ceramic called stone products obtained from mineral raw materials by molding and firing at high temperatures, as a result of which the raw material irreversibly passes into a durable, waterproof state.
The term "ceramics" comes from the Greek word "kerameia", which in ancient Greece was called the art of making products from clay. Ceramics is perhaps the first artificial building material obtained by mankind. The age of ceramic brick as a building material exceeds 5000 years.
In modern construction, ceramic products are used in almost all structural elements of buildings and structures.
By purpose, ceramic materials and products are divided into the following types:
According to the structure, ceramic materials are divided into porous having a water absorption by weight of more than 5%, on average 8 ... 20% (wall, roofing and cladding materials, etc.), and dense having a water absorption by weight of less than 5% (floor tiles, road bricks, some types of pipes, etc.).
Raw materials for the production of ceramic materials are divided into plastic and non-plastic. Clays are used as plastic components, and additives are used as non-plastic ones, which are introduced to control various properties of both the molding mass and finished products.
Clay- this is a sedimentary rock of a fine-earth structure, capable of forming a plastic dough when mixed with water, which, after firing, irreversibly turns into a stone-like state.
An important property of clays is their granulometric (grain) composition. Depending on the size of the particles, different fractions are included in the clay. Clay substances are scaly-shaped particles that have a size of less than 0.005 mm. Dust particles have a size of 0.005 to 0.16 mm, sand - from 0.16 to 2 mm, larger particles are called stony inclusions. The ratio between the fractions that make up clays affects the basic properties of clays (to be discussed below) as raw materials for the production of ceramic materials.
Another important characteristic of clays is their chemical composition, which includes various clay minerals, the main of which is kaolinite Al2O3 2SiO2 2H2O. In addition, clays may contain related minerals: halloysite Al2O3 2SiO2 4H2O, montmorillonite Al2O3 4SiO2 n H2O, etc. Clay can contain as impurities: crystalline silica SiO2, calcium carbonates CaCO3, iron compounds Fe(OH)2, Fe2O3, alkali metal oxides (Na2O, K2O), etc.
Clay, mixed with a certain amount of water, forms a clay dough, which has a number of physical, physico-chemical and chemical properties, collectively called ceramic.
Plastic- the property of clay dough to deform under load without the formation of cracks and ruptures and to retain the given shape after the load is removed.
When dry clay is wetted, water molecules are drawn between the scaly particles of the clay substance, wedge them, form a hydrated shell on the surface of the particles, and cause the clay to swell. Hydration shells act as a lubricant that facilitates the sliding of clay particles.
Plasticity depends on the content of the clay substance in the clay and on the size of the particles. The higher the clay content and the finer the particles, the more plastic the clay. According to the degree of plasticity, clays are divided into: highly plastic, the water demand of which is more than 28%; medium-plastic, having a water demand of 20 ... 28%, and low-plastic with a water demand of less than 20%.
connectedness is the force required to separate the clay particles. Clays containing an increased amount of clay fractions have high connectivity.
Binding ability- the ability of clays in a wet state to easily mix with non-plastic materials and, when dried, bind them into a sufficiently strong product - raw material.
Air shrinkage- reduction of linear dimensions and volume of clay during drying. During the drying process, the water evaporates, the thickness of the water shells around the clay particles is reduced and the individual clay particles approach each other. Air shrinkage is related to the plasticity of clays: the higher the plasticity, the greater the air shrinkage. Highly plastic clays have an air shrinkage of 10…15%; medium-plastic - 7 ... 10% and low-plastic - 5 ... 7%.
fire shrinkage- reduction of linear dimensions and volume of clay during firing. During the firing process, the most fusible clay compounds pass into the melt, which envelops the unmelted particles, fills the gaps between them, and, due to the action of the surface tension forces of the liquid phase, causes the particles to approach each other. Fire shrinkage is 2…6%.
Full shrinkage- the sum of air and fire shrinkage.
As noted above, these materials are introduced as additives to control the properties of both clay raw materials and finished products.
Skinny Supplements- are introduced to reduce the plasticity of clays and, as a result, to reduce air shrinkage. Fireclay, dehydrated clay, thermal power plant ash, crushed granulated slag, and natural sand are used as lean additives.
Chamotte - pre-fired and crushed to the required size (less than 2 mm) clay. Dehydrated clay is clay fired at a temperature of 500…600 °C. At this temperature, chemically bound water is removed from the clay minerals and the clay irreversibly loses its plasticity properties.
plasticizing additives- are introduced to improve the plasticity of clays. For these purposes, highly plastic clays, surfactants, and electrolytes are used.
Burnout Additives- are introduced into the molding mass in order to obtain highly porous products: sawdust, ground coal, peat, husks, etc. These additives are also lean.
Plavni- are introduced in order to reduce the sintering temperature and, as a result, save fuel and energy resources. Sintering refers to the appearance of a partial melt of the raw mixture during the firing process. Feldspars, dolomite, magnesite, etc. are used as fluxes.
To give increased resistance to external influences, water resistance and a certain decorative look, the surface of some ceramic products is covered with glaze or engobe.
A vitreous layer of glaze applied to the surface of a ceramic material is fixed by firing. Glazes can be transparent and opaque in various colors. The main raw materials of the glaze are quartz sand, kaolin, feldspar, salts of alkali and alkaline earth metals, various oxides, etc.
Engobe is made from white or colored clay and applied in a thin layer to the surface of an unfired item. Unlike glaze, engobe does not melt during firing, so the surface is matte. According to its properties, the engobe should be close to the main shard.
Ceramic materials and products manufactured by the industry have a variety of sizes, shapes, physical and mechanical properties and various purposes, but the main stages of the technological process of their production are approximately the same and consist of the extraction of raw materials, their transportation to the plant, the preparation of the raw mass, the molding of the product (raw), drying and firing.
Clay for the production of ceramic materials and products is mined in quarries, usually located in the immediate vicinity of the plant. For mining, one- or multi-bucket excavators are used; it is also possible to use hydraulic mechanization tools. Clay is delivered to the plant by rail in tipping trolleys, dump trucks, belt conveyors, cable car trolleys and other modes of transport.
Clay mined in a quarry and delivered to the plant in its natural state is usually unsuitable for molding products. It is necessary to destroy the natural structure of the clay, remove harmful impurities from it, grind or remove large inclusions, mix the clay with additives, and also moisten it in order to obtain an easily moldable mass. For this purpose, various mechanisms are used: rollers, disintegrators, runners, clay cutters, pug mills, mixers, etc. These mechanisms will be discussed below.
Clay is processed by semi-dry, plastic and wet methods. The choice of one or another method depends on the properties of raw materials, the composition of the ceramic masses and the method of molding products, as well as their size and purpose.
With a semi-dry (dry) method raw materials are dried, crushed, ground and thoroughly mixed. Clay is usually dried in drying drums, crushed and ground in dry grinding runners, disintegrators or ball mills, and mixed in paddle mixers. Moisture content of press powder is 8…12% (4…6%). Humidify the press powder with water or steam.
The semi-dry method is used in the production of semi-dry pressed building bricks, floor tiles, facing tiles, etc.
With the plastic method raw materials are mixed at natural humidity or with the addition of water until clay dough is obtained with a moisture content of 18 ... 25%. For grinding and processing of raw materials, rollers and runners of various types are used, and for mixing - clay mixers.
The plastic raw mix preparation method is widely used in the production of plastic molded ceramic bricks, ceramic stones, roof tiles, pipes and other types of building ceramics.
With the wet (slip) method Raw materials are preliminarily ground into powder, and then thoroughly mixed in the presence of a large amount (more than 40%) of water, obtaining a homogeneous fluid mass (slip). This method is used in the production of porcelain and faience products, facing tiles, etc.
Ceramic products are molded in various ways: plastic, semi-dry, dry and wet. The choice of molding method depends on the type of products, as well as on the composition and physical and mechanical properties of the raw material.
plastic molding method is the most common in the production of ordinary and hollow bricks, ceramic stones and blocks for various purposes, tiles, facing slabs and other products. With this method of molding, the prepared clay mass with a moisture content of 18 ... 25% is sent to the receiving hopper of the belt press. With screw mass
additionally mixed, compacted and squeezed out in the form of a bar through the outlet of the press, equipped with a replaceable mouthpiece. By changing the mouthpiece, you can get a bar of various shapes and sizes. So, for example, when forming a brick, it has a rectangular cross section. The bar continuously leaving the press is cut into individual pieces according to the dimensions of the manufactured products by an automatic cutting device. Modern belt presses are equipped with vacuum chambers in which air is partially removed from the clay mass. Vacuuming the mass increases its plasticity and reduces molding moisture, reduces the drying time of the raw material and at the same time increases its strength.
Semi-dry molding has become widespread in modern factories in the production of facing tiles, floor tiles and other thin-walled ceramic products. This method can be used to produce bricks and other products from low-plasticity clays, which expands the raw material base for the production of building ceramics. In addition, a significant advantage of the semi-dry method of molding in comparison with the plastic method is the use of clay mass with lower moisture content (8 ... 12%), which significantly reduces or even eliminates the drying of the raw material.
With the semi-dry method, each product is molded separately on high-performance presses of various designs, which provide two-sided pressing in the form of clay powder under a pressure of more than 15 MPa.
Semi-dry pressed raw material has a clear shape, precise dimensions, strong corners and ribs. Its strength is quite sufficient for subsequent loading and transportation for drying and firing.
Dry Forming used mainly for the manufacture of dense ceramic products, for example, floor tiles, road bricks. The raw material for pressing products is clay powder with a moisture content of 4 to 6%. The molded raw does not require drying, which saves fuel and energy resources.
Wet Forming used for the manufacture of sanitary ware, mosaic tiles, etc. With this method, the clay mass with a moisture content of more than 40% is poured into special porous molds.
Molded products (raw) must be dried in order to reduce their moisture content to 8 ... 10%. Due to drying, the strength of the raw material increases, and cracking and deformation of it during the firing process is also prevented. Drying may be natural(in drying sheds) and artificial(in special dryers).
Natural drying does not require fuel consumption, but lasts a very long time (10 ... 15 days) and depends on the temperature and humidity of the surrounding air. In addition, for natural drying, rooms with a large area are required. Currently, large factories, as a rule, produce artificial drying of raw materials in batch or continuous dryers.
Batch dryers are separate chambers in which raw materials are placed on rack shelves. Raw cheese is served in the chambers on trolleys. In chamber dryers, all operations for loading, drying and unloading raw materials are repeated at regular intervals.
Continuous dryers are tunnels in which the raw material, laid on trolleys, gradually passes through various zones in terms of temperature and humidity and dries.
The raw material is dried in chamber and tunnel dryers according to the mode selected for this type of product, taking into account the raw materials used. Flue gases from kilns, as well as gases obtained in special furnaces, are used as a heat carrier in dryers. Thin ceramics are dried with hot air from heaters. The duration of artificial drying of raw material is from one to three days.
Firing is the final stage of the technological process for the production of ceramic products. The firing process can be conditionally divided into three periods: raw material heating, actual firing and cooling of fired products.
In the process of high-temperature firing, clay undergoes complex physical and chemical changes.
With a gradual rise in temperature to 100 ... 120 ° C, the remains of free moisture are removed from the clay and the ceramic mass becomes non-plastic, but if water is added, the plastic properties of the mass are restored. With an increase in temperature to 500 ... 700 ° C, organic impurities burn out and chemically bound water is removed from clay minerals, while the ceramic mass irrevocably loses its plasticity property. At a temperature of 700...900 °C, anhydrous clay minerals decompose and an amorphous mixture of alumina Al2O3 and silica SiO2 is formed. With a further increase in temperature to 1000 ... 1300 ° C, reactions occur in the solid phase and artificial minerals are formed, for example, sillimanite (Al2O3SiO2) and mullite (3Al2O32SiO2). At the same time, the most fusible compounds of the ceramic mass pass into the melt, creating a certain amount of the liquid phase. The melt envelops unmelted particles, fills the voids between them, and, having the force of surface tension, pulls the particles together. After cooling, a hard stone-like shard is formed.
The maximum firing temperature for ceramic products depends on the composition of the clays. Firing of products from fusible clays is carried out at a temperature of 900 ... 1000 ° C, from refractory and refractory - at a temperature of 1200 ... 1400 ° C.
Ceramic products are fired in batch or continuous kilns using solid (coal), liquid (fuel oil) or gaseous fuels.
Batch ovens are chambers into which molded and dried products are loaded on racks, after which a gradual rise in temperature begins, which is brought to the required maximum, then the products are held at the maximum temperature and its gradual decrease.
Continuous furnaces have different designs. Ring kilns have an ellipsoid-shaped firing channel covered with a semicircular vault. The products to be fired are loaded into the channel and remain stationary, while the temperature zones move relative to the fired material. Tunnel kilns have a straight channel through which trolleys with products laid on them slowly move, which sequentially pass through the heating, firing and cooling zones.
In slotted kilns, ceramic products, stacked in one row in height, move slowly in the firing channel along a roller or other conveyor. In such furnaces, the firing is uniform, its duration is reduced and fuel consumption is reduced.
Wall ceramic products designed for laying and cladding load-bearing and self-supporting walls and other elements of buildings and structures, as well as for the manufacture of wall panels and blocks. They are made in the form of a regular parallelepiped. Depending on their size, they are divided into types indicated in Table. 1. Brick is made solid and hollow, stone - only hollow. The voids in the products can be through or non-through, they can be located perpendicular (vertical) or parallel to the bed (horizontal). According to the molding method, wall ceramic products are divided into products obtained by plastic molding and semi-dry pressing. In accordance with regulatory documents, wall products are divided into ordinary and front. Ordinary products are designed to ensure the performance characteristics of the masonry, the front products, in addition to ensuring the performance characteristics of the masonry, perform the functions of a decorative material.
Table 1
Nomenclature and nominal dimensions of wall products
| Product type | View designation | Nominal dimensions, mm | Size designation | ||
| Length | Width | Thickness | |||
| Normal format brick (single) | KO | 250 | 120 | 65 | 1 NF |
| Eurobrick | KE | 250 | 85 | 65 | 0.7 NF |
| Thickened brick | KU | 250 | 120 | 88 | 1.4 NF |
| Brick modular single | KM | 288 | 138 | 65 | 1.3 NF |
| Thickened brick with horizontal voids | KUG | 250 | 120 | 88 | 1.4 NF |
| Stone | To | 250 | 120 | 140 | 2.1 NF |
| 288 | 288 | 88 | 3.7 NF | ||
| 288 | 138 | 140 | 2.9 NF | ||
| 288 | 138 | 88 | 1.8 nf | ||
| Stone | To | 250 | 250 | 140 | 4.5 NF |
| 250 | 180 | 140 | 3.2 NF | ||
| Large format stone | QC | 510 | 250 | 219 | 14.3 NF |
| 398 | 250 | 219 | 11.2 NF | ||
| 380 | 250 | 219 | 10.7 NF | ||
| 380 | 255 | 188 | 9.3 NF | ||
| 380 | 250 | 140 | 6.8 NF | ||
| 380 | 180 | 140 | 4.9 NF | ||
| 250 | 250 | 188 | 6.0 NF | ||
| Stone with horizontal holes | KG | 250 | 200 | 70 | 1.8 nf |
By strength, bricks are divided into grades M100, M125, M150, M175, M200, M250, M300; large-format stones - M35, M50, M75, M100, M125, M150, M175, M200, M250, M300; brick and stone with horizontal voids - M25, M35, M50, M75, M100.
In terms of frost resistance, bricks are produced in four grades: F15, F25, F35, F50.
According to the average density, the products are divided into classes 0.8; 1.0; 1.2; 1.4; 2.0, which must correspond to the values given in table. 2.
table 2
Classes of wall products by average density
Depending on the thermal conductivity and average density class, wall products are divided into groups given in Table. 3.
Table 3
Product groups according to thermal characteristics
To roofing ceramic materials carry tiles. It must have high durability, water resistance, resistance to various atmospheric factors and aesthetics, have a uniform fracture structure and a fracture strength in the dry state of at least 7 MPa, a weight of 1 m 2 of the roof no more than 45 kg, and also have frost resistance not less than 25 cycles of alternate freezing and thawing, water absorption is not more than 10% by weight.
Facade ceramic tiles used for cladding facades and plinths of buildings, external surfaces of reinforced concrete wall panels, underground passages.
The main indicators characterizing the quality of facade tiles are frost resistance, water absorption, accuracy of geometric dimensions and appearance. The frost resistance of ordinary tiles with a thickness of more than 9 mm should be at least 35 cycles, with a thickness of less than 7 mm - at least 40 cycles with water absorption up to 12%. For special-purpose tiles, frost resistance should exceed 50 cycles, and water absorption is allowed no more than 5%.
Floor Tiles can be unglazed and glazed, one-color and multi-color, with a smooth, rough (embossed) or corrugated front surface. The shape of the tiles are square, rectangular, triangular, four-, five-, six and octagonal, figured. Their water absorption should be no more than 3.8 ... 5%, abrasion no more than 0.07 ... 0.06 g / cm 2.
Tiles for interior cladding are intended for facing of internal surfaces of walls and partitions. They differ in shape, texture and type of material that forms the textured layer (50 types). Ceramic tiles must have a water absorption of no more than 16%, a flexural strength of at least 15 MPa, and a glaze coating must have a heat resistance of at least 150 ° C and a hardness of at least 5 on the Mohs scale.
Russian Federation
Ministry of Education and Science of the Chelyabinsk Region
Vocational School No. 130
By discipline: "Materials Science"
Subject: Ceramic Materials
Completed by: student group 28 Beloborodov A.
Checked by: Teacher Dolin A.M.
Yuzhno-Uralsk 2008
Introduction
1. General information about ceramic materials
2. Raw materials for the production of ceramic materials and products
2.1 Clay materials
2.2 Skinny materials
Conclusion
Bibliography
Introduction
In the modern world, ceramic materials and products are widely used in construction. This is due to the high strength, significant durability, decorativeness of many types of ceramics, as well as the prevalence of raw materials in nature.
The purpose of this work is to consider and study ceramic materials. In accordance with the goal set, the tasks of the work can also be distinguished: to study general information about ceramic materials: the concept, types, properties of ceramic materials and products; raw materials for the production of ceramic materials and products: clay materials, thinning materials.
Ceramic products have different properties, which are determined by the composition of the feedstock, the methods of its processing, as well as the firing conditions - the gaseous medium, temperature and duration. The material (i.e. the body) of which ceramic products are composed is called a ceramic shard in ceramics technology.
1. General information about ceramic materials
Ceramics are materials and products made by molding and firing clays. "Keramos" - in ancient Greek meant pottery clay, as well as baked clay products. In ancient times, dishes were made from clay by firing, and later (about 5000 years ago) they began to make bricks, and then tiles.
Great strength, significant durability, decorativeness of many types of ceramics, as well as the prevalence of raw materials in nature, have led to the widespread use of ceramic materials and products in construction. The durability of ceramic materials can be seen in the example of the Moscow Kremlin, whose walls were built almost 500 years ago.
Among raw powdered materials is clay, which is mainly used in the production of building ceramics. It mostly contains impurities that affect its color and thermal properties. The least amount of impurities contains clay with a high content of the mineral kaolinite and therefore called kaolin, which has an almost white color. In addition to kaolinite clays of different colors and shades, montmorillonite, hydromicaceous clays are used.
In addition to clay, the powdered materials used, which are the main components of ceramic products, also include some other mineral substances of natural origin - quartzites, magnesites, chromium iron ore.
For technical ceramics (more commonly referred to as special), powders in the form of pure oxides, artificially obtained by special cleaning, are used, for example, oxides of aluminum, magnesium, calcium, zirconium, thorium dioxide, etc. They make it possible to obtain products with high melting points (up to above), which is important in reactive technology, radio engineering ceramics. Materials of higher refractoriness are made on the basis of carbides, nitrides, borides, silicides, sulfides and other metal compounds, as well as without clay raw materials. Some of them have melting points up to 3500 - 4000°C, especially from the group of carbides.
Of great practical interest are cermets, which usually consist of metal and ceramic parts with appropriate properties. Refractories of variable composition have been recognized. These materials have one surface represented by a pure refractory metal, such as tungsten, and the other by a refractory ceramic material, such as beryllium oxide. Between the surfaces in the cross section, the composition gradually changes, which increases the resistance of the material to thermal shock.
For building ceramics, as noted above, clay is quite suitable, which is a common, cheap and well-studied raw material in nature. In combination with some additional materials, various products are obtained from it in the ceramic industry and in a wide range. They are classified according to a number of criteria. According to the structural purpose, wall, facade, floor, finishing, flooring, roofing products, sanitary products, road materials and products, for underground utilities, refractory products, heat-insulating materials and products, chemically resistant ceramics are distinguished.
According to the structural feature, all products are divided into two groups: porous and dense. Porous ceramic products absorb more than 5% by weight of water (ordinary brick, tiles, drainage pipes). On average, the water absorption of porous products is 8 - 20% by weight or 15 - 35% by volume. Dense products are accepted with a water absorption of less than 5% by weight, and they are practically waterproof, for example, floor tiles, sewer pipes, acid-resistant bricks and tiles, road bricks, sanitary china. Most often it is 2 - 4% by weight or 4 - 8% by volume. Absolutely dense ceramic products are not available, since the evaporating mixing water introduced into the clay dough always leaves a certain amount of micro- and macropores.
According to the purpose in construction, the following groups of ceramic materials and products are distinguished:
wall materials (ordinary clay brick, hollow and light, hollow ceramic stones);
roofing materials and materials for floors (tiles, ceramic hollow products);
facing materials for exterior and interior cladding (facing bricks and stones, facade ceramic slabs, small-sized tiles);
materials for floors (tiles);
materials for special purposes (road, sanitary construction, chemically resistant, materials for underground utilities, in particular pipes, heat-insulating, refractory, etc.);
aggregates for lightweight concrete (claydite, agloporite).
Wall materials have reached the greatest development, and along with a general increase in production, special attention is paid to an increase in the production of efficient products (hollow bricks and stones, ceramic blocks and panels, etc.). It is also envisaged to expand the production of facade ceramics, especially for industrial decoration of buildings, glazed tiles for interior cladding, floor tiles, sewer and drainage pipes, sanitary construction products, artificial porous aggregates for concrete.
According to the melting temperature, ceramic products and original clays are divided into fusible (with a melting point below 1350°C), refractory (with a melting point of 1350-1580°C) and refractory (over 1580°C). Above, examples of products and raw materials of higher refractoriness (with a melting point in the range of 2000-4000X) used for technical (special) purposes were also noted.
A distinctive feature of all ceramic products and materials is their relatively high strength, but low deformability. Brittleness most often refers to the negative properties of building ceramics. It has high chemical resistance and durability, and the shape and dimensions of ceramic products usually comply with established standards or specifications.
Liquid ceramic heat-insulating materials are currently presented on the Russian market, which find their consumer due to a wide range of applications and ease of use at low labor costs. Since the proposed materials are mainly produced abroad, they are expensive, which limits the possibility of their mass use in construction, energy and housing and communal services, etc. Whereas domestic analogues often leave much to be desired, and with their "quality" they cause negative and bias in the end user towards liquid ceramic heat-insulating materials.
2. Raw materials for the production of ceramic materials and products
Raw materials used for the manufacture of ceramic products can be divided into plastic clay (kaolins and clays) and lean (chamotte, quartz, slag, burnable additives). To lower the sintering temperature, flux is sometimes added to the clay. Kaolin and clays are united by a common name - clay materials.
ceramic construction roofing cladding
2.1 Clay materials
Kaolins. Kaolins were formed in nature from feldspars and other aluminosilicates not contaminated with iron oxides. They consist mainly of the mineral kaolinite. After firing, their inherent white or almost white color is preserved.
Clay. Clays are called sedimentary rocks, which are fine-earth mineral masses, capable of forming plastic dough with water, regardless of their mineralogical and chemical composition, which, after firing, turns into a waterproof and durable stone-like body.
Clays consist of a close mixture of various minerals, among which the most common are kaolinite, montmorillonite and hydromicaceous. Representatives of kaolinite minerals are kaolinite and halloysite. The montmorillonite group includes montmorillonite, beidellite and their ferruginous varieties. Hydromicas are mainly a product of varying degrees of hydration of micas.
Along with these minerals, clays contain quartz, feldspar, sulfur pyrite, hydrates of iron and aluminum oxides, calcium and magnesium carbonates, titanium and vanadium compounds. Such impurities affect both the technology of ceramic products and their properties. For example, finely distributed calcium carbonate and iron oxides reduce the fire resistance of clays. If there are large grains and grains of calcium carbonate in the clay, then during firing, more or less large inclusions of lime are formed from them, which hydrates in air with an increase in volume (dutik), which causes cracking or destruction of products. Vanadium compounds cause the appearance of greenish deposits (efflorescence) on the brick, which spoils the appearance of the facades.
Clays often also contain organic impurities. In relation to the action of high temperatures, clays of three groups are distinguished: refractory (refractory above 1580 "C), refractory (1350 - 1580" C) and fusible (below 1350 "C). Refractory are mostly kaolinite clays containing few mechanical impurities. Such clays are used for the production of porcelain, faience and refractory products.Refractory clays contain iron oxides, quartz sand and other impurities in much greater quantities than refractory ones, and are used for the production of refractory, facing and facing bricks, floor tiles and sewer pipes. clays are the most diverse in terms of mineralogical composition, contain a significant amount of impurities (quartz sand, iron oxides, limestone, organic substances) They are used in brick and tile production, in the production of light aggregates, etc.
In the production of artificial firing materials, some other sedimentary rocks can also be used: diatomites, tripoli and their compacted varieties - flasks, as well as shale in its pure form and with an admixture of clays or pore-forming additives.
2.2 Skinny materials
To reduce shrinkage during drying and firing, as well as to prevent deformations and cracks, artificial or natural thinning materials are introduced into fatty plastic clays.
Dehydrated clay and fireclay, as well as production wastes (boiler and other slags, ash, hearth residues, etc.) are used as artificial lean materials. Dehydrated clay is obtained by heating ordinary clay to about 600-700 "C (at this temperature it loses its plasticity property) and is used as a thinning agent in the production of rough building ceramics. Fireclay is made by firing refractory or refractory clays at temperatures of 1000 - 1400" C. Fireclay is the main raw material in the production of refractory fireclay products.
Natural lean materials include substances that are unable to form a plastic mass when mixed with water, for example, quartz sand, powdered quartz.
Pore forming materials. In the production of products of coarse building ceramics, such as bricks, pore-forming additives are introduced into the raw mass to thin the mass, as well as to obtain products with increased porosity and, consequently, reduced thermal conductivity. Usually, organic additives are used, called burnable ones - sawdust, coal, peat dust, etc. They burn out during the firing of products and form pores.
Smooth. The introduction of flux into the clay helps to lower the temperature of its sintering. The floodplains include feldspars, iron ore, dolomite, magnesite, talc, etc.
Conclusion
In conclusion, the above can be summed up, the conclusions can be drawn:
Ceramic materials and products are called materials and products obtained from powdered substances in various ways and subjected to mandatory heat treatment at high temperatures during the technological period to harden and obtain a stone-like state. This processing is called roasting;
In addition to clay, the powdered materials used, which are the main components of ceramic products, also include some other mineral substances of natural origin - quartzites, magnesites, chromium iron ore;
On a structural basis, all products are divided into two groups: porous and dense;
Raw materials used for the manufacture of ceramic products can be divided into plastic clay (kaolins and clays) and lean (chamotte, quartz, slag, burnable additives). To lower the sintering temperature, flux is sometimes added to the clay. Kaolin and clays are united by a common name - clay materials.
Bibliography
1. Brief chemical reference book / V.A. Rabinovich, Z.Ya. Khazov, - L .: Chemistry, 1978. - 356 p.
2. Materials science: lectures / Maltsev I. M. - Nizh. Novgorod: NSTU, 1995 - 103p.
3. New materials / under scientific. ed. Yu.S. Karabasova, - M.: Misis, 2002 - 738s.
4. Fundamentals of materials science / Sazhin V.B. - M.: Teis, 2005. - 155p.
Fired clay dishes appeared several centuries ago and since then have become a part of human life. It has survived to this day almost unchanged, but today we want to talk not entirely about it, but about its more practical and beautiful follower - ceramics.
Ceramics differs from clay in only a few points, but they are enough for finished products to receive new practical properties.
This material consists of two main components: clay, which is used as a base, and additives. As the latter, various solid mineral substances can be used, for example, sand or ordinary chalk. All this affects the porosity, the degree of water absorption and even color.
Another important difference lies in the production technology. While the firing of a pottery is the final stage of its manufacture, for ceramic ware it is only half the battle. For additional protection and increase in strength, its surface is necessarily covered with a thin layer of glaze - a special composition based on glass. After its application, it is fired again at lower temperatures to fix the protective layer on the surface.
Depending on the selected components and differences in manufacturing technology, the final properties of ceramic dishes may vary slightly, but the “basic list” of qualities remains the same for all products:
As we have already noted, the components used in the composition affect the appearance and properties, in fact, forming several types of material:
Ceramics is used to create dishes and other kitchen utensils extremely widely. From it are made:
Most likely, this is not even a complete list, and if you look into your kitchen, you will surely find something that we forgot to mention.
And finally, it is worth focusing on pans and pots in which ceramics are used only as a non-stick coating. In terms of heat distribution, they are closer to ordinary metal utensils, but the coating, unlike Teflon, is much stronger and more durable. However, it will not be possible to achieve that very rich aroma and special taste characteristic of dishes cooked in ceramic dishes.
FIRED STONE MATERIALS
Protection of stone materials from destruction
The main reasons for the destruction of natural stone materials in structures are: freezing of water in pores and cracks, causing internal stresses; frequent changes in temperature and humidity, causing the appearance of microcracks in the material; dissolving action of water and lowering of strength at water saturation; chemical corrosion occurring under the action of gases contained in the atmosphere (SO 2 , CO 2 , etc.), and substances dissolved in ground or sea water.
Structural protection open parts of structures (plinths, cornices, belts, pillars, parapets) are reduced to giving them a shape that facilitates water drainage. This is also facilitated by the smooth polished surface of the cladding and profiled parts.
For porous stone materials that are not polished, use chemical protection, for example, by impregnating the surface layer with sealing compounds and applying hydrophobizing (water-repellent) compounds to the front surface. Kremnefluorization(or fluatation) is used to increase the resistance of external cladding and other materials obtained from carbonate rocks. When limestone is impregnated with a solution of fluate (a salt of fluorosilicic acid), a chemical reaction occurs
2СаСО 3 + MgSiF6 = 2CaF 2 + MgF 2 + SiO 2 + 2CO 2
The resulting water-insoluble substances CaF 2 , MgF 2 and SiO 2 are deposited in the pores and compact the front layer of the stone. As a result, its water absorption decreases and frost resistance increases; stone cladding is less polluted with dust.
Non-carbonate porous stone materials are pre-treated with aqueous solutions of calcium salts (for example, CaCl 2), and then impregnated with fluates.
Hydrophobization, i.e. impregnation with hydrophobic compounds (for example, organosilicon liquids) reduces the penetration of moisture into a porous stone, in particular with capillary suction. To protect the stone from corrosion, film-forming polymeric materials are used - transparent and colored. The surface of the stone is also impregnated with monomer, followed by its polymerization.
Ceramic (from the Greek "keramos" - clay) is called artificial stone materials and products obtained by high-temperature firing of clays with mineral additives.
Classification of ceramic products. According to the structure of the shard, they distinguish: a) dense products with a sintered shard (the material that makes up ceramic products after firing is called a ceramic shard in ceramic technology) and water absorption of less than 5% (floor tiles and facade cladding, clinker bricks); b) porous products with water absorption more than 5% (wall tiles, interior wall cladding tiles).
According to their purpose, ceramic products are distinguished: for walls (brick and ceramic stones); facade cladding (facing bricks and stones); tiles for interior wall and floor cladding; roofing (tiles); sanitary equipment (faience products); roads and underground utilities (road bricks, pipes, etc.); thermal insulation (light brick, shaped products); acid-resistant products (brick, tiles, pipes, etc.); refractories; aggregates for lightweight concrete (claydite, agloporite).
Raw materials for the production of ceramic products. The main raw material for the production of building ceramic products is clay raw materials, used in pure form, and more often in a mixture with additives - thinning, plasticizing, pore-forming, fluxes, etc.
The main properties of clays as raw materials for the production of ceramics: plasticity and cohesiveness of clay dough, the ability to harden when dried and go into an irreversible stone-like state when fired.
Plastic clay is provided by the content of lamellar clay particles in them with a size of 0.005 mm or less. The presence between these particles of thin layers of water due to the action of molecular and capillary forces ensures the connectivity of the particles and their ability to slide relative to each other without loss of connectivity.
When dried, clay dough loses water and shrinks in volume. This process is called air shrinkage(2-12% by volume). In this case, the clay hardens, but when water is added, it again goes into a plastic state. When fired at a temperature of about 1000 ° C, the ceramic mass irrevocably loses its plastic properties and, due to the formation of new minerals, acquires a stone-like state, water resistance and strength. At the same time, further compaction and shrinkage of the material occurs, which is called fire shrinkage(2-8%). The ability of clays to compact during firing and form a stone-like shard is called clay sintering. Depending on the firing temperature, a porous (about 1000 °C) or sintered (more than 1100 °C) shard is obtained.
The main types of ceramic products- these are wall products, facing materials and products, ceramic materials and products for special purposes.
Wall products. The group of wall ceramic materials includes bricks (single, thickened, modular sizes) and stones produced by semi-dry pressing or plastic molding, as well as large-sized blocks and panels. Single ceramic brick has the shape of a rectangular parallelepiped with even edges, straight edges and corners with dimensions of 250´120´65 mm; thickened - dimensions 250´120´88 mm. Brick can be produced solid (without voids and with technological voids in the amount of not more than 13%) and hollow (with a vertical or horizontal arrangement of voids), and stones - only hollow. The density of bricks and stones, depending on the presence and number of voids, ranges from 1400 to
1900 kg / m 3, thermal conductivity - from 0.4 to 0.8 W / (m × ºС). According to these indicators, hollow bricks and stones, as well as porous-hollow bricks (burnable additives are introduced into the composition of the ceramic mass) belong to the group of effective wall ceramic products. Moreover, these types of bricks and stones are divided into conditionally effective, which improve the thermal properties of walls, and effective, which allow to significantly reduce the thickness of the walls.
Brand of stones strength determined depending on the values of the compressive strength, and for brick - and taking into account the flexural strength. Strength grades of solid bricks, as well as hollow bricks and stones with a vertical arrangement of voids - 75, 100, 125, 150, 175, 200, 250 and 300, and with horizontally located voids - 25, 35, 50, 100. Brands of bricks and stones by frost resistance – F 15, F 25, F 35, F 50. Water absorption should not be less than 8% for solid bricks, and less than 6% for hollow products. Weight bricks in the dried state should not be more than 4.3 kg, stones - no more than 16 kg.
These products are used for laying external and internal walls, laying foundations (made of solid bricks).
Facing materials and products. Distinguish: facade cladding products - brick and ceramic facial stones (they are laid in the wall of the building in dressing with ordinary ones, they differ from the latter in increased physical and mechanical properties and improved appearance); ceramic products for interior cladding - tiles for interior wall cladding (used in bathrooms, kitchens, baths, laundries, metro stations, etc.); floor tiles. The value of the main, in addition to size and appearance normalized indicator for ceramic tiles - water absorption- is important when choosing a material for facing rooms with a wet regime and floor tiles. Under normal operating conditions (indoors), this parameter does not have a noticeable effect on the consumer properties of ceramic tiles. A completely different situation develops when using tiles outdoors: frost resistance ceramic products directly depends on water absorption. It is considered that tiles with a water absorption of less than 3% are suitable for outdoor use (porch, balcony, etc.) or in unheated rooms. Ceramic tiles to improve appearance and create additional protection cover glaze.
Ceramic granite belongs to the same class of finishing materials as ceramic tiles, but differs from it in increased mechanical characteristics (strength, hardness and wear resistance), as well as a texture that imitates natural stone. This set of properties is achieved as a result of using a mixture of clays and mineral additives, similar in composition to the porcelain mass. Tiles molded from this mixture under high (up to 50 MPa) pressure are subjected to high-temperature firing (over 1200 °C), which leads to sintering of the mass and provides an extremely hard and dense shard, practically devoid of pores and voids. This allows you to do without applying a protective layer of glaze to the surface of the tile.
Ceramic tiles and porcelain stoneware are produced in sizes: from 15´15 to 40´40 and 30´60 cm. The thickness of facing tiles is usually 5; 6 mm; floor tiles and porcelain stoneware - 8.5; 12; 15 mm.
Ceramic materials and products for special purposes. They produce bricks and ceramic stones for laying and lining industrial chimneys and furnaces; trapezoidal stones for underground collectors; road clinker bricks for paving streets and roads, floors, embankment cladding, etc.; clay tiles - the oldest type of roofing materials; ceramic pipes: sewer (with a dense shard) and drainage (with a porous shard); heat-insulating ceramic products - cellular ceramics, expanded clay; refractory materials (made in the form of bricks, blocks, slabs from various raw materials using a technology close to ceramic).
The basis of these materials are powders of refractory compounds such as carbides, oxides, borides, nitrides: Siu, PS, SG7C3, AlO3, SiO3, ZrO2?, CrB, Na3V, IV3, VY, PY, etc. Depending on the purpose, high-temperature ceramics are made , for cutting tools, welding, with a honeycomb structure, for lighting engineering, porous, special, etc. Advantages of ceramics:
The disadvantage of ceramics is significant fragility. When the heated ceramic is cooled abruptly, it cracks. To reduce these shortcomings, new types of ceramics are being created.
The new ceramic material based on silicon carbide has high mechanical strength and wear resistance at high temperatures, low coefficient of thermal expansion, high oxidation resistance at temperatures up to 1500 °C, high chemical inertness, biocompatibility, corrosion resistance, radiation resistance, high hardness and thermal conductivity. . Depending on the composition of ceramics, both structural and tool materials are used.
As a structural material, ceramics are used in plain bearings operating in aggressive environments and at high temperatures, in high-speed rolling bearings, dry gas-dynamic seals, heating elements, dies, spray nozzles, structural elements of rotary engines.
Metal-ceramics (metal-ceramic materials)- an artificial material, which is a tetragenic composition of metals and alloys with ceramics. In these materials, the basis is ceramics, to which a certain amount of metal is added, which is a binder and provides such properties as ductility and toughness. The ceramic phase includes oxides AlO3, SiO3, ZrO2, SG2O3, carbides (SiO, NPS, O3C2, borides (CleBs, TP33, ZrB2), silicides (MoS1), nitrides (IM) and carbon (diamond, graphite). metal binder will use metals N6, Mo, Co, Cr, A1, Her, TE
Cermets (another name for cermets) combine important structural and operational properties of metals and non-metals.
They are characterized by high strength, high wear and heat resistance, anti-corrosion properties. They are used as anti-friction or protective coatings for parts and independent structural materials in the aircraft industry, automotive industry, transport and chemical engineering, electrical instrumentation, turbine construction and other industries.
Glass.Ordinary glass- ego is extremely fragile and brittle material. It has very low tensile and flexural strengths and a relatively high surface hardness. The operational properties of glass can be significantly improved by changing the manufacturing technology, component composition or strengthening it with other materials, for example, by reinforcing glass with wire. In addition, organic or inorganic protective coatings can be applied to the glass surface.
Recently, chemical methods for improving performance have become known, such as ion exchange, which lead to a more significant increase in the strength of glass, sometimes up to 10 times.
The strength of glass and its resistance to temperature changes can be increased by directional crystallization. This is how glass-ceramics are obtained. These materials can withstand a sudden increase in temperature of 1000 °C, since there is practically no change in their volume.
Sitally They have high mechanical strength and heat resistance, water and gas tightness, low expansion coefficient, high dielectric constant and low dielectric losses. They are used for the manufacture of pipelines, chemical reactors, pump parts, spinnerets for spinning synthetic fibers, as a lining for electrolysis baths and material for infrared optics, in the electrical and electronic industries.
Highly reliable glasses are used for trucks and trains, as portholes for ships, submarines and spacecraft. In addition, due to its corrosion resistance, glass is increasingly being used for high pressure steam heat exchangers. In the machine tool industry, the use of glass is limited so far only to viewing windows, but glass-ceramic glass is already being tested here as a material for supports and foundations.
Quartz glass. It is obtained by melting at 1700 ° C pure quartz sand or rock crystal, having a composition of 5102. The most important property of quartz glass is the ability to withstand any temperature fluctuations. For example, quartz pipes with a diameter of 10...30 mm withstand repeated heating up to 800...900 °C and cooling in water. Quartz glass bars, cooled on one side, retain a temperature of 1500 °C on the opposite side and are therefore used as refractories. Thin-walled products made of quartz glass withstand sudden cooling in air from temperatures above 1300 °C and are therefore successfully used for high-intensity light sources. Quartz glass of all glasses is the most transparent to ultraviolet and infrared rays.
Quartz glass has high heat resistance, dielectric properties, chemical resistance. Quartz glass is used to make chemical refractory dishes, evaporating bowls for sulfuric acid; it is also widely used in electrical engineering, optics, and medicine. Preforms made of the purest quartz glass are used to draw quartz optical fibers.
Foam glass- porous glass material, has heat and sound insulation properties, low density (about 10 times lighter than brick) and high strength, comparable to concrete. Foam glass does not sink in water and is therefore used for the manufacture of pontoon bridges and life-saving equipment. It is easily machined by cutting.
glass fibre. When put on, the glass softens and is easily drawn into thin and long threads. Thin glass threads are not brittle. Their characteristic property is an extremely high specific tensile strength. A thread with a diameter of 3-5 microns has a tensile strength of 200-400 kg / mm "1, i.e., it approaches mild steel in this characteristic. Glass fibers, glass fabrics and glass wool are made from threads. Fabrics made from glass fibers have a high chemical resistance.Therefore, they are used in the chemical industry as filters for acids, alkalis and reactive gases.Due to the good fire resistance of glass fabrics, they are used for sewing protective clothing for specialists working in flammable areas.The main area of application of fiberglass and glass textile materials is the use of fiberglass plastics and composites and in the production of materials with high heat, cold and sound absorbing capacity.
glass wool It has excellent heat and sound insulation properties, therefore it is widely used in construction.
Organic glass (plexiglass)- a transparent colorless plastic mass formed during the polymerization of methacrylic acid methyl ester. Easily machinable. Organic glass is produced in several types: technical, lighting, oriented technical, extrusion ASYAUMA 72, ASYAUMA 82, etc. According to GOST 10667-90, sheet structural glass is produced in the form of transparent unpainted sheets with a thickness of 0.8 mm to 50.0 mm, dimensions 1150x1250 and 1400x1600 mm. Sheet glass is used in aircraft and mechanical engineering, for the manufacture of household products, protective equipment in laboratories, etc.
Liquid glass(GOST 13078-81) is used in construction as an additive to building materials, increases their durability, strength, fire resistance, weather resistance, for priming concrete, brick, plastered wooden surfaces, waterproofing tanks and pools, gluing paper, cardboard. It is an environmentally friendly antiseptic (prevents the formation of mold, rot, fungi).
Other applications: preparation of putty for water pipes, removal of old varnish and oil paints, manufacture of silicate paints (mixture of water glass with various dyes), prevention of metal corrosion (water glass with cement powder, then painting), prevention and removal of scale, removal of dirty , oily and greasy stains from clothes.
