Peculiarities of location of enterprises of ferrous metallurgy

The problems of the location of this sector are particularly complex due to the fact that the high level of development of the productive forces and the latest achievements of science and technology make it economically feasible to build the largest enterprises with multifaceted rear connections (mines, calcareous quarries, coke plants, etc.). Each of these features in one way or another affects the effectiveness of this industry, but the greatest importance, as a rule, belongs to the raw materials and fuel factors, since ferrous metallurgy is very material-intensive.

Large ferrous metallurgy in general can effectively develop only in areas that have natural prerequisites for this. Failure to comply with this requirement leads to a shortage of prepared ores and high-quality coking coal in individual enterprises. The efficiency of ferrous metallurgy is also affected by metal consumption. It was proximity to the largest metal-consuming centers in Russia that served as one of the main factors in the creation of metallurgy in the central and north-western regions in the 17th century and the first half of the 18th century.

The availability of water sources influences the location of metallurgical plants. In some cases, especially where there is a tense water balance, their role can become decisive.

Despite the current structural changes in industry caused by the chemicalization of production and the increasing use of light and non-ferrous metals, plastics and other chemical synthesis products, ferrous metals have not lost their role as the main constructional material in industry and transport. They are widely used in construction and other branches of the national economy. Their production remains one of the most important indicators of the industrial development of a country, reflecting its technical level.

Combines are the main type of ferrous metallurgy enterprises in most industrialized countries. Enterprises with a full cycle give over 9/10 pig iron, about 9/10 steel and rolled products. In addition, there are factories producing cast iron and steel, steel and rolled products (including pipe and metalware plants), as well as cast iron, steel and rolled products. Enterprises without cast iron smelting are referred to the so-called pig-iron metallurgy. A special group for technical and economic parameters are enterprises with electrothermal production of steel and ferroalloys.

Ferrous metallurgy with a full technological cycle is an important area-forming factor. In addition to the numerous industries that arise on the basis of the recycling of various kinds of waste during the smelting of cast iron and the coking of coal-heavy organic synthesis (benzene, anthracene, naphthalene, ammonia and their derivatives), production of building materials (cement, block products), tomato flour (in the redistribution of iron Ores with a high content of phosphorus), ferrous metallurgy attracts accompanying industries. Its most typical satellites are: thermal power engineering, primarily installations that are part of metallurgical plants and can operate on secondary fuel (excess blast furnace gas, coke, coke breeze); Metal-intensive mechanical engineering (metallurgical and mining equipment, heavy machine tools). The iron and steel industry forms around itself such powerful and diversely developed industrial complexes that arose in the Urals and in the Kuzbass.

Metallurgy of the full cycle, redistribution and “small” differ from each other in terms of placement. To place the first, raw materials and fuel are especially important, they account for 85-90% of all costs for smelting pig iron, including about 50% for coke and 35-40% for iron ore. On 1t of pig iron it is required 1,2-1,5t of coal (taking into account losses at enrichment and coking), 1.5t of iron ore, more than 0.5t of flux limestone and up to 30m3 of circulating water. This underlines the importance of the mutual transport-geographical position of raw and fuel bases, water supply sources and auxiliary materials.

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Process and products of metallurgical production

Requirements for the metallurgical process

Technological processes applied at operating enterprises of non-ferrous metallurgy in most cases far from completely meet modern requirements. A number of processes and their hardware design are obsolete and need replacing with new, more sophisticated ones.

Modern metallurgical processes for the production of non-ferrous metals and, especially, processes of the near future must satisfy at least the following requirements:

High specific productivity of used devices;
High labor productivity (output per employee);
High degree of extraction of all valuable components;
High degree of complex use of raw materials;
Minimal energy costs due to the use of external sources of thermal energy or electricity;
Maximum use of secondary energy resources;
Ensuring the possibility of comprehensive mechanization and automation of all operations;
The use of simple, cheap, durable and convenient in operation, start-up, adjustment and repair of equipment;
Providing the possibility of creating continuous, streamlined, fully automated production lines for the production of metals with partial or complete program control.

Products of metallurgical production

In addition to marketable products resulting from the processing of non-ferrous metal ores, non-ferrous metallurgy enterprises receive numerous wastes and intermediate products of metallurgical production. These include slags, dust, gases, agglomerates and cakes, cakes, sludges, solutions, etc.

Metals are the main type of production of metallurgical production. In non-ferrous metallurgy we distinguish between rough and refined metals. Ferrous metals are called, containing in their composition harmful impurities, impairing the consumer properties of the metal, as well as impurities of valuable satellite elements. Roughing metals must be cleaned of impurities – refining.

Slags are the second obligatory product of metallurgical processes leading to melting of processed materials. They are formed as a result of slagging of oxides of gangue and fluxes. In addition to the slag-forming components, the actual factory slag necessarily contains a certain amount of recoverable metals.

Steins are intermediate products of pyrometallurgical processing of copper, nickel and partially lead ores and concentrates. They are an alloy of sulfides of heavy non-ferrous metals (copper, nickel, zinc, lead, etc.) with iron sulphide, in which impurities are dissolved.

Gases and dust are also among the mandatory products of pyrometallurgical processes. As a rule, these two products are removed from the stoves together.
Solutions are the products of the leaching process, in which the dissolved substance is in a state of molecular disintegration, which makes them very stable systems that do not separate for an arbitrarily long standing.

Keki are solid powdery materials.
By the nature of education, there are two types of cakes:

1. Insoluble residues of the leach material.
2. Products (sediments) of cementation, chemical or hydrolytic deposition of dissolved metals in a free metallic state or in the form of insoluble chemical compounds.

Process of titanium extraction

The essence of the process of aluminum production is the production of anhydrous, free of impurities alumina (alumina), followed by the production of metallic aluminum by electrolysis of dissolved alumina in cryolite.

In the modern aluminum industry, several methods for obtaining aluminum oxide are used; They can be divided into three groups.
The essence of electrothermal methods is the restoration of aluminum ore in the electric furnace; The impurities present in the ore are reduced to an elementary state and, by transferring them to the metal (siliceous cast iron), only aluminum oxide remains unreduced in the slag. Some partially unrecovered impurities also remain in the slag. The alumina obtained in this way can be used for making grinding wheels and other abrasive products, but for the production of high-quality aluminum such alumina is not suitable.

Acidic methods boil down to the fact that the aluminum ore is treated with an acid, for example, hydrochloric acid or sulfuric acid. The acid is reacted with aluminum oxide and the corresponding soluble salt (for example, aluminum chloride) is obtained. The main impurities (silica, calcium oxide, etc.) do not react with acids. However, a number of impurities (for example, iron oxides) interact with many acids, which creates great additional difficulties, since it is very difficult to completely separate iron salts from aluminum salts in solution. These methods are used little, but they have many patents both abroad and with us. And since the ore can be treated with acid only in acid-proof equipment, this adds to the cost and complicates the production of alumina.

Alkaline methods are used in most countries to produce pure alumina. The essence of alkaline methods is that aluminum ore is exposed to some alkali.

As a result of the interaction of aluminum oxide present in the ore, for example with caustic soda, under certain conditions, so-called sodium aluminates are formed. Aluminates of alkali metals are readily soluble in water. The bulk of the impurities present in the aluminum ore with alkalis does not interact and therefore remains in the undissolved state, and aluminum passes into the solution. But there are impurities that can interact with alkalis. The most important of them is silica. Release the solution from it is not easy.
However, alkaline methods are more economical than acid ones, because all operations can be carried out in steel and cast-iron equipment.

Bauxite and limestone are crushed and dosed with a soda solution in the following proportion: one mole of soda is added to one mole of A1203 and Fe203 and two moles of CaCOs are added to the mash per mole of silica

The resulting wet batch is finely ground in ball mills and it emerges from them in the form of a liquid pulp. After testing and some adjustment of its composition, the pulp is sent to slowly rotating tubular furnaces with a length of 80-120 m and a diameter of 2.5-3.5 m. The pulp is fed to the “cold” end of the furnace, where it meets with waste furnace gases having a temperature of the order of 300-400 ° C. As a result, moisture evaporates; Dried batch, gradually heated, moves to the hot zone, in which the temperature reaches 1200-1250 “C.

As the material is heated, complicated chemical processes take place in the charge. Many other processes take place in the sintering furnace, which lead to the formation of aluminates and ferrites of calcium, and some other complex compounds.

The reaction products are extracted from the furnace in the form of a so-called guardian (resembling a gray porous pebble) consisting mainly of sodium aluminate, sodium ferrite and calcium silicate.

The resulting speck is cooled, crushed and leached, the essence of which is the effect of weak soda solutions on the spec. As a result of leaching from the speck, sodium aluminate passes into the solution, and hydrolysis of sodium ferrites takes place. The resulting hydroxide of iron precipitates, and the solution is enriched with caustic soda. The resulting solution is separated from insoluble impurities by settling and filtration.
Along with these desirable reactions, reactions occur that complicate the production of pure alumina. So, for example, a certain amount of sodium silicates passes into the solution, which causes a special operation called desiliconization of the solution. The essence of this operation is a prolonged heating with mixing of aluminate solution and lime milk in strong closed cylindrical vessels with spherical bottoms – autoclaves – at a temperature of 150-180 ° C. As a result, a number of chemical processes occur.

After filtering the solution from the particles suspended in it, the pure aluminate solution is carbonized. The purpose of this operation is to separate from the solution pure aluminum hydroxide, which is not contaminated with other substances. This operation is carried out in cylindrical tanks with agitators – carbonizers, which are fed with carbon dioxide (usually purified furnace gases). Under the action of C02, the aluminate solution decomposes, a white precipitate of aluminum hydroxide precipitates out of it, which separates from the soda solution. The remaining soda solution after adding a certain amount of fresh soda is returned to the preparation of the charge for the next sintering, and alumina hydrate is calcined in tubular furnaces (similar to sintering furnaces) at 1200 ° C, resulting in an anhydrous, non-hygroscopic alumina, Subsequent electrolysis.

The main raw materials for the production of aluminum are aluminum ores: bauxites, nephelines, alunites, kaolins. The most important are bauxites.

Currently, the most widely used electrolysis cells, calculated for a current strength exceeding 100 kA, with pre-burned anodes or with an upper current supply to self-baking anodes. The production of aluminum in such an electrolyzer is carried out continuously for two to three years; The following basic operations are performed: monitoring the composition of the electrolyte, ensuring the timely loading of alumina and extraction of aluminum, monitoring the stress and servicing the self-baking anode system.
The process of electrolysis is reduced to the discharge of the ions A13 + and 02 +, of which alumina is composed, which is continuously consumed. Cryolite is not subjected to direct electrolysis and is consumed little, but due to its physical losses (evaporation, spills, etc.), as well as the interaction of its individual constituents with alumina impurities and the lining of the cell, it is necessary to systematically monitor its level in the bath (layer thickness 18-25 cm) and chemical composition.

Some plants introduce into the electrolyte small additives CaF2 and MgF2 to reduce the melting point of the electrolyte by several tens of degrees.

When there is little alumina in the electrolyte (less than 1%), an anodic effect occurs. Externally, it manifests itself in a rapid voltage jump on the electrolyzer from the usual 4.0-4.7 V to 30-50 V; In the area of ​​the anode arcs appear, the electrolyte begins to overheat and bubble. To eliminate the anode effect, the crust of the electrolyte is pierced and, mixing, dissolve alumina in it (another portion of which is always poured into the crust of the electrolyte beforehand).

After dissolving the alumina in the electrolyte, the anode effect usually stops and the stress becomes normal. The anode effect during the production of aluminum plays both a positive and a negative role. On the one hand, he signals about the lack of alumina in the electrolyte and gives an opportunity to get an idea of ​​the course of electrolysis, on the other hand – it leads to a surplus of electricity and a violation of the thermal equilibrium of the bath. At factories, they try to prevent the frequent occurrence of anode effects, introducing alumina prior to their appearance. In turn, the excess of alumina introduced into the electrolyte does not dissolve, settles to the bottom under the aluminum layer, impedes the normal course of electrolysis. Therefore, it is considered normal that one or two anode effects per day occur in the electrolysis cell.

Many researchers have studied the nature of the anode effect. Based on research conducted at the Moscow Institute of Non-Ferrous Metals and Gold under the guidance of Prof. A.I. Belyaev, it can be concluded that the cause of the anode effect is the different wettability of the carbon anode by the molten electrolyte, with different contents of oxides in it. When there is a significant amount of aluminum oxide in the electrolyte, the electrolyte well wets the anode carbon surface and therefore the resulting anode gases are easily removed from its surface without interfering with the passage of the electric current. With a decrease in the amount of alumina, the wettability by the electrolyte changes slowly and when the alumina content is less than 1%, the quantity becomes quality – the electrolyte ceases to wet the coal surface; As a result, a gas film forms between the electrolyte and the carbon anode, preventing the passage of electric current, which leads to a sharp increase in the voltage on the bath.

Aluminum is extracted from the cell, piercing the crust of the frozen electrolyte and lowering the steel tube to the bottom of the refractory lined with aluminum, through which aluminum is pumped into the vacuum bucket. On a modern aluminum bath designed for a current of 100 kA, about 700 kg of aluminum is produced per day, so the metal is extracted no more often than once a day (from less powerful baths once in two days).

As the aluminum is extracted, the anode is gradually lowered, while carefully adjusting the voltage and the pole-to-pole distance of the cell. Since the lower part of the anode burns and it gradually descends, it must be increased in the upper part. Anodic mass is systematically charged into the anode casing, which is coked on the hot cone of the anode due to the heat from the bath. Current-carrying steel pins are gradually lowered with the anode and, in order to avoid melting, they are alternately pulled from its body and raised to a higher level, and anodic mass 1 flows into the resulting cavity and is coked in it.

To produce 1 ton of primary aluminum by electrolysis, 15,000-17,000 kWh of electricity and almost 2 tons of alumina are consumed.
To remove nonmetallic inclusions (particles of coal, alumina, fluoride salts, etc.), aluminum extracted from the cells is often subjected to 10-15-minute chlorination in a bucket at a temperature of 750 ° C. Then aluminum is sent to large electric resistance furnaces, from which its semi-continuous casting is conducted into calibrated blanks for the production of pipes, wire and sheet. These same furnaces are used to produce many alloys on an aluminum base.

Primary aluminum produces 13 grades, which are divided into three groups: aluminum of special purity A999, four grades of high purity aluminum and eight grades of aluminum of technical purity. The primary metal is allowed to contain impurities from 0.15 to 1.0%, with the name of the mark indicating the degree of purity of the metal. Thus, the grade of aluminum of technical purity A8 means that it contains 99.8% of aluminum, and impurities (mainly silicon and iron) of only 0.2%. In high purity aluminum, the A99 grade is 99.99% aluminum and only 0.01% impurities.
In electrolysis baths, aluminum is obtained for technical purity. To produce higher grades of aluminum, its additional refining is required.

Methods of obtaining titanium

Titanium – silver metal with a bluish tint; Has a low density of 4.507 g / cm3; Melts at a temperature of about 1660 ° C, boils at 3260 ° C. Titanium has two allotropic modifications; Up to 882 ° C there is a titanium having a hexagonal lattice and at higher temperatures titanium with a cubic body-centered lattice.

The mechanical properties of titanium vary considerably from the content of impurities in it. Pure titanium forging and has a low hardness HB ~ 70; Technical metal is fragile and hard (НВ180- 280).

Harmful impurities of titanium are nitrogen and oxygen, sharply reducing its ductility, as well as carbon, which reduces the ductility at a content of more than 0.15%, complicates the processing of titanium by cutting and sharply worsens the weldability. Hydrogen greatly increases the sensitivity of titanium to the notch, so this effect is called hydrogen embrittlement.

On the surface of titanium, a stable oxide film is formed, as a result of which titanium has a high resistance to corrosion in some acids, in sea and fresh water. In air, titanium is stable and slightly changes its mechanical properties when heated to 400 ° C. With higher heating, it begins to absorb oxygen and its mechanical properties gradually deteriorate, and above 540 ° C it becomes brittle. When heated above 800 “C, titanium energetically absorbs oxygen, nitrogen and hydrogen, which is used in metallurgy to deoxidize steel.

Titanium has long been widely used as a good deoxidizer and alloying additive in steel and non-ferrous alloys.

Recovery of titanium tetrachloride by magnesium

The reduction of titanium tetrachloride TiCl4 is carried out periodically in cylindrical steel hermetic retorts with a diameter of 850 to 1500 mm and a height of 1800 to 3000 mm. Such a volume of retort allows one to receive up to 1500 kg of titanium sponge in one operation.

Retorts are installed vertically usually in an electric resistance furnace. The top of the retort is covered with a lid, which has connections for magnesium charging, T1C14 supply of air evacuation and argon supply.

After the retort is installed in the furnace and the air is evacuated from it, it is filled with dried argon and heated to 740-800 ° C, after which liquid magnesium is poured into it and liquid titanium tetrachloride is introduced. The process of obtaining titanium can be simplified to be represented by the following reaction equation:

TiCl4 (gas) + 2Mg (g) = -2 MgC12 (liquid) + Ti (solid) + 935,000 J (223,000 cal)

After intensive development of the reaction, the heating is switched off and the temperature is maintained at 750-850 ° C. Titanium is released in the retort in the form of well-developed dendrites, which have been called the titanium sponge.

Titanium sponge is crushed and carefully sorted. The purest sponge is used for melting; Low-grade, containing inclusions of chlorides, briquetted and used as a deoxidizer of steel in ferrous metallurgy. For the production of critical products from titanium and its alloys, its good ductility and weldability, as well as heat resistance, are very important.

Production of high purity titanium

The usual purity of titanium obtained by remelting the sponge is 99.6-99.7C, but a more pure metal containing 99.9% titanium and higher is required.
Pure titanium is produced in small amounts by processing the sponge with an iodide method, using the reversibility of the reaction

Ti + 2I2 = Ti4

At a temperature of 100-200 ° C, the reaction proceeds to the right, and at 1300-1400 ° C to the left.
The sponge is loaded into the annular space between the retort wall and the molybdenum grid. On molybdenum holders, a wire of pure titanium with a diameter of 3-4 mm and a length of about 10 m is fixed in a zigzag manner. After the lid is tightly tightened and the air is evacuated to a residual pressure of 0.1-0.01 Pa (10 ~ 4-10 ~ 5 mm Hg .) retort placed in an incubator with temperature 100-200 ° C and in particular its fixture break ampoule with iodine. Iodine vapor, filling all the space of the retort, react with the titanium sponge and shavings, forming a pair of titanium iodide.
Titanium wires are heated up to 1300-1400 ° C by passing current through it. In these glow-wire pairs are decomposed, forming crystals of pure titanium, and free iodine, which reacts again with titanium sponge, heated to 100-200 ° C.

Metals of non-ferrous metallurgy

Non-ferrous metallurgy is a heavy industry industry that produces construction materials. It includes extraction, enrichment of metals, redistribution of non-ferrous metals, production of alloys, rolled products, recycling of secondary raw materials, and diamond mining. The development of technologies requires an increase in the production of strong, ductile, corrosion-resistant, light structural materials (aluminum and titanium-based alloys) . They are widely used in the aviation, missile industry, in space technologies, in shipbuilding, in the production of equipment for the chemical industry.

Copper is widely used in engineering and electrometallurgy, both in pure form and in the form of alloys – with tin (bronze), with aluminum (duralumin), with zinc (brass), and nickel (cupronickel).

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Lead is used in the production of batteries, cables, in the nuclear industry.

Zinc and nickel are used in ferrous metallurgy.

Tin is used in the production of tinplate and bearings.

Noble metals have high plasticity, and platinum has high refractoriness. Therefore, they are widely used in the manufacture of jewelry and equipment. Without silver salts, it is impossible to produce film and film. By physical properties and purpose, non-ferrous metals can be conditionally divided into 4 groups.

Classification of non-ferrous metals:

Basic
Heavy – copper, lead, zinc, tin, nickel
Light – aluminum, titanium, magnesium
Small – arsenic, mercury, antimony, cobalt
Alloying – molybdenum, vanadium, tungsten, silicon
Noble – gold, silver, platinum
Rare and scattered – gallium, selenium, tellurium, uranium, zirconium, germanium

According to the stages of the technological process, non-ferrous metallurgy is divided into:

Extraction and enrichment of ore raw materials (GOK – ore-dressing plants). GOKs are based at sources of raw materials, since for the production of one ton of non-ferrous metal an average of 100 tons of ore is required.

Ferrous metallurgy. In the redistribution enriched ore comes. The raw materials based production is related to copper and zinc. The sources of energy – production, associated with aluminum, zinc, titanium, magnesium. The consumer – production, associated with tin.
Processing, rolling, production of alloys. Enterprises are based on the consumer.

The specificity of non-ferrous metal ores consists of:

A) in their complex composition (multicomponent)
B) in the low content of useful components in the ore – only a few%, sometimes the percentage%:
Copper – 1-5%
Zinc – 4-6%
Lead – 1.5%
Tin – 0,01-0,7%

To produce 1 ton of copper concentrate, 100 tons of ore are used, 1 tonne of nickel concentrate – 200 tons, tin concentrate – 300 tons.
All ores are pre-enriched at the GOK and in the metallurgical operations. They produce concentrates:

Copper – 75%
Zinc – 42-62%
Tin – 40-70%

Due to the considerable material consumption, non-ferrous metallurgy is oriented towards raw materials bases. Since the ores of non-ferrous and rare metals have a multicomponent composition, the integrated use of raw materials is of practical importance. The integrated use of raw materials and utilization of industrial waste links non-ferrous metallurgy with other industries. On this basis, whole industrial complexes are formed, for example, the Urals. Of particular interest is the combination of non-ferrous metallurgy and basic chemistry. When using sulfur gases in the industry, zinc and copper are produced.

Placement factors:
Raw materials – copper, nickel, lead
Fuel and energy – titanium, magnesium, aluminum
Consumer – tin

Properties and applications of powdered metals

Antifriction porous materials are made on the basis of iron or copper powders impregnated with a liquid lubricant (oil) or with additives of a solid lubricant (graphite, lead, molybdenum disulphide, zinc sulfide). These materials have high tribotechnical properties, good processability, high thermal conductivity, sufficient viscosity under impact loading, provide a low coefficient of friction.

Friction materials include materials with a high coefficient of friction. They have high frictional heat resistance and corrosion resistance. They are made on the basis of copper or iron with metallic and non-metallic components for parts working in oil (75%) and with dry friction. Frictional products consist of a steel base and friction linings, which are baked to the substrate under pressure.

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Electrotechnical materials are subdivided into electrocontact (metal, metallographic, metal-oxide and metal-carbide), magnetically soft (iron-nickel alloys, iron alloys with silicon and aluminum or chromium and aluminum), magnetically hard (Fe-Al-Ni (Co) , Alnico, magneto), magneto-dielectrics (carbonyl iron, permalloy, alsifer), ferrites (Fe3O4 with additives NiO, MgO, MnO, ZnO).

Amorphous materials obtained by fast (with a speed of 105-106 0С / s) melt cooling are a new class of magnetic materials, from which magnetic screens, transformers and electrode devices are made.

Sintered construction materials are made on the basis of structural steel (carbonaceous, copper, siliceous, molybdenum, chromium-molybdenum), titanium and aluminum alloys.

The increase in the hardness of the processed blanks required the expansion of the range of cutting materials used from hard alloys, mineral ceramics materials to artificial diamonds and other ultrahard materials obtained by powder metallurgy methods.

Hard alloys are used in cutting and control instruments, working inserts of dies during drawing, matrices and punches during stamping and pressing. In mechanical engineering and instrument making, reinforced solid alloys are widely used. For example, in the textile industry, hard alloys are used for guide rings and other rubbing parts; In powder metallurgy, solid alloys are used for grinding bodies and a press tool.

Mineraloceramics are used for semi-finishing and finishing machining of cast irons, hardened and improved steels, non-ferrous and refractory alloys at high cutting speeds (up to 800 m / min). The basis of mineral ceramics is the modification of Al2O3 (electrocorundum) with a grain size of up to 1 μm. The density of the cermet (ceramics with a metal bond) is 3.96 g / cm3, the hardness is HRA up to 92 units. Oxydocarbide ceramics have a density of 4.2-4.6 g / cm3 and a hardness of HRA of 92 to 94 units.

Erosion-resistant and sweaty materials have a complex of properties that can not be obtained in alloys. They are made on the basis of refractory metals or carbon in the form of compositions.

For example, by impregnating the tungsten or carbon scaffolds with liquid copper or silver. Parts made of this material work in engines at temperatures above 2500 ° C. During operation, copper (silver) evaporates, which reduces the heat flow and improves the working conditions of tungsten or carbon scaffolds.

Sintering of metallic powder materials

The kind of heat treatment that allows to obtain the final properties of the material and product is called sintering. It consists in heating and holding the molded product (billet) at a temperature below the melting point of the main component. For multicomponent systems, solid-phase and liquid-phase sintering are distinguished.

Solid-phase sintering is accompanied by the appearance and development of bonds between particles, the formation and growth of contacts (necks), the closure of through porosity, enlargement and spheroidization of the pores, compacting the workpiece due to shrinkage. In the process of sintering, mass transfer of matter through the gas phase occurs due to surface and bulk diffusion, viscous flow, flow caused by external loads (sintering under pressure). During sintering, recrystallization is also observed (the growth of some grains at the expense of the others of the same phase). The heat seal is mainly due to the volume deformation of the particles, which is realized by the bulk self-diffusion of the atoms.

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Liquid-phase sintering takes place in the presence of the liquid phase of the low-melting component, which wets the solid phase well, improves cohesion between the particles, increases the diffusion rate of the components, facilitates the movement of the particles relative to each other. Poor wettability prevents compaction. The solid phase in the contact zone can dissolve in the liquid, intensifying the processes of mass transfer (Fig. 4, b). Distinguish systems with insoluble components, with limited solubility and with significant mutual solubility of components. Liquid-phase sintering of such systems has its own peculiarities associated with the predominance of one of the stages:

– viscous flow of liquid – rearrangement of particles;
– dissolution – precipitation; Formation of a rigid skeleton.

Combination of the pressing and sintering process is observed during hot pressing, which is carried out at a temperature (0.5-0.9 melting point) of the main component. The high temperature of pressing makes it possible to reduce the pressing pressure by several tens of times. The holding time is from 15-30 minutes. Up to several hours. Hot pressing is used for difficult-to-apply powders in order to obtain high physical-mechanical properties. Hot-pressed parts have a fine-grained structure. The mold in which hot pressing is carried out is made of heat-resistant materials, and when pressing the refractory compounds it is made of graphite, the strength of which increases with increasing temperature.