Highly Insensitive/Reactive Thermite Prepared from Cr2O3 Nanoparticles

Thermites prepared from nanoparticles are currently the subject of growing interest due to their increased performances compared to classical micrometer‐sized thermites. Here, we studied the combustion behavior of energetic composite composed of Al and chromium (III) oxide (Cr₂O₃) as function of the oxide particle size. Homogeneous composites were prepared by mixing Al nanoparticles (Φ≈50 nm) with Cr₂O₃ micro‐ and nanoparticles (Φ≈20 nm), respectively, in hexane solution. The dried Cr₂O₃/Al composite powders were ignited by using a CO₂ laser beam. The use of nanosized Cr₂O₃ particles incontestably improves the energetic performances of the Al/Cr₂O₃ thermite since the ignition delay time was shortened by a factor 3.5 (16±2 vs 54±4 ms) and the combustion rate (340±10 mm s⁻¹) was significantly accelerated in contrast to those reported until now. Interestingly, the sensitivity to friction of the Al‐based thermites formulated from Cr₂O₃ is two orders of magnitude lower than the thermite prepared from other metal oxide nanoparticles (MnO₂, WO₃). Finally, our study shows that the decrease of Cr₂O₃ particle size has an interesting and beneficial effect on the energetic properties of Cr₂O₃/Al thermites and appears as an alternative to tune the properties of these energetic materials.     

In situ TiC-reinforced austenitic steel composite by self-propagating high temperature synthesis

TiC-reinforced austenitic steel composites have been prepared by self-propagating high temperature synthesis (SHS). The in situ reinforcement of a Fe-Mn-based austenitic steel matrix with TiC was achieved upon aluminothermic reduction of iron oxide (Fe₂O₃), manganese dioxide (MnO₂) and titanium dioxide (TiO₂) powders in the presence of carbon (C). This highly exothermic thermite reaction was found to produce in situ the Fe-Mn-TiC austenitic steel composites. The reaction kinetics, recovery of Mn and TiC, yield of metal, and composite microstructure were found to strongly depend on the process parameters, such as green composition, blending sequence, and average particle size of Al powder used as a reducing agent. The text was submitted by the authors in English.     

Fabrication of WSi2–Al2O3 and W5Si3–Al2O3 composites by combustion synthesis involving thermite reduction

Formation of WSi₂–Al₂O₃ and W₅Si₃–Al₂O₃ composites was studied by thermite-based combustion synthesis. The addition of two thermite combinations composed of WO₃+2Al and 0.6WO₃+0.6SiO₂+2Al into the W-Si reaction systems facilitated the combustion wave propagating in a self-sustaining manner and contributed to the in situ formation of tungsten silicides along with Al₂O₃. Experimental results showed that the former thermite mixture is more exothermic than the latter, and a decrease in the combustion temperature and flame-front velocity with increasing silicide phase formed in the composite. Depending on the reaction stoichiometry, the combustion wave velocity varied from 9.5 to 3.7 mm/s and temperature from 1650 to 1280 °C. A complete phase conversion and a broad range of the molar ratio of WSi₂/Al₂O₃ from 0.8 to 4.0 were achieved for the production of the WSi₂–Al₂O₃ composites. Due to the lower formation exothermicity, the W₅Si₃–Al₂O₃ composites were produced with a narrower range of W₅Si₃/Al₂O₃ from 0.4 to 2.0, beyond which combustion failed to proceed. Moreover, there exist WSi₂ and unreacted W in the as-synthesized W₅Si₃–Al₂O₃ composites.     

Thermal behavior of Al/MoO3 xerogel nanocomposites

Sol–gel process using molybdenum alkoxides was employed to prepare Al/MoO₃ xerogel nanocomposites as a thermite with better performance by improvement of interfacial contact area between the oxidizer and fuel. Micromorphology and thermite reaction characteristics of Al/MoO₃ xerogel nanocomposites were analyzed by scanning electron microscopy (SEM) and thermogravimetry/differential scanning calorimetry (TG/DSC), respectively. In the present Al/MoO₃ xerogel system, it was found that exothermic enthalpy increases as the Al/Mo mole ratio increases and then decreases when Al/Mo mole ratio is larger than 6 indicating that optimum mole ratio of Al/Mo is 6 with reaction enthalpy of 420.58 J/g.     

Nanoenergetic Composites of CuO Nanorods,Nanowires, and Al‐Nanoparticles

This paper reports on the synthesis of the nanoenergetic composites containing CuO nanorods and nanowires, and Al‐nanoparticles. Nanorods and nanowires were synthesized using poly(ethylene glycol) templating method and combined with Al‐nanoparticles using ultrasonic mixing and self‐assembly methods. Poly(4‐vinylpyridine) was used for the self‐assembly of Al‐nanoparticles around the nanorods. At the optimized values of equivalence ratio, sonication time, and Al‐particle size, the combustion wave speed of 1650 m s⁻¹ was obtained for the nanorods‐based energetics. For the composite of nanowires and Al‐nanoparticles the speed was increased to 1900 m s⁻¹. The maximum combustion wave speed of 2400 m s⁻¹ was achieved for the self‐assembled composite, which is the highest known so far among the nanoenergetic materials. It is possible that in the self‐assembled composites, the interfacial contact between the oxidizer and fuel is higher and resistance to overall diffusional process is lower, thus enhancing the performance.     

Characterization of 1050Al/Al3Ni/ZrO2 hybrid surface composites fabricated by friction stir processing

Al/Al₃Ni and Al/nano-ZrO₂ mono and Al/Al₃Ni/ZrO₂ hybrid composites were produced by one- and four-pass friction stir processing (FSP). Then, the microstructure, hardness, and wear performance of the surface composites were evaluated. Results showed that the incorporation of Ni particles into the Al surface and their in situ reaction with the substrate resulted in the development of Al₃Ni particles in the stir zone. The formation mechanism of these particles was deeply studied from both thermodynamics and kinetics aspects. Similarly, the four-pass FSP led to the distribution of ZrO₂ nanoparticles and the formation of Al/ZrO₂ composites. With the addition of both Ni and ZrO₂ particles, a hybrid Al/Al₃Ni/ZrO₂ composite was produced. This caused a 60% improvement in hardness and a 35% improvement in wear resistance of Al substrate. In the case of monolithic composites, both abrasion and adhesion were responsible for the material removal during the wear test, whereas adhesion was specified as the dominant wear mechanism in the hybrid composite.     

Effects of NiO nanoparticles on the magnetic properties and diffuse phase transition of BZT/NiO composites

A new composite system, Ba(Zr_0.07Ti_0.93)O₃ (BZT93) ceramic/NiO nanoparticles, was fabricated to investigate the effect of NiO nanoparticles on the properties of these composites. M-H hysteresis loops showed an improvement in the magnetic behavior for higher NiO content samples plus modified ferroelectric properties. However, the 1 vol.% samples showed the optimum ferroelectric and ferromagnetic properties. Examination of the dielectric spectra showed that the NiO additive promoted a diffuse phase transition, and the two phase transition temperatures, as observed for BZT93, merged into a single phase transition temperature for the composite samples.     

A general strategy for the synthesis of reduced graphene oxide-based composites

Well-exfoliated graphene oxide sheets were initially fabricated through a modified pressurized oxidation method with powdered flake graphite as raw material. A variety of inorganic-reduced graphene oxide composites have been then successfully synthesized through a general solvothermal strategy with the graphene oxide sheets as supports, ethanol as solvent, and metal salts as precursors. After the solvothermal reactions, Ni(OH)₂ nanoparticles, Fe₂O₃ nanorods, W₁₈O₄₉ nanowires, ZnO nanoparticles, and Ag nanoparticles were in situ grown on the surfaces of the graphene oxide sheets, accompanied by effective reduction of graphene oxide to reduced graphene oxide. The as-prepared products have been systematically characterized by electron microscopy, X-ray diffraction, X-ray photoelectron spectrometry, and Raman spectroscopy. The present work opens up a versatile route for preparing the reduced graphene oxide-based composites.     

Highly sensitive and selective acetylene sensors based on p-n heterojunction of NiO nanoparticles on flower-like ZnO structures

Acetylene (C₂H₂) gas concentration is a key parameter in transformer monitoring. In current work, the selective acetylene sensors which based on flower-like ZnO structures with NiO nanoparticles were successfully fabricated. The NiO–ZnO composites were synthesized by two-step hydrothermal method. And various of characterization analyses had been applied to the exploration of crystal structure and the p-n heterojunction. According to the systematic gas sensitivity tests, the response of NiO–ZnO (5%) to 50 ppm C₂H₂ was 15.23 at 200 °C whereas the response of pure ZnO was 4.1 in the same condition. In addition, the response value of NiO–ZnO (5%) to 50 ppm C₂H₂ was 3.6 times to 50 ppm H₂. Such a good gas-sensing property of NiO–ZnO composites is due to p-n heterojunction and high catalytic activity of NiO.     

High‐Energy Pollen‐Like Porous Fe2O3/Al Thermite: Synthesis and Properties

A pollen‐like porous Fe₂O₃/Al thermite was prepared by a templated method, with aluminium nanoparticles (Al‐NPs) embedded in the porous channels. The thermite prepared by reduced pressure released the largest exothermic heat during DSC testing period compared with Fe₂O₃/Al thermites prepared by ultrasonic mixing and physical mixing. The exothermic heats in the range of 773 K to 1273 K are 3742.3 J g⁻¹, 2279.0 J g⁻¹, 1981.1 J g⁻¹, and 2621.0 J g⁻¹ for pollen‐like Fe₂O₃/Al by reduced pressure, pollen‐like Fe₂O₃/Al by ultrasonic mixing, pollen‐like Fe₂O₃/Al by physical mixing, and commercial Fe₂O₃/Al by ultrasonic mixing, respectively. The reactivity between Fe₂O₃ and Al‐NPs was efficiently improved, corresponding to its enlarged contact surface area between Al‐NPs and the porous pollen‐like Fe₂O₃, and the reduced pre‐combustion sintering. Furthermore, pollen‐like Fe₂O₃/Al has good compatibility with both RDX and HMX and it is not compatible with Cl‐20 and GAP.     

Titanium carbide by the SHS process ignited with aluminothermic reaction

We explored the ignition of Ti + C → TiC reaction with another highly exothermic thermite reaction, Fe₂O₃ + 2Al → 2Fe + Al₂O₃, used as a match. In order to decrease the combustion temperature and thus to avoid explosion mode, we studied the effect of alumina diluent on the thermite reaction. In order to ensure the stability of front propagation, we also tested the reactions involving enriched and non-enriched iron ores. The evolution of phase composition, grain size, and density of products during SHS reaction was determined by XRD and IR filming.      

Radial Combustion Propagation in Iron(III) Oxide/Aluminum Thermite Mixtures

The self‐sustained thermite reaction between iron oxide (Fe₂O₃) and aluminum is a classical source of energy. In this work the radial combustion propagation on thin circular samples of stoichiometric and over aluminized Fe₂O₃/Al thermite mixtures is studied. The radial geometry allows an easy detection of sample heterogeneities and the observation of the combustion behavior in their vicinity. The influence of factors like reactant mixtures stoichiometry, samples green density and system geometry on the rate of propagation of the combustion front is analyzed. The radial combustion front profiles are registered by digital video‐crono‐photography. Combustion thermograms are obtained for two sample radii. Theoretical calculations, based on the impurity levels reported by the reactants manufacturers and on the thermite reaction stoichiometry, were used to define the stoichiometric mixture with unitary equivalence ratio (E. R.). However, it was found from the experimental results that the excess of aluminum only starts for E. R. values between 1.12 and 1.27. This was explained by the further oxidation of aluminum during storage and/or by the reaction incompleteness. In the range studied, the combustion rates of the thermite mixtures did not show any significant dependence on the green density. Combustion rates obtained in this work were slightly higher than those obtained in an earlier work for long square channel geometry. A considerable dispersion of temperature values was observed and attributed to thermocouples sensitivity to micro‐scale variations.     

Self-assembly Ag2O nanoparticles into nanowires with the aid of amino-functionalized silica nanoparticles

This paper describes a novel self-assembly behavior of Ag₂O nanoparticles to Ag₂O nanowires. In the alkaline water-alcohol solution, Ag⁺ ions reacted with OH⁻ ions on silica nanoparticles functionalized by N-(2-aminoethyl)-3-aminopropyl-trimethoxy-silane (AEAPTS) to form Ag₂O nanoparticles. The Ag₂O nanoparticles further self-assembled into Ag₂O nanowires. The morphology of Ag₂O nanowires could be controlled by adjusting Ag/Si molar ratios in the systems. With low Ag/Si molar ratio, uniform Ag₂O nanowires were obtained with diameter of about 50 nm and length of tens micrometers. With the increase of Ag/Si molar ratio, Ag₂O nanowires became thicker, shorter and irregular. It was shown by high-resolution transmission electron microscopy (HRTEM) that all Ag₂O nanowires consisted of tiny Ag₂O nanoparticles with diameter of 10-20 nm. The self-assembly of Ag₂O nanoparticles into Ag₂O nanowires was observed by transmission electron microscopy (TEM) and the corresponding growth mechanism was proposed.     

Electromagnetic shielding and thermal conductive properties of SiC nanowires reinforced C/(PyC-SiC)n composites

SiC was introduced as nanowires and multilayered structure matrix to modify C/C composites, then SiC nanowires reinforced C/(PyC-SiC)_n (SM-CS) composites were prepared. The electromagnetic shielding and thermal conductive properties were investigated and the further relationship between these properties and the number of cycles of preparation (N) was also studied. The results showed that total shielding effectiveness (SET) values of modified composites were all higher than 30 dB which meant more than 99.9% electromagnetic wave was shielded. And the SET values increased with the rising of N (SM-CS4--47.6 dB > SM-CS3--42.7 dB > SM-CS2--37.1 dB). With the rising of N, not only the conductivity of SM-CSN composite increased, but also the interfaces inside the matrix increased, leading to a continuous increase in reflection and absorption of electromagnetic waves. Meanwhile, the thermal diffusivities and conductivities of the SM-CS composites in the temperature range from 25 to 1500 °C were all higher than those of pure C/C composites, and they were also almost increased by N. That was because the improvement of SiC nanowires in heat transport was very large, and even exceeded the reducing of multilayered structure. Due to these good functional properties, the modified composites would exhibit excellent potential in aerospace field.     

SnO2–polyaniline composites for the desensitization of Al/SnO2 thermite composites

Nanothermites consisting of a reducing metal and a metal oxide nanopowder represent a new generation of energetic materials in pyrotechnics due to their impressive reactive properties. However, their extreme sensitivity regarding electrostatic discharge appears to be detrimental to their future practical applications. Herein, the mitigation of the sensitivity thresholds of the aluminium/tin (IV) oxide energetic nanocomposite is successfully achieved by using a conducting polymer, polyaniline (PAni). PAni was introduced within the thermite by the chemical polymerization of an oxidizer/PAni hybrid matrix. The SnO₂–PAni composites were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric analysis, electrical conductivity measurements, and transmission electron microscopy. The derived Al/SnO₂–PAni thermites were investigated in terms of sensitivities and reactivity. Results revealed gradual desensitization of the Al/SnO₂ thermite as a function of the concentration of PAni for both the electrostatic discharge (0.14–1212 mJ) and friction (216–360 N) tests while maintaining reactive energetic composites. This work presents a way for the preparation of insensitive and reactive energetic formulations. © 2020 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48947.     

Nanoenergetic Gas‐Generators: Design and Performance

Nanoenergetic gas‐generator (NGG) mixtures may have various potential military applications from aircraft fuels to rocket propellants, explosives, and primers. To find reactions generating the highest pressure peak, we studied eight nanoenergetic reactions. The Al/Bi₂O₃ reaction generated the highest pressure pulse among the eight thermite reactions. We developed a highly efficient, one step process for synthesis of Bi₂O₃ nanostructured particles. Its use generated about a three times higher peak pressure (∼10 MPa) than when using commercial bismuth oxide nanoparticles (3 MPa). The pressure in the vessel rose very rapidly to a peak value for a duration of ∼0.02 ms and ΔP/Δt of up to 500 GPa s⁻¹. Increasing the crystallinity of the bismuth oxide nanoparticles increased the peak gas pressure by 25%. The maximum pressure×volume (PV) value obtained at m=0.1 g with our synthesized Bi₂O₃ was 707 Pa m³ much higher than that reported in the literature (33 Pa m³) for the same sample mass. Addition of carbon to the reactant mixtures did not increase the peak pressure. Addition of up to 3 wt.‐% of boron to the thermite systems increased the peak pressure by ∼50%.     

Structural evolution of hierarchical porous NiO/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> composites and their application for removal of dyes by adsorption

Hierarchical porous NiO/Al₂O₃ composites were successfully prepared by two-steps. First, the core-shell structured Al₂O₃ microspheres were prepared via a template-free hydrothermal route using KAl(SO₄)₂·12H₂O and Al₂(SO₄)₃·18H₂O as aluminum source. Then, the NiO/Al₂O₃ composites with micro- and nano-hierarchical structures were prepared by a hydrothermal method combining the subsequent calcination process. The obtained characterization result presented that the morphology of hierarchical Al₂O₃ microsphere tuned to irregular platelets by simply varying Ni/Al ratios. The BET analysis showed that the special surface area from 52.12m² g^?1 to 214.8m² g^?1 after two hydrothermal complex process. Effects of Ni/Al ratio, adsorbent dosage, Congo red (CR) concentration, coexisting ions, adsorption time and temperature were investigated. The obtained results indicated that NiO/Al₂O₃ composite had the high adsorption efficiency (99.6%) and great adsorption capacity (186.9mg g^?1) under the optimum conditions. The adsorption isotherm and kinetics data were found to be well fitted and in good agreement with the Langmuir isotherm model and pseudo-second order model, respectively. The hierarchical porous NiO/Al₂O₃ composites presented remarkably higher adsorption efficiency during five recycling, which showed their potential as the highly efficient adsorbent for removal of CR in wastewater.     

Study on combustion characteristics and pyrotechnic cutting effects of bimetal thermite Ni/Al/Fe2O3 system

Nano-thermite has become a subject of significant interest in the composite energetic materials field due to its high energy release rate. To cater to diverse engineering needs, thermite formulations are often customized to fulfill specific criteria. This study investigates the potential of metal nickel (Ni) as an additive to modify nano-thermite formulations, selected for its optimal calorific values and chemical reactivity. The base materials, nano-aluminum (Al) and iron oxide (Fe₂O₃), are blended with varying mass ratios of Ni (1 %, 3 %, 5 %, 7 %, 9 %) using the wet ball milling method. Pre-reaction and post-reaction morphological and compositional alterations in the resultant thermite samples are scrutinized through SEM and XRD characterization tests. Moreover, DSC analysis and combustion experiments were conducted to examine the pyrolysis and combustion behaviors of the evaluated samples. The results reveal a reduced exothermic peak on the DSC curves with the introduction of Ni, making the liquid-solid (L-S) phase reaction more challenging compared to the Al/Fe₂O₃ thermite. Intriguingly, Ni addition progressively decreases the combustion temperature of thermites as the Ni's mass ratio increases, with a peak efficiency at 7 % in the perforation tests on stainless-steel plates. This research further reveals that the thermite reaction mechanism is a combined consequence of the “pre-ignition-fusion” and “fusion-diffusion” mechanisms. These insights can provide valuable guidance for designing thermite formulations for potential applications in storage, management, and pyrotechnic cutting areas.     

Synthesis of spherical NiO nanoparticles using a solvothermal treatment with acetone solvent

Nanometer-sized nickel oxide (NiO) particles were synthesized by thermal reactions with nickel (II) carbonate as a metal-containing precursor and four solvents: water, ethanol, butanol, and acetone. The optimal reaction conditions to obtain spherical NiO were determined to be the acetone solvent, nickel carbonate precursor, and a reaction temperature and time of 200 °C and 48 h, respectively. TEM images revealed perfectly spherical NiO nanoparticles of size ranging from 2.0 to 10.0 nm in the acetone solvent. The reaction mechanism for the formation of the NiO nanoparticles is proposed based on a pathway of chelated Ni complex during crystal growth. Although metallic Ni was also formed from reactions using the two alcoholic solvents, the Ni(OH)₂ structure remained in the water solvent after thermal treatment.     

Preparation and characterization of NiO/MgO/Al2O3 supported CoPcS catalyst and its application to mercaptan oxidation

MgO/Al₂O₃ and NiO/MgO/Al₂O₃ solid bases were prepared by mixing method. The samples were characterized by X-ray diffraction (XRD), CO₂ temperature-programmed desorption (CO₂-TPD) and surface area measurements. After supported sulfonated cobalt phthalocyanine (CoPcS) the catalytic performance of these catalysts was evaluated in the mercaptan oxidation reaction. The effect of Mg/Al mole ratios on activity, crystal structure, basicity and stability in air was discussed. And the mechanism of the effect of NiO was identified. Results show that the base amount of MgO/Al₂O₃ increases with increasing Mg/Al mole ratio and catalyst with high Mg/Al mole ratio has a higher initial activity. NiO/MgO/Al₂O₃–CoPcS shows a higher initial activity and a much longer lifetime than MgO/Al₂O₃–CoPcS. When nickel oxide is doped into the MgO/Al₂O₃ support more crystal defects are generated, which increases the amount and types of basic sites.