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

Matrix based on pyrochlore Y₂Ti₂O₇ for immobilization of high-level radioactive waste was prepared via SHS process. The phase composition and structure of the synthesized matrices were characterized. The influence of aluminum additive and composition/amount of gases emitted during combustion on the porosity of the matrices was studied.

MgAlON was prepared by self-propagating high-temperature synthesis using powder mixture of aluminum, aluminum oxide, magnesium oxide, magnesium, and magnesium perchlorate as an oxidizer. The effect of magnesium oxidation and aluminum nitriding reactions on the combustion parameters was studied. It was revealed that combustion temperature and burning velocity increase as Mg is added. It was found that the combustion products derived from mixtures containing magnesium powder have a fine-grained structure composed by only MgAlON.

High-entropy alloys were produced by centrifugal self-propagating high-temperature synthesis and used as precursors for preparation of catalysts for CO and propane deep oxidation and CO₂ hydrogenation. The precursors were converted into catalysts by aluminum leaching and stabilization with hydrogen peroxide solution. Prepared FeCoNiCu, FeCoNiCuMo, FeCoNiCuMn, and FeCoNiCuCr catalysts were characterized by XRD, SEM/EDS, and BET methods and tested in the processes of deep oxidation of CO and propane and methanation of CO₂. The highest CO₂ conversion, 50.6%, with methane selectivity of 77.5% was achieved on FeCoNiCu catalyst at 400°C. The best catalyst for the deep oxidation process was shown to be FeCoNiCuCr, on which the temperature of 100% CO conversion was 250°C and 100% conversion of propane was achieved at 450°C.

A new phenomenon was discovered: an oscillatory combustion mode of hydrogen releasing under the non-isothermal decomposition of titanium hydride in air.

A new mode of combustion of granular mixtures Zr + 0.5C in a co-current argon flow with the formation of a finger-like front instability was discovered. The observed phenomena were explained under the assumption of a decrease in the permeability of synthesis products due to significant shrinkage of the sample in the longitudinal direction, which prevented the filtration of argon through the products. Redirection of the gas flow into the gap between the granules and the side surface of the cylindrical reactor contributed to the formation of a finger. It was shown that a decrease in the sample size in the longitudinal direction is provided by the pressure drop of argon, and a decrease in the cross-section occurs under the action of surface tension forces due to a transverse temperature gradient.

Alumina (Al₂O₃) is widely used in a variety of applications because it has superior physical and chemical properties which are high heat resistance, excellent electrical isolation, abrasion resistance, and high corrosion resistance. Generally, alumina is manufactured with a purity of 99.6–99.9% mainly by the Bayer process with bauxite as the starting material. It is used in refractory products, spark plugs, IC substrates, and so on. High-purity alumina (HPA), which has a purity of more than 99.99% and has a uniform fine particle, is widely used in translucent tubes for high-pressure sodium lamps, single crystal materials such as sapphires for watch covers, high-strength ceramic tools, abrasives for magnetic tape, and the like. In recent years, the demand for high-purity alumina has been expanding in fields that are expected to show a high growth rate e.g., display materials, energy, automobiles, semiconductors, and computers. There are several complicated processes reported in literature to produce single phase α-HPA, which consumes more energy, and power and are very costly. In this paper, we report the preparation of nano-α alumina powders with a purity of 3N (99.9%) by a simple, economical, and faster method i.e., one-step auto combustion method. To obtain single phase α-alumina, the calcination temperature required is 1200°C but, in our work, we achieved single phase α-alumina at 500°C temperature by one-step auto combustion method. The as-prepared HPA is characterized through XRD, BET surface area, SEM and ICP, TGA, and LIBS to test for purity and its application in LED fabrication.

Titanium carbide (TiC) powder was synthesized by the magnesiothermic combustion of the TiO₂-rich alteration product leucoxene and activated carbon (AC) in argon. Leucoxene and C were combined at a molar ratio of 1.0 : 1.5, and the effect of magnesium (Mg) fuel in the reaction system was studied at ratios of 1.0, 1.5, 2.0, 2.5, and 3.0. XRD analysis showed that the as-leached powder from a reactant mixture with a Mg molar ratio of 3.0 has fewer unwanted phases, and that leucoxene, C, Mg mixed at 1.0 : 1.5 : 3.0 produce TiC powder of a higher purity than the other reacted mixtures. The higher purity of the product was due to the more exothermic character of the combustion reaction, which had a higher enthalpy of reaction (ΔH) and adiabatic temperature (T_ad). SEM observation of the as-leached powder revealed agglomerated fine particles of sub-micrometer size. The TiC powder was successfully coated with nickel by an electroless plating process. SEM/EDX demonstrated that the Ni-coated TiC powder consists of Ni particles smaller than 500 nm, which are well distributed on TiC particles.

The fabrication of ternary Cu–Mn–Al alloys through self-propagating high-temperature synthesis and their thermoelectric properties, such as electrical resistivity and the Seebeck coefficient in a wide range of temperatures, were studied. XRD analysis identified the Heusler compound Cu₂MnAl in the synthesized compositions as a main precipitated phase. In addition, different secondary phases (Al₂Cu, Cu₃Al AlCu, and Mn) appear depending on an excess of aluminum or manganese in the green mixture. The magnetization (M–H) curves constructed for the studied alloys showed their weakly ferromagnetic behavior.

The initiation of combustion of a large mass of condensed mixture being in local contact with the end of the burning layer was mathematically modelled and experimentally studied. The influence of the instability of stationary combustion front in the igniting layer on the penetration of gasless combustion into large volume was showed. It was revealed that the critical conditions for initiating combustion of large volume are determined by front curvature.