International Journal of Self-Propagating High-Temperature Synthesis

We report on preparation of porous refractory ceramics from natural quartz sand and industrial wastes (fly ash and wastes of concrete production) by SHS in a mode of thermal explosion with preliminary mechanochemical treatment of charge mixtures in the presence of carbonaceous modifying agents (activated carbon and polystyrene). The Al2O3–AlN-based composite synthesized in optimized conditions exhibited low thermal conductivity [0.185–0.228 W/(m K)], finely porous structure, and high compression strength (30–96 MPa).

CaF2:RE phosphors have received attention of several research workers. CaF2:Sm2+ is well known as a solid-state laser material. CaF2:Dy and CaF2:Tm phosphors are used as phosphors for dosimetry of ionizing radiations through thermoluminescence. A new route to preparation of CaF2 by solid-state metathesis is reported. The method is very fast and CaF2 could be prepared in 10 min. Intense emission attributable to uranate group was observed in synthesized uranium-doped samples.

Powders of cubic niobium nitride δ-NbN x with a particle size of below 20 μm were prepared by reactive diffusion at T = 1455−1475°C under nitrogen pressures of P 1(N2) = 0.1−3 MPa and P 2(N2) = 25 MPa. For these powders, the values of the stoichiometric coefficient x, lattice parameter a, and the superconducting transition temperature Tc were measured and the a(x), T c(x) and T c(a) functions were analyzed. The T c values were found to linearly grow with increasing a (decreasing structure imperfection). A maximum value of T c (15.8 K) corresponded to a maximum value of a (4.3934 Å). Maximain the a(x) and T c(x) curves were found to correspond to a slightly substoichiometric nitride with x = 0.98. Having synthesized cubic niobium nitrides with 0.892 < x < 1.062, we managed to measure the dependences of a and T c on x all over the almost entire homogeneity range for δ-NbN x . Our a(x) and T c(a) functions were found to reasonably agree with those previously reported for SHS-produced δ-NbN x powders.

Numerically modeled are thermal conditions during the process of SHS extrusion of thick (above 3 mm in diameter) and relatively long (above 100 mm in length) rods.

Adsorptivity of some organic compounds to the copper nanoparticles prepared using the levitation-jet generator was characterized by inverse gas chromatography. The measured values of a specific volume of retained sorbate were used to calculate adsorption heats and entropy factors of the process.

Stepwise densification of non-activated and mechanically activated Ni-Al blends was used to prepare green compacts with an ordered structure. The latter ones were then used to explore combustion synthesis in these mixtures with special emphasis on the possibility of inheriting a structure of green compact by a combustion product. It has been demonstrated that, at some certain conditions, an ordered structure of green compact can be inherited by a combustion-synthesized product. This observation can be expected to open up new horizons for synthesis of new intermetallics with an ordered macrostructure.