Glass Physics and Chemistry最新文献

The electrical properties of glasses composed of 8Na₂O–(22 – x)B₂O₃–70SiO₂–xCr₂O₃, where x varies from 0.3 to 6 mol %, heat-treated at 550°C for 48 h, are studied. The structure of the glasses is studied using scanning electron microscopy and X-ray powder diffraction (XRPD). It is established that in all glasses of the selected compositions, during heat treatment, an interconnected phase-separated structure is formed and the eskolaite phase (α-Cr₂O₃) also crystallizes. When comparing the obtained values of electrical resistance and activation energy of electrical conductivity of chromium-containing glasses and glass without Cr₂O₃ composed of 8Na₂O⋅22B₂O₃⋅70SiO₂ and iron-containing glasses of similar compositions, it is suggested that the studied glasses with Cr₂O₃ possess ionic conductivity and the values of the specific volume resistance of chromium-containing and iron-containing glasses do not differ from each other. The introduction of Cr₂O₃ in sodium borosilicate glasses does not affect their electrical conductivity.

Xerogels and powders of solid solutions based on zirconium dioxide are synthesized by the method of the coprecipitation of hydroxides from aqueous solutions of nitrate salts of zirconium, yttrium, aluminum, and cerium with an aqueous solution of ammonia. The characteristics of the resulting materials are studied. The influence of stabilizers and additives on their synthesis, sintering, and properties is assessed.

The thermal behavior of aqueous sulfate NaHSO₄·H₂O and the product of its dehydration α‑NaHS-O₄ is studied. The studies are carried out using high temperature X-ray diffraction and complex thermal analysis. Based on the data of three experiments, the temperature, nature, and sequence of phase transformations are established: NaHSO₄·H₂O^(30–50°C) → α-NaHSO₄^{(140–180°C)} → Na₂S₂O₇ + Na₃H(SO₄)_2. With increasing temperature increasing in the NaHSO₄·H₂O structure hinge deformations occur at the level of a chain of NaO₃(OH)(H₂O)₂ polyhedra. The anisotropy of thermal expansion is α_max/α_min = 1.9 for NaHSO-₄·H₂O and α_max/α_min = 1.3 for NaHSO₄.

The results of a study of the GdAlO₃–SrO section, which is one of the internal sections of the Gd₂O₃–SrO–Al₂O₃ ternary system, are presented. In the GdAlO₃–SrO section three triple compounds, Gd₂SrAl₂O₇, GdSrAlO₄, and GdSr₂AlO₅, crystallizing in the tetragonal system, are synthesized. The data on the mechanism of their solid-phase formation are systematized. The results of the thermal stability of perovskite-like phases in the GdAlO₃–SrO system are presented in a wide temperature range of 1100–1800°C in air. The congruent character of the melting of Gd₂SrAl₂O₇, GdSrAlO₄, and GdSr₂AlO₅ complex oxides is established and their melting temperatures are determined.

Using computer methods (the ToposPro software package), combinatorial-topological analysis and modeling of self-assembly of the following crystal structures are carried out: RbNa₈Ga₃As₆-oP72 (a = 22.843Å, b = 4.789 c = 16.861 Å, V = 1844.6 ų, Pnma), Sr₂Ca₄In₃Ge₆-oP56 (a = 13.243 Å, b = 4.460 Å, c = 23.505 Å, V = 1388.47 ų, Pnma), and Sr₈Li₄In4Ge₈-oP24 (a = 7.503 Å, b = 4.619 Å, c = 17.473 Å, V = 605.6 ų, Pnma). For the RbNa₈Ga₃As₆-oP72 crystal structure, 93 variants of a cluster representation of a 3D atomic mesh with the number of structural units of 3, 4, and 6 are established. A variant of self-assembly involving three types of clusters-precursors is considered: double tetrahedra K6(4a) = 0@6 (Rb₂Na₂As₂) and K6(4b) = 0@6 (Na₄As₂) with symmetry g = –1, tetrahedron K4(8d) = 0@4(Na₃As), two triple rings K3-1 = 0@3(NaGaAs), and Ga and As spacer atoms. For the Sr₂Ca₄In₃Ge₆-oP56 crystal structure, 43 variants of a cluster representation of a 3D atomic mesh with the number of structural units of 3, 4, and 6 are established. A variant of self-assembly of a crystal structure involving three types of clusters-precursors from double tetrahedra K6(4a) = 0@6 (Sr) ₂In₂Ge₂) and K6(4b) = 0@6 (Ca₂In₂Ge₂) with symmetry g = –1, double tetrahedra K6(4c) = 0@6 (SrCa₂InGe₂), and Ge2 and Ge4 spacer atoms is considered. For the Sr₈Li₄In4Ge₈-oP24 crystal structure, three variants of a cluster representation of a 3D atomic mesh with two structural units are established. A variant of the self-assembly of a crystal structure involving two types of clusters-precursors in the form of double tetrahedra K6 = (Sr₂Li₂Ge₂) with symmetry g = –1 and triple rings K3 = 0@3 (SrInGe) is considered. The symmetry and topological code of the processes of self-assembly of 3D structures from clusters-precursors are reconstructed in the following form: primary chain → layer → framework.

The results of laboratory studies of the practical application of the reagent-free method of tensor-pulse regulation in the industrial method for obtaining gibbsite from aluminate solutions by the Bayer method are presented. During decomposition in regulatory regimes, the size and homogeneity of crystals increase, and an increase in the rate of dissolution of the seed and crystallization of gibbsite is observed. The quantitative characteristics of the degree of transformations are given and the parameters of gibbsite crystals obtained by the traditional method and in different regulation modes are determined. The results of the X-ray phase study and granulometric analysis of images obtained with a scanning electron microscope are described.

The influence of chemical elements in the composition of optical glasses on the quantitative characteristics of their attenuation of X-ray and gamma radiation is analyzed. The method of calculating the mass coefficients of radiation attenuation (MCRA) with quantum energy ranging from 0.2 to 3.0 MeV for oxides as glass components is proposed. The chemical elements and their oxides in the glass composition, which make the main contribution to their values of the linear coefficient of radiation attenuation (LCRA) with different quantum energies, E, are identified. In the field of quantum energies ranging from 0.2 to about 1.0 MeV, oxides such as PbO, Ta₂O₅, Gd₂O₃, La₂O₃, BaO, Sb₂O₃ (due to its low concentration, its contribution to LCRA is usually negligible), CdO, Nb₂O₅, ZrO₂, and Y₂O₃ have a strong effect (in decreasing order) on the LCRA values of glasses. It is shown that in the field of E values ranging from 0.2 to about 1.0 MeV, elements (or their oxides) can be very different from each other in terms of their MCRA values, and glasses of different compositions, in terms of their LCRA values, while at E > 1.0 MeV, both the first and second coefficients change approximately equally with an increase in the energy of radiation quanta.

For a multimode optical fiber, whose core is formed by quartz glass of the KU-1 type with a high content of hydroxyl groups, the dynamics of the reversible (recoverable) change in the optical absorption of these groups near 7200 cm^–1 when the light guide is heated to 1050°C, are studied. Based on the decomposition of the absorption band into spectral components at different temperatures, assumptions are made regarding the structure of absorption centers related to the OH groups.

Using computer methods (the ToposPro software package), a combinatorial topological analysis and modeling of the self-assembly of crystal structures of Ce₅₆Ni₂₄Si₄₄-mS124 (a = 34.08 Å, b = 4.245 Å, c = 21.37 Å, β = 113.52(3)°, V = 2835.14 ų, C12/m1) and Ba₁₀La₂Si₁₂-oP48 (a = 17.144 Å, b = 4.876 Å, c = 17.910 Å, V = 1497.46 ų, Pnma) are carried out. For the crystal structure of Ce₅₆Ni₂₄Si₄₄-mS124, 5511 variants of the cluster representation of the 3D atomic network are established with the number of structural units 5 (28 variants), 6 (943 variants), 7 (2316 variants), 8 (1704), and 9 (520 variants). The variant of the self-assembly of a crystal structure from the packing components of three types of cluster-precursors K13 = 0@13(Ce₆CeNi₂Si₄), K4 = 0@4(Ce₂NiSi), and K3 = 0@3(CeNiSi), as well as Si spacer atoms, is considered. For the crystal structure of Ba₁₀La₂Si₁₂-oP48, 21 variants of the cluster representation of the 3D atomic network with the number of structural units of 2 and 3 are established. The variant of self-assembly of the crystal structure with the participation of cluster-precursors forming the packing K11 = 0@11(Ba5LaSi5) and Si spacer atoms is considered. The symmetry and topological code of the processes of self-assembly of 3D structures from cluster-precursors is reconstructed in the following form: primary chain → layer → framework.

Using the method of the joint crystallization of solutions of nitrate salts with ultrasonic treatment, xerogels and highly dispersed mesoporous powders of the following composition are synthesized: (CeO₂)_1 – x(Nd₂O₃)_x (x = 0.02; 0.05; 0.10), Gd_1 – xSr_xCo_0.5O_3 – δ (x = 0.1, 0.15, 0.2, 0, 25), Gd_0.4Sr_0.1Ni_0.5O_3 – δ, and Gd_0.125La_0.125Sr_0.25Co_0.5O_3 – δ; and based on them, nanoceramic materials with a crystalline cubic structure of the fluorite type, as well as an orthorhombic and tetragonal structure of the perovskite type with CSR ~ 55–90 nm (1300°С), respectively, are obtained. The physicochemical properties of the resulting ceramics are studied; it is revealed that it has an open porosity of 7–11% for the composition (CeO₂)_1 – x(Nd₂O₃)_x and 17–42% for materials with the Gd_1 – xSr_xCo_0.5O_3 – δ, Gd_0.4Sr_0.1Ni_0.5O_3 – δ, and Gd_0.125La_0.125Sr_0.25Co_0.5O_3 – δ composition. Materials based on cerium oxide predominantly have the ionic (ion transport numbers t_i = 0.71–0.89 in the range 300–700°С) type of electrical conductivity due to the formation of mobile oxygen vacancies in the heterovalent substitution of Ce⁴⁺ by Nd³⁺; and σ_700°С = 0.31 × 10^–2 S/cm Solid solutions based on nickelate and lanthanum cobaltite have mixed electron-ionic conductivity, σ_700°С = 0.59 × 10^–1 S/cm with transfer numbers t_e = 0.92–0.99 and t_i = 0.08–0.01. The prospects for using the obtained ceramic materials as solid oxide electrolytes and electrodes for medium-temperature fuel cells (FCs) are shown.