VOL 95, No. 11 (2022)

The effect of boron oxide additives in the amount from 0 to 11 mol. % was studied on the melting characteristic of glasses in the SrO–Al2O3–TiO2–ZrO2–B2O3–SiO2 system for use as fillers in dental filling composites in order to reduce
the melting temperature to technologically acceptable values (no more than 1500 ?C) and increase the transparency of the produced granulate. It was found that with an increase in the B2O3 content, the melting temperature can be reduced from 1600 ?C (in glasses without B2O3 additives) to 1480 ?C with a B2O3 content of 11.8 mol. %, while the glass transition temperature decreases from 820 to 743 ?C. Already with a B2O3 content of 6 mol. % at a melting temperature of 1500 ?C, transparent glasses with light transmission of 80 % are produced, promising for the creation of sealing composites.

Glasses were obtained in the SiO2–Al2O3–SrO–P2O5–F system with a phosphorus oxide content in the range of 7 – 12 mol. %. The set of properties of the obtained glasses (refractive index 1.514 – 1.535, TCE 44?10–7 – 61?10–7 K–1, transmittance above 85 %, radiopacity not less than 300 %) in the aggregate with the processability of synthesis (melting temperature below 1500 ?C) indicates that they are promising candidates for use as fillers of glass ionomer cements for dentistry.

Modern trends in the development of technologies for matting glass and glass products are considered. An effective technology of glass matting using alternative energy sources, in particular low-temperature plasma, has been developed.
It is shown that when matting with iron powders with a dispersion of 160 and 450 microns, a high-quality matte surface of the “frosty” matting type is formed. The microstructure of the matted surface is investigated. Theoretical aspects of glass matting are considered. The technological parameters of matting are determined and the economic efficiency of the developed technology is shown.

A study was made of the heat maximum transfer coefficients and thermal conductivity of glass coatings of heat exchange tubes. A formula is obtained for determining the optimal value of the thermal conductivity coefficient of a glass coating.
It has been established that during long-term operation of the apparatus, the heat transfer coefficient of the glass coating of the pipe practically does not depend on the operating time due to the cleanliness of the glass surface.
It has been established that during long-term operation of the apparatus, the heat transfer coefficient of the glass coating of the pipe practically does not depend on the operating time due to the cleanliness of the glass surface. At the same time, in brass or copper pipes, over time, a sharp drop in the heat transfer coefficient occurs due to the formation of a durable layer of scale and corrosion products. For this purpose, a formula has been derived for calculating the value maximum of the heat transfer coefficient of coatings.

Dielectric properties of ceramic materials based on BN–ZrB2 and BN–ZrO2 systems synthesized in the mode of self-propagating high-temperature synthesis (SHS) from a mixture of boron B powders, boron nitride BN and zirconium dioxide ZrO2 in an atmosphere of nitrogen N2 have been studied. The experimental results showed that ceramics synthesized from the initial mixture of (30B + 10ZrO2 + 60BN, wt. %) composition have permittivity (?) and tangent of the dielectric loss angle (tg) values of 2.63 and 0.006, respectively, at room temperature.

The types of additive manufacturing and the prospects of their application for the production of articles from ceramic materials are considered. The most popular for obtaining parts of complex configurations are such additive technologies as laser stereolithography, digital light processing, inkjet printing, direct ink writing, three-dimensional printing, selective laser sintering, selective laser melting, lamination object manufacturing, layer-by-layer fusion of material.

The possibilities of obtaining metal-ceramic materials of the composition Al2O3–Al by liquid-phase oxidation of aluminum by purging the melt with oxygen are considered. The manufacturability of this process makes it possible to avoid the use of powder materials, which leads to a large variability in the formation of the phase components of the materials obtained and a reduction in the cost of their production in comparison with powder metallurgy methods. It is established that by regulating the oxidation process by changing the speed and supply of the gas mixture, it is possible to obtain metal-ceramic composites with different geometric configurations of the ceramic phase and its quantity. An algorithm is proposed for calculating the kinetics of aluminum oxidation during the production of the ceramic phase of a metal-ceramic composite, taking into account the peculiarities of the thermophysical process.

The effect of the concentration (from 18 to 6 %) of an alkaline activator (AA) solution on the viscosity and basic properties of geopolymer composites based on chamotte with additives of foam glass production waste, multi-walled carbon nanotubes (MWCNT) and air-entraining additive (AEA) after heat treatment at different temperatures. In specimens with АЕА, the density decreases from 1600 to 1240 kg/m3, strength from 20.0 to 2.6 MPa and shrinkage from 5.9 to 1.5 % after firing at a temperature of 1000 °C. Combined use of АЕА and MWCNT allows to increase strength up to 7.9 – 10.3 % and reduce specimen shrinkage up to 16.0 – 8.2 %.