Volume 49, Nº 4 (2023)

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 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.

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.

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 Zn0.5Ni0.5Fe2O4 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 Zn0.5Ni0.5Fe2O4 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.