One type of clay is fireclay. It is used in the laying of stoves, cladding of fireplaces, in the manufacture of refractory bricks, as a fastening material and for decorative purposes. Fireclay clay contains white kaolin, which after firing acquires strength and fire resistance.
High-temperature processing transforms clay into a material whose strength properties are compared to the strength of rocks.
Fireclay clay or chamotte is fired clay made from white kaolin, and firing is a prerequisite for the manufacture of the material, since at high temperatures chemically bound water is removed and the material loses its plasticity. There are zircon, corundum and high-alumina fireclay. Ceramists call chamotte a mixture of plastic clays of different types with the addition of granular chamotte chips.
Clay, properties, types and varieties, origin, extraction and use.
Clay is a sedimentary rock with a fine-grained structure and complex composition. Plasticity, viscosity, fire resistance and other properties of clay are determined by which rock-forming substance is the main one.
Clay
Characteristics and properties of clay. “Fat” and “skinny” clays. Color. Water resistance. Plastic. Fire resistance. Caking ability
Types and varieties of clay
Origin of clay
Clay mining. Quarrying methods
Application and use of clay. Advantages
Properties of granite
Sand, clay, granite, limestone are minerals. If we look at granite in more detail, it is an igneous platonic rock of acidic composition. It is based on:
- potassium feldspar;
- plagioclase;
- quartz;
- biotite;
- muscovite
Granite is common in the continental crust. Its density reaches 2600 kg/m³, while the compressive strength is 300 MPa. The material begins to melt at 1215 °C. In the presence of pressure and water, the melting point decreases to 650 °C.
Granite is the most important rock of the earth's crust, it is widespread and makes up the majority of all components. Among the varieties of granites, alaskite and plagiogranite can be distinguished. The latter has a light gray color with a sharp predominance of plagioclase. Alaskite is a pink granite, it contains a sharp predominance of potassium-sodium feldspar.
Clay:
Clay is a sedimentary rock with a fine-grained structure and complex composition. Plasticity, viscosity, fire resistance and other properties of clay are determined by which rock-forming substance is the main one.
These can be clay materials such as kaolinite (Al2O3 2SiO2 2H2O), andalusite, disthene and sillimanite (Al2O3 SiO2), montmorillonite (MgO Al2O3 3SiO2 1.5H2O), halloysite (Al2O3 SiO2 H2O), hydrargillite (Al2O3 3H2O), diaspore (Al2O3 H2O), corundum (Al2O3), monothermite (0.2[K2MgCa]O Al2O3 2SiO2 1.5H2O), muscovite (K2O Al2O3 6SiO2 2H2O), nacrite (Al2O3·SiO2·2H2O) and pyrophyllite (Al2O3·4SiO2·H2O).
For example, montmorillonite, which belongs to layered silicates, has sorption properties and has a pronounced ability to swell strongly.
Different types of clay may contain particles of kaolinite, andalusite, muscovite, hydrargillite, nacrite, corundum, pyrophyllite and other constituent minerals in different proportions.
Among the impurities, the most common particles are quartz, gypsum, calcium, dolomite, pyrite, siderite, magnetite, and glauconite.
Characteristics and properties of clay:
The characteristics of clay materials depend on their composition, granule size, moisture content of the material, and location of extraction. When assessing the properties of clay, a whole range of characteristics is used - from density and solubility in water to porosity and thermal conductivity.
Main properties of clay:
– when it gets into water, it gets wet and breaks up into separate particles, forming a suspension or forms a mass similar to dough;
– in a dry state it has the structure of dust, in a wet state it becomes soft, plastic, and easily takes any shape;
– after drying or firing, it becomes strong and durable. As it dries, it decreases slightly in volume due to natural shrinkage;
– when moistened, it has good binding abilities. Thanks to these qualities, it is used in the manufacture of bricks and some types of dishes;
– clay in a wet state has good covering qualities, so in the past it was often used for coating wood-burning stoves, walls of houses and outbuildings;
– this material is capable of absorbing substances dissolved in liquids. Sorption properties make it possible to use it for filtration and purification from foreign impurities of vegetable fats and petroleum products.
Technologies for processing clay , changing its composition or “fat content” make it possible to obtain raw materials with specified properties - the desired shade, with greater fire resistance, less shrinkage, etc.
Material characteristics
Fireclay clay is produced in powder form, with a fraction of up to 2 mm. If the substance was stored correctly (+15-25 C), then the consistency is homogeneous, without noticeable pieces or lumps. The material loses its properties after 3 years or when kept in damp conditions.
The melting point of all types of fireclay clay is from 1500 to 1850 C. As the degree increases, the performance properties do not change, which allows it to be used in the manufacture of stoves and fireplaces. After sintering, the substance loses its ability to absorb moisture without losing its fire resistance.
Properties of kaolin substance Source proraboff.rf
Kaolin and sand do not have binding capabilities, but when combined, a very strong, dense mass (raw material) is obtained. The strength level of the composition is 12-24 N/sq.mm. Fireclay clay mortar is not inferior in stability to concrete. The product has high adhesive properties, which facilitates subsequent processing.
One package of 20 kg of material is enough to lay 30 bricks. To cover the surface of the cube, use 100 kg of refractory substance. The kaolin composition allows oxygen and moisture to pass through itself, so a favorable microclimate is maintained in the room. Hardened natural fireclay is safe for human health.
Fireclay is a very expensive material with special rules for use. The treated surface takes a long time to dry (3-4 days). If you violate the technology for preparing the solution or do not comply with the exposure time, the mass will not become strong. Fireclay dust rising into the air is toxic, so a respirator with safety glasses is required when mixing ingredients.
Strengths and weaknesses Source yandex.ua
“Fat” and “skinny” clays:
Changing the proportions of the main components and impurities makes the clay “lean” or “fat”. The plasticity of the material and the quality of the final product depend on this property.
Products made from too “oily” clay deteriorate during the drying or firing stage - they become covered with cracks or warp. The use of thinning additives makes it possible to reduce the shrinkage of the material during natural drying or heat treatment. Sand is most often used as such an additive: fine, medium fine or coarse. It is thoroughly washed to get rid of dust, as it reduces the viscosity of the clay mass.
“Skinny” clay has low plasticity and is unsuitable for modeling or molding. To improve plastic properties, elutriation technology is used. This is the enrichment of material by separating clay particles from impurities. After diluting the raw material with water, slowly settling clay particles are filtered from heavier sand and stones.
Clay color:
The color of the breed can be yellow, brown, blue, greenish, black. The color depends on the concentration of chromophores - unsaturated atoms. Cobalt compounds give the material a blue tint, chromium makes it olive, and admixtures of magnesium and nickel make it brown and gray. After firing, clay products become red or white.
Description
The material contains one or more minerals of the kaolinite group. The base may be a mineral of the montmorillonite group and other layered aluminosilicates, which are also called clay minerals. May contain carbonate and sand particles.
The rock-forming mineral is kaolinite, which consists of silicon oxide in a volume of 47%, aluminum oxide - 39%, and water - 14%. A significant part of the chemical composition of yellow clay is Al2O3 and SiO2. The material can have the following colors:
- green;
- blue;
- brown;
- black;
- lilac.
The color is due to ion impurities, which are chromophores.
Fire resistance of clay:
According to their ability to withstand high temperatures without loss of strength, clay materials are:
– low-melting. Their processing is carried out at a temperature of +1350 °C. They are used in the production of facing bricks, tiles, decorative wall masonry elements;
– refractory. The minimum amount of impurities in the composition makes it possible to process at higher temperatures - up to +1580 °C. They are used in the production of facing building materials and sewer pipes;
– fireproof. Materials of this group contain virtually no impurities in their composition, so their melting requires a temperature above +1580 °C. They are mainly used in the production of fireclay bricks for lining stoves, laying fireplaces, and chimneys.
Plaster
Plastering with fireclay clay is similar to the process of working with simple plaster. To do this, use two spatulas of different sizes. Enough to finish the oven. For such work you do not need to prepare special tools.
When applying the solution, do not forget about spreading drops. They should be picked up with a spatula. When applying a layer of plaster, its thickness must be taken into account. It should not exceed 1-2 mm. Finishing work can begin only after the plaster has dried. Fireclay bricks are not wetted by water.
Clay sinterability:
This property is defined as the ability of a plastic material to transform into a solid, stone-like state when fired at high temperatures. Clay after firing should not soak in water. This property is acquired due to irreversible changes in the structure of the material, namely, the removal of physically bound water, the decomposition of clay material into silicon oxide and aluminum oxide. At temperatures from +1000 °C to +1200 °C, new water-resistant mineral compounds are formed. The melt of fusible components solidifies when cooled, making the mass hard and durable.
Types and varieties of clay:
In industry, construction, and cosmetology, clays of different composition, characteristics, and color are used. The division of materials into types is determined by a combination of properties such as plasticity, sinterability, fire resistance, and the amount of impurities. The most common are:
– kaolin (white) clay . White clay is used in the production of porcelain and earthenware;
- blue clay. In demand in cosmetology and medicine;
– bentonite clay . When preparing an aqueous solution, it increases in volume several times. This property makes it indispensable in the construction of pile foundations and drilling wells;
– fireclay clay . Used in the production of fire bricks;
– shale clay . Shale is used to make cement;
– pottery (lump) clay . Lump clay is used to make pottery;
– montmorillonite (full) clay . It is used to purify products such as molasses, beer, wine, syrups, juices, oils, petroleum products, and is also used as an improving additive in the manufacture of soap.
Basic properties
Clay is a mineral that has a number of properties, among them the following should be highlighted:
- air and fire shrinkage;
- plastic;
- sinterability;
- fire resistance;
- viscosity;
- color of ceramic shard;
- porosity;
- shrinkage;
- dispersion;
- swelling.
Clay is the most stable waterproofing material that does not allow moisture to pass through, which is one of the important qualities. Clay soil has stability. It is developed in wastelands and wastelands. The development of root vegetation in clay deposits is impossible.
To preserve the quality of groundwater, the material's water-impermeability is useful. Most of the high-quality artesian springs lie between the clay layers.
Origin of clay:
Clay is a naturally occurring product formed from feldspar and igneous rocks that has a fine texture when dry. By origin, these rocks are continental, formed on the mainland, and marine, formed at the bottom of the sea.
As a result of shifts in earth layers, earthquakes, and floods, granites, volcanic glass, tuffs, and porphyrites were crushed. The physical change and destruction of rocks was influenced by the crystallization of salts, freezing of water, and the vital activity of microorganisms.
The formation of sea clay layers occurred when clay substances were deposited by water currents, accumulated and settled. Clays of the marine group are:
– coastal-sea. Their place of formation is coastal regions, river deltas and bays. Clay layers often alternate with coal, sand, and silt;
– lagoon. Clays formed in sea lagoons contain high concentrations of sulfides, calcite, and iron. Fire-resistant species are common among lagoonal alluvial rocks;
– shelf. Rocks that were formed at a depth of more than 200 m have a denser structure and homogeneous composition.
Continental clays are also divided according to their place of origin. They are:
– deluvial. A characteristic feature is the mixed composition, its heterogeneity even in one time layer;
– lake. The best fire-resistant clays are formed precisely on the bottom and shores of lakes. They contain all the components necessary for the manufacture of fireclay materials;
– proluvial. They are formed by the destruction of rocks, washed away and carried along erosion furrows to the foot of the mountains. Their characteristic feature is layering, looseness, heterogeneous composition;
– river. They can be found in river floodplains; they contain a large amount of impurities in their composition and most often turn into pebbles.
There are also residual rocks with low plasticity, formed as a result of weathering of rocks.
Clay mining. Quarrying methods:
In our country, clay mining is carried out in the Urals, Eastern and Western Siberia. Often several types of clay are produced at one deposit. There are 3 groups according to the difficulty of quarrying:
- first group. Development of the top layers of soil with plant residues, work is underway to excavate loam;
- second group. This is compacted rock, saturated with moisture, as well as deposits of lumpy rocks, with admixtures of gravel;
- third group. The development of hardened shale strata and frozen clay soil is underway.
Quarry development methods depend on the volume and depth of deposits and their location. The most common method of extracting clay-containing rocks is the extraction of minerals using special equipment - gear hobbing excavators. Rock blasting is used in deep mining of large deposits. Kaolin white and blue clay is mined using devices that create a dense water jet. Most often, hydromonitors are used when the layer humidity is high.
Extraction of materials for ceramics manufacturing enterprises is carried out using gear hobbing excavators by cutting layers of different thicknesses. Before development begins, preparations are carried out:
– laying access roads;
– clearing the quarry horizon;
– delivery of equipment.
The developed soil and sand are removed from the quarry and poured into a dump, and the clay is transported to its destination. If several varieties of clays are found in one deposit, the development of the layers is carried out separately. This technology is called “Selective Generation”. It is more efficient than bulk mining, in which all layers are cut off at the same time.
Application and use of clay:
When dry clay is combined with water, a plastic mass is formed. Depending on the place of production and composition, it is used in a variety of fields and industries:
– production of ceramics . This is one of the main uses of clay. Different varieties are used to make ceramics, earthenware, and porcelain. These materials are used to make dishes, figurines, vases, and souvenirs. Although pottery has been known for a very long time, it continues to improve even now;
– production of building materials . Clay is the main component of mortars that are used in the manufacture of facing and masonry bricks and tiles. Clay or ceramic tiles are considered one of the best roofing materials. It is durable, strong, frost-resistant, holds heat well, and does not make noise when it rains;
– cement production . For the production of cement, shale is used, which contains 22% silicon dioxide, 5% calcium oxide. The clay content in cement does not exceed 25%, the second component, limestone, accounts for 75%. The components are diluted with water, and the resulting mass is sent for firing. The resulting granulated clinker is cooled, crushed to dust, and 5% gypsum is added;
– technical ceramics . This category includes a fairly large group of ceramic products, which are characterized by increased hardness, heat resistance, resistance to abrasive wear and mechanical deformation. The main types of technoceramics are structural, instrumental, electro-radiotechnical, ceramics with special properties. These are plumbing fixtures, electrical insulators, thread-conducting fittings, rollers, couplings, bushings. Corundum ceramic materials are used in the production of armor panels and body armor.
Features of working with refractory clay
The process of working with fireclay refractory clay for most novice stove makers causes certain difficulties. During operation, the masonry becomes fragile. Cracks may appear in the plaster. Such phenomena occur due to the loss of plastic properties of kaolin clay during firing. To prevent this from happening, you need to add special glue to the solution.
The refractory powder is diluted with plain water. To prepare the plaster you will need to perform the following steps:
- pour fireclay powder into the selected container;
- add water until the powder is completely covered;
- leave the diluted clay for 3 days;
- make the final batch;
- add quartz sand;
- stir the resulting mass.
The finished mixture should be creamy. In this case, the plaster will not drain. To speed up the setting of the material, cement should be added to the mixture - about 2 kg per package of clay.
There is no need to infuse the composition for instant mixing. However, the price of such powder is significantly higher. PVA glue is added to both compositions. The prepared solution is applied with a spatula. The solution will harden for about two days.
