The properties and specific features of contemporary low-melting borosilicate glazes for special and construction purposes are given.Low-melting borosilicate glazes are extensively used in the production of building materials. Materials whose surface is protected from the ambient medium and at the same time has good ornamental qualities enjoy a high demand lately. Such materials have become popular abroad. The challenge to be met by the Russian manufacturers is producing high-quality glazed ceramics for construction (facing brick, tiles, roof tiles). Therefore, revealing the regularities of the development of glaze formulas and preparation and production of low-melting glazes are topical problems.A ceramic surface can be glazed by fritted or non-fritted low-melting borosilicate glazes, since B 2 O 3 decreases melting temperature and increases the spreadability of glazes. Low-melting glazes contain water-soluble chemical compounds (soda, potash, saltpeter, borax, etc.). As glazes are deposited on ceramics in the form of aqueous suspensions, they are previously fused (fritted) at high temperatures for the purpose of transforming them into a water-insoluble state. Fritted glazes have a number of advantages over non-fritted ones. They are lasting, melt on articles at lower temperatures, and have higher quality. However, the production of fritted glazes raises energy consumption, which makes them more expensive than non-fritted raw glazes of the same compositions [1,2].A glaze for a particular ceramic base should be selected considering its TCLE and the melting point. One should also take into account data on viscosity (spreading), wettability, surface tension, and the evolution of the gaseous phase in glaze depending on increasing temperature.The fusibility of the glaze should be coordinated with the sintering of the ceramic substrate. The glaze should become completely melted after the end of the reactions involving gas emission from the ceramic base and from the glaze itself. The fusibility of glaze depends on its viscosity and the quantity of the liquid phase in the melted glaze.The main requirements imposed on glazes is the coordination between the TCLEs of glazes and ceramics. Only an insignificant difference (below 10%) in TCLE values is permissible. If the ceramic material has a higher TCLE, the glaze splits off in lumps. If the TCLE of the glaze is higher than the TCLE of the ceramic, the glaze in cooling develops cracks in the form of crackle.A glaze appropriately selected for the particular ceramics substantially increases its mechanical strength. The ratio between the TCLEs of the glaze and ceramics is responsible for stress formation, which affects the thermal resistance and mechanical strength of the article.Firing has a great effect on the strength of glazes. Unsatisfactory firing of a glazed product may produce crackle. Borosilicates formed at a high temperature partially dissolve the ceramic substrate; therefore, a zone of gradual transition from ceramic to glaze is formed at the site of contact of gl...
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A mix composition has been developed making it possible to obtain on the basis of diatomite from the Inzenskoe deposit (Ul'yanovsk Oblast') a heat-insulating brick with good strength characteristics exceeding previous values by a factor of 4 -5: compression strength 5.5 -6.5 MPa, density 0.5 -0.6 kg/cm 3 , thermal conductivity at 25°C 0.09 W/(m × K), and structure factor 0.95.The abundance of amorphous silica rocks on Russian territory makes all work on obtaining from them building and finishing materials, heat-insulating brick, and artificial porous fillers for concrete very promising.There are many deposits of diatomite and opoka on Russian territory within Middle and Lower Povolozh'e. In Ul'yanovsk Oblast', deposits of diatomite have been explored at the Zinov'evka station (town of Inza) and other locations. According to the data of [1], the thickness of the Inza formation of diatomite reaches 55 m, and the opoka formation reaches 30 m. Heat-insulating firing articles in the form of brick, shells and segments, as well as open filler for concrete are produced by "Diatomit-Invest" JSC (Ul'yanovsk Oblast') on the basis of diatomite. Two types of heatinsulating brick are produced: foam-diatomaceous articles by means of the slip technology and diatomaceous articles obtained by introducing burn-out additives by plastic molding technology. The drawback of these articles is low strength.A mix composition making it possible to obtain on the basis of diatomite a strong heat-insulating brick whose strength characteristics are four to five times greater than previous such indicators (RF Patent No. 2909793) has been developed at the Kazan State Architectural-Building University.The raw material was Inza diatomite, which is amorphous silica and light, porous, and loose and slightly clayey in places, with the following properties: molding moisture content of diatomite -50 -60%, refractoriness -1450 -1560°C, water absorption -43.3 -66.7%, true density -2.15 -2.2 g/cm 3 , apparent density -0.70 -0.97 g/cm 3 , and total porosity 54.9 -67.5%.According to the data obtained by All-Russia Scientific -Research Institute of Geology and Interior of the Earth (Republic of Tatarstan), Inza diatomite is an opaline-cristobalite rock with an admixture of feldspar, muscovite, and glauconite and containing 30 -50% 3 active silica. The chemical composition of diatomite (according to the All-Russia Scientific -Research Institute of Geology and Interior of the Earth data) is as follows (%): 79.46 -84.98 SiO 2 , 4.43 -8.37 Al 2 O 3 , 0.75 -2.86 Fe 2 O 3 , 0.01 -0.29 FeO, 0.19 -0.41 TiO 2 , 0.45 -1.90 CaO, 0.47 -0.97 MgO, traces -0.02 SO 3 , 0.96 -1.25 K 2 O, 0.18 -0.98 Na 2 O, and 5.44 -6.59 other impurities.According to [2], 1.1 -1.5 m 3 sawdust and 550 -600 kg diatomite, which amounts to 35 -50% sawdust relative to the diatomite mass, is used per 1 m 3 of diatomaceous articles obtained by burning out additives. For this content of sawdust it is impossible to obtain brick with even edges, so that the finished bricks must be straightened out wi...
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