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Manufacturing W-Cu composite nanopowders was performed via joint reduction of CuO and WO3 oxides with various ratios (W:Cu = 2:1, 1:1, 1:3, 1:13.5) using combined Mg–C reducer. Combustion synthesis was used to synthesize homogeneous composite powders of W-Cu and hot explosive consolidation (HEC) technique was utilized to fabricate dense compacts from ultrafine structured W-Cu powders. Compact samples obtained from nanometer sized SHS powders demonstrated weak relation between the susceptibility and the applied magnetic field in comparison with the W and Cu containing micrometer grain size of metals. The density, microstructural uniformity and mechanical properties of SHS&HEC prepared samples were also evaluated. Internal friction (Q-1) and Young modulus (E) of fabricated composites studied for all samples indicated that the temperature 1000 °С is optimal for full annealing of microscopic defects of structure and internal stresses. Improved characteristics for Young modulus and internal friction were obtained for the W:Cu = 1:13.5 composite. According to microhardness measurement results, W-Cu nanopowders obtained by SHS method and compacted by HEC technology were characterized by enhanced (up to 85%) microhardness.

Chemoselective transformations of functionalized sulfonyl fluorides and chlorides are surveyed comprehensively. It is shown that sulfonyl fluorides provide an excellent selectivity control in their reactions. Thus, numerous conditions are tolerated by the SO2F group – from amide and ester formation to directed ortho‐lithiation and transition‐metal‐catalyzed cross‐couplings. Meanwhile, sulfur (VI) fluoride exchange (SuFEx) is also compatible with numerous functional groups, thus confirming its title of "another click reaction". On the contrary, with a few exceptions, most transformations of functionalized sulfonyl chlorides typically occur at the SO2Cl moiety. [ABSTRACT FROM AUTHOR]

We have investigated the laws of technological combustion of (SiO + Al) and (SiO + CaSiO + Al) systems with the combustion reaction activated by preliminary mechanochemical treatment of the charge components with various modifying additives containing bound water, carbon, and amino groups. It has been shown that modifying the charge components in the regime of mechanochemical treatment leads to a change in the induction period of ignition, the combustion kinetics, and the thermodynamic characteristics of the process, which promotes intensification of the development of redox reactions and more complete conversion of the charge mixture components. [ABSTRACT FROM AUTHOR]

Nanopowders of nickel-doped β-silicon carbide (β-SiC) with improved dielectric properties (compared with pure β-SiC) were successfully produced using the mechanically activated selfpropagating high-temperature synthesis method in an argon (Ar) atmosphere. The molar substitution of nickel (Ni) for silicon (Si) was 1%, 3%, and 5%. Powders of poly(tetrafluoroethylene) and ammonium chloride (NH4Cl) were used to promote the combustion reaction. The experimental results indicated an active role of Ni in the mechanism of combustion synthesis of SiC powders, which was reflected in the increase in combustion temperature and the velocity of propagation of the combustion wave, the microstructure of the produced nanopowders with a grain size of 100 nm for 5% Ni, and an improvement in the dielectric properties, specifically the increase in real (ϵ') and imaginary parts (ϵ'') of the complex permittivity, in the frequency range of 8.2-12.4 GHz, compared with pure SiC. The X-ray analysis of the produced powders suggests that Ni is accommodated in the lattice of SiC, which shrinks with increasing amounts of Ni. [ABSTRACT FROM AUTHOR]

Phase and structure formation processes occurring in the system Al – MgCO3 – SiO2 in the course of selfpropagating high-temperature synthesis are examined. The dependences of the structure and the phase composition of the composite materials formed on the ratio of the initial components are determined. It is shown that self-propagating high-temperature synthesis can be used to produce ceramic composite materials based on the spinel and silicon carbide phases. [ABSTRACT FROM AUTHOR]

The internal and external surfaces of a percolation cluster, as well as the total surface of the entire percolation system, are investigated numerically and analytically. Numerical simulation is carried out using the Monte Carlo method for problems of percolation over lattice sites and bonds on square and simple cubic lattices. Analytic expressions derived by using the probabilistic approach describe the behavior of such surfaces to a high degree of accuracy. It is shown that both the external and total surface areas of a percolation cluster, as well as the total area of the surface of the entire percolation system, have a peak for a certain (different in the general case) fraction of occupied sites (in the site problem) or bonds (in the bond problem). Two examples of technological processes (current generation in a fuel cell and self-propagating high-temperature synthesis in heterogeneous condensed systems) in which the surface of a percolation cluster plays a significant role are discussed. [ABSTRACT FROM AUTHOR]

Alumina/silicon carbide composites were synthesized by the microwave induced SHS (Self-propagating High-temperature Synthesis) process. SiO2/Al/C powders were used as starting materials and samples were ignited by using a 2.45 GHz multimode home microwave oven (700W). Effects of the mixing ratio of SiO2/Al/C powders, reaction environments, and weight percent of KNO3 as a reaction promoter on the formation of the final product were studied. [ABSTRACT FROM AUTHOR]

The combustion of a mixture of molybdenum and carbon activated by a high-energy magnesium–fluoroplastic mixture was studied. The adiabatic combustion temperature and the equilibrium compositions of the combustion products were calculated and, experimental dependences of the combustion temperature and rate on the main parameters of the process are obtained. It is shown that the activation of the formation of molybdenum carbides is of a thermal nature. The two observed mechanisms of formation of molybdenum carbides are found to differ in combustion temperature: at T < 2470 K, formation of carbides proceeds by a diffusion mechanism, and at T > 2470 K it proceeds by crystallization from a melt. The possibility of synthesis of single-phase Mo2C in the combustion regime is shown. [ABSTRACT FROM AUTHOR]

The mechanism of initiation and combustion of the 3SiO2-4Al-3C system is studied under conditions of activation of the combustion reaction by a high-energy additive of Al+αKNO3. It is shown that combustion of this system is possible only when a certain quantity of the additive is introduced into the starting mixture. The mechanism of activation of the reaction is established, and the processes involved in the reduction stage of the combustion are shown to play a leading role in the reaction. Optimal conditions for synthesis of a SiC/Al2O3 composite powder containing SiC fibers are determined. [ABSTRACT FROM AUTHOR]