Steklo i Keramika (Glass and Ceramics). Monthly scientific, technical and industrial journal

 

ISSN 0131-9582 (Online)

The main industrial method for manufacturing precision metal parts with high surface finish, such as turbojet engine blades, is investment wax casting. When manufacturing a wax model, a ceramic embedded element (rod) is placed inside it to form a complex-shaped cavity designed to reduce the weight of the casting, and forming channels for the cooling system of the blades with secondary air after the rod is removed. The main technological problem in the removal of internal rods is their strength and high chemical inertness, which is why the duration of their removal and labor costs for this operation are quite large. The paper presents a study of a method for manufacturing ceramic rods with uneven strength in depth, which makes it quite easy to remove the soft core, followed by the dissolution of a stronger periphery.
It has been established that the high temperature of decomposition of amorphous Al(OH)3 makes it possible to directly sinter corundum ceramics from aluminum hydroxide, bypassing the stage of its preliminary thermal dehydration. Cold isostatic pressing at pressures of 200, 600, and 1000 MPa was used to make compacts with a density of 62, 69, and 79 % of the theoretical density. The temperature dependence of the shrinkage of compacts of amorphous Al(OH)3 as a function of the pressure of cold isostatic pressing has been studied. A region of intense shrinkage was found in the region of 1050 – 1150 ?C, which coincides both with the temperature of complete decomposition of amorphous Al(OH)3 and with the ???-Al2O3 transition.

A method of fastening optical fiber in a quartz connector with a sodium polysilicate hydrogel obtained in a cylindrical gap between the connector and the fiber due to the alkaline decomposition of quartz surfaces of parts was developed.
The conditions of thermal decomposition of the hydrogel are determined and it is shown that the decomposition of the hydrogel with the formation of a cellular structure is possible at temperatures below the temperature of thermal decomposition of the polymer coating of the fiber. The conditions for obtaining and thermal properties of the hydrogel are determined. Conclusions are drawn about the suitability of the proposed method for fixing optical fiber in a quartz connector.

Methods of laser micro- and nanomodification structure of transparent dielectrics open promising prospects for the creation of a new type glass-crystalline materials and new applications. In this work, after a brief excursion into the history of glass-ceramics, transparent aluminosilicate glass-ceramics are discussed, mainly using the example of the Li2O–Al2O3–SiO2 system, and the areas of their new applications. The recently discovered possibilities of laser micromodification of structures and direct laser writing of elements photonics and integrated optics in their volume are considered. In this case, special attention is paid to transparent glass-ceramics with coefficient of thermal expansion close to zero.
The influence of the eutectic additive of the Li2O–B2O3 system on the sintering process and dielectric properties of ceramics based on Li2MgTi3O8 has been investigated. It was determined that the introduction of an additive in the amount of 10.0 – 15.0 % contributes to the sintering of ceramics by a liquid-phase mechanism. Li2MgTi3O8 ceramics, containing a sintering additive in an amount of 15.0 % and obtained at a firing temperature of 900 ?С, demonstrates the following level of properties ?av = 3.04 g/cm3, Po = 5.7 %, ?r = 19.0 and tg? = 0.028. The lowered sintering temperature of ceramic will allow the production of various electronic components based on it using low-temperature cofiring ceramic (LTCC) technology, and the specified level of dielectric properties will allow to miniaturize the devices.
For the first time, a local Abrio method for estimating birefringence was applied to hardened glasses, and the distribution of microstresses in float glass subjected to ion exchange hardening was studied. The possibility of precision determination of the thickness of the stressed layer is shown, the correlation between the depth of the stressed layer and the penetration depth of potassium cations during ion exchange is established.
The purpose of this work is to study the effect of scandium in the dodecahedral and octahedral positions of the garnet crystal lattice on the features of vacuum sintering of optical ceramics Y3-хScxAl2-yScyAl3O12:Cr, as well as on its optical and luminescent properties. YSAG:Cr optical luminescent ceramics were manufactured for the first time from ceramic powders of metastable compositions with a high scandium content in a dodecahedral position. The considered compositions were described by the general formula Y3-хScxAl2-yScyAl3O12, where 0,12 ? x ? 1,50 and 0,08 ? y ? 1,00 f. u. with a total scandium content from 0.12 to 1.70 f. u. The following studies of YSAG:Cr: ceramic samples were carried out:
X-ray diffractometry, measurement of the shrinkage kinetics of ceramic compacts by dilatometry, study of the morphology and elemental composition of the ceramic surface by scanning electron microscopy (SEM). The light transmission and luminescence spectra were measured. It is shown that ceramics made from compositions with a predominant scandium content in the dodecahedral position reach maximum density at lower temperatures compared to compositions containing a greater amount of scandium in octahedral positions. It was found that with an increase in the sintering temperature of YSAG:Cr ceramics compositions with a high scandium content in the dodecahedral position become unstable.
An energy-efficient synthesis of highly porous ceramic materials based on Sc2O3 was carried out using a combination of compaction and technological combustion methods with the participation of active binders. Using XRD, SEM, and EDA methods, it was found that the material has a highly developed multilevel microstructure morphology based on Sc2O3 and tortveitite Sc2Si2O7. The main characteristics of the pore space of the material (porosity, pore size, specific surface area, permeability, etc.) were determined by mercury porosimetry and alternative methods.
In this study, the changes in the morphology and degree of agglomeration of both precursor powders and ceramic YAG powders under varying grinding conditions was considered. The effect of these parameters on the optical properties and structure of the ceramics was assessed. The YAG precursor powders were obtained through chemical co-precipitation.
The morphology, size of agglomerates, and crystallites was evaluated using scanning electron microscopy, laser diffraction analysis, X-ray phase analysis, and Brunauer–Emmett–Teller gas adsorption.
It was found that milling the YAG precursor powders allows for a reduction in the degree of agglomeration of the ceramic powders. It was discovered that optimal modes can be achieved at a mass ratio of grinding balls to precursor powder of 6.75/1 and a ratio of the mass of the grinding medium to the mass of the precursor powder of 4.5/1. These modes provide the necessary granulometric characteristics and the highest monodispersity. Therefore, it has been demonstrated that the use of an additional milling stage for powders synthesized by chemical precipitation, along with the selection of milling modes, can improve the properties of YAG optical ceramics.
The article discusses the possibility of using quartz sands from the Oynakum deposit as a promising source of high-quality quartz-containing raw materials for the glass industry in order to obtain higher grades of glass. The chemical, granulometric and mineralogical composition of quartz sands of the Oynakum deposit was studied, high concentrations of quartz sand were obtained using various enrichment schemes.