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

Ti₃SiC₂–Sn(Pb) cermet was produced by a new method combining SHS of porous Ti₃SiC₂ skeleton and spontaneous infiltration with Sn–10 wt % Pb melt. The effect of the time delay between the end of combustion and the start of infiltration with melt on spontaneous infiltration, density, microstructure, and phase composition of cermet was investigated. It was found that the phase composition of Ti₃SiC₂–Sn(Pb) cermet does not significantly depend on the time delay and consists mainly of Sn, Pb, TiC, and Ti₃SiC₂. It was shown that the compressive strength of the synthesized cermet is 117 MPa that is nearly twice as large as that of Sn–10 wt % Pb alloy (47 MPa).

The possibility of welding between Ti–Al and Ni–Al layers via self-propagating high-temperature synthesis was demonstrated by using the heat released from the exothermic chemical reaction. The applied pressure and the presence of reactive intermediate layers (Cu, Al) are the most important requirements for strong welding. In the TiAl/NiAl system, there is a temperature gradient, and the main heat transfer occurs toward the Ti–Al layer, resulting in increased Ni diffusion. The increased mobility of Ni atoms is due to their smaller atomic radius as compared to Ti. The proposed technique seems attractive for repair operations and deposition of coatings in special-purpose applications.

Ni/TiC catalysts were produced by SHS from granular Ti + C + Ni mixtures and leaching in NaOH solution followed by stabilization with H₂O₂ solution of intermetallic precursors prepared by SHS from TiC + (Ni + Al) mixtures. Prepared granular and powder catalysts were characterized by XRD, SEM, EDS, and BET method. The catalytic activity of catalysts was determined in the temperature range of 150–400°С using the CO₂ + H₂ mixtures with different Н₂ concentration. It was found that catalyst containing 10 wt % Ni leached from precursor with Ni : Al = 1 : 2 possesses the highest hydrogenating activity at 350°С and 20 vol % H₂.

High-temperature interaction of 30 wt % Cu–70 wt % Ag eutectic alloy with carbon fibers was studied. It was shown that Cu–Ag drops coated with carbon film are formed on the surface of carbon fibers. Carbon atoms dissolved in the molten Cu–Ag phase precipitated out on the drop surface at a lower temperature, thus resulting in growing few-layer graphene. Cu–Ag–carbon fibers composites sintered at 670°C was shown to represent a porous structure containing spherical Cu–Ag particles and carbon fibers. It was revealed that as C is added, the electrical resistivity of sintered samples decreases. Raman spectra of sintered composites containing 3.0 and 6.3 wt % C showed the formation of a multilayer graphene coating with a disordered structure.

The effect of various conditions of mechanical activation of Ti + Zr + Hf + Nb + Ta + 5C mixtures on the microstructure of composite particles, regularities of their ignition, and phase composition of final products was studied. The activation of mixtures was found to decrease the ignition temperature by 600–900°C. It was shown that the intense mechanical activation reduces the activity of the mixture and the subsequent ignition in the thermal explosion mode transforms the mixture into high-entropy compound. Such transformation is not observed in conditions of long-term low-intensity activation.

In this review, SHS method for preparing mineral-like matrices for immobilization of high-level radioactive waste (HLW) was considered. Matrices for immobilization of different types of solid HLW were presented. Matrices based on pyrochlore, zirconolite, perovskite, garnet, pollucite, and titanium carbide were prepared by SHS process. Studies showed that SHS process seems promising for immobilization of different HLW in mineral-like matrix systems for their environmentally safe disposal.

For the first time, a comparative study of the macrokinetic combustion parameters for granular and powder Ti + C and (Ti + C) + 20% Ni mixtures with variation in Ti particle sizes from 31 to 142 µm was carried out. It was found that the combustion velocity of (Ti + C) + 20% Ni powder mixture is 2–3 times higher than that of Ti + C mixture, in spite of the lower combustion temperature. The data obtained contradict theoretical concepts about the dependence of the combustion velocity on the maximum temperature, which leads to a formal negative value of the activation energy of combustion. In the convective–conductive model of combustion, these unusual results are explained by the strong effect of impurity gas release on the combustion velocity. For Ti + C and (Ti + C) + 20% Ni compositions, the conditions for heating particles of powder mixtures in the combustion wave warm-up zone were experimentally confirmed. The values of the reaction front velocity inside the granules were calculated using values of combustion velocities of samples with granules 0.6–1.7 mm in diameter for different sizes of Ti particles. They turned out to be several times higher than combustion velocities of powder mixtures with the same composition. The ratio of the values of the combustion velocity of the substance of the granules to the burning front velocity in the powder mixture can serve as a quantitative measure of the effect of the release of impurity gases on the burning velocity of powder mixtures. For both mixture compositions, the same power function ~d^–0.9 approximates dependences of the combustion velocity inside the granules on the Ti particle size, which indicates the leading role of the Ti + C reaction in the propagation of the combustion wave.

NiTi samples with a density of 6.65 g/cm³ were prepared by forced SHS compaction from Ni + Ti powder mixture in an equiatomic ratio. Synthesized alloy was studied by scanning electron microscopy and X-ray diffraction analysis. It was shown that SHS-compacted sample contain NiTi (B2 + R) in addition to secondary phases: Ti₂Ni, Ni₄Ti₃, and Ni. Electrical resistivity as a function of temperature in the range of 290–1150 K was studied.

Highly porous Y₂O₃ based ceramic with nanoscale pores was prepared from an ultrafine mixture containing Y₂O₃ powder as a filler and additives (MgO, SiC, and SiO₂) as binders by combined use of compaction and thermochemical synthesis. The synthesized material was characterized by XRD/SEM and revealed to consist of Y₂O₃, Y₂SiO₅, MgO, and Si. Physical and mechanical properties such as specific surface area, density, compressive strength, and permeability were determined.

A comparative analysis of the combustion profiles of SCS of lithium aluminate from a solution of aluminum nitrate and lithium nitrate or carbonate with glycine, leucine, and urea was performed. The influence of the starting solution composition on the maximum combustion temperature and combustion profile was considered. It was found that maximum combustion temperature, 771°C, is observed in case of synthesis of nitrate solution with glycine and urea (1 : 3). The appearance of ballast lithium aminoacetate during syntheses of aluminum nitrate with lithium carbonate and glycine was shown to reduce the maximum combustion temperature by almost 100°C. Replacing lithium nitrate with lithium carbonate decreased the temperature at which γ-LiAlO₂ started to form and made it possible to obtain monophasic α-LiAlO₂ after heat treatment at 500–550°C.