Aluminum position in the periodic table. Aluminum characteristic
Section 1. Name and history of the discovery of aluminum.
Section 2 general characteristics aluminum, physical and chemical properties.
Section 3. Obtaining castings from aluminum alloys.
Section 4 Application aluminum.
Aluminum- this is an element of the main subgroup of the third group, the third period of the periodic system of chemical elements of D. I. Mendeleev, with atomic number 13. It is designated by the symbol Al. Belongs to the group of light metals. The most common metal and the third most abundant chemical element in the earth's crust (after oxygen and silicon).
Simple substance aluminum (CAS number: 7429-90-5) - light, paramagnetic metal silver-white color, easy to form, cast, machined. Aluminum has high thermal and electrical conductivity, resistance to corrosion due to the rapid formation of strong oxide films that protect the surface from further interaction.
The achievements of industry in any developed society are invariably associated with the achievements of the technology of structural materials and alloys. The quality of processing and the productivity of manufacturing items of trade are the most important indicators of the level of development of the state.
Materials used in modern designs, in addition to high strength characteristics should have a complex of properties such as increased corrosion resistance, heat resistance, thermal and electrical conductivity, refractoriness, as well as the ability to maintain these properties under conditions of prolonged operation under loads.
Scientific developments and production processes in the field of foundry production of non-ferrous metals in our country correspond to the advanced achievements of scientific and technological progress. Their result, in particular, was the creation of modern chill casting and pressure casting workshops at the Volga Automobile Plant and a number of other enterprises. Large injection molding machines with a mold locking force of 35 MN are successfully operating at the Zavolzhsky Motor Plant, which produce aluminum alloy cylinder blocks for the Volga car.
At the Altai Motor Plant, an automated line for the production of castings by injection molding has been mastered. In the Union of Soviet Socialist Republics (), for the first time in the world, developed and mastered process continuous casting of ingots from aluminum alloys in an electromagnetic mold. This method significantly improves the quality of ingots and reduces the amount of waste in the form of chips during their turning.
The name and history of the discovery of aluminum
The Latin aluminium comes from the Latin alumen, meaning alum (aluminum and potassium sulfate (K) KAl(SO4)2 12H2O), which has long been used in leather dressing and as an astringent. Al, chemical element Group III periodic system, atomic number 13, atomic mass 26, 98154. Due to the high chemical activity, the discovery and isolation of pure aluminum stretched over almost 100 years. The conclusion that "" (a refractory substance, in modern terms - aluminum oxide) can be obtained from alum was made back in 1754. German chemist A. Markgraf. Later it turned out that the same "earth" could be isolated from clay, and it was called alumina. It was only in 1825 that he was able to obtain metallic aluminum. Danish physicist H. K. Oersted. He treated with potassium amalgam (an alloy of potassium (K) with mercury (Hg)) aluminum chloride AlCl3, which could be obtained from alumina, and after distilling off mercury (Hg), isolated a gray powder of aluminum.
Only a quarter of a century later, this method was slightly modernized. The French chemist A. E. St. Clair Deville in 1854 suggested using metallic sodium (Na) to produce aluminum, and obtained the first ingots of the new metal. The cost of aluminum was then very high, and jewelry was made from it.
An industrial method for the production of aluminum by electrolysis of a melt of complex mixtures, including oxide, aluminum fluoride and other substances, was independently developed in 1886 by P. Eru () and C. Hall (USA). Aluminum production is associated with high cost electricity, so it was only realized on a large scale in the 20th century. AT Union of Soviet Socialist Republics (CCCP) the first industrial aluminum was obtained on May 14, 1932 at the Volkhov aluminum plant, built next to the Volkhov hydroelectric power station.
Aluminum with a purity of over 99.99% was first obtained by electrolysis in 1920. In 1925 in work Edwards published some information about the physical and mechanical properties of such aluminum. In 1938 Taylor, Wheeler, Smith, and Edwards published an article that gives some of the properties of 99.996% purity aluminum, also obtained in France by electrolysis. The first edition of the monograph on the properties of aluminum was published in 1967.
In subsequent years, due to the relative ease of preparation and attractive properties, many works on the properties of aluminum. Pure aluminum has found wide application mainly in electronics - from electrolytic capacitors to the pinnacle of electronic engineering - microprocessors; in cryoelectronics, cryomagnetics.
Newer methods for obtaining pure aluminum are the zone purification method, crystallization from amalgams (alloys of aluminum with mercury) and isolation from alkaline solutions. The degree of purity of aluminum is controlled by the value of electrical resistance at low temperatures.
General characteristics of aluminum
Natural aluminum consists of one nuclide 27Al. The configuration of the outer electron layer is 3s2p1. In almost all compounds, the oxidation state of aluminum is +3 (valency III). The radius of the neutral aluminum atom is 0.143 nm, the radius of the Al3+ ion is 0.057 nm. The successive ionization energies of a neutral aluminum atom are 5, 984, 18, 828, 28, 44, and 120 eV, respectively. On the Pauling scale, the electronegativity of aluminum is 1.5.
Aluminum is soft, light, silvery-white, the crystal lattice of which is face-centered cubic, parameter a = 0.40403 nm. Melting point of pure metal 660°C, boiling point about 2450°C, density 2, 6989 g/cm3. The temperature coefficient of linear expansion of aluminum is about 2.5·10-5 K-1.
Chemical aluminum is a fairly active metal. In air, its surface is instantly covered with a dense film of Al2O3 oxide, which prevents further access of oxygen (O) to the metal and leads to the termination of the reaction, which leads to high anti-corrosion properties of aluminum. A protective surface film on aluminum is also formed if it is placed in concentrated nitric acid.
Aluminum actively reacts with other acids:
6HCl + 2Al = 2AlCl3 + 3H2,
3Н2SO4 + 2Al = Al2(SO4)3 + 3H2.
Interestingly, the reaction between aluminum and iodine (I) powders begins at room temperature if a few drops of water are added to the initial mixture, which in this case plays the role of a catalyst:
2Al + 3I2 = 2AlI3.
The interaction of aluminum with sulfur (S) when heated leads to the formation of aluminum sulfide:
2Al + 3S = Al2S3,
which is easily decomposed by water:
Al2S3 + 6H2O = 2Al(OH)3 + 3H2S.
Aluminum does not interact directly with hydrogen (H), however, indirectly, for example, using organoaluminum compounds, it is possible to synthesize solid polymeric aluminum hydride (AlH3)x - the strongest reducing agent.
In the form of a powder, aluminum can be burned in air, and a white refractory powder of aluminum oxide Al2O3 is formed.
The high bond strength in Al2O3 determines the high heat of its formation from simple substances and the ability of aluminum to reduce many metals from their oxides, for example:
3Fe3O4 + 8Al = 4Al2O3 + 9Fe and even
3СаО + 2Al = Al2О3 + 3Са.
This method of obtaining metals is called aluminothermy.
Being in nature
In terms of prevalence in the earth's crust, aluminum ranks first among metals and third among all elements (after oxygen (O) and silicon (Si)), it accounts for about 8.8% of the mass of the earth's crust. Aluminum is included in a huge number of minerals, mainly aluminosilicates, and rocks. Aluminum compounds contain granites, basalts, clays, feldspars, etc. But here is the paradox: with a huge number minerals and rocks containing aluminum, deposits of bauxite, the main raw material for the industrial production of aluminum, are quite rare. In the Russian Federation, there are bauxite deposits in Siberia and the Urals. Alunites and nephelines are also of industrial importance. As a trace element, aluminum is present in the tissues of plants and animals. There are organisms - concentrators that accumulate aluminum in their organs - some club mosses, mollusks.
Industrial production: at the index of industrial production, bauxites are first subjected to chemical processing, removing from them impurities of oxides of silicon (Si), iron (Fe) and other elements. As a result of such processing, pure aluminum oxide Al2O3 is obtained - the main one in the production of metal by electrolysis. However, due to the fact that the melting point of Al2O3 is very high (more than 2000°C), it is not possible to use its melt for electrolysis.
Scientists and engineers found a way out in the following. Cryolite Na3AlF6 is first melted in an electrolysis bath (melt temperature slightly below 1000°C). Cryolite can be obtained, for example, by processing nephelines from the Kola Peninsula. Further, a little Al2O3 (up to 10% by mass) and some other substances are added to this melt, improving the conditions for the subsequent process. During the electrolysis of this melt, aluminum oxide decomposes, the cryolite remains in the melt, and molten aluminum is formed on the cathode:
2Al2O3 = 4Al + 3O2.
Aluminum alloys
Most metal elements are alloyed with aluminum, but only a few of them play the role of the main alloying components in industrial aluminum alloys. However, a significant number of elements are used as additives to improve the properties of alloys. The most widely used:
Beryllium is added to reduce oxidation at elevated temperatures. Small additions of beryllium (0.01 - 0.05%) are used in aluminum casting alloys to improve fluidity in the production of internal combustion engine parts (pistons and cylinder heads).
Boron is introduced to increase electrical conductivity and as a refining additive. Boron is introduced into aluminum alloys used in nuclear power engineering (except for reactor parts), because it absorbs neutrons, preventing the spread of radiation. Boron is introduced on average in the amount of 0.095 - 0.1%.
Bismuth. Low melting point metals such as bismuth, cadmium are added to aluminum alloys to improve machinability. These elements form soft fusible phases that contribute to chip breakage and cutter lubrication.
Gallium is added in the amount of 0.01 - 0.1% to the alloys from which the consumable anodes are further made.
Iron. In small quantities (>0.04%) it is introduced during the production of wires to increase strength and improve creep characteristics. Same way iron reduces sticking to the walls of molds when casting into a mold.
Indium. The addition of 0.05 - 0.2% strengthens aluminum alloys during aging, especially at low cuprum content. Indium additives are used in aluminum-cadmium bearing alloys.
Approximately 0.3% cadmium is introduced to increase the strength and improve the corrosion properties of the alloys.
Calcium gives plasticity. With a calcium content of 5%, the alloy has the effect of superplasticity.
Silicon is the most used additive in foundry alloys. In the amount of 0.5 - 4% reduces the tendency to cracking. The combination of silicon and magnesium makes it possible to heat seal the alloy.
Magnesium. The addition of magnesium significantly increases strength without reducing ductility, improves weldability and increases the corrosion resistance of the alloy.
Copper strengthens alloys, maximum hardening is achieved when the content cuprum 4 - 6%. Alloys with cuprum are used in the production of pistons for internal combustion engines, high-quality cast parts for aircraft.
Tin improves cutting performance.
Titanium. The main task of titanium in alloys is grain refinement in castings and ingots, which greatly increases the strength and uniformity of properties throughout the volume.
Although aluminum is considered one of the least noble industrial metals, it is quite stable in many oxidizing environments. The reason for this behavior is the presence of a continuous oxide film on the surface of aluminum, which immediately re-forms on the cleaned areas when exposed to oxygen, water and other oxidizing agents.
In most cases, melting is carried out in air. If the interaction with air is limited to the formation of compounds insoluble in the melt on the surface and the resulting film of these compounds significantly slows down further interaction, then usually no measures are taken to suppress such interaction. Melting in this case is carried out with direct contact of the melt with the atmosphere. This is done in the preparation of most aluminum, zinc, tin-lead alloys.
The space in which melting of alloys takes place is limited by a refractory lining capable of withstanding temperatures of 1500 - 1800 ˚С. In all melting processes, the gas phase is involved, which is formed during the combustion of fuel, interacting with the environment and the lining of the melting unit, etc.
Most aluminum alloys have high corrosion resistance in the natural atmosphere, sea water, solutions of many salts and chemicals, and in most foods. Aluminum alloy structures are often used in sea water. Sea buoys, lifeboats, ships, barges have been built from aluminum alloys since 1930. At present, the length of aluminum alloy ship hulls reaches 61 m. There is experience in aluminum underground pipelines, aluminum alloys are highly resistant to soil corrosion. In 1951, a 2.9 km long pipeline was built in Alaska. After 30 years of operation, no leaks or serious damage due to corrosion have been found.
Aluminum in large volume used in construction facing panels, doors, window frames, electrical cables. Aluminum alloys are not subject to severe corrosion for a long time in contact with concrete, mortar, plaster, especially if the structures are not frequently wet. When wet frequently, if the surface of the aluminum trade items has not been further processed, it may darken, up to blackening in industrial cities with a high content of oxidizing agents in the air. To avoid this, special alloys are produced to obtain shiny surfaces by brilliant anodizing - applying an oxide film to the metal surface. In this case, the surface can be given a variety of colors and shades. For example, alloys of aluminum with silicon allow you to get a range of shades, from gray to black. Aluminum alloys with chromium have a golden color.
Industrial aluminum is produced in the form of two types of alloys - casting, parts of which are made by casting, and deformation - alloys produced in the form of deformable semi-finished products - sheets, foil, plates, profiles, wire. Castings from aluminum alloys are received by all possible ways casting. It is most common under pressure, in chill molds and in sandy-clay molds. When making small political parties applied casting in gypsum combined forms and casting for investment models. Cast alloys are used to make cast rotors for electric motors, cast parts for aircraft, etc. Wrought alloys are used in automotive production for interior trim, bumpers, body panels and interior details; in construction as a finishing material; in aircraft, etc.
AT industry aluminum powders are also used. Used in metallurgical industry: in aluminothermy, as alloying additives, for the manufacture of semi-finished products by pressing and sintering. This method produces very durable parts (gears, bushings, etc.). Powders are also used in chemistry to obtain aluminum compounds and as catalyst(for example, in the production of ethylene and acetone). Given the high reactivity of aluminum, especially in the form of a powder, it is used in explosives and solid propellants for rockets, using its ability to quickly ignite.
Given the high resistance of aluminum to oxidation, the powder is used as a pigment in coatings for painting equipment, roofs, paper in printing, shiny surfaces of car panels. Also, a layer of aluminum is covered with steel and cast iron trade item to prevent their corrosion.
In terms of application, aluminum and its alloys are second only to iron (Fe) and its alloys. The widespread use of aluminum in various fields of technology and everyday life is associated with a combination of its physical, mechanical and chemical properties: low density, corrosion resistance in atmospheric air, high thermal and electrical conductivity, ductility and relatively high strength. Aluminum is easily processed in various ways - forging, stamping, rolling, etc. Pure aluminum is used to make wire (the electrical conductivity of aluminum is 65.5% of the electrical conductivity of cuprum, but aluminum is more than three times lighter than cuprum, so aluminum is often replaced in electrical engineering) and foil used as packaging material. The main part of the smelted aluminum is spent on obtaining various alloys. Protective and decorative coatings are easily applied to the surface of aluminum alloys.
The variety of properties of aluminum alloys is due to the introduction of various additives into aluminum, which form solid solutions or intermetallic compounds with it. The bulk of aluminum is used to produce light alloys - duralumin (94% aluminum, 4% copper (Cu), 0.5% magnesium (Mg), manganese (Mn), (Fe) and silicon (Si)), silumin ( 85-90% - aluminum, 10-14% silicon (Si), 0.1% sodium (Na)) and others. In metallurgy, aluminum is used not only as a base for alloys, but also as one of the widely used alloying additives in alloys based on cuprum (Cu), magnesium (Mg), iron (Fe), >nickel (Ni), etc.
Aluminum alloys are widely used in everyday life, in construction and architecture, in the automotive industry, in shipbuilding, aviation and space technology. In particular, the first artificial Earth satellite was made of aluminum alloy. An alloy of aluminum and zirconium (Zr) is widely used in nuclear reactor building. Aluminum is used in the manufacture of explosives.
When handling aluminum in everyday life, you need to keep in mind that only neutral (by acidity) liquids (for example, boil water) can be heated and stored in aluminum dishes. If, for example, sour cabbage soup is boiled in aluminum dishes, then aluminum passes into food, and it acquires an unpleasant “metallic” taste. Since the oxide film is very easy to damage in everyday life, the use of aluminum cookware is still undesirable.
Silver-white metal, light
density — 2.7 g/cm
melting point for technical aluminum - 658 °C, for high purity aluminum - 660 °C
specific heat of fusion — 390 kJ/kg
boiling point - 2500 ° C
specific heat of evaporation - 10.53 MJ / kg
tensile strength of cast aluminum - 10-12 kg / mm², deformable - 18-25 kg / mm², alloys - 38-42 kg / mm²
Brinell hardness — 24…32 kgf/mm²
high plasticity: for technical - 35%, for clean - 50%, rolled into a thin sheet and even foil
Young's modulus - 70 GPa
Aluminum has high electrical conductivity (0.0265 μOhm m) and thermal conductivity (203.5 W / (m K)), 65% of the electrical conductivity of cuprum, and has a high light reflectivity.
Weak paramagnet.
Temperature coefficient of linear expansion 24.58 10−6 K−1 (20…200 °C).
Temperature coefficient electrical resistance 2.7 10−8K−1.
Aluminum forms alloys with almost all metals. The best known are alloys with cuprum and magnesium (duralumin) and silicon (silumin).
Natural aluminum consists almost entirely of the only stable isotope, 27Al, with traces of 26Al, a radioactive isotope with period a half-life of 720 thousand years, formed in the atmosphere during the bombardment of argon nuclei by cosmic ray protons.
In terms of prevalence in the earth's crust, the Earth occupies the 1st place among metals and the 3rd place among elements, second only to oxygen and silicon. aluminum content in the earth's crust data various researchers is from 7.45 to 8.14% of the mass of the earth's crust.
In nature, aluminum, due to its high chemical activity, occurs almost exclusively in the form of compounds. Some of them:
Bauxites - Al2O3 H2O (with admixtures of SiO2, Fe2O3, CaCO3)
Alunites - (Na,K)2SO4 Al2(SO4)3 4Al(OH)3
Alumina (mixtures of kaolins with sand SiO2, limestone CaCO3, magnesite MgCO3)
Corundum (sapphire, ruby, emery) - Al2O3
Kaolinite - Al2O3 2SiO2 2H2O
Beryl (emerald, aquamarine) - 3BeO Al2O3 6SiO2
Chrysoberyl (alexandrite) - BeAl2O4.
However, under certain specific reducing conditions, the formation of native aluminum is possible.
AT natural waters aluminum is contained in the form of low-toxic chemical compounds, for example, aluminum fluoride. The type of cation or anion depends, first of all, on the acidity of the aqueous medium. Aluminum concentrations in surface water bodies Russian Federation range from 0.001 to 10 mg/l, in sea water 0.01 mg/l.
Aluminum (Aluminum) is
Obtaining castings from aluminum alloys
The main challenge facing the foundry in our country, consists in a significant overall improvement in the quality of castings, which should find expression in a decrease in wall thickness, a decrease in machining allowances and gating systems while maintaining the proper operational properties of trade items. The end result of this work should be to meet the increased needs of mechanical engineering with the necessary number of cast billets without a significant increase in the total monetary emission of castings by weight.
Sand casting
Of the above methods of casting into disposable molds, the most widely used in the manufacture of castings from aluminum alloys is casting into wet sand molds. This is due to the low density of the alloys, the small force effect of the metal on the mold, and low casting temperatures (680-800C).
For the manufacture of sand molds, molding and core mixtures are used, prepared from quartz and clay sands (GOST 2138-74), molding clays (GOST 3226-76), binders and auxiliary materials.
The type of gating system is chosen taking into account the dimensions of the casting, the complexity of its configuration and location in the mold. The pouring of molds for castings of complex configuration of small height is carried out, as a rule, with the help of lower gating systems. At high altitude castings and thin walls, it is preferable to use vertically slotted or combined gating systems. Molds for castings of small sizes can be poured through the top gating systems. In this case, the height of the metal scab falling into the mold cavity should not exceed 80 mm.
To reduce the speed of the melt at the entrance to the mold cavity and to better separate the oxide films and slag inclusions suspended in it, additional hydraulic resistances are introduced into the gating systems - meshes (metal or fiberglass) are installed or poured through granular filters.
Sprues (feeders), as a rule, are brought to thin sections (walls) of castings dispersed around the perimeter, taking into account the convenience of their subsequent separation during processing. The supply of metal to massive units is unacceptable, as it causes the formation of shrinkage cavities in them, increased roughness and shrinkage "failures" on the surface of the castings. In cross section, the sprue channels most often have a rectangular shape with a wide side of 15-20 mm, and a narrow side of 5-7 mm.
Alloys with a narrow crystallization interval (AL2, AL4, AL), AL34, AK9, AL25, ALZO) are prone to the formation of concentrated shrinkage cavities in the thermal units of castings. To bring these shells out of the castings, the installation of massive profits is widely used. For thin-walled (4-5 mm) and small castings, the mass of the profit is 2-3 times the mass of the castings, for thick-walled castings, up to 1.5 times. Height arrived chosen depending on the height of the casting. When the height is less than 150 mm, the height arrived H-adj. take equal to the height of the casting Notl. For higher castings, the ratio Nprib / Notl is taken equal to 0.3 0.5.
The greatest application in casting aluminum alloys are the upper open profits round or oval section; lateral profits in most cases are made closed. To improve work efficiency profits they are insulated, filled with hot metal, topped up. Warming is usually carried out by a sticker on the surface of the form of sheet asbestos, followed by drying with a gas flame. Alloys with a wide crystallization range (AL1, AL7, AL8, AL19, ALZZ) are prone to the formation of scattered shrinkage porosity. Impregnation of shrinkage pores with profits ineffective. Therefore, in the manufacture of castings from the listed alloys, it is not recommended to use the installation of massive profits. To obtain high-quality castings, directional crystallization is carried out, widely using the installation of refrigerators made of cast iron and aluminum alloys for this purpose. Optimum conditions for directional crystallization are created by a vertical slot gate system. To prevent gas evolution during crystallization and to prevent the formation of gas-shrinkage porosity in thick-walled castings, crystallization under a pressure of 0.4–0.5 MPa is widely used. To do this, the casting molds are placed in autoclaves before pouring, they are filled with metal and the castings are crystallized under air pressure. For the manufacture of large-sized (up to 2-3 m high) thin-walled castings, a casting method with successively directed solidification is used. The essence of the method is the successive crystallization of the casting from the bottom up. To do this, the casting mold is placed on the table of a hydraulic lift and metal tubes 12–20 mm in diameter, heated to 500–700°C, are lowered inside it, performing the function of risers. The tubes are fixedly fixed in the gating cup and the holes in them are closed with stoppers. After the gating cup is filled with melt, the stoppers are lifted, and the alloy flows through the tubes into the gating wells connected to the mold cavity by slotted sprues (feeders). After the level of the melt in the wells rises by 20-30 mm above the lower end of the tubes, the mechanism for lowering the hydraulic table is turned on. The lowering speed is taken such that the filling of the mold is carried out under the flooded level and the hot metal continuously enters the upper parts of the mold. This provides directional solidification and makes it possible to obtain complex castings without shrinkage defects.
Filling sand molds with metal is carried out from ladles lined with refractory material. Before filling with metal, freshly lined ladles are dried and calcined at 780–800°C to remove moisture. The temperature of the melt before pouring is maintained at the level of 720-780 °C. Molds for thin-walled castings are filled with melts heated to 730-750°C, and for thick-walled castings up to 700-720°C.
Casting in plaster molds
Casting in gypsum molds is used in cases where increased requirements are placed on castings in terms of accuracy, surface cleanliness and reproduction of the smallest details of the relief. Compared to sand molds, gypsum molds have higher strength, dimensional accuracy, better resistance to high temperatures, and make it possible to obtain castings of complex configuration with a wall thickness of 1.5 mm according to the 5-6th accuracy class. Forms are made according to wax or metal (brass,) chrome-plated models. Model plates are made of aluminum alloys. To facilitate the removal of models from the molds, their surface is covered with a thin layer of kerosene-stearin lubricant.
Small and medium molds for complex thin-walled castings are made from a mixture consisting of 80% gypsum, 20% quartz sand or asbestos and 60-70% water (by weight of the dry mixture). The composition of the mixture for medium and large forms: 30% gypsum, 60% sand, 10% asbestos, 40-50% water. To slow down the setting, 1-2% slaked lime is added to the mixture. The necessary strength of the forms is achieved by hydration of anhydrous or semi-aqueous gypsum. To reduce strength and increase gas permeability, raw gypsum molds are subjected to hydrothermal treatment - they are kept in an autoclave for 6-10 hours under a water vapor pressure of 0.13-0.14 MPa, and then for a day in air. After that, the forms are subjected to stepwise drying at 350-500 °C.
A feature of gypsum molds is their low thermal conductivity. This circumstance makes it difficult to obtain dense castings from aluminum alloys with a wide range of crystallization. Therefore, the main task in the development of a sprue-profitable system for gypsum molds is to prevent the formation of shrinkage cavities, looseness, oxide films, hot cracks and underfilling of thin walls. This is achieved by the use of expanding gating systems that provide a low speed of movement of melts in the mold cavity, directed solidification of thermal units towards the risers with the help of refrigerators, and an increase in the compliance of molds by increasing the content of quartz sand in the mixture. Thin-walled castings are poured into molds heated to 100–200°C by the vacuum suction method, which makes it possible to fill cavities up to 0.2 mm thick. Thick-walled (more than 10 mm) castings are obtained by pouring molds in autoclaves. Crystallization of the metal in this case is carried out under a pressure of 0.4–0.5 MPa.
Shell casting
Casting into shell molds is expedient to use in serial and large-scale production of castings of limited dimensions with increased surface finish, greater dimensional accuracy and less machining than when casting into sand molds.
Shell molds are made using hot (250–300 °C) metal (steel,) tooling in a bunker way. Model equipment is performed according to the 4th-5th accuracy classes with molding slopes from 0.5 to 1.5%. The shells are made two-layer: the first layer is from a mixture with 6-10% thermosetting resin, the second from a mixture with 2% resin. For better shell removal, the model slab before backfilling molding sand cover with a thin layer of release emulsion (5% silicone fluid No. 5; 3% laundry soap; 92% water).
For the manufacture of shell molds, fine-grained quartz sands containing at least 96% silica are used. The half-molds are connected by gluing on special pin presses. Glue composition: 40% MF17 resin; 60% marshalite and 1.5% aluminum chloride (hardening). Filling of the assembled forms is carried out in containers. When casting into shell molds, the same gating systems are used and temperature conditions as in sand casting.
The low rate of metal crystallization in shell molds and the lower possibilities for creating directed crystallization result in the production of castings with lower properties than when casting in raw sand molds.
Investment casting
Investment casting is used to manufacture castings of increased accuracy (3rd-5th class) and surface finish (4-6th roughness class), for which this method is the only possible or optimal one.
Models in most cases are made from pasty paraffin stearin (1: 1) compositions by pressing into metal molds (cast and prefabricated) on stationary or carousel installations. In the manufacture of complex castings with dimensions of more than 200 mm, in order to avoid deformation of the models, substances are introduced into the composition of the model mass that increase the temperature of their softening (melting).
As a refractory coating in the manufacture of ceramic molds, a suspension of hydrolyzed ethyl silicate (30–40%) and powdered quartz (70–60%) is used. Sprinkling of model blocks is carried out with calcined sand 1KO16A or 1K025A. Each coating layer is dried in air for 10-12 hours or in an atmosphere containing ammonia vapor. The necessary strength of the ceramic mold is achieved with a shell thickness of 4–6 mm (4–6 layers of a refractory coating). To ensure smooth filling of the mold, expanding gating systems are used with metal supply to thick sections and massive nodes. Castings are usually fed from a massive riser through thickened sprues (feeders). For complex castings, it is allowed to use massive profits to power the upper massive units with the obligatory filling of them from the riser.
Aluminum (Aluminum) is
Models are melted from molds in hot (85–90°C) water acidified with hydrochloric acid (0.5–1 cm3 per liter of water) to prevent saponification of stearin. After melting the models, the ceramic molds are dried at 150–170°C for 1–2 hours, placed in containers, filled with dry filler, and calcined at 600–700°C for 5–8 hours. Filling is carried out in cold and heated molds. The heating temperature (50-300 °C) of the molds is determined by the thickness of the walls of the casting. The filling of molds with metal is carried out in the usual way, as well as using vacuum or centrifugal force. Most aluminum alloys are heated to 720-750°C before pouring.
Die casting
Chill casting is the main method of serial and mass production of castings from aluminum alloys, which makes it possible to obtain castings of the 4th-6th accuracy classes with a surface roughness Rz = 50-20 and a minimum wall thickness of 3-4 mm. When casting into a mold, along with defects caused by high speeds of the melt in the mold cavity and non-compliance with the requirements of directional solidification (gas porosity, oxide films, shrinkage looseness), the main types of rejects and castings are underfills and cracks. The appearance of cracks is caused by difficult shrinkage. Cracks occur especially often in castings made from alloys with a wide crystallization interval, which have a large linear shrinkage (1.25–1.35%). Prevention of the formation of these defects is achieved by various technological methods.
In the case of supplying metal to thick sections, provision should be made for feeding the supply point by installing a supply boss (profit). All elements of the gating systems are located along the chill mold connector. The following cross-sectional area ratios of the gate channels are recommended: for small castings EFst: EFsl: EFpit = 1: 2: 3; for large castings EFst: EFsl: EFpit = 1: 3: 6.
To reduce the rate of melt entry into the mold cavity, curved risers, fiberglass or metal meshes, and granular filters are used. The quality of castings from aluminum alloys depends on the rate of rise of the melt in the mold cavity. This speed should be sufficient to guarantee the filling of thin sections of castings under conditions of increased heat removal and at the same time not cause underfilling due to incomplete release of air and gases through the ventilation ducts and profits, swirling and flowing of the melt during the transition from narrow sections to wide ones. The rate of rise of the metal in the mold cavity when casting into a mold is taken somewhat higher than when casting into sand molds. The minimum allowable lifting speed is calculated according to the formulas of A. A. Lebedev and N. M. Galdin (see section 5.1, “Sand casting”).
To obtain dense castings, as in sand casting, directional solidification is created by proper positioning of the casting in the mold and control of heat dissipation. As a rule, massive (thick) casting units are located in the upper part of the mold. This makes it possible to compensate for the reduction in their volume during hardening directly from the profits installed above them. The regulation of the intensity of heat removal in order to create directional solidification is carried out by cooling or insulating various sections of the mold. To locally increase heat removal, inserts from heat-conducting cuprum are widely used, they provide for an increase in the cooling surface of the mold due to fins, local cooling of the molds with compressed air or water is carried out. To reduce the intensity of heat removal, a layer of paint 0.1–0.5 mm thick is applied to the working surface of the mold. For this purpose, a layer of paint 1-1.5 mm thick is applied to the surface of the sprue channels and profits. The slowdown in the cooling of the metal in the risers can also be achieved by local thickening of the mold walls, the use of various low-heat-conductive coatings and the insulation of the risers with an asbestos sticker. Painting the working surface of the mold improves the appearance of the castings, helps to eliminate gas pockets on their surface and increases the durability of the molds. Before painting, the molds are heated to 100-120 °C. An excessively high heating temperature is undesirable, since this reduces the rate of solidification of the castings and the duration deadline mold service. Heating reduces the temperature difference between the casting and the mold and the expansion of the mold due to its heating by the casting metal. As a result, tensile stresses in the casting are reduced, causing appearance cracks. However, heating the mold alone is not enough to eliminate the possibility of cracking. It is necessary to timely remove the casting from the mold. The casting should be removed from the mold before the moment when its temperature equals the temperature of the mold, and the shrinkage stresses reach the maximum value. Usually, the casting is removed at the moment when it is strong enough that it can be moved without destruction (450-500 ° C). By this time, the gating system has not yet acquired sufficient strength and is destroyed by light impacts. The holding time of the casting in the mold is determined by the rate of solidification and depends on the temperature of the metal, the temperature of the mold and the speed of pouring.
To eliminate metal sticking, increase service life and facilitate extraction, metal rods are lubricated during operation. The most common lubricant is a water-graphite suspension (3-5% graphite).
Parts of the molds that perform the external outlines of the castings are made of gray cast iron. The wall thickness of the molds is assigned depending on the wall thickness of the castings in accordance with the recommendations of GOST 16237-70. Internal cavities in castings are performed using metal (steel) and sand rods. Sand rods are used to decorate complex cavities that cannot be made with metal rods. To facilitate the extraction of castings from molds, the outer surfaces of the castings must have a casting slope from 30 "to 3 ° towards the parting. The internal surfaces of castings made with metal rods must have a slope of at least 6 °. Sharp transitions from thick to thin sections are not allowed in castings. The radius of curvature must be at least 3 mm. Holes with a diameter of more than 8 mm for small castings, 10 mm for medium and 12 mm for large castings are made with rods. The optimal ratio of the depth of the hole to its diameter is 0.7-1.
Air and gases are removed from the mold cavity with the help of ventilation ducts placed in the parting plane and plugs placed in the walls near deep cavities.
In modern foundries, molds are installed on single-station or multi-station semi-automatic casting machines, in which the closing and opening of the mold, insertion and removal of cores, ejection and removal of the casting from the mold are automated. Automatic control of the mold heating temperature is also provided. Filling molds on machines is carried out using dispensers.
To improve the filling of thin mold cavities and remove air and gases released during the destruction of binders, the molds are evacuated, poured under low pressure or using centrifugal force.
Squeeze casting
Squeeze casting is a type of die casting. It is intended for the manufacture of large-sized castings (2500x1400 mm) of panel type with a wall thickness of 2-3 mm. For this purpose, metal half-moulds are used, which are mounted on specialized casting-squeezing machines with one-sided or two-sided convergence of the half-moulds. Distinctive feature This method of casting is the forced filling of the mold cavity with a wide melt flow when the half-moulds approach each other. There are no elements of a conventional gating system in the casting mold. Data This method is used to make castings from AL2, AL4, AL9, AL34 alloys, which have a narrow crystallization range.
The melt cooling rate is controlled by applying a heat-insulating coating of various thicknesses (0.05–1 mm) to the working surface of the mold cavity. Overheating of the alloys before pouring should not exceed 15-20°C above the liquidus temperature. The duration of the convergence of the half-forms is 5-3 s.
Low pressure casting
Low pressure casting is another form of die casting. It has been used in the manufacture of large-sized thin-walled castings from aluminum alloys with a narrow crystallization interval (AL2, AL4, AL9, AL34). As in the case of mold casting, the outer surfaces of the castings are made with a metal mold, and the inner cavities are made with metal or sand cores.
For the manufacture of rods, a mixture consisting of 55% quartz sand 1K016A is used; 13.5% bold sand P01; 27% powdered quartz; 0.8% pectin glue; 3.2% resin M and 0.5% kerosene. Such a mixture does not form a mechanical burn. The molds are filled with metal by pressure of dried compressed air (18–80 kPa) supplied to the surface of the melt in a crucible heated to 720–750°C. Under the action of this pressure, the melt is forced out of the crucible into the metal wire, and from it into the gating system and further into the mold cavity. The advantage of low-pressure casting is the ability to automatically control the rate of metal rise in the mold cavity, which makes it possible to obtain thin-walled castings of better quality than gravity casting.
Crystallization of alloys in the mold is carried out under a pressure of 10–30 kPa until a solid metal crust is formed and 50–80 kPa after the formation of a crust.
Denser aluminum alloy castings are produced by low-pressure casting with back pressure. The filling of the mold cavity during casting with back pressure is carried out due to the pressure difference in the crucible and in the mold (10–60 kPa). Crystallization of the metal in the form is carried out under a pressure of 0.4-0.5 MPa. This prevents the release of hydrogen dissolved in the metal and the formation of gas pores. Increased pressure contributes to better nutrition of massive casting assemblies. In other respects, back-pressure casting technology is no different from low-pressure casting technology.
Back pressure casting successfully combines the advantages of low pressure casting and pressure crystallization.
Injection molding
Die-casting from aluminum alloys AL2, ALZ, AL1, ALO, AL11, AL13, AL22, AL28, AL32, AL34, castings of complex configuration of the 1st-3rd accuracy classes with a wall thickness of 1 mm and more, cast holes with a diameter of up to 1, 2 mm, cast external and internal thread with a minimum pitch of 1 mm and a diameter of 6 mm. The surface cleanliness of such castings corresponds to 5-8 roughness classes. The production of such castings is carried out on machines with cold horizontal or vertical pressing chambers, with a specific pressing pressure of 30–70 MPa. Preference is given to machines with a horizontal bale chamber.
The dimensions and weight of the castings are limited by the capabilities of the Injection Molding Machines: the volume of the pressing chamber, the specific pressing pressure (p) and the locking force (0). The area of projection (F) of the casting, the gate channels and the pressing chamber on the movable mold plate should not exceed the values determined by the formula F = 0.85 0/r.
The optimum slope values for outdoor surfaces are 45°; for internal 1°. The minimum radius of curvature is 0.5—1mm. Holes larger than 2.5 mm in diameter are made by casting. Castings from aluminum alloys, as a rule, are machined only along the seating surfaces. The processing allowance is assigned taking into account the dimensions of the casting and ranges from 0.3 to 1 mm.
Various materials are used to make molds. Parts of the molds that come into contact with liquid metal are made of steels ЗХ2В8, 4Х8В2, 4ХВ2С, mounting plates and holders of dies are made of steels 35, 45, 50, pins, bushings and guide columns - from U8A steel.
The supply of metal to the cavity of the molds is carried out using external and internal gating systems. The feeders are brought to the parts of the casting that are subjected to machining. Their thickness is assigned depending on the wall thickness of the casting at the point of supply and the specified nature of the filling of the mold. This dependence is determined by the ratio of the Feeder thickness to the wall thickness of the casting. Smooth, without turbulence and air entrapment, the filling of molds takes place if the ratio is close to one. For castings with wall thickness up to 2 mm. feeders have a thickness of 0.8 mm; with a wall thickness of 3mm. the thickness of the feeders is 1.2 mm; with a wall thickness of 4-6 mm-2 mm.
To receive the first portion of the melt enriched with air inclusions, special wash tanks are located near the mold cavity, the volume of which can reach 20–40% of the casting volume. Washers are connected to the cavity of the mold by channels, the thickness of which is equal to the thickness of the feeders. Removal of air and gas from the mold cavity is carried out through special ventilation channels and gaps between the rods (pushers) and the mold matrix. Ventilation channels are made in the split plane on the fixed part of the mold, as well as along the movable rods and ejectors. The depth of the ventilation ducts when casting aluminum alloys is assumed to be 0.05-0.15 mm, and the width is 10-30 mm in order to improve ventilation, the cavity of the washers with thin channels (0.2-0.5 mm) is connected to the atmosphere .
The main defects of castings obtained by injection molding are air (gas) subcrustal porosity due to air entrapment at high speeds of metal inlet into the mold cavity, and shrinkage porosity (or shells) in thermal nodes. The formation of these defects is greatly influenced by the parameters of the casting technology, the pressing speed, the pressing pressure, and the thermal regime of the mold.
The pressing speed determines the mold filling mode. The higher the pressing speed, the faster the melt moves through the gating channels, the greater the melt inlet speed into the mold cavity. High pressing speeds contribute to better filling of thin and elongated cavities. At the same time, they are the cause of air capture by the metal and the formation of subcrustal porosity. When casting aluminum alloys, high pressing speeds are used only in the manufacture of complex thin-walled castings. The pressing pressure has a great influence on the quality of castings. As it increases, the density of castings increases.
The value of the pressing pressure is usually limited by the value of the locking force of the machine, which must exceed the pressure exerted by the metal on the movable matrix (pF). Therefore, local pre-pressing of thick-walled castings, known as the Ashigai process, is gaining great interest. The low rate of metal entry into the mold cavity through large-section feeders and the effective pre-pressing of the crystallizing melt with the help of a double plunger make it possible to obtain dense castings.
The quality of castings is also significantly affected by the temperatures of the alloy and the mold. In the manufacture of thick-walled castings of a simple configuration, the melt is poured at a temperature of 20–30 °C below the liquidus temperature. Thin-walled castings require the use of a melt superheated above the liquidus temperature by 10–15°C. To reduce the magnitude of shrinkage stresses and prevent the formation of cracks in castings, the molds are heated before pouring. The following heating temperatures are recommended:
Casting wall thickness, mm 1—2 2—3 3—5 5—8
Heating temperature
molds, °С 250—280 200—250 160—200 120—160
The stability of the thermal regime is provided by heating (electric) or cooling (water) molds.
To protect the working surface of the molds from sticking and erosive effects of the melt, to reduce friction during the extraction of the cores and to facilitate the extraction of castings, the molds are lubricated. For this purpose, fatty (oil with graphite or aluminum powder) or aqueous (salt solutions, aqueous preparations based on colloidal graphite) lubricants are used.
The density of castings from aluminum alloys increases significantly when casting with vacuum molds. To do this, the mold is placed in a sealed casing, in which the necessary vacuum is created. Good results can be obtained using the "oxygen process". To do this, the air in the cavity of the mold is replaced with oxygen. At high rates of metal inlet into the mold cavity, which cause the capture of oxygen by the melt, subcrustal porosity is not formed in the castings, since all the trapped oxygen is spent on the formation of finely dispersed aluminum oxides that do not noticeably affect the mechanical properties of the castings. Such castings can be subjected to heat treatment.
Depending on the requirements of the technical specifications, aluminum alloy castings can be subjected to various types control: X-ray, gamma-ray or ultrasonic for the detection of internal defects; markings for determining dimensional deviations; luminescent to detect surface cracks; hydro- or pneumocontrol to assess tightness. The frequency of the listed types of control is specified specifications or determined by the department of the chief metallurgist of the plant. Identified defects, if allowed by the technical specifications, are eliminated by welding or impregnation. Argon-arc welding is used for welding of underfills, shells, looseness of cracks. Before welding, the defective place is cut in such a way that the walls of the recesses have a slope of 30 - 42 °. Castings are subjected to local or general heating up to 300-350C. Local heating is carried out by an oxy-acetylene flame, general heating is carried out in chamber furnaces. Welding is carried out with the same alloys from which the castings are made, using a non-consumable tungsten electrode with a diameter of 2-6 mm at expense argon 5-12 l/min. The strength of the welding current is usually 25-40 A per 1 mm of the electrode diameter.
Porosity in castings is eliminated by impregnation with bakelite varnish, asphalt varnish, drying oil or liquid glass. Impregnation is carried out in special boilers under a pressure of 490-590 kPa with preliminary holding of castings in a rarefied atmosphere (1.3-6.5 kPa). The temperature of the impregnating liquid is maintained at 100°C. After impregnation, the castings are subjected to drying at 65-200°C, during which the impregnating liquid hardens, and repeated control.
Aluminum (Aluminum) is
Application of aluminum
Widely used as a structural material. The main advantages of aluminum in this capacity are lightness, ductility for stamping, corrosion resistance (in air, aluminum is instantly covered with a strong Al2O3 film, which prevents its further oxidation), high thermal conductivity, and non-toxicity of its compounds. In particular, these properties have made aluminum extremely popular in the manufacture of cookware, aluminum foil in Food Industry and for packaging.
The main disadvantage of aluminum as a structural material is its low strength, therefore, to strengthen it, it is usually alloyed with a small amount of cuprum and magnesium (the alloy is called duralumin).
The electrical conductivity of aluminum is only 1.7 times less than that of cuprum, while aluminum is approximately 4 times cheaper per kilogram, but, due to 3.3 times lower density, to obtain equal resistance, it needs approximately 2 times less weight . Therefore, it is widely used in electrical engineering for the manufacture of wires, their shielding, and even in microelectronics for the manufacture of conductors in chips. The lower electrical conductivity of aluminum (37 1/ohm) compared to cuprum (63 1/ohm) is compensated by an increase in the cross section of aluminum conductors. The disadvantage of aluminum as an electrical material is the presence of a strong oxide film that makes soldering difficult.
Due to the complex of properties, it is widely used in thermal equipment.
Aluminum and its alloys retain strength at ultra-low temperatures. Because of this, it is widely used in cryogenic technology.
The high reflectivity combined with the low cost and ease of deposition makes aluminum an ideal material for making mirrors.
In the production of building materials as a gas-forming agent.
Aluminizing gives corrosion and scale resistance to steel and other alloys, such as piston engine valves, turbine blades, oil rigs, heat exchange equipment, and also replaces galvanizing.
Aluminum sulfide is used to produce hydrogen sulfide.
Research is underway to develop foamed aluminum as a particularly strong and lightweight material.
As a component of thermite, mixtures for aluminothermy
Aluminum is used to recover rare metals from their oxides or halides.
Aluminum is important component many alloys. For example, in aluminum bronzes, the main components are copper and aluminum. In magnesium alloys, aluminum is most often used as an additive. For the manufacture of spirals in electric heaters, Fechral (Fe, Cr, Al) is used (along with other alloys).
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When aluminum was very expensive, a variety of jewelry trade items were made from it. So, Napoleon III ordered aluminum buttons, and in 1889 Dmitry Ivanovich Mendeleev was presented with scales with bowls made of gold and aluminum. The fashion for them immediately passed when new technologies (developments) for its production appeared, which reduced the cost many times over. Now aluminum is sometimes used in the manufacture of jewelry.
In Japan, aluminum is used in the manufacture of traditional jewelry, replacing .
Aluminum and its compounds are used as a high performance propellant in bipropellant propellants and as a propellant in solid propellants. The following aluminum compounds are of the greatest practical interest as rocket fuel:
Powdered aluminum as a fuel in solid rocket propellants. It is also used in the form of powder and suspensions in hydrocarbons.
aluminum hydride.
aluminum borane.
Trimethylaluminum.
Triethylaluminum.
Tripropylaluminum.
Triethylaluminum (usually, together with triethylboron) is also used for chemical ignition (i.e., as a starting fuel) in rocket engines, as it ignites spontaneously in oxygen gas.
It has a slight toxic effect, but many water-soluble inorganic aluminum compounds remain in a dissolved state for a long time and can have a harmful effect on humans and warm-blooded animals through drinking water. The most toxic are chlorides, nitrates, acetates, sulfates, etc. For humans, the following doses of aluminum compounds (mg/kg of body weight) have a toxic effect when ingested:
aluminum acetate - 0.2-0.4;
aluminum hydroxide - 3.7-7.3;
aluminum alum - 2.9.
First of all, it acts on the nervous system (accumulates in the nervous tissue, leading to severe disorders of the central nervous system function). However, the neurotoxic property of aluminum began to be studied since the mid-1960s, since the accumulation of the metal in the human body is hindered by the mechanism of its excretion. Under normal conditions, up to 15 mg of an element per day can be excreted in the urine. Accordingly, the greatest negative effect is observed in people with impaired renal excretory function.
According to some biological studies, the intake of aluminum in the human body was considered a factor in the development of Alzheimer's disease, but these studies were later criticized and the conclusion about the connection of one with the other was refuted.
The chemical features of aluminum are determined by its high affinity for oxygen (in minerals aluminum is included in oxygen octahedra and tetrahedra), constant valence (3), poor solubility of most natural compounds. AT endogenous processes during solidification of magma and the formation of igneous rocks, aluminum enters the crystal lattice of feldspars, micas and other minerals - aluminosilicates. In the biosphere, aluminum is a weak migrant; it is scarce in organisms and the hydrosphere. In a humid climate, where the decaying remains of abundant vegetation form a lot of organic acids, aluminum migrates in soils and waters in the form of organomineral colloidal compounds; aluminum is adsorbed by colloids and precipitated in the lower part of soils. The connection of aluminum with silicon is partially broken and in some places in the tropics minerals are formed - aluminum hydroxides - boehmite, diaspore, hydrargillite. Most of the aluminum is part of the aluminosilicates - kaolinite, beidellite and other clay minerals. Weak mobility determines the residual accumulation of aluminum in the weathering crust of the humid tropics. As a result, eluvial bauxites are formed. In past geological epochs, bauxites also accumulated in lakes and the coastal zone of the seas of tropical regions (for example, sedimentary bauxites of Kazakhstan). In the steppes and deserts, where there is little living matter, and the waters are neutral and alkaline, aluminum almost does not migrate. The migration of aluminum is most vigorous in volcanic areas, where highly acidic river and underground waters rich in aluminum are observed. In places of displacement of acidic waters with alkaline - marine (at the mouths of rivers and others), aluminum is deposited with the formation of bauxite deposits.
Aluminum is part of the tissues of animals and plants; in the organs of mammals, from 10-3 to 10-5% of aluminum (per crude substance) was found. Aluminum accumulates in the liver, pancreas and thyroid glands. AT herbal products aluminum content ranges from 4 mg per 1 kg of dry matter (potato) to 46 mg (yellow turnip), in animal products - from 4 mg (honey) to 72 mg per 1 kg of dry matter (). In the daily human diet, the content of aluminum reaches 35-40 mg. Known organisms are aluminum concentrators, for example, club mosses (Lycopodiaceae), containing up to 5.3% aluminum in ash, mollusks (Helix and Lithorina), in whose ash 0.2-0.8% aluminum. Forming insoluble compounds with phosphates, aluminum disrupts the nutrition of plants (phosphate absorption by roots) and animals (phosphate absorption in the intestines).
The main purchaser is aviation. The most heavily loaded elements of the aircraft (skin, power reinforcing set) are made of duralumin. And they took this alloy into space. He even landed on the Moon and returned to Earth. And the stations "Luna", "Venus", "Mars", created by the designers of the bureau, which long years headed by Georgy Nikolaevich Babakin (1914-1971), they could not do without aluminum alloys.
Alloys of the aluminum-manganese and aluminum-magnesium system (AMts and AMg) are the main material for the hulls of high-speed "rockets" and "meteors" - hydrofoils.
But aluminum alloys are used not only in space, aviation, sea and river transport. Aluminum occupies a strong position in land transport. The following data speaks of the widespread use of aluminum in the automotive industry. In 1948, 3.2 kg of aluminum was used per one, in 1958 - 23.6, in 1968 - 71.4, and today this figure exceeds 100 kg. Aluminum appeared and railway transport. And the Russkaya Troika superexpress is more than 50% made of aluminum alloys.
Aluminum is being used more and more in construction. In new buildings, strong and light beams, ceilings, columns, railings, fences, elements of ventilation systems made of aluminum-based alloys are often used. AT last years aluminum alloys have entered the construction of many public buildings, sports complexes. There are attempts to use aluminum as roofing material. Such a roof is not afraid of impurities of carbon dioxide, sulfur compounds, nitrogen compounds and other harmful impurities, which greatly enhance atmospheric corrosion of roofing iron.
As casting alloys, silumins are used - alloys of the aluminum-silicon system. Such alloys have good fluidity, give low shrinkage and segregation (heterogeneity) in castings, which makes it possible to obtain parts of the most complex configuration by casting, for example, engine cases, pump impellers, instrument cases, internal combustion engine blocks, pistons, cylinder heads and jackets piston engines.
Fight for decline cost aluminum alloys also met with success. For example, silumin is 2 times cheaper than aluminum. Usually, on the contrary, alloys are more expensive (to obtain an alloy, it is necessary to obtain a pure base, and then by alloying - an alloy). Soviet metallurgists at the Dnepropetrovsk Aluminum Plant in 1976 mastered the smelting of silumins directly from aluminosilicates.
Aluminum has long been known in electrical engineering. However, until recently, the scope of aluminum has been limited to power lines and, in rare cases, power cables. The cable industry was dominated by copper and lead. The conductive elements of the cable structure were made of cuprum, and the metal sheath was made of lead or lead-based alloys. For many decades (for the first time, lead sheaths for protecting cable cores were proposed in 1851) was the only metal material for cable sheaths. He is excellent in this role, but not without flaws - high density, low strength and scarcity; these are just the main ones that made a person look for other metals that can adequately replace lead.
They turned out to be aluminum. The beginning of his service in this role can be considered 1939, and work began in 1928. However, a serious shift in the use of aluminum in cable technology occurred in 1948, when the technology for manufacturing aluminum sheaths was developed and mastered.
Copper, too, for many decades was the only metal for the manufacture of current-carrying conductors. Studies of materials that could replace copper have shown that aluminum should and can be such a metal. So, instead of two metals, essentially different purposes, aluminum entered the cable technology.
This substitution has a number of advantages. Firstly, the possibility of using an aluminum shell as a neutral conductor is a significant savings in metal and weight reduction. Secondly, higher strength. Thirdly, facilitating installation, reducing transportation costs, reducing the cost of the cable, etc.
Aluminum wires are also used for overhead power lines. But it took a lot of effort and time to make an equivalent replacement. Many options have been developed, and they are used based on the specific situation. [Produced aluminum wires increased strength and increased creep resistance, which is achieved by alloying with magnesium up to 0.5%, silicon up to 0.5%, iron up to 0.45%, hardening and aging. Steel-aluminum wires are used, especially for the implementation of large spans required at the intersection of various obstacles with power lines. There are spans of more than 1500 m, for example, when crossing rivers.
Aluminum in transfer technology electricity over long distances, they are used not only as a conductor material. A decade and a half ago, aluminum-based alloys began to be used for the manufacture of power transmission towers. They were first built in our country in the Caucasus. They are about 2.5 times lighter than steel and do not require corrosion protection. Thus, the same metal replaced iron, copper and lead in electrical engineering and electricity transmission technology.
And so or almost so it was in other areas of technology. Tanks, pipelines and other assembly units made of aluminum alloys have proven themselves in the oil, gas and chemical industries. They have supplanted many corrosion-resistant metals and materials, such as iron-carbon alloy containers enameled inside to store aggressive liquids (a crack in the enamel layer of this expensive design could lead to losses or even an accident).
Over 1 million tons of aluminum is spent annually in the world for the production of foil. The thickness of the foil, depending on its purpose, is in the range of 0.004-0.15 mm. Its application is extremely varied. It is used for packaging various food and industrial products - chocolate, sweets, medicines, cosmetics, photographic products, etc.
Foil is also used as a structural material. There is a group of gas-filled plastics - honeycomb plastics - cellular materials with a system of regularly repeating cells of regular geometric shape, the walls of which are made of aluminum foil.
Encyclopedia of Brockhaus and Efron
ALUMINUM- (clay) chem. zn. AL; at. in. = 27.12; beats in. = 2.6; m.p. about 700°. Silvery white, soft, sonorous metal; is in combination with silicic acid the main component of clays, feldspar, micas; found in all soils. Goes to…… Dictionary of foreign words of the Russian language
ALUMINUM- (symbol Al), a silver-white metal, an element of the third group of the periodic table. It was first obtained in its pure form in 1827. The most common metal in the bark the globe; its main source is bauxite ore. Process… … Scientific and technical encyclopedic dictionary
ALUMINUM- ALUMINUM, Aluminum (chemical sign A1, at. weight 27.1), the most common metal on the surface of the earth and, after O and silicon, the most important component of the earth's crust. A. occurs in nature, mainly in the form of silicic acid salts (silicates); ... ... Big Medical Encyclopedia
Aluminum- is a bluish-white metal, characterized by particular lightness. It is very ductile and can be easily rolled, drawn, forged, stamped, and cast, etc. Like other soft metals, aluminum also lends itself very well to ... ... Official terminology
Aluminum- (Aluminium), Al, a chemical element of group III of the periodic system, atomic number 13, atomic mass 26.98154; light metal, mp660 °С. The content in the earth's crust is 8.8% by weight. Aluminum and its alloys are used as structural materials in ... ... Illustrated Encyclopedic Dictionary
ALUMINUM- ALUMINUM, aluminum male., chem. alkali metal clays, alumina base, clays; as well as the basis of rust, iron; and yari copper. Aluminite male. an alum-like fossil, hydrous alumina sulphate. Alunit husband. fossil, very close to ... ... Dictionary Dalia
aluminum- (silver, light, winged) metal Dictionary of Russian synonyms. aluminum n., number of synonyms: 8 clays (2) … Synonym dictionary
ALUMINUM- (lat. Aluminum from alumen alum), Al, a chemical element of group III of the periodic system, atomic number 13, atomic mass 26.98154. Silvery white metal, light (2.7 g/cm³), ductile, with high electrical conductivity, mp 660 .C.… … Big Encyclopedic Dictionary
Aluminum- Al (from lat. alumen the name of alum, used in ancient times as a mordant in dyeing and tanning * a. aluminum; n. Aluminium; f. aluminium; and. aluminio), chem. group III element periodic. Mendeleev systems, at. n. 13, at. m. 26.9815 ... Geological Encyclopedia
ALUMINUM- ALUMINUM, aluminum, pl. no, husband. (from lat. alumen alum). Silvery white malleable light metal. Explanatory Dictionary of Ushakov. D.N. Ushakov. 1935 1940 ... Explanatory Dictionary of Ushakov
Properties 13 Al.
|
Atomic mass |
26,98 |
clarke, at.% (prevalence in nature) |
5,5 |
|
Electronic configuration* |
State of aggregation (well.). |
||
|
0,143 |
Color |
silver white |
|
|
0,057 |
695 |
||
|
Ionization energy |
5,98 |
2447 |
|
|
Relative electronegativity |
1,5 |
Density |
2,698 |
|
Possible oxidation states |
1, +2,+3 |
Standard electrode potential |
1,69 |
*External configuration shown electronic levels element atom. The configuration of the remaining electronic levels coincides with that for the noble gas that completes the previous period and is indicated in brackets.
Aluminum- the main representative of the metals of the main subgroup of group III of the periodic system. Properties of its analogues - gallium, india and thallium - in many ways resemble the properties of aluminum, since all these elements have the same electronic configuration of the outer level ns 2 np 1 and therefore they all exhibit an oxidation state of 3+.
physical properties. Aluminum is a silvery white metal with high thermal and electrical conductivity. The metal surface is covered with a thin but very strong film of aluminum oxide Al 2 Oz.
Chemical properties. Aluminum is very active if there is no protective film of Al 2 Oz. This film prevents aluminum from interacting with water. If you remove the protective film by chemical means(for example, with an alkali solution), then the metal begins to interact vigorously with water with the release of hydrogen:
Aluminum in the form of shavings or powder burns brightly in air, releasing a large amount of energy:
This feature of aluminum is widely used to obtain various metals from their oxides by reduction with aluminum. The method is called aluminothermy . Aluminothermy can only produce those metals in which the heat of formation of oxides is less than the heat of formation of Al 2 Oz, for example:
When heated, aluminum reacts with the halogens sulfur, nitrogen and carbon, forming, respectively, halides:
Aluminum sulfide and aluminum carbide are completely hydrolyzed with the formation of aluminum hydroxide and, accordingly, hydrogen sulfide and methane.
Aluminum is easily soluble in hydrochloric acid of any concentration:
Concentrated sulfuric and nitric acids in the cold do not act on aluminum (passivate). At heating aluminum is able to reduce these acids without hydrogen evolution:
AT diluted sulfuric acid dissolves aluminum with the release of hydrogen:
AT diluted nitric acid the reaction proceeds with the release of nitric oxide (II):
Aluminum dissolves in solutions of alkalis and alkali metal carbonates to form tetrahydroxoaluminates:
Aluminium oxide. Al 2 O 3 has 9 crystalline modifications. The most common a is a modification. It is the most chemically inert; on its basis, single crystals of various stones are grown for use in the jewelry industry and technology.
In the laboratory, aluminum oxide is obtained by burning aluminum powder in oxygen or by calcining its hydroxide:
aluminum oxide, being amphoteric can react not only with acids, but also with alkalis, as well as when fused with alkali metal carbonates, while giving metaaluminates:
and with acid salts:
aluminum hydroxide- white gelatinous substance, practically insoluble in water, possessing amphoteric properties. Aluminum hydroxide can be obtained by treating aluminum salts with alkalis or ammonium hydroxide. In the first case, an excess of alkali must be avoided, since otherwise the aluminum hydroxide will dissolve with the formation of complex tetrahydroxoaluminates[Al(OH) 4 ]` :
In fact, in the last reaction, tetrahydroxodiquaaluminate ions` , however, the simplified form [Al(OH) 4 ]` is usually used to write reactions. With weak acidification, tetrahydroxoaluminates are destroyed:
aluminum salts. Almost all aluminum salts can be obtained from aluminum hydroxide. Almost all salts of aluminum and strong acids are highly soluble in water and are highly hydrolyzed.
Aluminum halides are highly soluble in water and are dimers in their structure:
| 2AlCl 3 є Al 2 Cl 6 |
Aluminum sulfates are easily, like all its salts, hydrolyzed:
Potassium-aluminum alum is also known: KAl(SO 4) 2H 12H 2 O.
aluminum acetate Al(CH 3 COO) 3 used in medicine as a lotion.
Aluminosilicates. In nature, aluminum occurs in the form of compounds with oxygen and silicon - aluminosilicates. Their general formula is: (Na, K) 2 Al 2 Si 2 O 8-nepheline.
Also, natural aluminum compounds are: Al2O3- corundum, alumina; and compounds with general formulas Al 2 O 3 H nH 2 O and Al(OH) 3H nH 2 O- bauxites.
Receipt. Aluminum is obtained by electrolysis of Al 2 O 3 melt.
Aluminum
Aluminum- a chemical element of group III of the periodic system of Mendeleev (atomic number 13, atomic mass 26.98154). In most compounds, aluminum is trivalent, but at high temperatures it can also exhibit an oxidation state of +1. Of the compounds of this metal, the most important is Al 2 O 3 oxide.
Aluminum- silver-white metal, light (density 2.7 g / cm 3), ductile, good conductor of electricity and heat, melting point 660 ° C. It is easily drawn into wire and rolled into thin sheets. Aluminum is chemically active (in air it is covered with a protective oxide film - aluminum oxide.) Reliably protects the metal from further oxidation. But if aluminum powder or aluminum foil is heated strongly, the metal burns with a blinding flame, turning into aluminum oxide. Aluminum dissolves even in dilute hydrochloric and sulfuric acids, especially when heated. But in highly dilute and concentrated cold nitric acid, aluminum does not dissolve. When aqueous solutions of alkalis act on aluminum, the oxide layer dissolves, and aluminates are formed - salts containing aluminum in the composition of the anion:
Al 2 O 3 + 2NaOH + 3H 2 O \u003d 2Na.
Aluminum, devoid of a protective film, interacts with water, displacing hydrogen from it:
2Al + 6H 2 O \u003d 2Al (OH) 3 + 3H 2
The resulting aluminum hydroxide reacts with an excess of alkali, forming hydroxoaluminate:
Al (OH) 3 + NaOH \u003d Na.
The overall equation for the dissolution of aluminum in an aqueous solution of alkali has the following form:
2Al + 2NaOH + 6H 2 O \u003d 2Na + 3H 2.
Aluminum actively interacts with halogens. Aluminum hydroxide Al(OH) 3 is a white, translucent, gelatinous substance.
The earth's crust contains 8.8% aluminum. It is the third most abundant element in nature after oxygen and silicon, and the first among metals. It is a part of clays, feldspars, micas. Several hundred Al minerals are known (aluminosilicates, bauxites, alunites, and others). The most important mineral of aluminum - bauxite contains 28-60% of alumina - aluminum oxide Al 2 O 3 .
In its pure form, aluminum was first obtained by the Danish physicist H. Oersted in 1825, although it is the most common metal in nature.
Aluminum production is carried out by electrolysis of alumina Al 2 O 3 in NaAlF 4 cryolite melt at a temperature of 950 °C.
Aluminum is used in aviation, construction, mainly in the form of aluminum alloys with other metals, electrical engineering (substitute for copper in the manufacture of cables, etc.), food industry (foil), metallurgy (alloy additive), aluminothermy, etc.
Aluminum density, specific gravity and other characteristics.
Density - 2,7*10 3 kg/m 3 ;
Specific gravity -
2,7 G/ cm 3;
Specific heat at 20°C - 0.21 cal/deg;
Melting temperature - 658.7°C;
Specific heat capacity of melting - 76.8 cal/deg;
Boiling temperature - 2000°C ;
Relative volume change during melting (ΔV/V) - 6,6%;
Linear expansion coefficient(at approx. 20°C) :
- 22.9 * 10 6 (1 / deg);
Thermal conductivity coefficient of aluminum - 180 kcal / m * hour * hail;
Moduli of elasticity of aluminum and Poisson's ratio
Reflection of light by aluminum
The numbers given in the table show what percentage of light incident perpendicular to the surface is reflected from it.
ALUMINUM OXIDE Al 2 O 3
Aluminum oxide Al 2 O 3, also called alumina, occurs naturally in crystalline form, forming the mineral corundum. Corundum has a very high hardness. Its transparent crystals, colored in red or blue, are gems- ruby and sapphire. Currently, rubies are obtained artificially by fusing with alumina in an electric furnace. They are used not so much for jewelry as for technical purposes, for example, for the manufacture of parts for precision instruments, stones in watches, etc. Ruby crystals containing a small impurity of Cr 2 O 3 are used as quantum generators - lasers that create a directed beam of monochromatic radiation.
Corundum and its fine-grained variety, containing a large amount of impurities - emery, are used as abrasive materials.
ALUMINUM PRODUCTION
The main raw material for aluminum production are bauxites containing 32-60% alumina Al 2 O 3 . The most important aluminum ores also include alunite and nepheline. Russia has significant reserves of aluminum ores. In addition to bauxites, large deposits of which are located in the Urals and Bashkiria, a rich source of aluminum is nepheline mined on the Kola Peninsula. A lot of aluminum is also found in the deposits of Siberia.
Aluminum is obtained from aluminum oxide Al 2 O 3 by the electrolytic method. The aluminum oxide used for this must be sufficiently pure, since impurities are removed from smelted aluminum with great difficulty. Purified Al 2 O 3 is obtained by processing natural bauxite.
The main starting material for the production of aluminum is aluminum oxide. It does not conduct electricity and has a very high melting point (about 2050 °C), so it requires too much energy.
It is necessary to reduce the melting point of aluminum oxide to at least 1000 o C. This method was found in parallel by the Frenchman P. Eru and the American C. Hall. They found that alumina dissolves well in molten cryolite, a mineral of AlF 3 composition. 3NaF. This melt is subjected to electrolysis at a temperature of only about 950 ° C in aluminum production. The reserves of cryolite in nature are insignificant, so synthetic cryolite was created, which significantly reduced the cost of aluminum production.
Hydrolysis is subjected to a molten mixture of cryolite Na 3 and aluminum oxide. A mixture containing about 10 weight percent Al 2 O 3 melts at 960 °C and has the electrical conductivity, density and viscosity most favorable to the process. To further improve these characteristics, additives AlF 3 , CaF 2 and MgF 2 are introduced into the composition of the mixture. This makes electrolysis possible at 950 °C.
The electrolyser for aluminum smelting is an iron casing lined with refractory bricks from the inside. Its bottom (under), assembled from blocks of compressed coal, serves as a cathode. Anodes (one or more) are located on top: these are aluminum frames filled with coal briquettes. In modern plants, electrolyzers are installed in series; each series consists of 150 or more cells.
During electrolysis, aluminum is released at the cathode, and oxygen is released at the anode. Aluminum, which has a higher density than the original melt, is collected at the bottom of the electrolyzer, from where it is periodically discharged. As the metal is released, new portions of aluminum oxide are added to the melt. The oxygen released during electrolysis interacts with the carbon of the anode, which burns out, forming CO and CO 2 .
The first aluminum plant in Russia was built in 1932 in Volkhov.
ALUMINUM ALLOYS
Alloys, which increase the strength and other properties of aluminum, are obtained by introducing alloying additives into it, such as copper, silicon, magnesium, zinc, and manganese.
Duralumin(duralumin, duralumin, from the name of the German city where the industrial production of the alloy was started). Aluminum alloy (base) with copper (Cu: 2.2-5.2%), magnesium (Mg: 0.2-2.7%) manganese (Mn: 0.2-1%). It is subjected to hardening and aging, often clad with aluminum. Is structural material for aviation and transport engineering.
Silumin- light cast aluminum alloys (base) with silicon (Si: 4-13%), sometimes up to 23% and some other elements: Cu, Mn, Mg, Zn, Ti, Be). They produce parts of complex configuration, mainly in the automotive and aircraft industries.
magnalia- aluminum alloys (base) with magnesium (Mg: 1-13%) and other elements with high corrosion resistance, good weldability, high ductility. They make shaped castings (casting magnals), sheets, wire, rivets, etc. (deformable magnalia).
The main advantages of all aluminum alloys are their low density (2.5-2.8 g / cm 3), high strength (per unit weight), satisfactory resistance to atmospheric corrosion, comparative low cost and ease of production and processing.
Aluminum alloys are used in rocket technology, in aircraft, auto, ship and instrument making, in the production of utensils, sporting goods, furniture, advertising and other industries.
In terms of breadth of application, aluminum alloys rank second after steel and cast iron.
Aluminum is one of the most common additives in alloys based on copper, magnesium, titanium, nickel, zinc, and iron.
Aluminum is also used for aluminizing (aluminizing)- saturation of the surface of steel or cast iron products with aluminum in order to protect the base material from oxidation during strong heating, i.e. increase heat resistance (up to 1100 °C) and resistance to atmospheric corrosion.
PROPERTIES OF ALUMINUM
Content:
Aluminum grades
Physical properties
Corrosion properties
Mechanical properties
Technological properties
Application
aluminum grades.
Aluminum is characterized by high electrical and thermal conductivity, corrosion resistance, ductility, and frost resistance. The most important property of aluminum is its low density (about 2.70 g / cc). The melting point of aluminum is about 660 C.
The physicochemical, mechanical and technological properties of aluminum are very dependent on the type and amount of impurities, worsening most of the properties of pure metal. The main natural impurities in aluminum are iron and silicon. Iron, for example, present as an independent Fe-Al phase, reduces electrical conductivity and corrosion resistance, worsens ductility, but slightly increases the strength of aluminum.
Depending on the degree of purification, primary aluminum is divided into aluminum of high and technical purity (GOST 11069-2001). Technical aluminum also includes grades marked AD, AD1, AD0, AD00 (GOST 4784-97). Technical aluminum of all grades is obtained by electrolysis of cryolite-alumina melts. High purity aluminum is obtained by additional purification of technical aluminum. Features of the properties of aluminum of high and high purity are discussed in books
1) Metal science of aluminum and its alloys. Ed. I.N. Fridlyander. M. 1971.2) Mechanical and technological properties of metals. A.V. Bobylev. M. 1980.The table below provides a summary of most aluminum grades. The content of its main natural impurities - silicon and iron - is also indicated.
| Brand | Al, % | Si, % | Fe, % | Applications |
| High purity aluminum | ||||
| A995 | 99.995 | 0.0015 | 0.0015 | Chemical equipment Foil for capacitor plates Special Purposes |
| A98 | 99.98 | 0.006 | 0.006 |
|
| A95 | 99.95 | 0.02 | 0.025 |
|
| Technical grade aluminum | ||||
| A8 AD000 | 99.8 | 0.10 0.15 | 0.12 0.15 | Wire rod for production cable and wire products (from A7E and A5E). Raw materials for the production of aluminum alloys Foil Rolled products (rods, strips, sheets, wire, pipes) |
| A7 AD00 | 99.7 | 0.15 | 0.16 0.25 |
|
| A6 | 99.6 | 0.18 | 0.25 |
|
| A5E | 99.5 | 0.10 | 0.20 |
|
| A5 AD0 | 99.5 | 0.25 0.25 | 0.30 0.40 |
|
| AD1 | 99.3 | 0.30 | 0.30 |
|
| A0 HELL | 99.0 | 0.95 Up to 1.0% in total |
||
The main practical difference between commercial and highly purified aluminum is related to differences in corrosion resistance to certain media. Naturally, the higher the degree of purification of aluminum, the more expensive it is.
High purity aluminum is used for special purposes. For the production of aluminum alloys, cable and wire products and rolled products, technical aluminum is used. Next, we will talk about technical aluminum.
Electrical conductivity.
The most important property of aluminum is its high electrical conductivity, in which it is second only to silver, copper and gold. The combination of high electrical conductivity with low density allows aluminum to compete with copper in the field of cable and wire products.
The electrical conductivity of aluminum, in addition to iron and silicon, is strongly affected by chromium, manganese, and titanium. Therefore, in aluminum intended for the manufacture of current conductors, the content of several more impurities is regulated. So, in A5E grade aluminum with an allowable iron content of 0.35% and silicon of 0.12%, the sum of impurities Cr + V + Ti + Mn should not exceed only 0.01%.
The electrical conductivity depends on the state of the material. Long-term annealing at 350 C improves the conductivity, while cold hardening worsens the conductivity.
The value of electrical resistivity at a temperature of 20 C isOhm*mm 2 /m or µOhm*m :
0.0277 - annealed aluminum wire A7E
0.0280 - annealed aluminum wire A5E
0.0290 - after pressing, without heat treatment from AD0 aluminum
Thus, the specific electrical resistance of aluminum conductors is approximately 1.5 times higher than the electrical resistance of copper conductors. Accordingly, the electrical conductivity (the reciprocal of the resistivity) of aluminum is 60-65% of the electrical conductivity of copper. The electrical conductivity of aluminum increases with a decrease in the amount of impurities.
The temperature coefficient of electrical resistance of aluminum (0.004) is approximately the same as that of copper.
Thermal conductivityThe thermal conductivity of aluminum at 20 C is approximately 0.50 cal/cm*s*C and increases with increasing purity of the metal. In terms of thermal conductivity, aluminum is second only to silver and copper (about 0.90), three times higher than the thermal conductivity of mild steel. This property determines the use of aluminum in cooling radiators and heat exchangers.
Other physical properties.
Aluminum has a very high specific heat (approximately 0.22 cal / g * C). This is much higher than for most metals (0.09 for copper). Specific heat of fusion is also very high (about 93 cal/g). For comparison, for copper and iron, this value is approximately 41-49 cal / g.
Reflectivity aluminum is highly dependent on its purity. For aluminum foil with a purity of 99.2%, the white light reflectance is 75%, and for foil with an aluminum content of 99.5%, the reflectance is already 84%.
Corrosion properties of aluminum.Aluminum itself is a very reactive metal. This is connected with its use in aluminothermy and in the production of explosives. However, in air, aluminum is covered with a thin (about a micron) film of aluminum oxide. With high strength and chemical inertness, it protects aluminum from further oxidation and determines its high anti-corrosion properties in many environments.
In high-purity aluminum, the oxide film is continuous and non-porous, and has a very strong adhesion to aluminum. Therefore, aluminum of high and special purity is very resistant to the action of inorganic acids, alkalis, sea water and air. The adhesion of the oxide film to aluminum in the places where impurities are located significantly deteriorates and these places become vulnerable to corrosion. Therefore, aluminum of technical purity has a lower resistance. For example, in relation to weak hydrochloric acid, the resistance of refined and technical aluminum differs by 10 times.
Aluminum (and its alloys) usually exhibits pitting corrosion. Therefore, the stability of aluminum and its alloys in many media is determined not by a change in the weight of the samples and not by the rate of penetration of corrosion, but by a change in mechanical properties.
The iron content has the main influence on the corrosion properties of technical aluminum. Thus, the corrosion rate in a 5% HCl solution for different grades is (in):
| Brand | ContentAl | Fe content | Corrosion rate |
| A7 | 99.7 % | < 0.16 % | 0.25 – 1.1 |
| A6 | 99.6% | < 0.25% | 1.2 – 1.6 |
| A0 | 99.0% | < 0.8% | 27 - 31 |
The presence of iron also reduces the resistance of aluminum to alkalis, but does not affect the resistance to sulfuric and nitric acids. In general, the corrosion resistance of technical aluminum, depending on the purity, deteriorates in this order: A8 and AD000, A7 and AD00, A6, A5 and AD0, AD1, A0 and AD.
At temperatures above 100C, aluminum interacts with chlorine. Aluminum does not interact with hydrogen, but dissolves it well, so it is the main component of the gases present in aluminum. Bad influence aluminum is affected by water vapor, which dissociates at 500 C; at lower temperatures, the effect of steam is negligible.
Aluminum is stable in the following environments:
industrial atmosphere
Natural fresh water up to temperatures of 180 C. The corrosion rate increases with aeration,
impurities of caustic soda, hydrochloric acid and soda.
Sea water
Concentrated nitric acid
Acid salts of sodium, magnesium, ammonium, hyposulfite.
Weak (up to 10%) solutions of sulfuric acid,
100% sulfuric acid
Weak solutions of phosphoric (up to 1%), chromic (up to 10%)
Boric acid in any concentration
Vinegar, lemon, wine. malic acid, acidic fruit juices, wine
Ammonia solution
Aluminum is unstable in such environments:
Dilute nitric acid
Hydrochloric acid
Dilute sulfuric acid
Hydrofluoric and hydrobromic acid
Oxalic, formic acid
Solutions of caustic alkalis
Water containing salts of mercury, copper, chloride ions that destroy the oxide film.
contact corrosionIn contact with most technical metals and alloys, aluminum serves as an anode and its corrosion will increase.
Mechanical propertiesElastic modulus E \u003d 7000-7100 kgf / mm 2 for technical aluminum at 20 C. With an increase in the purity of aluminum, its value decreases (6700 for A99).
Shear modulus G \u003d 2700 kgf / mm 2.
The main parameters of the mechanical properties of technical aluminum are given below:
Parameter | Unit rev. | deformed | Annealed |
Yield strength? 0.2 | kgf/mm 2 | 8 - 12 | 4 - 8 |
Tensile Strength? in | kgf/mm 2 | 13 - 16 | |
Elongation at Break? | 5 – 10 | 30 – 40 |
|
Relative contraction at break | 50 - 60 | 70 - 90 |
|
Shear strength | kgf/mm 2 | ||
Hardness | HB | 30 - 35 |
The figures given are very indicative:
1) For annealed and cast aluminium, these values depend on the technical aluminum grade. The more impurities, the greater the strength and hardness and the lower the ductility. For example, the hardness of cast aluminum is: for A0 - 25HB, for A5 - 20HB, and for high purity aluminum A995 - 15HB. The tensile strength for these cases is: 8.5; 7.5 and 5 kgf / mm 2, and elongation 20; 30 and 45% respectively.
2) For deformed aluminum, the mechanical properties depend on the degree of deformation, the type of rolled product and its dimensions. For example, the tensile strength is at least 15-16 kgf / mm 2 for wire and 8 - 11 kgf / mm 2 for pipes.
However, in any case, technical aluminum is a soft and fragile metal. The low yield strength (even for hard-worked steel it does not exceed 12 kgf/mm 2) limits the use of aluminum in terms of allowable loads.
Aluminum has a low creep strength: at 20 C it is 5 kgf/mm 2 , and at 200 C it is 0.7 kgf/mm 2 . For comparison: for copper, these figures are 7 and 5 kgf / mm 2, respectively.
The low melting temperature and the temperature of the beginning of recrystallization (for technical aluminum is about 150 C), the low creep limit limits the temperature range of aluminum operation from the side of high temperatures.
The ductility of aluminum does not deteriorate at low temperatures, up to helium. When the temperature drops from +20 C to -269 C, the tensile strength increases 4 times for technical aluminum and 7 times for high-purity aluminum. The elastic limit in this case increases by a factor of 1.5.
The frost resistance of aluminum makes it possible to use it in cryogenic devices and structures.
Technological properties.
The high ductility of aluminum makes it possible to produce foil (up to 0.004 mm thick), deep-drawn products, and use it for rivets.
Technical purity aluminum exhibits brittleness at high temperatures.
Machinability is very low.
The temperature of recrystallization annealing is 350-400 C, tempering temperature is 150 C.
Weldability.
Difficulties in aluminum welding are due to 1) the presence of a strong inert oxide film, 2) high thermal conductivity.
Nevertheless, aluminum is considered a highly weldable metal. The weld has the strength of the base metal (annealed) and the same corrosion properties. For details on aluminum welding, see, for example,www. weldingsite.com.ua.
Application.
Due to its low strength, aluminum is used only for unloaded structural elements, when high electrical or thermal conductivity, corrosion resistance, ductility or weldability are important. The parts are connected by welding or rivets. Technical aluminum is used both for casting and for the production of rolled products.
In the warehouse of the enterprise there are always sheets, wire and tires made of technical aluminum.
(see the relevant pages of the website). Under the order pigs A5-A7 are delivered.
One of the most convenient materials in processing are metals. They also have their own leaders. For example, the basic properties of aluminum have been known to people for a long time. They are so suitable for use in everyday life that this metal has become very popular. What are the same as a simple substance and as an atom, we will consider in this article.
The history of the discovery of aluminum
From time immemorial, the compound of the metal in question has been known to man - It was used as a means capable of swelling and binding the components of the mixture together, this was also necessary when dressing leather goods. The existence of pure aluminum oxide became known in the 18th century, in its second half. However, it was not received.
For the first time, the scientist H.K. Oersted managed to isolate the metal from its chloride. It was he who treated salt with potassium amalgam and isolated a gray powder from the mixture, which was aluminum in its pure form.
Then it became clear that the chemical properties of aluminum are manifested in its high activity, strong reducing ability. Therefore, no one else worked with him for a long time.
However, in 1854, the Frenchman Deville was able to obtain metal ingots by melt electrolysis. This method is still relevant today. Especially mass production of valuable material began in the 20th century, when the problems of obtaining a large amount of electricity at enterprises were solved.
To date, this metal is one of the most popular and used in the construction and household industries.
General characteristics of the aluminum atom
If we characterize the element under consideration by its position in the periodic system, then several points can be distinguished.
- Ordinal number - 13.
- It is located in the third small period, the third group, the main subgroup.
- Atomic mass - 26.98.
- The number of valence electrons is 3.
- The configuration of the outer layer is expressed by the formula 3s 2 3p 1 .
- The name of the element is aluminum.
- strongly expressed.
- There are no isotopes in nature, it exists only in one form, with mass number 27.
- The chemical symbol is AL, read as "aluminum" in formulas.
- The oxidation state is one, equal to +3.
The chemical properties of aluminum are fully confirmed by the electronic structure of its atom, because having a large atomic radius and low electron affinity, it is able to act as a strong reducing agent, like all active metals.
Aluminum as a simple substance: physical properties
If we talk about aluminum, as a simple substance, then it is a silvery-white shiny metal. In air, it quickly oxidizes and becomes covered with a dense oxide film. The same thing happens with the action of concentrated acids.
The presence of such a feature makes products made of this metal resistant to corrosion, which, of course, is very convenient for people. Therefore, it is aluminum that finds such wide application in construction. also interesting in that this metal is very light, while durable and soft. The combination of such characteristics is not available to every substance.
There are several main physical properties which are characteristic of aluminum.
- High degree of malleability and plasticity. A light, strong and very thin foil is made from this metal, it is also rolled into a wire.
- Melting point - 660 0 C.
- Boiling point - 2450 0 С.
- Density - 2.7 g / cm 3.
- Crystal cell volumetric face-centered, metallic.
- Connection type - metal.
The physical and chemical properties of aluminum determine the areas of its application and use. If we talk about everyday aspects, then the characteristics already considered by us above play a big role. As a light, durable and anticorrosive metal, aluminum is used in aircraft and shipbuilding. Therefore, these properties are very important to know.
Chemical properties of aluminum
From the point of view of chemistry, the metal in question is a strong reducing agent that is capable of exhibiting high chemical activity, being a pure substance. The main thing is to eliminate the oxide film. In this case, the activity increases sharply.
The chemical properties of aluminum as a simple substance are determined by its ability to react with:
- acids;
- alkalis;
- halogens;
- gray.
It does not interact with water under normal conditions. At the same time, from halogens, without heating, it reacts only with iodine. Other reactions require temperature.
Examples can be given to illustrate the chemical properties of aluminum. Equations for interaction reactions with:
- acids- AL + HCL \u003d AlCL 3 + H 2;
- alkalis- 2Al + 6H 2 O + 2NaOH \u003d Na + 3H 2;
- halogens- AL + Hal = ALHal 3 ;
- gray- 2AL + 3S = AL 2 S 3 .
In general, the most important property of the substance under consideration is its high ability to restore other elements from their compounds.
Recovery ability
The reducing properties of aluminum are well traced in the reactions of interaction with oxides of other metals. It easily extracts them from the composition of the substance and allows them to exist in simple form. For example: Cr 2 O 3 + AL = AL 2 O 3 + Cr.
In metallurgy, there is a whole technique for obtaining substances based on such reactions. It is called aluminothermy. Therefore, in the chemical industry, this element is used specifically for the production of other metals.
Distribution in nature
In terms of prevalence among other metal elements, aluminum ranks first. Its content in the earth's crust is 8.8%. If compared with non-metals, then its place will be third, after oxygen and silicon.
Due to its high chemical activity, it is not found in its pure form, but only in the composition of various compounds. So, for example, there are many ores, minerals, rocks, which include aluminum. However, it is mined only from bauxite, the content of which in nature is not too high.
The most common substances containing the metal in question are:
- feldspars;
- bauxite;
- granites;
- silica;
- aluminosilicates;
- basalts and others.
In a small amount, aluminum is necessarily part of the cells of living organisms. Some species of club mosses and marine life are able to accumulate this element inside their bodies throughout their lives.
Receipt
The physical and chemical properties of aluminum make it possible to obtain it in only one way: by electrolysis of a melt of the corresponding oxide. However, this process is technologically complex. The melting point of AL 2 O 3 exceeds 2000 0 C. Because of this, it cannot be directly subjected to electrolysis. Therefore, proceed as follows.
The product yield is 99.7%. However, it is possible to obtain an even purer metal, which is used for technical purposes.
Application
The mechanical properties of aluminum are not good enough to be used in its pure form. Therefore, alloys based on this substance are most often used. There are many of them, we can name the most basic ones.
- Duralumin.
- Aluminum-manganese.
- Aluminum-magnesium.
- Aluminium-copper.
- Silumins.
- Avial.
Their main difference is, of course, third-party additives. All of them are based on aluminum. Other metals make the material more durable, resistant to corrosion, wear-resistant and pliable in processing.
There are several main areas of application of aluminum both in pure form and in the form of its compounds (alloys).
Together with iron and its alloys, aluminum is the most important metal. It is these two representatives of the periodic system that have found the most extensive industrial application in the hands of man.
Properties of aluminum hydroxide
The hydroxide is the most common compound that forms aluminum. Its chemical properties are the same as those of the metal itself - it is amphoteric. This means that it is capable of manifesting a dual nature, reacting with both acids and alkalis.
Aluminum hydroxide itself is a white gelatinous precipitate. It is easy to obtain it by reacting an aluminum salt with an alkali or. When reacting with acids, this hydroxide gives the usual corresponding salt and water. If the reaction proceeds with alkali, then aluminum hydroxocomplexes are formed, in which its coordination number is 4. Example: Na is sodium tetrahydroxoaluminate.
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