Electrostatic Sensitivity Research Articles

Core–Shell Copper Azide-Based Nanofiber Films Prepared by Coaxial Electrospinning for MEMS Microinitiators

The main bottleneck preventing powders from being used in a microinitiation system is the paradox between safety and detonation performance, as well as powders’ inherent brittleness and difficulty in shaping. To address this problem, we used the coaxial electrospinning technology to design and fabricate a core–shell film (CA@C–D) with low sensitivity and high energy. Electrostatic sensitivity (E50 = 5.22 mJ) and flame sensitivity (H50 = 51 cm) are both significantly lower than those of the raw copper azide (CA) material and can detonate secondary explosives. Extensive characterization and experiments show that the unusual core–shell structure of coaxial electrostatic spinning fibers is responsible for this significant improvement. This high specific surface area carbon shell wraps around the CA particles, providing double protection, while the superior thermal and electrical conductivity of the carbon material helps improve system safety and maintains the azide output performance. More importantly, it always maintains a good film structure and is simple to process, meeting the actual requirements of MEMS initiators and introducing a new scheme for the preparation of film-based initiators.

Safe and Efficient Strategy for Directly Preparing Azide Aerogels for Microinitiation Device.

The main bottlenecks limiting the practical application of primary explosives are the contradiction between safety and detonation performance, as well as the inherent brittleness of powder charge. Traditional methods to improve sensitivity performance such as adding carbon nanomaterials or embedding metal-organic framework (MOF) structure methods are mostly powders, which are inherently brittle and unsafe. Here, we report three types of typical azide aerogels that can be directly prepared and obtained in this paper by combining electrospinning with aerogel. Their electrostatic sensitivity and flame sensitivity were significantly improved and could be detonated successfully at an initiation voltage of 25 V, demonstrating good ignition performance. This enhancement is primarily due to the porous carbon skeleton structure evolved from a three-dimensional nanofiber aerogel, which has good thermal and electrical conductivity characteristics and can also uniformly load azide particles, contributing to improved explosive system sensitivity. The most important aspect of this method is that it can directly prepare molded explosives, which can be matched with the micro-electrical-mechanical system (MEMS) process, and it offers a new idea for the preparation of high-security molded explosives.

Preparation, Characterization and Properties of NC-coated Zirconium Composite Particles

Zirconium has certain application advantages compared with other metals due to its high density, high volume calorific value and combustion performance. Unfortunately, the applications of current Zirconium powders are limited due to its high electrostatic discharge sensitivity, making Zirconium powders more pyrophoric and less amenable to functionalization. To improve the security, Zr/NC composite particles with reduced electrostatic discharge sensitivity are prepared by solvent-antisolvent method and characterized by FT-IR, XRD, TG, SEM and ESD test. The measurement confirmed that the 50% firing energy (E50) of Zr/NC is increased from 5.13 mJ to 25.2 mJ, which is 5 times higher than that of raw Zr powder. The results show that surface coating modification is a feasible method for decreasing the ESD of Zr powder. This study provides technology support for its application in high density propellant.

Promising Energetic Melt-Castable Material with Balanced Properties.

As one of the most widely used energetic materials to date, trinitrotoluene (TNT) suffers from several generally known drawbacks such as high toxicity, oil permeability, and poor mechanical properties, which are driving researchers to explore new high-performance energetic melt-castable materials for replacing TNT. However, it still remains a great challenge to discover a promising TNT alternative due to the multidimensional requirements for practical applications. Herein, we reported a new promising energetic melt-castable molecule, 4-methoxy-1-methyl-3,5-dinitro-1H-pyrazole (named as DMDNP). Besides a reasonable melting point (Tm: 94.8 °C), good thermostability (Td: 293.2 °C), and excellent chemical compatibility, DMDNP exhibits some obvious advantages over TNT including more environmentally friendly synthesis, high yield, low toxicity, low volume shrinkage, low mechanical and electrostatic sensitivities, etc., demonstrating well-balanced properties and great promise as a TNT replacement.

“Green” PBX Formulations Based on High Explosives (RDX and HMX) and Water-Soluble pH-Sensitive Polymeric Binders

The increasingly harsher and more complex international and European environmental legislation drives the current development of "greener" energetics materials and munitions. The aerospace and defense industries rely on extensive research in the formulation and scale-up production of polymer-bonded explosives (PBX). In this context, this paper aims to present a versatile method for obtaining "green" PBX formulations based on two high explosives (hexogen (RDX) and octogen (HMX)) and acrylic acid-ethyl acrylate copolymeric binders. This study developed an innovative "eco-friendly" technology for coating the RDX and HMX crystals, allowing straightforward and safer manufacture of PBX, avoiding the use of traditional organic solvents. At the same time, these polymeric binders are soluble in water at a slightly alkaline pH and insoluble at acidic or neutral pH, thus ensuring a safer manipulation of the energetic materials during their entire life cycle and a facile recovery of the explosive in its original shape and morphology in demilitarization. The PBX formulations were characterized via specific analytical tools to evaluate the influence of their composition on the safety and performance characteristics: scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FT-IR), alkaline pH solubility tests, differential thermal analysis (DTA), impact sensitivity test (BAM Fall Hammer Test), friction sensitivity test (BAM Friction Test), electrostatic sensitivity test (ESD), vacuum stability test, small scale shock reactivity test (SSRT), detonation velocity test. The "green" PBX formulations obtained through a simple and innovative coating method, based on the polymeric binders' adjustable water solubility, demonstrated remarkable energetic performances and a facile recovery of the explosive crystals by the dissolution of the polymeric binder at pH 11 and 30 °C.

An effective catalyst carrier SiO2: Enhancing catalytic and combustion properties of CuFe2O4 on energetic components

To enhance the catalytic activity of copper ferrite (CuFe2O4) nanoparticle and promote its application as combustion catalyst, a low-cost silicon dioxide (SiO2) carrier was employed to construct a novel CuFe2O4/SiO2 binary composites via solvothermal method. The phase structure, morphology and catalytic activity of CuFe2O4/SiO2 composites were studied firstly, and thermal decomposition, combustion and safety performance of ammonium perchlorate (AP) and 1,3,5-trinitroperhydro-1,3,5-triazine (RDX) with it affecting were then systematically analyzed. The results show that CuFe2O4/SiO2 composite can remarkably either advance the decomposition peak temperature of AP and RDX, or reduce the apparent activation energy at their main decomposition zone. Moreover, the flame propagation rate of RDX was promoted by about 2.73 times with SiO2 content of 3 wt%, and safety property of energetic component was also improved greatly, in which depressing the electrostatic discharge sensitivity of pure RDX by about 1.89 times. In addition, the effective range of SiO2 carrier content in the binary catalyst is found to be 3 to 5 wt%. Therefore, SiO2 opens a new insight on the design of combustion catalyst carrier and will promote the application of CuFe2O4 catalyst in solid propellant.

Preparation and Properties of Pyrotechnic Binder Encapsulated α‐AlH3 Composites by Solvent/Anti‐solvent Method

AbstractAlpha‐aluminum hydride (α‐AlH3) is an ideal energetic combustion agent, but its poor stability and safety limit its application. Therefore, we prepare different composites by using the solvent/anti‐solvent method to coat different pyrotechnic binders on the surface of α‐AlH3. The vacuum stability test show that the minimum outgassing of Shellac‐coated α‐AlH3 composite is only 1.2 mL/g at 50 °C for 6 days. Due to the good electrical insulation properties of Viton, Viton‐coated α‐AlH3 composite have the highest E50 value of electrostatic sensitivity. In addition, the pyrotechnic binders coating not only protects the activity of the α‐AlH3 but also effectively increases its burning rate. Viton‐coated α‐AlH3 composite have more gaseous products and maximum flame area during combustion. This study illustrates that α‐AlH3 coated with pyrotechnic binders is a means to address its stability and safety, laying the foundation for its application in solid propellants.

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.

Efficient Synthesis of Nanoscale Cadmium Azide from Intercalated Cadmium Hydroxide for Nanoexplosive Applications

Due to its good sensitivity, detonation ability, and high-temperature resistance, cadmium azide is expected to be applied to microinitiating systems. Here we demonstrate an effective synthetic methodology (GAF-IH) to prepare nanoscale cadmium azide. A nanoscale mesoporous configuration is designed to construct azide precursor utilizing controlled self-assembly of inorganic and organic molecules followed by in situ carbonization crystallization. The nanoscale porous precursors can react with HN3 gas to form nanoscale cadmium azide composites (CdA/SA and CdA/C) in just 3 h, which takes much less time than traditional preparation methods of cadmium azide. The organic molecules and their carbonized skeletons can act as the carriers of nanoscale cadmium compounds to avoid agglomeration, as supporting materials for building HN3 azide gas channels, and as functional components in the nanoscale cadmium azide composites to influence their performance. CdA/C prepared by this route has favorable comprehensive properties, which not only has a high content of CdA (93.8%), indicating excellent detonation performance (tID < 10 μs), but also has good high-temperature resistance (Tp = 365 °C) and low electrostatic sensitivity (E50 = 1.76 J). Thanks to its nanoscale characteristics and outstanding performance, CdA/C has the potential to replace CA and modified CA in the application of microinitiating devices.

A three-dimensional energetic coordination compound (BLG-1) with excellent initiating ability for lead-free primary explosives.

Exploration of advanced lead-free primary explosives is a challenging issue in the field of energetic materials. Herein, we designed and synthesized a novel N-rich copper bromate energetic coordination compound (ECC) [Cu(ATRZ)(BrO3)2]n (BLG-1, ATRZ: 4,4'-azo-1,2,4-triazole) by a simple one-step reaction. BLG-1 is the first reported three-dimensional (3D) N-rich copper bromate ECC. Its interesting 3D reticular architecture contributed to its highest thermal decomposition temperature (Td: 226 °C) and crystal density (ρ: 2.69 g cm-3) among N-rich copper bromate ECCs. More importantly, a primary charge of BLG-1 as little as 3 mg could reliably detonate compressed RDX, and 1 mg could detonate CL-20. These incredible values indicated that BLG-1 had an ultra-powerful initiating ability far superior to that of previously reported primary explosives. BLG-1 had improved mechanical sensitivities (IS: 13 J; FS: 1 N) and electrostatic sensitivity (EDS: 240 mJ) compared with those of the typical lead-based primary explosive, lead azide (IS: 4J; FS: 0.75N; EDS: 5 mJ). In particular, BLG-1 had a low laser-initiation threshold of 13 mJ at 808 nm, suggesting that it could serve as a laser-ignitable primary explosive. This work suggests that BLG-1 is a promising candidate with engreat practical application prospects for lead-free primary explosives.

Performance enhancement strategy for tetrazoles based on nitrogen-boron bonds.

Based on N-B bonds, a novel strategy was developed for improving the energetic performance of tetrazoles. By employing the amino neighboring group participation, the azolyl borane compound 7 was selectively constructed, which exhibited excellent stability in water and air. This strategy solved the acidity problem of tetrazole as well as increasing the heat of detonation and combustion by 25% and 36%, respectively. Through laser ignition experiments, it also improved the combustion performance of tetrazoles. In DSC experiments, thermal decomposition temperatures of N-B covalent compounds were elevated as well. In an electrostatic potential calculation and sensitivity test, N-B covalent compounds exhibited good sensitivity (IS > 40 J and FS > 360 N). Through TG-DSC-FTIR-MS and in situ IR experiments, decomposition products were investigated to determine the next optimization stage for heat of detonation. It offered a significant potential for development to incorporate the N-B bond into nitrogen-rich compounds.

Modulation of Crystal Growth of an Energetic Metal–Organic Framework on the Surfaces of Graphene Derivatives for Improved Detonation Performance

Energetic materials are a special class of energy materials composed of C, H, O, and N. Their safety always deteriorates with increasing energy. Regulating the properties of energetic materials to meet application requirements is one of the focuses of research in this field. Energetic metal-organic frameworks (EMOFs) are good candidates as primary explosives to replace lead azide (LA) and other explosives containing toxic metal elements. However, safety remains the biggest concern in applications. In this paper, crystal morphology modulation of EMOF was carried out by stepwise coordination of metal ions and energetic ligands on surfaces of graphene oxide (GO) and amino-functionalized graphene oxide (AGO). Two energetic composite materials, Cu-AFTO@GO and Cu-AFTO@AGO, were successfully synthesized and also the EMOF (Cu-AFTO). The structures and morphologies of these materials were fully characterized. The thermal decomposition behaviors, mechanical sensitivity, and electrostatic discharge sensitivity were investigated in detail. The electric ignition ability of EMOF and two composite materials was tested. This study shows that it is possible to reduce the diameter of EMOF crystals from hundreds of microns to tens of nanometers by a stepwise coordination method. The high electrical conductivity and sensitivity-reducing effect of GO and/or AGO allow the nanosized EMOF crystals to have a lower ignition threshold and lower sensitivity.

A new ternary high-energy composite based on nano titanium powder with low sensitivity and stable combustion

For solving the low combustion efficiency caused by aggregation and further promoting the application of nano titanium powder (n-Ti), a new ternary composite high-substitute nitrochitosan/nano titanium/graphene oxide (NCh/n-Ti/GO) was prepared by a resonant acoustic mixing method. Herein the high-substitute nitrochitosan (NCh) was used as binder and oxidant to modify the surface of n-Ti powder, and GO was introduced as stabilizer and carrier. The energy release rate, laser ignition, combustion performance and sensitivity of NCh/n-Ti/GO were systematically studied in this work. The experiment results confirmed that GO plays a significant role in adjusting combustion performance and reducing the sensitivity of composite. Compared with n-Ti, NCh/n-Ti and NC/n-Ti, the introduction of GO can greatly increase the combustion time and reduce the flame propagation speed. In particular, NCh/n-Ti/GO (3 wt%) presentedan optimal linear flame morphology, the shortest ignition delay time and lowest pressurization rate. The combustion products were also determined and confirmed to be co-existence of TiO, a little TiN and unburned n-Ti powder. The introduction of GO can reduce the sensitivities to impact and electrostatic of composites greatly. The electrostatic sensitivity of NCh/n-Ti/GO (3 wt%) was 5.1 ± 0.1 mJ and decreased by 160% and 230%, compared with that of n-Ti and NCh/n-Ti. So the introduction of NCh and GO would be a good strategy to promote the combustion performances and safety of n-Ti powder.

Acid-base synthesis of aluminum iodate hexahydrate powder as a promising propellant oxidizer

An acid-base precipitation reaction is detailed to synthesize pure crystals of the oxidizer rich compound [Al(H2O)6](IO3)3(HIO3)2 and described here for the first time. The molecule is called aluminum iodate hexahydrate (AIH) and characterized for its energetic potential as an oxidizer in propellant applications. The synthesis method produced bipyramidal hexagonal crystals that are characterized physically and chemically by microscopy, pycnometry, and X-ray crystallography. Further energetic characterization is performed by bomb calorimetry, and impact, friction, and electrostatic discharge ignition sensitivity. This study introduces the potential of AIH as an alternative solid propellant by comparison to the properties of ammonium perchlorate (AP) and ammonium nitrate (AN).

Fabrication of electrostatic safety copper azide film with in situ growing MOF

Due to its extremely low electrostatic sensitivity, copper azide primary explosive is greatly limited in practical applications. In this study, a composite film with Cu-MOF in-situ growth on carbon nanofilm was prepared by electrospinning and solvothermal methods, and CNF@Cu–N3 film with electrostatic safety was obtained by carbonization and azide later. Its electrostatic sensitivity (E50) was greatly increased from 0.05 mJ of raw materials to 4.06 mJ, and still maintained a good detonation performance which could successfully detonate the CL-20 secondary explosive. This is mainly due to the synergistic effect of the carbon film and the MOF structure, which greatly improves the conductivity of the entire system and the uniform distribution of copper particles, providing a new preparation strategy for metal azide film that is suitable for the micro-initiator device.

Molding Fabrication of High‐Energy Nanoparticles of Lead Azide Encapsulated by Graphene‐Doped Porous Carbon Matrix with Excellent Ignition Ability

AbstractIn this work, graphene oxide‐doped lead‐containing metal‐organic framework (BTC−Pb/GO) and polyvinyl alcohol were used as raw materials to prepare spherical or cylindrical lead azide composites by freeze‐drying, carbonization, and in‐situ azide steps. Nanoscale lead azide is uniformly distributed on the graphene‐doped porous carbon framework. Detailed characterization and testing show that LA/C/rGO exhibits excellent electrostatic sensitivity (1.94 J) and flame sensitivity (40 cm) due to the excellent electrical and thermal conductivity of porous carbon and graphene, which are superior to most of the previously reported modified lead azide.

Energetic properties of copper azide nanoparticles encapsulated within a conductive porous matrix via electrosynthesis

The copper-based azide (CA), as a sustainable alternative to currently-used primary explosives, will play a critical role in the deployment of miniature initiating systems owing to its outstanding blasting power and environmentally benign nature. However, a secure and controlled synthesis still remains challenging for the high-performance CA-based energetic film. Here, a conductive metal–organic framework (MOF) of cuprous 7,7,8,8-tetracyanoquinodimethane (CuTCNQ) is employed as a template for the electrochemical preparation of the CA nanoparticles encapsulated with conductive porous matrix. Impressively, the composition, morphology, energetic characteristics (1090 ∼ 2780 J·g−1) and electrostatic sensitivity (0.19 ∼ 12.3 mJ) of such CA/CuTCNQ energetic films can be easily tuned by carefully adjusting current density and azidation time in order to achieve the tailored energy release in the form of combustion or detonation. Furthermore, density functional theory (DFT) calculations provide valuable insights for the electrochemical azidation mechanism of the CA/CuTCNQ film. This work pioneers a new pathway to develop the CA composite film as an interesting energetic material for advanced initiating applications.

Preparation and Characterization of PANI Surface Modified HMX/F2602 Microcapsule Composites

AbstractUsing HMX with a particle size of 1–10 μm as the main explosive, a dense polyaniline (PANI) shell was prepared on the surface of HMX/F2602 by in situ polymerization, and an energetic composite material HMX−F@PANI (HMX−F2602@PANI) with a microcapsule structure was constructed. The structure and properties of the samples were characterized by SEM, XRD, XPS, DSC, mechanical sensitivity and electrostatic spark sensitivity tests. The results showed that the chemical structure and polycrystalline morphology of the crystals did not change during the coating process, and remained β‐HMX. The preparation of PANI shell greatly improves the coating degree of the explosive surface and reduces the exposure of crystal. In addition, compared with HMX/F2602, HMX−F@PANI is more excellent in improving thermal stability and reducing the electrostatic spark sensitivity, which is attributed to the advantages of microcapsule structure and good electrical conductivity of PANI.

Spark Desensitization of Nanothermites via the Addition of Highly Electro-Conductive Carbon Particles

In the past decade, the formulation of spark-desensitized nanothermites has considerably advanced, making them safe to handle. When ignited, these materials reveal impressive properties such as high temperatures (&gt;1000 °C), intense heat releases (&gt;kJ/cm3), and sometimes gas generation. Unfortunately, these energetic systems are systematically characterized by an extreme sensitivity to electrostatic discharges, which can cause accidental ignitions during preparation, handling, and transport. The present study examines the electrostatic discharge sensitivity response of an Al/WO3 energetic formulation doped with highly conductive carbon nanoparticles (Ketjenblack EC600JD). The results showed an increased threshold from &lt;0.14 mJ to almost 40 mJ with 18.80 vol. % of KB EC600JD in the energetic mixture. The energetic material was also desensitized to friction stress with a threshold greater than 360 N, in contrast to a value of &lt;4.9 N for an un-doped Al/WO3 energetic composite material. The reactive performance of the system (w/o Ketjenblack additive) was verified in open medium by means of an optical igniter. The heat release was determined by a calorimetric bomb and a decrease of 50% was recorded for the carbon-doped energetic system compared to the pristine Al/WO3 composition.

Enhancement strategy of mechanical property by constructing of energetic RDX@CNFs composites in propellants, and investigation on its combustion and sensitivity behavior

In the domain of energetic materials (EMs), the high-energy and high-strength propellants are always what are the scientists pursuing to satisfy the great demands of fast development and replacement for artillery. Recently, the emerging of cellulose nanofibers (CNFs) has attracted great interests since its extraordinary performances like biocompatibility, carbon-neutral nature, tailorable surface chemistry, and unprecedented mechanical properties. Inspired by the fascinating high strengthen of CNFs, this study prepared a kind of energetic hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX)@CNFs composites firstly, and then applied them in conventional double-based gun propellant (GP) to study its energy, combustion and mechanical, and sensitivity performances. The results of the mechanical properties demonstrated that the impact strength of RDX@CNFs-GP with different content of CNFs was improved by 34.9-104.7%, 7.1-39.4%, 14.4-51.2% under the condition of low, room and high temperature, the compression strength was improved by 8.6-49.5%, 4.3-45.9%, 6.2-47.8%, while the tensile strength was improved by 0.6-21.2%, 7.0-19.5%, 9.0-26.0%, respectively. Moreover, the impact and electrostatic spark sensitivities have also been increased by 21.8% and 61.8% in terms of the maximum value and exert favorable desensitization effect compared with blank sample. Notably, the propellant added with CNFs could burn steadily without anomalous combustion behavior, and the energy level of the RDX@CNFs-2.0%-GP (1180.70 J/g) maintain relative close value to that of RDX@CNFs-0%-GP (1184.84 J/g) with regard to the gunpowder impetus. Lastly, the enhancement mechanism of the CNFs in GP was discussed and proposal. Hence, this present work could potentially provide fundamental theory and data support for the development of CNFs in high-strength and high energy propellants.