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As an innovative propulsion technique, laser augmented chemical propulsion (LACP) seems superior to the traditional ones. However, the corresponding combustion theories have still to be ascertained for LACP. Burning rate of 5-aminotetrazole (5-ATZ) propellant has been studied by testing pressed samples under different combustor pressures and laser powers. Based on micro computed tomography (MicroCT), an advanced thickness-over-time (TOT) method to characterize the regression of the produced non-planar burning surface is established. Because of a shell structure covering the combustion surface, the burning rate of the implemented 5-ATZ propellant is not constant during laser ablation. Resorting to functional fitting, a new law of non-constant burning including the effect of the observed unique burning surface structures is proposed. Accordingly, applicable combustion conditions of 5-ATZ based propellants have been preliminarily speculated for future research activities.

Conventional exploding foil initiator (EFI) in ignition or detonation applications hosts many performance advantages, but was hindered by the bulky, inaccurate, inefficient and expensive shortcomings. We highlight a novel micro-chip exploding foil initiator (McEFI) using printed circuit board (PCB) technology. The structural parameters were determined based on energy coupling relationship at the component interfaces. Next, the prototype McEFI has been batch-fabricated using PCB technology, with a monolithic structure of 7.0 mm (l) × 4.5 mm (w) × 4.0 mm (δ). As expected, this PCB-McEFI illustrated the successful firing validations for explosives pellets. This paper has addressed the cost problem in both military munitions and civil markets wherever reliable, insensitive and timing-dependent ignition or detonation are involved.

Microsatellites have been widely applied in the fields of communication, remote sensing, navigation and science exploration due to its characteristics of low cost, flexible launch mode and short development period. However, conventional solid-propellant have difficulties in starting and interrupting combustion because combustion is autonomously sustained after ignition. Herein, we proposed a new type of solid-propellant named laser-controlled solid propellant, which is sensitive to laser irradiation and can be started or interrupted by switching on/off the continuous wave laser. To demonstrate the feasibility and investigate the controllable combustion behaviors under different laser on/off conditions, the combustion parameters including burning rate, ignition delay time and platform pressure were tested using pressure sensor, high-speed camera and thermographic camera. The results showed that the increase of laser-on or laser-off duration both will lead to the decrease of propellant combustion performance during re-ignition and re-combustion process. This is mainly attributed to the laser attenuation caused by the accumulation of combustion residue and the change of chamber ambient temperature. Simultaneously, the multiple ignition tests revealed that the increased chamber ambient temperature after combustion can make up for the energy loss of laser attenuation and expansion of chamber cavity. However, the laser-controlled combustion performance of solid propellant displayed a decrease trend with the addition of ignition times. Nevertheless, the results still exhibited good laser-controlled agility of laser-controlled solid propellant and manifested its inspiring potential in many aspects of space missions.

The storage stability of energetic materials is important for its application. Here, the storage stability of Al/CuO nanothermite, which was prepared by electrospray method and stored with different storage time, was systematically researched. The activation energy of Al/CuO nanothermite was calculated by differential scanning calorimetry (DSC). The ignition temperature and the curve pressure history of Al/CuO nanothermite was measured using ignition temperature measuring device and constant-volume pressurization tests, respectively. Further, the thermites were characterized by X-ray Diffractometer (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM) and Transmission electron microscopy (TEM). The results show that the morphology of the thermites did not change significantly. The activation energy was decreased from 254.1 kJ/mol to 181.8 kJ/mol after storage for 13 months. When stored for 0, 7 and 13 months, the peak pressures of Al/CuO nanothermite were 685.8 kPa, 626.3 kPa and 625.5 kPa, respectively. In addition to the ignition temperature, it was 775 °C, 739 °C and 754 °C, respectively. This result indicated that the ignition and combustion properties of Al/CuO nanothermite are obviously reduced when stored for a long time, at room temperature.

The pulsed power switch plays an important role in a wide variety of pulsed power applications, such as plasma science and high-pressure-impact studies. This article develops a shock-induced pulsed power switch based on electroexplosion of exploding bridge wire (EBW). The electrical field distribution and electrothermal coupling of EBW are simulated using COMSOL Multiphysics software to assess the rationality of structural parameters. Employing microelectromechanical system technology, the switches are mass-produced with only three steps, improving experimental efficiency and lowering the cost. Electrical tests are conducted at a series of operation voltages varying from 600 to 1800 V, and the results indicated that peak current increases linearly with operation voltage, while delay time and rise time all show a slowly declined trend. A potential conduction mechanism is discussed for better understanding, and switch resistance is described mathematically. Finally, microchip exploding foil initiators are used as a test vehicle to verify the capability of the switch, and ultrafine hexanitrostilbene (HNS-IV) pellets are successfully detonated at 0.15 μ F/1300 V after the switch is closed.

In the controllable combustion field, hydroxyl ammonium nitrate (HAN)-based electrically controlled solid propellants (ECSPs) is of growing interest in green fuels with safety, throttle- ability and at-will on-off capability. However, the current research is confined to the ignition characteristics and ablation process of basic ECSP formulations (75 wt% HAN ionic liquid oxidizer, 5 wt% ammonium nitrate co-oxidizer and 20 wt% polyvinyl alcohol binder), rather than working in functional additives. Herein, multiwall carbon nanotubes (MWCNT) and nano/micro aluminum powders were introduced in ECSPs, facilitating electrical conductivity and energy release. It indicates that the homogeneous dispersed MWCNT in polyvinyl alcohol (PVA) microspheres, preparing by the micro-segmented flow method, results in a 9.8% increase in electrical conductivity of the ECSPs. At 0.5 MPa, ECSPs containing 1%, 3% and 5% 5 µm aluminum powder reinforce the burning rate by 38.0%, 186.3%, 214.7% and mass ablation by 10.7%, 95.2%, 175.6% at 200 V, yet the large heat release by excess aluminum powder shifts the non-self-sustaining combustion of ECSPs to self-sustaining combustion at high pressure (above 0.8 MPa). The mechanism of promoting ECSPs combustion by liberating aluminum-nitric acid (released by HAN ionization) reaction were proposed.

A planar trigger switch constituting of three electrodes was designed and fabricated using low-temperature cofired ceramic, and characterized under an atmospheric pressure. The results showed that when the operating voltage ranges between 77.2% and 86.8% of its self-breakdown voltage, the inductance of the switch was lower than that of commercial spark gap switch by approximately 60 nH, the current rising time was shortened by nearly 1/2, and the peak current increased by about 30%. The peak current and rising edge were 4000 A and 146 ns at 0.22 μF/2.0 kV, respectively, which was in agreement with simulation values well. Subsequently, the switch was devised to be in situ integrated with an exploding foil initiator together. The electrical characterizations were performed on the chip, obtaining the switch's rapid turn- on time of 29 ns and a large current density of $1.08 \times 10^{8}\,\text{A}\cdot \text{cm}^{-2}$ at 0.22 μF/2.25 kV. Furthermore, photon Doppler velocimetry was exploited to capture the detailed trajectory of a 50-μm-thick flyer with an extracted terminal velocity of 2200 m/s. Finally, boron–potassium nitrate pellets and hexanitrostilbene pellets were used to successfully verify the practicability of the chip in the ignition and detonation of explosives.

The crystal morphology of explosives has a great influence on their detonation performance and safety. In order to realize the crystal morphology control of explosives, a new strategy based on microfluidics was proposed. The new strategy consisting of morphology predictions and microfluidic verification experiments has the characteristics of excellent accuracy, less sample consumption, and fast verification. The shapes and sizes of explosives were predicted by simulations and theoretical analysis with different solvents, respectively. Considering an ideal crystallization environment for verification experiments, the parameters of the microfluidic platform were optimized. Under the optimal parameters, the verification experiments were conducted using a microfluidic platform. Here, we used hexanitrohexaazaisowurtzitane (HNIW, also known as CL-20) as a sample to study the applicability of the new strategy for crystal morphology control of explosives. The optimized flow rate ratio and number of chambers were adapted to the verification experiments. It was found that the thicknesses of HNIW have positive correlation with the polarities of the solvents and the sizes have negative correlation with the concentrations, which is in line with predictions. This study demonstrates the feasibility of an efficient, accurate strategy to realize the crystal morphology control of explosives based on a microfluidic platform.

Three types of Al/MoO3 energetic semiconductor bridge (ESCB) initiators were prepared by integrating Al/MoO3 reactive multilayer films (RMFs) of different stoichiometric ratios on semiconductor bridges through magnetron sputtering. The stoichiometric ratios of Al:MoO3 were 4:1, 2:1, and 4:3. An experimental investigation for obtaining the electrical explosive characteristics of the ESCBs with different stoichiometric ratios of Al/MoO3 RMFs was carried out under the stimulation of a 47 μF tantalum capacitor discharge. The results reveal a ‘stagflation’ phenomenon in the voltage–current–resistance curves of the ESCBs, which is obvious at low discharge voltages. The critical burst energy and critical burst time decrease with an increase in the MoO3 ratio in RMFs for initiators discharged with identical voltages. Moreover, among the three ESCBs, the one with a stoichiometric ratio of 4:3 exhibits the highest performance with the shortest critical burst time, lowest critical burst energy, and most violent explosion phenomenon. This suggests that the ignition performance of ESCBs can be enhanced by optimising the stoichiometric ratio of Al/MoO3 RMFs.

Aluminum/cupric oxide (Al/CuO) reactive multilayer films (RMFs) are widely used for micro-chip energetic initiator applications; however, there are only a few examples where they are initiated through the direct input of electrical energy. This study describes the preparation of micro-chip energetic initiators containing Al/CuO RMFs as an interlayer between two Al electrical contact pads that are prepared using an image reversal lift-off process and the magnetron sputtering technology. This design enables the direct transfer of current from the contact pads to Al/CuO RMFs, which results in fast ignition (less than 1.0 μs) and produces luminous flame ball that spread over a wide area (maximum flame area of 13.8 mm2). A metal–interlayer–metal (MIM) structured initiator will not be fired until the external voltage has exceeded the breakdown field strength of CuO layers. These initiators achieved a critical breakdown voltage (VB) of 32–50 V and a complete electrical-explosion voltage (VC) of 72–84 V. The ignition threshold rises with increasing the bilayer thicknesses of the RMFs. These characteristics of this specially structured initiator are well suited for applications in highly efficient and insensitive initiating explosive devices.

In this paper, a possible conduction model of a kind of plasma switch induced by electroexplosion of the p-n junction was established to better understand the underlying mechanism. The model showed that the resistance of the plasma switch is considerable before switching and a constant during closing, which was validated by complementary experiments. Additionally, several parameters were defined to evaluate the performance of this type of plasma switch. Finally, a highly integrated microchip exploding foil initiator (McEFI) was designed and fabricated using the microelectromechanical system (MEMS) technology. Electrical characterizations, ignition test, and initiation test were conducted to demonstrate the capability of the McEFI, as well as the plasma switch, and the results indicated that the minimum firing voltage is 1150 V/ $0.15~\mu \text{F}$ , providing new ideas for the development of not only McEFI but also low-energy EFI (LEEFI).

Hydroxyl-terminated polybutadiene (HTPB) is extensively used in propulsion; however, it's trapped in low regression rate, partly related to poor thermal transfer from combustion. Carbon nanotubes (CNT) act as an energy transfer media, potentially accelerating the heat transfer and combustion performance of HTPB. Herein, multiwall CNT (MWCNT)/HTPB composites were prepared by dispersing MWCNT and surfactant into HTPB and toluene solvent through ball milling. Low MWCNT content (≤1%) promoted combustion, and excess MWCNT (≥2%) depressed, despite MWCNT shifting the HTPB-O2 reaction to higher temperatures. (0.5%, 1%, 2% and 3%) MWCNT/HTPB composites reinforced the instantaneous regression rate by 11.2%, 31.6%, −21.3%, and −39.7% at Gox = 365 kg/m2·s; by 27.0%, 25.0%, −26.4%, and −36.6% at Gox = 150 kg/m2·s; while strengthened the average regression rate by 0.9%, 8.5%, −17.4%, and −36.7% at Gox = 365 kg/m2·s; and by 5.4%, 8.9%, −8.3%, −22.6% at Gox = 100 kg/m2·s. Specifically, the optimal MWCNT level was 1%, as demonstrated by the optimized reinforced thermal conductivity and slightly reduced energy release, since excessive MWCNT (>2%) hinders combustion through heat dissipation, high viscosity of the melting layer, low energy release and an attached carbon layer on the burning surface blocking the energy transfer.

Reactive multilayer films (RMFs) are a type of energetic nano-composite material and can be integrated into ablative layer structures using micro-electro-mechanical systems technology. They could potentially be applied to a laser-driven flyer detonator. In this study, TiO2/Al-based RMFs with two different modulation periods were integrated into multilayer flyer plates using magnetron sputtering technology, which produced nano-energetic multilayer films with optimised performance for laser-driven flyer plate systems. The effects of the TiO2/Al RMFs on the laser-driven properties of the RMF flyer were then systematically investigated in terms of the electron temperature and density using laser-induced breakdown spectroscopy. Measurements of the RMF flyer velocity were performed using a photonic Doppler velocimetry system. Electron temperatures of 6331.2–10563.0 K, electron densities of 4.03–12.69 × 1015 cm−3, and flyer velocities of 3854.7–6417.7 m/s were produced in the RMFs merely by changing the modulation period of the TiO2/Al RMF. This behaviour was also consistent with that found using a thermal conduction model in combination with a mass-diffusion reaction model. The RMF flyer exhibited a high level of integrity and promoted laser-driven energy efficiency, which are significant for improving the performance of a laser-driven flyer detonator for military and civilian applications.

A planar ignitor-based on low temperature co-fired ceramic (LTCC) and pyrotechnical micro electro mechanical system (PyroMEMS) technologies was designed and prepared in this paper. The planar ignitor is mainly composed of output charge layer, silicon safe and arm (Si-S&A) layer, and LTCC circuit base. Si/Pb3O4, C6H2(NO2)3OK/KClO4, and B/KNO3 were selected as ignition charge, gas charge, and transfer charge, respectively. The ignition circuit and main structure of the planar igniter were made by the LTCC process. Si-S&A was etched from monocrystalline silicon, which does not need environmental force to disarm. Preparation process of main components of planar ignitor that is suitable for mass production was introduced in detail. Simulation of PyroMEMS S&A actuation based on pendulum method was performed to save time for proof test. Finally, experimental verification on PyroMEMS S&A actuation and combustion propagation of B/KNO3 transfer charge were completed successfully. Results show that the idea of a planar ignitor inserted with PyroMEMS S&A device is feasible. [2018-0075]

Conventional propulsion systems are difficult to change between propelling and non-propelling modes. Throttleable propulsion that results from the control of the input energy is a significant further step toward application in various space missions. We present our work on a novel propulsion mode producing throttleable thrust under the control of our low power CW laser. This photosensitive propellant is fully capable of repeated ignition and interruption, while generating gases that are more environmentally friendly with decreased solid residues. Laser ignition and combustion performance of such modes are characterized. Laser-controlled combustion behavior examples are shown and discussed. These results show potential applications in many aspects of space missions, such as maneuvers in space, attitude control, orbit raising and microsatellite deorbiting.

Copper azide is a promising primary explosive with low toxicity and high energy density. However, due to the extreme electrostatic sensitivity, it does not have many practical applications in the miniaturized pyrotechnics. In this work, we constructed an energetic composite, embedding in oriented carbon nanotubes (CNTs) arrays grown on a silicon substrate, which is compatible with the microfabrication technique of Micro-Electro-Mechanical Systems (MEMS). Since it has excellent electrical conductivity and mechanical strength, oriented CNTs, as nano-containers of Cu(N3)2, can availably reduce the electrostatic sensitivity and bring about the directional output of detonation energy. The oriented CNTs arrays were prepared by magnetron sputtering, anodization and chemical vapor deposition successively. Electrochemical deposition was used to deposit copper nanoparticles in the cavities of CNTs, which were converted into copper azide by subsequent in-situ azide reaction. The electrostatic sensitivity test, thermal performance analysis and laser ignition experiment were conducted on the energetic composite, respectively. The results show that the energetic composite kept safe under an electrostatic stimulation of 3.18 mJ, while original copper azide exploded when subjected to stimulation of 0.05 mJ. The energetic composite opens a new route of introducing hazardous primary explosives into micro-initiators and modern pyrotechnics.

A green primary explosive with high energy density and electrostatic safety was synthesized in this work. A precursor consisting of wrinkled reduced graphene oxide sheets wrapped around copper nanowires (CuNWs@rGO) was fabricated through a facile one-pot hydrothermal approach. The as-prepared precursor was deposited on a silicon wafer by electrophoretic deposition technology, which significantly reduced the safety risks of directly handling the powder sample in the azide reaction. Wrinkled rGO sheets wrapped around copper azide nanowires (CANWs@rGO) were prepared in situ by reaction of the precursor with HN3 gas. The initiation capability was tested by using it to detonate hexogen (RDX) against a lead plate with a thickness of 5 mm, and its detonation performance was found to be better than that of commercial diazodinitrophenol (DDNP). The electrostatic sensitivity of the CANWs@rGO composite was investigated, and the result shows that the discharge energy at 50% (E50%) of CANWs@rGO was 0.96 mJ, which indicates that it has a much higher electrostatic safety than that of pure copper azide (0.05 mJ).

Since copper azide (Cu(N3)2) has high electrostatic sensitivity and is difficult to be practically applied, silicon-based Cu(N3)2@carbon nanotubes (CNTs) composite energetic films with higher electrostatic safety were fabricated, which can be compatible with micro-electro mechanical systems (MEMS). First, a silicon-based porous alumina film was prepared by a modified two-step anodic oxidation method. Next, CNTs were grown in pores of the silicon-based porous alumina film by chemical vapor deposition. Then, copper nanoparticles were deposited in CNTs by electrochemical deposition and oxidized to Cu(N3)2 by gaseous hydrogen azide. The morphology and composition of the prepared silicon-based Cu(N3)2@CNTs energetic films were characterized by field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD), respectively. The electrostatic sensitivity of the composite energetic film was tested by the Bruceton method. The thermal decomposition kinetics of the composite energetic films were studied by differential scanning calorimetry (DSC). The results show that the exothermic peak of the silicon-based Cu(N3)2@CNTs composite energetic film is at the temperature of 210.95 &deg, C, its electrostatic sensitivity is significantly less than that of Cu(N3)2 and its 50% ignition energy is about 4.0 mJ. The energetic film shows good electric explosion characteristics and is successfully ignited by laser.

In this paper, microchip exploding foil initiators were fabricated by micro-electro-mechanical system scale fabrication methods, such as magnetron sputtering, photolithography, and chemical vapor deposition. A small-scale capacitor discharge unit based on the metal-oxide-semiconductor controlled thyristor was designed and produced to study the performance of the microchip exploding foil initiator. The discharge performance of the capacitor discharge unit without load and the effect of protection devices on the metal-oxide-semiconductor controlled thyristor were studied by the short-circuit discharge test. Then, the electric explosion characteristic of the microchip exploding foil initiator was also conducted to study the circuit current, peak power, deposited energy, and other parameters. Hexanitrostilbene refined by ball-milling and microfluidic technology was adopted to verify the initiation capability of the microchip exploding foil initiator triggered by the metal-oxide-semiconductor controlled thyristor. The results showed that the average inductance and resistance of the capacitor discharge circuit were 22.07 nH and 72.55 m&Omega, respectively. The circuit peak current reached 1.96 kA with a rise time of 143.96 ns at 1200 V/0.22 &mu, F. Hexanitrostilbene fabricated by ball-milling and microfluidic technology was successfully initiated at 1200 V/0.22 &mu, F and 1100 V/0.22 &mu, F, respectively.

Nanothermites composed of nano-fuels and oxidants are attractive energetic materials, which have potential applications in microscale energy-demanding systems. Herein, nano-Al/CuO with nitrocellulose (NC) binder have been bottom-up assembled on semiconductor bridge (SCB) chip by electrospray, from nanoparticles to three-dimensional (3D) deposited structure. The morphological and compositional characterization confirms the constituents in Al/CuO@NC are homogeneously mixed at nano scale and the 3D structure at micro scale is tunable. The as-deposited Al/CuO@NC exhibits excellent energy output and superior chemical reactivity. Specifically, the heat release of Al/CuO@NC (1179.5 J g-1) is higher than that of random mixed Al/CuO (730.9 J g-1). Benefiting from outstanding exothermic properties, the material integrated with SCB initiator chip (Al/CuO@NC-SCB) for potential ignition application was investigated. The Al/CuO@NC-SCB micro energetic initiator can be functioned rapidly (with delay time of 2.8 μs) and exhibits superb ignition performances with violent explosion process, high combustion temperature (4636 °C) and successful ignition of B/KNO3 propellant, in comparison to SCB initiator. The strategy provides promising route to introduce nano reactive particles into various functional energy-demanding systems for potential energetic applications.

Hydroxyl ammonium nitrate (HAN)-based electrically controlled solid propellant (ECSP) is the advanced solid chemical propellant stimulated by electric energy, which has throttleable ability. This characteristic is impossible for traditional solid propellants, and greatly expands the potential applications for solid rocket motors that are fit with the ECSP. In this work, the ignition, combustion and extinguishment characteristics of propellant were studied at different voltages, initial temperatures and pressures. It is concluded that the incremental voltage, initial temperature and pressure enhance the burning rate, mass loss and extinguishment delay time, while reducing the ignition delay time, energy required for ignition and electrolysis mass ratio. Specially, as the initial temperature increases from -15 °C to 45 °C (at 200 V and 0.1 MPa), values of mean ignition delay time decrease from 247.4 ms to 116.2 ms, and values of mean burning rate and extinguishment delay time increase from 0.25 mm/s to 0.47 mm/s and 19.2 ms to 27.6 ms, respectively. Moreover, as the pressure increases from 0.1 MPa to 1.0 MPa (at 200 V and 25 °C), values of mean ignition delay time decrease from 151.6 ms to 74.2 ms, and values of mean burning rate and extinguishment delay time increase from 0.44 mm/s to 0.89 mm/s and 28.0 ms to 55.6 ms, respectively. Based on the experimental results, the processes of propellant from ignition to extinguishment were analyzed, and the ignition mechanism was proposed that the fracture of N OH in NH3OH+ in the electrochemical decomposition is a key step that affects the ignition of ECSP. Overall, those results reveal that the electrolysis reaction rather than the pyrolysis reaction exerts an important role for ECSP on achieving the controllable combustion.

Detailed knowledge of dissociation behavior and dissociation products is necessary to understand the stability, sensitivity, and the reactive mechanism of explosives under laser initiation. A time-of-flight mass spectrometer was utilized to detect the transient products of 1,1-diamino-2,2-dinitroethylene (FOX-7) produced under 532 nm pulse laser ablation, the possible attribution of intermediate ion fragments were confirmed. The laser fluence threshold for detectable fragments is about 3.6 J/cm2. The peak intensities of main ions (CN, CNO/C2H4N, NO2, C2N2O, HCN, C2NH2, etc.) increase with the increasing of laser fluence, and reach the maximum at 11.5 J/cm2. Moreover, time-depend changes of ion intensity indicate that the type and degree of reactions are different in different periods. According to the molecular structure of FOX-7 and the intermediate ions, the laser-induced dissociation mechanisms were proposed to illustrate the cause of the fragments which might throw some light on the laser initiation of FOX-7.

Nanothermites are attracting much attention for energetic applications. However, they suffer from high electrostatic discharge (ESD) sensitivity which makes their handling hazardous. Developing safe yet powerful nanothermites is still a challenge. In this work, nitrocellulose (NC) was adhered to the surface of Al and Bi2O3 nanoparticles by a facile electrospray method aiming to improve the ESD safety and energy output of Al/Bi2O3. The morphological and compositional characterization of Al/Bi2O3@NC confirms the NC-coated structure. Benefiting from the structure, the ESD safety of coated Al/Bi2O3 is improved, for instance, the Al/Bi2O3@NC containing 10 wt% of NC has a ESD ignition threshold to be 81 mJ instead of 1 mJ for the Al/Bi2O3 without NC. On the other hand, tunable energy output is obtained by the addition of NC coating. Specifically, Al/Bi2O3@NC (3 wt%) exhibits remarkably enhancements in pressurization, combustion reaction and heat release, which even outperforms the most widely used primary explosive lead styphnate (LTNR). The enhancements are attributed to the fact that NC serves as a gas-generating agent to prevent the nanoparticles from sintering to larger particles and enables sufficient combustion. These results suggest that the electrospray formation of NC-coated nanothermites is a facile strategy for obtaining novel nanothermites. Keywords: Al/Bi2O3 nanothermites, Energetic materials, Electrospray, Nitrocellulose coating, Electrostatic discharge safety, Energy output

Three types of multilayer flyer energy conversion elements (MFECEs) through integrating different laser pulse absorption/ablation layer of nano-film materials into a laser-driven flyer plates between thermal barrier of alumina and transparent substrate have been investigated in this study. The relationships among the velocity of flyer plates, initiation performance of hexanitrostilbene (HNS-IV), and initiation energy were analyzed, comparing with single-layer Al flyer plate. The photonics Doppler velocimetry and James criterion were utilized in the experiments to characterize the velocity of flyer plates and shock initiation of laser-driven flyer detonator, respectively. The surface reflectivity measurements of the Al, C/Al and Mg/Al layers were performed using laser reflectivity. HNS-IV without initiation was analyzed by scanning electron microscope and energy dispersive spectrometer. Caused by aluminum/alumina/aluminum (Al/Al2O3/Al) flyer plate, the residual fragments were found in the pit on the surface of charge. The results obtained were shows that three types of multilayer flyer plates can initiate HNS-IV successfully under the lower laser pulse energy, although all four kinds of flyer plates have successfully initiated HNS-IV with laser pulse energy in the range of 53.80–166.80 mJ. Changing the ablation layer structure and adding thermal insulation layer to the multilayer flyer plates, reduces the shock initiation laser pulse energy of HNS-IV to 53.80 mJ. The laser-driven flyer detonator has significant advantages in providing safety and reliability, especially in a strong electromagnetic environment. The MFECEs of laser-driven flyer detonator exhibited a high level of integration and proved to have promoted laser-driven energy coupling rate, which can significantly be used to improve the performance of the laser-driven flyer detonator in military and civilian applications.

Resorting to the continuous assistance of external laser radiation, laser augmented chemical propulsion (LACP) reveals superior combustion performance. However, the corresponding combustion theories have still to be ascertained for this innovative propulsion technique. Thermal characteristics of 5-aminotetrazole (5-ATZ) propellant are studied for LACP. In nitrogen environment, unique structures of burning surface are formed under laser ablation in bare samples of 5-ATZ propellant pressed powders. Resorting to an outer tube, a thermocouple is inserted in 5-ATZ propellant samples to obtain the temperature trace during combustion. In analogy with the burning surface structure reconstructed by micro computed tomography (MicroCT), the temperatures values of three significant regions were obtained. The experimental dependences of the measured temperatures on environment pressure and laser power are discussed.

This article describes the electro-explosive behaviors and the ignition performances of energetic igniters based on the combination of polysilicon film with Al/CuO nanoenergetic multilayer films (n...

Inspired by the crucial role of the carbon materials in tuning the reactivity of energetic materials, in this paper, nitrated graphene oxide (NGO) was endowed as an additive, and its catalytic effects on Al/CuO nanocomposites were studied. Compared with Al/CuO, the obtained composites showed superior properties in heat of reaction and pressurization rate by introducing a certain amount of NGO as an energetic additive. The results of the T-jump and propagation behavior tests show that the ignition temperature and the propagation velocity of the metastable Al/CuO/NGO composites are tunable due to the special partially crinkled structure of NGO. In addition, benefiting from the high electrical conductivity of the NGO, the composites exhibit better electrostatic discharge safety. Therefore, the NGO additives can be potentially used as a control medium, which can tune the exotherm, ignition, pressurization, combustion performance, and Electrostatic discharge (ESD) safety of nanothermites, and thus may be capable of facilitating the practical applications of nanothermites.

Laser ignition of energetic materials is limited by thermal sensitivity in the photosensitization process. In this paper, a laser-thermal differential composite system consisting of two components with different properties is proposed. The reaction process of the composite system changes under different stimuli. According to the above principle, the composites based on cyclotetramethylenete-tranitramine (HMX) and nano-thermite (Al/CuO) were prepared. Ignition tests show that the composites are sensitive to laser irradiation but difficult to ignite by heating. As expected, nano-thermite, which has a high reaction temperature, reacts first under the stimulation of a laser but not under thermal stimulus. The results show that the application of the composite system in laser ignition technology can bypass the consistency of photosensitivity and thermal sensitivity. Excitingly, the laser-thermal differential composite system can accommodate the existing photosensitive energetic materials and related research. This work provides a novel idea for laser ignition technology.

In this letter, a highly integrated conjoined device, single shot switch and an exploding foil initiator (S3-EFI) chip, was fabricated with microelectromechanical system scale fabrication methods. Photon Doppler velocimetry was utilized to characterize the behavior of the flyer at firing voltages ranging from 1.00 to 2.40 kV. Electrical characterizations were then performed on the chip to obtain some fundamental parameters, such as current and voltage, and a peak current of 1.73 kA was observed at 1.50 kV. Moreover, ultrafine hexanitrostilbene pellets were detonated over firing voltage range 1.80–1.40 kV. These results demonstrate the feasibility of the chip and pave the way to the non-lead high-voltage discharge circuit. To the best of our knowledge, this is the first time to integrate exploding foil initiator with a high-voltage switch.

Reactive multilayer films (RMFs) can be integrated into semiconducting electronic structures with the use of microelectromechanical systems (MEMS) technology and represent potential applications in the advancement of microscale energy-demanding systems. In this study, aluminum/molybdenum trioxide (Al/MoO3)-based RMFs with different modulation periods were integrated on a semiconductor bridge (SCB) using a combination of an image reversal lift-off process and magnetron sputtering technology. This produced an energetic semiconductor bridge (ESCB)-chip initiator with controlled ignition performance. The effects of the Al/MoO3 RMFs with different modulation periods on ignition properties of the ESCB initiator were then systematically investigated in terms of flame duration, maximum flame area, and the reaction ratio of the RMFs. These microchip initiators achieved flame durations of 60–600 μs, maximum flame areas of 2.85–17.61 mm2, and reaction ratios of ∼14–100% (discharged with 47 μF/30 V) by simply changin...

Three types of reactive multilayer films (RMFs) were integrated to the energetic flyer plates (EFPs) by depositing TiO2, MnO2, and CuO onto aluminum films with different modulation periods using magnetron sputtering technology in this study. The effects of the laser ignition property and laser reflectivity on the RMFs and the thermal behavior of the RMFs were analyzed and compared with those of a single-layer Al film. A high-speed video, photonic Doppler velocimetry (PDV), and a thermal analysis were utilized to characterize the flame morphology, EFP velocity, and chemical thermal behavior, respectively. The surface reflectivities of the TiO2/Al, MnO2/Al, and CuO/Al layers were measured using laser reflectivity spectrometers. The results showed that RMFs with smaller modulation periods exhibited excellent laser ignition performances, and EFP with MnO2/Al had the best performance. These RMFs achieved flame durations of 120–220 μs, maximum flame areas of 7.523–11.476 mm2, and reaction areas of 0.153–0.434 mm2 (laser-induced with 32.20 J/cm2). Flyer velocities of 3972–5522 m/s were obtained in the EFPs by changing the material and modulation period of the RMFs. Furthermore, the rate of the chemical reaction and laser energy utilization were also enhanced by reducing the modulation period and using different material. This behavior was consistent with a one-dimensional nanosecond-laser-induced plasma model. The RMFs of MnO2/Al exhibited the highest level of energy release and promoted laser energy utilization, which could better improve the performance of laser ignition for practical application. Graphical Abstract

As a new concept of space propulsion system, laser-ablation propulsion has attracted more and more attention due to its characteristics of low power consumption, high specific impulse, variable and controllable thrust. With an aim to further raise up the movement velocity of plasma, we combine the laser with high-voltage electrostatic field to accelerate the Cu plasma induced by laser ablation. To demonstrate the acceleration characteristics of plasma under different electric field intensity, the plasma conductivity, plasma shockwave intensity and plasma plume movement process were tested using parallel electrode plate device, self-made torsion pendulum impulse test bench and high-speed ICCD camera. The results showed that the conductive current and impulse formed by the plasma obviously increased under the applied electric field. The images captured by high-speed ICCD camera showed the plasma cross-sectional area was 0.194 mm2 at 900 ns and 0.217 mm2 at 1600 ns when the electric field intensity was 0 V/mm. With the electric field intensity increased to 30 V/mm, the plasma cross-sectional area elevated to 0.280 mm2 at 900 ns and 0.288 mm2 at 1600 ns. The acquisitions prove that the idea of this paper is feasible and favorable, which provide a theoretical basis for the combination of laser ablation propulsion and electric field.

We propose top ignition MEMS-based solid propellant microthruster (SPM) array to satisfy the precise propulsion requirements of small spacecraft, especially micro/nanosatellites. A 10 × 10 SPM array prototype was fabricated and assembled by standard microfabrication processes. Nano-Al/CuO was chosen as the solid propellant because of its high combustion heat and safety. To improve the propulsion performance of the microthruster, nanothermites mesoparticles were assembled by electrospray mixing (ES) process. The Chemical Equilibrium with Application calculation result indicates that the addition of nitrocellulose (NC) acting as binder into the nanothermites would enhance the thrust performance. The test results verified this. An impulse testing stand was employed to measure the impulse generated by the assembled SPM array, and a high-speed camera was used to record the combustion process. The specific impulse (I sp) and total impulse (I) of the binder-free nano-Al/CuO were 10.2 s and 155.9 μN s, respectively. The propulsion values of the ES nanothermites increased monotonically with increasing NC content, and the max I sp and I were 27.2 s and 346.9 μN·s, respectively. A 3D X-ray microscope was used to analyze the fired SPM array. The results show that the discontinuous bonding layer led to undesired ignition of the neighboring units.

Four types of Al/CuO energetic nichrome bridges (ENCBs) initiators are reported, prepared by integrating Al/CuO reactive multilayer films (RMFs) on different V-shaped nichrome bridges (NCBs) through magnetron sputtering technology. V-type angles of NCBs are 150°, 136°, 120° and 90°. The fabrication, electrical explosive characteristics of these ENCBs initiators under capacitor discharge, as well as its firing process under constant current conditions are systematically described. The results reveal a ‘stagflation’ phenomenon in high-speed photograph of ENCBs at low discharge voltage, which is consistent with the result of optical microscope images. It is noted the electric explosion delay time decreases with an increase in the discharged voltages, while the critical ignition energy has no relationship with discharged voltages. Moreover, among the four ENCBs, the one with V-angle of 90° exhibits the shortest electric explosion delay time and lowest critical burst energy. This suggests that the electrical explosion performance of ESCBs can be adjusted by optimising the V-shaped angle and the discharge voltage. At last, the high combustion efficiency of ENCB is proved by comparative test with NCB at 0.6 A. And ENCBs have better heating efficiency than nichrome wire with the same resistance at 0.4A and 0.6A.

Parallel bridge foils (PBF) with four strip foils, which is derived from traditional single bridge foil (SBF), was designed to study the effect of convergence and collision of plasmas and shock waves on driving flyer. Firstly, Electro-thermal simulation of PBF was performed to analyze temperature distribution before melting, which predicted the synchronous burst characteristic of PBF. Subsequently, a capacitor discharging circuit was designed to initiate bridge foils, results indicated PBF reached higher burst power in shorter time compared with SBF due to better matching between PBF and the test circuit. The flow fields of electrical explosion of bridge foils were photographed by ultra-high-speed camera, which displayed PBF almost burst simultaneously. Moreover, PBF had wider and brighter flow field visualization than SBF owing to convergence and superposition of plasma beams. Most importantly, flyer-accelerators inserted with bridge foils were prepared by MEMS technology, and comparative analysis from PDV revealed MEMS flyer-accelerator inserted with PBF had access to better velocity performances, compared with that inserted with SBF. For instance, PBF flyer-accelerator spent mere 168 ns to 2325 m/s at 900 V/0.22 µF, but SBF flyer-accelerator took 335 ns to 1073 m/s. Finally, we proposed a mathematical model for explaining the enhancement effect of flyer velocity, which to some extent showed good agreement with experimentation.

Laser-driven flyer technology not only has been widely applied in micro-scale material processing and dynamic high-pressure physics but also possesses obvious advantages in improving the instantaneity and safety of shock initiation. To investigate the launch and impact characteristics between different flyers, six types of typical laser-driven flyers were designed and prepared via magnetron sputtering. The photonic Doppler velocimetry (PDV) and a self-made polyvinylidene fluoride (PVDF) stress sensor were used to collect the velocities and impact stresses of flyers driven by ns-pulsed laser, so that the kinetic energy coupling efficiency and shock initiation property were able to be obtained. Comparisons of characteristics between different flyers were implemented. The effect of nanothermite formed between aluminum and copper oxide layers was verified. The kinetic energy coupling relationship with laser and factors that influenced impact stress of flyers were discussed as well. The results are of significance in optimizing the launch and impact characteristics of laser-driven flyers for practical application.

Laser-induced dissociation pathways of cyclotrimethylenetrinitramine have been investigated with a focused laser of 1064 nm by use of a time-of-flight mass spectrometer. The ions produced from the cyclotrimethylenetrinitramine surface were detected and the mass spectra of both positive and negative ions were obtained. According to the possible distribution of the decomposition products, possible dissociation paths of cyclotrimethylenetrinitramine were proposed. The influence of the intensity and the delay time of the laser beam to the decomposition have also been studied. The results may possibly throw some light on our understanding of the reactions taking place in laser ignition.

In an effort to get detailed information and provide insight into the basic physical process and elementary chemical reaction involved in laser-induced reactions in explosives, different research methods, including laser-induced breakdown spectroscopy (LIBS), mass spectrometry (MS), Fourier transform infrared spectroscopy (FTIR), ultraviolet-visible (UV-Vis) spectroscopy, X-ray photoelectron spectroscopy (XPS), fluorescence spectroscopy, electron paramagnetic resonance (EPR) spectroscopy, etc., have been used to investigate the laser-induced photodecomposition of explosives experimentally. These kinds of experiments based on interactions of explosives with a laser might provide a unique contribution to solve the complex problem of combustion and detonation of laser ignition. The review is concerned with studies on laser-induced decomposition of typical explosives (nitrate esters, aromatic nitro compounds, and nitramines).

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.

Three-dimensional ordered macroporous (3DOM) Al/NiFe2O4 nanothermite has been obtained by a colloidal crystal templating method combined with magnetron sputtering processing. Owing to the superior material properties and unique 3DOM structural characteristics of composite metal oxides, the heat output of the Al/NiFe2O4 nanothermite is up to 2921.7 J g−1, which is more than the values of Al/NiO and Al/Fe2O3 nanothermites in literature. More importantly, by comparison with the other two nanothermites, the onset temperature of about 300 °C from Al/NiFe2O4 is remarkably low, which means it can be ignited more easily. Laser ignition experiments indicate that the synthesized Al/NiFe2O4 nanothermite can be easily ignited by a laser. In addition, the preparation process is highly compatible with the MEMS technology. These exciting achievements have great potential to expand the scope of nanothermite applications.

The applications of laser propulsions to explore space have been discussed for long time. The laser ablation or laser plasma propulsions by high-power laser are discussed in terms of launching, orbit keeping, and attitude controlling for microsatellites and vehicles. The advantage of laser ablation propulsion is higher specific impulse than other conventional propulsions, but a lightweight and high-power laser is required. A new concept of laser-augmented chemical propulsion (LACP) is proposed to control variable thrust and to turn on/off thrust easily by a low-power laser. The principle of laser-augmented chemical propulsion is based on the solid propellant combustion under thermal radiation, in which the burning rate of solid propellant depends linearly on the radiation strength of a continuous wave (CW) laser. Some photosensitive and lower energetic propellants are used for the laser-augmented chemical thrusts, such as ammonium nitrate (AN), guanidine nitrate (GN), carbamide, and 5-aminotetrazole (5-ATZ), in which the propellants can burn under laser radiation, but flame off when turning off laser radiation. The propulsion energy comes from chemical reaction heat and laser energy. The feasibility and ballistics of laser-augmented chemical propulsion are discussed in experimental and theoretical analysis in the paper. The specific impulse and the thrust depend on the irradiation strength. The specific impulse equation \( {\mathrm{I}}_{\mathrm{s}}\propto 1/\sqrt{{\uprho \mathrm{b}\mathrm{A}}_{\mathrm{r}}\mathrm{q}} \) shows that the specific impulse will decrease with increase of radiant flux (q) and radiation sensitivity coefficient (b), but the thrust \( {\mathrm{F}}_{\mathrm{cp}}\propto \sqrt{{\uprho \mathrm{b}\mathrm{A}}_{\mathrm{r}}\mathrm{q}} \) will increase with the increase of radiant flux and radiation sensitivity coefficient.

Nanostructured energetic materials (NSEMs) have nanoscale objects at least in one dimension. In this chapter the research progress is reported on the synthesis, fabrication, thermal analysis, and the energetic chip performances of multidimensional nanostructured energetic materials, including carbon nanotubes/KNO 3 (KNO 3 @CNTs), CuO nanowires/Al, Ni nanorods/Al, Co 3 O 4 nanowires/Al, Al/Ti multilayer film, Al/Ni multilayer film, CuO/Al multilayer film, porous copper/NH 4 ClO 4 , porous copper/NaClO 4 , 3D Fe 2 O 3 and their energetic chips. The results obtained show that the reaction mechanism of NSEMs has a complex and multistep character, and the reaction heat depending on structure scale is lower than the theoretical value. The synthesis processes of NSEMs are compatible with the fabrication processes of MEMS to integrate energetic chips. It is also shown that the NSEM-impregnated bridges generate larger amount of energy than conventional bridges.

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.

The integration of composite energetic films (CEFs) with various types of initiators can effectively adjust their performance and represents potential applications in microscale energy-demanding systems. In this study, the Al/Bi2O3/graphene oxide (GO) CEFs were successfully integrated into copper micro-ignitors by electrophoretic deposition, a low-cost and time-saving method. The effects of the Al/Bi2O3/GO CEFs with different GO contents on exothermic performance and ignition properties of micro-ignitors were then systematically investigated in terms of heat release, activation energy, ignition duration, the maximum height of the ignition product, and ignition delay time. The results showed that the addition of GO promoted more heat releases and higher activation energies of Al/Bi2O3/GO CEFs. The addition of ≤3.5 wt. % GO prolonged the ignition duration from 450 μs to 950 μs and increased the maximum height of the ignition product from about 40 mm to 60 mm. However, the micro-ignitors with more than 3.5 wt. % GO cannot be ignited, which suggested that GO played a contradictory role in the ignition properties of micro-ignitors and the controlled GO content was a prerequisite for improved ignition performance. The ignition delay time gradually extended from 10.7 μs to 27.6 μs with increases in the GO contents of Al/Bi2O3 CEFs, revealing that an increase in the weight ratio of GO leads to lower ignition sensitivity of micro-ignitors.

Optical emission spectroscopic studies have been carried out on the laser-induced copper plasma generated in the process of laser-driven flyer (with the substrate confinement). The copper plasma in the air (without the substrate confinement) has also been researched in order to know the differences between the plasma with the confinement and that without the confinement. The plasma is assumed to be in local thermodynamic equilibrium. The result shows that, under the same laser fluence, the plasma exists a longer time with the confinement. The time-resolved electron temperature and density with the confinement are higher than those with no confinement. The substrate deposited with Cu foil plays an important role in enhancing the temperature and the density of the plasma. The electron temperature and density with confinement increase with a larger scope as the laser fluence increases than that with no confinement.

Laser driving flyer technology has been studied for many years and widely used in dynamic high-pressure physics and impact dynamics, rapid initiation of high explosives, simulation of space debris and micro-forming of metal foil. The coupling efficiency between the flyer kinetic energy and the laser energy could be improved by introducing a layer with stronger absorption at the 1064nm wavelength Nd:YAG laser, resulting in higher flyer velocity for a given laser energy. So a multilayer flyer (C/Al/Al2O3/Al) with Carbon absorption layer was designed and compared the flyer velocity with the flyer (Al/Al2O3/Al) without Carbon absorption layer. The experimental study was performed via the Photonic Doppler Velocimetry (PDV). The results show that the velocity of flyer with Carbon absorption layer rose with fluctuations as laser energy increasing, and was lower than that without Carbon layer at the same laser energy. That means the addition of Carbon absorption layer decreased the flyer coupling efficiency.