The article presents the results of a comprehensive study of the physicochemical properties of wollastonite raw material from the Koitash mine, located in the Gallaaral district of the Jizzakh region of Uzbekistan. The chemical-mineralogical composition, physicochemical characteristics, and crystal structure of wollastonite have been determined using modern methods of physicochemical analysis. It is shown that the wollastonite of the Koitash mine is a promising natural resource that can be widely used in the ceramic and construction industries of the Republic.
Ba2NaNb5O15 (BNN) ceramics were synthesized by the solid-state reaction method and investigated for their structural and dielectric properties. X-ray diffraction confirmed the formation of a single-phase orthorhombic structure (Cm2m space group). A sharp dielectric anomaly near 450 °C was observed, corresponding to the ferroelectric–paraelectric transition. Curie–Weiss and modified Curie–Weiss analyses indicated a first-order transition with moderately diffuse character (? ? 1.5). AC conductivity exhibited frequency dispersion consistent with Jonscher’s universal power law. The temperature dependence of the fitting parameters and extracted activation energies revealed that charge transport is dominated by thermally activated hopping, in agreement with the Correlated Barrier Hopping (CBH) model. These findings provide new insights into the dielectric response and charge transport mechanisms of BNN ceramics, highlighting their potential for ferroelectric and optoelectronic applications.
Commercially available reagents for the solid-phase synthesis of strontium titanate in Russia have been studied using X-ray phase analysis, inductively coupled plasma mass spectrometry, X-ray fluorescence analysis, and laser diffraction. Strontium carbonates and titanium oxides of various qualifications with the content of the main component were used in the work: >98 % (pure), >99 % (pure for analysis), ~99,9 % (сhemically pure), >99,9 % (extra pure). Micron-sized mixtures were obtained to average the particle size of the initial powders and reduce its effect on the synthesis process. Regardless of the purity of the reagents, single-phase strontium titanate samples were obtained at 1100 °C. SrTiO3 ceramics were obtained from synthesized powders by sintering in air at temperatures from 1400 to 1500 ° C for 1, 2 and 4 hours. The structural and dielectric characteristics of ceramic samples are studied depending on the qualification of reagents and sintering conditions. It has been found that the presence of the impurity phase SrAl4O7 in the case of TiO2 with an admixture of aluminum leads to a decrease in density (?app < 80 % during firing at 1500 °C) and a deterioration in the dielectric properties of SrTiO3 ceramics (tg? > 0,5). The formation of a closed-pored structure depending on the firing temperature in ceramics based on reagents with impurity elements Si, P and K. An increase in the firing temperature in the case of samples with closed porosity reduces their relative density from 98 to 90 %, but does not significantly affect the dielectric characteristics. It has been found that the relative permittivity of SrTiO3 ceramics increases with increasing purity of TiO2 from 200 to 300. The data obtained can be used in the design of capacitor ceramic elements based on strontium titanate.
Reactive sintering (siliconizing) at 1550?°C was employed to produce composite materials in the SiC–ZrB2 and SiC–ZrC systems. The influence of the initial zirconium compound on phase transformations, microstructure, and physical and mechanical properties was investigated. X-ray diffraction (XRD), scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS), and differential scanning calorimetry combined with thermogravimetric analysis (DSC-TG) revealed that ZrB2 remains chemically stable under siliconizing conditions: the bulk of the diboride is retained, with only trace amounts of zirconium silicide (ZrSi2) forming. This allows complete infiltration of the pore space by the silicon melt, resulting in a dense composite with a flexural strength of 195?MPa. In the ZrC-containing system, a liquid phase (ZrSi2–Si eutectic) appears at temperatures as low as 1360?°C, triggering intensive silicide formation on the particle surfaces. The resulting dense silicide crust impedes capillary transport, leaving the interior regions porous and unsintered. The findings demonstrate that ZrB2 is chemically stable and holds promise as a modifying phase in silicon carbide-based composites produced by reactive sintering.
The aim of this work was to optimize gel-based 3D printing technology for biocompatible ce-ramic implants based on an agar-agar–gelatin–brushite composition by applying the Linear Advance function – a pressure correction algorithm in the extruder that responds to changes in printing speed. Bio-inks were prepared by homogeneous mixing of 2 wt. % agar-agar, 10 wt. % gelatin, and 30 wt. % synthesized brushite; printing was performed on a modified gel 3D printer running Marlin 2.0 firmware with an adaptive Linear Advance algorithm. Samples were printed with K-factor values ranging from 0 to 1.0 at a base speed of 14 mm/s and an extruder temperature of 30 °C; quality was assessed by optical microscopy, SEM, X-ray com-puted tomography, and compression testing. It was found that at K = 0, sagging occurs at corners due to the inertia of viscous hydrogel extrusion, while at K > 0.5…0.6, over-extrusion arises from excessive pressure compensation. The optimal K-factor range was 0.3…0.4, at which complete defect elimination, uniform wall thickness, and geometric accuracy of the model were achieved while preserving the microarchitecture and phase composition of the biomaterial. The compressive strength of samples containing 20 wt. % brushite reached 9.92 MPa, which is more than twice the value for the unfilled matrix.
The process of obtaining microneedle powdered ZrO2 from an aqueous solution of zirconium oxychloride, as well as zirconium dioxide doped with Y2O3 and CeO2 oxides, has been studied. Their chemical and phase composition has been proven using a combination of physical and chemical methods. Microneedle particles with a length of 100…200 ?m and a cross-section of about 1 ?m have been obtained. These powders are in demand for microreinforcement of special alloys and the production of lightweight and high-strength ceramics.
The paper investigates the possibility of obtaining green inorganic pigments with the simultaneous presence of luminescent properties during the heat treatment of chemical industry waste phosphogypsum. It is shown that as a result of partial reduction of calcium sulfate, a material containing mainly calcium sulfide, as well as calcium sulfate and chromite is formed. It was found that when illuminated by daylight, the resulting material is colored reed green (RAL 6013), when illuminated by ultraviolet radiation, the samples glow blue-blue with a maximum wavelength of 480…490 nm. The dependence of the luminescence intensity on the content of copper (II) cations in the samples is shown; the maximum luminescence intensity is set for compositions containing 9 mmol of copper (II) cations. The studied patterns make it possible to obtain colored inorganic pigments with the simultaneous presence of luminescent properties using phosphogypsum, a chemical industry waste, as starting materials.
The electrical properties of the complex oxide Bi2Сu0.25Ni0.75Ta2O9 with a pyrochlore structure (space group Fd-3m, 10.5200(5) ?), synthesized by the solid-phase method, were studied using impedance spectroscopy. The porous microstructure of the ceramic is formed by partially fused, rounded ceramic grains with longitudinal dimensions of 1…2 ?m. Impedance plots were analyzed, and electrical circuits describing the sample's behavior with increasing temperature were modeled. The activation energy for the sample's conductivity is virtually independent of temperature and is 0.466(5) eV, typical of semiconductors. No dielectric relaxation was observed for the sample. A bipolar conductivity model was proposed to describe the sample's electrical behavior.
One of the main disadvantages of sulfur concrete is the formation of a crack defect when cooled in metal molds. The proposed way of using sequential addition of components, temperature control at the entire mixing stage of the mixture is based on previous studies, which showed that the main factors determining the compressive strength of samples are both sulfur itself and its interaction with fine filler, as well as its strength properties. The work is devoted to determining the influence of technological factors and methods of preparing mineral components on the strength of sulfur-concrete samples. To prepare sulfur-concrete samples, ground industrial sulfur produced by Kaspiigaz LLC, natural zeolite of the Kempendyaysky field, and crushing waste from carbonate rocks of the Sasaabytsky field were used. For experimental studies, compositions were prepared with the following content: ground sulphur 30 wt. %, filled with fine zeolite powder in amount of 5 wt. % and limestone crushed stone screening – 65 wt. %, using three methods of preparing mineral components. For mixing, a developed forced mixer was used, which provided an upper load of raw materials and unloading of the finished sulfur-concrete mixture. The determination of the compressive strength of sulfur-concrete samples was carried out on an IP-1A-1000 test machine, structural studies of samples were carried out on a JEOL JSM-6480LV high-resolution scanning electron microscope. A scheme of a mixing installation is proposed, which made it possible to optimize the multivariable stages of preparing a mixture for making sulfur-concrete samples due to the special shape of the blades and their location on the rotating shaft, as well as uniform heating of the mixture, high-quality mixing of ingredients is ensured to obtain a homogeneous technological mixture, the properties of which are the same in any individual volume. A method has been selected that makes it possible to produce sulfur-concrete samples without defects and increase the compressive strength by 17 %.
The present study investigates the physicochemical and biological characteristics of 45S5 bioglass under conditions of its interaction with a buffer solution simulating a biological environment. The primary focus was placed on examining biodegradation and the dynamics of acid-base balance changes in the model medium. It has been confirmed that the effectiveness of the material for biomedical applications is determined by the particle size employed. The study addresses the problem of accurate fractionation and provides a comparative analysis of two sample preparation methods: wet and dry sieving. It was established that wet sieving promotes the removal of fine fragments from the surface of larger fractions and reduces the material's influence on local alkalinization of the medium. Using Ehrlich ascites adenocarcinoma cells, it was demonstrated that the cytotoxic effect is attributable to chemical necrosis induced by the alkaline environment localized at the surface of the bioglass particles. It is concluded that the material holds potential for application in the field of adjuvant therapy for malignant neoplasms. The findings obtained are of significant importance for the development of novel biomedical implants and therapeutic systems.
