What is the specificity of the structure of Citalls?

Sitalls are glass-crystalline materials consisting of one or more crystalline phases uniformly distributed in the glassy phase. Unlike ordinary glasses, the properties of which are determined mainly by their chemical composition, for glass ceramics the structure and phase composition are of decisive importance. The reason for the valuable properties of glass ceramics lies in their exceptional fine grain, almost ideal polycrystalline structure, which provides a combination of high hardness and mechanical strength with excellent electrical insulating properties, high softening temperature, good thermal and chemical resistance. The properties of glass ceramics are isotropic. They have absolutely no viscous porosity. The shrinkage of the material during processing is insignificant. Their high abrasive resistance makes them insensitive to surface defects. The density of glass ceramics is in the range of 2400-2950 kg/m 3, bending strength is 70-350 MPa, tensile strength is 112-161 MPa, compressive strength is 7000-2000 MPa. Elastic modulus 84 – 141 GPa. The strength of glass ceramics depends on temperature. Their hardness is close to the hardness of hardened steel (V – 7000-10500 MPa). They are very wear-resistant (f_mp = 0,07—0,19). The linear expansion coefficient lies in the range (7–300)10 -7 s -1 . Citales with a small coefficient of linear expansion are very heat resistant. As a result of their increased density, glass-ceramics are superior to glass in thermal conductivity. Thermal resistance is high in the temperature range 50 -9000°C. The thermal stability of glass ceramics is ensured by very small and sometimes negative (from -7 -10 to +7 -3) thermal expansion coefficients. Specific volume resistivity 10 7 -10 8 Ohm.m, electrical strength 10-12 MV/m, dielectric loss tangent at 25 75 Hz (10-6).10 -800. Many glass ceramics have high chemical resistance to strong acids (except fusible acid) and alkalis. Glass-crystalline materials are divided into a number of types, the most important of which are glass-ceramics, obtained from technically pure materials, and slag-ceramics, obtained from cheap raw materials – metallurgical slag. Sitalls are also divided into technical and construction. According to their main properties, technical glass is divided into: high-strength; radio transparent chemical resistant, transparent heat resistant, wear resistant and chemical resistant; photositals; mica ceramics; biositals; glass cement; ceramic enamel; glass ceramics with special electrical properties. The technology for producing glass ceramics consists of several operations. First, products are made from glass melt using the same methods as ordinary glass. Then it is most often subjected to two-stage heat treatment at temperatures of 500-700°C and 900-1100°C. At the first stage, the formation of crystallization nuclei occurs, at the second – the development of crystalline phases. To ensure uniform fine crystallization throughout the entire volume, two approaches have been developed: homogeneous and heterogeneous nucleation. If the formation of crystallization centers during the nucleation of a new phase of a substance inside another phase occurs in the absence of foreign particles, then such a process is defined as homogeneous crystallization. Otherwise, it is catalyzed or heterogeneous crystallization. Using homogeneous crystallization, ruby, opal and some photosensitive glasses are obtained, and using the second technology, glass-crystalline materials are obtained. The content of crystalline phases by the end of the technological process reaches about 95%, the sizes of optimally developed crystals are 0,05-1 microns. The change in size during crystallization does not exceed 1-2%. Since the synthesis of glass-ceramics can be carried out taking into account pre-specified requirements, glass-ceramics can differ in one main property, for example, mechanical or thermal strength, chemical resistance, wear resistance, transparency, etc., or have a complex of necessary properties. This predetermined a wide range of uses of these crystalline materials. The high performance characteristics of glass ceramic products (strength and wear resistance, chemical resistance, ability to withstand high temperature changes) provide this class of materials with the possibility of widespread use in construction as a facing material, elements of laminated panels in the structures of industrial buildings. Slag-sitall has proven itself well as a material for flooring in industrial and civil buildings, for cladding external and internal walls, and for lining building structures exposed to chemical influences and abrasive wear. To expand the color range of slag ceramic, its surface can be decorated with silicate enamels. Sitall has high strength, hardness, chemical and thermal resistance, and a low thermal expansion coefficient, which is why enterprises in the chemical, coke-chemical and oil refining industries use products made from glass-ceramic (panels, pipes, electrical insulators, etc.). They are produced using glass or ceramic technology. Sitalls are also used for sealing electric vacuum devices, in optics, etc. Photositalls are widely used in microelectronics, rocket technology, space, optics, printing and household appliances: perforated disks are made from photositalls, used in cathode ray tubes, etc. . Glass-crystalline coatings applied to the surface of various metals to protect them from corrosion, oxidation and wear at normal and elevated temperatures have become very widespread in chemical engineering. The areas of application of glass ceramics in the electronics industry are expanding. They are used as dielectric insulation of microcircuits and interlayer insulation of printed circuits on ceramic and other substrates. Sitalls based on rocks (perlite and dolomite) are recommended for the manufacture of high-voltage rod and pin electrical insulators. In everyday life, heat-resistant household utensils are made from glass ceramics – pots, braziers, stewpans.

Sitalls and slag-sitalls. Cast stone products

Sitalls and slag-sitalls

Sitally – glass-crystalline materials obtained by directional crystallization of glass, i.e., the structure of glass ceramics – the type of crystals, their size and quantity – are regulated during the production process. The peculiarity of the structure of glass ceramics is characterized by the fact that between very small crystals (several microns) the glassy phase is evenly distributed (with a layer of about 1 micron), the amount of which in well-crystallized materials is 5. 10%. The structure of glass ceramics, ensuring the preservation of the positive properties of glass, gives them increased mechanical strength, thermal and chemical resistance, dielectric properties, and reduces fragility. The basis glass ceramic technology The principle of catalyzed crystallization is based. To do this, additives are introduced into the melt to catalyze crystallization during subsequent heat treatment of the material. Heat treatment is carried out according to a stepwise regime: first, the material is kept at a temperature corresponding to the maximum rate of formation of crystallization centers, and then at the temperature of the maximum rate of crystal growth. In this way, the required degree of crystallization of the material is achieved, with the required crystal size. Sitall – a modern, beautiful and reliable material with a fine-grained structure and the thinnest layers of glass between the crystals. In the Soviet Union, it was obtained in the 50s at the Moscow Institute of Chemical Technology named after D.I. Mendeleev, at the Department of Glass (now “Glass and Sitall”). Sitally – glass-crystalline materials obtained by volumetric crystallization of glasses and consisting of one or more crystalline phases uniformly distributed in the glassy phase. The structure of glass ceramics resembles microconcrete, where the filler is crystals and the binder is layers of glass. The proportion of glass phase in glass ceramics is usually 20. 40%. The crystalline phase consists of microcrystals with a size of about 1 micron. Thanks to this structure, glass ceramics retain many of the positive properties of glass, including its manufacturability, but are free from its disadvantages: fragility, low heat resistance. The raw materials for the production of glass ceramics are the same as for glass, but modifier substances are introduced into the melt to ensure directional crystallization. Sitally are obtained from the same raw materials as glass, with the addition of special additives (for example, lithium compounds), but very high requirements are placed on the purity of the raw materials. Fluorides and phosphates of alkali and alkaline earth metals are used as crystallization catalysts. By selecting the glass composition, which in most cases contains additives that accelerate bulk crystallization (catalysts, nucleators), it is possible to design the corresponding crystalline and glassy phases. Crystals of the designed phases appear and grow uniformly throughout the entire volume as a result of heat treatment. The technology for producing glassware products differs slightly from the production of glass products. In some cases, products can be molded using ceramic technology. Sometimes photosensitive additives are introduced into the glass to nucleate crystals. Slag is used to produce certain types of glass ceramics. There are lithium, boron-barium, magnesium, titanium and other glass ceramics. Citales have low density (they are lighter than aluminum), high mechanical strength, especially compressive strength, hardness, heat resistance, thermal resistance, chemical resistance and other valuable properties. Citaals have most of the positive properties that glass has, including manufacturability. There are glass ceramics with special properties: transparent, magnetic, semiconductor, radiotransparent and others. The hardness of most glass ceramics is 6,5-7 Mohs units, bending strength is up to 250 MPa, heat resistance is up to 1000 °C. Sitally used mainly in special branches of technology (for example, in radio electronics). In industrial and civil construction they can find application in the form of structural finishing material. There are significantly greater prospects for construction slag ceramics. This is due to the availability of raw materials – metallurgical slags, while maintaining the valuable technical properties characteristic of glass ceramics. The word “ceramic glass” was introduced into scientific use by Professor Isaac Ilyich Kitaygorodsky – as a derivative of the words “glass” and “crystal”. And he also came up with the idea of ​​widely using waste from various industries, including blast furnace slag, as a raw material for the production of glass and glass ceramics. The first slag ceramics, depending on the purity of the slag raw material and its composition, were obtained in gray, brown, greenish-brown tones. The composition of the slag is not constant. And the ratio of oxides in it is not always the same as it should be in slag ceramic. Therefore, additives were introduced into the mixture (a mixture of components), the main one of which was sand. In any glass-ceramic there are two phases – crystalline and amorphous, glassy. The properties of the material are ultimately determined by the properties of the crystalline phase. Crystallization occurs during the heat treatment of glass obtained from slag, and this process is catalytic. A catalyst is needed so that crystallization occurs not only from the surface, but throughout the entire volume of the glass. Catalysts include sulfides, fluorides, metal oxides and combinations of these compounds. The work on creating new material was led by I. I. Kitaigorodsky. He demanded a lot from his employees and at the same time did not forgive disregard for other people’s business, for the requests and requirements of production. For example, such a case is known. When slag ceramic had already been obtained and its introduction into practice began, one of the builders asked a question at the meeting: “What is the nailability of slag ceramic?” For a builder, the question is reasonable, but the chemists understood that the question was absurd. It’s almost like asking, “Can you drive a nail into glass?” The mentioned “unstickability” reflects the main drawback of slag glass – its fragility, although less than that of glass. And this is perhaps its only serious drawback. And slag glass has many advantages: it is durable, hard, and reliable. The abrasion strength of slag ceramic is especially high. It wears out more slowly than cast stone, not to mention marble, granite, ordinary technical glass and ceramics. In addition, it is frost-resistant and does not absorb dust and moisture. Gray slag-sitall – the floors of the Moscow department store are covered with slabs of this material. Black-brown-gray slag ceramic has been used in technology and construction since 1966. To use it as a decorative material, it was necessary to expand the color range. Colored slag ceramics could be obtained using dyes – from white. White slag-sitall did not turn out right away, but chance helped. At the glass factory in Konstantinovka, slag glass was boiled in four crucibles in a small furnace. It was assumed that the result would be glass of the same composition, but when the samples were cast, it turned out that in two crucibles the glass was dark, as it should be, and in the other two it was white due to an error in the composition. Instead of alumina, zinc oxide was poured into two crucibles. As a result, the sulfide sulfur contained in the slag, which usually interacted with the oxides of iron and manganese, this time reacted with zinc oxide. Zinc sulfide colored the glass white. However, in repeated experiments, white slag-sitall was not obtained immediately. The composition of the slag is variable, and the amount of sulfur it contains is also variable. In order to retain the required amount of sulfur (in the form of ZnS) in the glass, for the sake of white color, black coal was also added to the charge. When white slag glass was obtained, they tried to make everything from it: slabs, pipes, sinks. But the technology for producing complex profile products from slag-ceramic turned out to be expensive and complex. And sheet slag glass is produced by conventional glassmaking methods – continuous rolling. The production of white slag glass was launched in 1970 at the Avtosteklo plant in the city of Konstantinovka. Panels and slabs made of this material are widely used for cladding facades. This material is needed not only by builders. In electrical engineering, slag-sitall insulators are used. At coal processing factories in Donbass, slag-vitamin cones of hydrocyclones are used instead of similar parts made of steel and cast iron, the service life of which is several times shorter. Still, the main thing is construction. Slagositala obtained on the basis of metallurgical slags and modifiers – CaF₂, TiO₂ etc. Slag ceramics have very high strength (R_squeeze = 300. 600 MPa; R_izh = 90…120 MPa), wear resistance and chemical resistance. In terms of durability, slag ceramic can compete with natural stone materials (granite, gabbro, etc.). The use of slag-sitalls is promising for the chemical industry (pipes, tiles, pump parts), in hydraulic engineering (for lining turbine chambers, spillways), in road construction, etc. Slag-sitalls were first synthesized in 1959 as a result of joint work at the Konstantinovsky (Donetsk region) plant “Avtosteklo” and the Moscow Institute of Chemical Technology. Mendeleev. Slag crystals obtained from fire-liquid slags, into which additives are introduced that correct their chemical composition, and crystallization catalysts (TiO modifiers₂,CaF₂, P₂O₅ and etc.). Slag ceramics with a density of 2500. 2650 kg/m3 have high strength (in compression up to 650 MPa, in bending up to 120 MPa), low water absorption (close to zero). Particularly valuable qualities of slag ceramics are high chemical and thermal resistance, frost resistance and low abrasion. Slag crystals are manufactured in the form of continuous strip and pressed plates. They are painted white or gray in bulk and can be coated with colored ceramic paints. Products made from slag ceramics are used in construction, chemical, mining and other industries to protect building structures and equipment from corrosion and abrasive wear. Slag ceramics are also used for paving floors, external and internal cladding of walls and for other purposes. Flat sheets are used to cover the plinths and walls of buildings; They are used to cover the floors of buildings with heavy traffic (shops, metro stations, etc.). It is advisable to use corrugated sheets for roofing of chemical plants. Slag ceramics can be used for lining building structures and devices subject to chemical aggression and abrasive wear (lining of hydraulic structures, floors and chemical production devices), as well as pipes and other products. It is also possible to obtain porous slag-sitall (foamed slag-sitall) with a density of 300. 600 kg/m3 and a compressive strength of 6. 14 MPa. It is very possible to combine dense sheet slag-sitall with foam slag-sitall in wall and other structures. The production of slag glass consists of melting slag glass, molding products from it, and then crystallizing it. The charge for glass production consists of slag, sand, alkali-containing and other additives. The use of fiery liquid metallurgical slags is effective, which saves up to 30-40% of the total heat spent on cooking. Slag glass is prepared in two stages: 1) the raw material is pre-cooked in a converter, where liquid slag and other raw materials are mixed; 2) the resulting glass melt is clarified in bath furnaces. To obtain white and gray slag glass, zinc oxide is added to the glass composition, blue shades – chromium oxide, black – iron and manganese sulfides. The surface of slag ceramics can be painted with colored ceramic paints. Slag ceramics in the form of rolled sheets, pressed plates, pipes and other products are produced on mechanized production lines. The molded products enter the crystallizer, where they are subjected to heat treatment. Slag ceramics differ from most building materials in having higher physical and mechanical properties (Table 2.16). Thus, their strength is several times higher than the strength of the original glass and is close to the strength of cast iron and steel. At the same time, slag ceramics are 3 times lighter. The heat resistance of slag crystals reaches 150-200 °C. The indicators of chemical resistance and abrasion resistance are especially high. Slag ceramics can be subjected to various methods of mechanical processing: grinding, polishing, cutting, drilling with diamond or carborundum tools. This material can be strengthened by hardening by 50-100%. Slabs of sheet slag-sitall are used to cover the plinths and facades of buildings, to finish internal walls and partitions, and to make fencing for balconies and roofs. Slag ceramic is an effective material for steps, window sills and other structural elements of buildings, as well as floors of industrial and civil buildings. Pipes, high-voltage insulators, etc. are made from slag ceramics. High wear resistance and chemical resistance make it possible to successfully use slag ceramics to protect building structures and equipment in the chemical, mining and other industries. Along with dense, porous slag-sitall (foam-slag-sitall) is obtained, which is a good thermal insulation material. The economic effect of using slag glass depends on the area of ​​construction and the type of traditional materials being replaced.

Cast stone products

Cast stone products made from molten rocks or slag by casting into molds followed by heat treatment. In terms of uniformity of structure and technical properties, cast products are superior to many natural stone materials. The raw materials for producing stone casting are igneous rocks, most often basalts and diabases. The use of metallurgical slag for these purposes is very effective. Melted products from such raw materials are dark in color. To obtain light stone casting, sedimentary rocks, mainly carbonate rocks (dolomite, chalk, marble), and quartz sand are used. The technology of stone cast products includes the preparation of raw materials (crushing, grinding, mixing), melting, casting of products, crystallization and annealing. Melting of diabase and basalt is most often carried out in bath furnaces or cupola furnaces at a temperature of 1400. 1500 °C, and in the production of light stone casting – in electric furnaces. When the castings are cooled below 1300°C, the crystallization process begins, followed by annealing – slow cooling of the products. During the annealing process, internal stresses that arose during the initial stage of cooling and crystallization of the mass are removed. It is more economical to produce cast stone products from slag using fire-liquid slag, since in this case no additional fuel is required to melt the raw materials. The porosity of cast stone products does not exceed 2%; all pores are closed and therefore the material practically does not absorb water, has high frost resistance and great strength: in compression – up to 400 MPa, in bending – up to 65 MPa and low abrasion (3. 5 times less than that of granite, basalt, diabase) . They are characterized by high dielectric properties, heat resistance and chemical resistance. In construction, cast stone products are used in particularly difficult operating conditions (floors of industrial enterprises, tiles and other products for cladding critical parts of buildings and anti-corrosion coatings, stones and slabs for roads, pipes and lining of chemical equipment and mills). The cost of stone casting, especially light-colored ones, as well as glass ceramics, is relatively high, but taking into account their durability, their use is economically profitable. 1. Instrument Designer’s Handbook. Design. Basic norms / V. L. Solomakho, R. I. Tomilin, B. V. Tsitovich, L. G. Yudovin. – Mn.: Higher School, 1988. – P. 130. – 272 p. — 16 copies. — ISBN 600-5-339-00091

• Materials and products from silicate melts
• Glass: general information, composition and properties
• Modern glass production
• Types of glass and glass products in construction
• Sitalls and slag-sitalls. Cast stone products