Glass Physics and Chemistry最新文献

This paper analyzes the experimental and theoretical studies of the problem of a diffuse phase transition (PTC) in a composite material xPbSe⋅(1 – x)PbSeO₃, in which x varies from 0 to 1. The decrease in stability in the virtual cubic phase of lead selenide (PbSe) is achieved by oxidizing it with atmospheric oxygen and forming a ferroelectric disordered monoclinic phase of lead selenite (PbSeO₃). The mechanism of lead selenide oxidation by air oxygen is studied by X-ray diffractometry, optical reflection in the infrared region of the spectrum, X-ray emission analysis (the chemical shift method), nuclear magnetic resonance, studies of AC and DC conductivity, differential scanning calorimetry, and other methods. The reason for the smearing of the phase transition in the xPbSe⋅(1 – x)PbSeO₃ composite, in which x varies from 0 to 1, is analyzed based on the previously obtained experimental results of its detection.

Nickel-zinc ferrites, which have pronounced ferrimagnetic and semiconductor properties, can be used as promising magnetically controlled photocatalysts for the purification of aqueous media from organic pollutants. The value of the specific surface area largely affects the photocatalytic properties of the material; therefore, the possibility of its control and variation at the stage of synthesis is of great scientific and technical interest. In this study, nanocrystalline ferrite of the Zn_0.5Ni_0.5Fe₂O₄ composition is obtained under conditions of solution combustion using various types of organic fuel as the main factor affecting the formation of the specific surface area, and subsequent heat treatment in air at a temperature of 500°C for 2 h. The crystal structure, chemical composition, and morphology of Zn_0.5Ni_0.5Fe₂O₄ are studied by methods of X‑ray phase analysis, X-ray spectral microanalysis, and scanning electron microscopy. The values of the specific surface area of the synthesized nanopowders are calculated based on the method of liquid-phase adsorption from a Methylene Blue solution and the low-temperature adsorption-desorption of nitrogen. The results of the X‑ray phase analysis show that a single-phase nanocrystalline product with a spinel structure is formed, where the average crystallite size varies within 11–23 nm and is inversely related to the value of the specific surface area, respectively, after the reaction with succinic acid (39.1 m²/g) and with glycine (20.2 m²/g). It is established that the choice of the fuel largely affects the formation of nanocrystals and the specific surface area of the samples, and the approach used makes it possible to control its values.

A model is proposed that makes it possible to calculate the temperature dependence of the microhardness of glass over the entire temperature range from the softening temperature to absolute zero. The calculation uses the temperature dependence of the glass enthalpy and the value of its microhardness at the glass transition temperature. The proposed model is tested on the example of glassy selenium. For this, the temperature dependence of the microhardness of selenium on the softening temperature up to 100 K, which is 50 K below its Debye temperature, is measured. Thus, a relationship is established between the strength and thermodynamic properties of glass.

This paper presents the results of a study of the thermal behavior of fedotovite K₂Cu₃O(SO₄)₃ and piypite K₄Cu₄O(SO₄)₄∙(Na,Cu)Cl minerals in a wide temperature range. The crystal structure of the holotype piypite specimen is refined at room temperature. The mechanisms of thermal expansion of minerals depending on the crystal structure are described.

In this study, Ba₃Lu(BO₃)₃ borate obtained by solid-phase synthesis is explored by high-temperature X-ray powder diffraction in the temperature range from 25 to 900°C. At room temperature, the compound expands slightly anisotropically (α_max/α_min = 1.2), and with an increase in temperature, the degree of anisotropy increases significantly (α_max/α_min = 6.9 at 900°C). The maximum expansion is observed along the crystallographic axis c (α_c = 10.45 × 10^–6°C^–1 at 25°C and 36.34 × 10^–6°C^–1 at 900°C), perpendicular to which the boron-oxygen triangles [BO₃] are located, and the minimum is in the plane where the triangles are located.

The aggregation process of 2D nanofillers (organoclay and graphene oxide (GO)) is studied within the framework of micromechanical models. The degree of aggregation of these nanofillers, expressed as the number of individual plates in one aggregate (tactoid), is determined by the ratio of the nominal moduli of elasticity of the nanofiller and the matrix polymer. It is found that increasing the first of these moduli leads to an increase in the degree of aggregation, whereas increasing the second one, leads to its reduction. This means that it is practically impossible to obtain exfoliated (separate) graphene plates in a polymer matrix. Both the studied polymer/2D nanofiller nanocomposites are reinforced with separate nanofiller aggregates, which is the optimal variant of reinforcing them.

Using computer methods (the ToposPro software package), a combinatorial topological analysis and modeling of the self-assembly of U₈Ni₁₀Al₃₆-mC54 (a = 15.5470 Å, b = 4.0610 Å, c = 16.4580 Å, β = 120.00°, V = 899.89 ų, C m), U₂₀Ni₂₆-mC46 (a = 7.660 Å, b = 13.080 Å, c = 7.649 Å, β = 108.88°, V = 725.26 ų, C2/m), and U₈Co₈-cI16 (a = 6.343 Å, V = 255.20 ų, I 2₁3) are carried out. For the U₈Ni₁₀Al₃₆-mC54 crystal structure, 960 variants of the cluster representation of the 3D atomic grid with the number of structural units 5, 6, and 7 are established. Six crystallographically independent structural units in the form of a pyramid K5 = 0@Al(U₂Al₂), pyramid K6A = 0@U(NiAl₄), and pyramid K6B = 0@U(NiAl₄), as well as rings K3A = 0@NiAl₂, K3B = 0@NiAl₂, and K3C = 0@Al₃, are determined. For the U₂₀Ni₂₆-mC46 crystal structure, the structural units K5 = Ni(Ni₂U₂) and icosahedra K13= Ni@Ni₆U₆ are defined. For the crystal structure U₂Co₂-cI16, the structural units—tetrahedra K4 = U₂Co₂—are defined. 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.

Tempered glass is a transparent material that can withstand various shocks and constant loads, which is widely used in the field of safety protection. This manuscript presents the determination of Johnson–Holmquist (JH-2) model parameters for tempered glass and investigates the effect of strain rate on its strength through quasi-static and dynamic compression tests. The hydrostatic tensile pressure was indirectly determined via split tensile tests, and literature data were employed to calculate the value of HEL and EOS. The JH-2 model accurately predicted the real shapes of strain waves in the input and output bar of SHPB tests and was capable of describing the mechanical behavior of the brittle material from elasticity to fracture. The determined parameters for tempered glass were validated to represent the response to shock and impact loads.

Two approaches to the synthesis of nanosized precursor powders 0.5LaPO₄·nH₂O–0.5ZrO(OH)₂ and 0.5LaPO₄·nH₂O–0.5Y(OH)₃ for the fabrication of ceramic composites 0.5LaPO₄–0.5ZrO₂ and 0.5LaPO₄–0.5Y₂O₃ were used. In the first case, sol-gel synthesis of components (LaPO₄·nH₂O, ZrO(OH)₂ or Y(OH)₃) was carried out separately by reverse precipitation technique. In the second case, reverse precipitation was used too but without separate preparation of sols of the components. The results of the synthesis were compared by XRD analysis, thermal behavior of precursor powders by DSC/TG technique, as well as Vickers microhardness values of 0.5LaPO₄–0.5ZrO₂ and 0.5LaPO₄–0.5Y₂O₃ ceramic composites.

A forcefield for high-performance molecular dynamics (MD) simulation of inorganic oxide substances, including borosilicate glasses, based on a combination of electrostatic interactions with the 6–12 type of Lennard–Jones potentials is developed. The forcefield parameters are selected to reproduce the structures and bulk moduli of the binary oxides of a wide spectrum of elements. The proposed forcefield is able to accurate reproduce structures of minerals containing two to three types of cations during the MD simulations. Application of the 6–12 potential makes it possible to carry out simultaneous MD simulations of the organic and inorganic phases, for example, in modeling composite materials with mineral and glass fillers.