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

The combustion patterns of powder mixtures (100 – X)(Ti + C) + XNiCr, X = 0–20%, and phase composition of synthesis products were studied. The different nature of the dependence of the burning velocity on the nichrome content for blends containing titanium powders with particles of characteristic sizes of 60 and 120 μm was explained within the framework of the convective–conductive model by the retarding influence of impurity gases released ahead of the combustion front. The conditions for warming up Ti particles before the front were not met for mixtures of fine and coarse titanium powders. XRD spectra of combustion products showed the necessity of using fine titanium powder to obtain cermets without side phases of intermetallic compounds.

TiC-based composites with various initial compositions can be successfully synthesized by self-propagating high-temperature synthesis (SHS) from either mixtures containing thermite reactions or from pure elements. The effect of various experimental parameters on the combustion reaction kinetics and the relationship between structure, microstructure and mechanical behavior of products was identified. It was found that the matrix’s strengthening is one of the most important variables in boosting the composite’s strength, and adding alloy elements reduces the rate and size of cracks and pores in the cermet microstructure. The presence of TiC particles inhibits dislocation motion and has a significant effect on the composite’s mechanical behavior.

The catalytic properties of materials based on terbium-doped and nickel-modified mesoporous silica gels prepared by the high-temperature template method were studied. The surface morphology and textural characteristics of the obtained samples were studied by scanning electron microscopy, X-ray phase analysis, and inductively coupled plasma mass spectrometry. The catalytic activity of the obtained catalysts was studied in the hydrogenation reaction of benzene, m-, p-, and o-xylene in the temperature range of 80–170°C and at a hydrogen pressure of 3 atm. It was established that doping with terbium leads to an increase in the catalytic activity of the catalyst modified with nickel in the hydrogenation reaction of benzene derivatives. Therefore, it was shown that mesoporous silica gel doped with terbium and modified with nickel is an effective catalyst for the hydrogenation of benzene and xylenes.

In this study, α-Fe₂O₃ was synthesized by solution combustion method using 6-aminohexanoic acid (AH) as a fuel and with different oxidizer-to-fuel ratios (Φ) of 0.6, 0.8, 1.0, 1.2, and 1.4. The as-prepared powders were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), infrared spectroscopy (IR), and UV–Vis spectroscopy. The results showed that the Φ ratio played a crucial role in determining the crystallinity and purity of the powders of α-Fe₂O₃. The α-Fe₂O₃ powder synthesized at an Φ ratio of 0.6 exhibited phase purity of hematite. This study demonstrates the importance of controlling the Φ ratio in the synthesis of α-Fe₂O₃ which could be used as an inorganic pigment in paints.

The aim of this investigation was to synthesis Ti–5Al–2.5Fe alloy by “hydride cycle” (HC) method. The crystal structure of obtained alloy was studied by powder X-ray diffraction. It was found that the alloy was a near α-alloy containing main α phase (hexagonal close-packed structure, space group 194: P6₃/mmc) and small amount of β phase (body-centered cubic structure, space group 229: Im-3m). The microstructure of obtained materials was studied using scanning electron microscope (SEM) in a back-scattered electron (BSE) mode. On the SEM image of the synthesized compacted alloy no cracks and pores were observed. The SEM measurements showed that the particles synthesized hydride have size distribution in the range of 1–10 μm. Energy dispersive X-ray spectrometry (EDS) analysis showed that the chemical compositions of observed main grey phase were close to the nominal composition of Ti–5Al–2.5Fe α-phase. The hydride of Ti–5Al–2.5Fe alloy was synthesized by self-propagating high temperature synthesis (SHS) method. It was shown that Ti–5Al–2.5Fe tablets reacted with hydrogen without preliminary crushing in SHS mode at range of hydrogen pressure P(H₂) = 1–2.5 MPa. Hydrogen capacity of synthesized (Ti–5Al–2.5Fe)H_1.45 hydride was equal to 3.04 wt %. The density of synthesized alloy before (ρ₁ = 4.0487 g/cm³) and after (ρ₂ = 4.2511 g/cm³) the repeating of hydrogenation–dehydrogenation cycle was measured. It was found that as a result of cycle the density of sample was increased by 5%.

The stability of combustion of titanium + carbon black powder mixture to a local excess of the component was experimentally studied. The influence of the spreading of titanium melt or liquid reaction product on the stability of the combustion transition through transverse carbon powder barrier was considered. The direction of melt movement with respect to the front propagation direction was determined. It was shown that the stability of the combustion transition through the barrier is determined by thermal interaction between the combustion wave and the barrier and is not directly related to the convective heat transfer by the melt.

This paper presents an in-depth study on the combustion synthesis, solid-solution formation, processing, and characterization of NbB₂–HfB₂ ceramics, aiming to explore their potential applications, particularly in industries requiring high-performance materials. We conducted macrokinetic measurements and fitted regression models to predict combustion temperature and velocity for compositions ranging from 50 to 100% HfB₂. A combined method of ball milling and hot pressing was developed for processing the combustion products into dense ceramics. These methods resulted in samples with relative densities reaching 97%, hardness of up to 34 GPa, and Young’s modulus of up to 530 GPa, with NbB₂–50% HfB₂ solid solution exhibiting the best mechanical properties. The study revealed a linear increase in thermal properties and density with the rise in HfB₂ content. The thermal conductivity of the solid solutions in the Nb–Hf–B system ranged from 34 to 40 W/mK and was found to increase with temperature, making these ceramics suitable for ultra-high-temperature applications. The findings have significant implications for aerospace and high-performance engineering sectors and provide a solid foundation for further investigation of Nb–Hf–B ceramics under real-world operational conditions.

Co–Ni supported catalysts were prepared by low-temperature combustion of dried mixture of solutions of cobalt and nickel nitrates and urea after impregnation of silica fabric (>97% SiO₂) premodified with 5, 10, and 15 wt % Al₂O₃. Modification of support was carried out by low-temperature combustion of dried mixture of solutions of aluminum nitrate and urea. Prepared supports and related catalysts were characterized by XRD, SEM, EDS, and BET method. The unreduced catalysts were found to contain oxides and complex oxides of nickel and cobalt. Reduction of catalysts with hydrogen at 400°C for 1 h was shown to contribute to forming metallic phases of Co and Ni; however, the nickel phase was detected only in reduced catalyst on unmodified fabric. The catalytic activity of catalysts was determined in the temperature range of 150–400°С. It was found that the reduced catalyst on support modified with 5 wt % Al₂O₃ possesses the highest CO₂ conversion (61.8%) and methane yield (3.61 vol %) at 400°С.