Nanothermite Research Articles

Ammonium perchlorate catalyzed with novel n-Al modified on ZIF-67 with silane coupling agent: Superior catalytic activity, advanced decomposition kinetics and mechanisms

Ammonium perchlorate (AP) is commonly utilized as an oxidizer in composite solid propellants (CSPs), and the thermal decomposition of AP has a significant impact on the combustion behaviour of CSPs. Aluminum nanoparticles (n-Al) as a prospective metal fuel have received a lot of interest, however properly extracting energy from n-Al remains a great challenge. Native oxide layer limits the energetic performance of n-Al by impeding sufficient combustion and slowing down mass/heat transport. Development of the high energy storage based on metastable intermolecular composite (MIC) is always a desirable way. This group of hybrid materials uses zeolitic imidazole framework (ZIF) as the precursors of the metal oxides as the oxidizers in conventional nanothermite. Coating n-Al on the surface of ZIF-67 with a silane coupling agent to erase or disturb the oxide layer on the n-Al surface improves n-Al combustion. n-Al@ZIF-67 was synthesized and integrated into AP matrix. The catalytic activity of n-Al@ZIF-67 on AP decomposition was assessed via DSC and TGA/DTG. Whereas n-Al@ZIF-67/AP nanocomposite demonstrated decomposition enthalpy of 2350 J/g; pure AP demonstrated 836 J/g, ZIF-67/AP demonstrated 1680 J/g, and n-Al/AP demonstrated 1170 J/g. While Al@ZIF-67/AP nanocomposite demonstrated one decomposition temperature at 327 oC; pure AP decompose at two decomposition stages at 298 oC, and 453 oC. n-Al@ZIF-67/AP showed a violent reaction with high intensity of flame, and micro-explosion occurred due to rapidly disrupted oxide layer that covered Al core. Decomposition kinetics was investigated. n-Al@ZIF-67/AP demonstrated apparent activation energy of 125.3 ± 1.23 kJ/mol compared with 173.16 ± 1.95 kJ/mol for pure AP. Co3O4 NPs as the combustion product from ZIF-67 can expose active surface sites; the ability of adsorption of released NH3 gas, which inhibition AP from decomposition, offering efficient combustion. This work provides a new strategy for advanced CSPs by introducing ZIF-67 to construct bifunctional properties for AP decomposition, and n-Al combustion.

Considerable enhancement of nanothermites propagation through worm-like expansion of expandable graphite

Metastable intermolecular composites (MICs) are known for their high energy density, high burn rate, and low diffusion distance, and they have various applications in military and civilian equipment and tasks. However, the introduction of binders, which facilitate shaping, during the processing of MICs for practical applications can lead to a decrease in the energy release rate and an increase in the required ignition energy. Herein, we incorporated graphene nanoplatelets (GNPs), multi-walled carbon nanotubes (MWCNTs), and expandable graphite (EG) into 90- wt% Al/CuO nanothermites stick using simple extrusion-based direct ink writing to improve their overall performance. The high-temperature expansion characteristics and unique structure after expansion caused EG to perform an important role during Al/CuO nanothermites system combustion, which effectively promotes heat transfer and considerably increases the burn rate (81.6%) and pressure rising rate (103.0%). This study demonstrated EG as a low-cost and efficient combustion catalyst for MICs and introduced a simple approach to modulate the energy release rate, combustion pressure and semiconductor bridge (SCB) ignition performance of MICs through incorporation of small amounts of carbon materials.

Fine-Tuning Combustion Behavior in Microscale Energetic Lines Fabricated by Direct Ink Writing Using Nano Thermite Microspheres for Applications in Pyro-MEMS

Fine-Tuning Combustion Behavior in Microscale Energetic Lines Fabricated by Direct Ink Writing Using Nano Thermite Microspheres for Applications in Pyro-MEMS

Synthesis of boron-based High-Energy composite microspheres via the Co-Flow microchannel method

Boron-based metastable intermolecular composites (MIC), renowned for their swift energy release and elevated thermal output, exhibit significant promise for utilization in domains such as gunpowder, propellants, and powdered fuel ramjet fuels. The work successfully accomplished the safe and efficient preparation of B/Bi2O3 microunits by utilizing co-flow microchannel technology. The choice of the optimal binder, F2603, for this system was determined by simulation analysis. The practicality of the microchannel platform was then verified using Fluent. SEM analysis demonstrated that an amount of 10 % F2603 resulted in the formation of spherical particles. In terms of physical properties, boron treated with 10 % F2603 exhibits a reduction in its angle of repose from 35° of the raw material to 15°, along with a significant enhancement in hydrophobicity. Furthermore, the MICs lower the reaction temperature of raw boron from 840℃ to 770℃. In the constant volume combustion test, the MIC output pressure increased by 33.3 %. In the constant pressure combustion test, the MIC ignition delay time was reduced from 0.7262 s to 0.5566 s. The structural characteristics of the system decrease the distance for mass and heat transmission across components, resulting in improved overall performance. The study unequivocally demonstrates the efficacy of co-flow microchannel technology in swiftly, effectively, and securely producing energetic molecules. It establishes a solid foundation for future industrial manufacturing.

In-situ synthesis of MEMS compatible Al/Cu2HIO6/PVDF Metastable composites film with high combustion performance

To address the challenges related to significant pressure loss and weakened combustion performance of energetic materials when ignited on Micro-Electro-Mechanical Systems (MEMS), periodate-based MICs (Metastable Intermolecular Composites) have emerged as promising candidates due to their high energy density and combustion pressure. However, the integration of periodate-based MICs onto MEMS has not been effectively achieved thus far. Herein, we propose a simple, environmentally friendly, and cost-effective approach to fabricate a MEMS-compatible Al/Cu2HIO6/PVDF (polyvinylidene difluoride) energetic composite film. Our method involves utilizing a Cu(OH)2 array as a template and employing an in-situ and spin-coating process. The resulting Al/Cu2HIO6/PVDF film was characterized using various techniques including SEM, TEM, XRD, and XPS. These analyses reveal a tightly packed nano array morphology with a porous structure. DSC-TG analysis was conducted to investigate the thermal reaction of the Al/Cu2HIO6/PVDF composite film. The results demonstrate that the thermal reaction involved a complex multi-step process, with higher heat release (1121 J g-1), a faster reaction rate, and a lower initial reaction temperature (294.5 °C) compared to the Al/CuO/PVDF composite film. the reaction process of Al/Cu2HIO6/PVDF film was also been proposed by analyzing the products at different temperatures. combustion diagnostic tests were carried out to evaluate the combustion performance of the Al/Cu2HIO6/PVDF composite film. The results indicate that as CuO transformed into Cu2HIO6, the film exhibits a reduced ignition delay (8 ms) and combustion duration (50 ms), higher combustion temperature (3710 K), and stronger flame intensity (8630 a.u.).

Fabrication and energy release study of metastable intermolecular composite microspheres with enhanced combustion performance

Metastable intermolecular composites (MICs) are often used in military and aerospace applications because of their high energy density. However, the traditional preparation methods are either complicated and unsafe, or the prepared composites have incomplete combustion and low energy release rates. In this paper, a series of aluminum/metal oxide/nitrocellulose (AMxN) composite microspheres were prepared by spray drying technique. The field emission scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR) results show that the prepared AMxN composite microspheres have regular morphology and uniform particle size, and nitrocellulose (NC) is successfully coated between fuel (Al) and oxidizers (CuO, MoO3, and Bi2O3). The thermal reactivity, energy, and combustion properties of AMxN were investigated and compared with physically mixed aluminum/metal oxide (AMx). The explosion heat of AMxN is higher than AMx, while the thermal reaction exothermic peak temperature is lower. Among them, the composite containing copper oxide has the highest explosive heat value (5034 J/g), and the composite containing bismuth oxide has the shortest burning time (2.8 ms). These results prove that NC as a binder shortens the reaction distance between the oxidizer and the fuel in the presence of spray drying. Different oxidizers can modulate the energy release rate of AMxN composites, which is beneficial for applying MICs in energetic materials.

Improving the combustion efficiency and agglomeration of aluminum-water propellants via n-Al/CuO metastable intermolecular composites

In this work, we investigated the combustion and agglomeration characteristics of aluminum-water propellants by replacing the original Al with binary n-Al/CuO metastable intermolecular composites (MICs). Through laser ignition tests and thermogravimetric-differential scanning calorimetry, we evaluated the oxidation reactivity, ignition delay, burning rate, agglomeration properties, and condensed combustion products of aluminum-water propellants containing different CuO loadings. Compared with conventional aluminum-water propellants, the introduction of binary MICs is found to lower the initial temperature of Al and improve its oxidation activity. Both the burning and heating rates scale linearly with the CuO loading, increasing by a factor of 5 and 6, respectively, when the CuO loading reaches 5 wt.%. The combustion efficiency of the modified propellants is found to improve by 5−12 %. The mean size of the condensed combustion products drops from over 400 μm to around 200 μm due to MICs addition, indicating weakened agglomeration. The ignition delay time is slightly shortened, and the combustion intensity first increases but then decreases as the CuO loading increases. In summary, this work indicates that replacing Al with binary Al/CuO-MICs can significantly alter the combustion and agglomeration properties of aluminum-water propellants. The experimental data and insight from this work could help guide the development of advanced aluminum-water propellants for various propulsion and energy applications.

Preparation of microstructure controllable Al/WO3/F2603 MICs by droplet microfluidic technology to improve combustion performance

The microstructure of metastable intermolecular composites (MICs) is crucial for their energy release and combustion performance. In this paper, Al/WO3/F2603 composites with controllable microstructure were prepared by droplet microfluidic technology. The microstructure control method of composite materials based on droplet microfluidic technology (DMT) was studied. Particles with controllable size, shape, composition, structure and function were prepared by droplet template, and the formation mechanism of particle microstructure was introduced. The Al/W/F-2 composites with high-quality spherical encapsulation have excellent flow properties and wettability. The ignition delay, combustion time and pressure output of the composites were monitored by a combustion and pressure test system. Compared with the physically mixed samples, the Al/W/F-x composites prepared by DMT have shorter ignition delay, shorter combustion duration, and higher pressurization rate. The analysis of combustion products showed that the encapsulated Al/W/F-x composites reduced the sintering and agglomeration of reactants and promoted the combustion efficiency. The results show that the characteristic structure design of the composite material can establish the interface synergy, enhance the thermal mass transfer between the components, and thus reduce the ignition delay and improve the combustion performance. DMT can realize the controllable preparation of composite microstructure, which provides a reference for the design and preparation of other composite materials.

Effect of core-shell structure of MgAl-CuO nanothermite coated with potassium perchlorate on the thermo-kinetic behavior of NC/DEGDN composite

ABSTRACT In this study, a core-shell structure of MgAl-CuO nanothermite coated with ammonium perchlorate (KClO4@MgAl-CuO) has been successfully prepared by a solvent/non-solvent synthetic method, and its catalytic influence on the thermo-kinetic behavior of nitrated cellulose (NC)/diethylene glycol dinitrate (DEGDN) composite has been studied using differential scanning calorimetry (DSC) combined with three isoconversional kinetic models. Beforehand, scanning electron microscopy (SEM) and Fourier-transform infrared spectroscopy (FTIR) findings showed that the prepared KClO4@MgAl-CuO particles were uniformly distributed within the NC/DEGDN matrix. Moreover, the obtained DSC thermograms indicated that the thermolysis of the developed NC/DEGDN composite was shifted to a lower temperature after the incorporation of the coated nanothermite. Additionally, a significant decrease in the activation energy (from approximately 136 to 94 kJ/mol) was also observed, demonstrating that the presence of the KClO4@MgAl-CuO nanothermite catalyzed the decomposition of NC/DEGDN propellant. Therefore, this study could serve as a reference for future research on the coated metastable intermolecular composites and their effects on double-base propellants.

Electrostatic spraying preparation of Si/NiF2/PVDF energetic composites and their reaction characteristics

Metastable intermolecular composites are widely used in energy-demanding fields, where metal fluorides/fluoropolymers as oxidants have been a hot research topic in recent years. In this study, Si/NiF2/PVDF ternary energetic composites were prepared by the electrostatic spraying method for the first time, where NiF2 functions as the oxidant. At the same time, PVDF serves as both the oxidant and the binder. The energetic characteristics of the samples were studied through thermal analysis and preliminary ignition and combustion tests. It is found that the prepared samples are generally in the form of microspheres, in which PVDF binds Si and NiF2 particles together. The addition of Si nanopowder can promote the early decomposition of NiF2, which can improve reactivity. Compared with a physically mixed counterpart, the exothermic reaction between Si and PVDF in microspheres starts at lower temperatures and proceeds to more completion. The electrostatically sprayed sample also shows a shorter combustion time and a more intense luminescence phenomenon.

Fabrication and reaction mechanism study of Co(OH)F@Al nanowire arrays: A functional fluorine-containing metastable intermolecular composite

Metastable intermolecular composites (MICs) comprising solid fuels and oxidizers at nano-scale exhibit high energy densities and fast reaction speeds. As most metal and metalloid fuels are passivated by the natural oxide layer on the surface which acts as a reaction barrier, fluorine-containing oxidizers are of particular interest to promote the reactivity through interfacial fluoridation. In this work, cobalt hydroxy fluoride (Co(OH)F) was introduced as a functional fluorine-containing oxidizer, and core-shell structured Co(OH)F@Al nanoarray was fabricated onto a glass substrate. The thermal behavior and reaction mechanism of pure Co(OH)F and Co(OH)F@Al composites were thoroughly investigated, and Co(OH)F@Al was compared with CoO@Al and Co3O4@Al with identical morphology. In the Co(OH)F@Al composite, a pre-ignition reaction was observed which was attributed to the etching of Al2O3 shell by HF and the fluoridation of Al core by HF and CoF2. With the assistance of pre-ignition reaction, Co(OH)F@Al can complete main exothermal reaction before Al melting in a solid-state mechanism, and its peak temperature is around 200 ℃ lower than those of MICs employing CoO and Co3O4 as oxidizers.

Experimental study on internal explosion of thermobaric explosives containing metastable intermolecular composite (MIC) materials

In order to study the influence of metastable intermolecular composite (MIC) materials on the internal implosion properties of thermobaric explosive, the calorimetric bomb and closed chamber were used to measure the detonation heat, quasi-static pressure and energy impulse of five explosive formulations containing different MIC materials. Compared with the traditional aluminized warm compressed explosives, the energy release characteristics and output characteristics were analyzed. The results show that the explosive formula containing MIC material has lower detonation heat value in air and vacuum than that containing traditional Al powder; The quasi-static pressure and energy impulse of the former are higher than those of the latter, indicating that MIC materials can improve the output energy of thermobaric explosives. The results can be used to guide the formulation design of thermobaric explosives.

Preparation and properties of spherical super thermite for 3D printing of energetic materials

3D printing technology is a new rapid prototyping technology that has attracted much attention since its inception. It is promising to apply 3D printing technology to energetic materials. However, the 3D printing of energetic materials requires high raw materials, and there is no suitable thermite powder as the printing raw materials at present. In this paper, Al@CuO energetic composites with single core spherical core-shell structure were prepared by spray drying method. The prepared powder was confirmed to have a single core spherical core-shell structure by SEM/EDS/XRD, and it was proved to have good fluidity by the fluidity test. High-speed photographic ignition tests show that the Al@CuO Micron spheres have excellent energy release performance and can be used as burning rate catalysts. In addition, this method has the advantages of simple operation, good process performance, mass preparation, and can be applied to the thermite system of most metal oxides (such as Bi2O3, Fe2O3).

Synthesis of Co(OH)F@Al nanobelt array on various substrates for pyro-MEMS

Metastable intermolecular composites (MICs) composed by solid fuel and oxidizer can undergo violent redox reaction with release of huge amount of energy. Integration of MIC with microelectromechanical-system (MEMS) is of particular interest to meet the demand of miniaturization in modern pyrotechnic devices. Meanwhile, fluorine-containing oxidizers are favored in MIC owing to their potential to fluorinate the oxide passivation layer in common elemental fuels. Herein, Co(OH)F was employed for the first time as a novel fluorine-containing oxidizer in Al-based MIC. Vertically aligned Co(OH)F@Al nanobelt arrays (NAs) with tunable morphology were successfully fabricated on a variety of substrates (Si, glass, Ni, Cu, Ti) via a facile hydrothermal synthesis followed by electron beam evaporation. The whole fabrication process is highly compatible with modern MEMS technology. The thermal behavior of pure Co(OH)F and Co(OH)F@Al composites was comprehensively investigated by TG-DSC and a series of ex-situ and in-situ characterization. It was found that, Co(OH)F@Al composites achieved main exothermal reaction before melting of Al regardless of morphology and equivalence ratio. This feature is attributed to the etching of Al2O3 shell by HF released from Co(OH)F which is termed as pre-ignition reaction. To elucidate the effect of micro-structure on the actual specific heat release, we proposed a phenomenological model which can be a reference for future micro-structure design of MIC.

Oxidation mechanism of perfluorooctanoic acid-functionalized aluminum metastable intermolecular composites regulated by Preignition reactions interface fuel-oxidizer ratio

PFOA-functionalized Al Metastable Intermolecular Composites (MICs) refer to the system using aluminum nanoparticles as fuel and PFOA as oxidant. Aluminum is the most widely used metal fuel in energetic materials. Al NPs are widely used because they are relatively cheap, easily accessible, nontoxic, excellent in thermodynamic performance. Fluorine has higher density and stronger oxidation capacity than oxygen element. PFOA has a high fluorine content (68.8%). PFOA-functionalized Al MICs mixed the high calorific value of aluminum and oxidizing fluorine in nano-sized. In this paper, PFOA-functionalized Al MICs with different PIR interface fuel-oxidizer ratios were prepared by electrostatic spray. The microstructure of the MICs was characterized by TEM. PFOA is uniformly coated on the Al NPs. The composition of MIC system was analyzed by FTIR and XRD. The combustion performance of MICs was tested by laser ignition, and the decomposition mechanism of PFOA-functionalized Al MICs was studied by DSC-TG. Results show that the exothermic process and activation energy of MICs are affected by the Preignition reactions (PIR) interface fuel-oxidizer ratios. The ignition and combustion processes of MICs and pressurization rate increase with the increase of oxidizer, and the burning rate decreases with the increase of oxidizer.

Preparation of Mesoporous Si Nanoparticles by Magnesiothermic Reduction for the Enhanced Reactivity.

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.

Effect of Perchlorate on Combustion Properties of Directly-Written Al/PVDF Composites

Metastable intermolecular composites (MICs) based on Al/PVDF have become one of the most important materials in the field of additive manufacturing of energetic materials due to their high energy density and designability. In this work, the energy utilization efficiency and energy release performance of directly written Al/PVDF composites were regulated by introducing ammonium perchlorate (AP) and potassium perchlorate (KP) as gas generators and oxidants. The effect of AP/KP on the combustion performance of MICs systems has been studied in depth. It was found that the addition of AP/KP can increase the combustion temperature and flame duration of the Al/PVDF system. Moreover, the flame propagation rate of the Al/PVDF system decreases as AP/KP addition increases. Therefore, the strategy of introducing AP/KP into directly written Al/PVDF composites can effectively control the energy performance of this energetic system, thereby promoting its practical application in propellants, heterogeneous explosives and gas generators.

Al/CuO@CNFs Conductive Flexible Energetic Films with High Electrical Safety.

The development of energetic materials with both high energy and high safety has always been the focus of the field of energetic materials. In this paper, a low-current-sensitivity flexible energetic film composed of carbon nanofibers (CNFs)-coated Al/CuO metastable intermolecular composites (MICs) was prepared by a blow-spinning combined with controlled heat treatment technique. Hotspots can hardly generate in this kind of energetic film due to the increased electrical and thermal conductivity, leading to low sensitivity of MICs. It evenly stays at a high voltage (60 V) for 24 h without raising the temperature significantly. The energetic films keep the high energy release of MICs due to the additional violent reactions between CuO and CNFs as well as the light weight of CNFs, showing the heat release of 2864 J/g. In addition, the obtained films exhibit good mechanical properties and can maintain the structural integrity after 1000 cycles of repeated bending to a 6 mm curvature radius. The above characteristics reveal that energetic films presented in this paper have certain safety, high energy, and flexibility and have potential applications in transient electronics with flexible requirements such as micro-electromechanical system.

High dispersity and ultralight PVP-mediated Al/MFe2O4/g-C3N4 (M = Cu, Mg, Ni) nanothermites synthesized by a novel sol-freeze-drying technology

Nanothermite is a reactive system of nanoscale metal-based energetic materials, which is also known as metastable intermolecular composites (MICs). In this study, graphitic carbon nitride (g-C3N4) as a new typical polymer semiconductor was firstly employed to replace GO as an additive in nanothermite. For solving the dispersity of g-C3N4 in nanothermite, a simple and novel sol-freeze-drying technology was firstly proposed to prepare Al/MFe2O4/g-C3N4 (M = Cu, Mg, Ni). The as-prepared Al/MFe2O4/g-C3N4 (M = Cu, Mg, Ni) nanothermites present a similar shape to the host container and have high dispersity, ultralight weight (0.035 g·cm−3) and large specific volume (28.19 cm3·g−1). The optimal PVP and g-C3N4 content were determined. Al/MFe2O4/g-C3N4 (M = Cu, Mg, Ni) all have superior combustion performance, lower electrostatic discharge sensitivity (EDS) and better catalytic performance on ammonium perchlorate (AP) and dihydroxy-lammonium 5,5′-bistetrazole-1,1′-diolate (TKX-50). g-C3N4 plays an important role in suppressing unstable combustion and is beneficial to reduce the electrostatic discharge sensitivity of MICs. This work demonstrates that PVP-mediated sol-freeze-drying technology is an effective approach for obtaining g-C3N4-based nanothermite with high dispersity and ultralight characteristic.

Thermal decomposition behavior and kinetic study of nitrocellulose in presence of ternary nanothermites with different oxidizers

Nanothermites have recently attracted a great deal of interest in both military and civilian domains owing to their capability of igniting or exploding and releasing a significant quantity of heat via a redox reaction. In this study, three ternary nanothermites, which contain MgAl alloy as fuel and different metal oxides (MXOY = CuO, NiO, TiO2) as oxidizers, were prepared through the arrested reactive milling technique. These metastable intermolecular composites were introduced to nitrocellulose (NC), using a fast solution drying technique, to assess their catalytic behavior. The as-obtained energetic composites, namely, NC/MgAl-MXOY, were scrutinized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), powder X-ray diffraction (XRD), and differential scanning calorimetry (DSC). The ignition delay time of NC/MgAl-MXOY composite films was also determined, and the results revealed the positive effect of the introduction of nanothermite through the decrease of its value compared to pure NC. Using the isoconversional kinetic analysis, the Arrhenius parameters associated with the thermal decomposition of the as-obtained NC/MgAl-MXOY energetic composites films were also evaluated. The findings indicated that the choice of the oxidizer within the nanothermite composition significantly influences the decomposition behavior of the NC/MgAl-MXOY energetic composites. Based on the obtained results, the MgAl-CuO nanothermite provides better performance than MgAl-NiO and MgAl-TiO2 nanoparticles.