AbstractThis 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.

AbstractThe combustion dynamics of Ni–Al twisted wires under (1.0–3.0) × 105 Ра of oxygen was studied by using rapid video filming and time-resolved spectrometry. Burning velocity and combustion temperature were found to grow with increasing oxygen pressure within the range 30–35 cm/s and 3125–3361 K, respectively. The formation of high-temperature (up to 4900 K) gas-dust phase around the reaction zone was observed. The present results are discussed in comparison with those previously obtained for combustion of the same twisted wires in argon and air. Out results shed new light on the kinetics of metals combustion and may turn useful in designing new energetic ingredients for solid rocket propulsion and bimetal Al–Ni nanopowders for energetic formulations.

AbstractFor combustion of powdered and granulated 5Ti + 3Si mixtures in a cylindrical channel, we explored the retarding action of impurity gases released from Ti particles of varied particle size. Green mixtures for combustion experiments were prepared from: (a) coarse and fine Si powders and (b) Ti powders of the following fractions: <169 μm, <54 μm, <40 μm, 40–80 μm, 90–125 μm, and 125–200 μm. The behavior of burning velocity in powdered mixtures was rationalized in terms of the CCM theory, while that of granulated ones turned to obey the classical theory for flame propagation in condensed disperse systems. Our results may turn interesting to those engaged in R & D of silicide powders.

AbstractIn this work, we prepared a composite material comprising of Mn and Ag nanoparticles supported on graphene nanoplatelets embedded into a matrix of polyethylene glycol. The synthesized material was tested as a catalyst for pyrolytic conversion of high-density polyethylene into the methane-based gaseous mixture and solid char carbon in a fixed bed reactor and showed good performance.

AbstractCo-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.

AbstractLow-temperature combustion synthesis was used both for modifying silica gel support with 10 and 20 wt % Al2O3 and for producing supported catalysts with 10 wt % of Co active phase. Prepared catalysts were characterized by XRD, SEM, EDS, and BET method. It was revealed that these catalysts contain oxides, aluminates, and silicates of cobalt. It was shown that modification of support noticeably reduces its specific surface, while its calcination decreases the catalyst activity. The catalysts synthesized from supports with lower content of Al2O3 demonstrated higher specific surface and lower activity in deep oxidation of propane and CO. The catalyst on an uncalcinated support modified with 20 wt % Al2O3 was found to possess the highest activity in the process of deep oxidation.

AbstractMacrokinetic parameters of combustion of powder and granular mixtures were studied upon dilution of Ti + C with various metal powders. The combustion velocities of powder mixtures (Ti + C) + 20% Me (Me = Ni, Cu) turned out to be higher than those of Ti + C blend, despite the lower temperature of combustion. When diluting Ti + C mixture with Ti or TiC powders, there was no such a contradiction. The convective-conductive model of combustion explains obtained data by a strong influence of impurity gas release from titanium particles ahead the combustion front. The time of combustion transfer between the granules, the combustion velocity inside the granules, and the quantitative assessment of the retarding effect of impurity gases in powder mixtures were determined. When comparing the combustion parameters of granular Ti + C mixtures diluted with various metal powders and titanium carbide, the efficiency of the combustion transfer between the granules in the presence of hot Ni melt was explained. In addition, the impurity gas reabsorption by titanium carbide was confirmed.

AbstractIn 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.

AbstractComposite powders comprising of SiC, SiO2, C, and Si were prepared by SHS method from starting Si + xC mixtures (x = 0–30 wt %) and characterized by XRD, SEM/EDS, and chemical analysis. In the presence of carbon black, the SiС content of combustion products was found to increase from 23 wt % (at x = 0) to 73 wt % (at x = 30 wt %). Our results may turn interesting to those engaged in R & D of new composites for high-temperature applications.

AbstractA 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.

AbstractUltra-refractory Ta4HfC5 ceramic was prepared by electro-thermal explosion (ETE) under pressure in a one-stage process, with a focus on the influence of high-energy ball milling (HEBM) of starting Ta–Hf–C powder mixtures. Synthesized Ta4HfC5 ceramics had a grain size of below 0.5 μm and a porosity of 10–12%.

AbstractHighly 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.

AbstractSince 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.

AbstractUltra-high-temperature TiC–ZrC composites with submicron structure were synthesized by electro-thermal explosion (ETE) under pressure. The precursors for synthesis were prepared from a mixture containing Ti, Zr, and carbon black powders by high energy ball milling in hexane. The influence of mechanical activation (MA) on the metal crystalline structure was studied. It was shown that the phase composition of the precursor depends on MA duration. The partial amorphization of metal particles occurred after 40 min of MA; while after 90 min, the amorphization was completed. In the last case, carbide phase crystallites with a cubic structure were formed. It was shown that the composite synthesized from precursor activated for 40 min contains Zr0.50Ti0.50C single-phase solid solution with a grain size of 3–5 μm, while the composite synthesized from precursor activated for 90 min consists of Zr0.14Ti0.86C and Zr0.74Ti0.26C phases with a grain size of about 0.2 μm. The Vickers hardness of composites with a residual porosity of no more than 10% was found to be in the range from 11.3 to 18.53 GPa.

AbstractSubmicron-porous ceramic materials were prepared from mixtures consisting of coarse α-Al2O3 filler and ultrafine binders by combined use of SHS, compaction, and sintering. Variation in starting reagent size and filler/binders ratio made it possible to control the porosity, pore size, and permeability of synthesized materials. It was found that in materials with pore size between 0.4 to 1.3 µm, pore size has a dominating influence on their permeability rather than porosity.

AbstractCobalt doped Mg–Zn ferrite (Mg(0.56)Co(0.14)Zn(0.30)Fe2O4) was synthesized by the modified sol–gel auto combustion method (MSG) in which lemon extracts were used as the source of energy. X-ray diffraction (XRD) technique was employed to confirm the formation of cubic spinel ferrite phase. The lattice parameter was evaluated to be 8.39 Å with an average crystallite size ranging from 41–51 nm. Dislocation density, mechanical properties, and hopping length were determined. Crystallite size and strain were evaluated using W–H plot and size–strain plot.

AbstractSHS reaction in non-activated and mechanically activated (Ti + 2B) + x(Fe + Co + Cr + Ni + Al) systems (x = 0–80 wt %) was explored by XRD, SEM, and granulometric analyses aiming at the synthesis of HEA-matrix TiB2 composite. The reaction in non-activated mixtures yielded integral samples of HEA–TiB2 cermet. Reaction in activated mixtures yielded highly porous brittle products. Combustion temperature, burning velocity, and the size of TiB2 grains in resultant material were found to decrease with increasing x. Our results may turn useful to those engaged in R and D of new cermet composites.

AbstractHighly 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.

AbstractThe 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.