Vol 49, No 2 (2023)

Geometric and topological analysis of the Pd112Co204Al684-cP1000 crystal structure with the sp. gr. Pa-3, a = 24.433 Å, and V = 14587.24 Å3 is performed using the ToposPro software package. Metal precursor clusters of crystalline structures are determined using an algorithm for decomposing structural graphs into cluster structures and by constructing a basic grid of the structure in the form of a graph whose nodes correspond to the position of the centers of precursor clusters 
 A total of 26 906 variants of the cluster representation of a 3D atomic mesh with the number of structural units ranging from 3 to 12 are established. The self-assembly of the crystal structure from new three-layer K155(4a) = Al@Al6Pd8)@Pd12Al30@Pd8Co18Al72 and bilayer precursor clusters K55(4b) = Co@Al12@Co12Al30 with symmetry g = –3 is considered. In the unit cell, positions 4a are occupied by Al atoms, which are the central atoms of the 15-atom polyhedron K15(4a) = Al@Al8Pd6, and positions 4b are occupied by Co atoms, which are the central atoms of the 13-atom icosahedron K13(4b) = Co@Al12. The symmetric and topological code of the processes of self-assembly of 3D structures from precursor clusters K155 and K55 is reconstructed as follows: primary chain → microlayer → microframework. Al atoms are established as spacers occupying voids in the 3D framework of the K155 and K55 nanoclusters.

The phase tree of the previously studied СаO–MgO–SiO2 system was constructed. The phase tree includes three cycles. The phase tree is represented by fifteen simplices separated by fifteen stable secants. The formation of six double and four ternary compounds of congruent and incongruent melting was noted in the system. On the basis of the phase tree, taking into account the data on faceting elements, a forecast of crystallizing phases in stable secants and in phase secondary triangles was carried out. For the figurative points of the composition, corresponding to the intersections of stable and unstable secants, the chemical interaction is described on the basis of thermodynamic data. It has been shown that ternary compounds can be synthesized by several reactions.

The main cause of global warming is the steady increase in greenhouse gases in the atmosphere. The largest share of greenhouse gases is carbon dioxide CO2. Therefore, it is important to efficiently separate it in different gas systems. The article examines the sorption of carbon dioxide from polysilicic acid—silica gels modified with hydroxyethyl carbamate (HEC). It is shown that the modification is optimal in 30% HEC solutions. The fact of modification is confirmed by the presence of amino, hydroxyl, and carbonyl groups in the sorbents. Thermal stability is studied by the thermogravimetric method. Sorption at high pressures is studied by the gravimetric method and sorption at atmospheric pressure is studied by the thermogravimetric method. It is found that the presence of amino groups contributes to the sorption of carbon dioxide by silica gel more than doubling. The highest sorption rates are found to be 8.8% of the mass of the sorbent at 30°C. After five cycles of sorption/desorption processes in sorbents, the maximum sorption capacity decreased by 10%. The sorption rate increases at high pressures of up to 3 atm. Sorbents modified with a 30% HEC solution at 3 atm sorb up to 9.96 mol CO2/g. The relatively fast growth of the sorption rate at high pressures and its relatively slow growth at low pressures prove that the process corresponds to type-2 sorption. Such sorption systems are promising for use in various technological systems containing CO2.

The effect of the hydrothermal synthesis conditions (temperature, duration, mixing), composition, and presynthetic processing of narrow fractions of cenospheres of fly ash, which act as a template and source of Si and Al, on the production of microspherical zeolite materials of the given structural type in the Na2O–H2O–(SiO2–Al2O3)glass of two molar compositions is studied. The synthesis products are characterized by XRD, SEM-EDS, and low-temperature nitrogen adsorption, and their sorption properties in relation to Cs+ and Sr2+ are studied. The factors contributing to the predominant formation of NaX zeolite of the faujasite structural type are revealed. It is established that zeolite products based on cenospheres with a glass phase content of about 95 wt % demonstrate the highest sorption parameters, including the maximum capacity for Cs+ and Sr2+ of up to 250 and 180 mg/g, distribution coefficient of about 104 and 106 mL/g, and degree of extraction of 99.1 and 99.9%, respectively.

Glass composition of 6Na2O 22B2O3·70SiO2·2Cr2O3 is studied by scanning electron microscopy, X‑ray powder diffractometry (XRPD), and differential thermal analysis, depending on the duration of heat treatment at a temperature of 550°C. It is established that during heat treatment for 24–96 h, a phase separation structure with interpenetrating phases is formed in the studied glass, and a crystalline phase of eskolaite—Cr2O3 is also formed. With the maximum heat treatment duration of 96 h, cristobalite is formed in the bulk of the glass, which is accompanied by a decrease in the glass transition temperature of the low-viscosity phase. In this case, the intensity of eskolaite peaks decreases. Cr2O3 and SiO2 crystallize apparently due to the substance of the low-viscosity phase.

Based on the data obtained by complex methods of physicochemical analysis on studying various sections of ternary Tm–As–S(Se) systems and using the published data, the boundary of the glass formation region of the Tm–As–S and Tm–As–Se system is determined. It is established that at a cooling rate of 10 deg/min in the Tm–As–S system, the glass formation area of the system’s glass is 33 at % of the total area of the triangle; and at a cooling rate of 102 deg/min, 51 at % of the total area of the triangle. In the Tm–As–Se system under the specified cooling regimes, the glass area is 35 and 54 at %, respectively.