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.     

Role of Oxalic Acid in Promoting Ignition and Combustion of Boron: an Experimental and Theoretical Study

Boron is an attractive fuel for propellants and explosives because of its high energy density. However, its combustion is inhibited by the oxide layer that covers the particles. The use of oxalic acid as an additive was shown to promote boron oxidation. In this study, the thermodynamic model FactSage 6.2 and a laser ignition facility were used to investigate the effect of oxalic acid on the burning characteristics of boron particles. The results of the thermodynamic analyses show that oxalic acid can reduce B₂O₃(l) production during boron combustion. This enables removal of the the oxide film and promotes the burning of boron. However, only at high temperatures (>1500 K) H₂O(g) (produced from H₂C₂O₄) can react with B₂O₃ and remove the oxide film. The evolution of boron combustion flame takes place in three stages: ignition, stable combustion, and extinction; the bright yellow color in the flame indicates boron ignition, the bright white color indicates boron combustion, and the bright green color is interpreted as BO₂ emission. Addition of oxalic acid into boron powders can significantly promote boron ignition and combustion. The ignition delay time of the resulting mixture is reduced by 42.4 %, the combustion intensity is raised by 16.7 %, and the combustion efficiency of boron is increased by 21.5 percentage points. The mechanism of action of oxalic acid on enhancing the combustion of boron was studied by scanning electron microscopy.     

Kinetic model of single boron particle ignition based upon both oxygen and (BO) n diffusion mechanism

A comprehensive ignition model for single boron particles in an oxygenated environment containing O₂ and H₂O is developed. Microcharacteristics of the boron oxide layer on the surface of boron particles at elevated temperatures are studied. Two typical distributions of species inside the surface oxide layer are detected. One is composed of three layers [B₂O₃, (BO) _n , and B₂O₃], while the other is composed of two layers [(BO) _n and B₂O₃], both according to the order from the internal to external side of the layer. In the model development, two submodels, submodel I and submodel II, are developed with regard to two different observed species distributions in the surface oxide layer. For submodel I, it is assumed that both (BO) _n and O₂ are the governing species diffusing into the liquid oxide layer. For submodel II, only (BO) _n is the governing species. These two submodels are combined into a new bi-directional model consisting of four key kinetic processes: evaporation of the liquid oxide layer, global surface reaction between oxygen from the environment and boron, reaction between the inner boron core and oxygen, and global reaction of boron with water vapor. The ignition time predicted by the model is in good agreement with previous experimental data.     

Calorimetric study of the thermodynamic properties of Mn5O8

Manganese oxides occur widely in nature and have technical applications in various areas. This study quantitatively evaluates the thermodynamic properties of Mn₅O₈, a binary manganese oxide that has a layered structure and contains coexisting divalent and tetravalent manganese. Three samples of the Mn₅O₈ phase with slightly different manganese average oxidation states (Mn AOS) were synthesized using a wet chemical method and annealing. Synchrotron X-ray analysis revealed that the samples contain a small amount of a secondary MnO₂ phase that cannot be identified using laboratory X-ray diffraction. High-temperature oxide melt solution calorimetry in molten sodium molybdate at 700°C showed that all three samples are slightly higher in enthalpy than an isochemical mixture of bixbyite (Mn₂O₃) and pyrolusite (MnO₂), probably rendering them metastable in free energy with respect to isochemical mixtures of bixbyite and pyrolusite. However, the energetic metastability (endothermic enthalpy) of Mn₅O₈ is very small (<6 kJ/mol) and does not depend significantly on the Mn AOS. Thus, although Mn₅O₈ probably does not appear on the equilibrium Mn-O phase diagram, its small metastability allows its synthesis by a variety of low temperature reactions.     

N2O Decomposition Catalysed by Transition Metal Ions

The ignition processes for the catalytic partial oxidation of methane (POM) to synthesis gas over oxidic nickel catalyst (NiO/Al₂O₃), reduced nickel catalyst (Ni⁰/Al₂O₃), and Pt-promoted oxidic nickel catalyst (Pt–NiO/Al₂O₃) were studied by the temperature-programmed surface reaction (TPSR) technique. The complete oxidation of methane usually took place on the NiO catalyst during the CH₄/O₂ reaction, even with a pre-reduced nickel catalyst, and Ni⁰ is inevitably first oxidized to NiO if the temperature is below the ignition temperature. It is above a certain temperature that Ni⁰ is formed again, which leads to the start of the POM. The POM can be initiated at a much lower temperature on a Pt–NiO catalyst because of Pt promotion of the reduction of NiO. The POM in a fluidized bed can be easily initiated due to the addition of Pt.     

Behavior of impurity metals in the fusion of magmatic rocks with a mixture of sodium carbonate and calcium oxide

The method of physicochemical simulation is used to calculate the equilibrium compositions of SiO₂-Al₂O₃-(TiO₂)-CaO-MgO-Fe₂O₃-(MnO)-Na₂O-(Cr₂O₃)-(V₂O₅) systems in the temperature range of 1273–1473 K at various ratios of (Na₂CO₃ + CaO): rock. It is shown that the impurity metals are present in fusion products in the form of calcium polytitanate (Ca₃Ti₂O₇), manganese(II, III) oxide (Mn₃O₄), chromium(III) oxide (Cr₂O₃), and calcium orthovanadate (Ca₃V₂O₈).     

Factors affecting coal particle ignition under oxyfuel combustion atmospheres

A set of 13 coals of different rank has been tested for ignition propensity in a 20-L explosion chamber simulating oxyfuel combustion gas conditions. Their char residues were also analysed thermogravimetrically. The effects of coal type, coal concentration (from 100 to 600 g/m³), O₂ in CO₂ atmospheres (up to 40% v/v) and particle size were investigated.The higher rank coals were significantly more difficult to ignite and mostly required higher energy chemical igniters (1000 or 2500 J) whereas the lower rank coals could be ignited with a 500 J igniter even at low coal dust concentrations.The minimum explosibility limit/ignition concentration in air varied slightly around a value of 200 g/m³, a little higher for low volatile coals and a little lower for high volatile coals.The ignition limit changed significantly, however, with O₂ concentration in CO₂, where coals required more oxygen to ignite. Most coals failed to ignite at all in 21% v/v O₂ in CO₂, but an increase to 30 or 35% v/v O₂ gave ignition patterns similar to those in air. In addition, the minimum ignition concentration decreased with increase in O₂. However, a further increase to 40% v/v O₂ did not generally affect the minimum ignition concentration.Particle size had a non-linear effect on coal ignition. The fine particles (<53 μm) behaved almost identical to the whole coal. However, the larger size fraction (>53 μm) was generally more difficult to ignite and exhibited a much lower weight loss.     

Nitrogen-doped reduced graphene oxide/Fe2O3 hybrid as efficient catalyst for ammonium nitrate

In this investigation, we successfully synthesized a hybrid material, N-rGO@Fe₂O₃, via a one-step hydrothermal process, comprising nitrogen-doped reduced graphene oxide and α-Fe₂O₃. Thorough characterization using diverse analytical methods validated its structure. Employing this hybrid composite as a catalyst, we studied its efficacy in the catalytic thermal decomposition of ammonium nitrate (AN). The N-rGO@Fe₂O₃/AN composite was prepared using a recurrent spray coating method with 3 % mass of the hybrid material. Thermo-gravimetric (TG) and differential scanning calorimetric (DSC) analyses were employed to investigate the catalytic effect. Computational assessment of Arrhenius parameters was conducted through isoconversional kinetic approaches. Results from the kinetic analysis allowed the determination of the critical ignition temperature. Furthermore, calorific values for pure AN and N-rGO@Fe₂O₃/AN were measured using an oxygen calorimetric bombe, revealing a 41 % reduction in activation energy barrier and a lowering of the critical ignition temperature from 292 °C to 283 °C upon incorporation of the hybrid material. Notably, the surface modification of AN with N-rGO@Fe₂O₃ resulted in an increase of 1440 J/g in the observed calorific values. These findings highlight the potential of N-rGO@Fe₂O₃ as an effective catalyst, offering promising implications for applications in enhancing ammonium nitrate thermal decomposition.     

On the Comparison of Small Nitrogen and Phosphorus Oxide Cages

Ab initio electronic structure calculations, including a natural bond orbital (NBO) analysis, are employed to compare the stabilities of larger nitrogen oxide cages and phosphorus oxide cages relative to the cage compound c‐N₂O₃ , which has been previously investigated as a potential energetic oxidizer. The larger N O cages, c‐N₂O₆ and c‐N₄O₆ exhibit less internal strain but have significantly lower barriers to decomposition of 1.9 kJ mol⁻¹ and 5.6 kJ mol⁻¹ respectively, compared to 37.6 kJ mol⁻¹ for c‐N₂O₃, at the MP2/aug‐cc‐pVDZ level of theory. In contrast, the phosphorus oxide cage c‐P₂O₃ exhibits similar internal strain but has a significantly larger barrier to decomposition of 40.2 kJ mol⁻¹ compared to the 24.4 kJ mol⁻¹ of c‐N₂O₃ at CCSD(T)/CBS(Q‐5). Furthermore, NBO analysis shows that the P O bond is more ionic in nature compared to the N O bond. The reduced degree of ionic character leads to the kinetic instability of the nitrogen oxide cages and therefore renders them impractical as energetic oxidizers.     

Surface modification of sintered magnesium oxide (MgO) with chromium oxide (Cr2O3) by pulsed laser irradiation in air and liquids

Surface modification of ceramic materials by laser irradiation is widely used as a non-contact, fast and thermally activated process to generate micro and nanostructures. The effects of liquids while surface modification by laser irradiation of ceramic materials under liquid environment are least explored so far. This study reports the effects of pulsed laser irradiation in air and liquids on the microstructure and morphologies of ceramic materials. Chromium oxide (Cr₂O₃) was mixed in different concentrations (3, 5 and 7% in weight) into magnesium oxide (MgO) matrix and was sintered at 1650 °C. The structure and morphology of the sintered ceramic pellets were characterized using X-ray diffraction and scanning electron microscopy. Presence of the spinel magnesium chromium oxide (MgCr₂O₄) was identified in these samples. For surface modification of these samples, laser irradiation is carried out in air and liquids (methanol, isopropyl alcohol and acetone) using 2 ns pulsed lasers (532 nm) of different pulse repetition rates and energies. The microstructure and morphologies of the samples after irradiation was analyzed and their crystalline structure and composition were maintained after laser irradiation. It was observed that the surface morphologies of the ceramic pellets were modified by laser irradiation as a combined effect of the medium (air/liquids), energy fluence and the concentration of the Cr₂O₃ in MgO. Our results show that pulsed laser irradiation especially in liquids is an effective technique for modifying surface morphology of ceramic materials.     

Activation of Chain Processes in Combustible Mixtures by Laser Excitation of Molecular Vibrations of Reactants

The combustion kinetics of H₂-air mixtures containing small amounts (<1%) of ozone is analyzed for the case of excitation of asymmetric vibrations of O₃ molecules by CO₂ laser radiation with a wavelength of ≈ 9.7 µm. It is shown that the irradiation leads to acceleration of the collisional dissociation of O₃ molecules, activation of the chain ignition mechanism, and a decrease in the induction period and ignition temperature. The excitation of asymmetric vibrations of O₃ molecules by the CO₂ laser radiation is 10–10³ times more effective than the currently used method of combustion initiation based on local heating of a medium by IR radiation.__________Translated from Fizika Goreniya i Vzryva, Vol. 41, No. 4, pp. 29–38, July–August, 2005.     

Study on the Compatibility of Tetraethylammonium Decahydrodecaborate (BHN) with some Energetic Components and Inert Materials

The compatibility of tetraethylammonium decahydrodecaborate (BHN) with some energetic components and inert materials of solid propellants was studied by DSC method, where glycidyl azide polymer (GAP), cyclotrimethylenetrinitramine (RDX), cyclotetramethylenetetranitroamine (HMX), lead 3‐nitro‐1,2,4‐triazol‐5‐onate (NTO‐Pb), hexanitrohexaazaisowurtzitane (CL‐20), 3,4‐dinitrofurzanfuroxan (DNTF), N‐guanylurea‐dinitramide (GUDN), aluminum powder (Al, particle size=12.18 μm) and magnesium powder (Mg, particle size: 44–74 μm) were used as energetic components and polyoxytetramethylene‐co‐oxyethylene (PET), polyethylene glycol (PEG), addition product of hexamethylene diisocyanate and water (N‐100), hydroxyl terminated polybutadiene (HTPB), cupric adipate (AD‐Cu), cupric 2,4‐dihydroxy‐benzoate (β‐Cu), lead phthalate (ϕ‐Pb), carbon black (C. B.), aluminum oxide (Al₂O₃), 1,3‐dimethyl‐1,3‐diphenyl urea (C₂), di‐2‐ethylhexyl sebacate (DOS) and potassium perchlorate (KP), were used as inert materials. It was concluded that the binary systems of BHN with NTO‐Pb, CL‐20, aluminum powder, magnesium powder, PET, PEG, N‐100, AD‐Cu, β‐Cu, ϕ‐Pb, C. B., Al₂O₃, C₂, DOS, and KP are compatible, and systems of BHN with GAP and HMX are slightly sensitive, and with RDX, DNTF, and GUDN are incompatible. The impact and friction sensitivity data of BHN and BHN in combination with the energetic materials under present study were obtained, and there was no consequential affiliation between sensitivity and compatibility.     

Phase equilibria during crystallization of melts in the uranium oxide-iron oxide system in air

The uranium oxide-iron oxide system is investigated. It is revealed that, upon both quenching and slow cooling of samples after their melting in air, the solid phase contains five crystalline phases, such as the oxide of quadruply charged uranium UO₂, the mixed oxide UO_2.66(U₃O₈), hematite FeO_1.5(Fe₂O₃ ), magnetite Fe_1.33(Fe₃O₄), and the binary compound Fe²⁺U⁶⁺O₄.     

Oxide ion/electronic polarizability,optical basicity and linear dielectric susceptibility of TeO2 – B2O3 – SiO2 glasses

A system of bio-silica borotellurite glasses was fabricated based on the chemical formula [(TeO₂)_0.7 (B₂O₃)_0.3]_1-x (SiO₂)_x with x = 0.1, 0.2, 0.3, and 0.4 using the melt-quenching technique using silica (98.548% SiO₂, from rice husk), TeO₂ (Alfar Aeser, 99.9%) and B₂O₃ (Alfar Aeser, 99.9%). Measurements and characterizations such as density and molar volume measurements, XRD analysis, FTIR, and UV–Vis spectroscopes were performed on the studied glasses. The objective was to determine the glasses’ applicability in optoelectronics, non-linear optics, and laser technologies through polarizability, linear electric susceptibility, and optical basicity study. Apart from confirming the amorphous nature of the glasses, the XRD analysis identified the presence of a crystalline phase of tellurium oxide (α-TeO₂) formed. The FTIR spectral study revealed the presence of TeO₃, BO₃, and SiO₄ structural units in the studied glasses. The refractive index (2.3026 – 2.2651), molar polarizability (8.0696 – 9.4334 Å³), oxide ion polarizability (3.2970 – 3.6202 Å³), electronic polarizability (0.2296 – 0.2335 Å³), dielectric constant (5.1307 – 5.3019), optical basicity (0.6719 – 0.7998), metallization criterion (0.410853 – 0.420714) and electric susceptibility (0.3286 – 0.3422 esu) of the glasses were presented. With the high refractive index and favourable electronic/oxide ion polarizability as well as good electric susceptibility, the glasses have shown great potential for optical fibre and laser applications. Metallization criterion value falls in the range of glasses with great potentials for non-linear optical application. The dielectric value suggests the glasses represent wideband semiconducting glasses believed to be good for application in microelectronic substrates fabrication.     

Zirconia nanopowder synthesis via detonation of trinitrotoluene

Zirconium (IV) oxide nanopowder was successfully synthesized through the detonation of a mixture composed of 2,4,6 trinitrotoluene (TNT, C₇H₅N₃O₆) and zirconium sulfate tetrahydrate (Zr(SO₄)₂·4H₂O) as the energetic material and ceramic precursor, respectively. TNT, one of the most popular explosives, is a secondary energetic molecule and exhibits high stability and low sensitivity toward external stresses, making its handling safe. After detonation of the energetic material/ceramic precursor mixture and purification of the detonation soot, a crystallized zirconium oxide (ZrO₂) powder composed of nanosized particles with a spherical morphology was produced and analysed by the usual characterization techniques (X-ray diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy and nitrogen physisorption). The reaction mechanism, considering the thermochemical aspect of the explosive, is offered. This approach could provide promising opportunities for the synthesis of various nano-sized oxide ceramic powders.     

Study of Ignition of High-Energy Materials with Boron and Aluminum and Titanium Diborides

This paper describes the ignition of high-energy materials (HEMs) on the basis of ammonium perchlorate and ammonium nitrate and an energetic binder, containing the powders of Al (base composition), B, AlB₂, AlB₁₂, and TiB₂, upon initiation of the process by a CO2 laser in the heat flux density range of 90–200 W/cm². The ignition delay time and surface temperature of the reaction layer during the heating and ignition of HEMs in air are determined. It is obtained that the complete replacement of a micron-sized aluminum powder by amorphous boron in the composition of HEMs significantly reduces the ignition delay time of the sample (by 2.2–2.8 times) with the same heat flux density, and this occurs due to the high chemical activity of and difference between the mechanisms of oxidation of boron particles. The use of aluminum diboride in HEMs reduces the ignition delay time by 1.7–2.2 times in comparison with the base composition. The ignition delay time of the HEM sample with titanium diboride decreases slightly (by 10–25%) relative to the ignition delay time of the base composition.     

The effect of mannitol and pH of the solution on the properties of sintered magnesium oxide obtained from sea water

In order to reduce the B₂O₃ content in sintered magnesium oxide as much as possible, in precipitation with 80% of the stoichiometric quantity of dolomite lime, the effect of the pH of the agent used for rinsing the magnesium hydroxide precipitate was examined, as well as the effect of mannitol in sea water before precipitation. Mannitol binds orthoboric acid present in sea water into a weakly dissociated complex acid HB(OC)₄. Experiments have shown that the B₂O₃ content in the sintered magnesium oxide samples is satisfactorily low. The lowest B₂O₃ content is obtained when mannitol is added; no B₂O₃ was found in these samples after sintering. Magnesium oxide samples were sintered at 1500°C; duration of isothemal sintering was one hour. Values for density and porosity of individually sintered samples are listed. The ratio CaO/SiO₂ indicates that forsterite (Mg₂SiO₄), monticellite (CaMgSiO₄) and mervinite (Ca₃MgSi₂O₈) are formed during sintering of the samples.     

Laser Ignition of DAAF,DHT and DAATO3.5

CO₂ laser ignition experimental results are reported for the high‐nitrogen materials 3,6‐dihydrazino‐1,2,4,5‐tetrazine (DHT), 3,3′‐diamino‐4,4′‐azoxyfurazan (DAAF), and mixed N‐oxides of 3,3′‐azo‐bis(6‐amino‐1,2,4,5‐tetrazine) (DAATO_3.5, where the “3.5” indicates the average oxide content) at a maximum irradiance level of approximately 140 W/cm². Diagnostics include a photodiode, indium antimonide (InSb) IR detector, high speed (HS) video and a CO₂ photodetector. “First light” is measured for DAATO_3.5 and DAAF, however, due to the low visible light emission of the gas phase, thermal runaway, as measured by the InSb, is used as the ignition criterion for DHT. Ignition in the gas phase is captured by the high speed camera. It is observed that an increase in laser irradiance results in an increase in ignition and flame stand‐off distance for DAATO_3.5. The high‐nitrogen material laser ignition results are compared to the common nitramine explosive, octahydro‐1,3,5,7‐tetranitro‐1,3,5,7‐tetrazocine (HMX). Laser ignition delays for the different high‐nitrogen materials are also compared in the context of Differential Scanning Calorimetry (DSC) data. It is determined that DSC onset temperature, while a rough indicator of ignition delay trends, is not the equivalent of a direct measure of ignition temperature.     

Assessment of Physico‐Thermal Properties,Combustion Performance,and Ignition Delay Time of Dimethyl Amino Ethanol as a Novel Liquid Fuel

Dimethyl amino ethanol (DMAE) contains both hydroxyl and amino functional groups, which may be introduced as a new liquid fuel with high safety and less toxicity with respect to common high performance liquid fuels. Physico‐thermal properties, combustion performance and ignition delay time of DMAE are compared with the usual high performance liquid fuels as well as ethanol and dimethylamine. Combustion performances of DMAE (specific impulse at sea level) with common liquid oxidizers including white fuming nitric acid (WFNA), inhibited red fuming nitric acid (IRFNA), nitrogen tetroxide (N₂O₄), hydrogen peroxide (H₂O₂), liquid oxygen (LOX), and the mixed oxides of nitrogen (MON) are also evaluated. Maximum and minimum specific impulses of DMAE are obtained with LOX (299.6 s) and WFNA (262.4 s), respectively. Maximum density‐specific impulse is obtained with DMAE‐N₂O₄ bipropellant. The ignition delay time of DMAE with several liquid oxidizers are measured with open cup test method. DMAE‐WFNA and DMAE‐IRFNA bipropellants are hypergolic where their ignition delay times are 26 and 42 milliseconds, respectively.     

Combustion Behavior of Highly Energetic Thermites: Nano versus Micron Composites

Combustion behavior of energetic composite materials was experimentally examined for the purpose of evaluating the unique properties of nano‐scale compared with traditional micron‐scale particulate media. Behavior of composite systems composed of aluminum (Al) and molybdenum trioxide (MoO₃) were studied as a function of Al particle size, equivalence ratio and bulk density. Samples were prepared by mechanically mixing individual fuel and oxidizer particles and combustion experiments included measurements of ignition and flame propagation behavior. Ignition was achieved using a 50‐W CO₂ laser and combustion velocities were measured from photographic data. Reaction kinetics were studied with differential scanning calorimetry (DSC). Results indicate that the incorporation of nano‐Al particles (1) significantly reduces ignition temperatures and (2) produces unique reaction behavior that can be attributed to a different chemical kinetic mechanism than observed with micron‐Al particles.