Search Results (12)

Thermite mixtures are attractive for downhole well plug-and-abandonment (P&A) sealing, where a consistent, controllable burn matters more than peak energy. Because propagation is governed by particle size and packing, predictive blend design needs a model that resolves microstructure. I present a zero-tuning multiscale framework that links a discrete element method (DEM) packing directly to combustion-front behaviour. The DEM contact graph sets a contact-resistance effective conductivity (a thermal-network solve on the contacts, cross-checked against a packed-bed model); the particle sizes set a diffusion-limited, product-layer (shrinking-core) reaction rate with the measured activation energy of the Al-Fe₂ O₃ reaction (Eₐ = 145 kJ mol⁻¹); and these feed an analytical condensed-phase travelling-wave speed that is mesh-free by construction and confirmed against a converged numerical eigenvalue solve. Here “zero-tuning” means no coefficient is fitted to the blend dataset: every transport and kinetic parameter is DEM-derived or taken from the literature, and a single diffusion pre-factor is anchored to an independent fine-powder benchmark. Applied to a generic Fe₂ O₃/Al+ sand system across eight coarse (∼256–462 µm) +40/+70 blends, the framework predicts front speeds of ∼2–4 mm/s—about an order of magnitude below fine powders (27–47 mm/s)—i.e., finer-is-faster, as expected for diffusion-controlled aluminothermic reactions; the residual size dependence is the net of competing diffusion-kinetic and radiative effects rather than a clean monotonic lever. A DEM-derived Kozeny–Carman permeability shows gas convection contributes ≲15% of the front enthalpy, justifying the conduction–radiation formulation. The DEM-microstructure-to-rate mapping is validated externally on Ni–Al self-propagating high-temperature synthesis (SHS), whose measured particle-size ordering it reproduces. The contribution is the framework itself—a predictive, microstructure-resolved route requiring no blend-specific fitting. The computational implementation used a supervised AI-agent workflow (implementation, execution, verification); all scientific content was conceived and verified by the author. Full article

Increasing the serviceability of industrial components intended for the petrochemical industry is possible through their superficial saturation with silicon (silicon cementation). Obtaining a silicon-rich surface coating results in a considerable increase in corrosion resistance, refractoriness, and wear resistance. One of the most economically convenient options for silicon cementation is pack siliconizing in powdery solid media. This paper presents the possibility of pack siliconizing that contains ferrosilicon (FeSi75C) and a thermite mixture (SiO₂ + Al) as active, silicon-providing components, in P265GH grade steel, which is frequently used in the petrochemical industry. The aim of the study was to determine the most suitable active component of the two that were analyzed and at the same time identify the processing conditions in which the siliconized coating has the greatest thickness, is free of porosity, and is in direct contact with the support. The use of experimental programming methods allowed the optimization of the operation to obtain the optimal solution. It was concluded that the thermite mixture is not compatible with pack siliconizing because it results in a superficial saturation predominantly composed of aluminum. When ferrosilicon is used as the active component, it determines the particularly intense formation kinetics of the non-porous siliconized coating with its maximum thickness being reached at high processing temperature values (over 1100 °C) with a proportion of 60% FeSi75 and, simultaneously, with the lowest possible proportion of ammonium chloride (max. 3%), which is the surface activation/cleaning component. Full article

TiB₂–MgAl₂O₄ composites were fabricated by combustion synthesis involving metallothermic reduction reactions. Thermite reagents contained Al and Mg as dual reductants and TiO₂ or B₂O₃ as the oxidant. The reactant mixtures also comprised elemental Ti and boron, as well as a small amount of Al₂O₃ or MgO to serve as the combustion moderator. Four reaction systems were conducted and all of them were exothermic enough to proceed in the mode of self-propagating high-temperature synthesis (SHS). The reaction based on B₂O₃/Al/Mg thermite and diluted with MgO was the most exothermic, while that containing TiO₂/Al/Mg thermite and Al₂O₃ as the diluent was the least. Depending on different thermites and diluents, the combustion front temperatures in a range from 1320 to 1720 °C, and combustion wave velocity from 3.9 to 5.7 mm/s were measured. The XRD spectra confirmed in situ formation of TiB₂ and MgAl₂O₄. It is believed that MgAl₂O₄ was synthesized through a combination reaction between Al₂O₃ and MgO, both of which can be totally or partially produced from the metallothermic reduction of B₂O₃ or TiO₂. The microstructure of the TiB₂–MgAl₂O₄ composite exhibited fine TiB₂ crystals surrounded by large densified MgAl₂O₄ grains. This study demonstrated an energy-saving and efficient route for fabricating MgAl₂O₄-containing composites. Full article

Fe–Si intermetallics–Al₂O₃ composites were fabricated by thermite-assisted combustion synthesis. Combustion reactions were conducted with powder compacts composed of Fe₂O₃, Al, Fe, and Si. The starting stoichiometry of powder mixtures had an atomic Fe/Si proportion ranging from Fe-20% to Fe-70.5% Si to explore the variation of silicide phases formed with Si percentage. Combustion in the mode of self-propagating high-temperature synthesis (SHS) was achieved and the activation energy of the SHS reaction was deduced. It was found that the increase of Si content decreased the combustion temperature and combustion wave velocity. Three silicide compounds, Fe₃Si, FeSi, and α-FeSi₂, along with Al₂O₃ were identified by XRD in the final products. Fe₃Si was formed as the single-phase silicide from the reactions with Si percentage from Fe-20% to Fe-30% Si. FeSi dominated the silicide compounds in the reactions with atomic Si content between Fe-45% and Fe-55% Si. As the Si percentage increased to Fe-66.7% Si and Fe-70.5% Si, α-FeSi₂ became the major phase. The microstructure of the composite product showed that dispersed granular or nearly spherical iron silicides were embedded in Al₂O₃, which was dense and continuous. Most of the silicide grains were around 3–5 μm and the atomic ratio of silicide particles from the EDS analysis confirmed the presence of Fe₃Si, FeSi, and FeSi₂. Full article

Composite energetic nanomaterials, otherwise known as nanothermites, consist of physical mixtures of fuel and oxidizer nanoparticles. When a combustion reaction takes place between both components, extremely impressive conditions are created, such as high temperatures (>1000 °C), intense heat releases (>kJ/cm³), and sometimes gas generation. These conditions can be adjusted by modifying the chemical nature of both reactants. However, these energetic composites are extremely sensitive to electrostatic discharge. This may lead to accidental ignitions during handling and transportation operations. This study examines the use of a n-type semiconductor ITO material as an alternative oxidizer combined with aluminum fuel. Indium tin oxide (ITO) ceramic is widely used in the elaboration of conducting coatings for antistatic applications because of its ability to conduct electrical charges (n-type semiconductor). The energetic performance of the Al/ITO thermite was determined, i.e., the sensitivity threshold regarding mechanical (impact and friction) and electrostatic discharge (ESD) stresses, as well as the reactive behavior (heat of reaction, combustion front velocity). The results demonstrate insensitivity toward mechanical stresses regardless of the ITO granulometry. As regards the spark sensitivity, using ITO microparticles considerably raises the sensitivity threshold value (<0.21 mJ vs. 13.70 mJ). A combustion velocity of nearly 650 m/s was also determined. Full article

In this paper, we offer a laboratory facility for in situ visualization of the combustion of ultrafine metal powders, which combines laser initiation and simultaneous high-speed recording of images of the flame of a burning material and a surface covered by a flame. Visualization of the surface through the flame is realized using a laser monitor—an optical projection system with brightness amplification. The proposed imaging system makes it possible to get more detailed information about the combustion process, in particular, to study the change in the surface through the flame in the area of laser initiation, and the propagation of heating and combustion waves over the sample, as well as to study the change in the surface reflectance during combustion. To study the area of laser initiation, it is proposed to simultaneously record images of a laser monitor with two cameras. The symmetry of the combustion wave front propagation and the combustion products’ formation during laser initiation of the nanoAl + Fe₃O₄ thermite mixture was demonstrated. The nature of propagation in the form of a ring is a consequence of the symmetry of the properties of the system under study, at the micro and macro levels. Full article

This article is devoted to the characterization of a new Co-W-Al alloy prepared by an aluminothermic reaction. This alloy is used for the subsequent preparation of a special composite nanopowder and for the surface coating of aluminum, magnesium, or iron alloys. Due to the very high temperature (2000 °C–3000 °C) required for the reaction, thermite was added to the mixture. Pulverized coal was also added in order to obtain the appropriate metal carbides (Co, W, Ti), which increase hardness, resistance to abrasion, and the corrosion of the coating and have good high temperature properties. The phase composition of the alloy prepared by the aluminothermic reaction showed mainly cobalt, tungsten, and aluminum, as well as small amounts of iron, titanium, and calcium. No carbon was identified using this method. The microstructure of this alloy is characterized by a cobalt matrix with smaller regular and irregular carbide particles doped by aluminum. Full article

The results of experiments to determine the role of structural schemes for the ignition of a mechanically activated thermite mixture Al–CuO and the formation of its combustion flame are presented. The reaction initiated in the bulk of the experimental assembly transforms into torch combustion in an open space. The dynamics of the volume of the flame reaction region was determined. The stage of flame formation has a stochastic character, determined by the random distribution of the reaction centres in the initial volume of the components. A high-speed camera, a pyrometer and electro contact sensors were used as diagnostic tools. The ultimate goal of the study was to optimize the conditions for the flame formation of this mixture for its effective use with a single ignition of various gas emissions. Full article

Thermites or composite energetic materials are mixtures made of fuel and oxidizer particles at micron-scale. Thermite reactions are characterized by high adiabatic flame temperatures (>1000 °C) and high heats of reaction (>kJ/cm³), sometimes combined with gas generation. These properties strongly depend on the chemical nature of the couple of components implemented. The present work focuses on the use of indium (III) oxide nanoparticles as oxidizer in the elaboration of nanothermites. Mixed with an aluminum nanopowder, heat of reaction of the resulting Al/In₂O₃ energetic nanocomposite was calculated and its reactive performance (sensitivity thresholds regarding different stimuli (impact, friction, and electrostatic discharge) and combustion velocity examined. The Al/In₂O₃ nanothermite, whose heat of reaction was determined of about 11.75 kJ/cm³, was defined as insensitive and moderately sensitive to impact and friction stimuli and extreme sensitive to spark with values >100 N, 324 N, and 0.31 mJ, respectively. The spark sensitivity was decreased by increasing In₂O₃ oxidizer (27.71 mJ). The combustion speed in confined geometries experiments was established near 500 m/s. The nature of the oxidizer implemented herein within a thermite formulation is reported for the first time. Full article

The formation of NbB₂–MgAl₂O₄ composites from the MgO-added thermite-based reaction systems was investigated by self-propagating high-temperature synthesis (SHS). Two thermite mixtures, Nb₂O₅/B₂O₃/Al and Nb₂O₅/Al, were, respectively, adopted in Reactions (1) and (2). The XRD analysis confirmed the combination of Al₂O₃ with MgO to form MgAl₂O₄ during the SHS process and that excess boron of 30 atom.% was required to yield NbB₂–MgAl₂O₄ composites with negligible NbB and Nb₃B₄. The microstructure of the composite reveals that rod-shaped MgAl₂O₄ crystals are closely interlocked and granular NbB₂ are embedded in or scattered over MgAl₂O₄. With the addition of MgAl₂O₄, the fracture toughness (K_IC) of 4.37–4.82 MPa m^1/2 was obtained for the composites. The activation energies E_a = 219.5 ± 16 and 167.9 ± 13 kJ/mol for Reactions (1) and (2) were determined from combustion wave kinetics. Full article

Fabrication of Fe₃Al–TiB₂–Al₂O₃ composites with a broad range of phase compositions was studied by combustion synthesis involving aluminothermic reduction of oxide precursors. Two reaction systems composed of elemental Fe, amorphous boron, and a thermite mixture of Fe₂O₃/TiO₂/Al were conducted in the mode of self-propagating high-temperature synthesis (SHS). One was to produce the composites of 1.25Fe₃Al + xTiB₂ + Al₂O₃ with x = 0.3–1.0. The other was to fabricate the products of yFe₃Al + 0.6TiB₂ + Al₂O₃ with y = 1.0–1.6. Reduction of Fe₂O₃ by Al acted as an initiation step to activate the SHS process. Complete phase conversion from the reactants to Fe₃Al–TiB₂–Al₂O₃ composites was achieved. The variation of combustion front velocity with sample stoichiometry was consistent with that of the reaction exothermicity. Based on combustion wave kinetics, the activation energy of E_a = 86.8 kJ/mol was determined for formation of the Fe₃Al–TiB₂–Al₂O₃ composite through the thermite-based SHS reaction. In addition, with an increase in TiB₂, the fracture toughness of the 1.25Fe₃Al + xTiB₂ + Al₂O₃ composite was found to increase from 5.32 to 7.92 MPa·m^1/2. Full article

Formation of MoSi₂–Al₂O₃ composites with a broad range of the MoSi₂/Al₂O₃ ratio was conducted by thermite-based combustion synthesis in the SHS mode. The addition of two thermite mixtures composed of MoO₃ + 2Al and 0.6MoO₃ + 0.6SiO₂ + 2Al into the Mo–Si reaction systems facilitated self-sustaining combustion and contributed to in situ formation of MoSi₂ and Al₂O₃. The samples adopting the former thermite reagent were more exothermic and produced composites with MoSi₂/Al₂O₃ from 2.0 to 4.5, beyond which combustion failed to proceed. Because of lower exothermicity of the reactions, the final products with MoSi₂/Al₂O₃ from 1.2 to 2.5 were fabricated from the SHS process involving the latter thermite mixture. Combustion temperatures of both reaction systems decreased from about 1640 to 1150 °C with increasing MoSi₂/Al₂O₃ proportion, which led to a phase transition of MoSi₂. It was found that the dominant silicide was β-MoSi₂ when the combustion temperature of the synthesis reaction exceeded 1550 °C and shifted to α-MoSi₂ as the combustion temperature fell below 1320 °C. The results of this study showed an energy-efficient fabrication route to tailor the phase and content of MoSi₂ in the MoSi₂–Al₂O₃ composite. Full article