Characteristics of aluminum metal according to the plan. Chemical and physical properties of aluminum. Physical properties of aluminum hydroxide

Obtaining potassium alum

Aluminum(lat. Aluminum), - in the periodic system, aluminum is in the third period, in the main subgroup of the third group. Core Charge +13. The electronic structure of the atom is 1s 2 2s 2 2p 6 3s 2 3p 1 . The metal atomic radius is 0.143 nm, the covalent one is 0.126 nm, the conditional radius of the Al 3+ ion is 0.057 nm. Ionization energy Al - Al + 5.99 eV.

The most characteristic oxidation state of the aluminum atom is +3. A negative oxidation state is rare. There are free d-sublevels in the outer electron layer of the atom. Due to this, its coordination number in compounds can be not only 4 (AlCl 4-, AlH 4-, aluminosilicates), but also 6 (Al 2 O 3, 3+).

History reference. The name aluminum comes from lat. alumen - so back in 500 BC. called aluminum alum, which was used as a mordant in the dyeing of fabrics and for tanning leather. The Danish scientist H. K. Oersted in 1825, acting with an amalgam of potassium on anhydrous AlCl 3 and then driving away mercury, obtained relatively pure aluminum. The first industrial method for the production of aluminum was proposed in 1854 by the French chemist A.E. St. Clair Deville: the method consisted in the reduction of aluminum and sodium double chloride Na 3 AlCl 6 with sodium metal. Similar in color to silver, aluminum was very expensive at first. From 1855 to 1890 only 200 tons of aluminum were produced. The modern method of producing aluminum by electrolysis of a cryolite-alumina melt was developed in 1886 simultaneously and independently by C. Hall in the USA and P. Héroux in France.

Being in nature

Aluminum is the most abundant metal in the earth's crust. It accounts for 5.5–6.6 mol. share% or 8 wt.%. Its main mass is concentrated in aluminosilicates. An extremely common product of the destruction of the rocks formed by them is clay, the main composition of which corresponds to the formula Al 2 O 3. 2SiO2. 2H 2 O. Of the other natural forms of aluminum, bauxite Al 2 O 3 is of the greatest importance. xH 2 O and minerals corundum Al 2 O 3 and cryolite AlF 3 . 3NaF.

Receipt

At present, aluminum is produced in industry by electrolysis of a solution of alumina Al 2 O 3 in molten cryolite. Al 2 O 3 must be sufficiently pure, since impurities are removed from smelted aluminum with great difficulty. The melting point of Al 2 O 3 is about 2050 o C, and that of cryolite is 1100 o C. A molten mixture of cryolite and Al 2 O 3 containing about 10 wt.% Al 2 O 3 is subjected to electrolysis, which melts at 960 o C and has electrical conductivity , density and viscosity, the most favorable for the process. By adding AlF 3 , CaF 2 and MgF 2 electrolysis is possible at 950°C.

The electrolytic cell 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 are located on top: this is - aluminum frames filled with coal briquettes.

Al 2 O 3 \u003d Al 3+ + AlO 3 3-

Liquid aluminum is released at the cathode:

Al 3+ + 3e - \u003d Al

Aluminum is collected at the bottom of the furnace, from where it is periodically released. Oxygen is released at the anode:

4AlO 3 3- - 12e - \u003d 2Al 2 O 3 + 3O 2

Oxygen oxidizes graphite to carbon oxides. As the carbon burns, the anode is built up.

Aluminum is also used as an alloying addition to many alloys to give them heat resistance.

Physical properties of aluminum. Aluminum combines a very valuable set of properties: low density, high thermal and electrical conductivity, high ductility and good corrosion resistance. It can be easily forged, stamped, rolled, drawn. Aluminum is well welded by gas, contact and other types of welding. The aluminum lattice is face-centered cubic with parameter a = 4.0413 Å. The properties of aluminum, like those of all metals, depend to a large extent on its purity. Properties of high purity aluminum (99.996%): density (at 20 °C) 2698.9 kg/m 3 ; t pl 660.24 °C; t bale about 2500 °C; thermal expansion coefficient (from 20 ° to 100 ° C) 23.86 10 -6; thermal conductivity (at 190 °C) 343 W/m K, specific heat capacity (at 100 °C) 931.98 J/kg K. ; electrical conductivity with respect to copper (at 20 °C) 65.5%. Aluminum has low strength (tensile strength 50–60 MN/m2), hardness (170 MN/m2 according to Brinell) and high ductility (up to 50%). During cold rolling, the tensile strength of Aluminum increases to 115 MN/m 2 , hardness - up to 270 MN/m 2 , relative elongation decreases to 5% (1 MN/m 2 ~ and 0.1 kgf/mm 2). Aluminum is well polished, anodized and has a high reflectivity close to silver (it reflects up to 90% of the incident light energy). Possessing a high affinity for oxygen, aluminum in air is covered with a thin, but very strong oxide film Al 2 O 3 , which protects the metal from further oxidation and determines its high anti-corrosion properties. The strength of the oxide film and protective action it greatly decreases in the presence of impurities of mercury, sodium, magnesium, copper, etc. Aluminum is resistant to atmospheric corrosion, sea and fresh water, practically does not interact with concentrated or highly diluted nitric acid, with organic acids, food products.

Chemical properties

When finely divided aluminum is heated, it burns vigorously in air. Its interaction with sulfur proceeds similarly. With chlorine and bromine, the combination occurs already at ordinary temperature, with iodine - when heated. At very high temperatures, aluminum also combines directly with nitrogen and carbon. On the contrary, it does not interact with hydrogen.

Aluminum is quite resistant to water. But if the protective effect of the oxide film is removed mechanically or by amalgamation, then an energetic reaction occurs:

Highly dilute, as well as very concentrated HNO3 and H2SO4, have almost no effect on aluminum (in the cold), while at medium concentrations of these acids, it gradually dissolves. Pure aluminum is quite stable with respect to hydrochloric acid, but the usual technical metal dissolves in it.

Under the action of alkali aqueous solutions 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 = Na

The overall equation for the dissolution of aluminum in an aqueous solution of alkali:

2Al + 2NaOH + 6H 2 O = 2Na + 3H 2

Aluminum noticeably dissolves in solutions of salts that have an acidic or alkaline reaction due to their hydrolysis, for example, in a solution of Na 2 CO 3 .

In a series of stresses, it is located between Mg and Zn. In all of its stable compounds, aluminum is trivalent.

The combination of aluminum with oxygen is accompanied by an enormous release of heat (1676 kJ/mol Al 2 O 3), much greater than that of many other metals. In view of this, when a mixture of the corresponding metal oxide with aluminum powder is heated, a violent reaction occurs, leading to the release of free metal from the taken oxide. The reduction method with Al (aluminum) is often used to obtain a number of elements (Cr, Mn, V, W, etc.) in a free state.

Aluminothermy is sometimes used for welding individual steel parts, in particular the joints of tram rails. The mixture used ("termite") usually consists of fine powders of aluminum and Fe 3 O 4 . It is ignited with a fuse from a mixture of Al and BaO 2. The main reaction goes according to the equation:

8Al + 3Fe 3 O 4 = 4Al 2 O 3 + 9Fe + 3350 kJ

Moreover, the temperature develops around 3000 o C.

Aluminum oxide is a white, very refractory (mp 2050 o C) and water-insoluble mass. Natural Al 2 O 3 (corundum mineral), as well as artificially obtained and then strongly calcined, are distinguished by high hardness and insolubility in acids. Al 2 O 3 (so-called alumina) can be converted into a soluble state by fusion with alkalis.

Natural corundum, normally contaminated with iron oxide, is used for the manufacture of grinding wheels, bars, etc. due to its extreme hardness. In finely crushed form, it is called emery and is used to clean metal surfaces and make sandpaper. For the same purposes, Al 2 O 3 is often used, obtained by fusing bauxite (technical name - alund).

Transparent colored corundum crystals - red ruby ​​- an admixture of chromium - and blue sapphire - an admixture of titanium and iron - precious stones. They are also obtained artificially and used 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.

Due to the insolubility of Al 2 O 3 in water, the hydroxide Al(OH) 3 corresponding to this oxide can only be obtained indirectly from salts. The production of hydroxide can be represented as the following scheme. Under the action of alkalis, OH ions gradually replace 3+ water molecules in aquocomplexes:

3+ + OH - \u003d 2+ + H 2 O

2+ + OH - = + + H 2 O

OH - \u003d 0 + H 2 O

Al(OH) 3 is a voluminous gelatinous precipitate white color, practically insoluble in water, but easily soluble in acids and strong alkalis. It therefore has an amphoteric character. However, its basic and especially acidic properties are rather weakly expressed. In excess of NH 4 OH, aluminum hydroxide is insoluble. One form of dehydrated hydroxide, aluminum gel, is used in engineering as an adsorbent.

When interacting with strong alkalis, the corresponding aluminates are formed:

NaOH + Al(OH) 3 = Na

Aluminates of the most active monovalent metals are highly soluble in water, but due to strong hydrolysis, their solutions are stable only in the presence of a sufficient excess of alkali. Aluminates produced from weaker bases are almost completely hydrolyzed in solution and therefore can only be obtained in a dry way (by alloying Al 2 O 3 with oxides of the corresponding metals). Metaaluminates are formed, which in their composition are produced from metaaluminum acid HAlO 2 . Most of them are insoluble in water.

Al(OH) 3 forms salts with acids. The derivatives of most strong acids are highly soluble in water, but are rather hydrolyzed, and therefore their solutions show an acidic reaction. Soluble salts of aluminum and weak acids are even more strongly hydrolyzed. Due to hydrolysis, sulfide, carbonate, cyanide and some other aluminum salts cannot be obtained from aqueous solutions.

In an aqueous medium, the Al 3+ anion is directly surrounded by six water molecules. Such a hydrated ion is somewhat dissociated according to the scheme:

3+ + H 2 O \u003d 2+ + OH 3 +

Its dissociation constant is 1. 10 -5 i.e. it is a weak acid (similar in strength to acetic acid). The octahedral environment of Al 3+ with six water molecules is also retained in crystalline hydrates of a number of aluminum salts.

Aluminosilicates can be considered as silicates, in which part of the silicon-oxygen tetrahedra SiO 4 4 - is replaced by aluminum-oxygen tetrahedra AlO 4 5- Of the aluminosilicates, feldspars are the most common, accounting for more than half of the mass of the earth's crust. Their main representatives are minerals

orthoclase K 2 Al 2 Si 6 O 16 or K 2 O . Al 2 O 3 . 6SiO2

albite Na 2 Al 2 Si 6 O 16 or Na 2 O . Al 2 O 3 . 6SiO2

anorthite CaAl 2 Si 2 O 8 or CaO. Al 2 O 3 . 2SiO2

The minerals of the mica group are very common, for example muscovite Kal 2 (AlSi 3 O 10) (OH) 2. big practical value has the mineral nepheline (Na, K) 2 , which is used to produce alumina, soda products and cement. This production consists of the following operations: a) nepheline and limestone are sintered in tube furnaces at 1200°C:

(Na, K) 2 + 2CaCO 3 = 2CaSiO 3 + NaAlO 2 + KAlO 2 + 2CO 2

b) the resulting mass is leached with water - a solution of sodium and potassium aluminates and CaSiO 3 sludge are formed:

NaAlO 2 + KAlO 2 + 4H 2 O \u003d Na + K

c) CO 2 formed during sintering is passed through a solution of aluminates:

Na + K + 2CO 2 = NaHCO 3 + KHCO 3 + 2Al(OH) 3

d) heating Al (OH) 3 alumina is obtained:

2Al(OH) 3 \u003d Al 2 O 3 + 3H 2 O

e) by evaporation of the mother liquor, soda and potage are isolated, and the previously obtained sludge is used for the production of cement.

In the production of 1 t of Al 2 O 3, 1 t of soda products and 7.5 t of cement are obtained.

Some aluminosilicates have a loose structure and are capable of ion exchange. Such silicates - natural and especially artificial - are used for water softening. In addition, due to their highly developed surface, they are used as catalyst carriers, i.e. as materials impregnated with a catalyst.

Aluminum halides under normal conditions are colorless crystalline substances. In the series of aluminum halides, AlF 3 differs greatly in properties from its counterparts. It is refractory, slightly soluble in water, chemically inactive. The main method for obtaining AlF 3 is based on the action of anhydrous HF on Al 2 O 3 or Al:

Al 2 O 3 + 6HF = 2AlF 3 + 3H 2 O

Aluminum compounds with chlorine, bromine and iodine are fusible, highly reactive and highly soluble not only in water, but also in many organic solvents. The interaction of aluminum halides with water is accompanied by a significant release of heat. In an aqueous solution, they are all highly hydrolyzed, but unlike typical non-metal acid halides, their hydrolysis is incomplete and reversible. Being noticeably volatile already under normal conditions, AlCl 3 , AlBr 3 and AlI 3 smoke in moist air (due to hydrolysis). They can be obtained by direct interaction of simple substances.

Vapor densities of AlCl 3 , AlBr 3 and AlI 3 at relatively low temperatures correspond more or less exactly to the doubled formulas - Al 2 Hal 6 . The spatial structure of these molecules corresponds to two tetrahedra with a common edge. Each aluminum atom is bonded to four halogen atoms, and each of the central halogen atoms is bonded to both aluminum atoms. Of the two bonds of the central halogen atom, one is donor-acceptor, with aluminum functioning as an acceptor.

With halide salts of a number of monovalent metals, aluminum halides form complex compounds, mainly of the M 3 and M types (where Hal is chlorine, bromine or iodine). The tendency to addition reactions is generally strongly pronounced in the halides under consideration. This is the reason for the most important technical application of AlCl 3 as a catalyst (in oil refining and in organic syntheses).

Of the fluoroaluminates, cryolite Na 3 has the greatest application (for obtaining Al, F 2 , enamels, glass, etc.). The industrial production of artificial cryolite is based on the treatment of aluminum hydroxide with hydrofluoric acid and soda:

2Al(OH) 3 + 12HF + 3Na 2 CO 3 = 2Na 3 + 3CO 2 + 9H 2 O

Chloro-, bromo- and iodoaluminates are obtained by fusing aluminum trihalides with halides of the corresponding metals.

Although aluminum does not react chemically with hydrogen, aluminum hydride can be obtained indirectly. It is a white amorphous mass of composition (AlH 3) n . Decomposes when heated above 105 ° C with the release of hydrogen.

When AlH 3 interacts with basic hydrides in an ether solution, hydroaluminates are formed:

LiH + AlH 3 = Li

Hydridoaluminates are white solids. Rapidly decomposed by water. They are powerful restorers. Used (especially Li) in organic synthesis.

Aluminum sulfate Al 2 (SO 4) 3. 18H 2 O is obtained by the action of hot sulfuric acid on aluminum oxide or kaolin. It is used to purify water, as well as in the preparation of some types of paper.

Potassium alum KAl(SO 4) 2 . 12H 2 O are used in large quantities for tanning leather, as well as in dyeing as a mordant for cotton fabrics. In the latter case, the effect of alum is based on the fact that the aluminum hydroxide formed as a result of their hydrolysis is deposited in the fabric fibers in a finely dispersed state and, adsorbing the dye, firmly holds it on the fiber.

Of the other aluminum derivatives, we should mention its acetate (otherwise, the acetic salt) Al(CH 3 COO) 3, used in dyeing fabrics (as a mordant) and in medicine (lotions and compresses). Aluminum nitrate is easily soluble in water. Aluminum phosphate is insoluble in water and acetic acid, but soluble in strong acids and alkalis.

aluminum in the body. 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. In vegetable products, the 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 (beef). In the daily human diet, the aluminum content reaches 35-40 mg. There are known organisms - aluminum concentrators, for example, club mosses (Lycopodiaceae), containing up to 5.3% aluminum in the ash, mollusks (Helix and Lithorina), in the ashes of which 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).

Geochemistry of aluminum. The geochemical features of aluminum are determined by its high affinity for oxygen (in minerals, aluminum is included in oxygen octahedrons and tetrahedra), constant valency (3), and low solubility of most natural compounds. In endogenous processes during the 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 bond between aluminum and silicon is partially broken and in 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 Application. The combination of physical, mechanical and chemical properties of aluminum determines its wide application in almost all areas of technology, especially in the form of its alloys with other metals. In electrical engineering, Aluminum successfully replaces copper, especially in the production of massive conductors, for example, in overhead lines, high-voltage cables, switchgear busbars, transformers (the electrical conductivity of Aluminum reaches 65.5% of the electrical conductivity of copper, and it is more than three times lighter than copper; with a cross section that provides the same conductivity, the mass of aluminum wires is half that of copper wires). Ultra-pure Aluminum is used in the production of electrical capacitors and rectifiers, the operation of which is based on the ability of the aluminum oxide film to transmit electricity only in one direction. Ultra-pure aluminum, purified by zone melting, is used for the synthesis of type A III B V semiconductor compounds used for the production of semiconductor devices. Pure Aluminum is used in the production of various mirror reflectors. High-purity aluminum is used to protect metal surfaces from atmospheric corrosion (cladding, aluminum paint). Having a relatively low neutron absorption cross section, aluminum is used as a structural material in nuclear reactors.

Large-capacity aluminum tanks store and transport liquid gases (methane, oxygen, hydrogen, etc.), nitric and acetic acids, clean water, hydrogen peroxide and edible oils. Aluminum is widely used in equipment and apparatus Food Industry, for food packaging (in the form of foil), for the production of various household products. There has been a sharp increase in the consumption of aluminum for finishing buildings, architectural, transport and sports facilities.

In metallurgy, aluminum (besides alloys based on it) is one of the most common alloying additives in alloys based on Cu, Mg, Ti, Ni, Zn, and Fe. Aluminum is also used to deoxidize steel before pouring it into a mold, as well as in the processes of obtaining certain metals by aluminothermy. On the basis of aluminum, SAP (sintered aluminum powder) was created by powder metallurgy, which has high heat resistance at temperatures above 300 °C.

Aluminum is used in the production of explosives (ammonal, alumotol). Widely used various connections aluminum.

The production and consumption of aluminum is constantly growing, significantly outpacing the production of steel, copper, lead, and zinc in terms of growth rates.

List of used literature

1. V.A. Rabinovich, Z.Ya. Khavin "Concise Chemical Reference"

2. L.S. Guzey "Lectures on General Chemistry"

3. N.S. Akhmetov "General and inorganic chemistry"

4. B.V. Nekrasov "Textbook of General Chemistry"

5. N.L. Glinka "General Chemistry"

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, which worsen 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 electrical resistivity of aluminum conductors is approximately 1.5 times higher than the electrical resistance 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 conductivity

The 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 melting 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 brands 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. Water vapor, which dissociates at 500 C, has a harmful effect on aluminum, at more low temperatures steam action 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 corrosion

In contact with most technical metals and alloys, aluminum serves as an anode and its corrosion will increase.

Mechanical properties

Elastic 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 mechanical properties depend on the degree of deformation, the type of rolled products and their 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.

Lesson type. Combined.

Tasks:

Educational:

1. Update students' knowledge about the structure of the atom, the physical meanings of the serial number, group number, period number using aluminum as an example.

2. To form students' knowledge that aluminum in the free state has special, characteristic physical and chemical properties.

Developing:

1. Generate interest in the study of science by providing brief historical and scientific reports on the past, present and future of aluminum.

2. To continue the formation of students' research skills when working with literature, performing laboratory work.

3. Expand the concept of amphoteric by revealing the electronic structure of aluminum, the chemical properties of its compounds.

Educational:

1. Raise a respect for the environment by providing information about the possible use of aluminum yesterday, today, tomorrow.

2. To form the ability to work as a team for each student, to take into account the opinion of the whole group and defend their own correctly by doing laboratory work.

3. To introduce students to the scientific ethics, honesty and decency of natural scientists of the past, providing information about the struggle for the right to be the discoverer of aluminum.

REVIEW on the topics of alkaline and alkaline earth M (REPEAT):

What is the number of electrons in the outer energy level of alkaline and alkaline earth M?

What products are formed when sodium or potassium reacts with oxygen? (peroxide), is lithium capable of producing peroxide in reaction with oxygen? (No, the reaction produces lithium oxide.)

How are sodium and potassium oxides obtained? (calcination of peroxides with the corresponding Me, Pr: 2Na+Na 2 O 2 =2Na 2 O).

Do alkali and alkaline earth metals exhibit negative oxidation states? (No, they do not, as they are strong reducing agents.).

How does the radius of an atom change in the main subgroups (from top to bottom) of the Periodic system? (increases) what is the reason for this? (with an increase in the number of energy levels).

Which of the groups of metals studied by us is lighter than water? (in alkaline).

Under what conditions does the formation of hydrides occur in alkaline earth metals? (at high temperatures).

Which substance calcium or magnesium reacts more actively with water? (Calcium reacts more actively. Magnesium reacts actively with water only when it is heated to 100 0 C).

How does the solubility of alkaline earth metal hydroxides in water change in the series from calcium to barium? (solubility in water increases).

Tell us about the features of storage of alkali and alkaline earth metals, why are they stored this way? (since these metals are very reactive, they are stored in a container under a layer of kerosene).

CONTROL WORK on the topics of alkaline and alkaline earth M:

LESSON SUMMARY (STUDYING NEW MATERIAL):

Teacher: Hello guys, today we are moving on to the study of the IIIA subgroup. List the elements located in the IIIA subgroup?

Trainees: It includes such elements as boron, aluminum, gallium, indium and thallium.

Teacher: How many electrons do they contain in their outer energy level, oxidation state?

Trainees: Three electrons, +3 oxidation state, although thallium has a more stable oxidation state of +1.

Teacher: The metallic properties of the elements of the boron subgroup are much less pronounced than those of the elements of the beryllium subgroup. Bor is a non-M. In the future, within the subgroup, with increasing nuclear charge M, the properties are enhanced. BUTl- already M, but not typical. Its hydroxide has amphoteric properties.

Of the M of the main subgroup of group III, aluminum is of the greatest importance, the properties of which we will study in detail. It is of interest to us because it is a transitional element.

Aluminum

Aluminum - chemical element III group 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 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, tinted red or blue color, represent gems- ruby ​​and sapphire. Currently, rubies are obtained artificially by alloying with alumina in electric oven. 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 number 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 for 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 and more electrolyzers.

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 industrial production alloy). 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. It is a 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 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.

Chemical element of group III of the periodical system of Mendeleev.

Latin name— Aluminium.

Designation— Al.

atomic number — 13.

Atomic mass — 26,98154.

Density- 2.6989 g / cm 3.

Melting temperature- 660 °С.

Simple, light, paramagnetic metal of light gray or silvery white color. It has high thermal and electrical conductivity, corrosion resistance. Distribution in the earth's crust - 8.8% by weight - it is the most common metal and the third most common chemical element.

It is used as a structural material in the construction of buildings, aircraft and shipbuilding, for the manufacture of conductive products in electrical engineering, chemical equipment, consumer goods, the production of other metals using aluminothermy, as a component of solid rocket fuel, pyrotechnic compositions, and the like.

Metallic aluminum was first obtained by the Danish physicist Hans Christian Oersted.

In nature, it occurs exclusively in the form of compounds, as it has a high chemical activity. Forms a strong chemical bond with oxygen. Due to the reactivity, it is very difficult to obtain metal from ore. Now the Hall-Héroult method is used, which requires high costs electricity.

Aluminum forms alloys with almost all metals. The most famous are duralimium (an alloy with copper and magnesium) and silumin (an alloy with silicon). Under normal conditions, aluminum is covered with a strong oxide film, therefore it does not react with classical oxidizing agents water (H 2 O), oxygen (O 2) and nitric acid (HNO 3). Due to this, it is practically not subject to corrosion, which ensured its demand in the industry.

The name comes from the Latin "alumen", which means "alum".

The use of aluminum in medicine

traditional medicine

The role of aluminum in the body is not fully understood. It is known that its presence stimulates the growth of bone tissue, the development of epithelium and connective tissues. Under its influence, the activity of digestive enzymes increases. Aluminum is related to the recovery and regeneration processes of the body.

Aluminum is considered a toxic element for human immunity, but nevertheless, it is part of the cells. At the same time, it has the form of positively charged ions (Al3 +), which affect the parathyroid glands. IN different types cells, a different amount of aluminum is observed, but it is known for sure that the cells of the liver, brain and bones accumulate it faster than others.

Medicines with aluminum have analgesic and enveloping effects, antacid and adsorbent actions. The latter means that when interacting with hydrochloric acid medicines can reduce the acidity of the stomach. Aluminum is also prescribed for external use: in the treatment of wounds, trophic ulcers, acute conjunctivitis.

The toxicity of aluminum is manifested in its replacement of magnesium in the active centers of a number of enzymes. Its competitive relationship with phosphorus, calcium and iron also plays a role.

With a lack of aluminum, weakness in the limbs is observed. But such a phenomenon in the modern world is almost impossible, since the metal comes with water, food and through polluted air.

With an excess of aluminum in the body, changes in the lungs, convulsions, anemia, disorientation in space, apathy, and memory loss begin.

Ayurveda

Aluminum is believed to be poisonous, so it should not be used for treatment. Just as you should not use aluminum utensils for preparing decoctions or storing herbs.

The use of aluminum in magic

Due to the difficulty of obtaining a pure element, the metal was used in magic on a par with, it was made from Jewelry. When the process of obtaining was simplified, the fashion for aluminum crafts immediately passed.

Protective Magic

Only aluminum foil is used, which has the properties of shielding energy flows, preventing them from spreading. Therefore, as a rule, objects are wrapped in it that can spread around them negative energy. Very often dubious magical gifts are wrapped in foil - wands, masks, daggers, especially those brought from Africa or Egypt.

They do the same with unknown objects thrown up, found in the yard or under the door. Instead of lifting it with your hands or through a cloth, it is better to cover it with foil, without touching the object itself.

Sometimes foil is used as a protective screen for amulets and talismans that are not currently needed, but may be needed in the future.

Aluminum in astrology

Zodiac sign: Capricorn.