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

In this study, the initial materials including aluminum nitrate nonahydrate and silicon powder were used to produce alumina–mullite composite through solution combustion synthesis (SCS). This paper aimed to investigate the influence of ammonium nitrate added as co-fuel to urea on the formation of alumina–mullite. For this purpose, ammonium nitrate/urea ratios of 0, 0.2, 0.4 and 0.5 were used for SCS. It was revealed through thermo-chemical calculations that increasing this ratio enhances the adiabatic temperature of combustion and facilitates the formation of crystalline mullite that is confirmed by structural analysis. XRD patterns showed that with increasing ammonium nitrate/urea ratio, the mullite peaks are intensified, and its trend is into the crystalline structure. Hence the mullite volume fraction increased from 4.12 to 30.52%. SEM studies showed that this ratio decreases a mean particles size from 264 to 133 nm.

The influence of mechanical activation and amount of added Mn on SHS process in the ternary Ni–Al–Mn system was studied. Dependences of maximum combustion temperature, burning velocity, and sample elongation on the Mn concentration for activated and non-activated mixtures were constructed. Phase composition and morphology of combustion products were characterized by XRD and SEM.

A discrete 2D model of combustion process in donor–acceptor mixture consisting of activated and non-activated reaction cells was proposed. The influence of the activated composition fraction and cell size on the burning velocity of a combined mixture was analyzed. Calculations showed that an increase in the activated composition fraction elevates the average burning velocity. It was found that burning velocity vs cell size dependence passes through a maximum.

Unsteady spatial modes of gasless combustion in parallelepiped-shaped sample containing two powder mixtures separated by low-melting inert layer were numerically modelled. Samples with square cross section were found to burn both in stationary and in unsteady periodic modes depending on the thermal conductivity of the inert inner layer. Combustion of sample with an active inner layer in quasi-stationary control modes when the average burning velocities of the donor and acceptor mixtures are the same were studied.

Ultra-high-temperature Ta₄HfC₅–HfB₂ composites were prepared by electrothermal explosion (ETE) under pressure in a one-stage process, with special emphasis on the influence of high-energy ball milling (HEBM) of starting Ta–Hf–C–B powder mixtures. Synthesized Ta₄HfC₅–HfB₂ composites had a grain size smaller than 0.2 μm and a porosity of 10–12%. A synthesized composite has high temperature resistance at heating in the flame of an oxygen-acetylene burner.

Nanocomposites of nickel oxide/yttria-stabilized zirconia (NiO/YSZ) particles were synthesized via solution combustion synthesis using glycine and urea as fuels in one step. The powders were characterized by X-ray diffraction (XRD) analysis, where the synthesis with urea showed the formation of the NiO/YSZ composite, while the presence of Ni with NiO/YSZ were observed when the glycine was used. The morphology of the as-prepared powders and the presence of Ni were corroborated by field emission scanning electron microscopy and energy dispersive X-ray spectroscopy (FE-SEM; EDX). The powders showed catalytic behavior which was evidenced by H₂-TPR measurements. These materials could be used for the fabrication of Ni/YSZ anode for fuel cells.

This work explains the different ratio of the burning velocities of powder and granulated 5Ti + 3Si mixtures with Ti particles 35 and 120 μm in size due to the influence of impurity gases, which depends on the conditions for heating up the particles ahead of the combustion front. For the first time, the burning velocity inside the granule was obtained using the measured combustion velocities of mixtures of different granule sizes 0.6 ≤ D ≤ 1.7 mm. It turned out to be equal to the velocity of the combustion front in the granulated mixture for fine Ti particles and the velocity of the combustion front in the powder mixture for coarse Ti particles. The difference in the burning rates of the substance of granule and powder mixture serves as a quantitative measure of the influence of impurity gases. The results confirmed the applicability of the developed conditions for heating up the powder components to predict the retarding effect of impurity gases on the synthesis velocity in 5Ti + 3Si powders.

Regularities of combustion of Co₃O₄/Cr₂O₃/WO₃/MoO₃/C/Al mixtures with additive of Ti under the action of artificial gravity were studied. At the centrifugal acceleration of more than 40 g, combustion products were obtained as two-layer ingots of target CoTiCrWMoCAl alloy (lower) and Al₂O₃ slag (upper). Variation in the amount of additive (up to 17 wt %) affected the composition and structure of cast CoTiCrWMoCAl alloy. SHS-produced alloys were characterized by XRD, SEM, and EDS. CoCrWMoCAl alloy containing 5% Ti was used for preparing powder by vacuum induction melting followed by inert gas sputtering. It was shown that the chemical compositions of powder and its precursor are the same.

The influence of Mn addition on combustion synthesis, morphology, phase composition, and magnetic properties of the Ni–Al–Mn alloys was investigated. Ni–Al–xMn alloys with various Mn concentration (x = 0–1.5) were prepared by combined use of mechanical activation and self-propagating high-temperature synthesis (SHS). It was found that the phase composition of synthesized alloys is changed by increasing Mn content, which in turn causes the change in magnetic properties. Ni–Al–0.5Mn alloy at room temperature showed the normal σ–H curve typical of conventional ferromagnetic materials. The maximum values of coercive force (179.7 Oe) and specific magnetization (0.8 emu/g) were observed for alloy containing 24 wt % Mn.