Chemical properties of al. What is aluminum

aluminum oxide(alumina) A1 2 O 3, colorless. crystals; m.p. 2044°C; t. kip. 3530 °С. The only stable up to 2044 ° C crystalline. modification of aluminum oxide-A1 2 O 3 (corundum): rhombohedral lattice, a \u003d 0.512 nm, \u003d 55.25 ° (for hexagonal installation a \u003d 0.475 nm, c \u003d 1.299 nm, space group D 6 3d, z \u003d 2); dense 3.99 g / cm 3; N ° pl 111.4 kJ / mol; temperature dependence equations: heat capacity C ° p \u003d \u003d 114.4 + 12.9 * 10 -3 T - 34.3 * 10 5 T 2 JDmol * K) (298T 1800 K), vapor pressure Igp (Pa) \u003d -54800/7+1.68 (up to ~ 3500 K); temperature coefficient. linear expansion (7.2-8.6) * 10 -6 K -1 (300T1200 K); thermal conductivity sintered at 730°C sample 0.35 W/(mol*K); Mohs hardness 9; the refractive index for an ordinary beam is n 0 1.765, for an extraordinary beam it is 1.759.

Aluminum oxide (Al2O3) has an exceptional set of properties, such as:

• High hardness
• Good thermal conductivity
• Excellent corrosion resistance
• low density
• Strength retention over a wide temperature range
• electrical insulating properties
• Low cost compared to other ceramic materials

All these combinations make the material indispensable in the manufacture of corrosion-resistant, wear-resistant, electrically insulating and heat-resistant products for various industries.

Main applications:

• Lining of mills, hydrocyclones, concrete mixers, extruders, conveyors, pipes and other wear equipment
• Mechanical seal rings
• Dies, wires, guides
• Plain bearings, shafts and lining of wet parts of chemical pumps
• Grinding bodies
• Parts of papermaking equipment
• Burners
• Extruder nozzles (cores)
• crucibles
• Elements of valves and valves
• Nozzles for argon-arc welding machines
• electrical insulators

There are several modifications of aluminum oxide, depending on the content of the main phase and impurities, which are distinguished by strength and chemical resistance.

aluminum hydroxide

Aluminum hydroxide Al(OH) 3 is a colorless solid, insoluble in water, which is part of many bauxites. Exists in four polymorphic modifications. In the cold, α-Al (OH) 3 - bayerite is formed, and when deposited from a hot solution γ-Al (OH) 3 - gibbsite (hydargilite), both crystallize in a monoclinic syngony, have a layered structure, the layers consist of octahedrons, between the layers acts hydrogen bond. There is also triclinic gibbsite γ'-Al(OH) 3 , triclinic nordstrandite β-Al(OH) 3 and two modifications of AlOOH oxohydroxide - orthorhombic boehmite and diaspore. Amorphous aluminum hydroxide has a variable composition Al 2 O 3 nH 2 O. When heated above 180°C, it decomposes.

Chemical properties

Aluminum hydroxide is a typical amphoteric compound, freshly obtained hydroxide dissolves in acids and alkalis:

2Al(OH) 3 + 6HCl = 2AlCl 3 + 6H 2 O

Al(OH) 3 + NaOH + 2H 2 O = Na.

When heated, it decomposes, the dehydration process is rather complicated and can be schematically represented as follows:

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

2AlOOH \u003d Al 2 O 3 + H 2 O.

aluminum hydroxide - Chemical substance, which is a compound of aluminum oxide with water. It can be in liquid and solid states. Liquid hydroxide is a jelly-like transparent substance that is very poorly soluble in water. Solid hydroxide is a white crystalline substance that has passive chemical properties and does not react with almost any other element or compound.

aluminum chloride

Sublimates at 183°C under normal pressure (melts at 192.6°C under pressure). It is highly soluble in water (44.38 g in 100 g H 2 O at 25 ° C); due to hydrolysis, smokes in moist air, releasing HCl. Crystal hydrate AlCl 3 6H 2 O precipitates from aqueous solutions - yellowish-white deliquescent crystals. It is highly soluble in many organic compounds (in ethanol - 100 g in 100 g of alcohol at 25 ° C, in acetone, dichloroethane, ethylene glycol, nitrobenzene, carbon tetrachloride and etc.); however, it is practically insoluble in benzene and toluene.

aluminum sulfate

Aluminum sulfate is a white salt with a gray, blue or pink tint, under normal conditions exists in the form of crystalline Al 2 (SO 4) 3 18H 2 O - colorless crystals. When heated, it loses water without melting; when ignited, it decomposes into Al 2 O 3 and SO 3 and O 2. It dissolves well in water. Technical aluminum sulfate can be obtained by treating bauxite or clay with sulfuric acid, and a pure product by dissolving Al (OH) 3 in hot concentrated H 2 SO 4.

Aluminum sulfate is used as a coagulant for water purification for household and industrial purposes and for use in paper, textile, leather and other industries.

Used as food additive E-520

aluminum carbide

Aluminum carbide is obtained by direct reaction of aluminum with carbon in an arc furnace.

Iron with aluminum

Alni- a group of hard magnetic (high-coercivity) iron (Fe) - nickel (Ni) - aluminum (Al) alloys.

Alloying of alni alloys improves their magnetic characteristics, copper alloying is used (for example, an alloy of 24% nickel, 4% copper, 13% aluminum and 59% iron), cobalt (alnico and magnico alloys). The impurity of carbon reduces the magnetic properties of the alloy; its content should not exceed 0.03%.

Alni alloys are characterized by high hardness and brittleness, so casting is used to make permanent magnets from them.

sodium aluminate

sodium aluminate- an inorganic compound, a complex oxide of sodium and aluminum with the formula NaAlO 2, a white amorphous substance, reacts with water.

Orthoaluminic acid

Alumina "you, salts of aluminum acids: orthoaluminum H3 AlO3, metaaluminum HAlO2, etc. Aluminates of the general formula R are most common in nature, where R is Mg, Ca, Be, Zn, etc. Among them, there are: 1) octahedral varieties, so-called. spinels - Mg (noble spinel), Zn (ganite or zinc spinel), etc. and 2) rhombic varieties - Be (chrysoberyl), etc. (in the formulas minerals atoms that make up a structural group are usually enclosed in square brackets).

Alkali metal aluminates are obtained by reacting Al or Al (OH) 3 with caustic alkalis: Al (OH) 3 + KOH \u003d KAlO2 + 2H2 O. Of these, a sodium luminates NaAlO2, formed during the alkaline process of obtaining alumina , used in the textile industry as a stain. Aluminates of alkaline earth metals are obtained by fusing their oxides with Al2 O3; of these, calcium aluminates CaAl2 O4 serves as the main component of fast-hardening aluminous cement.

Aluminates of rare earth elements have gained practical importance. They are obtained by joint dissolution of oxides of rare earth elements R2 03 and Al(NO3)3 in nitric acid, evaporation of the resulting solution until the salts crystallize and calcination of the latter at 1000-1100°C. The formation of aluminates is controlled by X-ray diffraction as well as chemical phase analysis. The latter is based on the different solubility of the initial oxides and the compound formed (A., for example, are stable in acetic acid, while the oxides of rare earth elements dissolve well in it). Aluminates of rare earth elements have a high chemical resistance, depending on the temperatures of their pre-calcination; in water are steady at high temperatures (to 350 °C) under pressure. The best solvent for rare earth aluminates is hydrochloric acid. Rare earth aluminates are characterized by high refractoriness and characteristic coloration. Their densities range from 6500 to 7500 kg /m3.

Aluminum - destruction of metal under the influence of the environment.

For the reaction Al 3+ + 3e → Al, the standard electrode potential of aluminum is -1.66 V.

The melting point of aluminum is 660 °C.

The density of aluminum is 2.6989 g / cm 3 (under normal conditions).

Aluminum, although it is an active metal, has fairly good corrosion properties. This can be explained by the ability to be passivated in many aggressive environments.

The corrosion resistance of aluminum depends on many factors: the purity of the metal, the corrosive environment, the concentration of aggressive impurities in the environment, temperature, etc. The pH of solutions has a strong influence. Aluminum oxide on the metal surface is formed only in the pH range from 3 to 9!

Its purity greatly affects the corrosion resistance of Al. For the manufacture of chemical aggregates, equipment, only high-purity metal (without impurities) is used, for example, aluminum grades AB1 and AB2.

Corrosion of aluminum is not observed only in those environments where a protective oxide film is formed on the metal surface.

When heated, aluminum can react with some non-metals:

2Al + N 2 → 2AlN - interaction of aluminum and nitrogen with the formation of aluminum nitride;

4Al + 3С → Al 4 С 3 - reaction of interaction of aluminum with carbon with the formation of aluminum carbide;

2Al + 3S → Al 2 S 3 - the interaction of aluminum and sulfur with the formation of aluminum sulfide.

Corrosion of aluminum in air (atmospheric corrosion of aluminum)

Aluminum, when interacting with air, passes into a passive state. When pure metal comes into contact with air, a thin protective film of aluminum oxide instantly appears on the aluminum surface. Further, the growth of the film slows down. The formula of aluminum oxide is Al 2 O 3 or Al 2 O 3 H 2 O.

The reaction of interaction of aluminum with oxygen:

4Al + 3O 2 → 2Al 2 O 3 .

The thickness of this oxide film is between 5 and 100 nm (depending on operating conditions). Aluminum oxide has good adhesion to the surface, satisfies the condition of the continuity of oxide films. When stored in a warehouse, the thickness of aluminum oxide on the metal surface is about 0.01 - 0.02 microns. When interacting with dry oxygen - 0.02 - 0.04 microns. During heat treatment of aluminum, the thickness of the oxide film can reach 0.1 µm.

Aluminum is quite resistant both in clean rural air and in an industrial atmosphere (containing sulfur vapor, hydrogen sulfide, gaseous ammonia, dry hydrogen chloride, etc.). Because aluminum corrosion in gaseous media is not affected by sulfur compounds - it is used for the manufacture of sour oil processing plants, rubber vulcanization devices.

Corrosion of aluminum in water

Corrosion of aluminum is almost not observed when interacting with clean fresh, distilled water. Increasing the temperature to 180 °C has no particular effect. Hot water vapor also has no effect on aluminum corrosion. If a little alkali is added to water, even at room temperature, the rate of aluminum corrosion in such an environment will slightly increase.

The interaction of pure aluminum (not coated with an oxide film) with water can be described using the reaction equation:

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

When interacting with sea water, pure aluminum begins to corrode, because. sensitive to dissolved salts. To exploit aluminum in sea water, a small amount of magnesium and silicon is introduced into its composition. Corrosion resistance of aluminum and its alloys, when exposed to sea ​​water, is significantly reduced if copper is included in the composition of the metal.

Corrosion of aluminum in acids

As the purity of aluminum increases, its resistance to acids increases.

Corrosion of aluminum in sulfuric acid

For aluminum and its alloys, sulfuric acid (it has oxidizing properties) of medium concentrations is very dangerous. The reaction with dilute sulfuric acid is described by the equation:

2Al + 3H 2 SO 4 (razb) → Al 2 (SO 4) 3 + 3H 2.

Concentrated cold sulfuric acid has no effect. And when heated, aluminum corrodes:

2Al + 6H 2 SO 4 (conc) → Al 2 (SO 4) 3 + 3SO 2 + 6H 2 O.

This forms a soluble salt - aluminum sulfate.

Al is stable in oleum (fuming sulfuric acid) at temperatures up to 200 °C. Due to this, it is used for the production of chlorosulfonic acid (HSO 3 Cl) and oleum.

Corrosion of aluminum in hydrochloric acid

In hydrochloric acid, aluminum or its alloys quickly dissolve (especially with increasing temperature). Corrosion equation:

2Al + 6HCl → 2AlCl 3 + 3H 2 .

Solutions of hydrobromic (HBr), hydrofluoric (HF) acids act similarly.

Corrosion of aluminum in nitric acid

A concentrated solution of nitric acid has high oxidizing properties. Aluminum in nitric acid at normal temperature is exceptionally stable (higher resistance than stainless steel 12X18H9). It is even used to produce concentrated nitric acid by direct synthesis.

When heated, the corrosion of aluminum in nitric acid proceeds according to the reaction:

Al + 6HNO 3 (conc) → Al(NO 3) 3 + 3NO 2 + 3H 2 O.

Corrosion of aluminum in acetic acid

Aluminum has a sufficiently high resistance to acetic acid of any concentration, but only if the temperature does not exceed 65 ° C. It is used for the production of formaldehyde and acetic acid. At higher temperatures, aluminum dissolves (with the exception of acid concentrations of 98 - 99.8%).

In bromine, weak solutions of chromic (up to 10%), phosphoric (up to 1%) acids at room temperature, aluminum is stable.

Citric, butyric, malic, tartaric, propionic acids, wine, fruit juices have a weak effect on aluminum and its alloys.

Oxalic, formic, organochlorine acids destroy the metal.

The corrosion resistance of aluminum is greatly affected by vaporous and droplet-liquid mercury. After a short contact, the metal and its alloys corrode intensively, forming amalgams.

Corrosion of aluminum in alkalis

Alkalis easily dissolve the protective oxide film on the surface of aluminum, it begins to react with water, as a result of which the metal dissolves with the release of hydrogen (corrosion of aluminum with hydrogen depolarization).

2Al + 2NaOH + 6H 2 O → 2Na + 3H 2;

2(NaOH H 2 O) + 2Al → 2NaAlO 2 + 3H 2.

aluminates are formed.

Also, the oxide film is destroyed by salts of mercury, copper and chloride ions.

Aluminum is an element with the atomic number 13 and a relative atomic mass of 26.98154. It is in the III period, III group, the main subgroup. Electronic configuration: 1s 2 2s 2 2p 6 3s 2 3p 1 3d 0 . The stable oxidation state of aluminum is "+3". The resulting cation has a noble gas shell, which contributes to its stability, but the ratio of charge to radius, that is, the charge concentration, is quite high, which increases the energy of the cation. This feature leads to the fact that aluminum, along with ionic compounds, forms a number of covalent compounds, and its cation undergoes significant hydrolysis in solution.

Aluminum can exhibit valency I only at temperatures above 1500 ° C. Al 2 O and AlCl are known.

In terms of physical properties, aluminum is a typical metal with high thermal and electrical conductivity, second only to silver and copper. The ionization potential of aluminum is not very high, so one could expect a high chemical activity from it, but it is significantly reduced due to the fact that the metal is passivated in air due to the formation of a strong oxide film on its surface. If the metal is activated: a) mechanically remove the film, b) amalgamate (bring into interaction with mercury), c) use a powder, then such a metal becomes so reactive that it even interacts with moisture and oxygen in the air, while being destroyed in accordance with the process:

4(Al,Hg) + 3O 2 + 6H 2 O = 4Al(OH) 3 + (Hg)

Interaction with simple substances.

1. Powdered aluminum reacts with strong heating with oxygen. These conditions are necessary because of passivation, and the reaction itself of the formation of aluminum oxide is highly exothermic - 1676 kJ/mol of heat is released.

2. With chlorine and bromine reacts under standard conditions, is even capable of igniting in their environment. Only does not respond with fluorine because aluminum fluoride, like oxide, forms a protective salt film on the metal surface. With iodine reacts when heated and in the presence of water as a catalyst.

3. With sulfur reacts upon fusion to give aluminum sulfide of the composition Al 2 S 3 .

4. It also reacts with phosphorus when heated to form a phosphide: AlP.

5. Directly with hydrogen aluminum does not interact.

6. With nitrogen reacts at 800 o C, giving aluminum nitride (AlN). It should be said that the combustion of aluminum in air occurs at about these temperatures, so the products of combustion (taking into account the composition of the air) are both oxide and nitride at the same time.

7. With carbon aluminum interacts at an even higher temperature: 2000 o C. Aluminum carbide of the composition Al 4 C 3 belongs to methanides, it does not contain C-C connections, and methane is released during hydrolysis: Al 4 C 3 + 12H 2 O \u003d 4Al (OH) 3 + 3CH 4

Interaction with complex substances

1. With water activated (devoid of a protective film) aluminum actively interacts with hydrogen evolution: 2Al (act.) + 6H 2 O \u003d 2Al (OH) 3 + 3H 2 Aluminum hydroxide is obtained in the form of a white loose powder, the absence of a film does not prevent the reaction from going to completion.

2. Interaction with acids: a) Aluminum actively interacts with non-oxidizing acids in accordance with the equation: 2Al + 6H 3 O + + 6H 2 O = 2 3+ + 3H 2,

b) With oxidizing acids, the interaction occurs with the following features. Concentrated nitric and sulfuric acids, as well as very dilute nitric acid, passivate aluminum (rapid surface oxidation leads to the formation of an oxide film) in the cold. When heated, the film is broken, and the reaction proceeds, but only products of their minimal reduction are released from concentrated acids when heated: 2Al + 6H 2 SO 4 (conc) = Al 2 (SO 4) 3 + 3SO 2 6H 2 O Al + 6HNO 3 ( conc) \u003d Al (NO 3) 3 + 3NO 2 + 3H 2 O With moderately dilute nitric acid, depending on the reaction conditions, NO, N 2 O, N 2, NH 4 + can be obtained.

3. Interaction with alkalis. Aluminum is an amphoteric element (according to its chemical properties), because has a sufficiently large electronegativity for metals - 1.61. Therefore, it dissolves quite easily in alkali solutions with the formation of hydroxo complexes and hydrogen. The composition of the hydroxocomplex depends on the ratio of reagents: 2Al + 2NaOH + 6H 2 O = 2Na + 3H 2 2Al + 6NaOH + 6H 2 O = 2Na 3 + 3H 2 The ratio of aluminum and hydrogen is determined by the electronic balance of the redox reaction occurring between them and the ratio of reagents does not depend.

4. Low ionization potential and high affinity for oxygen (great oxide stability) lead to the fact that aluminum actively interacts with many metal oxides restoring them. The reactions take place at initial heating with further heat release, so that the temperature rises to 1200 o - 3000 o C. A mixture of 75% aluminum powder and 25% (by mass) Fe 3 O 4 is called "thermite". Previously, the combustion reaction of this mixture was used to weld rails. The recovery of metals from oxides using aluminum is called aluminothermy and is used in industry as a method for obtaining metals such as manganese, chromium, vanadium, tungsten, and ferroalloys.

5. With salt solutions aluminum interacts in two different ways. 1. If, as a result of hydrolysis, the salt solution has an acidic or alkaline environment, hydrogen is released (with acidic solutions, the reaction proceeds only with significant heating, since the protective oxide film dissolves better in alkalis than in acids). 2Al + 6KHSO 4 + (H 2 O) \u003d Al 2 (SO 4) 3 + 3K 2 SO 4 + 3H 2 2Al + 2K 2 CO 3 + 8H 2 O \u003d 2K + 2KHCO 3 + 3H 2. 2. Aluminum can displace from the composition of the salt metals that are in the stress row to the right than it, i.e. will actually be oxidized by the cations of these metals. Due to the oxide film, this reaction does not always take place. For example, chloride anions are capable of destroying the film, and the reaction 2Al + 3FeCl 2 = 2AlCl 3 + 3Fe takes place, while a similar reaction with sulfates does not proceed at room temperature. With activated aluminum, any interaction that does not contradict general rule, will go.

aluminum compounds.

1. Oxide (Al 2 O 3). It is known in the form of several modifications, most of which are very durable and chemically inert. Modification α-Al 2 O 3 occurs in nature in the form of the mineral corundum. In the crystal lattice of this compound, aluminum cations are sometimes partially replaced by cations of other metals, which gives the mineral its color. The admixture of Cr(III) gives a red color, such corundum is already a ruby ​​gemstone. An admixture of Ti(III) and Fe(III) gives a blue sapphire. The amorphous modification is chemically active. Aluminum oxide is a typical amphoteric oxide that reacts both with acids and acidic oxides, and with alkalis and basic oxides, and it is preferable with alkalis. The reaction products in solution and in the solid phase during fusion differ: Na 2 O + Al 2 O 3 \u003d 2NaAlO 2 (fusion) - sodium metaaluminate, 6NaOH + Al 2 O 3 \u003d 2Na 3 AlO 3 + 3H 2 O (fusion) - orthoaluminate sodium, Al 2 O 3 + 3CrO 3 = Al 2 (CrO 4) 3 (fusion) - aluminum chromate. In addition to oxides and solid alkalis, during fusion, aluminum reacts with salts formed by volatile acid oxides, displacing them from the composition of the salt: K 2 CO 3 + Al 2 O 3 \u003d 2KAlO 2 + CO 2 Reactions in solution: Al 2 O 3 + 6HCl \u003d 2 3+ + 6Cl 1- + 3H 2 O Al 2 O 3 +2 NaOH + 3H 2 O \u003d 2 Na - sodium tetrahydroxoaluminate. Tetrahydroxoaluminate anion is actually tetrahydroxodiaqua anion 1- , because a coordination number of 6 is preferred for aluminum. With an excess of alkali, hexahydroxoaluminate is formed: Al 2 O 3 + 6NaOH + 3H 2 O \u003d 2Na 3. In addition to acids and alkalis, reactions with acidic salts can be expected: 6KHSO 4 + Al 2 O 3 \u003d 3K 2 SO 4 + Al 2 (SO 4) 3 + 3H 2 O.

3. Aluminum hydroxides. Two aluminum hydroxides are known - metahydroxide - AlO (OH) and ortho hydroxide - Al (OH) 3. Both of them do not dissolve in water, but are also amphoteric, therefore they dissolve in solutions of acids and alkalis, as well as salts that have an acidic or alkaline environment as a result of hydrolysis. When fused, the hydroxides react similarly to the oxide. Like all insoluble bases, aluminum hydroxides decompose when heated: 2Al (OH) 3 \u003d Al 2 O 3 + 3H 2 O. Dissolving in alkaline solutions, aluminum hydroxides do not dissolve in aqueous ammonia, so they can be precipitated with ammonia from a soluble salt: Al (NO 3) 3 + 3NH 3 + 2H 2 O \u003d AlO (OH) ↓ + 3NH 4 NO 3, this reaction produces exactly metahydroxide. It is difficult to precipitate hydroxide with alkalis, because the resulting precipitate dissolves easily, and the overall reaction is: AlCl 3 +4 NaOH = Na + 3NaCl

4. aluminum salts. Almost all aluminum salts are highly soluble in water. AlPO 4 phosphate and AlF 3 fluoride are insoluble. Because the aluminum cation has a high charge concentration, its aqua complex acquires the properties of a cationic acid: 3+ + H 2 O = H 3 O + + 2+ , i.e. aluminum salts undergo strong cationic hydrolysis. In the case of salts of weak acids, hydrolysis becomes irreversible due to the mutual enhancement of hydrolysis by the cation and anion. In solution, they are completely decomposed by water or cannot be obtained by the exchange reaction of carbonate, sulfite, sulfide and aluminum silicate: Al 2 S 3 + 6H 2 O \u003d 2Al (OH) 3 ↓ + 3H 2 S 2Al (NO 3) 3 + 3K 2 CO 3 + 3H 2 O \u003d 2Al (OH) 3 ↓ + 3CO 2 + 6KNO 3. For some salts, hydrolysis becomes irreversible when heated. Wet aluminum acetate decomposes when heated according to the equation: 2Al(OOCCH 3) 3 + 3H 2 O = Al 2 O 3 + 6CH 3 COOH \u003d Al (OH) 3 ↓ + 3HCl. Of the aluminum halides, only fluoride is an ionic compound, the rest of the halides are covalent compounds, their melting points are significantly lower than that of fluoride, aluminum chloride is able to sublimate. At a very high temperature, the vapor contains single molecules of aluminum halides, which have a flat triangular structure due to the sp 2 hybridization of the atomic orbitals of the central atom. The ground state of these compounds in vapors and in some organic solvents is dimers, for example, Al 2 Cl 6 . Aluminum halides are strong Lewis acids because have a vacant atomic orbital. Dissolution in water, therefore, occurs with the release a large number warmth. An interesting class of aluminum compounds (as well as other trivalent metals) are alums - 12-aqueous double sulfates M I M III (SO 4) 2, which, when dissolved, like all double salts, give a mixture of the corresponding cations and anions.

5. complex compounds. Let us consider aluminum hydroxocomplexes. These are salts in which the complex particle is an anion. All salts are soluble. Destroyed by interaction with acids. In this case, strong acids dissolve the resulting orthohydroxide, and weak or corresponding acid oxides (H 2 S, CO 2, SO 2) precipitate it: K + 4HCl \u003d KCl + AlCl 3 + 4H 2 O K + CO 2 \u003d Al (OH) 3 ↓ + KHCO3

When calcined, hydroxoaluminates turn into ortho- or metaaluminates, losing water.

Iron

Element with atomic number 26, with a relative atomic mass of 55.847. It belongs to the 3d-family of elements, has an electronic configuration: 3d 6 4s 2 and is in the IV period, VIII group, side subgroup in the periodic system. In compounds, iron predominantly exhibits oxidation states +2 and +3. The Fe 3+ ion has a half-filled d-electron shell, 3d 5 , which gives it additional stability. The oxidation states +4, +6, +8 are much more difficult to achieve.

In terms of physical properties, iron is a silvery-white, shiny, relatively soft, malleable, easily magnetized and demagnetized metal. Melting point 1539 o C. It has several allotropic modifications that differ in the type of crystal lattice.

Properties a simple substance.

1. When burning in air, it forms a mixed oxide Fe 3 O 4, and when interacting with pure oxygen - Fe 2 O 3. Powdered iron is pyrophoric - ignites spontaneously in air.

2. Fluorine, chlorine and bromine easily react with iron, oxidizing it to Fe 3+. FeJ 2 is formed with iodine, since the trivalent iron cation oxidizes the iodide anion, and therefore, the FeJ 3 compound does not exist.

3. For a similar reason, there is no Fe 2 S 3 compound, and the interaction of iron and sulfur at the melting point of sulfur leads to the FeS compound. With an excess of sulfur, pyrite is obtained - iron (II) disulfide - FeS 2. Non-stoichiometric compounds are also formed.

4. With the rest of the non-metals, iron reacts with strong heating, forming solid solutions or metal-like compounds. You can give a reaction that takes place at 500 o C: 3Fe + C \u003d Fe 3 C. This combination of iron and carbon is called cementite.

5. Iron forms alloys with many metals.

6. In air at room temperature, iron is covered with an oxide film, so it does not interact with water. Interaction with superheated steam gives the following products: 3Fe + 4H 2 O (steam) = Fe 3 O 4 + 4H 2 . In the presence of oxygen, iron interacts even with air moisture: 4Fe + 3O 2 + 6H 2 O \u003d 4Fe (OH) 3. The above equation reflects the rusting process, which is subjected to up to 10% of metal products per year.

7. Since iron is in the series of voltage to hydrogen, it easily reacts with non-oxidizing acids, but is oxidized only to Fe 2+.

8. Concentrated nitric and sulfuric acids passivate iron, but when heated, the reaction occurs. Dilute nitric acid also reacts at room temperature. With all oxidizing acids, iron gives iron (III) salts (according to some reports, with dilute nitric acid, the formation of iron (II) nitrate is possible), and reduces HNO 3 (dilute) to NO, N 2 O, N 2, NH 4 + depending on the conditions, and HNO 3 (conc.) - to NO 2 due to the heating that is necessary for the reaction to proceed.

9. Iron is able to react with concentrated (50%) alkalis when heated: Fe + 2KOH + 2H 2 O = K 2 + H 2

10. Reacting with solutions of salts of less active metals, iron removes these metals from the composition of the salt, turning into a divalent cation: CuCl 2 + Fe = FeCl 2 + Cu.

Properties of iron compounds.

Fe2+ The charge-to-radius ratio of this cation is close to that of Mg 2+ , so the chemical behavior of the oxide, hydroxide, and ferrous salts is similar to that of the corresponding magnesium compounds. In an aqueous solution, the ferrous cation forms a pale green aquacomplex 2+. This cation is easily oxidized even directly in solution by atmospheric oxygen. The solution of FeCl 2 contains complex particles 0 . The charge concentration of such a cation is low, so the hydrolysis of salts is moderate.

1. FeO - basic oxide, black, insoluble in water. Easily soluble in acids. When heated above 500 0 C, it disproportionates: 4FeO \u003d Fe + Fe 3 O 4. It can be obtained by careful calcination of the corresponding hydroxide, carbonate and oxalate, while thermal decomposition of other Fe 2+ salts leads to the formation of ferric oxide: FeC 2 O 4 \u003d FeO + CO + CO 2, but 2 FeSO 4 \u003d Fe 2 O 3 + SO 2 + SO 3 4Fe (NO 3) 2 = 2Fe 2 O 3 + 8NO 2 + O 2 Iron (II) oxide itself can act as an oxidizing agent, for example, when heated, the reaction occurs: 3FeO + 2NH 3 = 3Fe + N 2 +3H2O

2. Fe (OH) 2 - iron (II) hydroxide - an insoluble base. Reacts with acids. Acid-base interaction and oxidation to ferric iron occur simultaneously with oxidizing acids: 2Fe (OH) 2 + 4H 2 SO 4 (conc) \u003d Fe 2 (SO 4) 3 + SO 2 + 4H 2 O. Can be obtained by exchange soluble salt reactions. This is a white compound, which first turns green in air due to interaction with air moisture, and then turns brown due to oxidation with atmospheric oxygen: 4Fe (OH) 2 + 2H 2 O + O 2 \u003d 4Fe (OH) 3.

3. Salt. As already mentioned, most Fe(II) salts are slowly oxidized in air or in solution. The most resistant to oxidation is Mohr's salt - double iron (II) and ammonium sulfate: (NH 4) 2 Fe (SO 4) 2. 6H 2 O. The Fe 2+ cation is easily oxidized to Fe 3+, so most oxidizing agents, in particular oxidizing acids, oxidize ferrous salts. When iron sulfide and disulfide are burned, iron (III) oxide and sulfur oxide (IV) are obtained: 4FeS 2 + 11O 2 = 2Fe 2 O 3 + 8SO 2 Iron (II) sulfide also dissolves in strong acids: FeS + 2HCl = FeCl 2 + 2H 2 S Iron (II) carbonate is insoluble, while bicarbonate dissolves in water.

Fe3+ The ratio of charge to radius this cation corresponds to the aluminum cation , therefore, the properties of iron(III) cation compounds are similar to those of the corresponding aluminum compounds.

Fe 2 O 3 - hematite, amphoteric oxide, in which basic properties predominate. Amphotericity manifests itself in the possibility of fusion with solid alkalis and alkali metal carbonates: Fe 2 O 3 + 2NaOH \u003d H 2 O + 2NaFeO 2 - yellow or red, Fe 2 O 3 + Na 2 CO 3 \u003d 2NaFeO 2 + CO 2. Ferrates (II) are decomposed by water with the release of Fe 2 O 3 . nH2O.

Fe 3 O 4- magnetite, a black substance, which can be considered either as a mixed oxide - FeO. Fe 2 O 3, or as iron (II) oxometaferrate (III): Fe (FeO 2) 2. When interacting with acids, it gives a mixture of salts: Fe 3 O 4 + 8HCl \u003d FeCl 2 + 2FeCl 3 + 4H 2 O.

Fe (OH) 3 or FeO (OH) - red-brown gelatinous precipitate, amphoteric hydroxide. In addition to interactions with acids, it reacts with a hot concentrated solution of alkali and alloys with solid alkalis and carbonates: Fe (OH) 3 + 3KOH \u003d K 3.

Salt. Most ferric salts are soluble. Like aluminum salts, they undergo strong cation hydrolysis, which in the presence of anions of weak and unstable or insoluble acids can become irreversible: 2FeCl 3 + 3Na 2 CO 3 + 3H 2 O \u003d 2Fe (OH) 3 + 3CO 2 + 6NaCl. When a solution of iron (III) chloride is boiled, hydrolysis can also be made irreversible, because the solubility of hydrogen chloride, like any gas, decreases when heated and it leaves the reaction sphere: FeCl 3 + 3H 2 O \u003d Fe (OH) 3 + 3HCl (when heated).

The oxidizing ability of this cation is very high, especially in relation to the transformation into the Fe 2+ cation: Fe 3+ + ē \u003d Fe 2+ φ o \u003d 0.77v. As a result:

a) solutions of ferric salts oxidize all metals up to copper: 2Fe (NO 3) 3 + Cu \u003d 2Fe (NO 3) 2 + Cu (NO 3) 2,

b) exchange reactions with salts containing easily oxidized anions take place simultaneously with their oxidation: 2FeCl 3 + 2KJ = FeCl 2 + J 2 + 2KCl 2FeCl 3 + 3Na 2 S = 2FeS + S + 6NaCl

Like other trivalent cations, iron (III) is capable of forming alum - double sulfates with alkali metal or ammonium cations, for example: NH 4 Fe (SO 4) 2. 12H2O.

complex compounds. Both iron cations tend to form anionic complexes, especially iron(III). FeCl 3 + KCl \u003d K, FeCl 3 + Cl 2 \u003d Cl + -. The latter reaction reflects the action of iron (III) chloride as a catalyst for electrophilic chlorination. Cyanide complexes are of interest: 6KCN + FeSO 4 = K 4 - potassium hexacyanoferrate (II), yellow blood salt. 2K 4 + Cl 2 \u003d 2K 3 + 2KCl - potassium hexacyanoferrate (III), red blood salt. The ferrous iron complex gives a blue precipitate or solution with the ferric salt, depending on the ratio of the reagents. The same reaction occurs between red blood salt and any ferrous salt. In the first case, the precipitate was called Prussian blue, in the second - turnbull blue. Later it turned out that at least the solutions have the same composition: K is iron(II,III) potassium hexacyanoferrate. The described reactions are qualitative for the presence of the corresponding iron cations in the solution. A qualitative reaction to the presence of a ferric cation is the appearance of a blood-red color when interacting with potassium thiocyanate (thiocyanate): 2FeCl 3 + 6KCNS = 6KCl + Fe.

Fe+6. The oxidation state +6 for iron is unstable. It is possible to obtain only the FeO 4 2- anion, which exists only at pH>7-9, but is a strong oxidizing agent.

Fe 2 O 3 + 4KOH + 3KNO 3 = 2K 2 FeO 4 + 3KNO 2 + 2H 2 O

Fe (sawdust) + H 2 O + KOH + KNO 3 = K 2 FeO 4 + KNO 2 + H 2

2Fe(OH) 3 + 3Cl 2 + 10KOH = 2K 2 FeO 4 + 6KCl + 6H 2 O

Fe 2 O 3 + KClO 3 + 4KOH = 2K 2 FeO 4 + KCl + 2H 2 O

4K 2 FeO 4 + 6H 2 O \u003d 4FeO (OH) ↓ + 8KOH + 3O 2

4BaFeO 4 (heating) = 4BaO + 2Fe 2 O 3 + 3O 2

2K 2 FeO 4 + 2CrCl 3 + 2HCl = FeCl 3 + K 2 Cr 2 O 7 + 2KCl + H 2 O

Obtaining iron in industry:

A) domain process: Fe 2 O 3 + C \u003d 2FeO + CO

FeO + C = Fe + CO

FeO + CO \u003d Fe + CO 2

B) aluminothermy: Fe 2 O 3 + Al \u003d Al 2 O 3 + Fe

CHROMIUM - element with serial number 24, with a relative atomic mass of 51.996. It belongs to the 3d-family of elements, has an electronic configuration of 3d 5 4s 1 and is in the IV period, VI group, side subgroup in the periodic system. Possible oxidation states: +1, +2, +3, +4, +5, +6. Of these, +2, +3, +6 are the most stable, and +3 has the minimum energy.

In terms of physical properties, chromium is a grayish-white, shiny, hard metal with a melting point of 1890 o C. The strength of its crystal lattice is due to the presence of five unpaired d-electrons capable of partial covalent bonding.

Chemical properties of a simple substance.

At low temperatures, chromium is inert due to the presence of an oxide film, does not interact with water and air.

1. It interacts with oxygen at temperatures above 600 ° C. In this case, chromium oxide (III) - Cr 2 O 3 is formed.

2. Interaction with halogens occurs in different ways: Cr + 2F 2 = CrF 4 (at room temperature), 2Cr + 3Cl 2 (Br 2) = 2CrCl 3 (Br 3), Cr + J 2 = CrJ 2 (with significant heating ). It should be said that chromium (III) iodide can exist and is obtained by an exchange reaction in the form of CrJ 3 crystalline hydrate. 9H 2 O, but its thermal stability is low, and when heated, it decomposes into CrJ 2 and J 2 .

3. At temperatures above 120 ° C, chromium interacts with molten sulfur, giving chromium (II) sulfide - CrS (black).

4. At temperatures above 1000 ° C, chromium reacts with nitrogen and carbon, giving non-stoichiometric, chemically inert compounds. Among them, one can note carbide with an approximate composition of CrC, which is close to diamond in hardness.

5. Chromium does not react with hydrogen.

6. The reaction with water vapor proceeds as follows: 2Cr + 3H 2 O \u003d Cr 2 O 3 + 3H 2

7. The reaction with non-oxidizing acids occurs quite easily, and a sky-blue aqua complex 2+ is formed, which is stable only in the absence of air or in an atmosphere of hydrogen. In the presence of oxygen, the reaction proceeds differently: 4Cr + 12HCl + 3O 2 = 4CrCl 3 + 6H 2 O. Diluted acids saturated with oxygen even passivate chromium due to the formation of a strong oxide film on the surface.

8. Oxidizing acids: nitric acid of any concentration, concentrated sulfuric acid, perchloric acid passivate chromium so that after surface treatment with these acids, it no longer reacts with other acids. Passivation is removed by heating. This produces salts of chromium (III) and sulfur or nitrogen dioxide (from perchloric acid - chloride). Passivation due to the formation of a salt film occurs when chromium interacts with phosphoric acid.

9. Chromium does not react directly with alkali, but reacts with alkaline melts with the addition of oxidizing agents: 2Cr + 2Na 2 CO 3 (g) + 3O 2 \u003d 2Na 2 CrO 4 + 2CO 2

10. Chromium is able to react with salt solutions, displacing less active metals (to the right of it in the voltage series) from the composition of the salt. Chromium itself is converted into the Cr 2+ cation.

Aluminum- an element of the main subgroup of the third group of the third period of the periodic system of chemical elements of D. I. Mendeleev, atomic number 13. It is designated by the symbol Al (Aluminum). Belongs to the group of light metals. The most common metal and the third most common (after oxygen and silicon) chemical element in the earth's crust.

The simple substance aluminum (CAS number: 7429-90-5) is a light, paramagnetic silver-white metal, easily molded, cast, and 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.

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.

Story

For the first time, aluminum was obtained by Hans Oersted in 1825 by the action of potassium amalgam on aluminum chloride, followed by distillation of mercury.

Receipt

The modern preparation method was developed independently by the American Charles Hall and the Frenchman Paul Héroux. It consists in the dissolution of aluminum oxide Al 2 O 3 in a melt of cryolite Na 3 AlF 6 followed by electrolysis using graphite electrodes. This method of obtaining requires large amounts of electricity, and therefore was in demand only in the 20th century.

For the production of 1 ton of rough aluminum, 1.920 tons of alumina, 0.065 tons of cryolite, 0.035 tons of aluminum fluoride, 0.600 tons of anode mass and 17 thousand kWh of direct current electricity are required.

Physical Properties

Silver-white metal, light, density - 2.7 g / cm³, melting point for technical aluminum - 658 ° C, for high-purity aluminum - 660 ° C, specific heat of melting - 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 ductility: technical - 35%, clean - 50%, rolled into a thin sheet and even foil.

Aluminum has high electrical and thermal conductivity, 65% of the electrical conductivity of copper, has a high light reflectivity.

Aluminum forms alloys with almost all metals.

Being in nature

Natural aluminum consists almost entirely of a single stable isotope, 27 Al, with traces of 26 Al, a radioactive isotope with a half-life of 720,000 years produced in the atmosphere by nuclear bombardment. argon cosmic ray protons.

In terms of prevalence in nature, it occupies the 1st place among metals and the 3rd place among elements, second only to oxygen and silicon. The percentage of aluminum content in the earth's crust, according to various researchers, ranges from 7.45 to 8.14% of the mass of the earth's crust.

In nature, aluminum is found only in compounds (minerals). Some of them:

• Bauxites - Al 2 O 3. H 2 O (with impurities SiO 2, Fe 2 O 3, CaCO 3)
• Nephelines - KNa 3 4
• Alunites - KAl (SO 4) 2. 2Al(OH)3
• Alumina (mixtures of kaolins with sand SiO 2, limestone CaCO 3, magnesite MgCO 3)
• Corundum - Al 2 O 3
• Feldspar (orthoclase) - K 2 O × Al 2 O 3 × 6SiO 2
• Kaolinite - Al 2 O 3 × 2SiO 2 × 2H 2 O
• Alunite - (Na,K) 2 SO 4 × Al 2 (SO 4) 3 × 4Al (OH) 3
• Beryl - 3BeO. Al 2 O 3 . 6SiO2

In natural waters, aluminum is found in the form of low-toxic chemical compounds, such as 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 in Russia range from 0.001 to 10 mg/l.

Chemical properties

aluminum hydroxide

Under normal conditions, aluminum is covered with a thin and strong oxide film and therefore does not react with classical oxidizing agents: with H 2 O (t °); O 2, HNO 3 (without heating). Due to this, aluminum is practically not subject to corrosion and therefore is widely demanded by modern industry. However, when the oxide film is destroyed (for example, upon contact with solutions of ammonium salts NH 4 + , hot alkalis or as a result of amalgamation), aluminum acts as an active reducing metal.

Easily reacts with simple substances:

• with oxygen: 4Al + 3O 2 = 2Al 2 O 3
• with halogens: 2Al + 3Br 2 = 2AlBr 3
• reacts with other non-metals when heated:
  • with sulfur, forming aluminum sulfide: 2Al + 3S = Al 2 S 3
  • with nitrogen, forming aluminum nitride: 2Al + N 2 = 2AlN
  • with carbon, forming aluminum carbide: 4Al + 3C \u003d Al 4 C 3

The method, invented almost simultaneously by Charles Hall in France and Paul Héroux in the USA in 1886 and based on the production of aluminum by electrolysis of alumina dissolved in molten cryolite, marked the beginning of the modern method of aluminum production. Since then, in connection with the improvement of electrical engineering, aluminum production has improved. A significant contribution to the development of alumina production was made by Russian scientists K. I. Bayer, D. A. Penyakov, A. N. Kuznetsov, E. I. Zhukovsky, A. A. Yakovkin and others.

The first aluminum plant in Russia was built in 1932 in Volkhov. The metallurgical industry of the USSR in 1939 produced 47.7 thousand tons of aluminum, another 2.2 thousand tons were imported.

In Russia, the actual monopoly in the production of aluminum is JSC Russian Aluminum, which accounts for about 13% of the world aluminum market and 16% of alumina.

The world reserves of bauxite are practically unlimited, that is, they are incommensurable with the dynamics of demand. Existing capacities can produce up to 44.3 million tons of primary aluminum per year. It should also be taken into account that in the future some of the aluminum applications may be reoriented to the use of, for example, composite materials.

Application

A piece of aluminum and an American coin.

Widely used as a structural material. The main advantages of aluminum in this quality are lightness, ductility for stamping, corrosion resistance (in air, aluminum is instantly covered with a strong Al 2 O 3 film, which prevents its further oxidation), high thermal conductivity, non-toxicity of its compounds. In particular, these properties have made aluminum extremely popular in the manufacture of cookware, aluminum foil in the food industry, and for packaging.

The main disadvantage of aluminum as a structural material is its low strength, so it is usually alloyed with a small amount of copper and magnesium - duralumin alloy.

The electrical conductivity of aluminum is only 1.7 times less than that of copper, while aluminum is approximately 2 times cheaper. 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 copper (63 1/ohm) is compensated by an increase in the cross section of aluminum conductors. The disadvantage of aluminum as an electrical material is 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 platforms, 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 restorer

• As a component of thermite, mixtures for aluminothermy
• Aluminum is used to recover rare metals from their oxides or halides.

Aluminum based alloys

As a structural material, not pure aluminum is usually used, but various alloys based on it.

— Aluminum-magnesium alloys have high corrosion resistance and are well welded; they make, for example, the hulls of high-speed ships.

- Aluminum-manganese alloys are in many ways similar to aluminum-magnesium alloys.

- Aluminum-copper alloys (in particular, duralumin) can be heat treated, which greatly increases their strength. Unfortunately, heat-treated materials cannot be welded, so aircraft parts are still connected with rivets. An alloy with a higher copper content is very similar in color to gold, and is sometimes used to imitate the latter.

— Aluminum-silicon alloys (silumins) are best suited for casting. Cases of various mechanisms are often cast from them.

— Complex alloys based on aluminum: avial.

- Aluminum goes into a superconducting state at a temperature of 1.2 Kelvin.

Aluminum as an additive in other alloys

Aluminum is an important component of 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).

Jewelry

When aluminum was very expensive, various products were made from it. jewelry. The fashion for them immediately passed when new technologies for its production appeared, which reduced the cost many times over. Now aluminum is sometimes used in the manufacture of jewelry.

Glassmaking

Fluoride, phosphate and aluminum oxide are used in glassmaking.

food industry

Aluminum is registered as a food additive E173.

Aluminum and its compounds in rocketry

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:

— Aluminum: fuel in rocket propellants. It is used in the form of powder and suspensions in hydrocarbons, etc.
— Aluminum hydride
— aluminum borane
— Trimethylaluminum
— Triethylaluminum
— Tripropylaluminum

Theoretical characteristics of fuels formed by aluminum hydride with various oxidizers.

Aluminum in world culture

The poet Andrei Voznesensky wrote the poem "Autumn" in 1959, in which he used aluminum as artistic image:
... And outside the window in the young hoarfrost
aluminum fields lie ...

Viktor Tsoi wrote the song "Aluminum Cucumbers" with the refrain:
Planting aluminum cucumbers
On a canvas field
I plant aluminum cucumbers
On a canvas field

Toxicity

It has a slight toxic effect, but many water-soluble inorganic aluminum compounds remain in a dissolved state. long time and can have harmful effects 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. Primarily acts on nervous system(accumulates in the nervous tissue, leading to severe disorders of the central nervous system function). However, the neurotoxic property of aluminum has been 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.

Additional Information

— Aluminum hydroxide
— Encyclopedia about aluminum
– Aluminum compounds
— International Aluminum Institute

Aluminium, Al (13)

Binders containing aluminum have been known since ancient times. However, under alum (Latin Alumen or Alumin, German Alaun), which is mentioned, in particular, by Pliny, various substances were understood in antiquity and in the Middle Ages. In Roeland's Alchemical Dictionary, the word Alumen, with the addition of various definitions, is given in 34 meanings. In particular, it meant antimonium, Alumen alafuri - alkaline salt, Alumen Alcori - nitrum or alkaline alum, Alumen creptum - tartar (tartar) of good wine, Alumen fascioli - alkali, Alumen odig - ammonia, Alumen scoriole - gypsum, etc. Lemery, the author of the well-known "Dictionary of Simple Apothecary Products" (1716), also gives a large list of varieties of alum.

Until the 18th century aluminum compounds (alum and oxide) could not be distinguished from others similar in appearance connections. Lemery describes the alum as follows: “In 1754 r. Marggraf separated from the solution of alum (by the action of alkali) a precipitate of aluminum oxide, which he called "aluminous earth" (Alaunerde), and established its difference from other lands. Soon the alum earth was called alumina (Alumina or Alumine). In 1782, Lavoisier suggested that alumina is an oxide of an unknown element. In the "Table of Simple Bodies" Lavoisier placed alumina among "simple bodies, salt-forming, earthy". Synonyms for the name of alumina are also given here: argile, alum. earth, base of alum. The word argyla, or argilla, as Lemery points out in his dictionary, comes from the Greek. pottery clay. Dalton in his "New System of Chemical Philosophy" gives a special sign for alumina and gives a complex structural (!) formula for alum.

After the discovery of the alkali metals by means of galvanic electricity, Davy and Berzelius unsuccessfully attempted to isolate aluminum metal from alumina in the same way. Only in 1825 was the problem solved by the Danish physicist Oersted by a chemical method. He passed chlorine through a hot mixture of alumina and coal, and the resulting anhydrous aluminum chloride was heated with potassium amalgam. After the evaporation of mercury, Oersted writes, a metal was obtained, similar in appearance to tin. Finally, in 1827, Wehler isolated metallic aluminum more effective way- heating anhydrous aluminum chloride with potassium metal.

Around 1807, Davy, who was trying to carry out the electrolysis of alumina, gave the name of the metal supposed in it, aluminum (Alumium) or aluminum (Aluminum). The last name has since become accustomed in the USA, while in England and other countries the name aluminum (Aluminium), which was subsequently proposed by the same Davy, has been adopted. It is quite clear that all these names come from the Latin word alum (Alumen), about the origin of which there are different opinions, based on the evidence of various authors, starting from antiquity.

A. M. Vasiliev, noting the unclear origin of this word, cites the opinion of a certain Isidore (obviously Isidore of Seville, a bishop who lived in 560 - 636, an encyclopedist who was engaged, in particular, in etymological studies): “Alumen is called a lumen, so how it imparts lumen (light, brightness) to paints when it is added when dyeing. However, this explanation, although very old, does not prove that the word alumen has just such origins. Only a random tautology is quite possible here. Lemery (1716) in turn points out that the word alumen is related to the Greek (halmi), meaning salinity, brine, brine, etc.

Russian names of aluminum in the first decades of the 19th century. quite varied. Each of the authors of books on chemistry of this period, obviously, sought to offer his own name. So, Zakharov calls aluminum alumina (1810), Giese - alumium (1813), Strakhov - alum (1825), Iovsky - clay content, Shcheglov - alumina (1830). In the Dvigubsky Store (1822-1830), alumina is called alumina, alumina, alumina (for example, phosphoric acid alumina), and the metal is called aluminum and aluminum (1824). Hess in the first edition of The Foundations of Pure Chemistry (1831) uses the name of alumina (Aluminium), and in the fifth edition (1840) - clays. However, he forms the names for salts on the basis of the term alumina, for example, alumina sulphate. Mendeleev in the first edition of Fundamentals of Chemistry (1871) uses the names aluminum and clay. In subsequent editions, the word clay is no longer found.

Aluminum is the metal with the highest content in nature among all known. The late start of its use is due to the fact that, since it has a high chemical activity, it is found in the earth's crust only as part of various chemical compounds. The recovery of pure metal is associated with a number of difficulties, which became possible to overcome only with the development of metal mining technologies.

Pure aluminum is a soft, malleable silver-white metal. This is one of the lightest metals, which, moreover, lends itself well to a variety of machining, stamping, rolling, casting. In the open air, it is almost instantly covered with a thin and durable oxide film, which counteracts further oxidation.

The mechanical properties of aluminum, such as softness, pliability for stamping, ease of processing, have been widely used in many industries. Especially often aluminum is used in alloys with other metals.

The physical and chemical properties of aluminum alloys have led to their widespread use as structural materials that reduce the overall weight of the structure without compromising strength properties.

Physical Properties

Aluminum does not have any unique physical properties, but their combination makes the metal one of the most widely sought after.

The hardness of pure aluminum on the Mohs scale is three, which is significantly lower than that of most metals. This fact is practically the only obstacle to the use of pure metal.

If you carefully consider the table of physical properties of aluminum, you can highlight such qualities as:

• Low density (2.7 g / cm 3);
• High plasticity;
• Low electrical resistivity (0.027 Ohm mm 2 /m);
• High thermal conductivity (203.5 W/(m K));
• High light reflectivity;
• Low melting point (660°C).

Such physical properties of aluminum as high ductility, low temperature melting, excellent casting qualities, allow the use of this metal in its pure form and in the composition of alloys based on it for the production of products of any most complex configuration.

At the same time, it is one of the few metals whose brittleness does not increase when cooled to ultra-low temperatures. This property determined one of the areas of application in the structural elements of cryogenic technology and equipment.

Aluminum-based alloys have a significantly higher strength, comparable to the strength of some steel grades. The most widespread are alloys with the addition of magnesium, copper and manganese - duralumin alloys and with the addition of silicon - silumins. The first group is distinguished by high strength, and the last one by one of the best casting qualities.

The low melting temperature reduces production costs and the cost of technological processes in the production of structural materials based on aluminum and its alloys.

For the manufacture of mirrors, such qualities as a high reflection coefficient comparable to that of silver, the ease and manufacturability of vacuum deposition of aluminum films on various bearing surfaces (plastics, metal, glass) are used.

When melting aluminum and casting Special attention refers to the ability of the melt to absorb hydrogen. Having no effect on the chemical level, hydrogen contributes to a decrease in density and strength due to the formation of microscopic pores during the solidification of the melt.

Due to their low density and low electrical resistance (slightly higher than copper), pure aluminum wires are primarily used in the transmission of electricity in power lines, the entire range of currents and voltages in electrical engineering, as an alternative to copper power and winding wires. The resistance of copper is somewhat less, so aluminum wires must be used with a larger cross section, but the final mass of the product and its cost are several times less. The only limitation is the slightly lower strength of aluminum and the high resistance to soldering due to the oxide film on the surface. A large role is played by the presence of a strong electrochemical potential in contact with a metal such as copper. As a result, a strong oxide film with high electrical resistance is formed at the place of mechanical contact between copper and aluminum. This phenomenon leads to heating of the junction up to the melting of the conductors. There are strict restrictions and recommendations for the use of aluminum in electrical engineering.

High ductility makes it possible to produce thin foil, which is used in the production of high-capacity capacitors.

The lightness of aluminum and its alloys have become fundamental when used in the aerospace industry in the manufacture of most aircraft structural elements: from load-bearing structures to skin elements, instrument and equipment cases.

Chemical properties

Being a fairly reactive metal, aluminum actively resists corrosion. This is due to the formation of a very strong oxide film on its outer surface under the action of oxygen.

A strong oxide film protects the surface well even from such strong acids as nitric and sulfuric. This quality has found distribution in chemistry and industry for the transportation of concentrated nitric acid.

The film can be destroyed with highly diluted nitric acid, alkalis when heated or in contact with mercury, when an amalgam forms on the surface. In these cases, the oxide film is not a protective factor, and aluminum actively interacts with acids, alkalis, and oxidizing agents. The oxide film is also easily destroyed in the presence of halogens (chlorine, bromine). Thus, hydrochloric acid HCl interacts well with aluminum under any conditions.

The chemical properties of aluminum depend on the purity of the metal. The use of the composition of alloying additives of some metals, in particular manganese, makes it possible to increase the strength of the protective film, thus increasing the corrosion resistance of aluminum. Some metals, for example, nickel and iron, contribute to a decrease in corrosion resistance, but increase the heat resistance of alloys.

The oxide film on the surface of aluminum products plays a negative role during welding. The instantaneous oxidation of the molten metal pool during welding does not allow the formation of a weld, since alumina has a very high temperature melting. For welding aluminum, special welding machines with a non-consumable electrode (tungsten) are used. The process itself is carried out in an inert gas environment - argon. In the absence of the oxidation process, the welding seam is strong, monolithic. Some alloying additives in alloys further improve the welding properties of aluminum.

Pure aluminum practically does not form toxic compounds, therefore it is actively used in the food industry in the production of kitchen utensils, food packaging, and beverage containers. Only some inorganic compounds can have a negative effect. Studies have also established that aluminum is not used in the metabolism of living beings, its role in life is negligible.