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

A comparative analysis of forced SHS compaction of single- and double-layer pressed Ti + 2B mixtures was carried out. High-velocity impurity gases were found to be able to initiate SHS reaction in the green mixture. It was shown that the use of double-layer combustion scheme permits to reduce the burning time of pellet in half due to the propagation of red-hot impurity gases between its layers. Their propagation velocity was found to be determined by total pellet mass: the larger the pellet mass, the higher the propagation velocity of impurity gases through artificially organized channels (gaps between the layers). Short burning time reduces the delay interval for the onset of consolidation of SHS products and facilitates the consolidation of synthesis products (hot pressing) at higher temperature and lower temperature gradient over the burned pellet.

Regularities of passage of gasless combustion wave through a quartz glass layer separating two cylindrical Ni–Al samples were considered. The time of passage of combustion wave through the quartz glass layer was calculated as a function of layer thickness and initial temperature. The unsteady dynamics and critical conditions of transient combustion process for Ni–Al system were investigated. The mathematical model and calculation results can be used to estimate the critical thickness of quartz glass layer separating SHS-produced samples.

High-temperature thermoelectric SrTiO₃ powders, including La-doped (Sr_0.95La_0.05)TiO₃, were synthesized using solution combustion synthesis. It was found that using urea as the organic fuel leads to the formation of a polyphase material consisting of 80 wt % SrTiO₃ and 20 wt % TiO₂ along with Sr₂TiO₄. The introduction of a fuel mixture of urea and glycine into the reaction solution significantly improved homogeneity of the powder, increasing the proportion of the target phase to 95 wt %. Spark plasma sintering further homogenized the powder, reducing amount of the impurity phase TiO₂ to less than 5 wt %. The study demonstrated that doping, phase composition, and porosity have a significant impact on the thermoelectric properties of SrTiO₃. The presence of TiO₂ secondary phase and porosity was shown to regulate the material’s electrical and thermal conductivities. La doping affected the charge carrier concentration, and together with the other factors, enabled the production of a dense (Sr_0.95La_0.05)TiO₃ sample with a figure of merit ZT ≈ 0.23 at 950 K. The findings underscore the significance of controlling phase composition, doping, and defect structure to enhance the thermoelectric performance of SrTiO₃, paving the way for the design of energy-efficient materials applicable in thermal energy conversion technologies.

In this study, NiCo composite materials were synthesized via the solution combustion synthesis (SCS) method using nickel and cobalt nitrates with hexamethylenetetramine as fuel. Thermodynamic calculations were first conducted to identify optimal fuel-to-oxidizer ratios (φ) and water content, revealing that the maximum adiabatic temperature (2670 K) occurs at φ = 1.25. Experimental results showed that combustion could not be initiated at φ = 0.5, while φ = 1.5 yielded the highest combustion temperature (1580 K) and a pure NiCo composite phase, as confirmed by XRD analysis. The synthesized materials exhibited a porous sintered microstructure with an average crystallite size of ~25 nm. Pressure variation from 0.1 to 1.5 MPa had negligible influence on the phase composition but significantly affected combustion wave velocity, which increased by two orders of magnitude. SEM analysis confirmed that all samples retain porous and sintered morphology, with higher pressures leading to more pronounced sintering. These results demonstrate that the SCS method enables the rapid and effective synthesis of structurally uniform NiCo composites with tunable properties.

The features of high-temperature interaction between the eutectic Cu–Ag |alloy and the Al melt were studied. It was shown that Cu–Ag–Al alloy represents Cu₃Al₂ dendrites in Ag(Al,Cu) eutectic matrix. The specific electrical resistance of sintered composite was 31.4 × 10^–8 Ω m, its temperature coefficient of resistance was 3.25 × 10^–3 K^–1.

In this study, surface-oxidized copper nanoparticles were synthesized through a time and energy-efficient solid-state self-propagating combustion (SSPC) reaction by making use of sodium borohydride (NaBH₄) and calcium carbonate (Cu₂(CO₃)(OH)₂). The microstructure, phase composition, and crystalline structure were examined using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM) studies. XRD and XPS analyses confirmed the formation of crystalline copper (Cu) and Cu₂O. The percentages of Cu₂O and Cu were calculated to be 13 and 87%, respectively; based on the XRD peak profile. TEM studies confirmed that the Cu nanoparticles (CuNPs) were surface oxidized with a Cu₂O layer of thickness 3–5 nm. Electrochemical studies using a three-electrode setup in a 1 M KOH aqueous solution demonstrated a specific capacitance of 144.44 F/g at 0.15 A/g.

Direct nitriding of spherical microparticles of carbonyl iron powder was carried out by means of chemical oven technique. Experimental selection of highly exothermic mixtures (“chemical ovens”) and nitrogen-containing additives was realized. It was shown that the nitriding products contain Fe₃N_x where x ranges from 0.93 to 1.15 as a basis and are represented by spherical core–shell particles where the core is iron and the shell consisting of sub-microcrystals includes Fe, Fe₃C, and Fe_xN (x = 3 and 4). According to XRD-Rietveld method calculations, the maximum yield of Fe_xN was 66 wt %.

Titanium carbonitride was synthesized for the first time in a closed reactor (constant pressure bomb) from granular mixtures Ti + 0.5C and TiC + Ti. Changes in sample mass, titanium carbide particle size, and granule size had a weak effect on the phase composition of the product. As in the case of synthesis of powder charge, the determining factor for increasing the nitrogen content in titanium carbonitride was an increase in nitrogen pressure. Chemical analysis showed that the product obtained from Ti + 0.5C granular mixture at a pressure of 16 atm contains 5.1% nitrogen, which is close to 6% in titanium carbonitride synthesized from bulk-density powder charge. Replacing Ti + 0.5C with TiC + Ti led to an increase in the nitrogen content to 9% for both granular and powder mixtures. Thus, the nitrogen content in products synthesized in a constant pressure bomb at 4–16 atm was independent of green mixture structure. According to XRD data, the product with composition close to TiC_0.5N_0.5 was obtained from more massive TiC + Ti granular mixture, which is associated with a longer cooling time. In contrast to the synthesis from powder mixtures, titanium carbonitride granules were easily crushed into powders.

The series of Sm³⁺ substituted nickel copper ferrites, Ni_0.5Cu_0.5Sm_xFe_2–xO₄ with (x = 0.1, 0.2, and 0.3), was synthesized by standard double sintered ceramic technique. The phase analysis was characterized by X-ray diffraction studies, which confirmed the creation of single phase. Crystallite size was calculated by using Debye Scherer formula for high intensity peak and found to be in the range from 71 to 90 nm. Surface morphology was studied using a scanning electron microscope and no cluster was observed. The elemental composition of synthesized samples was verified by using energy dispersive spectroscopy and no other elements were detected in the ferrites. Owing to interatomic vibrations in tetrahedral and octahedral sites of present samples two absorption bands were formed which were detected from the spectrum produced by means of Fourier transform infrared spectroscopy. Conductivity of Sm substituted nickel copper ferrites was determined by studying the variation of DC resistivity of ferrites with the temperature. Maxwell–Wagner interfacial polarization in present samples was detected through the use of dielectric spectroscopy and declined when the applied frequency was raised. Dielectric characteristics such as change in dielectric constant, dielectric loss, and AC conductivity versus frequency were studied.

In this study, porous Co₃O₄ nanoparticles (NPs) were synthesized through solution combustion synthesis (SCS) method. Precursor cobalt nitrate hexahydrate as the oxidizer and glycine as the fuel were used, focusing on the regular alterations to the fuel-to-oxidizer (F/O) ratio so as to achieve the desired characteristics of the produced nanoparticles in terms of their morphology and structure. XRD analysis confirmed the formation of spinel-phase Co₃O₄ with an average crystallite size of approximately 40 nm. SEM imaging revealed an interconnected nanoporous structure with pore sizes ranging from 100 to 500 nm. Raman spectroscopy identified a strong F₂g mode at 600 cm^–1, corresponding to asymmetric stretching vibrations of oxygen atoms coordinated to tetrahedral cobalt ions. Co₃O₄ NPs have been widely reported for their applications in catalysis, energy storage, and environmental remediation due to their superb electrochemical performance and stability. Through examining the effects of varied F/O ratios, this work aimed to extend the knowledge on how the synthesis parameters could be utilized to optimize the characteristics of Co₃O₄ NPs towards advanced technological uses. The results will be significant for enhancing functional materials, catalysts and the creation of energy conversion and storage systems of the future.