V. S. Shevchenko

A study of the mechanochemical synthesis of TlCl nanoparticles by the method of dilution with the final product

The kinetics of the solid-state mechanochemical synthesis of the nanosized product (TlCl) in the reaction 2NaCl + Tl2SO4 + zNa2SO4 = (z + 1)Na2SO4 + 2TlCl was studied experimentlaly. The method used was based on the dilution of the initial mixture of powdered reagents (2NaCl + Tl2SO4) with another exchange reaction product (Na2SO4) at the optimum theoretically estimated z value, z = z* = 11.25. Several special features of the development of this reaction were established. The parameters of the kinetic curve obtained for the mechanochemical synthesis of the desired product were compared with those of the kinetic curve determined theoretically for the model reaction KBr + TlCl + zKCl = (z + 1)KCl + TlBr with z = z1* = 13.5. This allowed us to experimentally estimate the mass transfer coefficient in a mechanochemical reactor by mobile milling bodies. This estimate was obtained for the first time. The dynamics of changes in the size of desired product nanoparticles depending on the time of mechanochemical activation in an AGO-2 ball planetary mill was studied.

Application of Mechanically Stimulated Combustion Reactions in Processing of Geological Materials

Based on the literature review, the use of methods for metallothermy and self-propagating high-temperature synthesis is considered for processing different geological materials. Combination of mechanochemistry and these methods allows to avoid agglomeration of the products due to high temperature. Mechanically stimulated exothermic processes proceed both in combustion regime and at lower temperature, which makes it possible to combine opening and processing of mineral and technogenic raw material with production of highly dispersed materials.

Growth of MBO3 (M = La, Y, Sc) and LaSc3(BO3)4 crystals from LiBO2-LiF fluxes

The solubility of rare-earth orthoborates and LaSc3(BO3)4 in LiBO2-LiF solvents has been studied. Spontaneous crystals have been grown and the solvent used has been shown to be attractive for the growth of bulk crystals at t ≤ 1000°C. The α- and γ-phases of LaSc3(BO3)4 have been shown to be identical.

Influence of mechanical activation on the properties of the charge for growing NaBi(WO4)2 and ScBaNa(BO3)2 single crystals

A comparative study was performed on the influence of “pollution-free” mechanical activation (without abrasive-reactive wear of the milling tools of mechanochemical reactors) in oxide-carbonate-acid systems on synthesis and the properties of the charge for growing of bulk crystals.

KBaR(BO 3 ) 2 orthoborates (R = REE): Synthesis and study

The search for compounds with the formula composition KBaR(BO3)2 has been performed by solid-phase synthesis and differential thermal analysis. The compounds synthesized in this series are KBaPr(BO3)2 and KBaNd(BO3)2, which are isostructural to KBaY(BO3)2, are isotypical to butschliite K2Ca(CO3)2, and crystallize in a trigonal system with space group R3m. The structural characteristics of compounds calculated for the entire series of REEs are given.

Synthesis of New Isostructural Orthoborates NaBaR(BO3)2 with R = Tb, Dy, Ho, Er, Tm and Lu

Six new rare-earth orthoborates NaBaR(BO3)2, with R = Tb, Dy, Ho, Er, Tm, Lu were synthesized using a multiple-step solid-state reaction. These new orthoborates continue the previously described isostructural lines of three-cation orthoborates NaBaR(BO3)2, by R = Sc, Y, Yb. The structure of synthesized solid compounds is isotypic with the mineral eitelite, Na2Mg(CO3)2, crystallizing in the trigonal system with space group R3. All prepared borates are isostructural, as evidenced by the presence of the same vibration modes in Raman spectra and of the same diffraction peaks in X-ray patterns. The photoluminescence of NaBaTb(BO3)2 have been investigated in a detail.

Chemical reactions and phase equilibria in BaB2O4-MF (M = Li, N, or K) systems

Chemical processes and phase equilibria in BaB2O4-MF (M = Li, Na, or K) systems were studied. Liquidus curves for these sections were constructed. The primary crystallization field of the low-temperature barium borate phase (β-BaB2O4) for the BaB2O4-(LiF)2 system was found to lie in the range 65-50 mol % BaB2O4; for the BaB2O4-NaF system, in the range 70-52.5 mol % BaB2O4; and for the BaB2O4-KF system, 65-50 mol % BaB2O4.

Mechanochemical synthesis of noncentrosymmetric compounds in oxide systems

We study the influence of anomalous anisotropy in the elastic constants of paratellurite (α-TeO2) on the rate of the following mechanochemical reactions: Bi2O3 + SeO2 = BiSeO5; Bi2O3 + TeO2 = Bi2TeO5; SeO2 + TeO2 = TeSeO4. The formation of the following compounds was registered by means of X-ray analysis and thermal annealing: Bi6SeO11, Bi2TeO5, and TeSeO4.

Phase equilibria in the ternary reciprocal system Li, Ba // BO2, F and growth of bulk β-BaB2O4 crystals

In order to find the optimum solvent for the growth of nonlinear optical β-BaB2O4 crystals, the phase relationships in the ternary reciprocal system Li, Ba // BO2, F have been studied using solid state synthesis, differential thermal analysis and X-ray powder diffraction. Isothermal and polythermal sections of the system Li, Ba // BO2, F are reported. In the studied system, the following compounds are formed: LiBa2B5O10 (melts by peritectic reaction at 930°C, i.e. 1203 K) and LiBaF3 (melts incongruently at 850°C, i.e. 1123 K). Visual polythermal analysis of seeding and growth of β-BaB2O4 crystals in this system was carried out. The primary crystallization field of β-BaB2O4 was defined. Using the top-seeded pulling technique, a β-BaB2O4 crystal of 93 mm in diameter, 34 mm in height and 520 g in weight has been grown.

Preparation of double Y-Sc orthoborates by means of mechanical activation

Mechanical activation was used to prepare new YSc(BO3)2 and Y3Sc(BO3)4 double borates from the Y2O3-Sc2O3-HBO2 system. The existence of two series of solid solutions of yttrium-scandium borates based on the YBO3 or ScBO3 structure is established. It is shown that a morphotropic transition occurs in the range of Y/Sc = 1.5−1.