Glass and Ceramics最新文献

Areview of the dielectric properties of ceramic materials based on solid solutions of alkaline earth metal titanates of perovskite structure is presented. Solubility ranges of components of two- and three-phase solid solutions are determined. The influence of the component concentration ratios, production methods, and technological parameters on the dielectric properties of ceramics is shown. On the basis of literature data, a three-component phase diagram for BaTiO₃, CaTiO₃, and SrTiO₃ has been compiled for the first time, which shows the relative permittivity values characteristic of various regions in the phase diagram. Ceramics with a content of Ba²⁺ > 40 mol.%, Sr²⁺ < 60 mol.%,, and Ca²⁺ < 40 mol.%, were found to exhibit the highest values of relative permittivity (> 700). An increase in the proportion of Sr²⁺ and Ca²⁺ leads to its significant decrease.

The influence of diamond grinding modes on the structure and mechanical properties of ceramics based on zirconium dioxide stabilized with magnesium oxide was studied. Powders of the ZrO₂ – 6 mol.% MgO composition were obtained by chemical coprecipitation from solutions of zirconium and magnesium chloride salts. The powders were pressed into specimens by cold isostatic pressing at maximum pressures of 55 and 200 MPa, followed by sintering at a temperature of 1700°C for 4 h. The resulting — both porous and high-density — specimens were machined at different cutting depths in the range of 0.003 – 0.010 mm. The surface roughness of the specimens was found to increase with an increase in the cutting depth. The machining of high-density specimens obtained at the maximum pressure of 200 MPa was established to create conditions for the implementation of a phase transition on their surface. Grinding facilitates the transition of the tetragonal phase of zirconium dioxide (t-ZrO₂) to a monoclinic phase (m-ZrO₂) on the surface of the specimens, which leads to an increase in the critical stress intensity factor (K_Ic) from 4.3 to 6.4 MPa · m^1/2. Machining of the specimens with an open porosity of 3.0 – 3.5% obtained by pressing at the maximum pressure of 55 MPa did not lead to phase transformations on their surface, with K_Ic remaining within the margin of error.

In this paper, we demonstrate the process of ultrafast femtosecond laser writing of birefringent waveplates in the bulk of nanoporous glass (NPG) and confirm the possibility of its acceleration by an order of magnitude relative to that in silica glass. In situ measurements of birefringent plate retardance were performed for heating and cooling stages in the 20 – 650°C temperature range. Femtosecond laser-written birefringent elements were found to exhibit a greater thermal stability relative to conventional crystal quartz plates under broad temperature variations. The results obtained are of particular interest to those involved in industrial fabrication of laser-written phase optical elements in NPG.

In this article, we analyze the process of obtaining VK94-1 ceramics modified with zirconium dioxide ZrO₂ and determine its properties, such as apparent density, mechanical bending strength, and Vickers hardness (microhardness) in comparison with those of VK94-1 ceramics. The effect of changes in the share of zirconium dioxide in the samples on the above properties is shown. The influence of firing temperatures on the sintering of samples is studied. Samples with different component ratios of VK94-1/ZrO₂ (90/10, 80/20, and 70/30) were pressed using an isostatic pressing machine at a pressure of 150 MPa. Firing was carried out at different temperatures of 1500, 1550, and 1600°C in different firing media.

Within the framework of the quasi-static unrelated problem of thermoelasticity, a criterion for the thermal strength of a freely pinched plate during pulsed laser annealing is obtained, taking into account the reflection of laser radiation from the back surface of the plate. The possibility of reducing the maximum tensile stresses in the plate by 15 – 65% and energy costs for annealing by 8 – 30% is shown. It was established that consideration of the reflection of laser radiation from the back surface of the plate leads to a decrease in the interval of variations of the dimensionless parameter ÷h (the product of the absorption index by the plate thickness), in which thermoelastic stresses may cause plate destruction.

This work is aimed at developing a method for forming an octacalcium phosphate (OCP, Ca₈H₂(PO₄)₆ · 5H₂O) coating on the surface of β-tricalcium phosphate (TCP, Ca₃(PO₄)₂ ) ceramics. Coatings were formed by immersing ceramic samples in buffer solutions with the main ionic composition of CH₃COO^– and Na⁺ under varying conditions (duration, pH value, and temperature). Crystallization of the OCP coating occurred sequentially by partial dissolution of the surface layers of TCP ceramics and crystallization of the intermediate phase of dicalcium phosphate dihydrate (DCPD, CaHPO₄ · 2H₂O). The effect of the buffer solution composition and the process conditions (duration, pH value, and temperature) on the phase composition, morphology, and thickness of the coatings was studied.

Materials based on silicon carbide (SiC) and the SiC–20B4C–1C–0.5B system were synthesized by spark plasma sintering. The characteristics of the powder mixtures and final materials were investigated using thermal analysis, electron microscopy, x-ray diffraction, and flexural strength testing. Thermal analysis revealed that SiC powders with boron (B) and carbon (C) additives exhibited accelerated mass loss, indicating enhanced sinterability and the formation of a grain boundary phase composed of boron–carbon compounds. The introduction of boron carbide promoted the formation of a secondary strengthening phase in the silicon carbide matrix. The primary phase of the material was the 6H–SiC polytype, which possesses a hexagonal α-SiC lattice. The mechanical testing of the SiC–20B4C–1C–0.5B composition demonstrated a flexural strength of 332 MPa at 20°C.

In this article, we describe the synthesis of a new oxide pyrochlore containing antimony (V) and bismuth (III) cations, Bi_2.7Ni_0.7Mg_0.46Sb₂O_10+∆ (sp. gr. Fd–3m, a = 10.4703 Å), from a stoichiometric mixture of oxide precursors using a modified sol–gel method (Pechini). It was established that the formation of antimony (III, V) and bismuth (III) compounds, which are volatile upon calcination, can be prevented by dissolving the precursors in sulfuric or nitric acid solutions and excluding the use of hydrochloric acid or chloride solutions. A step-by-step synthesis of two samples in sulfuric and nitric acid media was carried out; the phase composition of the materials calcined in the temperature range of 350 – 950°Ñ was analyzed. The calcination of the sample synthesized in a sulfuric acid solution led to the formation of the Bi_12.67O₁₄(SO₄)₅ phase, which prevented the formation of pyrochlore in the low-temperature region. In the sample synthesized in a nitric acid solution, Bi₃SbO₇ and BiNbO₄ bismuth stibates were recorded as intermediate phases. Sb₂O₄, Bi₁₂MgO₁₉, Bi_7.47Ni_0.53O_11.73, Bi₃Ni_2/3Sb_5/3O₁₁, and NiSb₂O₆ were identified as other intermediate phases. The synthesis temperature of single-phase Bi_2.7Ni_0.7Mg_0.46Sb₂O_10+∆ with a pyrochlore structure was found to be 950°C. The phase purity and chemical composition of the sample were established by XRD analysis and energy-dispersive x-ray spectroscopy (EDS).

Statistical data on the strength of flat glass is analyzed. The following issues are considered: theoretical models of the strength of flat glass, parameters determining the strength value, the probabilistic nature of destruction of flat glass when used as building glazing, selection of a strength value distribution of flat glass, data censoring, determination of the probabilistic characteristics of flat glass strength, including the normative value of bending strength.

Samples of zinc–tellurite glasses, activated by magnetite and barium titanate nanoparticles, were synthesized by the melt quenching technique. Functional properties of the glasses were experimentally investigated by the methods of XRD analysis, optical and polarization spectroscopy, and SQUID magnetometry. The XRD data confirmed the amorphous structure of the glasses. The bandgap values of the samples were obtained based on the optical spectroscopy data. The study of electric and magnetic field dependencies of electric polarization and specific magnetization established the evolutionary development of the shape of electric and magnetic hysteresis loops depending on the composition of glasses due to the interaction of charged γ-Fe₂O₃ clusters and barium titanate nanoparticles.