Ceramic materials are obtained. Ceramic and composite materials

Ceramics as a polycrystalline solid generally consists of three main phases:

• crystalline, consisting of grains,
• glassy (amorphous) - in the form of layers located between the grains,
• gas - in the form of pores between grains surrounded by layers of the amorphous phase.

Porcelain
Faience
Thin stone products
Majolica
Terracotta
Pottery ceramics
Fireclay ceramics

The main difference between ceramic materials is the different composition and relationship between the three phases that determine the properties of ceramic products. Structure, i.e. The structure of the ceramic body depends on the composition of the raw materials and the technology of the material. By dispersion (size) of structure elements ceramic materials There are fine ceramic and coarse ceramic. If the ceramics consists of finely dispersed grains, its fracture is uniform and the particles are indistinguishable, then such a material is classified as fine ceramic (primarily porcelain, earthenware, majolica, etc.). If large grains are observed in the structure of the ceramic, the structure itself is heterogeneous, then we have a coarse ceramic product (fireclay products, pottery ceramics, terracotta). Pottery and terracotta, made from high-quality clays without the admixture of large particles, can also be classified as fine ceramic products, which indicates the conventions of such a division.

The main types of ceramic materials: porcelain, faience, fine stone products, majolica, terracotta, pottery ceramics, fireclay ceramics.

Porcelain is a type of ceramic white with a dense conchoidal fracture, the highest achievement of ceramic technology. To make porcelain, refractory white-burning clays and kaolins, quartz and feldspars are used (the ratio of plastic and waste materials is 1:1). There are soft and hard porcelain. Distinctive features porcelain are: whiteness, translucency, mechanical strength, hardness, thermal and chemical resistance. Scope of application: from the manufacture of dishes and technical products to the creation of unique works of art.

Faience (from the name of the Italian city of Faenza) is a type of white ceramic with a finely porous fracture. To make faience, refractory white-burning clays, quartz and various additives are used. Unlike porcelain, it has an opaque porous shard; the temperature of the waste firing exceeds the temperature of the poured one. There are soft and hard faience. Scope of application: manufacturing of tableware, technical products, decorative products, building ceramics.

Fine-stone products are a type of ceramics characterized by a white or colored sintered shard with a uniform conchoidal fracture. For the manufacture of fine-stone products, refractory and refractory clays are used, chemical composition which varies within a fairly wide range. Thin-stone products of low-temperature and high-temperature sintering are distinguished. Depending on the raw materials used, the degree of sintering and color of the shard, and the features of the technology, thin-stone products have different names: semi-porcelain, low-temperature porcelain, “stone goods”, etc. Thin-stone products are characterized by low water absorption (0.5...5.0%). Their area of ​​application: manufacturing of tableware, decorative and interior ceramics.

Majolica (from the name of the island of Mallorca) is a type of ceramic with a porous, naturally colored shard from light cream to red (brick) color, covered with a transparent or dull (opaque) glaze. To make majolica, low-melting clays are used pure form or with the introduction of thinning and fluxing additives. Often majolica products are covered with a layer of white clay, engobe, which hides natural color shard. The low temperature of glaze firing of majolica (960–1050? C) allows the use of a wide palette of colored glazes and enamels for decoration. Scope of application: manufacturing of dishes, facing tiles, decorative ceramics.

Terracotta (terra (Italian) – earth, cotta – burnt) is a type of ceramic, unglazed ceramic products with a porous shard. To make terracotta, high-quality low-shrinkage clays that have a uniform color and a relatively high melting point are used. Sometimes terracotta is covered with engobe. Area of ​​application: making sculptures, tiles, tiles, etc.

Pottery ceramics are ceramic products with the natural color of fired clay, relatively high porosity, fine-grained, usually unglazed. To make this type of ceramics, local fusible pottery clays are used without the use of any other components except for small additions of quartz sand. Sometimes products are covered with a layer of engobe or glaze. Area of ​​application: making dishes, jewelry, souvenirs.

Fireclay ceramics is a type of coarse ceramic products that has a porous, coarse-grained, often light-colored shard. Chamotte is burnt ground clay. To bind chamotte grains in chamotte products, clays are used, kneading them until a plastic mass is formed. Small sculptures, floor vases, bricks and some other types of architectural ceramics are made from fireclay masses.

All of the above ceramic materials, no matter how different they may be in the composition of raw materials and, consequently, in the final chemical composition and properties of the products, they are united by technology that determines the sequence of operations.

Fundamental technology system obtaining ceramics

1. Procurement of raw materials (clay, fireclay, sand, etc.)
2. Preparing the molding material
3. Molding
4. Drying
5. Burning

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Introduction

Conclusion

Introduction

Ceramics are the third most widely used material in industry after metals and polymers. It is the most competitive class of materials compared to metals for use in high temperatures. The use of transport engines with parts made of ceramics, ceramic materials for cutting and optical ceramics for information transmission opens up great prospects. This will reduce the consumption of expensive and scarce metals: titanium and tantalum in capacitors, tungsten and cobalt in cutting tools, cobalt, chromium and nickel in heat engines.

The main developers and producers of ceramic materials are the USA and Japan.

Ceramic materials used in technology as technical ceramics or high-quality ceramics must meet the highest requirements for material properties. These properties include:

Bending strength;

Biological compatibility;

Chemical resistance;

Density and stiffness (Young's modulus);

Compressive strength;

Electrical insulating properties;

Dielectric strength;

Hardness;

Corrosion resistance;

Suitability for food purposes;

Piezoelectric properties and dynamic characteristics;

Heat resistance;

Resistance to thermal shock and temperature fluctuations;

Metallization (bonding technology);

Wear resistance;

Thermal expansion coefficient;

Thermal insulation;

Thermal conductivity;

These diverse properties enable technical ceramics to be used in a variety of applications in the automotive, electronics, medical technology, energy and industrial ecology industries, as well as mechanical and equipment manufacturing.

1. Ceramic technology and classification of ceramics

Ceramic technology involves the following main stages: obtaining initial powders, consolidating powders, i.e., manufacturing compact materials, their processing and control of products.

In the production of high-quality ceramics with high structural homogeneity, powders of starting materials with a particle size of up to 1 micron are used. Grinding is carried out mechanically with the help of grinding bodies, as well as by spraying the crushed material in a liquid state, deposition on cold surfaces from the vapor-gas phase, vibration-cavitation effects on particles in the liquid, using self-propagating high-temperature synthesis and other methods. For ultrafine grinding (particles less than 1 micron), vibration mills, or attritors, are the most promising.

The consolidation of ceramic materials consists of molding and sintering processes. The following main groups of molding methods are distinguished:

1) Pressing under the influence of compressive pressure, at which the powder is compacted due to a decrease in porosity;

2) Plastic molding by squeezing rods and pipes through a die (extrusion) of molding compounds with plasticizers that increase their fluidity;

3) Slip casting for the manufacture of thin-walled products of any complex shape, in which liquid suspensions of powders are used for molding.

When moving from pressing to plastic molding and slip casting, the possibilities for manufacturing products of complex shapes increase, but the process of drying products and removing plasticizers from ceramic materials becomes more complicated. Therefore, for the manufacture of products of relatively simple shapes, preference is given to pressing, and for more complex ones, extrusion and slip casting.

During sintering, individual powder particles are transformed into a monolith and the final properties of the ceramic are formed. The sintering process is accompanied by a decrease in porosity and shrinkage.

Table 1 shows the classification of the main types of ceramics.

They use sintering furnaces at atmospheric pressure, hot isostatic pressing units (gasostats), and hot pressing presses with a pressing force of up to 1500 kN. The sintering temperature, depending on the composition, can be up to 2000 - 2200°C.

Combined consolidation methods are often used, combining molding with sintering, and in some cases, synthesis of the resulting compound with simultaneous molding and sintering.

Ceramic processing and inspection are the main components in the balance of the cost of ceramic products. According to some data, the cost of raw materials and consolidation is only 11% (for metals 43%), while processing accounts for 38% (for metals 43%) and control 51% (for metals 14%). The main methods of processing ceramics include heat treatment and dimensional surface treatment. Heat treatment of ceramics is carried out with the aim of crystallizing the intergranular glass phase. At the same time, the hardness and fracture toughness of the material increase by 20 - 30%.

Most ceramic materials are difficult to machine. Therefore, the main condition for ceramic technology is to obtain practically finished products during consolidation. To polish the surfaces of ceramic products, abrasive processing with diamond wheels, electrochemical, ultrasonic and laser processing are used. It is effective to use protective coatings that allow you to heal the smallest surface defects - irregularities, risks, etc.

To control ceramic parts, X-ray and ultrasonic flaw detection are most often used.

The strength of chemical interatomic bonds, due to which ceramic materials have high hardness, chemical and thermal resistance, simultaneously determines their low ability to undergo plastic deformation and their tendency to brittle fracture. Most ceramic materials have low viscosity and ductility and, accordingly, low crack resistance. The fracture toughness of crystalline ceramics is about 1 - 2 MPa/m1/2, while for metals it is more than 40 MPa/m1/2.

There are two possible approaches to increasing the fracture toughness of ceramic materials. One of them is traditional, associated with improving methods of grinding and cleaning powders, their compaction and sintering. The second approach is to inhibit crack growth under load. There are several ways to solve this problem. One of them is based on the fact that in some ceramic materials, for example, zirconium dioxide ZrO 2, a restructuring of the crystalline structure occurs under pressure. The initial tetragonal structure of ZrO 2 becomes monoclinic, having a 3-5% larger volume. As they expand, the ZrO 2 grains compress the crack, and it loses its ability to propagate (Figure 1, a). In this case, the resistance to brittle fracture increases to 15 MPa/m 1/2.

Figure 1 - Scheme of strengthening structural ceramics with ZrO 2 inclusions (a), fibers (b) and small cracks (c): 1 - tetragonal ZrO 2; 2 - monoclinic ZrO 2

ceramics technical viscosity technology

The second method (Figure 1, b) consists of creating a composite material by introducing fibers from a more durable ceramic material, such as silicon carbide SiC, into ceramics. A developing crack encounters a fiber on its way and does not propagate further. The fracture resistance of glass ceramics with SiC fibers increases to 18 - 20 MPa/m 1/2, significantly approaching the corresponding values ​​for metals.

The third method is that, using special technologies, the entire ceramic material is penetrated with microcracks (Figure 1, c). When the main crack meets a microcrack, the angle at the tip of the crack increases, the crack becomes blunt and it does not propagate further.

Of particular interest is the physicochemical method of increasing the reliability of ceramics. It has been implemented for one of the most promising ceramic materials based on silicon nitride Si 3 N 4 . The method is based on the formation of a certain stoichiometric composition of solid solutions of metal oxides in silicon nitride, called sialons. An example of high-strength ceramics formed in this system are sialons of the composition Si 3-x Al x N 4-x O x, where x is the number of substituted silicon and nitrogen atoms in silicon nitride, ranging from 0 to 2.1. An important property of sialon ceramics is its resistance to oxidation at high temperatures, which is significantly higher than that of silicon nitride.

2. Properties and applications of ceramic materials

The fundamental disadvantages of ceramics are their fragility and difficulty in processing. Ceramic materials do not perform well under mechanical or thermal shock, or under cyclic loading conditions. They are characterized by high sensitivity to cuts. At the same time, ceramic materials have high heat resistance, excellent corrosion resistance and low thermal conductivity, which allows them to be successfully used as thermal protection elements.

At temperatures above 1000°C, ceramics are stronger than any alloys, including superalloys, and their creep resistance and heat resistance are higher.

The main areas of application of ceramic materials include:

1) Ceramic cutting tools - characterized by high hardness, including when heated, wear resistance, and chemical inertness to most metals during the cutting process. In terms of the complex of these properties, ceramics are significantly superior to traditional cutting materials - high-speed steels and hard alloys (Table 2).

The high properties of cutting ceramics have made it possible to significantly increase the speed of machining of steel and cast iron (Table 3).

For the manufacture of cutting tools, ceramics based on aluminum oxide with additions of zirconium dioxide, titanium carbides and nitrides, as well as on the basis of oxygen-free compounds - boron nitride with a cubic lattice (-BN), usually called cubic boron nitride, and silicon nitride Si 3 N are widely used 4 . Cutting elements based on cubic boron nitride, depending on the production technology, produced under the names elbor, borazon, composite 09, etc., have a hardness close to the hardness of a diamond tool and remain resistant to heating in air up to 1300 - 1400°C. Unlike diamond tools, cubic boron nitride is chemically inert towards iron-based alloys. It can be used for rough and finish turning of hardened steels and cast irons of almost any hardness.

The composition and properties of the main grades of cutting ceramics are given in Table 4.

Ceramic cutting inserts are used to equip various milling cutters, turning tools, boring heads, and special tools.

2) Ceramic engines - from the second law of thermodynamics it follows that to increase the efficiency of any thermodynamic process it is necessary to increase the temperature at the entrance to the energy converting device: efficiency = 1 - T 2 / T 1, where T 1 and T 2 are the temperatures at the inlet and outlet energy conversion device, respectively. The higher the temperature T1, the greater the efficiency. However, the maximum permissible temperatures determined by the heat resistance of the material. Structural ceramics allow the use of higher temperatures compared to metal and are therefore a promising material for internal combustion engines and gas turbine engines. In addition to higher engine efficiency due to increased operating temperature, the advantage of ceramics is low density and thermal conductivity, increased thermal and wear resistance. In addition, when using it, the cost of the cooling system is reduced or eliminated.

At the same time, it should be noted that a number of unresolved problems remain in the technology of manufacturing ceramic engines. These primarily include problems of ensuring reliability, resistance to thermal shocks, and developing methods for connecting ceramic parts with metal and plastic ones. The most effective use of ceramics is for the manufacture of diesel adiabatic piston engines with ceramic insulation and high-temperature gas turbine engines.

Structural materials of adiabatic engines must be stable in the operating temperature range of 1300 - 1500 K, have a bending strength of at least 800 MPa and a stress intensity factor of at least 8 MPa * m 1/2. These requirements are best met by ceramics based on zirconium dioxide ZrO 2 and silicon nitride. The most extensive work on ceramic engines is carried out in Japan and the USA. The Japanese company Isuzu Motors Ltd mastered the production of the prechamber and valve mechanism of an adiabatic engine, Nissan Motors Ltd - the turbocharger impeller, and Mazda Motors Ltd - the prechamber and pusher pin.

The Cummin Engine company (USA) has mastered Alternative option truck engine with plasma coatings of ZrO 2 applied to the piston bottom, the inner surface of the cylinder, intake and exhaust ports. Fuel savings per 100 km were more than 30%.

Isuzu (Japan) announced the successful development of a ceramic engine running on gasoline and diesel fuel. The engine reaches speeds of up to 150 km/h, the fuel combustion efficiency is 30 - 50% higher than that of conventional engines, and the weight is 30% less.

Structural ceramics for gas turbine engines, unlike an adiabatic engine, do not require low thermal conductivity. Considering that ceramic parts of gas turbine engines operate at higher temperatures, they must maintain strength at a level of 600 MPa at temperatures up to 1470 - 1670 K (in the future up to 1770 - 1920 K) with plastic deformation of no more than 1% over 500 hours of operation. Silicon nitrides and carbides, which have high heat resistance, are used as a material for such critical parts of gas turbine engines as the combustion chamber, valve parts, turbocharger rotor, and stator.

Promotion tactical and technical characteristics aircraft engines is impossible without the use of ceramic materials.

3) Ceramics special purpose- special-purpose ceramics include superconducting ceramics, ceramics for the manufacture of containers with radioactive waste, armor protection military equipment and thermal protection of missile warheads and spaceships.

4) Containers for storing radioactive waste - one of the limiting factors in the development of nuclear energy is the difficulty of disposing of radioactive waste. For the manufacture of containers, ceramics based on B 2 O 3 oxide and boron carbide B4C are used in a mixture with lead oxide PbO or compounds such as 2PbO * PbSO 4. After sintering, such mixtures form dense ceramics with low porosity. It is characterized by a strong absorption capacity in relation to nuclear particles - neutrons and quanta.

5) Impact-resistant armor ceramics - by their nature, ceramic materials are fragile. However, at a high loading rate, for example in the case of an explosive shock, when this speed exceeds the speed of movement of dislocations in the metal, the plastic properties of metals will not play any role and the metal will be as brittle as ceramics. In this particular case, ceramics are significantly stronger than metal.

Important properties of ceramic materials that determine their use as armor are high hardness, elastic modulus, and melting (decomposition) temperature at 2-3 times lower density. Maintaining strength when heated allows the use of ceramics for protection against armor-piercing projectiles.

The following relationship can be used as a criterion for the suitability of a material for armor protection M:

where E is the elastic modulus, GPa; Nk - Knoop hardness, GPa; - tensile strength, MPa; T pl - melting temperature, K; - density, g/cm 3.

Table 5 shows the main properties of widely used armor ceramic materials in comparison with the properties of armor steel.

Materials based on boron carbide have the highest protective properties. Their mass application limited by the high cost of the pressing method. Therefore, boron carbide tiles are used when it is necessary to significantly reduce the weight of armor protection, for example, to protect seats and automatic control systems of helicopters, crew and troops. Titanium diboride ceramics, which have the highest hardness and elastic modulus, are used for protection against heavy armor-piercing and armor-piercing tank shells.

For mass production of ceramics, relatively cheap aluminum oxide is the most promising. Ceramics based on it are used to protect manpower, land and sea military equipment.

According to Morgan M. Ltd (USA), a 6.5 mm thick boron carbide or 8 mm thick aluminum oxide plate stops a 7.62 mm caliber bullet flying at a speed of more than 800 m/s when fired at point-blank range. To achieve the same effect, steel armor must have a thickness of 10 mm, while its mass will be 4 times greater than that of ceramic. The most effective is the use of composite armor, consisting of several heterogeneous layers. The outer ceramic layer absorbs the main shock and thermal load, is crushed into small particles and dissipates the kinetic energy of the projectile. The residual kinetic energy of the projectile is absorbed by the elastic deformation of the substrate, which can be steel, duralumin or several layers of Kevlar fabric. It is effective to coat the ceramics with a low-melting inert material, which acts as a kind of lubricant and slightly changes the direction of the flying projectile, which ensures a rebound.

The design of ceramic armor is shown in Figure 2.

Figure 2 - Design of a ceramic armor panel: a, b - constituent elements of the armor panel for protection against armor-piercing bullets different calibers; c - fragment of an armored panel assembled from elements a and b; 1 - armor-piercing bullet of 12.7 mm caliber; 2 - 7.62 mm caliber bullet; 3 - protective coating partially removed

The armor panel consists of individual ceramic plates connected in series with dimensions of 50 * 50 or 100 * 100 mm. To protect against armor-piercing bullets with a caliber of 12.6 mm, plates of Al 2 O 3 with a thickness of 15 mm and 35 layers of Kevlar are used, and against bullets with a caliber of 7.62 mm, plates of Al 2 O 3 with a thickness of 6 mm and 12 layers of Kevlar are used.

During the Gulf War, the widespread use by the US Army of ceramic armor made of Al 2 O 3, SiC and B 4 C showed its high efficiency. For armor protection, the use of materials based on AlN, TiB 2 and polyamide resins reinforced with ceramic fibers is also promising.

6) Ceramics in rocket and space engineering - when flying in dense layers of the atmosphere, the head parts of rockets, spacecraft, reusable ships, heated to high temperatures, need reliable thermal protection.

Materials for thermal protection must have high heat resistance and strength in combination with minimum values ​​of the coefficient of thermal expansion, thermal conductivity and density.

The US NASA Research Center (NASA Ames Research Center) has developed compositions of heat-protective fiber ceramic tiles intended for reusable spacecraft. The properties of boards of a number of compositions are given in Table 6. The average diameter of the fibers is 3 - 11 microns.

To increase the strength, reflectivity and ablative characteristics of the outer surface of heat-protective materials, they are coated with a layer of enamel about 300 microns thick. Enamel containing SiC or 94% SiO 2 and 6% B 2 O 3 is applied to the surface in the form of a slip and then sintered at 1470 K. Coated plates are used in the most heated areas of spacecraft, ballistic missiles and hypersonic aircraft. They can withstand up to 500 ten-minute heating in electric arc plasma at a temperature of 1670 K. Options for a ceramic thermal protection system for the frontal surfaces of aircraft are shown in Figure 3.

Figure 14.3 - Ceramic thermal protection system for the frontal surfaces of aircraft for temperatures from 1250 to 1700 o C: 1 - ceramics based on SiC or Si 3 N 4; 2 - thermal insulation; 3 - sintered ceramics

The highly porous fibrous thermal insulation layer based on FRCI, AETB or HTR is protected by a cladding layer of silicon carbide. The facing layer protects the heat-insulating layer from ablative and erosive destruction and absorbs the main thermal load.

Conclusion

Industrial ceramics have been used for many decades in mechanical engineering, metallurgy, the chemical industry, woodworking and the aviation industry. Often, enterprises, firms, factories simply cannot do without products that could work in extreme operating conditions.

The development of this industry has high prospects, which entails an increase in the quality of materials processing, their service life, productivity, wear resistance and many other factors.

List of sources used

1. Lakhtin Yu.M. "Materials Science Textbook for Higher Technical educational institutions": 1990. - 514 p.

2. Knunyants I.L. “Brief Chemical Encyclopedia” Volume 2. - M.: Khimiya, 1963. - 539 p.

3. Karabasov Yu.S. “New materials” 2002. - 255 p.

4. Balkevich V.L. "Technical Ceramics".: 1984.

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Types of ceramic materials. Ceramic materials are among the main materials that have a decisive influence on the level and competitiveness of industrial products. This influence will continue in the near future. Having entered engineering and technology in the late 1960s, ceramic materials made a real revolution in materials science, in a short time becoming, by all accounts, the third industrial materials after metals and polymers.

Ceramic materials were the first class of materials competitive with metals for use at high temperatures.

The main developers and producers of ceramic materials are the USA and Japan. In table Table 2.1 shows the classification of the main types of ceramic materials.

A study conducted by the US National Bureau of Standards showed that the use of ceramic materials had resulted in savings of more than $3 billion in national resources by the year 2000. The expected savings were achieved primarily through the use of transportation engines with parts made from ceramic materials, ceramic materials for cutting and optoceramics for information transmission. In addition to direct savings, the use of ceramic materials will reduce the consumption of expensive and scarce metals: titanium and tantalum in capacitors, tungsten and cobalt in cutting tools, cobalt, chromium and nickel in heat engines.

Production of ceramic materials. Ceramic technology involves the following main stages: obtaining initial powders, consolidating powders, i.e. production of compact materials, their processing and control of products.

In the production of high-quality ceramic materials with high structural homogeneity, powders of starting materials with a particle size of up to 1 micron are used. The process of obtaining such a high degree of dispersion requires a lot of energy and is one of the main stages of ceramic technology.

Characteristics of the main types of ceramic materials

Functional type of ceramic materials	Properties used	Application	Connections used
Electroceramics	Electrical conductivity, electrical insulation, dielectric and piezoelectric properties	Integrated circuits, capacitors, vibrators, ignitors, heaters, thermistors, transistors, filters, solar cells, solid electrolytes	BeO, MgO, V2O3, ZnO, A1 2 0 3, Zr0 2, SiC, B 4 C, TiC, CdS, titanates, Si 3 N 4
Magnestoceramics	Magnetic properties	Magnetic recording heads, magnetic media, magnets	Soft and hard magnetic ferrites
Optoceramics	Transparency, polarization, fluorescence	Lamps high pressure, IR transparent windows, laser materials, light guides, optical memory elements, display screens, modulators	А1 2 0 3 , MgO, Y 2 0 2 , Si0 2 , Zr0 2 , T0 2 , Y 2 0 3 , Th0 2 , ZnS, CdS
Chemoceramics	Absorption and adsorption capacity, catalytic activity, corrosion resistance	Sorbents, catalysts and their carriers, electrodes, gas humidity sensors, elements of chemical reactors	ZnO, Fe 2 0 3, SnO, Si0 2, MgO, BaS, CeS, TiB 2, ZrB 2, A1 2 0 3, SiC, titanides
Bioceramics	Biological compatibility, resistance to biocorrosion	Dentures, joints	Oxide systems

Thermoceramics	Heat resistance, heat resistance, fire resistance, thermal conductivity, coefficient of thermal expansion (CTE), heat capacity	Refractories, heat pipes, lining of high-temperature reactors, electrodes for metallurgy, heat exchangers, thermal protection	SiC, TiC, B4C, TiB 2 , ZrB 2 , Si 3 N 4 , BeS, CeS, BeO, MgO, Zr0 2 , A1 2 0 3 , TiO, composite materials
Mechanical ceramics	Hardness, strength, elastic modulus, fracture toughness, wear resistance, tribotechnical properties, CTE, heat resistance	Parts for heat engines; sealing, antifriction and friction parts; cutting tool; press tools, guides and other wear-resistant parts	Si 3 N 4 , Zr0 2 , SiC, TiB 2 , ZnB 2 , TiC, TiN, WC, B 4 C, A1 2 0 3 , BN, composite materials
Nuclear ceramics	Radiation resistance, heat resistance, heat resistance, neutron capture cross section, fire resistance, radioactivity	Nuclear fuel, reactor lining, shielding materials, radiation absorbers, neutron absorbers	U0 2 , U0 2 , Pu0 2 , UC, US, ThS, SiC, B 4 C, A1 2 0 3 , BeO
Superconducting ceramics	Electrical cable and bridge	Power transmission lines, magnetogasdynamic generators, energy storage devices, integrated circuits, railway transport maglev, electric vehicles	Oxide systems: La-Ba-Cu-O; La-Sr-Ci-O; Y-Ba-Cu-0

Grinding produced mechanically using grinding media, and also by spraying the crushed material in a liquid state, deposition on cold surfaces from the vapor-gas phase, vibrocavitation effect on particles in the liquid, using self-propagating high-temperature synthesis and other methods.

For ultrafine grinding (particles less than 1 micron), vibration mills, or attritors, are the most promising.

Consolidation of ceramic materials consists of molding and sintering processes. There are three main groups of molding methods:

• pressing under compressive pressure, at which the powder is compacted by reducing porosity;
• plastic molding by squeezing rods and pipes through a die (extrusion) of molding compounds with plasticizers that increase their fluidity;
• slip casting for the manufacture of thin-walled products of any complex shape, in which liquid suspensions of powders are used for molding.

When moving from pressing to plastic molding and slip casting, the possibilities for manufacturing products of complex shapes increase, but the process of drying products and removing plasticizers from ceramic materials becomes more complicated. Therefore, for the manufacture of products of relatively simple shapes, preference is given to pressing, and for more complex ones, extrusion and slip casting.

During sintering, individual powder particles are transformed into a monolith and the final properties of the ceramic are formed. The sintering process is accompanied by a decrease in porosity and shrinkage.

In the production of ceramic materials, sintering furnaces at atmospheric pressure, hot isostatic pressing units (gasostats), and hot pressing presses with a pressing force of up to 1,500 kN are used. The sintering temperature, depending on the composition, can be 2000...2200 °C.

Combined consolidation methods are often used, combining molding with sintering, and in some cases, synthesis of the resulting compound with simultaneous molding and sintering.

Processing of ceramic materials and quality control are the main components in the balance of the cost of ceramic products.

According to some data, the cost of raw materials and consolidation is only 11% (for metals 43%), while processing accounts for 38% (for metals 43%) and control 51% (for metals 14%).

To the main methods processing of ceramic materials include heat treatment and dimensional surface treatment.

Thermal treatment of ceramic materials is carried out for the purpose of crystallization of the intergranular glass phase. At the same time, the hardness and fracture toughness of the material increase by 20...30%.

Most ceramic materials are difficult to machine. Therefore, the main condition for ceramic technology is to obtain practically finished products during consolidation. To polish the surfaces of ceramic products, abrasive processing with diamond wheels, electrochemical, ultrasonic and laser processing are used. It is effective to use protective coatings that eliminate even the smallest surface defects - irregularities, risks, etc.

To control the quality of manufacturing of ceramic parts, X-ray and ultrasonic flaw detection are most often used.

Considering that most ceramic materials have low viscosity and plasticity and, accordingly, low crack resistance, methods of fracture mechanics are used to certify products with determination of the stress intensity factor K k. At the same time, a diagram is constructed showing the kinetics of defect growth.

Quantitatively, the fracture toughness of crystalline ceramics and glass is approximately 1...2 MPa/m |/2, while for metals the values ​​/G| C is significantly higher (more than 40 MPa/m |/2). The strength of chemical interatomic bonds, due to which ceramic materials have high hardness, chemical and thermal resistance, simultaneously determines their low ability to undergo plastic deformation and their tendency to brittle fracture.

There are two possible approaches to increasing the fracture toughness of ceramic materials. One of them, traditional, is associated with improving methods of grinding and cleaning powders, their compaction and sintering. The second approach is to inhibit crack growth under load. There are several ways to solve this problem. One of them is based on the fact that in some ceramic materials, for example, in zirconium dioxide Zr0 2, a restructuring of the crystalline structure occurs under pressure. The initial tetragonal structure of Zr0 2 becomes monoclinic, having a 3...5% larger volume.

Expanding, Zr0 2 grains compress the crack, and it loses its ability to propagate (Fig. 2.1, A). In this case, the resistance to brittle fracture increases to 15 MPa/m |/2.

The second method (Fig. 2.1, b) consists of creating a composite material by introducing fibers from a more durable material into ceramics

Rice. 2.1. Strengthening of structural ceramics with Zr0 2 (a) inclusions and fibers (b) and microcracks (c):

/ - tetragonal Zr0 2 ; 2 - monolithic Zr0 2

ceramic material, such as silicon carbide SiC. A developing crack encounters a fiber on its way and does not propagate further. The fracture resistance of glass ceramics with SiC fibers increases to 20 MPa/m |/2, significantly approaching the corresponding values ​​for metals.

The third method is that, using special technologies, the entire ceramic material is penetrated with microcracks (Fig. 2.1, V). When the main crack meets a microcrack, the angle at the tip of the crack increases, the crack becomes blunt and it does not propagate further.

Of particular interest is the physicochemical method of increasing the reliability of ceramic materials. It has been implemented for one of the most promising ceramic materials based on silicon nitride Si 3 N 4 . The method is based on the formation of a certain stoichiometric composition of solid solutions of metal oxides in silicon nitride, called sialons. An example of high-strength ceramics formed in this system are sialons of the composition Si^^Ai^Ng^O^, where X - the number of substituted silicon and nitrogen atoms in silicon nitride, ranging from 0 to 4.2. An important property of sialon ceramics is its resistance to oxidation at high temperatures, which is significantly higher than that of silicon nitride.

Properties and application of ceramic materials. IN In modern mechanical engineering, the use of ceramic materials is constantly increasing. They are diverse in chemical composition and physical and mechanical characteristics. Ceramic materials can operate at high temperatures - 1600... 2500 °C (heat-resistant steels 800... I 200 °C, molybdenum - 1500 °C, tungsten - 1800 °C), they have a density of 2-3 times less than that of heat-resistant materials, hardness close to the hardness of diamond, excellent dielectric characteristics, high chemical resistance. The reserves of raw materials for the production of ceramics on earth are inexhaustible. Parts of gas turbines and diesel engines, fuel elements of nuclear reactors, light armor and thermal protection elements of spaceships, thin-walled floats and containers for deep-sea equipment, cutting plates and equipment for hot deformation of metals, plungers and sealing rings in pumps for pumping aggressive media, elements of high-precision gyroscopes and computer boards, bearings , permanent magnets, etc.

The use of ceramic materials in automobile engines will make it possible to increase the operating temperature in the cylinders from I 200 to 1600 °C, while reducing heat loss, reducing fuel consumption, and improving performance characteristics. When making products from ceramic materials, you cannot simply replace metal parts with ceramic ones. Their operating conditions and operating loads must be especially taken into account, since all parts are made entirely and this can reduce the strength of the entire structure. In addition, it does not undergo plastic deformation and has low impact strength.

The basic requirements that should be taken into account when designing ceramic parts are formulated.

In loaded areas, the ceramic part should not have stress concentrators. Bolted connections are practically not used in ceramic structures; they try not to drill holes, make ledges, or grooves in them in order to avoid microcracks. Damping pads are installed at the points of contact between ceramics and metal.

Metal and ceramic parts of the same product must have the same thermal expansion coefficient; otherwise, compensation gaskets must be installed, and transient processes when heating or cooling occurs are also taken into account.

Ceramics have a heat capacity 2 times greater than metal, which causes thermal deformation and stress. It is highly desirable that the temperature of the ceramic part be the same throughout the entire volume. Compressive stresses are perceived most favorably. In the absence of load, residual polymerization stresses should not remain in ceramic parts.

Currently, ceramic materials based on silicon nitride are used - reaction-bonded, sintered and hot-pressed silicon nitrides with alloying additives. Reaction-bonded silicon nitride has relatively low strength compared to other materials, but complex profile parts made from it exhibit consistently low shrinkage. Hot-pressed silicon nitride has maximum strength. The properties of ceramic materials significantly depend on the operating parameters and their manufacturing technology. Ceramics compositions have been developed that, in terms of their performance characteristics, can replace heat-resistant steels, but developments in the field of compositions and technology for their production continue. The fundamental disadvantages of ceramic materials are their fragility and difficulty in processing. Ceramic materials do not perform well under mechanical or thermal shock, or under cyclic loading conditions. They are characterized by high sensitivity to cuts. At the same time, ceramic materials have high heat resistance, excellent corrosion resistance and excellent thermal conductivity, which allows them to be successfully used as thermal protection elements.

At temperatures above 1 000°C, ceramic materials are stronger than any alloys, including superalloys, and their creep resistance and heat resistance are higher. The main areas of application of ceramic materials include cutting tools, parts of internal combustion engines and gas turbine engines, etc.

Ceramic cutting tool. Ceramic cutting materials are characterized by high hardness, including when heated, wear resistance, and chemical inertness to most metals during the cutting process. In terms of the complex of these properties, ceramic materials are significantly superior to traditional cutting materials - high-speed steels and hard alloys (Table 2.2).

The high properties of cutting ceramic materials have made it possible to significantly increase the speed of machining of steel and cast iron (Table 2.3).

For the manufacture of cutting tools, ceramic materials based on aluminum oxide with added

Table And tsa 2.2

Comparative values ​​of the properties of tool materials

kami zirconium dioxide, titanium carbides and nitrides, as well as based on oxygen-free compounds - boron nitride with a cubic lattice (p-BN), usually called cubic boron nitride, and silicon nitride Si 3 N 4. Cutting elements based on cubic boron nitride, depending on the production technology, produced under the names elbor, borazon, composite 09 and others, have a hardness close to the hardness of a diamond tool and remain resistant to heating in air up to 1,400 °C. Unlike diamond tools, cubic boron nitride is chemically inert towards iron-based alloys. It can be used for rough and finish turning of hardened steels and cast irons of almost any hardness.

Ceramic cutting inserts are used to equip various milling cutters, turning tools, boring heads, and special tools.

Ceramic engines. From the second law of thermodynamics it follows that to increase the efficiency of any thermodynamic process it is necessary to increase the temperature at the entrance to the energy converting device: efficiency = 1 - T 2 /T b Where T t And T 2- temperature, respectively, at the input and output of the energy converting device. The higher the temperature T and the more efficiency.

The maximum permissible temperatures are determined by the heat resistance of the material. Structural ceramic materials allow the use of higher temperatures compared to metal and are therefore promising materials for internal combustion engines and gas turbine engines. In addition to higher engine efficiency due to increased operating temperature, the advantages of ceramic materials are low density and thermal conductivity, increased

Table 2.3

Comparative values ​​of cutting speed when turning with ceramic tools and carbide tools

high thermal and wear resistance. In addition, when using ceramic materials, cooling system costs are reduced or eliminated.

At the same time, a number of unsolved problems remain in the technology of manufacturing ceramic engines. These primarily include problems of ensuring reliability, resistance to thermal shocks, and developing methods for connecting ceramic parts with metal and plastic ones.

The most effective use of ceramic materials is for the manufacture of diesel adiabatic piston engines with ceramic insulation and high-temperature gas turbine engines.

Structural materials of adiabatic engines must be stable in the operating temperature range of 1,300... 1,500 K, have a bending strength of at least 800 MPa and a stress intensity factor of at least 8 MPam |/2. These requirements are best met by ceramic materials based on zirconium dioxide Zr0 2 and silicon nitride. The most extensive work on ceramic engines is carried out in Japan and the USA. Japanese company lsuzu Motors Ltd. mastered the production of the prechamber and valve mechanism of an adiabatic engine, Nissan Motors Ltd. - turbocharger impellers, Mazda Motors Ltd. - pre-chamber and pusher fingers.

The Cammin Engine company (USA) has developed an alternative version of a truck engine with plasma coatings of Zr0 2 applied to the piston bottom, the inner surface of the cylinder, intake and exhaust channels. Fuel savings per 100 km were more than 30%.

Lsuzu Motors Ltd. announced the successful development of a ceramic engine running on gasoline and diesel fuel. A car with such an engine reaches speeds of up to 150 km/h, the fuel combustion efficiency is 30...50% higher than that of conventional engines, and the weight is 30% less.

Structural ceramic materials for gas turbine engines, unlike an adiabatic engine, do not require low thermal conductivity. Considering that ceramic parts of gas turbine engines operate at higher temperatures, they must maintain strength at a level of 600 MPa at temperatures up to 1,670 K (in the future up to 1,920 K) with plastic deformation of no more than 1% over 500 hours of operation. Silicon nitrides and carbides, which have high heat resistance, are used as a material for such critical parts of gas turbine engines as the combustion chamber, valve parts, turbocharger rotor, and stator.

Improving the performance characteristics of aircraft engines is impossible without the use of ceramic materials.

Ceramic materials for special purposes. Special-purpose ceramic materials include superconducting ceramics, ceramics for the manufacture of containers with radioactive waste, armor protection for military equipment and thermal protection for the head parts of missiles and spacecraft.

Containers for storing radioactive waste. One of the limiting factors for the development of nuclear energy is the difficulty of disposing of radioactive waste. For the manufacture of containers, ceramic materials are used based on B2O3 oxides and B4C boron carbides in a mixture with lead oxides PbO or compounds such as 2PbO PbS04. After sintering, such mixtures form dense ceramics with low porosity. It is characterized by a strong absorption capacity towards nuclear particles - neutrons and y-quanta.

Impact-resistant armor ceramic materials. These materials were first used by US Army aviation during the Vietnam War. Since then, the use by armies has been continuously increasing. different countries armor made of ceramic materials in combination with other materials to protect ground combat vehicles, ships, airplanes and helicopters. According to various estimates, the growth in the use of ceramic armor protection is about 5...7% per year. At the same time, there is an increase in the production of composite armor for individual protection of law enforcement forces, due to the increase in crime and acts of terrorism.

By their nature, ceramic materials are fragile. However, at a high loading rate, for example in the case of an explosive shock, when this speed exceeds the speed of movement of dislocations in the metal, the plastic properties of metals will not play any role and the metal will be as brittle as ceramics. In this particular case, ceramic materials are significantly stronger than metal.

Important properties of ceramic materials that determine their use as armor are high hardness, elastic modulus, and melting (decomposition) temperature at a density that is 2 to 3 times less than the density of materials. Maintaining strength when heated allows the use of ceramic materials for armor-piercing projectiles.

As a criterion M suitability of the material for armor protection, the following ratio can be used:

Where E - modulus of elasticity, GPa; N k - Knoop hardness, GPa; o„- tensile strength, MPa; T t - melting point, K; p - density, g/cm3.

In table Table 2.4 shows the main properties of widely used armor ceramic materials in comparison with the properties of armor steel. Materials based on boron carbide have the highest protective properties. Their mass use is hampered by the high cost of the pressing method. Therefore, boron carbide tiles are used when it is necessary to significantly reduce the weight of armor protection, for example, to protect seats and automatic control systems of helicopters, crew and troops. Ceramic materials made from titanium diboride, which have the highest hardness and elastic modulus, are used for protection against heavy armor-piercing and armor-piercing tank shells.

For the mass production of ceramic materials, relatively cheap aluminum oxide is the most promising. Ceramic materials based on it are used to protect manpower, land and sea military equipment.

Filed by Morgan M. Ltd. (USA), a 6.5 mm thick boron carbide or 8 mm thick aluminum oxide plate stops a 7.62 mm caliber bullet traveling at a speed of more than 800 m/s when fired at point-blank range. To achieve the same effect

Table 2.4

Properties of impact-resistant ceramic materials

Material	Density	T hardness according to Knoop # k, GPa	Tensile strength o in, MPa	Elastic modulus E, GPa	Melting temperature T pl, TO	Armor resistance criterion L/, (GPa m) 3 - K/kg
Hot pressed boron carbide B 4 C
Hot pressed titanium diboride TiB 2
Silicon carbide SiC
Sintered aluminum oxide A1 2 0 3
Armored

steel armor should have a thickness of 20 mm, while its mass will be 4 times greater than that of ceramic.

The most effective is the use of composite armor, consisting of several heterogeneous layers. The outer ceramic layer absorbs the main shock and thermal load, is crushed into small particles and dissipates the kinetic energy of the projectile. The residual kinetic energy of the projectile is absorbed by the elastic deformation of the substrate, which can be steel, duralumin or several layers of Kevlar fabric. It is effective to coat the ceramic layer with a low-melting inert material, which acts as a kind of lubricant and slightly changes the direction of the flying projectile, which ensures a rebound. The design of the ceramic armor panel is shown in Fig. 2.2. The armored panel consists of individual ceramic plates connected in series with dimensions of 50x50 or 100 mm. To protect against armor-piercing bullets with a caliber of 12 mm, plates made of A1 2 0 3 with a thickness of 12 mm and 35 layers of Kevlar are used, and against bullets with a caliber of 7.62 mm, which are in NATO service, plates made of A1 2 0 3 with a thickness of 6 mm and 12 layers are used. Kevlar.

During the Gulf War, the widespread use by the US Army of ceramic armor made of A1 2 0 3, SiC and B 4 C showed its high effectiveness. For armor protection, the use of materials based on AIN, TiB and polyamide resins reinforced with ceramic fibers is also promising.

Ceramic materials in rocket and space engineering. When flying in dense layers of the atmosphere, the head parts of rockets, spacecraft, and reusable ships, heated to high temperatures, require reliable thermal protection. Materials for thermal protection should

Rice. 2.2.

and at b - components of an armor panel for protection against armor-piercing bullets of various calibers; V - fragment of an armored panel assembled from elements a and b; I - armor-piercing bullet with a caliber of 12.7 mm; 2- bullet caliber 7.62 mm; 3 - protective

the coating is partially removed and has high heat resistance and strength in combination with minimal values ​​of the coefficient of thermal expansion, thermal conductivity and density.

The US NASA Research Center (NASA Ames Research Center) has developed compositions of heat-protective fiber ceramic tiles intended for reusable spacecraft.

To increase the strength, reflectivity and ablative characteristics of the outer surface of heat-protective materials, they are coated with a layer of enamel about 300 microns thick. Enamel containing SiC or 94% Si0 2 and 6% B 2 0 3 is applied to the surface in the form of a slip and then sintered at a temperature of 1,470 K. Coated slabs are used in the hottest areas of spaceships, ballistic missiles and supersonic aircraft . They can withstand up to 500 ten-minute heating in electric arc plasma at a temperature of 1,670 K. Variants of the ceramic thermal protection system for the frontal surfaces of aircraft are shown in Fig. 2.3.

The facing layer protects the heat-insulating layer from ablative and erosive destruction and absorbs the main thermal load.

Radiotransparent ceramic materials. For the development of modern radio, electronic and computer technology, materials based on aluminum oxide, boron nitrides, and silicon are needed, having an operating temperature of up to 3,000 ° C, having stable values ​​of dielectric constant and low dielectric losses with a dielectric loss tangent tg 8 = 0, 0001 ...0.0002.

Such materials include pure aluminum oxide, hot-pressed boron nitride, ceramic materials TSM 303 and ARP-3, sintered boron nitride, glass-ceramic D-2, quartz ceramic materials, pure silicon nitride, etc.

Radiotransparent materials must have a set of properties: stability of dielectric characteristics over the entire range of operating temperatures, heat resistance, erosion

Rice. 2.3.

/ - ceramic material based on SiC or SijN 4; 2 - thermal insulation; 3 - sintered ceramic material

resilience, high quality surface, resistance to ionizing radiation, etc. They act as a structural material from which load-bearing radio-transparent structural elements are made. Since the porosity of oxide ceramics can be varied within 0...90%, this makes it possible to obtain materials with fundamentally different properties from the same oxide.

Materials obtained by structuring, for example from zirconium dioxide, are generally not destroyed when exposed to a heat flow of any intensity.

An example of structuring is also the production of glass ceramics, in which the optimal ratio of crystalline and amorphous phases is selected. By changing the chemical composition and structure, it is possible to obtain entire classes of glass ceramics with desired properties.

Another direction in the production of radiotransparent materials is the use of alloying additives. In particular, the introduction of several percent of magnesium and boron oxides into aluminum oxide increases its heat resistance and impact strength at zero moisture absorption by 2-3 times. The introduction of 2...5% chromium oxide into quartz ceramic material increases the integral degree of emissivity by 2-3 times and slows down the attenuation of the radio signal at high temperatures by 2 times.

The third direction in the development of radiotransparent materials is the development of nitride materials and compositions based on them, in particular boron, silicon and aluminum nitrides.

Boron nitride has the best dielectric characteristics of all currently known materials operating at temperatures up to 2,000 °C, although it has relatively low strength and hardness. On its basis, for example, sibonite is made containing boron nitride and silicon dioxide. By changing their ratio and dispersion, it is possible to obtain a number of new materials that combine the advantages of boron nitride and quartz ceramics.

The latest direction in the development of radiotransparent materials is the creation of composite materials, in particular ceramic materials impregnated with organic and inorganic substances, resins and salts. They combine good dielectric properties at high temperatures due to the use of a ceramic base and high strength and toughness due to the binder.

Depending on the purpose and operational characteristics of the product, appropriate radio-transparent ceramic materials are developed for it. The dielectric constant of quartz ceramic materials increases monotonically with increasing temperature up to 1,500 °C, and in the range of 1,500... 1,700 °C it sharply

increases by 18%, which is associated with the melting of the material, accompanied by an increase in its density to the theoretical value (2,210 kg/m3 at 20 °C). After melting, the material remains radiotransparent and its dielectric constant increases to 4.3 at a temperature of 2,500 °C. Since, according to operating conditions, the change should not exceed 10%, quartz ceramic materials are suitable for operating temperatures up to 1,350 °C, and aluminum oxide - up to 815 °C. With an increase in volume porosity from 5 to 20%, the dielectric constant decreases in direct proportion to the decrease in the density of the ceramic. The dielectric loss tangent tan 6 of quartz ceramic materials is 0.0002 - 0.0004 at room temperature at a frequency of 10 Hz. When the temperature increases to 1,000 °C, tg 6 increases to 0.005.

Boron nitride is so far the only material whose tg5 at temperatures up to 1,500 °C remains below 0.001. Moreover, the change in tg8 of sintered boron nitride in the range of 20... 1,350 ”C does not exceed 3%; for quartz ceramic materials this value is 10%.

A technology has been mastered for the synthesis of highly active boron nitride powder, capable of sintering at temperatures above 1,600 °C to form sufficiently strong workpieces. Such materials have impurities up to 1% and have an isotropic structure. They are good insulators - specific volume resistance at room temperature is not less than 1 10 14 Ohm cm. Under the influence of a pulse nuclear radiation tan 8 in boron nitride increases to 0.01, but in quartz ceramics it does not change. Due to its excellent heat resistance, sintered boron nitride is used as a structural material, although it has a fairly low strength.

Materials based on boron nitride, especially hot-pressed ones, have high thermal conductivity, while quartz ceramic materials are closer to heat insulators. Its thermal conductivity, depending on the porosity, fluctuates at a temperature of 600...700 K within the range of 0.2...1.0 W/(m K). High thermal conductivity can be both an advantage of the material (the higher the thermal conductivity, the lower the thermal stresses), and a disadvantage if the radiotransparent material also performs heat-protective functions. For boron nitride and alumina ceramic materials, thermal conductivity decreases as temperature increases.

For quartz ceramic materials and glass ceramics D-2, the glassy, ​​amorphous phase is of decisive importance.

Optimal design of products operating on land, in water, in the air and in space allows for the wider use of radio-transparent materials.

Dishes made from baked clay appeared several centuries ago and have since become an integral part of human life. It has survived to this day practically unchanged, but today we want to talk not exactly about it, but about its more practical and beautiful successor - ceramics.

Difference from simple clay

Ceramics differs from clay in only a few ways, but they are enough to give the finished product new practical properties.

This material consists of two main components: clay, used as a base, and additives. Various solid mineral substances, for example, sand or ordinary chalk, can be used as the latter. All this affects porosity, water absorption and even color.

Another important difference lies in production technology. While firing a clay product is the final stage of its manufacture, for ceramic tableware that's only half the battle. For additional protection and increased 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 secure the protective layer on the surface.

Properties of ceramics

Depending on the selected components and differences in manufacturing technology, the final properties of ceramic tableware may vary slightly, but the “basic list” of qualities remains the same for all products:

• They are durable, but do not withstand shocks and falls.
• Walls ceramic tableware have a porous structure, due to which heat, when heated, begins to spread smoothly, evenly distributed over the entire surface. This has a positive effect on the taste of the dishes, making them more juicy and rich, reminiscent of soups and stews from the Russian oven.
• The glaze reliably protects the base from moisture absorption and is scratch resistant.
• The presence of glass in the coating adds non-stick properties to the cookware. Even with a minimal amount of oil, products in high-quality ceramics do not stick or burn during cooking.
• The material is environmentally friendly and safe.
• It has no odor of its own, so it cannot spoil the taste of the finished dish.
• The temperature range for using ceramic products is very wide - you can cook in them in the oven, as well as store food in the refrigerator. The only thing that ceramics cannot tolerate is sudden temperature changes. Due to the sudden expansion of air in the pores, it cracks easily.

Kinds

As we have already noted, the components used in the composition affect the appearance and properties, in fact, forming several types of material:

• Porcelain is one of the most famous and easily distinguishable types. It can be recognized by its light weight and thin, slightly transparent walls porcelain dishes. For its production, white clay is used, which gives that “signature” white-blue shade. Despite its elegance and subtlety, porcelain has fairly high strength and heat resistance.
• Faience - it is similar to porcelain, as it is also made from white clay, but has a more porous structure, due to which the walls of the products have to be made thicker. The overall strength of earthenware is about a quarter lower than that of porcelain.
• Terracotta clay - unlike previous types, this material has dark shades - from mustard yellow to rich brown, reddish or even black. This feature is often turned into an advantage by covering the surface with a transparent glaze. Without additional protection, such clay strongly absorbs water, so it was previously used only for making containers for storing bulk dry products.
• Glass ceramics is a modern material that does not contain clay. However, dishes made from it are made according to approximately the same principle - the products are not just formed from a special glass composition, but are also additionally fired.
• Dolomite is another variety that has gained popularity relatively recently. In fact, it is also not ceramic (it is a type of limestone), but appearance and a number of properties are very similar to it. Utensils for cooking and use in the oven are not made from it, but are used to create, for example, teapots, sugar bowls and vases.

What kitchen utensils are made from ceramics?

Ceramics are used to create dishes and other kitchen utensils extremely widely. It is made from:

• pots,
• frying pans,
• peas,
• baking and baking dishes,
• cups, teapots, sets,
• sugar bowls, vases for sweets,
• plates and large dishes,
• stands for ladles and tea bags,
• salt shakers,
• kitchen knives.

Most likely it's not even full list, and if you take a look in your kitchen, you'll probably find something we forgot to mention.

And finally, it is worth focusing on frying 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 rich aroma and special taste characteristic of dishes prepared in ceramic dishes.