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

5 wt % Co–5 wt % Ni catalysts supported on natural opoka and diatomite silica minerals from the Republic of Kazakhstan were prepared via low-temperature combustion and characterized using XRD, SEM/EDS, and BET analyses. The supports primarily comprised various SiO₂ modifications, with opoka also containing sodium, magnesium, and iron silicate and aluminosilicate impurities. Diatomite-supported catalysts exhibited specific surface areas ranging from 60.0 to 71.5 m²/g, while for opoka-supported catalysts, it ranged from 28.6 to 62.8 m²/g. During CO₂ hydrogenation to methane, the highest conversion (50.9% at 450°C) was achieved with a catalyst supported on untreated diatomite. However, the highest methane selectivity (90.1% at 450°C) was observed for a catalyst supported on opoka calcined at 500°C.

This study focused on synthesizing a Ti–23Zr–25Nb alloy by the energy-efficient hydride cycle (HC) method. The results demonstrated that alloy formation occurs at 1050(16)°C, a temperature is significantly lower than the individual melting points of the alloy components. X-ray powder diffraction analysis revealed that the synthesized alloy consists of two phases: α (hexagonal close packed (HCP) structure, space group P6₃/mmc) and β (body-centered cubic (BCC) structure, space group Im-3m) solid solutions. The crystal lattice parameters of these phases were determined. Scanning electron microscopy (SEM) revealed distinct microstructural features of the alloy, distinguishing two primary phases with noticeable contrast between light and dark regions. These phases corresponded to those identified by X-ray phase analysis. The interaction of the Ti–23Zr–25Nb alloy with hydrogen in self-propagating high-temperature synthesis (SHS) mode was investigated. It was demonstrated that the compacted alloy, without prior crushing or mechanical treatment, absorbed 2.78(6) wt % hydrogen during the SHS process. Furthermore, X-ray analysis demonstrated that the synthesized hydride of the multicomponent alloy consists of two phases: TiH₂ (face-centered cubic (FCC), space group Fm-3m) and TiZrH_1.68 (HCP, space group P6₃/mmc). The thermal stability of the synthesized hydride was analyzed by differential thermal analysis (DTA), revealing hydrogen desorption characterized by two endothermic peaks at 362(2) and 855(4)°C.

High-temperature interaction between a melt of Co₂MnSi Heusler alloy produced via self-propagating high-temperature synthesis and a silicon substrate was first investigated. Electron microscopy and X-ray phase analysis revealed that Co₂MnSi melt actively interacts with Si, forming wide diffusion zones containing cobalt silicides (CoSi₂ and CoSi).

The Nd³⁺ substituted Ni–Cu ferrites having the general chemical composition of Ni_0.5Cu_0.5Nd_xFe_2–xO₄ (x = 0.1, 0.2, and 0.3) were synthesized by solid state reaction method. The XRD analysis revealed the confirmation and formation of cubic spinel structure of ferrites. The lattice parameter value varied from 8.318 to 8.343 Å. The lattice parameter and X-ray density were found to increase with increasing Nd³⁺ ion concentration due to higher ionic radius of Nd³⁺ ion. The SEM images illustrated that crystallite size decreases with increasing Nd³⁺ ion concentration due to unit cell growth and lattice distortion, which produces an internal stress preventing grain growth. From the FTIR spectra, the higher frequency band in the range of 500–600 cm^–1 confirmed the vibrations due to M–O stretching at the tetrahedral site, while the lower band in the range of 400–500 cm^–1 confirmed the movement of Fe⁺³–O^2– band group at the octahedral site. The higher the concentration of Nd³⁺ ions, the higher the resistivity of Nd-doped ferrites due to change in crystal structure and electronic configuration. For all Nd³⁺ doped samples, the dielectric constant and dielectric loss decreased with increasing frequency, representing the typical dielectric dispersion behaviour, and the AC conductivity increased. The optical band gap of Nd³⁺ substituted compounds were studied using UV-Vis spectrum. The absorbance wavelength of ferrites reduced with the substitution, the indirect band gap energy increased. When Nd³⁺ ions replaced Fe³⁺ ions on the tetrahedral B-site, the saturation magnetization increased. The coercivity decreased due to an increase in grain size which happens owing to substitution of Nd³⁺ ion. Gas sensing properties of Nd³⁺ doped ferrites were studied by using NO₂ gas. Sensitivity of ferrites was enhanced by Nd³⁺ doping via increasing the number of oxygen vacancies which improves the absorption of NO₂ gas.

NiAl, NiCoAl, and CoCuAl intermetallics on ceramic TiB₂ and TiCB supports were produced through SHS of granular mixtures and used as precursors for preparation of catalysts for CO and propane deep oxidation and CO₂ hydrogenation. The precursors were converted into catalysts by leaching with 20% NaOH solution and stabilization with 10% H₂O₂ solution. The activity and selectivity of catalysts was found to be determined by active phase composition. In CO₂ methanation, NiCo/TiB₂ catalyst gave the highest CO₂ conversion (69.5% at 350°C) with 100% methane selectivity. In addition, NiCo/TiB₂ was shown to the most active in propane oxidation (15.7% conversion at 450°C). 100% CO conversion was observed on catalysts with CoCu active phase at 400°C.

This study presents, for the first time, the mechanisms governing the formation of the ternary Ti_0.5V₂Cr_0.5 base alloy and its composite alloys (incorporating 4 wt % ZrNi and 4 wt % Zr₇Ni₁₀ activating additives), synthesized via hydride cycle (HC) method. Additionally, the interaction of these alloys with hydrogen was systematically investigated. The synthesis was conducted through two distinct technological routes, each resulting in different formation mechanisms of the final composite materials. XRD analysis confirmed that all synthesized alloys form solid solutions with BCC crystal structure, exhibiting nearly identical lattice parameters. The hydrogen interaction of the synthesized alloys was examined under self-propagating high-temperature synthesis (SHS) and short-term activation method (STAM, 15–30 min). In both cases, the hydrides of FCC structure with hydrogen storage capacities ranging from 2.46 to 3.06 wt % were formed. The desorption temperatures of the synthesized hydrides differ due to the different microstructures of the alloys. Hydrides synthesized via STAM using composites obtained through the first synthesis route exhibited a hydrogen capacity of 3.01 wt % and a lower decomposition temperature characterized by a single endothermic peak at 280°C on the differential thermal analysis (DTA) curve. These findings demonstrate the potential of using Ti_0.5V₂Cr_0.5-based alloys for hydrogen storage applications.

At present, vehicle exhausts are among the major factors of environmental pollution. This problem is particularly acute in developing countries, where the share of used cars is high because the catalytic converters in used cars are partially or often completely out of order, which leads to the increase of toxic substances in the air such as carbon monoxide, nitric oxides, and hydrocarbons. We used the SHS method to obtain a new type of catalytic substrate, in which precious metals (platinum, palladium, rhodium) can be partially or completely replaced with metals such as copper, nickel, chromium, etc. When obtaining the catalytic substrate by the SHS method, the correct selection of a chemical composition of the initial charging material of the reaction is a determining factor that ultimately leads to obtaining products with the desired properties. Due to the high degree of dispersion of additive metals (copper, chromium, nickel, etc.), they do not participate in the reaction, therefore, they do not form chemical compounds, and they are evenly distributed in the final product, which significantly increases the quality of their catalytic activity. The porosity of the obtained sample is significantly affected by the density of the initial sample. By changing the initial porosity of the sample, it is possible to vary the porosity of the final product from 5 to 45%. Application of the proposed technology reduces the neutralizer-catalyst’s production cost and solves the problem of its scarcity. The obtained materials can be used in all types of vehicles with internal combustion engines, as well as in enterprises where catalytic purification of exhaust gases and liquids takes place.

Cast materials based on MAX V₂AlC phase were prepared by self-propagating high-temperature synthesis (SHS) under 5 MPa of Ar pressure from green mixtures containing V₂O₅, VO₂, Al, and C powders. Variation in an excess of aluminum markedly affected the process parameters and phase composition/microstucture of combustion products. The synthesized samples were shown to contain V₂AlC as a basis with additions of carbide and intermetallic phases of vanadium, whose presence is probably associated with a short lifetime of the liquid phase due to small green mixture mass and strong heat loss into the environment. A maximum content of MAX V₂AlC phase in the ingot (68 wt %) was reached at 15% of excess aluminum.