Vol 59, No 8 (2023)

We have proposed compositions of titanyl hydrogen phosphate-based sorption materials modified with zirconium(IV) cations and containing both cation and anion exchange functional centers, represented by НРО
 and OH– groups, respectively. The synthesized materials were tested in sorption of antimony(III) cations and anions from high-salt solutions. Increasing the concentration of functional groups in ion exchange matrices has been shown to increase their affinity for antimony(III) ions. Such compositions can be regarded as promising ion exchange materials for efficient extraction of antimony radionuclides from multicomponent high-salt liquid radioactive waste.

In this paper, we report the synthesis of crystalline platinum ditelluride, PtTe2, a synthetic analog of the mineral moncheite, and its thermodynamic properties. Using the isobaric heat capacity of PtTe2 determined in the range 2–305 K by the relaxation and adiabatic calorimetry methods, we have evaluated its standard thermodynamic functions: entropy, enthalpy increment, and reduced Gibbs energy. The following parameters have been obtained for PtTe2 at 298.15 K: 
 = 75.11 ± 0.15 J/(K mol), S° = 121.5 ± 0.2 J/(K mol), Н°(298.15 K) − Н°(0) = 16.69 ± 0.03 kJ/mol, and Ф° = 65.55 ± 0.13 J/(K mol). Using data in the literature and handbooks, we have estimated the standard Gibbs energy of formation of PtTe2: ΔfG°(PtTe2, cr, 298.15) = –75.4 ± 0.8 kJ/mol. Fractal analysis of the heat capacity data indicates that PtTe2 has a layered structure and that its Debye temperature is 250 K.

We present results of a detailed study of defect formation processes and their effect on the optical properties of gadolinium aluminum gallium garnet crystals with partial aluminum substitution for gallium in the cation sublattice—Gd3Al1Ga4O12 (Al : Ga = 1 : 4), Gd3Al2Ga3O12 (Al : Ga = 2 : 3), and Gd3Al3Ga2O12 (Al : Ga = 3 : 2) and cerium-doped crystals: Gd3Al2Ga3O12:Сe3+ (GAGG:Ce). X-ray photoelectron spectroscopy and X-ray fluorescence analysis data demonstrate gallium deficiency relative to the stoichiometric composition in all of the crystals studied. The results obtained are used to analyze processes underlying the formation of structural growth point defects in gadolinium aluminum gallium garnet crystals. F-centers have been shown to be the predominant point defect species. We also have demonstrated the formation of Schottky defects and V-centers. The formation of additional F-centers in cerium-doped garnet crystals is happening. The refractive indices and attenuation coefficients of the crystals have been shown to depend on the Al : Ga ratio and doping with cerium.

In this paper, we report an experimental study concerned with the synthesis of MgAl2O4 spinel via plasma-assisted melting of powder components at an Al2O3/MgO weight ratio varied from 1 to 4. The presence of excess Al2O3 in the starting mixture has been shown to cause the characteristic Bragg peak 111 (~65°) of crystalline MgAl2O4 to shift to larger 2θ angles and broaden. According to scanning electron microscopy results, the surface microstructure of the synthesized materials is formed by densely packed octahedral stoichiometric MgAl2O4 crystals ranging in size from 10 to 500 μm. The materials have been found to contain local regions that allow the dynamics of crystal growth during melt solidification to be examined. The proposed spinel synthesis method can find application in the fabrication of small thermally stable parts by casting.

The quinary reciprocal system Li+,K+||F–,Cl–,Br–,
 has been divided into simplexes using graph theory: by making up an adjacency matrix and solving a logical expression. The results have been used to construct the phase tree of the system, which has a linear structure and consists of four stable secant tetrahedra, four stable pentatopes, and one stable hexatope. The number and composition of phases crystallizing in the system have been predicted. The LiF–KCl–KBr–Li2CrO4 stable tetrahedron has been studied using differential thermal analysis and X-ray diffraction. The tetrahedron has no invariant equilibrium points. The continuous series of solid solutions between potassium chloride and potassium bromide has been shown to be stable, without decomposition. Three solid phases have been shown to crystallize in the tetrahedron: LiF, Li2CrO4, and KClxBr1–x.

We demonstrate the conceptual feasibility of step-by-step calculation of the effective separation factor β in distillation and sublimation processes as a function of the evaporation temperature T and degree of distillation g. The variation of β with T and g is thought to stem from the influence of T and g on the impurity distribution over the vaporizing material. The β(T) and β(g) dependences can be found using the Burton–Prim–Slichter equation and calculated impurity distributions in the vaporizing material at particular parameters of the substance and material. We present examples of such calculations for a beryllium-based model material.

α-Si3N4-based powder composites containing 3 wt % Y2O3–Al2O3 sintering aids with 2 : 1, 1 : 1, and 3 : 5 stoichiometries have been prepared by the Pechini process and spray drying. We have studied four ceramic samples produced by spark plasma sintering of the powder composites. The sintering process was run under a load of 70 MPa at a heating rate of 50°C/min as long as shrinkage of the powder composites continued. We have analyzed the shrinkage behavior of the powder composites during the sintering process; evaluated the activation energy for sintering; and measured the density, microhardness, and fracture toughness (cracking resistance) of the ceramic samples. The highest hardness, HV = 16.5 GPa, in combination with a fracture toughness KIc = 3.8 MPa m1/2, was offered by the material with an Y2O3 : Al2O3 molar ratio of 3 : 5 sintered at 1860°C. The corresponding densification factor was 99.0%. The starting mixture for this material was synthesized using spray drying.

In this paper, we report a process for lithium extraction from spodumene raw materials. We demonstrate that a promising approach for processing spodumene is sintering with sodium acetate. In the reaction between these components, the crystal structure of spodumene remains intact. Ion exchange reaction between CH3СOONa⋅3Н2О and LiAlSi2O6 yields water-soluble sodium acetate and water-insoluble sodium aluminosilicate (NaAlSi2O6). The sodium acetate dissolved in water is converted to lithium carbonate by adding a Na2CO3 solution. The lithium carbonate precipitate is essentially free of foreign impurities. We analyze the effect of process parameters on the degree of Li+ extraction from spodumene.