Aluminum parsing element. Aluminum: chemical and physical properties

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

The table below provides a summary of most aluminum grades. The content of its main natural impurities - silicon and iron - is also indicated.

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.

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 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%.

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 corrosion penetration, but by a change in mechanical properties.

The iron content has the main influence on the corrosion properties of commercial aluminum. Thus, the corrosion rate in a 5% HCl solution for different grades is (in):

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 lower temperatures, the effect of steam is insignificant.

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.

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

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:

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.

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 (copper substitute 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 precious stones - 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, nepheline, mined on the Kola Peninsula, is a rich source of aluminum. 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. 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 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.

This light metal with a silvery-white tint is found almost everywhere in modern life. The physical and chemical properties of aluminum allow it to be widely used in industry. The most famous deposits are in Africa, South America, in the Caribbean region. In Russia, bauxite mining sites are located in the Urals. The world leaders in aluminum production are China, Russia, Canada, and the USA.

Al mining

In nature, this silvery metal, due to its high chemical activity, is found only in the form of compounds. The most well-known geological rocks containing aluminum are bauxite, alumina, corundum, and feldspars. Bauxite and alumina are of industrial importance, it is the deposits of these ores that make it possible to extract aluminum in its pure form.

Properties

The physical properties of aluminum make it easy to draw blanks of this metal into wire and roll into thin sheets. This metal is not durable; to increase this indicator during smelting, it is alloyed with various additives: copper, silicon, magnesium, manganese, zinc. For industrial purposes, another physical property of aluminum is important - this is its ability to quickly oxidize in air. The surface of an aluminum product in natural conditions is usually covered with a thin oxide film, which effectively protects the metal and prevents its corrosion. When this film is destroyed, the silvery metal is rapidly oxidized, while its temperature rises noticeably.

The internal structure of aluminum

The physical and chemical properties of aluminum largely depend on its internal structure. The crystal lattice of this element is a kind of face-centered cube.

This type of lattice is inherent in many metals, such as copper, bromine, silver, gold, cobalt and others. High thermal conductivity and the ability to conduct electricity have made this metal one of the most sought after in the world. The remaining physical properties of aluminum, the table of which is presented below, fully reveal its properties and show the scope of their application.

Alloying of aluminum

The physical properties of copper and aluminum are such that when a certain amount of copper is added to an aluminum alloy, its crystal lattice is bent, and the strength of the alloy itself increases. Alloying of light alloys is based on this property of Al to increase their strength and resistance to aggressive environments.

The explanation of the hardening process lies in the behavior of copper atoms in the aluminum crystal lattice. Cu particles tend to fall out of the Al crystal lattice and are grouped in its special areas.

Where copper atoms form clusters, a CuAl 2 mixed-type crystal lattice is formed, in which silver metal particles are simultaneously part of both the general aluminum crystal lattice and the composition of the CuAl 2 mixed-type lattice. The forces of internal bonds in a distorted lattice are much greater than in normal. This means that the strength of the newly formed substance is much higher.

Chemical properties

The interaction of aluminum with dilute sulfuric and hydrochloric acid is known. When heated, this metal dissolves easily in them. Cold concentrated or highly dilute nitric acid does not dissolve this element. Aqueous solutions of alkalis actively affect the substance, during the reaction forming aluminates - salts, which contain aluminum ions. For example:

Al 2 O 3 + 3H2O + 2NaOH \u003d 2Na

The resulting compound is called sodium tetrahydroxoaluminate.

A thin film on the surface of aluminum products protects this metal not only from air, but also from water. If this thin barrier is removed, the element will violently interact with water, releasing hydrogen from it.

2AL + 6H 2 O \u003d 2 AL (OH) 3 + 3H 2

The resulting substance is called aluminum hydroxide.

AL (OH) 3 reacts with alkali, forming hydroxoaluminate crystals:

Al(OH) 2 +NaOH=2Na

If this chemical equation is added to the previous one, we get the formula for dissolving an element in an alkaline solution.

Al (OH) 3 + 2NaOH + 6H 2 O \u003d 2Na + 3H 2

Burning aluminum

The physical properties of aluminum allow it to react with oxygen. If the powder of this metal or aluminum foil is heated, it flares up and burns with a blinding white flame. At the end of the reaction, aluminum oxide Al 2 O 3 is formed.

Alumina

The resulting aluminum oxide has the geological name alumina. Under natural conditions, it occurs in the form of corundum - solid transparent crystals. Corundum has a high hardness, its index is 9 on the solids scale. Corundum itself is colorless, but various impurities can color it red and blue, so precious stones are obtained, which are called rubies and sapphires in jewelry.

The physical properties of aluminum oxide make it possible to grow these gemstones under artificial conditions. Technical gemstones are used not only for jewelry, they are used in precision instrumentation, for making watches and other things. Artificial ruby ​​crystals are also widely used in laser devices.

A fine-grained variety of corundum with a large amount of impurities, deposited on a special surface, is known to everyone as emery. The physical properties of aluminum oxide explain the high abrasive properties of corundum, as well as its hardness and resistance to friction.

aluminum hydroxide

Al 2 (OH) 3 is a typical amphoteric hydroxide. In combination with an acid, this substance forms a salt containing positively charged aluminum ions; in alkalis, it forms aluminates. Amphotericity of a substance is manifested in the fact that it can behave both as an acid and as an alkali. This compound can exist in both jelly and solid form.

It practically does not dissolve in water, but reacts with most active acids and alkalis. The physical properties of aluminum hydroxide are used in medicine, it is a popular and safe means of reducing acidity in the body, it is used for gastritis, duodenitis, ulcers. In industry, Al 2 (OH) 3 is used as an adsorbent, it perfectly purifies water and precipitates harmful elements dissolved in it.

Industrial use

Aluminum was discovered in 1825. At first, this metal was valued above gold and silver. This was due to the difficulty of extracting it from the ore. The physical properties of aluminum and its ability to quickly form a protective film on its surface made it difficult to study this element. Only at the end of the 19th century was a convenient method of melting a pure element suitable for use on an industrial scale discovered.

Lightness and ability to resist corrosion are the unique physical properties of aluminum. Alloys of this silvery metal are used in rocket technology, in auto, ship, aircraft and instrument making, in the production of cutlery and utensils.

As a pure metal, Al is used in the manufacture of parts for chemical equipment, electrical wires and capacitors. The physical properties of aluminum are such that its electrical conductivity is not as high as that of copper, but this disadvantage is compensated by the lightness of the metal in question, which makes it possible to make aluminum wires thicker. So, with the same electrical conductivity, an aluminum wire weighs half as much as a copper wire.

Equally important is the use of Al in the aluminizing process. This is the name of the reaction of saturation of the surface of a cast-iron or steel product with aluminum in order to protect the base metal from corrosion when heated.

At present, the explored reserves of aluminum ores are quite comparable to the needs of people in this silvery metal. The physical properties of aluminum can present many more surprises to its researchers, and the scope of this metal is much wider than one might imagine.

DEFINITION

Aluminum located in the third period, group III of the main (A) subgroup of the Periodic Table. This is the first p-element of the 3rd period.

Metal. Designation - Al. Ordinal number - 13. Relative atomic mass - 26.981 a.m.u.

The electronic structure of the aluminum atom

The aluminum atom consists of a positively charged nucleus (+13), inside which there are 13 protons and 14 neutrons. The nucleus is surrounded by three shells, along which 13 electrons move.

Rice. 1. Schematic representation of the structure of the aluminum atom.

The distribution of electrons in orbitals is as follows:

13Al) 2) 8) 3 ;

1s 2 2s 2 2p 6 3s 2 3p 1 .

There are three electrons on the outer energy level of aluminum, all electrons of the 3rd sublevel. The energy diagram takes the following form:

Theoretically, an excited state is possible for an aluminum atom due to the presence of a vacant 3 d-orbitals. However, electron depairing 3 s- sublevel does not actually occur.

Examples of problem solving

EXAMPLE 1

Properties 13 Al.

*The configuration of the external electronic levels of the element atom is given. 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 the protective film is removed chemically (for example, with an alkali solution), then the metal begins to interact vigorously with water, releasing 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:

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.