Construction of High Energy Nanoscale Lead Azide Composite with Improved Flame Sensibility from Intercalated Hydroxide.

It is of great significance to develop efficient methods for preparing high-content modified nanoscale lead azide (LA) composites used in microinitiating devices. In this work, a structurally controllable salicylate-intercalated lead hydroxide with a nanoscale mesoporous structure is designed. Using it as a precursor, carbon-based lead azide (LA/C) and salicylate-based lead azide (LA/SA) are fabricated by the gas-solid azidation of the framework (GAF) method within 3 h, greatly reducing the preparation time of nano-LA composites. The characterizations of the composites demonstrate that the Pb in the precursors is transformed into nanoscale LA attached to the salicylate radical or its carbonized skeleton. Due to the unique embedded nanostructures and excellent electrical and thermal conductivity of salicylate-derived carbon materials, LA/C exhibits excellent electrostatic safety (E50 = 0.25 J) and flame sensitivity (H50 = 28 cm). The adjustable organic-inorganic ratio of intercalated hydroxides allows the LA content in LA/C to reach as high as 92.5%, enabling 6.50 mg of LA/C to successfully detonate secondary explosive CL-20 in a microinitiating device, demonstrating an amazing detonation ability superior to other reported LA complexes. The research provides a new perspective for the development of nanoscale LA composites with high LA content and appropriate sensitivity.

Facile Synthesis of Energetic Nanoparticles of Copper Azide with High Initiation Ability for Micro-Initiator Applications Using Layered Copper Hydroxide.

Copper azide (CA) is one of the preferred primary explosives in the micro-initiating device, and it is of conducive significance to develop high-content CA-modified materials. In this work, we reported two types of CA composites with CA nanorods embedded in carbon nanosheets (CA/C) and CA distributed on salicylic acid (CA/SA) using layered copper hydroxide nanosheets intercalated with salicylic acid as the precursor. The detailed characterizations demonstrated that CA/C exhibits eximious electrostatic sensitivity (1.06 mJ) due to the inherent structural characteristics of CA/C such as the limitation of the free movement of CA by the layered structure and preeminent electrical conductivity of carbon nanosheets. Surprisingly, CA/C with nearly 1.0 mg in the miro-initiating device can reliably detonate Hexanitrohexaazaisowurtzitane (CL-20). CA/C exhibits extremely high CA content (93%), excellent ignition ability, and detonation ability, and its performance is superior to pure CA and most CA-modified materials reported previously. CA/SA also has an excellent detonation ability and its electrostatic sensitivity is as low as 0.92 mJ. These findings provide a new perspective for the development of high-performance primary explosives for the micro-initiating device.

Molding fabrication of copper azide/porous graphene with high electrostatic safety by self-assembly of graphene oxide.

In the wake of the development of micro-initiation systems, traditional lead-based primary explosives hardly satisfy the needs of high energy output. Copper azide (CA), one of the most promising primary explosives, is restricted in practical applications because of its high electrostatic sensitivity and the method of charge in micro-initiation systems. To tackle these issues, two synthetic paths of CA based on a porous graphene skeleton are proposed. First, a viscous homogeneous mixed solution is rapidly frozen in liquid nitrogen to form a spherical copper-containing precursor material. The copper azide/carbon/graphene composite (CA/C/GA) was fabricated by freeze-drying, high-temperature thermal decomposition andin situazidation. Second, A cylindrical copper/graphene gel formed by high-temperature hydrothermal self-assembly is served as a precursor material. Also, hydrogen reduction andin situazidation procedures were utilized to synthesize copper azide@graphene foam (CA@GF). Detailed characterization indicates that the excellent performance of composite materials is ascribed to the excellent electrical and thermal conductivity of graphene material. The electrostatic sensitivities of CA/C/GA and CA@GF were 3.6 mJ and 2.5 mJ, respectively, and the flame sensitivity was 50 cm. The course of fabrication is environmentally friendly and easy to perform and it may be well-matched with the charge of the micro-detonation system.

Enhanced Thermal Decomposition and Safety of Spherical CL-20@MOF-199 Composites via Micro-Nanostructured Self-Assembly Regulation.

The characteristics of high burning rate, high energy output, and low pressure exponent have always been the focus of development in the field of composite solid rocket propellants. In this paper, a metal-organic framework (MOF-199) compound is introduced to prepare micro-nanospherical CL-20@MOF-199 composites via the spray-drying self-assembly technique to reach the above goals. MOF-199, which acts as an attractive combustion catalyst and a safety regulator, is uniformly coated on the surface of CL-20 with close interface contact between particles, effectively accelerating the thermal decomposition of CL-20 and ensuring safety performance. The average noncovalent interaction (aNCI) analysis illustrates that there are strong C-H···O hydrogen bonds and van der Waals interaction between CL-20 and MOF-199 molecules, greatly enhancing the effect of interparticle assembly. The effects of different contents of MOF-199 on the thermal, safety, and energy properties of CL-20 were discussed. The thermal analysis demonstrates that MOF-199 has a significant thermal catalytic effect on CL-20, with an advanced peak temperature of thermal decomposition of 14.2 °C and a reduced activation energy barrier of 34.2 kJ·mol-1, mainly benefitting from more exposed catalytic active sites and close interface contact. In addition, CL-20@MOF-199 composites exhibit decreased mechanical sensitivity (IS: 21-40 cm, FS: 80-240 N) and excellent energy performance. This work clearly demonstrates that MOF-199 is both a superior combustion catalyst and a good safety buffer for CL-20, and it opens new potential for further applications of CL-20 in composite solid propellants.

Preparation of a nanoscale homogeneous energetic lead azides@porous carbon hybrid with high ignition ability by in situ synthesis.

The ever-increasing demand for miniaturized explosive systems urgently calls for better performance studies through the synthesis of novel nanoscale materials. In this work, lead azide@porous carbon hybrids (LA@PC) are synthesized by in situ carbonization and azidation of a lead-containing cross-linked gel, in which the nanoscale LA is uniformly distributed on the porous carbon skeleton. The detailed characterization has shown that such outstanding performance stems from the LA nanoscale effect and the excellent conductivity and thermal conductivity of carbon cages. Because of the favorable unique structure, the prepared composite material exhibits excellent ignition performance, and its flame sensitivity can reach 42 cm, which solves the problem of poor ignition capacity of LA on all occasions. In addition, the composite has very low electrostatic sensitivity, further improving the safety of practical application. This work makes it possible for LA to be detonated without using lead styphnate, paving a new way for improving the flame sensitivity of primary explosives.

Fabrication of Copper Azide Film through Metal-Organic Framework for Micro-Initiator Applications.

The paradox between safety and detonation performance, along with the intrinsic fragility of primary explosives, is the main bottleneck precluding their application in a micro-initiation system. To tackle these issues, we fabricate a flexible copper azide film (CA-C film@PF) via employing the metal-organic framework (MOF) film produced by electrospinning technique as the precursor, followed by pyrolysis treatment, in situ azide reaction, and perfluorinated coating procedures. The synergetic effect of MOF and interweaved polymer fiber endow the resultant copper azide film with excellent electrostatic stability and remarkable detonation performance. In particular, the electrostatic discharge sensitivity ( E50) value (9 mJ) is 180 times higher than that of the original copper azide powder (0.05 mJ) and the static electricity accumulation value (- Q) is 430 times lower than that of copper azide powder (0.04 vs 17.2 nC g-1). As the proof of concept, the copper azide film is further assembled in a micro-initiation device, which can successfully detonate the secondary explosives CL-20. Additionally, the superhydrophobic surface of the CA-C film@PF merit the initiation power even after being soaked in water.

Nanoscale Homogeneous Energetic Copper Azides@Porous Carbon Hybrid with Reduced Sensitivity and High Ignition Ability.

Research on green primary explosives with lead-free and excellent ignition performance is of significance for practical applications. In this work, we have developed a novel, green, and facile strategy for synthesizing copper azide@porous carbon hybrids (CA@PC) based on ionic cross-linked hydrogel with low-cost cellulose derivatives as the starting material, in which the CA nanoparticles are uniformly distributed in the porous carbon skeletons. The detailed characterizations and control experiments demonstrated that such an outstanding performance originates from the excellent electric conductivity of nanoscale carbon cages. With the favorable unique structures, the as-prepared hybrids can greatly benefit a new type of energetic materials, which exhibit a very low electrostatic sensitivity of 1.06 mJ. Interestingly, the hybrids possess a high ignition ability, and the flame sensitivity can even achieve 47 cm, superior to those well-developed CA-based materials reported previously. This work paves the way toward the design and development of next-generation highly efficient energetic materials.