Nanothermites: A short Review. Factsheet for Experimenters, Present and Future Challenges

Role of Surface Tension on Heat Feedback and Power from Energetic Composites

Heat feedback to the unburned reaction interface is an important controlling factor of the velocity of the reaction front and power delivery. In this paper, we investigate the effect of agglomerate surface tension and its relationship to surface residence time and heat feedback on the combustion characteristics by Si addition to an Al/KClO4 composite. Macroscopic imaging demonstrates a significant increase in burn rate with the addition of Si despite the fact that Si/KClO4 has a slightly lower energy density than Al/KClO4. Microscopic imaging coupled with three-color pyrometry reveals that molten liquid forms and evolves into spherical droplets on the burning surface, which are subsequently ejected from the surface. We find that the addition of Si results in a small increase in droplet size and a negligible impact on droplet temperature. However, the droplet formation rate on the surface is slower, leading to a significantly longer surface residence time. This leads to enhanced conductive heat feedback to the unburnt materials, thereby increasing the burn rate and energy release rate. We attribute the decreased droplet growth rate to the lowered surface tension of the liquid mixture with Si addition. This study highlights the crucial role of agglomerate physical property (e.g., surface tension) in influencing the combustion behavior of energetic composites.

Ti/CuO Nanothermite Doped with Secondary Energetic Materials: A Study of Combustion Parameters

Nanothermites have found broad applications; however, due to being systems largely reacting in condensed phases, their performance is somewhat limited by heat and mass transfer. In order to alleviate this issue, nanothermites doped with gas-generating energetic materials have been developed. In this work, we present an investigation of a model Ti/CuO nanothermite doped by four classical energetic materials and investigate their properties and combustion performance. Mechanical and laser irradiation sensitivity, as well as ignition/explosion temperatures have been determined for the studied systems to establish their safety features. In terms of combustion performance, thrust force parameters and linear combustion velocity have been determined and the structure of the evolving flame front was recorded during open-air combustion experiments. The obtained results indicate that the developed doped nanothermite formulations are extremely promising materials for future applications.

Nitroglycerin trapping in melamine matrices

Melamine (Mel) was used as host matrix for liquid nitroglycerin (NG), to prepare Mel/NG solid powdered compounds containing up to 45 wt% of this explosive. The two preparation processes used for this purpose consisted in evaporating a solution of both components, either in ambient conditions or under reduced pressure by the Spray Flash-Evaporation (SFE) process. In Mel/NG materials, amorphous nitroglycerin is distributed in the crystallized melamine matrix as inclusions, which were found to be smaller in size in the material prepared by the SFE process. Mel/NG materials are not stable over time: they gradually lose the nitroglycerin they contain by evaporation.

Carbon Nanotubes for Confinement-Induced Energetic Nanomaterials

Oxidized carbon nanotubes obtained by catalytic chemical vapor deposition were filled with an aqueous solution of nano-energetic materials using a very simple impregnation method. The work compares different energetic materials but focuses especially on an inorganic compound belonging to the Werner complexes, [Co(NH₃)₆][NO₃]₃. Our results show a large increase in released energy upon heating, which we demonstrate to be related to the confinement of the nano-energetic material either directly by filling of the inner channel of carbon nanotubes or to insertion in the triangular channels between adjacent nanotubes when they form bundles.

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

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

Quo Vadis, Nanothermite? A Review of Recent Progress

One of the groups of pyrotechnic compositions is thermite compositions, so-called thermites, which consist of an oxidant, usually in the form of a metal oxide or salt, and a free metal, which is the fuel. A characteristic feature of termite combustion reactions, apart from their extremely high exothermicity, is that they proceed, for the most part, in liquid and solid phases. Nanothermites are compositions, which include at least one component whose particles size is on the order of nanometers. The properties of nanothermites, such as high linear burning velocities, high reaction heats, high sensitivity to stimuli, low ignition temperature, ability to create hybrid compositions with other high-energy materials allow for a wide range of applications. Among the applications of nanothermites, one should mention igniters, detonators, microdetonators, micromotors, detectors, elements of detonation chain or elements allowing self-destruction of systems (e.g., microchips). The aim of this work is to discuss the preparation methods, research methods, direction of the future development, eventual challenges or problems and to highlight the applications and emerging novel avenues of use of these compositions.

Progress in Electrohydrodynamic Atomization Preparation of Energetic Materials with Controlled Microstructures

Constructing ingenious microstructures, such as core-shell, laminate, microcapsule and porous microstructures, is an efficient strategy for tuning the combustion behaviors and thermal stability of energetic materials (EMs). Electrohydrodynamic atomization (EHDA), which includes electrospray and electrospinning, is a facile and versatile technique that can be used to process bulk materials into particles, fibers, films and three-dimensional (3D) structures with nanoscale feature sizes. However, the application of EHDA in preparing EMs is still in its initial development. This review summarizes the progress of research on EMs prepared by EHDA over the last decade. The morphology and internal structure of the produced materials can be easily altered by varying the operation and precursor parameters. The prepared EMs composed of zero-dimensional (0D) particles, one-dimensional (1D) fibers and two-dimensional (2D) films possess precise microstructures with large surface areas, uniformly dispersed components and narrow size distributions and show superior energy release rates and combustion performances. We also explore the reasons why the fabrication of 3D EM structures by EHDA is still lacking. Finally, we discuss development challenges that impede this field from moving out of the laboratory and into practical application.

Theoretical Calculations and Experiments on the Thermal Properties of Fluorinated Graphene and Its Effects on the Thermal Decomposition of Nitrate Esters

Fluorinated graphene contains F atoms with high levels of chemical activity, and the application of fluorinated graphene in energetic materials may greatly contribute to the progress of combustion reactions. However, there is a lack of research on the thermal properties of fluorinated graphene and its application on nitrate esters. In this paper, theoretical calculations and experiments were used to study the thermal properties of fluorinated graphene and its application on nitrate esters. The anaerobicity and poor thermal stability of fluorinated graphene were proved by ab initio molecular dynamics (AIMD) calculations and TG-DSC experiments. The ester weakening effect of fluorinated graphene on nitroglycerin was determined via wavefunction analysis, with the greater the fluorination degree, the stronger the ester weakening effect. The existence of fluorinated graphene can significantly increase the heat dissipation of the composites, which was concluded by TG-DSC experiments and TG-DSC-MS-FTIR. The research in this article provides an important reference for the application of fluorinated graphene in energetic materials.

Review of the Problems of Additive Manufacturing of Nanostructured High-Energy Materials

This article dwells upon the additive manufacturing of high-energy materials (HEM) with regards to the problems of this technology’s development. This work is aimed at identifying and describing the main problems currently arising in the use of AM for nanostructured high-energy materials and gives an idea of the valuable opportunities that it provides in the hope of promoting further development in this area. Original approaches are proposed for solving one of the main problems in the production of nanostructured HEM—safety and viscosity reduction of the polymer-nanopowder system. Studies have shown an almost complete degree of deagglomeration of microencapsulated aluminum powders. Such powders have the potential to create new systems for safe 3D printing using high-energy materials.

Carbon Fibers Enhance the Propagation of High Loading Nanothermites: In Situ Observation of Microscopic Combustion

A major challenge in formulating and manufacturing energetic materials lies in the balance between total energy density, energy release rate, and mechanical integrity. In this work, carbon fibers are embedded into ∼90 wt % loading Al/CuO nanothermite sticks through a simple extrusion direct writing technique. With only ∼2.5 wt % carbon fiber addition, the burn rate and heat flux were promoted >2×. In situ microscopic observation of combustion shows that the carbon fiber intercept ejected hot agglomerates near the burning surface and enhanced heat feedback to the unreacted material. This study outlines how these approaches may enhance the propagation and reduce the two-phase flow losses.

Effect of the Ni and NiO Interface Layer on the Energy Performance of Core/Shell CuO/Al Systems

The interface layer is responsible for the outward migration of oxygen atoms, which subsequently leads to an adjustment in the energetic performance of nanothermite films. In this study, sandwich-structured CuO@Ni/Al and CuO@NiO/Al nanowire thermite films were successfully prepared to investigate the effects of the interface layer on the heat-release, ignition, and combustion performance. The effects of the Ni and NiO interface layers are extremely different on the heat-release performance and combustion properties of the CuO/Al nanowire thermite film. Herein, the introduced Ni layer decreased the heat release (1979.7 J/g), reactivity (E_a = 177.3 kJ/mol), and maximum pressure (2.32 MPa) compared with the CuO/Al composite. Al/Ni alloys can be formed at the interface to prevent oxygen from diffusing between CuO and Al. Moreover, the incorporation of the Ni interface layer into the CuO/Al systems results in a heat drop due to its heat-absorption capability as well as its blockage of heat transfer from the thermite reaction. The deposition of the NiO layer between CuO and Al leads to an increase in the heat release (3014.2 J/g) and a decrease in the activation energy (E_a = 178.6 kJ/mol). The NiO layer endows the CuO/Al system with a high energy-release rate and chemical reactivity. NiO can participate in a thermite reaction, which promotes the reaction of CuO/Al and induces the condensed phase.

Interpol review of detection and characterization of explosives and explosives residues 2016-2019

This review paper covers the forensic-relevant literature for the analysis and detection of explosives and explosives residues from 2016-2019 as a part of the 19th Interpol International Forensic Science Managers Symposium. The review papers are also available at the Interpol website at: https://www.interpol.int/Resources/Documents#Publications.

From nanoparticles to on-chip 3D nanothermite: electrospray deposition of reactive Al/CuO@NC onto semiconductor bridge and its application for rapid ignition

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.

Synergistically Chemical and Thermal Coupling between Graphene Oxide and Graphene Fluoride for Enhancing Aluminum Combustion

Metal combustion reaction is highly exothermic and is used in energetic applications, such as propulsion, pyrotechnics, powering micro- and nano-devices, and nanomaterials synthesis. Aluminum (Al) is attracting great interest in those applications because of its high energy density, earth abundance, and low toxicity. Nevertheless, Al combustion is hard to initiate and progresses slowly and incompletely. On the other hand, ultrathin carbon nanomaterials, such as graphene, graphene oxide (GO), and graphene fluoride (GF), can also undergo exothermic reactions. Herein, we demonstrate that the mixture of GO and GF significantly improves the performance of Al combustion as interactions between GO and GF provide heat and radicals to accelerate Al oxidation. Our experiments and reactive molecular dynamics simulation reveal that GO and GF have strong chemical and thermal couplings through radical reactions and heat released from their oxidation reactions. GO facilitates the dissociation of GF, and GF accelerates the disproportionation and oxidation of GO. When the mixture of GO and GF is added to micron-sized Al particles, their synergistic couplings generate reactive oxidative species, such as CF_x and CF_xO_y, and heat, which greatly accelerates Al combustion. This work demonstrates a new area of using synergistic couplings between ultrathin carbon nanomaterials to accelerate metal combustion and potentially oxidation reactions of other materials.

Facile fabrication of highly exothermic CuO@Al nanothermites via self-assembly approach

CuO@Al nanothermites with Al shell and CuO core were successfully fabricated via a simple self-assembly route. The composition and morphology of CuO@Al nanothermites were analyzed by x-ray diffraction and field-emission scanning electron microscopy in detail. When the equivalence ratio was 1.0, the heat output of CuO@Al nanothermites reached 1252 J g^-1, which was significantly larger than that of the Al/CuO prepared by ultrasonic mixing. The greatest heat output of CuO@Al nanothermites reached 1860 J g^-1, demonstrating outstanding exothermic properties, which ascribed to their unique core-shell structure. This study provides a new strategy about the design and advancement of highly exothermic nanothermites.