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

A coupled model of solid-phase combustion was formulated for the conditions of plane stressed and plane deformed state. It was shown that the influence of coupling on the stationary combustion wave in these two cases exhibits different effects, which is reflected in the change in the effective parameters. The possibility of synthesizing in situ composites of Al–Ni–Fe₂O₃ and Al–Ti–Cr₂O₃ mixtures on a substrate, which responded differently to changes in the reaction conditions, was demonstrated. Laser radiation was used to initiate combustion. It is possible that continuous control of laser radiation will stabilize the process when the reaction conditions change.

Stages of structure/phase formation in Ni + Al powder mixture enclosed in a steel cartridge in the course of hot gas extrusion (HGE) were studied. It was shown that the formation of target NiAl phase is preceded by the appearance of NiAl₃, Ni₂Al₃, and Ni₃Al phases. It was determined that the phase composition is formed prior to the onset of plastic deformation and retains constant in the course of extrusion process; meanwhile, the structure undergoes the changes, its grains are deformed, taking an elongated shape. It was found that HGE is characterized by a redistribution of elements. It can be assumed that to increase the target phase yield, it is necessary to compensate or eliminate the redistribution of elements.

Since the critical temperature of MgB₂ (39 K) is the highest in the superconductors and the chemical composition and crystal structure are very simple as compared to high temperature superconductors, MgB₂ has attracted a lot of attention in the world. This paper is a brief study of self-propagating high-temperature synthesis of MgB₂ superconductor. Sample preparation, ignition mode, and relationship between structure and magnetic properties of finals SHS products were identified. This method has demonstrated significant success in the synthesis of MgB₂ superconductor and the introduction of pinning centers into the superconducting matrix is practice to improve superconducting properties.

Co-containing blue spinel pigments of the system ZnO–Co₃O₄–Mg(NO₃)₂·6H₂O–Al₂O₃–Al were prepared by combined use of SHS and mechanochemical activation (MA). IR spectroscopic studies revealed the following processes that accompany the MA: release of water from magnesium nitrate hexahydrate, as evidenced by absorption bands related to free water; phase transformation γ-Al₂O₃ → α-Al₂O₃; and nucleation of spinels. MA was shown to affect the combustion parameters. The combustion products derived from non-activated and activated charges were characterized by XRD, SEM, and optical metallography. It was found that SHS in combination with MA improves the color of pigments due to an increase in the completeness of the conversion of reactions.

Highly dispersed ceramic composites Si₃N₄–SiC were prepared by SHS under 4 MPa of nitrogen pressure from powder mixtures containing silicon, halide salt Na₂SiF₆, carbon, and sodium azide (NaN₃) as a nitriding reagent. Variation in the silicon and carbon content in the green mixture affected the process parameters, structure, and phase composition of combustion products. It was found that the combustion product containing no more than 10% SiC represents a mixture of ultrafine equiaxed and fiber-like particles, and its composition coincides with the theoretically calculated one. At the SiC content more than 10%, the product compositions were distinctive from the theoretical compositions by a lower SiC content and had α- and β-Si₃N₄ in almost equal amounts. Their structure was shown to contain ultrafine (150–300 nm) and coarse (up to 5 μm) particles.

The influence of geometric factors on the filtration combustion of metal powder layer was mathematically modelled and experimentally studied. The structure and stability of combustion front of porous sample were studied in conditions of compression and stretching of the reaction zone. Experimental methods were used to study the change in the structure of a cellular front during the combustion of variable cross-section titanium powder layer.

Ti₃AlC₂–Al cermets were produced by a new method combining SHS and spontaneous infiltration. SHS was applied to obtain a ceramic Ti₃AlC₂ MAX phase with a porous structure, which in the hot state was brought into contact with Al melt and Al-based melts for spontaneous high-temperature infiltration. The optimum time delay between the end of combustion and the start of infiltration with melt was found to be 7–8 s. This time pause was shown to be enough to complete the structure formation of MAX phase in the porous skeleton and to spontaneously infiltrate the pores with melt. Upon infiltration with pure Al melt, Ti₃AlC₂ MAX-phase was shown to completely decompose to TiC and TiAl₃. The presence of 12% Si or 32% Cu in Al melt contributed to the partial retention of Ti₃AlC₂ in SHS cermet. It was found that the yield stress of cermets obtained by infiltration of SHS skeleton with Al–12% Si melt is 410 MPa that exceeds that for pure Al–12% Si alloy (~260 MPa) by approximately 58%.

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.