Nanocomposite Thermite Research Articles

Hot Bridge-Wire Ignition of Nanocomposite Aluminum Thermite Synthesized Using Sol-Gel-Derived Aerogel with Tailored Properties for Enhanced Reactivity and Reduced Sensitivity

The development of nano-energetic materials has significantly advanced, leading to enhanced properties and novel applications in areas such as aerospace, defense, energy storage, and automobile. This research aims to engineer multi-dimensional nano-energetic material systems with precise control over energy release rates, spatial distribution, and temporal and pressure history. In this context, sol–gel processing has been explored for the manufacture of nanocomposite aluminum thermites using aerogels. The goal is to produce nano-thermites (Al/Fe2O3) with fast energy release rates that are insensitive to unintended initiation while demonstrating the potential of sol–gel-derived aerogels in terms of versatility, tailored properties, and compatibility. The findings provide insightful conclusions on the influence of factors such as secondary oxidizers (KClO3) and dispersants (n-hexane and acetone) on the reaction kinetics and the sensitivity, playing crucial roles in determining reactivity and combustion performance. In tandem, ignition systems contribute significantly in terms of a high degree of reliability and speed. However, the advantages of using nano-thermites combined with hot bridge-wire systems in terms of ignition and combustion efficiency for potential, practical applications are not well-documented in the literature. Thus, this research also highlights the practicality along with safety and simplicity of use, making nano-Al/Fe2O3-KClO3 in combination with hot bridge-wire ignition a suitable choice for experimental purposes and beyond.

RELATIVE EXPLOSIVE FORCE OF Al/MoO3 NANOCOMPOSITE/POLYMERIC BINDER

We briefly overview the common and most studied nanothermite composites of different formulations. The paper primarily deals with systems whose main representatives are nanothermite composites for pyroautomatic delay and special devices and initiator primers. The problem of the development of gas-free (low-gas), fast-burning pyrotechnic compositions based on nanothermites is considered herein. The experimental part discusses an understudied issue of explosive transformation mechanisms, including the identification of governing chemical reactions. A study on the effect of fluoropolymer F-42L on the relative explosive force of a pyrotechnic composition based on a thermite reaction between nanopowdered aluminum as the fuel and molybdenum oxide as the basic oxidizer is also reported. The fluoropolymer was shown to reduce the explosive force of the nanocomposite, in which case the governing chemical reaction of explosive transformation was found to be the reaction of Al with the fluoropolymer.

Nanothermite composites with a novel cast curable fluoropolymer

Structural nanoenergetic (SNE) composites consisting of nanothermites dispersed in a polymer binder are attractive for combustion applications due to their substantially higher volumetric energy, density, and tailorable energy release characteristics. Cast curing is an extensively utilized, safe, and economical method for processing energetic materials into structural composites possessing macroscale geometries. The use of cast curing as a route for processing SNE composites is limited by the lack of suitable binder systems. The widely used cast curable binder such as hydroxyl terminated polybutadiene (HTPB) if used for this purpose will render the SNE composites thermally non-ignitable. Fluoropolymers have emerged as energetic binders for aluminum containing nanothermites due to their capability to induce pre-ignition reaction and sustain the ignitability of composites. Herein, we report the synthesis of a novel cast curable fluoropolymer (FP) with 58 wt% fluorine content produced through the cationic ring opening polymerization of 3-Perfluorohexyl-1, 2-epoxypropane. We demonstrate the utility of the synthesized FP as a cast curable binder for aluminum/copper oxide (Al/CuO) nanothermite to prepare SNE composites. The SNE composites were cast cured as cylindrically shaped specimens with the FP content ranging from 30 to 50% by weight. All the SNE composites were observed to be thermally ignitable even under an inert environment, suggestive of the unique role of FP on promoting the ignitability of SNE composites. SNE composite containing 40 wt% FP recorded the highest energetic performance in terms of heat of reaction (880 cal/g) and pressure generation characteristics (pressurization rate = 3.81kPsi/s; time to maximum pressure = 340 ms). Additionally, the 40 wt% FP SNE composite generates time averaged combustion temperature of 2530 K as estimated by spectroscopic technique.

Silicon Nanoparticles for the Reactivity and Energetic Density Enhancement of Energetic-Biocidal Mesoparticle Composites.

Biocidal nanothermite composites show great potential in combating biological warfare threats because of their high-energy-release rates and rapid biocidal agent release. Despite their high reactivity and combustion performance, these composites suffer from low-energy density because of the voids formed due to inefficient packing of fuel and oxidizer particles. In this study, we explore the potential of plasma-synthesized ultrafine Si nanoparticles (nSi, ∼5 nm) as an energetic filler fuel to increase the energy density of Al/Ca(IO3)2 energetic-biocidal composites by filling in the voids in the microstructure. Microscopic and elemental analyses show the partial filling of mesoparticle voids by nSi, resulting in an estimated energy density enhancement of ∼21%. In addition, constant-volume combustion cell results show that nSi addition leads to a ∼2-3-fold increase in reactivity and combustion performance, as compared to Al/Ca(IO3)2 mesoparticles. Oxidation timescale analyses suggest that nSi addition can promote initiation due to faster oxygen transport through the oxide shell of Si nanoparticles. At nSi loadings higher than ∼8%, however, slower burning characteristics of nSi and sintering effects lead to an overall degradation of combustion behavior of the composites.

Stability study of iodinated reduced graphene oxide and its application in self-assembled Al/Bi2O3 nanothermite composites

The direct reduction of graphene oxide (GO) by hydroiodic acid is an established method to produce iodine functionalized reduced GO (I-rGO). However, the stability of the iodine species within I-rGO upon heating and dispersing into different solvents, as required for many applications, has not been examined. Herein we examined the stability of I-rGO and utilized it to promote self-assembled nanoenergetic composites. I-rGO intercalated with polyiodide was found to be unstable at elevated temperature and when dispersed in organic solvents. The I-rGO exhibited excellent dispersion in dimethylformamide but resulted in a loss of iodine content as exfoliation released weakly-bound intercalated iodine species. The dispersed I-rGO was utilized as a scaffold to self-assemble I-rGO/Al and I-rGO/Al/Bi2O3 nanoenergetic composites. The I-rGO both prevented the phase separation of Al and Bi2O3 particles and provided a source for reactive iodine to etch the alumina shell surrounding Al fuel nanoparticles. Differential scanning calorimetry showed that the use of the I-rGO assembly template reduced the temperature of initiation and peak reaction and produced 70% greater energy release than randomly mixed Al/Bi2O3 nanoenergetic powder. In fact, 95% of the exothermal energy released by the reaction occurred while Al was in the solid state, suggesting that the reaction between free iodine and alumina was significant enough to greatly reduce the diffusion barrier between solid Al fuel and surrounding oxidizer. Further, the underlying conductive I-rGO scaffold reduces electrostatic discharge sensitivity of the nanoenergetic composite by almost four orders of magnitude.

Effect of nitrocellulose and 1-methyl-3-nitro-1,2,4-triazole on properties of CuO/Al and Bi2O3/Al nanothermites

Here we examined how the addition of high-energy materials such as nitrocellulose and 1-methyl-3-nitro-1,2,4-triazole (1Me-3N) would influence the properties of Bi2O3/Al and CuO/Al nanothermite composites. The additives allowed the improvement in explosion force (F) and burning rate (u) of the composites, achieving the maxima at concentrations of 5 % NC and 9 % 1Me-3N for the Bi2O3/Al/1Me-3N mixture, and of 15 % 1Me-3N for CuO/Al/1Me-3N. A further increase in concentrations of the additives decreased the combustion performance of the composites. The effect of the said additives on the properties of nanothermite composites has been considered herein from the standpoint of a simplified model of convective burning in a single pore.

Reactivity of Al/CuO Nanothermite Composites with Fluoropolymers

ABSTRACT Aluminum/copper oxide (Al/CuO) nanothermite is a promising metal fuel due to its high combustion enthalpy and excellent gas-producing characteristics. Fluoropolymers are energetic binders that can potentially be used to make moldable reactive composites without compromising the ignitability of thermites for structural applications. Herein, we report the reactivity of Al/CuO nanothermite composites with two processable fluoropolymers, THV, and Viton. The reactivities of the prepared composites were investigated from pressure measurement. The corresponding reaction mechanism was also studied by post-reaction products analysis. The results showed that both THV and Viton composites, even those containing up to 30 wt.% of fluoropolymer, were ignitable. However, the reactivities of the prepared composites were observed to reduce to different extent depending on the type of fluoropolymers used. The reduced reactivity was ascribed to the subdued nanothermite reaction due to the consumption of copper oxide and aluminum by reacting with the fluoropolymers. Among the two fluoropolymers studied, the THV composite exhibited a relatively higher reactivity. The ignition delay and combustion temperature of the THV composite were further determined.

Synthesis, characterization and nanoenergetic utilizations of fluorine, oxygen co-functionalized graphene by one-step XeF2 exposure

The energetic performance of aluminum(Al)-based nanothermite composites is hindered by the native alumina shell on the surface of Al nanoparticles. To maximize the energetic release and lower the reaction temperature between Al and metal oxide nanoparticles, a novel fluorine and oxygen co-functionalized graphene (FGO) is reported. The material was synthesized by gas–solid reaction between graphene oxide paper and XeF2 gas. The stability of FGO in atmospheric humidity, heating, and exfoliation by sonication in different solvents were obtained by FTIR and SEM-EDS. The FGO contained both unstable acyl fluoride groups and stable carbon-fluorine covalent/semi-ionic bonds in its structure. The FGO was introduced as a functional additive in an Al/Bi2O3 nanothermite composite, leading to a heat of reaction heat of 1123 J/g, 58% greater than that from loose Al/Bi2O3 powder. The reaction completed before reaching the melting temperature of Al, indicating a novel all-solid-state reaction between Al and Bi2O3. The decreased reaction temperature is attributed to fluorine etching of the native alumina shell surrounding the Al nanoparticle fuel.

Al–NiO energetic composites as heat source for joining silicon wafer

Abstract Silicon wafers with the thickness of approximately 250 μm were joined successfully using Al/NiO nano-thermite composites and with an aluminum foil interlayer (thickness of 30 μm), due to energy production from the exothermic reaction between Al (40 nm) and NiO (50 nm) powders. This reaction heat was subsequently transferred across the silicon wafer and reached the Si–Al–Si interface. This joining method reduces the possibility of introducing unwanted impurity and residual from the thermite reaction and subsequently improves the joint quality. Experimental data shows, adding Al micro-powder (5 μm, 60 % by mass) or Ni micro-powder (1 μm, 30 % by mass) into the nano-thermite composite was necessary and effective in joining the silicon wafer. The micro-hardness of the joined zone was measured as 129.3 ± 15.5 HV and 42.3 ± 4.0 HV for the Al and Ni micro-powder modified nano-thermite composites, respectively. The localized yield strength data confirmed the Al micro-powder produced a higher yield strength (350.6 ± 17.8 MPa) than the Ni micro-powder (327.1 ± 55.0 MPa). Energy production from the nano-thermite composites with different mixing ratios with the additive was characterized by Differential Scanning Calorimetry (DSC), and the apparent activation energy of the respective thermite reaction were calculated to investigate the effects of reaction kinetics to the joining process. The reduced joint quality produced by the Ni micro-powder modified Al/NiO nano-thermite composite was due to the low energy release from its thermite reaction (1.06 kJ/g), which was not sufficient to melt the silicon wafer. Moreover, the large activation energy of this thermite reaction (696.09 kJ/mol) hindered the joining process. In contrast, the Al micro-powder modified Al/NiO nano-thermite composite, via a two-step energy release process, produced sufficient energy (1.89 kJ/g) which led to a superior joint quality. In the first step, a pilot reaction (corresponding to the activation energy of 332.96 kJ/mol) between Al (40 nm) and NiO (50 nm) nanoparticles was dominant. In the following step, the reaction between Al micro-powder (5 μm) and NiO (50 nm) nanoparticles became significant and contributed greatly to successful joining.

Pre-stressing aluminum nanoparticles as a strategy to enhance reactivity of nanothermite composites

Aluminum (Al) fuel particles are used in a variety of energetic formulations yet harvesting their full chemical potential energy and increasing their energy release rate upon ignition have been a challenge and are key motivators to advancing energy generation technologies. One approach to improving combustion performance is to alter the mechanical properties of the Al particle by inducing an elevated stress state through prestressing. This study examines the combustion performance of prestressed nanoscale aluminum (nAl) particles that were annealed to temperatures ranging from 200 to 400 °C and quenched at slow (exponential) and faster (linear) cooling rates. Powder X-ray diffraction measurements show that prestressing nAl particles at 300 °C increases the strain by an order of magnitude. Constant volume combustion cell tests on nAl combined with copper oxide nanopowder (nAl + CuO) revealed higher peak pressures and pressurization rates for prestressed nAl + CuO composites compared to their untreated counterpart. High speed emission spectroscopy was employed to deduce condensed phase temperatures from the reaction confined within the combustion cell. Burn time measurements, obtained by integrating the emission spectra, were observed to correlate inversely with generated pressure. High heating rate (∼5 × 105 K/s) in-situ TEM results augment the combustion cell results. The results imply that prestressing mechanically alters the nanoparticles which subsequently accelerate the release of aluminum core through outward diffusion. This results in the rapid loss of nanostructure which was observed at the nanoscale through in-situ electron microscopy. The released aluminum thus reacts rapidly with the oxidizer in the condensed phase resulting in a faster and more violent reaction. Improved performance of prestressed nAl coupled with the simplicity of processing provides a low cost and scalable approach to improving metal fuel particle combustion.

Combustion of a rapidly initiated fully dense nanocomposite Al–CuO thermite powder

Very short burn times of nanocomposite, fully dense, stoichiometric 2Al·3CuO thermite particles ignited by electro-static discharge (ESD) observed in earlier experiments are interpreted assuming that the reaction occurs heterogeneously at the Al–CuO interfaces while the initial nanostructure is preserved even after the melting points of various phases present in the particle are exceeded. The heating rate for the ESD-ignited particles is very high, reaching 109 K s−1. The reaction model assumes that the rate of reaction is limited by transport of the reacting species across the growing layer of Al2O3 separating Al and CuO. The model includes the redox reaction steps considered earlier to describe ignition of 2Al·3CuO nanocomposite thermites and adds steps expected at higher temperatures, when further polymorphic phase changes may occur in Al2O3. A realistic distribution of CuO inclusion sizes in the Al matrix is obtained from electron microscopy and used in the model. The model accounts for heat transfer of the nanocomposite particles with surrounding gas and radiative heat losses. It predicts reasonably well the burn times observed for such particles in experiments. It is also found that neglecting polymorphic phase changes in the growing Al2O3 layer and treating it as a single phase with the diffusion-limited growth rate similar to that of transition aluminas (activation energy of ca. 210 kJ mol−1) still leads to adequately predicted combustion temperatures and times for the nanocomposite particles rapidly heated by ESD. The model highlights the importance of preparing powders with fine CuO inclusion sizes in the nanocomposite particles necessary to complete the redox reaction; it is also found that the particle combustion temperatures may vary widely depending on their dimensions. Higher combustion temperatures generally lead to greater reaction rates and, respectively, to the more complete combustion.

Interaction between Single-Walled Carbon Nanotubes and Reactive Nanoparticle Constituents in Multilayered Al/NiO Nanocomposite

Single walled carbon nanotubes (CNTs) were added into layered Al/NiO nano-thermite composites, to tune their energetic and reaction properties. Scanning Electron Microscopy (SEM) images showed a direct contact between the Al and NiO layers, where the presence of CNTs in a designated layer was clearly visible. Thermal-chemical data obtained from Differential Scanning Calorimetry (DSC) demonstrated these composites, although modified with CNTs in either the Al or the NiO layer, exhibited a nearly constant onset temperature, implying comparable reaction initiation mechanisms. However, different amounts of energy release, accompanied with formation of distinct layer composition and microstructures of their products, was produced. It was further revealed that, by means of mass spectrometry, SEM and X-ray Diffraction (XRD) analysis, upon the initiation of the thermite reaction between Al and NiO at the interface layer, the reaction between CNTs and NiO nanoparticles produced CO and CO2, which promoted the gas-s...

High speed 2-dimensional temperature measurements of nanothermite composites: Probing thermal vs. Gas generation effects

This work investigates the reaction dynamics of metastable intermolecular composites through high speed spectrometry, pressure measurements, and high-speed color camera pyrometry. Eight mixtures including Al/CuO and Al/Fe2O3/xWO3 (x being the oxidizer mol. %) were reacted in a constant volume pressure cell as a means of tuning gas release and adiabatic temperature. A direct correlation between gas release, peak pressure, and pressurization rate was observed, but it did not correlate with temperature. When WO3 was varied as part of the stoichiometric oxidizer content, it was found that Al/Fe2O3/70% WO3 achieved the highest pressures and shortest burn time despite a fairly constant temperature between mixtures, suggesting an interplay between the endothermic Fe2O3 decomposition and the higher adiabatic flame temperature sustained by the Al/WO3 reaction in the composite. It is proposed that the lower ignition temperature of Al/WO3 leads to the initiation of the composite and its higher flame temperature enhances the gasification of Fe2O3, thus improving advection and propagation as part of a feedback loop that drives the reaction. Direct evidence of such gas release promoting reactivity was obtained through high speed pyrometry videos of the reaction. These results set the stage for nanoenergetic materials that can be tuned for specific applications through carefully chosen oxidizer mixtures.

Nanocomposite thermite powders with improved flowability prepared by mechanical milling

Nanocomposite thermite powders can be used in reactive parts and components. Manufacturing these components requires tailoring powder particle size distributions, particle shapes, and powder flowability. Specifically, an improved flowability is desired to use such powders as feedstock in additive manufacturing. Arrested reactive milling (ARM) offers a versatile and practical approach for preparing nanocomposite thermites with fully dense particles, which will retain their structures and mixedness between reactive components while being stored, handled, and processed. However, ARM products usually have broad particle size distributions, rock-like particle shapes, and poor flowability. Here, ARM is modified to include a low-energy milling step to tune the shapes and flowability of the prepared powders. Experiments are performed with aluminum-rich Al·Fe2O3 thermites. After the initial nanocomposite thermite is prepared in a planetary mill, it is additionally milled at a reduced rotation rate, replacing milling balls with smaller glass beads, and adding different liquid process control agents. Powders with modified particle shapes and size distributions are obtained, which have substantially improved flowability compared to the initial material. The reactivity of the initial and modified powders is evaluated using their ignition on a heated wire, by electro-static discharge, by thermal analysis (DSC) and in constant volume explosion tests. The reactivity of the modified powders is not diminished; instead, an improved reactivity is observed for selected samples.

The Effect of Heating Rate on Combustion of Fully Dense Nanocomposite Thermite Particles

ABSTRACTThe effect of heating rate on the combustion pathways of fully dense, micron-sized, nanocomposite thermite particles is examined. Stoichiometric nanocomposite thermites utilizing aluminum or zirconium as fuels were prepared by arrested reactive milling with several oxidizers (WoO3, MoO3, CuO, Fe2O3, and Bi2O3). The powders were ignited using both electrostatic discharge (ESD) and CO2 laser beam. The particles ignited directly by ESD were heated at ca. 109 K/s while the particles ignited by laser were heated at ca. 106 K/s. Additional reference laser ignition experiments were performed with particles of pure Al and Zr. Optical emission of burning particles was recorded. For both Al- and Zr-based thermites, burn times of particles ignited by the laser were slightly longer than for similarly sized particles of pure Al and Zr, respectively. This suggests that both Al- and Zr-based thermite particles heated by laser lose their nanostructure immediately upon their ignition. Burn times and temperatures were compared for the particles of the same materials ignited using different heating rates. For Zr-based thermites, ESD generated burning particle clouds, with many particles ignited with a substantial delay and heated much slower than those ignited by ESD directly. Thus, direct comparisons were possible only for the Al-based thermites, for which both laser and ESD ignition yielded individual burning particles. It is observed that the ESD-ignited Al-based thermite particles burn much faster than the same particles ignited by the laser. The difference in the burning regime of particles heated at different rates is interpreted observing that the rate of reaction in a particle heated up to the Al melting point is substantially higher in the ESD-heated particle compared to the same particle heated by the laser. After Al melts, the nanostructure of the composite particles may be lost; when this occurs the extent of thermite reaction in the ESD-heated particle is much greater than that in the particle heated by the laser.

Mechanochemically prepared reactive and energetic materials: a review

Reactive and energetic materials are typically metastable and are expected to transform into thermodynamically favorable reaction products with substantial energy release. Preparation of such materials by mechanical milling is challenging: They are easily initiated by impact or friction. At the same time, milling offers a simple, scalable, and controllable technology capable of mixing reactive components on the nanoscale. In most cases, for reactive materials milling should be interrupted or arrested to preserve the metastable phases. Arrested reactive milling was exploited to prepare many inorganic reactive materials, including nanocomposite thermite, metal–metalloid, and intermetallic systems. Prepared materials are fully dense composites with unique properties, combining high density with extremely high reactivity. Different milling devices were used to prepare reactive materials and an approach was developed to transfer the process conditions between different mills. Different milling protocols, such as milling at cryogenic temperatures or staged milling can be used to prepare hybrid reactive materials with different components mixed on different scales; it was also used to tune the particle size distributions of metal-based reactive material powders. Metal–halogen composites were prepared, with metal matrix stabilizing a halogen (e.g., iodine) at temperatures substantially exceeding its boiling point. Mechanochemically prepared reactive materials can be classified based on the energy of reaction between components and the energy of oxidation of the bulk material composition. Work on mechanochemical preparation of reactive and energetic materials is reviewed with the focus on unique properties and ignition and combustion mechanisms of the mechanochemically prepared reactive materials. An ignition mechanism for nanothermites involving preignition reaction leading to a gas release preceding rapid temperature rise is discussed. A combustion mechanism is also discussed, in which the nanostructure of the mechanochemically prepared material is preserved despite the very high combustion temperatures.

Incomplete reactions in nanothermite composites.

Exothermic reactions between oxophilic metals and transition/ post transition metal-oxides have been well documented owing to their fast reaction time scales (≈ 10 μs). This article examines the extent of reaction in nano-aluminum based thermite systems through a forensic inspection of the products formed during reaction. Three nanothermite systems (Al/CuO, Al/Bi2O3 and Al/WO3) were selected owing to their diverse combustion characteristics thereby providing sufficient generality and breadth to the analysis. Microgram quantities of the sample were coated onto a fine platinum wire, which was resistively heated at high heating rates (≈ 105 K/s) to ignite the sample. The subsequent products were captured/quenched very rapidly (≈ 500 μs) in order to preserve the chemistry/morphology during initiation and subsequent reaction and were quantitatively analyzed using electron microscopy (EM), focused ion beam (FIB) cross-sectioning followed by energy dispersive X-ray spectroscopy (EDX). Elemental examination of the cross-section of the quenched particles show oxygen predominantly localized in the regions containing aluminum, implying the occurrence of redox reaction. The Al/CuO system, which has simultaneous gaseous oxygen release and ignition (TIgnition ≈ TOxygen Release ), shows substantially lower oxygen content within the product particles as opposed to Al/Bi2O3 and Al/WO3 thermites, which are postulated to undergo a condensed phase reaction (TIgnition << TOxygen Release ). An effective Al:O composition for the interior section was obtained for all the mixtures, with the smaller particles generally showing higher oxygen content than the larger ones. The observed results were further corroborated with the reaction temperature, obtained using a high-speed spectro-pyrometer, and bomb calorimetry conducted on larger samples (≈ 15 mg). The results suggest that thermites that produce sufficient amounts of gaseous products generate smaller product particles and achieve higher extents of completion.

Nanocomposite Thermites with Calcium Iodate Oxidizer

Iodine bearing reactive materials and fuel additives are being developed to inactivate harmful aerosolized spores and bacteria by combined thermal and chemical effects. Nanocomposite thermites with aluminum and boron serving as fuels and calcium iodate as an oxidizer were prepared by arrested reactive milling. Both materials contained 80 wt % of calcium iodate. Morphology and particle sizes of the prepared materials were characterized using scanning electron microscopy (SEM). Both powders comprised particles finer than ca. 10 μm with fuel and oxidizer mixed on the submicrometer scale. Powders were exposed to room air to assess their stability. They were ignited as a thin coating on an electrically heated filament. Powders were injected in an air-acetylene flame to observe combustion of individual particles. Pressed pellets for both prepared materials were prepared and ignited using a CO2 beam. Al ⋅ Ca(IO3)2 oxidizes rapidly in room air, whereas no aging was detected for B ⋅ Ca(IO3)2. Ignition of Al ⋅ Ca(IO3)2 occurs around 1150 K, after both aluminum and calcium iodate melt. Ignition is accompanied by ejection of sintered particles undergoing microexplosions while they are combusting. Ignition of B ⋅ Ca(IO3)2 occurs between 600 and 700 K, before either of the components melt. Combustion is accompanied by the formation of a luminous halo above the material, suggesting a vapor-phase reaction involving boron suboxides. Longer ignition delays are observed for the pellets of Al ⋅ Ca(IO3)2 heated by the CO2 laser beam compared to similar pellets of B ⋅ Ca(IO3)2. Burn rates of B ⋅ Ca(IO3)2 pellets are nearly twice as fast as those of Al ⋅ Ca(IO3)2, primarily due to the lower ignition temperature for the boron-based thermite. The flame temperatures obtained from the time-integrated optical spectra are close to 2140 and 2060 K for Al ⋅ Ca(IO3)2 and B ⋅ Ca(IO3)2, respectively. Individual particles of B ⋅ Ca(IO3)2 injected into an air-acetylene flame burn slower than similar Al ⋅ Ca(IO3)2 particles. Based on their better stability, lower ignition temperatures, shorter ignition delays, and longer burn times leading to a more gradual release of iodine, B ⋅ Ca(IO3)2 composites are suggested to be better suited as components of energetic formulations aimed to defeat stockpiles of biological weapons.

Ignition and Combustion Characteristics of Nanoaluminum with Copper Oxide Nanoparticles of Differing Oxidation State

The importance of the oxidation state of an oxidizer and its impact on gaseous oxygen and total gas production in nanocomposite thermite combustion was investigated by probing the reaction and ignition properties of aluminum nanoparticles (Al-NPs) with both cupric oxide (CuO) and cuprous oxide (Cu2O) nanoparticles. The gas release and ignition behavior of these materials were tested with >105 K/s temperature jump (T-jump) heating pulses in a high temporal resolution time-of-flight mass spectrometer (ToF-MS) as well as in an argon environment. Reactivity was tested using a constant volume combustion cell with simultaneous pressure and optical measurements. A variety of Cu2O particle sizes ranging from 200 to 1500 nm were synthesized and found to release oxygen at ∼1200 K, which is higher than the values found for a variety of CuO particle sizes (∼1000 K). Both oxides were found to ignite around 1000 K, which implies a consistent ignition mechanism for both through a condensed phase pathway. The higher oxid...

Preparation and Properties of Boron-Based Nano-B/CuO Thermite

&lt;p&gt;We adopt &lt;a href="http://dict.cnki.net/dict_result.aspx?searchword=%e6%b2%89%e6%b7%80%e6%b3%95&amp;amp;tjType=sentence&amp;amp;style=&amp;amp;t=precipitation"&gt;precipitation&lt;/a&gt; to prepare the nanometer CuO and coat it on boron particles of micro- and nano-size. The &lt;a href="http://dict.cnki.net/dict_result.aspx?searchword=%e5%bd%a2%e8%b2%8c&amp;amp;tjType=sentence&amp;amp;style=&amp;amp;t=morphology"&gt;morphology&lt;/a&gt; and coating result of B/CuO nanocomposite thermite were characterized using different techniques, such as scanning electron microscopy, X-ray diffraction, and energy-dispersive X-ray spectroscopy. The results indicated that the boron particles were coated completely by nanocomposite CuO and well distributed. The B/CuO nanocomposite thermite reaction process was tested by thermogravimetric/differential scanning calorimetry. The obtained reaction temperature of B/CuO particles is about 116.86° lower than that of boron particles. The B/CuO thermite and boron powder were added to Mg/PTFE propellant to be measured for their respective combustion performance. The results showed that the B/CuO-Mg/PTFE propellant burning rate increased by 12.87%, mass burning rate by 13.48%, and combustion temperature increased by 56.3° compared to the B-Mg/PTFE propellant. The above results indicate that the CuO coating of boron particles increases the combustion performance of propellant compared with uncoated particles.&lt;/p&gt;