International Journal of Self-Propagating High-Temperature Synthesis最新文献

The study focused on the synthesis of cerium and europium co-doped yttrium aluminum garnet (YAG) phosphors. Pure phase YAG:Ce,Eu powders were synthesized using a mixed fuel combustion method around 500°C furnace temperature. The crystallinity and luminescence spectra of YAG:Ce,Eu were examined.

The present study explored the hydrogen storage properties of the Ti₃₀V₆₀Mn_3.3Cr_6.6 alloy. The alloy was synthesized using arc melting method and activated under dynamic vacuum for 2 h. The X-ray diffraction study confirmed the formation of a single-phase bcc structure. The Ti₃₀V₆₀Mn_3.3Cr_6.6 alloy exhibited a hydrogen absorption capacity of 3.61 wt % at room temperature under 20 bar hydrogen pressure. The hydrogen storage capacity of the alloy reduced with increase in temperature. Quick absorption was observed with short incubation time in the kinetic study. The alloy absorbed nearly 90% of its saturation value in 5 min. The alloy exhibited accelerated kinetics at elevated temperatures. The enthalpy and entropy change during absorption were found as –45.26 kJ/mol H₂ and –113.93 J/mol H₂/K, respectively. The maximum hydrogen desorption in this alloy was observed at 410 K during in-situ temperature-programmed desorption study.

Mg₂Si was prepared via self-propagating high-temperature synthesis. Characterization by XRD and SEM confirmed Mg₂Si as a basis. The synthesized product density, porosity, electrical resistivity, and Seebeck coefficient were measured. Electrical resistivity showed a nonlinear, semiconductor-like dependence. Similarly, the Seebeck coefficient followed a nonlinear trend, reaching a minimum of –367 µV/K at 589 K.

The combustion and ignition behaviors of W–PTFE powder mixtures, incorporating both tungsten micro- and nanoparticles along with high-energy additives, such as Ti, Ni + Al, Ti + 2B, and TiH₂, were examined. Through thermodynamic and experimental analysis, it was determined that mixtures containing tungsten nanoparticles (nW) achieve 50–60% faster ignition and up to fivefold higher burning velocities compared to those with microparticles (μW), primarily due to an enlarged contact surface area. Among the additives, Ni + Al in nW–PTFE led to the highest synthesis completeness (50–65%), whereas 10 wt % Ti significantly boosted both the combustion temperature (reaching 2000°C) and burning velocity (up to 2.8 mm/s). Specifically, the nW + PTFE + 5 wt % (Ni + Al) and nW + PTFE + 10 wt % Ti mixtures demonstrated exceptional overall performance in terms of synthesis completeness, burning velocity, and combustion temperature, positioning them as compelling reactive material candidates. These results emphasize the crucial role of high-energy additives and particle size in controlling reaction mechanisms and achieving desired energetic characteristics.

This study presented the formation and oxidation of refractory materials investigated with a high-speed electro-thermographic method specifically designed to probe rapid exothermic gas–solid reactions. Thin metallic wire specimens of Ta or tantalum carbide (TaC, Ta₂C) coated Ta served as both heating elements and reactants, enabling controllable heating of specimen up to 5 × 10⁵ K/s under various gas environments. Real-time measurements of electrical parameters and temperature at 10 kHz captured reaction dynamics across 900–2500 K. Two distinct heating modes were employed: (i) temperature-controlled (isothermal or linear heating) and (ii) power-controlled, which simulates quasi-isothermal reaction conditions. This dual approach allowed detailed exploration of TaC/Ta₂C coating synthesis on Ta wires and identification of the critical parameters separating slow oxidation from ignition of tantalum and tantalum carbides. Gravimetric measurements provided kinetic data on carbidization and oxidation across varied experimental conditions, while rapid quenching of specimens preserved intermediate states for ex-situ characterization by X-ray diffraction and electron microscopy.

The effect of low-energy mechanical activation (LEMA) of 3Ni + Al powder mixtures on their ignition temperature was theoretically and experimentally investigated. LEMA proved instrumental in creating structural defects and significant morphological changes, thereby critically influencing subsequent high-temperature synthesis kinetics. It was determined that LEMA reduces ignition temperature by lowering chemical reaction activation energy and increasing the interfacial surface area. During the initial stages of activation, crystal defect formation served as the primary mechanism, raising the internal energy and lowering the ignition barrier. Extended activation led to prominent morphological transformations, including particle size reduction, decreased structural heterogeneity, and layered mechanocomposite formation. These alterations transitioned the reaction mechanism from diffusion-controlled to interfacial-controlled, subsequently lowering the required activation energy. The findings underscore the critical role of morphological evolution in enhancing system reactivity, especially under prolonged activation. This research establishes a scientific foundation for developing efficient methods to produce Ni–Al-based materials, highly relevant for high-temperature applications in the energy, aerospace, and chemical industries.

High-entropy nitrides have the potential to enhance mechanical properties and high-temperature stability compared to mono- or binary nitrides. They are particularly promising for applications requiring high temperatures and hardness. Here, we report on a facile one-step route for the fabrication of a high-entropy nitride powder (TiZrHfNbTa)N_x. The novel approach employs the mechanical alloying of metal powders within a planetary ball mill under elevated nitrogen pressure. Ball milling a mixture of five transition metals under a nitrogen pressure of 0.6 MPa for 60–90 min leads to the formation of a high-entropy nitride with a rock-salt crystal structure. The as-prepared powder exhibits nanoscale crystallites and a uniform distribution of metals within the cationic sublattice. The total nitrogen content of the synthesized powder is 8.9 wt %, indicating the formation of a non-stoichiometric high-entropy nitride (TiZrHfNbTa)N_0.83. The scalable technological approach developed in the current study could also be used to produce other multielement nitrides, thereby expanding the range of nitride ceramics available.

The regularities of carbonyl iron powder nitriding were investigated using Ti + C “chemical oven” mixture and urea as a source of atomic nitrogen. Increasing the urea content was found to lower maximum nitriding temperatures and decelerate cooling rates, the latter being attributed to the exothermic nature of iron–nitrogen reaction. Although maximum temperatures decreased as sample diameter was reduced, the phase composition exhibited minimal sensitivity to these geometric variations.

A numerical investigation was conducted to explore the impact of external heat transfer on combustion wave propagation in a cylindrical Ti–Si layer, employing a solid-flame combustion model. Calculations revealed the average burning velocity of the sample, presenting it as a function of layer thickness, inner radius, and outer radius. Critical conditions for the synthesis process in the combustion mode of a hollow cylindrical sample, driven by environmental heat loss, were identified. In the near-critical synthesis mode, periodic temperature fluctuations arose within the combustion wave when the layer thickness was less than 0.5 mm. Conversely, for samples with a layer thickness exceeding 1 mm, combustion consistently proceeded in a stationary manner.

The effect of mechanical activation (MA) on the characteristics of Ti + C reaction mixtures, their combustion kinetics, and the microstructure of TiC ceramics synthesized via forced SHS compaction was studied. It was shown that increasing MA time enhances the Ti–C contact surface, which directly dictates a ten-fold rise in burning velocity and a 3.5-fold decrease in TiC grain size.