactions at the temperatures, at which ignition is observed experimentally; however, strong thermal contact between the metal filament and powder prevents the model from predicting the thermal runaway. It is suggested that oxygen gas release from decomposing CuO, as observed from particles exploding upon ignition in the laser beam, disrupts the thermal contact of the powder and filament; this phenomenon must be included in the filament ignition model to enable prediction of the temperature runaway.
Nanochargers are energetic materials consisting of fuel metal particles and metallic oxide particles that absorb and store energy up to an ignition threshold. Once ignited a controlled exothermic reaction ensues producing energy. Nanotechnology has spurred the understanding of unique nanoparticle combustion behaviors that enable creation of nanochargers with optimized heat capacity for storing energy. Although in the initial stages, these experiments demonstrate evidence of the nanocharger's potential for energy storage and transfer.
Energetic materials are chemical compounds or mixtures that store significant quantities of energy. In this review, we explore recent approaches to property prediction and new material synthesis. We show how the successful design of new energetic materials with tailored properties is becoming a practical reality.
Inactivation of airborne microorganisms due to thermal or chemical air treatment has gained considerable attention. Destruction of aerosolized biothreat agents in environments containing combustion products is particularly relevant to military and counterterrorism situations because some pathogens may survive an explosion or fire in a bio-weapon facility and be dispersed in the atmosphere. Energetic materials with biocidal properties are being sought to effectively inactivate stress-resistant aerosolized microorganisms. Consequently, appropriate methods are needed to test these materials. We designed and built a state-of-the-art experimental facility and developed protocols for assessing the survival of aerosolized microorganisms exposed to combustion. The facility uses a continuous-flow design and includes an aerosolization unit, a test (combustion) chamber, and a measurement system for bioaerosol particles exposed to combustion environments for sub-second time intervals. The experimental method was tested with Bacillus endospores. We assessed the inactivation of aerosolized spores exposed to a gaseous hydrocarbon flame and to combustion of aluminum-based energetic composites (including a novel iodine-containing filled nanocomposite material). Two combustion configurations were evaluated – a vertical strand containing a consolidated material and a specially designed burner in which a fuel powder is fed into a gaseous hydrocarbon flame. It was established that the bioaerosol inactivation may be overestimated due to exposure of spores on collection filters to the combustion products throughout the test. The overestimation can be mitigated by reducing the collection time and minimizing the formation of soot. The experimental facility and method developed in this study enables evaluating effects caused by biocidal products during combustion. The present version of the set-up provides the capability of detecting inactivation levels of ~2.2 × 10 5 (over five-log viability reduction) its further design modifications can potentially enable measuring bioaerosol inactivation as high as ~10 7 . The method was utilized for establishing feasibility of the new iodine-containing material for microbial agent defeat applications. Keyword: Bioaerosols; Combustion aerosols; Hazardous air pollutants.
A method of generating power uses a nanoenergetic material. The nanoenergetic material comprising thermite is obtained and deposited on a substrate. An igniter is placed on the nanoenergetic material. When power is desired, the nanoenergetic material is ignited. A transducer receives thermal, sonic, magnetic, optic and/or mechanical energy from combustion of the nanoenergetic material and converts it into electrical energy. Preferably, the transducer is a thermoelectric, piezoelectric or magneto device. Preferably, multiple transducers are integrated in one power generators to maximize the power from nanoenergetic thermites.
The experimrntal and theoretical works dealing with heterogeneous exothermic reaction waves in multilayer nanofilms are analysed. Mathematical models of reaction wave propagation are described. The dynamics of phase and structural transitions during heterogeneous reactions in nanosystems is considered. The prospects of the studies of reaction waves for the investigation of the mechanisms of processes in nanosystems and for diverse practical applications (in particular, for the development of new welding and soldering techniques) are demonstrated.
A recently developed model for low-temperature exothermic reactions in nanocomposite Al-CuO thermites described the evolution of an alumina layer growing between Al and CuO and changes in its diffusion resistance as critically affecting ignition of the composite reactive material. The model was successful in describing ignition of individual composite particles in a CO2 laser beam. However, it was unable to conclusively predict ignition of the same powder particles coated onto an electrically heated filament. In this work, ignition of fully-dense 2Al·3CuO nanocomposite powder prepared by arrested reactive milling was studied using a modified electrically heated filament experiment, located in a miniature vacuum chamber. Thin layers of the powders coated on a nickel-chromium filament were ignited at heating rates between 200 and 16,000 K/s. The ignition was accompanied by both optical emission and pressure signals. The pressure signals occurred before emission, with increasing delay at higher heating rates. Ignition temperatures were only slightly affected by the heating rate. The results are interpreted proposing that the low-temperature redox reaction produces a metastable CuO1-x phase with 0 < x « 1 which releases oxygen upon heating. It is shown that despite a relatively small heat release, the low-temperature reactions in nanocomposite thermites are important as producing destabilized, partially reduced oxides that decompose with gas release upon heating. In the present experiments, the gas release changed thermal properties of the powder coating, reducing the efficiency of heat exchange with the supporting filament and thus enabling its thermal runaway and ignition.
Highly reactive nanothermites prepared by mixing bismuth trioxide or cupric oxide nanoparticles with aluminum nanoparticles were evaluated as solid propellants for small-scale propulsion applications. Miniaturized engines were fabricated from steel in three-piece configurations without a converging/diverging nozzle. Bismuth trioxide-aluminum generated 46.1 N average thrusts for 1.7 ms durations with a specific impulse of 41.4 s. Cupric oxide-aluminum generated 4.6 N thrusts for 5.1 ms durations with a specific impulse of 20.2 s. Convective and conductive reaction regimes were identified as functions of bulk packing density and confinement geometry. Average thrusts and burning durations differed by greater than an order of magnitude for equivalent nanothermites dependent on the reaction regime. Adding small amounts of nitrocellulose to the nanothermites increased specific and volumetric impulses to maximum values of 59.4 s and 2.3 mN . s/mm(3) while controllably reducing average thrusts and prolonging burning durations. The energy-conversion efficiencies of the thrusters were evaluated using a rotary-arm measurement, and a maximum efficiency of 0.19% was observed. Last, a miniaturized four-engine array was fabricated with micromachined initiators and sequentially fired. The high specific and volumetric impulses, fast combustion, and tailored reactions of nanothermites are appealing for many small-scale propulsion applications.
Highly reactive metastable nano-scale composites of aluminum and metal oxides have been produced by arrested reactive milling (ARM). Aluminum powder has been milled with powders of MoO3 and Fe2O 3. These composites belong to a novel class of energetic materials characterized by an intimate mixing of reactive components on nanometer to atomic scale. Reactive components can be metal/metal oxide pairs or combinations of other materials capable of highly exothermic reactions such as B-Ti or B-Zr. High-energy milling of these components leads to mechanical initiation of the reaction. Highly reactive composites are obtained by arresting this process immediately before the initiation would occur if milling were allowed to proceed. An experimental parametric study of reactive milling in the Al-MoO3 and Al-Fe2O3 systems was conducted to establish at which milling times the reaction is spontaneously initiated under various conditions. An expression for the milling dose - the degree of refinement - was introduced and is an adequate characteristic of the milling progress. Experimental results from the milling parametric study are compared to Discrete Element Modeling currently in development for describing mechanical alloying in SPEX shaker mills. The Discrete Element Models produce an equivalent milling dose that correlates with the experimental results. Samples of nano-composite powders were synthesized by arresting the milling process, and characterized using electron microscopy, x-ray diffraction, and particle size analysis. Copyright © 2005 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.
This paper details the synthesis and combustion characteristics of silicon-based nanoenergetic formulations. Silicon nanostructured powder (with a wide variety of morphologies such as nanoparticles, nanowires, and nanotubes) were produced by DC plasma arc discharge route. These nanostructures were passivated with oxygen and hydrogen post-synthesis. Their structural, morphological, and vibrational properties were investigated using X-ray diffractometry, transmission electron microscopy (TEM), nitrogen adsorption-desorption analysis, Fourier transform infrared (FTIR) spectrometry and Raman spectroscopy. The silicon nanostructured powder (fuel) was mixed with varying amounts of sodium perchlorate (NaClO4) nanoparticles (oxidizer) to form nanoenergetic mixtures. The NaClO4 nanoparticles with a size distribution in the range of 5–40 nm were prepared using surfactant in a mixed solvent system. The combustion characteristics, namely (i) the combustion wave speed and (ii) the pressure-time characteristics, were measured. The observed correlation between the basic material properties and the measured combustion characteristics is presented. These silicon-based nanoenergetic formulations exhibit reduced sensitivity to electrostatic discharge (ESD).
A nanocomposite energetic material was prepared using sol-gel processing. It was incorporated into the nano or submicrometer-sized pores of the gel skeleton with a content up to 95 %. AP, RDX, and silica were chosen as the energetic crystal and gel skeleton, respectively. The structure and its properties were characterized by SEM, BET methods, XRD, TG/DSC, and impact sensitivity measurements. The structure of the AP/RDX/SiO2 cryogel is of micrometer scale powder with numerous pores of nanometer scale and the mean crystal size of AP and RDX is approx. 200 nm. The specific surface area of the AP/RDX/SiO2 cryogel is 36.6 m2 g−1. TG/DSC analyses indicate that SiO2 cryogel can boost the decomposition of AP and enhance the interaction between AP and RDX. By comparison of the decomposition heats of AP/RDX/SiO2 at different mass ratios, the optimal mass ratio was estimated to be 6.5/10/1 with a maximum decomposition heat of 2160.8 J g−1. According to impact sensitivity tests, the sensitivity of the AP/RDX/SiO2 cryogel is lower than that of the pure energetic ingredients and their mixture.
This paper exploits an energetic initiator realized by integrating Al/Ni
multilayer nanofilms with semiconductor bridge (SCB). The as-deposited
nanofilms have been characterized with varied analytical techniques.
Results show that distinct nanofilms are sputter deposited in a layered
geometry and give a heat of reaction equal to 1134 J/g. The firing tests
of the initiators were accomplished using capacitor discharge unit.
Results show that the initiators possess several excellent
characteristics such as fast ignition time, low power consumption, high
output energy and so on. Therefore, Al/Ni multilayer nanofilms are
suitable heat source for improving the reliability of SCB initiators.
In this paper, the in-situ preparation and characterization of a porous copper-sodium perchlorate energetic nano-composite (PCu/NaClO4) and its electrical ignition properties are presented. Porous copper was in-situ produced by electro-deposition on a Ni/Cr alloy wire, which acts as a cathode during the electro-deposition. The PCu/NaClO4 nano-composite was produced by dipping the bridge with porous copper into a saturated sodium perchlorate acetone solution. SEM, EDS, and XRD were used to characterize the composite and DSC was used to study the thermal decomposition of the composite. The copper grain size was reduced by using additives such as CTAB in the electrolyte. The PCu/NaClO4 nano-composite on the bridge can be ignited by feeding a current through the bridge and the ignition delay time and electrical ignition sensitivity were measured.
As the capability and complexity of robotic platforms continue to evolve from the macro to the micron scale, the challenge of achieving autonomy requires the development of robust, lightweight architectures. These architectures must provide a platform upon which actuators, control, sensing, power, and communication modules are integrated for optimal performance. In this paper, the first autonomous jumping microrobotic platform is demonstrated using a hybrid integration approach to assemble on-board control, sensing, power, and actuation directly onto a polymer chassis. For the purposes of this paper, jumping is defined as brief parabolic motion achieved via an actuation pulse at takeoff. In this paper, the actuation pulse comes from the rapid release of chemical energy to create propulsion. The actuation pulse lasts several microseconds and is achieved using a novel high-force/low-power thrust actuator, nanoporous energetic silicon, resulting in 250 μJ of kinetic energy delivered to the robot and a vertical height of approximately 8 cm.
Interface layers between reactive and energetic materials in nanolaminates or nanoenergetic materials are believed to play a crucial role in the properties of nanoenergetic systems. Typically, in the case of Metastable Interstitial Composite nano-laminates, the interface layer between the metal and oxide controls the onset reaction temperature, reaction kinetics and stability at low temperature. So far, the formation of these interfacial layers is not well-understood for lack of in-situ characterization, leading to a poor control of important properties. We have combined in-situ infrared spectroscopy and ex-situ X-ray photoelectron spectroscopy, differential scanning calorimetry, and high resolution transmission electron microscopy, in conjunction with first-principles calculations to identify the stable configurations that can occur at the interface and determine the kinetic barriers for their formation. We find that (i) an interface layer formed during physical deposition of alumimum is composed of a mixture of Cu, O and Al through Al penetration into CuO, and constitutes a poor diffusion barrier (i.e., with spurious exothermic reactions at lower temperature); and in contrast (ii) atomic layer deposition (ALD) of Al2O3 using trimethylaluminum (TMA) produces a conformal coating that effectively prevents Al diffusion even for ultra-thin layer thicknesses (~0.5 nm), resulting in better stability at low temperature and reduced reactivity. Importantly, the initial reaction of TMA with CuO leads to the extraction of oxygen from CuO to form an amorphous interfacial layer that is an important component for superior protection properties of the interface and is responsible for the high system stability. Thus, while Al e-beam evaporation and ALD growth of Al2O3 on CuO both lead to CuO reduction, the mechanism for oxygen removal is different, directly affecting the resistance to Al diffusion. This work reveals that it is the nature of the monolayer interface between CuO and Al2O3/Al rather than the thickness of the Al2O3 layer that controls the kinetics of Al diffusion, underscoring the importance of the chemical bonding at the interface in these energetic materials.
Nanoscale metal oxide materials have been attracting much attention because of their unique size- and dimensionality-dependent physical and chemical properties as well as promising applications as key components in micro/nanoscale devices. Cupric oxide (CuO) nanostructures are of particular interest because of their interesting properties and promising applications in batteries, supercapacitors, solar cells, gas sensors, bio sensors, nanofluid, catalysis, photodetectors, energetic materials, field emissions, superhydrophobic surfaces, and removal of arsenic and organic pollutants from waste water. This article presents a comprehensive review of recent synthetic methods along with associated synthesis mechanisms, characterization, fundamental properties, and promising applications of CuO nanostructures. The review begins with a description of the most common synthetic strategies, characterization, and associated synthesis mechanisms of CuO nanostructures. Then, it introduces the fundamental properties of CuO nanostructures, and the potential of these nanostructures as building blocks for future micro/nanoscale devices is discussed. Recent developments in the applications of various CuO nanostructures are also reviewed. Finally, several perspectives in terms of future research on CuO nanostructures are highlighted.
Al/CuOx based micro- and nanoenergetic materials (EMs) have been made by the thermal oxidation of Cu thin films deposited onto silicon substrates followed by Al integration through thermal evaporation. The micro- and nano-EMs are then characterized by scanning electron microscopy, energy dispersive X-ray analysis, X-ray diffraction, differential thermal analysis, and differential scanning calorimetry. By comparing the thermite reactions and ignition properties of Al with micro-CuOx and Al with nano-CuOx, we show experimentally that one-dimensional nanostructures (CuO nanowires) and nano-Al affect greatly the exothermic behaviors and ignition properties of the Al/CuOx based EMs. The higher surface energy associated with the CuO nanowires and the deposited nano-Al is believed to be a possible factor contributing to the enhanced exothermic reactions that occur below the melting point of Al and the smaller ignition delay and lower ignition energy.
Several binary intermetallic compounds—each containing a rare-earth (RE) element paired with a transition metal (TM)—were prepared by self-propagating, high-temperature synthesis (SHS). Thin multilayers, composed of alternating Sc or Y (RE element) and Ag, Cu, or Au (TM), were first deposited by direct current magnetron sputtering. Once the initially distinct layers were stimulated and caused to mix, exothermic reactions propagated to completion. X-ray diffraction revealed that Sc/Au, Sc/Cu, Y/Au, and Y/Cu multilayers react in vacuum to form single-phase, cubic B2 structures. Multilayers containing Ag and a RE metal formed cubic B2 (RE)Ag and a minority (RE)Ag2 phase. The influence of an oxygen-containing environment on the reaction dynamics and the formation of phase were investigated, providing evidence for the participation of secondary combustion reactions during metal-metal SHS. High-speed photography demonstrated reaction propagation speeds that ranged from 0.1–40.0 m/s (dependent on material system and foil design). Both steady and spin-like reaction modes were observed.
We have developed a new nanothermite based polymeric electro-thermal initiator for non-contact ignition of a propellant. A reactive Al/CuO multilayer nanothermite resides on a 100 µm thick SU-8/PET (polyethyleneterephtalate) membrane to insulate the reactive layer from the silicon bulk substrate. When current is supplied to the initiator, the chemical reaction Al+CuO occurs and sparkles are spread to a distance of several millimeters. A micro-manufacturing process for fabricating the initiator is presented and the electrical behaviors of the ignition elements are also investigated. The characteristics of the initiator made on a 100 µm thick SU-8/PET membrane were compared to two bulk electro-thermal initiators: one on a silicon and one on a Pyrex substrate. The PET devices give 100% of Al/CuO ignition success for an electrical current >250 mA. Glass based reactive initiators give 100% of Al/CuO ignition success for an electrical current >500 mA. Reactive initiators directly on silicon cannot initiate even with a 4 A current. At low currents (<1 A), the initiation time is two orders of magnitude longer for Pyrex initiator compared to those obtained for PET initiator technology. We also observed that, the Al/CuO thermite film on PET membrane reacts within 1 ms (sparkles duration) whereas it reacts within 4 ms on Pyrex. The thermite reaction is 40 times greater in intensity using the PET substrate in comparison to Pyrex.
We present an experimental and theoretical study of electrically exploded nickel-aluminum (Ni/Al) laminates, lithographically patterned into bow-tie bridge regions, and encapsulated with parylene. The exothermic nature of Ni/Al reactions is well-known at typical self-heating rates of 103–106 K/s, but electrical heating allows the interrogation of phenomena at heating rates which are five to six orders of magnitude higher. The use of time-resolved streak camera emission spectroscopy revealed that Ni/Al laminates heated at these higher rates exhibited brighter emission during the first 150 ns of emission than samples composed of either Al or Ni alone, suggesting an exothermic effect which rapidly started and persisted for at least this length of time. We also measured the transduction of electrical energy into kinetic energy through velocity measurements of encapsulation layers ejected from the bridge region. An empirical model using experimental power curves and one empirical fitting parameter successfully predicted these velocities. This model agreed well with experiments from different Al and Ni samples using the same fitting parameter, but an apparent 1.2 J/mg of additional energy from the mixing of Ni and Al was necessary to accurately predict velocities from Ni/Al laminate samples. This energy quantity corresponded to a reference value for the enthalpy of mixing Ni and Al, and likely contributed to both brighter emission and higher than expected velocities observed.
This paper describes the ignition characteristics of Al/CuO nanoenergetic multilayer films (nEMFs) integrated with semiconductor bridge (SCB). The as-deposited Al/CuO nEMFs were identified with SEM and differential scanning calorimetry. Results show that distinct Al/CuO nEMFs are sputter deposited in a layered geometry, and the Al/CuO nEMFs gives a reaction heat equal to 2181 J/g. The firing experiments show that Al/CuO nEMFs have no influence on the electrical properties of SCB. Furthermore, the rapid combustion of Al/CuO nEMFs is able to assist SCB generating high-temperature plasma and products, such that enhance the ignition reliability.
Electrophoretic deposition was used to deposit thin films (∼10–200 μm) of nano-aluminum/copper oxide thermites, with a density of 29% the theoretical maximum. The reaction propagation velocity was examined using fine-patterned electrodes (0.25 × 20 mm), and the optimum velocity was found to correspond to a fuel-rich equivalence ratio of 1.7. This value did not correlate with the calculated maximum in gas production or temperature, and it is suggested that it is a result of enhanced condensed-phase transport, which is speculated to increase for fuel-rich conditions. A ∼25% drop in propagation velocity occurred above an equivalence ratio of 2.0, where Al2O3 is predicted to undergo a phase change from liquid to solid. This is expected to hinder the kinetics by decreasing the mobility of condensed-phase reacting species. The effect of film thickness on propagation velocity was investigated, using the optimum equivalence ratio. The velocity was seen to exhibit a two-plateau behavior, with one plateau between 13 and 50 μm film thickness, and the other above ∼120 μm. The latter had nearly an order of magnitude faster velocity than the former, 36 m/s vs. 4 m/s, respectively. For film thicknesses in the 50-120 μm range, a linear transitional regime was observed. Images from the combustion studies showed an increase in forward-transported particles as the film thickness increased, along with more turbulent behavior of the flame. It was suggested that the two-plateau behavior indicated a shift in the energy transport mechanism. While nanocomposite thermites have been traditionally thought to exhibit convective energy transport, we find in this work that particle advection may also be important. The velocity of particles ejected through a thin slit mounted above a thermite strip was measured, and was found to be even faster (∼2-3×) than the flame propagation velocity. The morphology of captured particles was examined with an electron microscope, and indicated that reactive sintering had occurred. A non-dimensional number (A) was used to relate the rate of gas pressurization (1/τp) to the rate of gas escape by Fickian diffusion (D/L2), A = L2/(D*τp). For small values of A, gases rapidly escape and do not accumulate within the thermite films. Thus, the resultant energy transport is relatively slow. For large values of A, gases are entirely trapped, thus activating enhanced energy transport via oscillating pressure buildup and unloading of the material. This analysis is suitable for thermites which can produce sufficient gas to raise the local pressure above some critical value to overcome material adhesion strength, inducing pressure-driven unloading and resulting in enhanced energy transport. We suggest that further improvements in nanocomposite thermites can be made by examining the coupling of multiple length scales. Not only is nano-scale mixing important, in this work we found that a second length scale (∼120 μm) was necessary to fully activate a pressure buildup/unloading mechanism, which significantly enhances the reactivity.
A micro initiator was developed by integrating KNO3@CNTs nanoenergetic materials with a Cu thin-film microbridge realized onto a glass substrate. It was fabricated by magnetron sputtering with Cu and subsequent electrophoretic deposition with KNO3@CNTs nanoenergetic materials, which were prepared by wet chemical method, embedding KNO3 in carbon nanotubes (CNTs). The samples were characterized by TEM, XRD, TG/DSC and SEM, respectively. The electrical explosion performances of the micro initiator under capacitor discharge were investigated. The process of electrical explosion was observed by high-speed photography and the temperature distribution versus time was acquired by a temperature measurement system with double line of atomic emission spectroscopy. The results show that the hollow cavities of the CNTs were filled with crystalline KNO3, and that the entire surface of the micro initiator was well distributed without large reunion. Compared with single-layer Cu thin-film microbridge, the micro initiator possessed more violent electrical explosion process, the electrical explosion duration was longer, and the peak temperature was higher, which indicate that chemical reactions of KNO3@CNTs nanoenergetic materials were involved in the electrical explosion process of the micro initiator, accompanied by more heat release.
Al/Ni multilayer bridge films, which were composed of alternate Al and Ni layers with bilayer thicknesses of 50, 100 and 200 nm, were prepared by RF magnetron sputtering. In each bilayer, the thickness ratio of Al to Ni was maintained at 3:2 to obtain an overall 1:1 atomic composition. The total thickness of Al/Ni multilayer films was 2 μm. XRD measurements show that the compound of AlNi is the final product of the exothermic reactions. DSC curves show that the values of heat release in Al/Ni multilayer films with bilayer thicknesses of 50, 100 and 200 nm are 389.43, 396.69 and 409.92 J g−1, respectively. The temperatures of Al/Ni multilayer films were obviously higher than those of Al bridge film and Ni bridge film. Al/Ni multilayer films with modulation of 50 nm had the highest electrical explosion temperature of 7000 K. The exothermic reaction in Al/Ni multilayer films leads to a more intense electric explosion. Al/Ni multilayer bridge films with modulation period of 50 nm explode more rapidly and intensely than other bridge films because decreasing the bilayer thickness results in an increased reaction velocity.
Considering the demand for low temperature bonding processes in 3D integration and packaging of microelectronic or micromechanical components, this paper introduces a method that uses a specific form of local heat generation, which is based on nano scale reactive material systems. Such systems consist of several layers of minimum two different materials with nano scale thicknesses. These layers generate a self-propagating and exothermic reaction during their intermixing. The resulting heat can be used as the heat source for bonding processes such as solder bonding of micro components. In contrast to other researchers, who focus on relatively thick Ni/Al foils for joining macroscopic parts, we focus on the direct deposition of reactive multilayer systems. The principle of this method is demonstrated by reactive bonding, for which we use different energetic systems. The main part of this paper deals with the preparation and investigation of integrated reactive material systems.
Fluorinated materials, such as poly(tetrafluoroethylene) and its co-polymers, have attracted significant interest throughout the energetic materials community due to their strong reactivity with aluminum powders. Herein, we report the synthesis of a novel composite material produced through the in situ polymerization of 1H,1H,2H,2H-perfluorodecyl methacrylate in the presence of aluminum nanoparticles which have been previously functionalized with phosphoric acid 2-hydroxyethyl methacrylate ester to promote chemical integration into the polymer matrix. These materials, which we have termed aluminized fluorinated acrylic (AlFA) composites, have been prepared with particle contents ranging from 10% to 70% by weight. At particle loadings of 60 wt.% or less, the AlFA composites exhibited thermoplastic behavior and were able to be processed by melt extrusion. The AlFA-50 composite demonstrated the highest reactivity (most intense flame and shortest time to achieve complete deflagration) during air combustion experiments performed on consolidated pellets. Chemical analysis of the char indicated the presence of AlF3, in addition to Al2O3, Al4C3 and residual Al, indicating that reaction with the fluoropolymer matrix does result in fluorination of the aluminum during the deflagration, however, this mechanism competes kinetically with air oxidation and carbide formation at higher particle loadings.
Nanoenergetic materials (nEMs) have better performance in ignition and energy release rate compared to conventional energetic materials. This makes them have promising applications in actuation, ignition, propulsion, power, fluidic, and electro-explosive devices at the micro and nanoscale. In this study, Co3O4 is used for the first time to achieve novel Al/Co3O4 based nEMs by integrating nano-Al with Co3O4 nanorods that are synthesized by a chemical method. The total heat of reaction, especially the exothermic reaction before Al melting, is greatly enhanced by using Co3O4 pure nanostructures (no microscale film exits). The nEMs are fabricated onto a silicon substrate, which is very convenient to achieve promising functional nanoenergetics-on-a-chip. The fabricated nEMs are confirmed to have nanoscale mixing, very high heat of reaction, and significantly reduced onset temperature of the major exothermic reaction by scanning electron microscopy, differential thermal/thermogravimetric analysis, and differential scanning calorimetry.
We have developed a novel, operator-friendly, nanothermite reaction actuator which generates transient pressures comprised of a shock wave superimposed on a broad pressure pulse to facilitate intranuclear molecular transport. The actuator demonstrates the delivery of ∼70 kDa FITC-Dextran into chicken cardiomyocytes with cytoplasmic delivery efficiency greater than 90%, maximum intranuclear delivery efficiency of 84%, and cell survival rates exceeding 95% in minimum operating pressure conditions. Tunable nanothermite reactions enable versatile pressure generating characteristics which can extend the technology to a spectrum of biomedical molecular delivery applications.
While nanotechnology advancements should be fostered, the environmental health and safety (EHS) of nanoparticles used in technologies must be quantified simultaneously. However, most EHS studies assess the potential implications of the free nanoparticles which may not be directly applicable to the EHS of particles incorporated into in-use technologies. This investigation assessed the aquatic toxicological implications of copper oxide (CuO) nanospheres relative to CuO nanorods used in nanoenergetic applications to improve combustion. Particles were tested in both the as-received form and following combustion of a CuO/aluminum nanothermite. Results indicated nanospheres were more stable and slowly released ions, while higher surface area nanorods initially released more ions and were more toxic but generally less stable. After combustion, particles sintered into larger, micron-scale aggregates, which may lower toxicity potential to pelagic organisms due to deposition from water to sediment and reduced bioavailability after complexation with sediment organic matter. While the larger nanothermite residues settled rapidly, implying lower persistence in water, their potential to release dissolved Cu was higher which led to greater toxicity to Ceriodaphnia dubia relative to parent CuO material (nanosphere or rod). This study illustrates the importance of considering the fate and toxicology of nanoparticles in context with their relevant in-use applications.
Fluoropolymers have long served as potent oxidizers for metal-based pyrolant designs for the preparation of energetic materials. Commercial perfluoropolyethers (PFPEs), specifically known as Fomblins®, are well-known to undergo accelerated thermal degradation in the presence of native metals and Lewis acids producing energetically favorable metal fluoride species. This study employs the use of PFPEs to coat nano-aluminum (n-Al) and under optimized stoichiometric formulations, harness optimized energy output. The PFPEs serve as ideal oxidizers of n-Al because they are non-volatile, viscous liquids that coat the particles thereby maximizing surface interactions. The n-Al/PFPE blended combination is required to interface with an epoxy-based matrix in order to engineer a moldable/machinable, structurally viable epoxy composite without compromising bulk thermal/mechanical properties. Computational modeling/simulation supported by thermal experimental studies showed that the n-Al/PFPE blended epoxy composites produced an energetic material that undergoes latent thermal metal-mediated oxidation. Details of the work include the operationally simple, scalable synthetic preparation, thermal properties from DSC/TGA, and SEM/TEM of these energetic metallized nanocomposite systems. Post-burn analysis using powder XRD of this pyrolant system confirms the presence of the predominating exothermic metal-mediated oxidized AlF3 species in addition to the production of Al2O3 and Al4C3 during the deflagration reaction. Details of this first epoxy-based energetic nanocomposite entrained with a thermally reactive formulation of PFPE coated n-Al particles are presented herein.
Energetic composite powders consisting of sol-gel derived nanostructured tungsten oxide were produced with various amounts of micrometer-scale tantalum fuel metal. Such energetic composite powders were ignition-tested and the results show that the powders are not sensitive to friction, spark and/or impact ignition. Initial consolidation experiments, using the High-Pressure Spark Plasma Sintering (HPSPS) technique, on the sol-gel derived nanostructured tungsten oxide produced samples with higher relative density than can be achieved with commercially available tungsten oxide. The sol-gel derived nanostructured tungsten oxide with immobilized tantalum fuel metal (Ta-WO) energetic composite was consolidated to a density of 9.17 g cm³ or 93% relative density. In addition, those samples were consolidated without significant pre-reaction of the constituents, thus retaining their stored chemical energy. (author)
Transient normal flame propagation in reactive Ni/Al multilayers is analyzed computationally. Two approaches are implemented, based on generalization of earlier methodology developed for axial propagation, and on extension of the model reduction formalism introduced in Part I. In both cases, the formulation accommodates non-uniform layering as well as the presence of inert layers. The equations of motion for the reactive system are integrated using a specially-tailored integration scheme, that combines extended-stability, Runge-Kutta-Chebychev (RKC) integration of diffusion terms with exact treatment of the chemical source term. The detailed and reduced models are first applied to the analysis of self-propagating fronts in uniformly-layered materials. Results indicate that both the front velocities and the ignition threshold are comparable for normal and axial propagation. Attention is then focused on analyzing the effect of a gap composed of inert material on reaction propagation. In particular, the impacts of gap width and thermal conductivity are briefly addressed. Finally, an example is considered illustrating reaction propagation in reactive composites combining regions corresponding to two bilayer widths. This setup is used to analyze the effect of the layering frequency on the velocity of the corresponding reaction fronts. In all cases considered, good agreement is observed between the predictions of the detailed model and the reduced model, which provides further support for adoption of the latter. (author)
A lead-free percussion primer composition and a percussion cup containing e composition. The lead-free percussion primer composition is comprised of a mixture of about 45 wt % aluminum powder having an outer coating of aluminum oxide and molybdenum trioxide powder or a mixture of about 50 wt % aluminum powder having an outer coating of aluminum oxide and polytetrafluoroethylene powder. The aluminum powder, molybdenum trioxide powder and polytetrafluoroethylene powder has a particle size of 0.1 .mu.m or less, more preferably a particle size of from about 200-500 angstroms.
We report the synthesis of a novel hierarchical MnO2/SnO2 heterostructures via a hydrothermal method. Secondary SnO2 nanostructure grows epitaxially on the surface of MnO2 backbones without any surfactant, which relies on the minimization of surface energy and interfacial lattice mismatch. Detailed investigations reveal that the cover density and morphology of the SnO2 nanostructure can be tailored by changing the experimental parameter. Moreover, we demonstrate a bottom-up method to produce energetic nanocomposites by assembling nanoaluminum (n-Al) and MnO2/SnO2 hierarchical nanostructures into a free-standing MnO2/SnO2/n-Al ternary thermite membrane. This assembled approach can significantly reduce diffusion distances and increase their intimacy between the components. Different thermite mixtures were investigated to evaluate the corresponding activation energies using DSC techniques. The energy performance of the ternary thermite membrane can be manipulated through different components of the MnO2/SnO2 heterostructures. Overall, our work may open a new route for new energetic materials.
This paper deals with the energetic igniters realized by integrating Al/CuO reactive multilayer films (RMFs) with Cr Films, which could be used in micro-ignition system. The as-deposited Al/CuO RMFs has been characterized with varied analytical techniques. Results show that distinct Al/CuO RMFs is sputter deposited in a layered geometry, and the Al/CuO RMFs gives a heat of reaction equal to 2760 J/g. The structure of igniter is similar to a capacitor, which may place an electric field across the igniter and allow the instantaneous large-current to drift through the igniter. Firing characteristics of the igniter were accomplished using constant voltage firing set. The experiment shows that the ignition delay time and total released energy of the igniter discharged in 40 V are 0.7 ms and 482.34 mJ, respectively. In addition, the explosion temperature could keep an approximately constant value of 3500 °C for 1.4 ms.
Thermochemical metal/metal oxide redox reactions have twice the energy density of 2,4,6-trinitrotoluene (TNT). They suffer, however, from low pressure-volume work due to low gas expansion from the reaction. This study focuses on the development of a nanocomposite that delivers a high energy density and the potential of rapid gas release. Hollow CuO spheres with nanosized building blocks are fabricated using a droplet-to-particle aerosol spray pyrolysis method with the introduction of gas-blowing agents in the synthesis procedure. Nanoaluminum with hollow CuO as an oxidizer ignites in a very violent manner and exhibits excellent gas-generation behavior, demonstrating a high pressurization rate of 0.745 MPa s1 and a transient peak pressure of 0.896 MPa with a charge density of 1 mg cm3, as well as a rapid oxygen release. Compared with wet-chemistry methods, gas-phase processes are relatively low cost, nominally offer a higher purity product, and are usually configured as continuous production processes, with a limited number of steps. The synthesis strategy demonstrated is simple and should be extendable to the preparation of other hollow metal oxide structures.
Optimization of the crystallization of amorphous silicon (a-Si) using a mixture of nanoenergetic materials of iron oxide/aluminum (Fe2O3/Al) was studied. To achieve high-quality polycrystalline Si (poly-Si) thin films, silicon oxide (SiO2) and silver (Ag) layer were deposited on the a-Si as buffer layers to prevent the metal diffusion in a-Si during thermite reaction and to transport the thermal energy released from nanoenergetic materials, respectively. Raman measurement was used to define the crystallinity of poly-Si. For molar ratio of Al and Fe of 2 with 100-nm-thick-SiO2, Raman measurement showed the 519.59 cm−1 of peak position and the 5.08 cm−1 of full width at half maximum with 353 MPa of low tensile stress indicating high quality poly-Si thin film. These results showed that optimized thermite reaction could be used successfully in crystallization of a-Si to high -quality poly-Si thin films.