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

Lithium aluminate samples were obtained in reactions of solution combustion synthesis (SCS) with various types of fuel (glycine, leucine, and urea) from aluminum and lithium nitrate solutions. The simultaneous thermal analysis (STA) of precursors obtained in conditions of fuel and oxidizer stoichiometry showed the presence of impurities due to incomplete decomposition of initial salts containing carbon fragments of fuel and nitrate groups. An exception was the precursor from the dual-fuel SCS reaction, φ (glycine : urea) = 1 : 3, in which pure γ-LiAlO₂ powder was formed. Replacement of lithium nitrate with lithium carbonate was found to reduce the process temperature and the relative amount of organic fuel. As a result, the content of carbon fragments in the precursor significantly decreased after synthesis.

TiC–NiTi cermet composites were fabricated by forced SHS compaction from (Ti + C + Ni) mixtures with varying content of Ni + Ti from 28 to 90 wt %. The phase composition and microstructure were characterized by X-ray diffraction method, scanning electron microscopy, and energy dispersive spectroscopy. The microstructure of composites was shown to contain spherical TiC particles surrounded by the matrix including TiNi₃, TiNi(B2), Ti₂Ni, and Ti₃Ni₄ phases. As Ni + Ti content was increased, there was a change in the stoichiometry of TiC (from TiC₁ to TiC_0.43) and its particle size (from 6.5 to 0.2 μm). It was found that the microhardness of TiC–NiTi composites dropped markedly from 23.5 to 6.4 GPa.

A brief review of the history, current state, and prospects of using titanium powders to produce porous products and in SHS in Belarus, as well as in the world, was presented. New methods for obtaining materials, billets, raw materials, and products from commercially pure titanium powders were considered. Promising directions of applying methods and technologies of powder metallurgy and SHS using titanium powders toward producing new types of products were shown.

The optimum composition of components in the Hf/PTFE system was determined by thermodynamic calculation. The composition 65Hf/35PTFE (in wt %) was chosen based on the maximum adiabatic combustion temperature (T_ad = 2381°C) and the fraction of condensed products (70 wt %). The study on the ignition of compositions in argon, air, and vacuum showed that in the latter case, the intensity of ignition decreases. The maximum combustion temperature and rate in argon were found to be 2250°C and 4.5 mm/s for compositions with 10 and 15 wt % Al. XRD analysis revealed the formation of a monophase HfC product in all compositions. Shock-wave loading of compositions with a steel plate at an impact velocity of 1 km/s showed the absence of exothermic reaction in the 65Hf/35PTFE composition. Increasing the impact velocity to 1.5 km/s resulted in an exothermic reaction in this composition. The maximum yield of HfC under shock-wave loading was achieved in the composition 62Hf/33PTFE/5Al, indicating its high reactivity. Thus, this composition is the most optimal for use as a reactive material.

TiB₂–Ti metal–ceramic composites were produced by forced SHS compaction. The influence of superstoichiometric amount of Ti (6–20 wt %) relative to TiB₂ on the regularities of combustion and phase composition/structure formation of TiB₂–Ti composites was studied. It was shown that the phase composition of composites is inconsistent with the Ti–B phase diagram. The microhardness of composites was determined to drop from 34 to 18 GPa with increasing the binder content. Cutting properties of composites were evaluated.

Calcium phosphates are materials of wide interest in the medical and agricultural industries. Advanced in the standardization of protocols to obtain them by combustion in solution in a single step is highly desirable. This is particularly so for the alpha-tricalcium phosphate (α-TCP) phase, widely used in the development of bone cement. In this research, citrulline was used as a fuel for the first time in the one-step synthesis of calcium phosphates, and the effect of adding 0–15 g of ammonium nitrate (AN) as an extra oxidizer agent was studied, allowing the temperature of the reaction to increase from 648 to 950°C. The temperature was measured using low-cost equipment with infrared and type-K thermocouple and contrasted with the estimated theoretical values of adiabatic flame temperature. X-ray diffraction analysis showed the formation of a mixture of α-TCP and hydroxyapatite phases at the lowest combustion temperature, corresponding to 0 g of AN. When the amount of AN was increased, the XRD showed that α-TCP was obtained as a metastable phase, while the amount of hydroxyapatite decreased considerably. At higher combustion temperatures, the crystallite size estimated by Scherrer equation, in turn, increased to a value of 51.61 nm. The SEM images showed the presence of necks between particles in the powders that coincide with the estimation of high reaction temperatures.

The structure as well as the phase and granulometric compositions of the submicron-sized heterophase HfB₂–34 at % HfC powders fabricated by mechanical activation assisted self-propagating high-temperature synthesis from (Hf + B + C) mixtures were studied. It was demonstrated that HfB₂–HfC powders can be produced from (Hf + B + C) mixtures by mechanochemical synthesis in a planetary ball mill (centrifugal factor, 60 g) during more than 15 min. The SHS product with composition HfB₂–34 at % HfC consisted of a combination of highly porous agglomerates sized 5–100 µm, which can be easily broken into composite HfB₂–HfC particles sized 1–10 µm. Important that each composite particle of powder have a heterophase structure which consists of HfB₂ grains sized 0.5–2.0 µm and equiaxial HfC grains sized 0.3–1 µm. Impurity oxygen content in the SHS products did not exceed 0.29 wt %. Milling of the SHS product allowed to obtain the HfB₂–34 at % HfC powder characterized by the average particle size of 4 µm with heterophase submicron-sized microstructure and oxygen content of 0.72 wt %.

This study extensively concentrates on recent industrial applications like photoluminescence, photocatalytic, corrosion protection, and sensors using spinel ferrites; this review provides a basic overview of the many synthesis methods, such as co-precipitation, sol–gel, hydrothermal, solid-state etc., and a detailed discussion of pure and doped nickel ferrites. Spinel ferrite’s features would change according to the synthesis method used including the magnetic, electrical, mechanical, and chemical properties. Some significant discoveries in nickel ferrite research are summarised and tabulated in this review study. This work also involves the study of spinel ferrites, which explains the classifications of spinel ferrites and their structural details, covering spinel ferrites and their potential applications. Nickel–spinel ferrites are also studied with different derivatives using other doping agents. The several applications where nickel and substituted nickel ferrites are also crucial are briefly covered in this Review Article.

Low-temperature combustion synthesis was used both for modifying silica gel support with 10 and 20 wt % Al₂O₃ and for producing supported catalysts with 10 wt % of Co active phase. Prepared catalysts were characterized by XRD, SEM, EDS, and BET method. It was revealed that these catalysts contain oxides, aluminates, and silicates of cobalt. It was shown that modification of support noticeably reduces its specific surface, while its calcination decreases the catalyst activity. The catalysts synthesized from supports with lower content of Al₂O₃ demonstrated higher specific surface and lower activity in deep oxidation of propane and CO. The catalyst on an uncalcinated support modified with 20 wt % Al₂O₃ was found to possess the highest activity in the process of deep oxidation.

The effect of sodium chloride (NaCl) on the magnetism of nanopowders of the spinel ferrite (MgFe₂O₄) produced using a salt-assisted solution combustion synthesis was investigated. X-ray diffraction (XRD) analysis was conducted to evaluate crystalline structure and phase composition of the synthesized materials. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) was used to evaluate the particle size and morphology. Magnetic behavior was analyzed by measuring and analyzing the respective hysteresis loops using a vibrating sample magnetometer (VSM). The characterization showed that the presence of NaCl affects the phase composition, size, and dispersion of the nanoparticles, as well as their magnetic behavior. The theoretical size of the nanoparticles was calculated using the Scherrer equation, obtaining sizes of about 21.07 nm for the nanoparticles without salt, 5.90 nm for the sample salt content of 1.7 mol and 6.48 nm—for 3.4 mol. The synthesized nanoparticles showed a drastic decrease in coercivity field, remanence, and saturation with increasing salt content. Therefore, the salt content is a crucial parameter in controlling the morphology and magnetic properties of the nanoparticles obtained by the solution combustion route.