Glass and Ceramics最新文献

This paper investigates borophosphate glasses containing FLiNaK salt additive, a eutectic mixture of alkali metal fluorides (46.5 mol.% LiF, 11.5 mol.% NaF, and 42 mol.% KF) that is a byproduct of developing molten salt nuclear reactors and a form of radioactive waste. The synthesized glasses exhibit a high degree of FLiNaK incorporation, reaching 20 – 25 wt.%, while maintaining a homogeneous, amorphous structure and uniform elemental distribution. However, at FLiNaK concentrations exceeding 25 wt.%, the glasses crystallize, forming an elpasolite (K₂NaAlF₆) phase. X-ray diffraction analysis reveals specific trends in the fluoride content of the glass. These trends suggest a correlation between the transformation of the glass local structure and the formation of a crystalline phase. This relationship will be examined more closely in future studies. Studies of the chemical and mechanical stability of synthesized glasses containing up to 20 wt.% FLiNaK demonstrate that these materials meet regulatory requirements for glass matrices used to immobilize radioactive waste. Additionally, the dependence of these properties on FLiNaK content shows an extremum at a concentration of 7 wt.%. However, no direct correlations with structural changes have been identified.

The properties of composite ceramic materials sintered from SiO₂–Al₂O₃–ZrO₂ nanopowders were studied. Prior to sintering, the powders were subjected to mechanical activation in a planetary ball mill using zirconia balls as grinding bodies. The activated powders were pressed under compacting pressures of 50, 100, 200, and 300 MPa. Consolidation was carried out in an atmospheric high-temperature furnace at 1700°C. The surface of the sintered bulk samples was examined using a scanning electron microscope. Elemental analysis made it possible to establish patterns in the distribution of chemical elements. All the studied samples revealed the presence of two phases — Al₆Si₂O₁₃ and ZrSiO₄. The sample porosity and its dependence on the applied pressure were established. The mechanical properties of the samples were studied using nanoindentation, including indentation hardness and elastic modulus. The bending strength limits of the studied samples were determined by scratch testing. The crack resistance of the samples was determined by the indentation method using the Marshall–Evans relationship. The effect of the ratio of the initial components and the applied compacting pressure on the physical and mechanical properties of the resulting composite ceramics was determined.

This study examines the phase formation process of a novel antimony-containing pyrochlore (space group Fd-3m) Bi_2.7Zn_0.46Ni_0.70Sb₂O_10+∆. The solid-state synthesis of this pyrochlore using oxide precursors is a complex, multi-stage process. The active interaction of the oxide precursors commences at temperatures exceeding 600°C, leading to the formation of an initial intermediate phase, Bi₃SbO₇. Individual oxide precursors, including bismuth trioxide and antimony tri- and pentoxides, are present in the sample up to 750°C. At temperatures above this threshold, a stable cubic phase, Bi₃M_2/3Sb_7/3O₁₁ (space group Pn-3), is formed, which remains stable up to 900°C. The pyrochlore phase first emerges in the sample at 650°C, with a substantial increase in its proportion observed at temperatures above 850°C. The formation of a pure pyrochlore phase occurs within the temperature range of 950 – 1050°C. The sintering of fine-grained ceramic is carried out at 1050°C. The obtained microstructure is characterized by low porosity, which is attributed to the coalescence of small grains into larger crystallites with a longitudinal size of 2 – 4 μm. The unit cell parameter of the pyrochlore varies unsteadily within the temperature range of 650 – 1050°C, reaching a minimum value of 10.464 Å at 800°C. The lattice parameter of the pure pyrochlore phase Bi_2.7Zn_0.46Ni_0.70Sb₂O_10+∆ is 10.474 Å.

This study developed technical ceramics for grinding media and examined how a dispersed oxide affects its key properties. The alumina-containing component used was waste catalyst from the gas processing industry. Nanodispersed aluminum oxide was synthesized from chemical reagents via the citrate sol-gel method. The results show that adding 3 wt.% of nanodispersed alumina (over 100 wt.% of the total mass leads) improves abrasion, acid resistance, and mechanical strength of technical ceramics.

This study investigates the processing characteristics of clay from the Stolinskie Khutory deposit (Vidibar sector, Brest Region, Belarus). The results indicate that the natural fine-grained material can be classified in accordance with GOST 9169–2021. The clay was identified as a refractory material, characterized by high plasticity. Depending on the depth of the occurrence, the material exhibits either semi-acidity or acidity, with a high to medium content of coloring oxides. The material displays a coarse-grained structure and does not sinter within the firing temperature range of 900 – 1200°C. We analyzed the phase composition of the clay and the processes occurring during its heat treatment. The findings indicate that this clay is suitable for the production of common bricks, coarse stone, and clinker material, as well as ceramic floor tiles. Samples of ceramic material produced under laboratory conditions using the Stolinskie Khutory clay demonstrate the requisite set of physical, chemical, and performance characteristics.

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.