Volume 49, Nº 1 (2023)

A geometric and topological analysis of the crystal structure of the Li10Mg34Cu24Ga71-hP139 (a = 14.080 Å, c = 13.625 Å, V = 2339.36 Å3, P-6m2) and Ca2LiInGe2-oP24 (a = 7.251, 4.940 Å, b = 4.438 Å, c = 16.902 Å, V = 543.9 Å3, Pnma) intermetallic compounds is carried out. For the Li10Mg34Cu24Ga71-hP139 intermetallic compound, using the method of the complete decomposition of the 3D factor graph into cluster structures, 1319 variants of the cluster representation of the 3D atomic grid with three to nine structural units are found. Two frame-forming nanoclusters K57 = Li@15(Ga6Cu9)@41(Cu15Mg26) with the internal Frank–Kasper polyhedron Li@15(Ga6Cu9) and K41 = 0@8(Mg2Ga6) @ 33(Li6Mg3Ga24) with an internal polyhedron in the form of a hexagonal bipyramid 0@8(Mg2Ga6) are established. The center of the K57 and K41 cluster-precursor is in positions 1f and 1c with symmetry g = –6m2. The large frame cavity contains double LiGa13, which are polyhedra centered at position 1b. For the Ca2LiInGe2-oP24 intermetallic compound, the K5 = 0@Ca2LiInGe cluster-precursor is found in the form of a triangular bipyramid with Li, In, and Ge atoms lying at the base of the bipyramid and Ca atoms, which are the vertices of the bipyramid. The symmetry and topological code of the processes of self-assembly of the Li10Mg34Cu24Ga71-hP139 and Ca2LiInGe2-oP24 crystal structures of the cluster-precursors is reconstructed in the following form: primary chain → layer → framework.

The results of studying the state of the surface of silica glass with a high content of OH groups obtained by high-temperature hydrolysis of SiCl4 and that it finely annealed are presented. A comparison of the IR reflection spectra before and after annealing showed the decomposition of silanol groups with the release of water from the material and the appearance of nonbridging Si–O– groups. Some of the nonbridging bonds are reduced to form three- and four-membered siloxane rings. To assess the change in the mechanical properties of the glass surface during annealing, the samples were subjected to point impact damage, in which the intensity of microcrack accumulation in the damaged layer were controlled by acoustic emission method. The marked attenuation of the mechanical strength of the annealed glass surface is attributed to the formation of small siloxane rings and a decrease in the connectivity of the silicate network due to the presence of residual nonbridging bonds.

Vaporization and thermodynamic properties of the SrO–Al2O3–SiO2 system are studied by high-temperature differential mass spectrometry in the concentration range from 90 to 10 mol % of SrO and the molar ratio of x(Al2O3)/x(SiO2) = 1.5. The samples are evaporated from Knudsen effusion cell made of tungsten. The partial pressures of the molecular forms of the vapor, the activities of the condensed phase components, the Gibbs energies, and the excess Gibbs energies are determined. It is established that the studied system is characterized by a slight negative deviation from the ideal behavior. For mullite (Al6Si2O13) the value of the standard enthalpy of formation is determined. The melting points of the synthesized samples are established by high-temperature microscopy.

NdBa1 – xMgxFeCo0.5Cu0.5O5 + δ (0.00 ≤ x ≤ 0.40) double perovskites are synthesized by the ceramic method and their structure, oxygen nonstoichiometry (δ), and thermal and electrical transport properties are studied. NdBa1 – xMgxFeCo0.5Cu0.5O5 + δ compounds have a tetragonal structure (space group P4/mmm) and are semiconductors of the p-type, whose electrical conductivity characteristics at elevated temperatures changes to metal-like characteristics due to the release of oxygen from the samples (δ). The partial replacement of barium with magnesium in NdBaFeCo0.5Cu0.5O5 + δ leads to a decrease in the oxygen content (δ) in the solid solutions formed in this case, an increase in the size of their unit cell and the thermo-EMF coefficient, and a decrease in the thermal stability, linear thermal expansion coefficient, and electrical conductivity. The values of electrical transport energy, weighted mobility, and concentration of charge carriers in the studied materials are calculated.

This article investigates the fire resistance of a structure with a fire barrier based on super-thin basalt fiber for the fire-resistant sealing of joints in reinforced concrete structures under conditions of alternating deformation. In European regulations, such fire barriers are specifically designed for use in expansion joints and operate in the compression, tension, and shear of the joint. In Russia, products and materials that perform the function of a fire barrier are not tested under conditions of alternating load. This article presents a test method for fire resistance for an expansion joint in a reinforced concrete structure. The results are obtained on the parameters of integrity (E) and heat-insulating capacity (I) for reinforced concrete slabs, followed by an increase in the width of the gap between the slabs and their shift relative to each other by +25% of at least 245 min.

The effect of electron-beam treatment (EBT) and heat treatment (HT) of silica-based aggregates and mineral additives in Portland cement mortars on the intensity of alkali-silica reactions (ASRs) with their participation, which are dangerous for concrete structures, is studied. It is established that heating to a temperature of 900°C and the EBT of sand free of alkali-reactive inclusions, leads to a significant increase in the reactivity of cement-sand mortar mixtures, which increases with an increase in the absorbed dose and a corresponding increase in the content of acid hydroxyl groups on the sand surface. In the case of sand containing reactive inclusions of chalcedony, EBT leads to an increase in reactivity, and HT, to a decrease. Treatment of microsilica and metakaolin mineral additives capable of ASR inhibition leads to an increase in their inhibitory effect. The results obtained are promising for modeling the expansion of concrete as a result of ASR and increasing their resistance to fracture in alkaline media.