Vol 59, No 9 (2023)

Experimental temperature-dependent density data for boron have been used to evaluate its linear thermal expansion coefficient. Applying the mixing rule to components of amorphous alloy, we have estimated the thermophysical properties of amorphous Fe80B20 alloy in the locally equilibrium two-phase region model. The dominant role of iron atoms in the formation of a disordered medium has been demonstrated. The theoretical results obtained in this study are prognostic and require experimental verification.

We report the preparation of molybdenum–tungsten alloy powders via magnesium and calcium vapor reduction of the Mo0.3W0.7O3, MgМо0.7W0.3O4, and CaМо0.7W0.3O4 compounds in the temperature range 750–880°C at residual pressures in the reactor from 5 to 15 kPa. The specific surface area of the Mo–W alloy powders prepared by reducing Mo0.3W0.7O3 slightly exceeds that of the mixture of metal powders obtained by reducing a mixture of WO3 and MoO3 under similar conditions. The specific surface area of the Mo–W alloy powders prepared via magnesium vapor reduction of the CaМо0.7W0.3O4 and MgМо0.7W0.3O4 compounds exceeds that in the case of calcium vapor reduction. We have obtained molybdenum–tungsten alloy powders having lattice parameters of 0.3153 ± 0.0001 and 0.3160 ± 0.0001 nm and ranging in specific surface area from 9 to 22 m2/g. The average crystallite size of the alloys, evaluated using the Scherrer formula, lies in the range 12–35 nm. The powders have a mesoporous structure.

Nanostructured Li4Ti5O12-based composites in the form of microspheres consisting of randomly packed prism-like particles have been prepared via hydrothermal treatment of TiO2 xerogel in aqueous LiOH solutions, followed by calcination of the reaction products at t ≥ 550°C. The phase composition of the hydrothermally prepared spherical particles has been shown to correspond to α-Li2TiO3. According to elemental analysis data, the titanium and oxygen were nonuniformly distributed over the microspheres. Sequential calcination of the microspheres at t ≤ 750°C led first to the α-Li2TiO3 → β-Li2TiO3 phase transformation and then to the formation of nanostructured Li4Ti5O12 spinel or spinel-based composites (Li4Ti5O12/TiO2 and Li4Ti5O12/β-Li2TiO3). The Li4Ti5O12 microspheres calcined at 750°C consisted of not only the major crystalline phase but also X-ray amorphous TiO2 (anatase) and β-Li2TiO3 as impurity phases, which could not be detected by X-ray diffraction.

We have studied the effect of sodium fluoride as a sintering aid for β-sialons on the phase composition and physicomechanical properties of Si5AlON7 and Si4Al2O2N6. Two-step high-temperature firing of the β-sialons in the presence of NaF under a nitrogen atmosphere has been shown to cause no significant changes in the phase composition of the materials. The density and microhardness of the materials prepared using 0.5 and 5.0 wt % NaF are lower than those of the materials prepared without sintering aids, but the bending strength is higher by up to 14.3% in the case of Si5AlON7 prepared using 0.5 wt % NaF and by 4.9% in the case of Si4Al2O2N6 prepared using 5.0 wt % NaF.

Using LaBWO6 as a host, we have prepared a series of erbium-doped lanthanum borotungstates (LBTs), La1 – xErxBWO6, and Yb/Er-codoped La1 – x – yYbxEryBWO6, which crystallize in monoclinic crystal system (sp. gr. P21). The materials have been synthesized by ceramic route and a sol–gel (Pechini) process, followed by annealing. We have studied the spectral properties of the synthesized LBTs exhibiting the luminescence in the green spectral region upon the excitation in the near-infrared region. The highest efficiency, with Ben = 0.55%, has been obtained for La0.97Yb0.02Er0.01BWO6 composition. Sol–gel synthesis (Pechini process) has been shown to be the optimal approach for the preparation of such phosphors. Due to a combination of high upconversion efficiency and thermal stability, the synthesized upconversion phosphors can be used for the design of white light sources pumped in the near-IR spectral region.

Using content analysis and the Python programming environment, we have found a number of general relationships determining the thermal properties of fluoride and modified fluoride glasses. Their compositions have been classified according to their glass transition temperature (Tg) and the difference between their crystallization onset temperature (Tx) and glass transition temperature: Tx – Tg. The use of Kauzmann’s rule for fluoride glasses, unmodified and modified with other halogens, has been shown to be more reliable if the Tg/Tm ratio is used, compared to the Tg/Tl ratio. We have qualitatively assessed how anion modification influences characteristic temperatures (glass transition temperature Tg, crystallization onset temperature Tx, crystallization peak temperature Tc, melting onset temperature Tm, and liquidus temperature Tl) and crystallization stability criteria (Hruby criterion K, Saad–Poulain criterion S, reduced thermal stability interval H, thermal stability interval Tx – Tg, and reduced glass transition temperatures Tg/Tm and Tg/Tl).

The CsZr2(PO4)3 phosphate isostructural with the mineral kosnarite has been prepared via sol–gel synthesis at 900°C, and ceramics based on this phosphate have been produced by spark plasma sintering. The relative density of the ceramics has been determined to be 75.5%. The chemical stability of the ceramic materials has been assessed at 90°C in static mode in distilled and mineral water, weakly acidic solution, and weakly alkaline solution. The minimum rates of Cs leaching were ~10–5 to 10–4 g/(cm2 day). We have assessed the effect of contact medium on the mechanism of cesium leaching from the CsZr2(PO4)3 ceramics.