Classification of materials according to functional purpose

1. Classification of materials

Classification of materials: metal, non-metallic and composite materials. Metal materials are divided into non-ferrous metals, powder materials. Non-metallic materials: rubber, glass, ceramics, plastic masses, sitals. Composite materials are composite materials, which include two or more materials (fiberglass).

There is a classification of materials depending on the type of semi-finished products: sheets, powders, granules, fibers, profiles, etc.

The technique of creating materials is based on the classification by structure.

Metal materials are divided into groups in accordance with the component that underlies them. Materials of ferrous metallurgy: steel, cast iron, ferroalloys, alloys in which the main component is iron. Materials of non-ferrous metallurgy: aluminum, copper, zinc, lead, nickel, tin.

The basis of modern techniques is metals and metal alloys. Today, metals are the most universal on the use of the class of materials. In order to improve the quality and reliability of products, new materials are required. To solve these problems, composite, polymer, powder materials are used.

Metals are substances that have forging, glitter, electrical conductivity and thermal conductivity. In the technique, all metal materials are called metals and divide into two groups.

Simple metals are metals that have a small amount of impurities of other metals.

Painting metals are metals that represent the combinations of a simple metal as a basis with other elements.

Three quarters of all elements in the periodic system are metals.

2. The mechanism of condensation of the substance. Education of chemical ties

Condensation (from Late. Condensatio is a seal, condensation), transition to-wa from a gaseous state into a liquid or solid during bottom. parameters; Phase transition of the first kind. Condensation - Exothermich. The process, the heat of the phase transition is highlighted with the heat of the condensation. Condensier. Phase can be formed in the volume of steam or on the pray of solid and fluid having more low T-rurather than the saturation of the pair at this pressure (see dew dot). Condensation occurs when isothermich. compression, adiabatich. Expansion and cooling steam or simultane. lowering its pressure and T-ry, to-rye leads to the fact that condenses. The phase becomes thermodynamically more stable than gaseous. If, while the pressure and T-ra is higher than in the triple point for a given in-be, a liquid is formed (liquefying), if lower in-in enters the solid state, bypassing liquid (desubamation). Condensation is widely used in Chem. Technologies for the separation of mixtures by condensation of fractional, drying and cleaning in-in et al., in power engineering, eg. In the condensers of steam turbines, in refrigeration technology to condensate the working fluid, to the desalination. Installations, etc. When condensation of vapors in the narrow pores of adsorbents, the latter can absorb. Number of in-va from the gas phase (see capillary condensation). Consequence of water vapor condensation in the atmosphere - rain, snow, dew, frost. Condensation in liquid state. In the case of condensation in the volume of steam or vapor-gas mixture (homogeneous condensation) condensib. The phase is formed in the form of small drops of liquid (fog) or small crystals. To do this, it is necessary to have condensation centers, can serve as very small droplets of liquid (embryos), resulting from fluctuations of the density of the gas phase, dust and particles carrier electrical. Charge (ions). In the absence of centers of condensation, steam may for long. time is in t. Naz. Metastable (perverted) state. Stable homogue. Condensation begins at t. Critic. The submission of P kp \u003d p to / p n where p k is an equilibrium pressure corresponding to critic. The diameter of the embryos, r n - pressure of the saturation. A steam above the flat poverty of the liquid (for example, for water vapor in the air, purified from solid particles or ions, p cr \u003d 5-8). Fog formation is observed both in nature and to tehnol. devices, eg When cooling the vapor-gas mixture due to radiation, mixing wet gases. The condensation on the pity of the solid body of a saturated or superheated steam occurs at T-repeated, K-paradium is less than the T-Ra of the saturation of the steam during its equilibrium pressure above it. Observed in many prom. The devices, which serve to condensate the target products, was heated. media, separation of steam and vapor-gas mixtures, cooling wet gases, etc. When the steam is liquefied on a solid, well-wetting condensate, a solid fluid film is formed (film condensation); on the pitch, not wetting condensate or wettable partially, - separate drops (drip condensation); On the pitch with the heterogeneous century (for example, on polished metallic with oxidized contaminated areas) - zones covered with condensate film and drops (mixed condensation). When film condensation of pure vapors of non-metals Cooph. The heat transfer is determined in the OSN. Termich. The resistance of the condensate film, which depends on the mode of its flow. The latter in the case of almost fixed steam is determined by the number of Reynolds Film: R P pl \u003d W / V to, where W, - acc. The average speed and thickness of the film condensate, V to - kineetich. Condensation viscosity. For condensation on a vertical plate or pipe at R, at least 5-8, the flow of the film is purely laminar, when these values \u200b\u200bare exceeded by the RE pl - laminar-wave, with Realls \u003e\u003e 350-400 - turbulent. On vertical, soils means. Heights may be observed area with Split. Condensate film flow modes. For laminar current An increase in re plus with an increase in film thickness leads to a decrease in the COEF. heat transfer, with turbulent flow - to its increase. If steam is overheated, the condensation is accompanied by convective heat transfer from steam to condensate, the surface of the surface of the K-pogo is almost equal to the saturation at a steam pressure. For in-B with a large heat of condensation (eg, water, alcohols) of the heat of overheating is usually insignificant compared to the heat of condensation, and it can be neglected. In the case of film condensation of a moving pair, the dues of the phase separation voltage due to the interfacial friction and the pulse transfer by particles of the condensed pair, which are connected to the condensate film, causes the speed to increase the speed and reduce the film thickness, resulting in the COEF. The heat transfer increases. At higher steam stream speeds, its effects on the condensate film can lead not only to the change in its speed and thickness, but also to the perturbation of the flow (the formation of waves, turbulization), intense heat transfer in the film. If the flow of the steam point is directed upward, the movement of the condensate laminar film is inhibited, its thickness increases and coefficients. The heat transfer decreases as the steam speed increases as long as the effect of interfacial friction causes T. Naz. Inverted (directed up) Condensate film. When condensation of a moving pair inside the pipe (channel), the flow regimes and the nature of the completion. The steam and liquid phases can be significantly changed as a result of a change as the condensation of steam velocity condensate, tangent of friction voltage on the interfacial pray and Re pl. At high steam speeds (when the effect of gravity on the condensate film is negligible, it is negligible and its current is determined in the string. The heat transfer does not depend on spaces. Pipe orientation. If the forces of gravity and friction are commensurate, the conditions of condensation are determined by the angle of inclination of the pipe and the mutual direction of the phase movement. In the case of condensation inside the horizontal pipe and the low steam speed, the circular film condensate is formed only on top, parts of the inner panel of the pipe. On the bottom Parts arises with a "stream", in the zone of a relatively large thickness of the heat transfer layer, the heat transfer is significantly less intense than on the rest of the PC. In the case of condensation on the bunch of horizontal pipes, the flowing condensate consumption is incremented from top to bottom due to condensation with overlying pipes to the underlying, and the steam consumption is reduced along the path of its movement. In a beam with a constant or relatively slightly decreased living cross-section between pipes, the speed of the downstream pair gradually decreases, and the condensate flows from the top, the pipes to the lower. Initially, this leads to a decrease in local coefficients. heat transfer (averaged over the perimeter of pipes) with an increase in the number of the horizontal row of pipes counting on top. However, starting with a certain row, as a result of condensate, the flow of the film is indignant and its thermal. Resistance decreases. Thanks to this coefficient. The heat transfer can be stabilized, and with the increasing impact of the perturbation of the film to the bottom. Tubes - increase with increasing number of rows. The intensification of heat transfer during film condensation can be achieved by profiling its prai (eg, using T, Naz. Small-old PRI), K-rye helps to reduce the average thickness of the condensate film, creating on the pole of art, roughness leading to the tour Bulization of film, exposed to it with dielectric. liquid phase (eg, when condensation of chladone) electrostatic. Field, condensate suction through the porous piste and others. When condensing the vapor of liquid metals, the thermal conductivity of the liquid phase is very high. Therefore, the share of thermal. The resistance of the condensate film in the total heat transfer resistance is insignificant, and the interfacial thermal is determined. Resistance due to molecular kinetich. Effects on the border of the phase partition. Sometimes film condensation on the PC is accompanied by Homog. condensation in the section adjacent to the phase section of the pair layer. If the formation of fog is undesirable (for example, in the production of H 2 SO 4 nitrous way or when catching volatile rters), the process is carried out at max. Speeding steam below P cr. With drip condensation, primary small drops formed on a dry vertical or inclined pray, grow as a result of the continuation of the process, the fusion of close and touching each other drops and pull up to them arising between drops and a quickly tearing fine film of condensate. The drops that have reached the "tear-off" diameter flow down, uniting (coales) with the underlying small drops, after which small drops are formed on the liberated pray, and the cycle is repeated. Conditions that determine the spontaneous occurrence of drip condensation are rarely observed. Usually, a thin layer of the lyophobizer is applied to the fixed condensation to solid, which has a low surface tension and a condensive (for example. , Fats, waxes). In the case of drip condensation KOEF. The heat transfer is much higher (5-10 times or more) than when film. However, maintaining a prom. Sustainable drip condensation devices are difficult. Therefore, condenses. Him devices. Proms, as a rule, operate in film condensation mode. Condensation of a pair on the pray liquid of the same in the WA occurs in tehnol. Devices on the pity of the pair of dispersed (eg, with a spray, nozzles) of jets or driving thin liquid films on the nozzle. Dispersing or distribution of fluid on thin films allows you to strongly develop a phase contact. In some cases, condensation is observed when steam is received into the volume of fluid in the form of jets or bubbles (bubble), as well as in the formation of steam bubbles in the volume of fluid, for example. at cavitation. Condensation of steam from a mixture of it with non-condensable gases (or non-condensable with a given T-REA) on the pray of a solid or fluid is less intense compared to the condensation of pure steam. Since when condensation from a steam-gas mixture of T-ra and partial pressure (concentration) of steam into its main. The mass is higher than on solid POP, in the mixture adjacent to the last layer (when the mixture moves, in the boundary layer), co-heat and mass exchange occurs. If the steam is immobile, even insignificant. The content of gas in it leads to a sharp decrease in condensation intensity. As the velocity increases (the number of Reynolds Rem cm) of the vapor-gas mixture, the influence of gas on the intensity of the process is gradually weakened. In condensation of vapors from multicomponent mixtures (steam or steam-gas) in the gas phase, interrelated heat and mass transfer also occur. In this case, effective coefficients. Thermal conductivity of the mixture and efficient coefficients. Diffusion of its individual components are determined by nature and concentrations of other components. In the case of homogue. Mixtures of condensates on the rough of solid body occurs only film condensation, in the case of heterogeneous - mixed. For example, with a condensingbar mixture of water vapor and org. A liquid film of this in-Ba is formed on the solid pity, which covers moisture drops.

In the formation of a chemical bond, a redistribution in the space of electronic densities originally belonged to different atoms occurs. Since the least firmly connected to the core electrons of the external level, then these electrons belong to the main role in the formation of a chemical bond. The number of chemical bonds formed by this atom in the compound is called valence. Electrons participating in the formation of chemical bond are called valence: the S- and P of elements are external electrons, in the D-elements - the external (last) S-electrons and the penultimate D-electrons. From an energy point of view, an atom is most stable, at the external level of which contains the maximum number of electrons (2 and 8 electrons). Such a level is called completed. Completed levels are distinguished by high strength and are characteristic of the atoms of noble gases, so under normal conditions, they are in a state of chemically inert monoomic gas.

Atoms of other elements, external energy levels are unfinished. In the process of the chemical reaction, the external levels are completed, which is achieved by either attachment or electron impact, as well as the formation of general electronic pairs. These methods lead to the formation of two main types of communication: covalent and ionic. Thus, in the formation of a molecule, each atom seeks to acquire a stable outer electron shell: either two-electron (doublet) or eight-α-octetric (octet). This pattern is based on the theory of chemical education. The formation of chemical bonds due to the completion of the external levels in the forming bobes of atoms is accompanied by the release of a large amount of energy, that is, the occurrence of chemical bond always processes exothermally, since it leads to the emergence of new particles (molecules), which have greater resistance under normal conditions, and therefore they are less energy than the initial. One of the essential indicators determining which link is formed between atoms is electronegativity, that is, the ability to atom attract electrons from other atoms. The electronegability of the atoms of the elements varies gradually: in periodic periodic systems, its value increases, and in groups from top to bottom, it decreases.

3. Types of chemical ties

Chemical bond, carried out by the formation of general (binding) electronic pairs, is called covalent. 1) We will analyze an example of the formation of a chemical bond between atoms with the same electric negativity, for example, hydrogen molecules H2. + -N -\u003e H: H or inquar, which symbolizes a pair of electrons: HH covalent bond formed by atoms with the same electronegitability is called non-polar. Such a connection form dioment molecules consisting of atoms of a single chemical element: H 2, CL 2, etc.) the formation of a covalent bond between atoms whose electronenence varies slightly. The covalent bond formed by atoms with different electronegitability is called polar. With a covalent polar communication, the electronic density of the total pair of electrons is shifted to the atom with greater electronegitability. Examples include H2O, NH4, H3S, CH4CL molecules. Covalent (polar and non-polar) Communication in our examples was formed due to unpaired electrons of binding atoms. Such a mechanism for the formation of a covalent connection is called exchange rate. Another covalent communication mechanism is donor-acceptor. In this case, communication occurs due to two paired electrons of one atom (donor) and the free orbital of the other atom (acceptor). Okay famous example - Education of ammonium ion: H + +: NH 3 -\u003e [H: NH 3 | + NH 4 + acceptor donor ion ammonium electrons. When an ammonium ion is formed, an electron pair of nitrogen becomes common to N and H atoms, that is, a fourth relationship occurs that does not differ from the other three. They are depicted equally:

The ion connection occurs between atoms, the electronegability of which dramatically consider the method of education on the example of sodium chloride NaCl. The electronic configuration of sodium and chlorine atoms can be submitted: 11 Na LS2 2S2 2P 6 3S1; 17 Cl ls2 2p 6 zs2 3r5 as atoms with incomplete energy levels. Obviously, to complete the sodium atom easier to give one electron than to attach seven, and the chlorine atom is easier to attach one electron than to give seven. In the chemical interaction, the sodium atom completely gives one electron, and the chlorine atom takes it. Schematically, this can be written as follows: na. - LE -\u003e Na + sodium ion, stable eight-electron 1s2 2S2 2p6 shell due to the second energy level. : CL + 1E -\u003e. CL - chlorine ion, stable eight-electron shell. There are electrostatic attraction forces between Na + ions and clown, resulting in a compound.

Chemical bond, carried out by electrostatic attraction between ions, is called ionic communication. The compounds formed by attraction of ions are called ionic. Ionic compounds consist of separate molecules only in a vapor state. In solid (crystalline) state, ionic compounds consist of naturally located positive and negative ions. There are no molecules in this case. The ionic compounds form sharply different electronegability elements of the main subgroups I and II groups and the main subgroups of VI and VII groups. Ionic compounds are relatively few. For example, inorganic salts: NH5Cl (ammonium ion NH5 + and ion chlorine CL-), as well as saline organic compounds: alcoholates of carboxylic acid salts, Aminic salts Non-polar covalent bonds and ionic communication - two limits of electronic density distribution. Non-polar communication corresponds to the uniform distribution of the binder of two electronic clouds between the same atoms. On the contrary, with ion communication, the binders of the electronic cloud practically fully belongs to one of the atoms. In most compounds, chemical bonds are intermediate between these types of communication, that is, a polar covalent bond is carried out.

Metal communication exists in metals in solid in liquid state. In accordance with the position in the periodic system, the metals atoms have a small number of valence electrons (1-3 electron) and low ionization energy (electron separation). Therefore, the valence electrons are poorly held in the atom, they are easily separated and have the ability to move throughout the crystal. In the nodes of the crystal lattice of metals there are free atoms, positively charged horses, and a part of the valence electrons, fluidly moving in the volume of the crystal lattice, forms "electronic gas", which ensures the relationship between metal atoms. The relationship that relatively free electrons is carried out between the metal ions in the crystal lattice is called a metallic bond. Metal communication occurs due to the generalization of the atoms of valence electrons. However, between these types of communication there is a significant difference. Electrons exercising covalent bond are mainly in close proximity to the two connected atoms. In the case of metallic coupling, electrons communicating are moved throughout the piece of metal. These are determined by general features of metals: metal shine, good conductivity of heat and electricity, pupidity, plasticity, etc. The total chemical property of metals is their relatively high reducing ability.

Hydrogen bonds can be formed between the hydrogen atom associated with an atom of an electroneary element, and an electroneary element having a free pair of electrons (O, F, N). The hydrogen bond is due to electrostatic attraction, which contributes to the small size of the hydrogen atom, and in part, donor-acceptor interaction. Hydrogen bond can be intermolecular and intramolecular. Communication 0-H has a pronounced polar character: hydrogen bond is much weaker than ionic or covalent, but stronger than intermolecular interaction. Hydrogen bonds determine some physical properties of substances (for example, high boiling temperatures). Especially common hydrogen bonds in protein molecules, nucleic acids and other biologically important compounds, providing them with a certain spatial structure (organization).

4. Crystal structure of the substance. Types of crystal lattice.

Crystalline substances

Solid crystals - three-dimensional formations characterized by strict repeatability of the same element of the structure ( elementary cell) in all directions. The elementary cell is the smallest volume of the crystal in the form of a parallelepiped, repeating in the crystal an infinite number of times.

The geometrically correct form of crystals is due primarily to their strictly natural inner structure. If instead of atoms, ions or molecules in the crystal, you can depict the points as the centers of gravity of these particles, then the three-dimensional regular distribution of such points, called the crystal lattice, will be obtained. The points themselves are called nodes crystal lattice.

Types of crystal lattices

Depending on which particles, a crystal lattice is constructed and what the character of the chemical bond between them is distinguished by various types of crystals.

Ion crystals are formed by cations and anions (for example, salts and hydroxides of most metals). They have an ion connection between particles.

Ionic crystals may consist of monatomic ions. So crystals are built sodium chloride, potassium iodide, calcium fluoride.
Monatomic metal cations and polyhydric anions, for example, nitrate-ion NO 3 -, SU-ion SO 4 2-, carbonate ion CO 3 2, are involved in the formation of ionic crystals of many salts.

In the ion crystal it is impossible to single out single molecules. Each cation is attracted to each anion and repel from other cations. The whole crystal can be considered a huge molecule. The dimensions of such a molecule are not limited because it can grow by attaching new cations and anions.

Most ionic compounds crystallized according to one of the structural types, which differ from each other by the value of the coordination number, that is, the number of neighbors around this ion (4, 6 or 8). For ionic compounds with an equal number of cations and anions, four main types of crystalline lattices are known: sodium chloride (the coordination number of both ions is 6), cesium chloride (the coordination number of both ions is 8), sphalerite and wurcite (both structural types are characterized by the coordination number of cation and Anion, equal to 4). If the number of cations is twice as smaller than the number of anions, the coordination number of cations should be twice as much as the coordination number of anions. In this case, structural types of fluorite (coordination numbers 8 and 4) are implemented, rutila (coordination numbers 6 and 3), crystobalite (coordination numbers 4 and 2).

Usually, ionic crystals are solid, but fragile. Their fragility is due to the fact that even with a small deformation of the crystal, the cations and anions are shifted in such a way that the repulsion forces between the ions of the same name begin to prevail over the attraction forces between cations and anions, and the crystal is destroyed.

Ion crystals are distinguished by high melting temperatures. In the molten state of the substance forming ionic crystals, electrically conductive. When dissolved in water, these substances dissociate into cations and anions, and the resulting solutions conduct an electric current.

High solubility in polar solvents accompanied by electrolytic dissociation is due to the fact that in the solvent medium with a high dielectric constant ε, the energy of attraction between ions is reduced. The dielectric permeability of water is 82 times higher than the vacuum (conditionally existing in the ion crystal), the attraction between ions in aqueous solution decreases at the same time. The effect is intensified by the solvation of ions.

Atomic crystals consist of separate atoms combined by covalent bonds. Of the simple substances, only boron and elements of IVA groups have such crystalline lattices. Often compounds of non-metals with each other (for example, silicon dioxide) also form atomic crystals.

As well as ionic, atomic crystals can be considered gigantic molecules. They are very durable and solid, poorly carried out heat and electricity. Substances having atomic crystalline lattices are melted at high temperatures. They are practically insoluble in any solvents. They are characterized by low reactivity.

Molecular crystals are constructed from individual molecules inside which the atoms are connected by covalent bonds. There are weaker intermolecular forces between molecules. They are easily destroyed, so molecular crystals have low melting temperatures, low hardness, high volatility. Substances forming molecular crystal lattices do not have electrical conductivity, their solutions and melts also do not conduct an electric current.

Intermolecular forces arise from the electrostatic interaction of negatively charged electrons of one molecule with positively charged nuclei of adjacent molecules. For the force of intermolecular interaction, many factors affect. The most important among them is the presence of polar bonds, that is, shifts of electron density from one atoms to others. In addition, the intermolecular interaction manifests itself stronger between molecules with a large number of electrons.

Most non-metals in the form of simple substances (for example, iodine I 2, Argon AR, sulfur S 8) and compounds with each other (for example, water, carbon dioxide, chloride), and also almost all solid organic substances form molecular crystals.

For metals, a metal crystal lattice is characteristic. It has a metal connection between atoms. In metal crystals, the kernel of atoms are located in such a way that their packaging is as dense as possible. Communication in such crystals is delocalized and extended to the whole crystal. Metal crystals have high electrical conductivity and thermal conductivity, metal glitter and opacity, light deformability.

Classification of crystal lattices meets limit cases. Most of the crystals of inorganic substances belong to the intermediate types - covalently ion, molecular-covalent, etc. For example, in a crystal nemetallic graphite ... composite) 22 4352 1 Forming Products on the ... -materials on the ... Liquid)) colored 23 1723 ... METAL Dry 2881 catalyst METAL Dry 2881 catalyst METAL ... on the classification ...

Ferromagnetics.

Diamagnetism is the property of magnetic materials in the outer magnetic field in the direction, the program. Diamagnetism is inherent in all things.

Diamagnetics have negative magnetic susceptibility. In an external magnetic field, they are magnetized against the field. In the absence of external magnetic field Diamagnetics are non-magnetic.

Paramagnetics have positive magnetic susceptibility. They are weakly magnetized in the direction of the field, and in the absence of the field - are non-magnetic.

Ferromagnets are characterized by large values \u200b\u200bof magnetic susceptibility and its dependence on field strength and temperature. They have itself arbitrary magnetization even in the absence of an external magnetizing field.

Antiferromagnetics- Materials whose magnetization in the absence of a magnetic field is zero.

Magnetic susceptibility is usually essential but depends on temperature: in paramagnetics - it is reduced during heating, ferromagnets - increases with a jump.

Technological properties

The technological properties of materials characterize the susceptibility of materials of the technological effects when processing in the product. Knowledge of these properties allows you to rationally carry out the processes of combustion of products.

The main characteristics of the materials are: - Cutting processes;

Pressureability of pressure;

- foundry characteristics;

Weldability;

- a tendency to warp during thermal

botke et al.

The processability of cutting is characterized by the following indicators:

- quality processing of materials - roughness of the treated surface and accuracy of times;

- resistance of the cutting tool;

- cutting resistance - speed and cutting force;

- view of chip formation.

The processability of pressure is determined in the process of technological testing (samples) of materials on the plan. Methods for assessing the process of pressure depend on the type of materials and the technology of their processing. In more detail, the description of technological samples is given in section. 2, ch. 3.

The processability of pressure of powder materials characterizes their fluidity, sealability and formability. Methods for determining the characteristics of powder materials are installed state Standardmi.

Foundation characteristics of materials - a combination of technological indicators characterizing the formation of castings by filling the molten material into a casting form.

Liquid flow -the property of the molten mother of Alla fill out the casting form.

Foundry Shrinkage -reducing the volume of the melt when moving from a liquid state into solid. Watching coefficient individual for each type of material.

Weldability - the property of the material to form a welded joint, the performance of which is

Chapter 3. The main properties of materials

the quality of the main material subjected to welding. On the weldability are judged by the results of the test of welded samples and characteristics of the main material in the weld zone.

Control questions

1. What are the main indicators of the properties of materials?

2. What parameters determine the technical strength of the materials?

3. What do you understand under tributery?

4. How to improve the corrosion resistance of the material?

5. Name the main technological characteristics of the materials of the materials.

2 Materials Science

Application areas of materials

Nomenclature - a list of titles and terms used in a particular industry.

The nomenclature of technical materials is used to streamline the description of the enormous mass of materials used for the manufacture of machines and other technical products. Validation of materials and principles of their classification are necessary for justifying bathroom Material, technology of its processes and operating modes in the art. Special rules for the manufacture and processing of materials in compliance with the requirements of quality, occupational safety and security ambient - Standards. Standardization of materials is based on the nephery of technology and aims to increase the efficiency of industrial production.

Classification of materials

The most important in the technique has classification on structural and functional features of materials.

Chapter 4. Regional Applications

The main criterion for the classification of materials on structural features is state of aggregationDepending on which materials are divided into the following types:

- solid materials;

Liquids;

Gases;

Plasma.

In fig. 2 shows the classification of solids by structural feature. The limitations of this class of fiction is that technical materialsAs a rule, inhomogeneous in structure and include several phases. Depending on the number of phases and stations of the inhomogeneity of the structure, the materials are subdivided into:

Simple, consisting of one element or compound and having a homogeneous macrostructure;

Composite composed of several phases and having an inhomogeneous structure;

Alloys, materials with a homogeneous macrostructure of swarm formed as a result of hardening races

floa chemical heterogeneous substances.

For appointment, technical materials are divided into the following groups.

Construction materials - solid materials intended for the manufacture of products subjected to mechanical loads. They must have a complex mechanical propertiesproviding the required efficiency and resource of products during the work of the working environment. K. It is imposed techno logical requirements that determine the smallest complexity of manufacturing products, and economic relating to the cost and availability of material.

Construction materials are divided into types:

non-crystalline

crystal

Section 1. Basics of Materials

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2. Classification of solid structural materials

Metals;

- silicates and ceramics;

Polymers;

Rubber;

Wood;

- composite materials. Electrical materials are characterized by

bye electrical and magnetic parameters and are intended for the manufacture of products, use it for production, transformation, transformation and for electricity requires.

The tribotechnical materials are intended for change in friction sites in order to regulate the mating of friction and wear to ensure the specified performance and resource of these nodes. The main types of such materials are:

Lubricating - lubricants in solid (graphite, talc), liquid (motor, transmission oils), ha zoo-shaped (air, pairs and other gases) phases;

- antifriction- alloys of non-ferrous metals (babbits, bronze, etc.), gray cast iron, plastics (textolites, fluoroplastics, etc.), metal detergent compositions (bridzovograph, chapels, etc.), wood and alcoholic plastics, rubber;

Friction having a large coefficient

friction and high wear resistance (some types of plastics, cast iron and metal rims and other composite materials).

Instrumental materials are distinguished by high performance, wear resistance and firmware. They are intended for the manufacture of cutting, measurable, fitting and assembly and other instrument (tool steel and solid alloys, al

Section 1. Basics of Materials

mAZ, some types of ceramic materials, many composite materials).

Working bodies - gaseous or liquid materials, with which energy is converted into mechanical work (hydraulic oil, air in pneumatic systems, gaseous combustion products Top Liva in internal combustion engines).

Fuel - combustible materials, the main part of which is carbon, used in order to gain when burning thermal energy. According to incidents, the fuel is divided into:

Natural (oil, coal, natural gas, wood);

Artificial (coke, motor fuels, general gases).

According to the type of machines in which the fuel is burned, it is de poured on: rocket, engine, reactor, turbine, etc.

Technological materials - an extensive group of undermining materials used to ensure the optimal flow of technological processes of the processing of the main technological materials

in products or maintenance of normal machines

and mechanisms. These include: adhesives and sealants, La Cocking materials; fluxes, solders, welding electrodes used during welding and soldering; lubricant but cooling fluids; conservative mothers of ALL (lubricants, films, mastic), ensuring the protection of the products from corrosion; Washing materials, etc.

IN the technique has developed a tradition to group Mothers Alla for the mostimportant operational parameters,namely:

On electrical conductivity (conductors, semi-window vodries and dielectrics);

Chapter 4. Application areas of materials

- by magnetic susceptibility (dia-, para-, far degree);

- on thermal characteristics (thermal insulation and refractory);

- by resistance to the effects of the working medium (heat resistant, acid-resistant, corrosion-resistant and

Such a classification is not strict, but its ter mines and concepts are accepted in the technique and are used in the practice of mechanical engineering.

Standardization of materials

Standardization of materials is the establishment and application of the rules of production and processing Mate Rial to achieve their optimal use and compliance with security requirements.

1 of the following materials are improved production efficiency, improving the quality of industrial products, the establishment of the optimal nomenclature of materials, as well as normal environmental conditions, health care for the village and safety of labor. To achieve these goals, it is planned to establish:

- control characteristics of raw materials, materials and semi-finished products, providing the manufacture of products with high quality indicators;

- a unified system of quality indicators, methods and means of control and testing, as well as the need for the level of reliability of materials depending on the purpose and operating conditions;

- standards and requirements in the field of production Mate Rials in order to eliminate ineffective sections, brands and sizes;

Section 1. Basics of Materials

- materials and coding classification systems technical and economic information on their properties;

- rules for labor safety in the manufacture and processing of materials;

- norms in the field of labor protection of working and improving

usage use natural resources. Regulatory technical documents I install

the rules complex, the rules, the quality requirements of the Ma Terry, are divided into the following types.

State standards (GOST) are binding on the application by all enterprises, organizations and institutions in all industries and hoiciness.

Industry standards (OST) are required for all enterprises and organizations of the industry, as well as industries (customers) using its products.

Specifications (TU) are set for one or more types (species, grades) of materials operational characteristics, rules for the reception of KI, quality control methods, requirements for Markirov, packaging, transportation and storage, manufacturer's guarantees, safety requirements and use Materials.

Control questions

1. How are the materials classified by their structons?

2. List the regulatory and technical documentation that establishes the set of norms, rules and requirements for materials.

can be divided into two large groups - Basic and auxiliary. Main materials provide specified specifications Products (machines, mechanisms, facilities, etc.): Strength, power, speed, stability of the structure, etc. Auxiliary - provide stabilization of the parameters of structures, machines and aggregates during their operation (materials for lubrication of friction assemblies, heat removal , protection against corrosion and erosion, from physical and chemical impact, for decorative finish and ensuring the aesthetic parameters and design requirements, etc.).
Materials that ensure the strength of the structures should have a certain structural strength; possess a certain technological in the manufacture of structures; Have a relatively low cost and not be deficient.
Structural strength is a generalized characteristic of a material determined by a complex of structurally resistant properties. These properties include the basic parameters of mechanical properties: strength - yield strength, strength limit; Plasticity - relative elongation and narrowing; Shock viscosity (work of destruction).
Technologicalness - material being developed in the process of manufacturing the product. Technologicalness is estimated by standard methods inherent in one or another material during its technological processing, the formation of cracks during pressure processing or casting of metals, bundle - for wood, shrinkage when casting plastics and metals, etc.
Materials providing the strength of the structure usually constitute the bulk of this design. therefore an important requirement Such materials are their definition and independence from the situation in the sales market, as well as the material should not lose its working consumer properties during the operation of the product.
A variety of materials with specific properties can be used in various nodes of machines and devices that ensure reliability and quality of equipment that can be divided into a number of groups. One of these includes materials with high elastic properties. These are spring materials that are on the manufacture of springs, springs, membranes, bellows, etc. They have high strength under static, dynamic and cyclic loading conditions, sufficient plasticity and viscosity, as well as high resistance to small plastic deformations and destruction. With some appointments, these materials should be non-magnetic, corrosion-racks, electrically conductive, have a low temperature coefficient of elasticity module (for example, for elastic elements of watch mechanisms).
As spring materials, carbonaceous and alloyed steel, subjected to thermal or deformation hardening, beryllium and phosphorous bronze (copper alloys), etc. are most often used.
In moving nodes of machines and mechanisms, materials of tribotechnical purposes are used, ensuring quite certain conditions of friction of contacting elements of structures. The basic condition for these materials is a small wear in mechanical, physical, chemical or combined effects.
The implementation of this condition is achieved through the use of high hardness materials or materials with a complex structure, each phase of which carries a certain functional load (one provides hardness, the other is a good work of surfaces to each other). High hardness materials include solid and superhard materials: Cubic modifications of carbon (diamond) and boron nitride (elbor), metal-like compounds (carbides, nitrides, borides and silicides of titanium type, zirconium, vanadium, niobium, chromium, molybdenum, tungsten), Non-metallic heartless compounds of silicon carbides (carboorund), ceramics (aluminum oxides - ruby, beryllium, zirconium, chromium and other metals; sitals - crystalline glasses, solid alloys, etc.).
In case of shock contact, materials must withstand high pressure and shock load. In such conditions, solid tool steel is usually used.
With quick movement of fluid near the surface solid It arises cavitation phenomena. Cavitation - a breakdown of continuity inside the liquid in the form of gas bubbles, which slamming the local pulling voltages in the body of the order of 1260-2500 MPa and a temperature of 230-720 ° C. This leads to cavitation wear - surface erosion. To prevent cavitation destruction, materials are used, the structure of which absorbs excess energy and this prevents the erosion of the surface layers of the product. Such quality has some doped steel of austenitic and martensitic class (the classification of steels is given in further sections). A special class of steels has been developed - tryptal, in which the transformations are initiated by deformation. In these steels, high strength and viscosity are combined. They include elements such as chrome, nickel, molybdenum, manganese, silicon.
In cavitation conditions, satisfactory results show some non-ferrous metals, in particular copper alloys and titanium alloys.
A large group in tribotechnics is represented by antifriction materials used in sliding, rolling bearings, etc. products. These materials should provide a low friction coefficient, high wear resistance and at workability. Such requirements are satisfied with metal materials (cast iron, babbit, steel, aluminum and copper alloys), non-metallic (polymeric, graphite, wood) and combined (metal-polymers, graphiteometallometallic) materials.
To create large friction efforts, for example, in brake devices, friction materials are used, which are separated on metal and non-metallic. Metal include steel, cast iron, bronze, to non-metallic - asbopolymers. As a substitute asbestos use various kinds of fibers - metal, carbon, aluminosylicate, glass, etc.
In a separate group, materials are allocated to provide special physico-mechanical parameters of devices. This group includes a variety of materials subjected to one or another physical or chemical impact - thermal, radiation, vacuum, chemically active medium, electric, magnetic, etc. In each of these cases, the material must have specific properties that make it suitable for This application.

Plastics are plastic materials based on polymers with plasticity (fluidity) and capable of taking a given shape when heated under pressure and steadily save it after cooling. Plastics, obtained on the basis of thermoplastic polymers, are called thermoplastic, or thermoplasts, and obtained on the basis of thermosetting polymers - reactoplasts. In construction, polyvinyl chloride-based thermoplastics are widely used - decorative films, linoleums for floating floors, pipes, etc.; polyethylene - pipes, films, connecting parts; Polypropylene - handles for windows and doors, decorative and ventilation grids, housings for various products. Paper-layered and wood-layered plastics based on phenolofehyde and urea-formaldehyde resins are used as reactive plates. According to the compositional composition, two types of plastics distinguish; Uncolished and filled. Uncolished plastics consist only of polymer and some special additives. These include polyethylene film, polystyrene products, etc. Filled plastics contain except polymer fillers, stabilizers, pigments. The filled plastics includes various types of linoleum and handling products from polyvinyl chloride, paper-layered plastics, etc. Depending on the physicomechanical properties when normal temperatureBased on which the elastic module lies, plastics divide on hard, semi-rigid, soft and elastic. Hard plastics - solid elastic materials of the amorphous structure. Characterized by a minor elongation, brittle destruction when breaking. Examples of rigid plastics are phenoplasts and aminoplasts. Semi-rigid plastics - solid viscoelastic materials of the crystal structure. Characterized by a high relative lengthening at break. Such plastics includes polypropylene pipes, polyamide plastics. Soft plastics have a high relative elongation at break and low modulus of elasticity. These include polyethylene film, pipes, polyvinila acetate films. Elastic plastics are soft, flexible materials characterized by large strain deformations. An example of elastic plastics serve rubber rubber. In the appointment and distinguishing features of plastics are common, high-strength, anti-corrosion, transparent, frost and heat-resistant, electrical insulating. General Purpose Plastics - Materials, Physico-Mechanical Indicators and chemical properties which do not impose special requirements. These materials include finishing, decorative, packaging, household and other products from plastics (polyvinyl chloride, polypropylene, phenoplasts, etc.). High-strength plastics - polyformaldehyde, polyester plastics, polycarbonates are characterized by a high strength limit for compression and bending, large wear resistance and high friction coefficient (frictional properties). These materials are able to replace bronze and babbit, for example, in bearings, bushings; They are used for the manufacture of pipes, gear wheels, rowing screws. Anticorrosion plastics - rubber, polyisobutylene, epoxyplists - have high chemical resistance to water, acids, salts and organic solvents. These materials are used instead of metal parts in the equipment and structures operating in aggressive environments, of which liquid fuel tank containers are manufactured. Transparent plastics - polymethyl methacrylate, polystyrene - skip the rays of light in a wide range of waves, and in particular the ultraviolet part of the spectrum, so that they are not inferior in their optical properties with the best grades of glass and crystal and significantly exceed the silicate glass. Of these plastics manufactures optical systems of lighting reinforcement. Frost-resistant plastics - polyisobutylene, ethyl cellulose, polycarbonate - retain elastic properties and flexibility at low (minus) temperatures. Products and structures made from such plastics can be operated under atmospheric conditions. Heat resistant plastics - polyorganosyloxanes, polytricher-ethylene, phenoplasts - have the ability to not soften while increasing the temperature. Such plastics are widely used in industry and everyday life, in some cases they replace metal and ceramics. Electric insulating plastics - polyethylene, polyvinyl chloride, polystyrene - are characterized by low dielectric constant, high electrical strength, high volume surface resistance. They are used for insulation of wires and electrical equipment in electrical engineering, to replace the ebonite. Thermal insulation plastics - polyvinyl chloride, polystyrene, polyurethane, phenoplasts are distinguished by low thermal conductivity. These plastics include porous gas-filled materials - foam and poroplasts used for thermal insulation of refrigeration instruments and installations, residential premises, multilayer wall panels, etc. P.