Gallium is an element of the main subgroup of the third group of the fourth period of the periodic system of chemical elements of D.I. Mendeleev, with atomic number 31. Denoted by the symbol Ga (lat. Gallium). Belongs to the group of light metals. The simple substance gallium is a soft, ductile metal of silvery-white color with a bluish tint.

Atomic number - 31

Atomic mass - 69.723

Density, kg/m³ - 5910

Melting point, °C - 29.8

Heat capacity, kJ/(kg °C) - 0.331

Electronegativity - 1.8

Covalent radius, Å - 1.26

1st ionization potential, eV - 6.00

History of the discovery of gallium

French chemist Paul Emile Lecoq de Boisbaudran went down in history as the discoverer of three new elements: gallium (1875), samarium (1879) and dysprosium (1886). The first of these discoveries brought him fame.

At that time he was little known outside of France. He was 38 years old and was primarily engaged in spectroscopic research. Lecoq de Boisbaudran was a good spectroscopist, and this ultimately led to success: he discovered all three of his elements by spectral analysis.

In 1875, Lecoq de Boisbaudran examined the spectrum of zinc blende brought from Pierrefitte (Pyrenees). A new violet line was discovered in this spectrum. The new line indicated the presence of an unknown element in the mineral, and, quite naturally, Lecoq de Boisbaudran made every effort to isolate this element. This turned out to be difficult to do: the content of the new element in the ore was less than 0.1%, and in many ways it was similar to zinc*. After lengthy experiments, the scientist managed to obtain a new element, but in a very small quantity. So small (less than 0.1 g) that Lecoq de Boisbaudran was not able to fully study its physical and chemical properties.

The discovery of gallium - this is how the new element was named in honor of France (Gallia is its Latin name) - appeared in the reports of the Paris Academy of Sciences.

This message was read by D.I. Mendeleev and recognized in gallium eka-aluminium, which he had predicted five years earlier. Mendeleev immediately wrote to Paris. “The method of discovery and isolation, as well as the few properties described, lead us to believe that the new metal is none other than eka-aluminium,” his letter said. He then repeated the properties predicted for that element. Moreover, without ever holding grains of gallium in his hands, without seeing it in person, the Russian chemist argued that the discoverer of the element was mistaken, that the density of the new metal cannot be equal to 4.7, as Lecoq de Boisbaudran wrote, - it must be greater, approximately 5.9...6.0 g/cm 3! But experience showed the opposite: the discoverer was mistaken. The discovery of the first element predicted by Mendeleev significantly strengthened the position of the periodic law.

The average gallium content in the earth's crust is 19 g/t. Gallium is a typical trace element with a dual geochemical nature. Gallium's only mineral, gallite CuGaS 2, is very rare. The geochemistry of gallium is closely related to the geochemistry of aluminum, which is due to the similarity of their physicochemical properties. The main part of Gallium in the lithosphere is contained in aluminum minerals. Due to the similarity of its crystal chemical properties with the main rock-forming elements (Al, Fe, etc.) and the wide possibility of isomorphism with them, gallium does not form large accumulations, despite the significant clarke value. The following minerals with a high gallium content are distinguished: sphalerite (0 – 0.1%), magnetite (0 – 0.003%), cassiterite (0 – 0.005%), garnet (0 – 0.003%), beryl (0 – 0.003%), tourmaline (0 – 0.01%), spodumene (0.001 – 0.07%), phlogopite (0.001 – 0.005%), biotite (0 – 0.1%), muscovite (0 – 0.01%), sericite ( 0 – 0.005%), lepidolite (0.001 – 0.03%), chlorite (0 – 0.001%), feldspars (0 – 0.01%), nepheline (0 – 0.1%), hecmanite (0.01 – 0.07%), natrolite (0 – 0.1%).

Perhaps the most famous property of gallium is its melting point, which is 29.76 °C. It is the second most fusible metal in the periodic table (after mercury). This allows you to melt metal while holding it in your hand. Gallium is one of the few metals that expand when the melt solidifies (the others are Bi, Ge).

Crystalline gallium has several polymorphic modifications, but only one (I) is thermodynamically stable, having an orthorhombic (pseudo-tetragonal) lattice with parameters a = 4.5186 Å, b = 7.6570 Å, c = 4.5256 Å. Other modifications of gallium (β, γ, δ, ε) crystallize from supercooled dispersed metal and are unstable. At elevated pressure, two more polymorphic structures of gallium II and III were observed, having, respectively, cubic and tetragonal lattices.

The density of gallium in the solid state at a temperature of T=20 °C is 5.904 g/cm³.

One of the features of gallium is the wide temperature range of existence of the liquid state (from 30 to 2230 °C), while it has a low vapor pressure at temperatures up to 1100÷1200 °C. The specific heat capacity of solid gallium in the temperature range T=0÷24 °C is 376.7 J/kg K (0.09 cal/g deg.), in the liquid state at T=29÷100 °C - 410 J/ kg K (0.098 cal/g deg).

The electrical resistivity in the solid and liquid states is equal to, respectively, 53.4·10−6 ohm·cm (at T=0 °C) and 27.2·10−6 ohm·cm (at T=30 °C). The viscosity of liquid gallium at different temperatures is 1.612 poise at T=98 °C and 0.578 poise at T=1100 °C. Surface tension measured at 30 °C in a hydrogen atmosphere is 0.735 n/m. The reflectances for wavelengths 4360 Å and 5890 Å are 75.6% and 71.3%, respectively.

Natural gallium consists of two isotopes 69 Ga (61.2%) and 71 Ga (38.8%). The thermal neutron capture cross section for them is 2.1·10−28 m² and 5.1·10−28 m², respectively.

Gallium is a low-toxic element. Due to the low melting temperature, it is recommended to transport gallium ingots in polyethylene bags, which are poorly wetted by molten gallium. At one time, the metal was even used to make fillings (instead of amalgam ones). This application is based on the fact that when copper powder is mixed with molten gallium, a paste is obtained, which after a few hours hardens (due to the formation of an intermetallic compound) and can then withstand heating up to 600 degrees without melting.

At high temperatures, gallium is a very aggressive substance. At temperatures above 500 °C, it corrodes almost all metals except tungsten, as well as many other materials. Quartz is resistant to molten gallium up to 1100 °C, but a problem can arise due to the fact that quartz (and most other glasses) are highly wetted by this metal. That is, gallium will simply stick to the walls of the quartz.

The chemical properties of gallium are close to those of aluminum. The oxide film formed on the surface of the metal in air protects gallium from further oxidation. When heated under pressure, gallium reacts with water, forming the compound GaOOH according to the reaction:

2Ga + 4H 2 O = 2GaOOH + 3H 2.

Gallium reacts with mineral acids to release hydrogen and form salts, and the reaction occurs even below room temperature:

2Ga + 6HCl = 2GaCl3 + 3H2

The products of the reaction with alkalis and potassium and sodium carbonates are hydroxogallates containing Ga(OH) 4 - and, possibly, Ga(OH) 6 3 - and Ga(OH) 2 - ions:

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

Gallium reacts with halogens: the reaction with chlorine and fluorine occurs at room temperature, with bromine - already at −35 °C (about 20 °C - with ignition), interaction with iodine begins when heated.

Gallium does not interact with hydrogen, carbon, nitrogen, silicon and boron.

At high temperatures, gallium is capable of destroying various materials and its effect is stronger than the melt of any other metal. Thus, graphite and tungsten are resistant to gallium melt up to 800 °C, alundum and beryllium oxide BeO - up to 1000 °C, tantalum, molybdenum and niobium are resistant up to 400÷450 °C.

With most metals, gallium forms gallides, with the exception of bismuth, as well as metals of the subgroups of zinc, scandium, and titanium. One of the V 3 Ga gallides has a rather high transition temperature to the superconducting state of 16.8 K.

Gallium forms polymer hydrides:

4LiH + GaCl 3 = Li + 3LiCl.

The stability of ions decreases in the series BH 4 - → AlH 4 - → GaH 4 - . The BH 4 ion is stable in aqueous solution, AlH 4 and GaH 4 are quickly hydrolyzed:

GaH 4 - + 4H 2 O = Ga(OH) 3 + OH - + 4H 2 -

When Ga(OH) 3 and Ga 2 O 3 are dissolved in acids, aqua complexes 3+ are formed, therefore gallium salts are isolated from aqueous solutions in the form of crystalline hydrates, for example, gallium chloride GaCl 3 * 6H 2 O, gallium potassium alum KGa(SO 4) 2 * 12H2O.

An interesting interaction between gallium and sulfuric acid occurs. It is accompanied by the release of elemental sulfur. In this case, sulfur envelops the surface of the metal and prevents its further dissolution. If you wash the metal with hot water, the reaction will resume and will continue until a new “skin” of sulfur grows on the gallium.

• Ga2H6- volatile liquid, melting point −21.4 °C, boiling point 139 °C. In an ethereal suspension with lithium or thallium hydrate it forms the compounds LiGaH 4 and TlGaH 4 . Formed by treating tetramethyldigallane with triethylamine. There are banana bonds, as in diborane

• Ga2O3- white or yellow powder, melting point 1795 °C. Exists in the form of two modifications. α- Ga 2 O 3 - colorless trigonal crystals with a density of 6.48 g/cm³, slightly soluble in water, soluble in acids. β- Ga 2 O 3 - colorless monoclinic crystals with a density of 5.88 g/cm³, slightly soluble in water, acids and alkalis. It is obtained by heating gallium metal in air at 260 °C or in an oxygen atmosphere, or by calcining gallium nitrate or sulfate. ΔH° 298(sample) −1089.10 kJ/mol; ΔG° 298(sample) −998.24 kJ/mol; S° 298 84.98 J/mol*K. They exhibit amphoteric properties, although the basic properties, compared to aluminum, are enhanced:

Ga 2 O 3 + 6HCl = 2GaCl 2 Ga 2 O 3 + 2NaOH + 3H 2 O = 2Na Ga 2 O 3 + Na 2 CO 3 = 2NaGaO 2 + CO 2

• Ga(OH)3- falls out in the form of a jelly-like precipitate when treating solutions of trivalent gallium salts with hydroxides and carbonates of alkali metals (pH 9.7). Dissolves in concentrated ammonia and concentrated ammonium carbonate solution, and precipitates when boiled. By heating, gallium hydroxide can be converted to GaOOH, then to Ga 2 O 3 *H 2 O, and finally to Ga 2 O 3. Can be obtained by hydrolysis of trivalent gallium salts.

• GaF 3- White powder. t melt >1000 °C, t boil 950 °C, density - 4.47 g/cm³. Slightly soluble in water. GaF 3 ·3H 2 O crystalline hydrate is known. It is obtained by heating gallium oxide in a fluorine atmosphere.

• GaCl3- colorless hygroscopic crystals. t melt 78 °C, boil t 215 °C, density - 2.47 g/cm³. Let's dissolve well in water. Hydrolyzes in aqueous solutions. Obtained directly from the elements. Used as a catalyst in organic syntheses.

• GaBr 3- colorless hygroscopic crystals. t melt 122 °C, t boil 279 °C density - 3.69 g/cm³. Dissolves in water. Hydrolyzes in aqueous solutions. Slightly soluble in ammonia. Obtained directly from the elements.

• GaI 3- hygroscopic light yellow needles. t melt 212 °C, t boil 346 °C, density - 4.15 g/cm³. Hydrolyzes with warm water. Obtained directly from the elements.

• GaS 3- yellow crystals or white amorphous powder with a melting point of 1250 °C and a density of 3.65 g/cm³. It interacts with water and is completely hydrolyzed. It is obtained by reacting gallium with sulfur or hydrogen sulfide.

• Ga 2 (SO 4) 3 18H 2 O- colorless, highly soluble substance in water. It is obtained by reacting gallium, its oxide and hydroxide with sulfuric acid. It easily forms alum with sulfates of alkali metals and ammonium, for example, KGa(SO 4) 2 12H 2 O.

• Ga(NO 3) 3 8H 2 O- colorless crystals soluble in water and ethanol. When heated, it decomposes to form gallium(III) oxide. It is obtained by the action of nitric acid on gallium hydroxide.

The main source of obtaining Gallium is aluminum production. When processing bauxite using the Bayer method, gallium is concentrated in circulating mother liquors after the separation of Al(OH) 3 . Gallium is isolated from such solutions by electrolysis at a mercury cathode. From the alkaline solution obtained after treating the amalgam with water, Ga(OH) 3 is precipitated, which is dissolved in alkali and Gallium is isolated by electrolysis.

In the soda-lime method of processing bauxite or nepheline ore, Gallium is concentrated in the last fractions of sediment released during the carbonization process. For additional enrichment, the hydroxide precipitate is treated with lime milk. In this case, most of the Al remains in the sediment, and Gallium goes into solution, from which gallium concentrate (6-8% Ga 2 O 3) is isolated by passing CO 2; the latter is dissolved in alkali and gallium is isolated electrolytically.

The source of Gallium can also be the residual anode alloy from the Al refining process using the three-layer electrolysis method. In the production of zinc, the sources of Gallium are sublimates (Welz oxides) formed during the processing of zinc cinder leaching tailings.

Liquid Gallium obtained by electrolysis of an alkaline solution, washed with water and acids (HCl, HNO 3), contains 99.9-99.95% Ga. A purer metal is obtained by vacuum melting, zone melting, or by drawing a single crystal from the melt.

Applications of gallium

Gallium arsenide GaAs is a promising material for semiconductor electronics.

Gallium nitride is used in the creation of semiconductor lasers and LEDs in the blue and ultraviolet range. Gallium nitride has excellent chemical and mechanical properties typical of all nitride compounds.

As a group III element that enhances “hole” conductivity in a semiconductor, gallium (with a purity of at least 99.999%) is used as an additive to germanium and silicon. Intermetallic compounds of gallium with group V elements - antimony and arsenic - themselves have semiconductor properties.

The gallium-71 isotope is the most important material for detecting neutrinos, and in this regard, technology faces a very urgent task of isolating this isotope from a natural mixture in order to increase the sensitivity of neutrino detectors. Since the content of 71 Ga in a natural mixture of isotopes is about 39.9%, the isolation of a pure isotope and its use as a neutrino detector can increase the detection sensitivity by 2.5 times.

The addition of gallium to the glass mass makes it possible to obtain glasses with a high refractive index of light rays, and glasses based on Ga 2 O 3 transmit infrared rays well.

Gallium is expensive; in 2005, on the world market, a ton of gallium cost 1.2 million US dollars, and due to the high price and at the same time the great need for this metal, it is very important to establish its complete extraction in aluminum production and processing of coal in liquid fuel.

Liquid gallium reflects 88% of the light incident on it, solid gallium reflects slightly less. Therefore, they make gallium mirrors that are very easy to manufacture - the gallium coating can even be applied with a brush.

Gallium has a number of alloys that are liquid at room temperature, and one of its alloys has a melting point of 3 °C, but on the other hand, gallium (alloys to a lesser extent) is quite aggressive to most structural materials (cracking and erosion of alloys at high temperature), and As a coolant, it is ineffective and often simply unacceptable.

Attempts have been made to use gallium in nuclear reactors, but the results of these attempts can hardly be considered successful. Not only does gallium quite actively capture neutrons (capture cross section 2.71 barns), it also reacts at elevated temperatures with most metals.

Gallium did not become an atomic material. True, its artificial radioactive isotope 72 Ga (with a half-life of 14.2 hours) is used to diagnose bone cancer. Gallium-72 chloride and nitrate are adsorbed by the tumor, and by detecting the radiation characteristic of this isotope, doctors almost accurately determine the size of foreign formations.

Gallium is an excellent lubricant. Almost very important metal adhesives have been created on the basis of gallium and nickel, gallium and scandium.

Gallium metal is also used to fill quartz thermometers (instead of mercury) to measure high temperatures. This is due to the fact that gallium has a significantly higher boiling point compared to mercury.

Gallium oxide is a component of a number of strategically important laser materials.

Gallium production in the world

Its world production does not exceed two hundred tons per year. With the exception of two recently discovered deposits - in 2001 in Gold Canyon, Nevada, USA and in 2005 in Inner Mongolia, China - gallium is not found in industrial concentrations anywhere in the world. (In the latter deposit, the presence of 958 thousand tons of gallium in coal was established - this is a doubling of the world's gallium resources).

The world's gallium resources in bauxite alone are estimated to exceed 1 million tons, and the mentioned deposit in China contains 958 thousand tons of gallium in coal - doubling the world's gallium resources).

There are not many gallium producers. One of the leaders in the gallium market is GEO Gallium. Its main capacities until 2006 consisted of a plant in Stade (Germany), where about 33 tons per year is mined, a plant in Salindres, processing 20 tons/year (France) and in Pinjarra (Western Australia) - potential (but not introduced into construction) capacity up to 50 tons/year.

In 2006, the position of the No. 1 manufacturer weakened - the Stade enterprise was purchased by the English MCP and the American Recapture Metals.

The Japanese company Dowa Mining is the world's only producer of primary gallium from zinc concentrates as a by-product of zinc production. The full capacity for primary material of Dowa Mining is estimated to be up to 20 tons/year. In Kazakhstan, the Aluminum of Kazakhstan enterprise in Pavlodar has a full capacity of up to 20 tons/year.

China has become a very serious supplier of gallium. There are 3 large producers of primary gallium in China - Geatwall Aluminum Co. (up to 15 tons/year), Shandong Aluminum Plant (about 6 tons/year) and Guizhou Aluminum Plant (up to 6 tons/year). There are also a number of co-productions. Sumitomo Chemical has established joint ventures in China with a capacity of up to 40 tons/year. The American company AXT has created a joint venture Beijing JiYa semiconductor Material Co. with the largest Chinese aluminum enterprise Shanxi Aluminum Factory. with a productivity of up to 20 tons/year.

Gallium production in Russia

In Russia, the structure of gallium production is determined by the formation of the aluminum industry. The two leading groups that announced the merger, Russian Aluminum and SUAL, are owners of gallium sites created at alumina refineries.

“Russian Aluminum”: Nikolaevsky Alumina Refinery in Ukraine (classical Bayer hydrochemical method for processing tropical bauxite, site capacity - up to 12 tons of gallium / year) and Achinsk Alumina Refinery in Russia (processing by sintering of nepheline raw materials - urtites of the Kiya-Shaltyrskoye deposit, Krasnoyarsk Territory, site capacity – 1.5 tons of gallium/year).

"SUAL": Capacities in Kamensk-Uralsky (Bayer-sintering technology for bauxite of the North Ural bauxite ore region, site capacity - up to 2 tons of gallium / year), at the Boksitogorsk alumina refinery (processes bauxite of the Leningrad region by sintering method, capacity - 5 tons of gallium / year, currently mothballed) and "Pikalevsky Alumina" (processes nepheline concentrates from apatite-nepheline ores of the Murmansk region by sintering, site capacity - 9 tons of gallium / year). In total, all enterprises of Rusal and SUAL can produce over 20 tons/year.

Actual production is lower - for example, in 2005, 8.3 tons of gallium were exported from Russia and 13.9 tons of gallium from the Nikolaev Alumina Refinery from Ukraine.

When preparing the material, information from the Kvar company was used.

Gallium thermometers allow, in principle, to measure temperatures from 30 to 2230 ° C. Gallium thermometers are now produced for temperatures up to 1200 ° C.

Element No. 31 is used for the production of low-melting alloys used in signaling devices. The alloy of gallium with indium melts already at 16 ° C. This is the most fusible of all known alloys.

As a group III element that enhances “hole” conductivity in a semiconductor (with a purity of at least 99.999%), it is used as an additive to germanium and silicon.

Intermetallic compounds of gallium with group V elements - antimony and arsenic - themselves have semiconductor properties.

The addition of gallium to the glass mass makes it possible to obtain glasses with a high refractive index of light rays, and glasses based on Ga2O3 transmit infrared rays well.

Liquid reflects 88% of the light falling on it, solid - a little less. That’s why they make gallium mirrors that are very easy to manufacture—the gallium coating can even be applied with a brush.

Sometimes the ability of gallium to wet solid surfaces well is used, replacing it in diffusion vacuum pumps. Such pumps “hold” vacuum better than mercury pumps.

Attempts have been made to use it in nuclear reactors, but the results of these attempts can hardly be considered successful. Not only does gallium quite actively capture neutrons (capture cross section 2.71 barns), it also reacts at elevated temperatures with most metals.

Gallium did not become an atomic material. True, its artificial radioactive isotope 72Ga (with a half-life of 14.2 hours) is used to diagnose bone cancer. Gallium-72 chloride and nitrate are adsorbed by the tumor, and by detecting the radiation characteristic of this isotope, doctors almost accurately determine the size of foreign formations.

As you can see, the practical possibilities of element No. 31 are quite wide. It is not yet possible to use them completely due to the difficulty of obtaining gallium - a rather rare element (1.5-10-3% of the weight of the earth's crust) and very scattered.

Few native gallium minerals are known. Its first and most famous mineral, gallite CuGaS2, was discovered only in 1956. Later, two more minerals, already very rare, were found.

Typically, gallium is found in zinc, aluminum, iron ores, as well as in coal - as a minor impurity. And what is characteristic: the larger this impurity, the more difficult it is to extract it, because there is more gallium in the ores of those metals (,), which are similar to it in properties. The bulk of terrestrial gallium is contained in aluminum minerals.

Extracting gallium is an expensive “pleasure”. Therefore, element number 31 is used in smaller quantities than any of its neighbors on the periodic table.

It is possible, of course, that science in the near future will discover something in gallium that will make it absolutely necessary and irreplaceable, as happened with another element predicted by Mendeleev - germanium.

SEARCHING FOR REGULARITIES. The properties of gallium were predicted by D.I. Mendeleev five years before the discovery of this element. The brilliant Russian chemist based his predictions on the patterns of changes in properties across groups of the periodic system. But for Lecoq de Boisbaudran, the discovery of gallium was not a happy accident. A talented spectroscopist, back in 1863 he discovered patterns in the changes in the spectra of elements with similar properties. Comparing the spectra of indium and aluminum, he came to the conclusion that these elements may have a “brother” whose lines would fill the gap in the short-wave part of the spectrum. It was precisely this missing line that he looked for and found in the spectrum of zinc blende from Pierrefit.

WORD PLAY? According to which historians of science see in the name of element No. 31 not only patriotism, but also the immodesty of its discoverer. It is commonly believed that the word “gallium” comes from the Latin Gallia (France). But if you wish, in the same word you can see a hint of the word “rooster” 1 In Latin “rooster” is gallus, in French - le coq. Lecoq de Boisbaudran?

DEPENDING ON THE AGE, gallium often accompanies aluminum in minerals. Interestingly, the ratio of these elements in a mineral depends on the time of formation of the mineral. In feldspars, there is one gallium atom for every 120 thousand aluminum atoms. In nephelines, which formed much later, this ratio is already 1:6000, and in even “younger” petrified wood it is only 1:13.

FIRST PATENT. The first patent for the use of gallium was taken at the very beginning of the 20th century. They wanted to use element No. 31 in electric arc lamps.

SULFUR IS REPLACED, GRAY IS DEFENDED BY SULFUR. The interaction of gallium with sulfuric acid occurs interestingly. It is accompanied by the release of elemental sulfur. At the same time, it envelops the surface of the metal and prevents its further dissolution. If you wash the metal with hot water, the reaction will resume and continue until a new “skin” of sulfur grows on the gallium.

BAD INFLUENCE. Liquid gallium interacts with most metals, forming intermetallic compounds with rather low mechanical properties. This is why contact with gallium causes many structural materials to lose strength. The most resistant to the action of gallium: at temperatures up to 1000° C, it successfully resists the aggressiveness of element No. 31.

AND OXIDE TOO! Minor additions of gallium oxide significantly affect the properties of the oxides of many metals. Thus, the admixture of Ga2O3 to zinc oxide significantly reduces its sintering ability. But there is much more zinc in such an oxide than in pure oxide. And titanium dioxide's electrical conductivity drops sharply when Ga2O3 is added.

HOW GALLIUM IS OBTAINED. No industrial deposits of gallium ores have been found in the world. Therefore, gallium has to be extracted from zinc and aluminum ores that are very poor in it.

Since the content of gallium in them is not the same, the methods for obtaining element No. 31 are quite varied. Let us tell you, for example, how gallium is extracted from zinc blende, the mineral in which this element was discovered first.

First of all, the zinc blende ZnS is fired, and the resulting ones are leached with sulfuric acid. Together with manyother metals, gallium goes into solution. Zinc sulfate predominates in this solution - the main product that must be purified from impurities, including gallium. First stagecleaning - sedimentation of the so-called iron sludge. With the gradual neutralization of the acidic solution, this sludge precipitates. 13 it turns out to be about 10% aluminum, 15% iron and (which is most important for us now) 0.05-0.1% gallium. To extract gallium, the sludge is leached with acid or sodium hydroxide - gallium hydroxide is amphoteric. The alkaline method is more convenient, since in this case the equipment can be made from less expensive materials.

Under the influence of alkali, aluminum and gallium compounds go into solution. When this solution is carefully neutralized, gallium hydroxide precipitates. But some of the aluminum also precipitates. Therefore, the precipitate is dissolved again, this time in hydrochloric acid. The result is a solution of gallium chloride, contaminated predominantly with aluminum chloride. These can be separated by extraction. Ether is added and, unlike AlCl3, GaCl3 almost completely passes into the organic solvent. The layers are separated, the ether is distilled off, and the resulting gallium chloride is once again treated with concentrated caustic soda to precipitate and separate the iron impurity from the gallium. Gallium metal is obtained from this alkaline solution. Obtained by electrolysis at a voltage of 5.5 V. Gallium is deposited on a copper cathode.

Chemistry

Gallium No. 31

Gallium subgroup. The content of each member of this subgroup in the earth's crust along the series gallium (4-10~4%) - indium (2-10~6) - thallium (8-10-7) decreases. All three "elements are extremely dispersed, and it is not typical for them to be found in the form of certain minerals. On the contrary, minor impurities of their compounds contain ores of many metals. Ga, In and Ti are obtained from waste during the processing of such ores.
In the free state, gallium, indium and thallium are silvery-white metals. Their most important constants are compared below:
Ga In Tl

Physical properties of gallium

Density, g/cjH3 5.9 7.3 11.9
Melting point, °C. . . 30 157 304
Boiling point, °C... . 2200 2020 1475
Electrical conductivity (Hg = 1). . 2 11 6

By hardness gallium close to lead, In and Ti - even softer 6-13.
In dry air, gallium and indium do not change, and thallium is covered with a gray oxide film. When heated, all three elements energetically combine with oxygen and sulfur. They interact with chlorine and bromine at ordinary temperatures, but with iodine only when heated. Located in the voltage series around iron, Ga, In and Ti are soluble in acids.14’ 15
The usual valence of gallium and indium is three. Thallium gives derivatives in which it is tri- and monovalent. 18
Oxides of gallium and its analogues - white Ga 2 O 3, yellow In203 and brown T1203 - are insoluble in water - the corresponding hydroxides E (OH) 3 (which can be obtained from salts) are gelatinous sediments, practically insoluble in water, but soluble in acids. White Ga and In hydroxides are also soluble in solutions of strong alkalis with the formation of gallates and indates similar to aluminates. They are, therefore, amphoteric in nature, and the acidic properties are less pronounced in 1n(OH) 3, and more pronounced in Ga(OH) 3 than in Al(OH) 3. Thus, in addition to strong alkalis, Ga(OH) 3 is soluble in strong solutions of NH 4 OH. On the contrary, red-brown Ti(OH) 3 does not dissolve in alkalis.
The Ga" and In" ions are colorless, the Ti" ion has a yellowish color. The salts of most acids produced from them are highly soluble in water, but are highly hydrolyzed; Of the soluble salts of weak acids, many undergo almost complete hydrolysis. While derivatives of lower valences Ga and In are not typical for them, for thallium it is those compounds in which it is monovalent that are most characteristic. Therefore, T13+ salts have noticeably pronounced oxidizing properties.

Gallium supplements

1. All three members of the subgroup under consideration were discovered using a spectroscope: 1 thallium - in 1861, indium - in 1863 and gallium - in 1875. The last of these elements was predicted and described by D. I. Mendeleev 4 years before its discovery (VI § 1). Natural gallium is composed of isotopes with mass numbers 69 (60.2%) and 71 (39.8); indium-113 (4.3) and 115 (95.7); thallium - 203 (29.5) and 205 (70.5%).
2. In the ground state, atoms of elements of the gallium subgroup have the structure of outer electron shells 4s2 34p (Ga), 5s25p (In), 6s26p (Tl) and are monovalent, i Excitation of trivalent states requires costs of 108 (Ga), 100 (In) or 129, (Ti ) kcal/g-atom. Consecutive ionization energies are 6.00; 20.51; 30.70 for Ga; 5.785; 18.86; 28.03 for In: 6.106; 20.42; 29.8 eV for T1. The electron affinity of the thallium atom is estimated at 12 kcal/g-atom.
3. The rare mineral gallite (CuGaS 2) is known for gallium. Traces of this element are constantly found in zinc ores. Significantly large amounts of it: E (up to 1.5%) were found in the ash of some coals. However, the main raw material for the industrial production of gallium is bauxite, which usually contains minor impurities (up to 0.1%). It is extracted by electrolysis from alkaline liquids, which are an intermediate product of processing natural bauxite into technical alumina. The annual global production of gallium is currently only a few tons, but can be significantly increased.
4. Indium is obtained mainly as a by-product during the complex processing of sulfur ores Zn, Pb and Cu. Its annual global production amounts to several tens of tons.
5. Thallium is concentrated mainly in pyrite (FeS2). Therefore, sludge from sulfuric acid production is a good raw material for obtaining this element. The annual global production of thallium is less than that of indium, but also amounts to tens of tons.
6. To isolate Ga, In and T1 in the free state, either electrolysis of solutions of their salts or incandescence of the oxides in a stream of hydrogen is used. The heats of fusion and evaporation of metals have the following values: 1.3 and 61 (Ga), 0.8 and 54 (In), 1.0 and 39 kcal/g-atom (T1). Their heats of sublimation (at 25 °C) are 65 (Ga), 57 (In) and 43 kcal/g-atom (T1). In pairs, all three elements consist almost exclusively of monatomic molecules.
7. The crystal lattice of gallium is formed not by individual atoms (as is usual for metals), but by diatomic molecules (rf = 2.48A). It thus represents an interesting case of the coexistence of molecular and metallic structures (III § 8). Ga2 molecules are also preserved in liquid gallium, the density of which (6.1 g/cm) is greater than the density of the solid metal (analogy with water and bismuth). An increase in pressure is accompanied by a decrease in the melting temperature of gallium. At high pressures, in addition to the usual modification (Gal), the existence of two other forms has been established. Triple points (with a liquid phase) lie for Gal - Gall at 12 thousand atm and 3 °C, and for Gall - Gall at 30 thousand atm and 45 °C.
8. Gallium is very prone to hypothermia, and it has been possible to keep it in a liquid state down to -40 ° C. Repeated rapid crystallization of a supercooled melt can serve as a method for purifying gallium. In a very pure state (99.999%), it was obtained by electrolytic refining, as well as by the reduction of carefully purified GaCl3 with hydrogen. Its high boiling point and fairly uniform expansion when heated make gallium a valuable material for filling high-temperature thermometers. Despite its external similarity to mercury, the mutual solubility of both metals is relatively low (in the range from 10 to 95 ° C it varies from 2.4 to 6.1 atomic percent for Ga in Hg and from 1.3 to 3.8 atomic percent for Hg in Ga). Unlike mercury, liquid gallium does not dissolve alkali metals and wets many non-metallic surfaces well. In particular, this applies to glass, by applying gallium to which mirrors can be obtained that strongly reflect light (however, there is evidence that very pure gallium, which does not contain indium impurities, does not wet glass). Deposition of gallium onto a plastic base is sometimes used to quickly produce radio circuits. An alloy of 88% Ga and 12% Sn melts at 15 °C, and some other gallium-containing alloys (for example, 61.5% Bi, 37.2 - Sn and 1.3 - Ga) have been proposed for dental fillings. They do not change their volume with temperature and hold up well. Gallium can also be used as a sealant for valves in vacuum technology. However, it should be borne in mind that at high temperatures it is aggressive towards both glass and many metals.
9. In connection with the possibility of expanding the production of gallium, the problem of assimilation (i.e., mastering by practice) of this element and its compounds becomes urgent, which requires research to find areas for their rational use. There is a review article and monographs on gallium.
10. The compressibility of indium is slightly higher than that of aluminum (at 10 thousand atm the volume is 0.84 of the original). With increasing pressure, its electrical resistance decreases (to 0.5 from the original at 70 thousand atm) and the melting temperature increases (up to 400°C at 65 thousand atm). Indium metal sticks crunch when bent, like tin ones. It leaves a dark mark on the paper. An important use of indium is associated with the manufacture of germanium alternating current rectifiers (X § 6 add. 15). Due to its low fusibility, it can act as a lubricant in bearings.
11. The introduction of a small amount of indium into copper alloys greatly increases their resistance to sea water, and the addition of indium to silver enhances its shine and prevents tarnishing in air. The addition of indium gives increased strength to alloys for dental fillings. Electrolytic coating of other metals with indium protects them well from corrosion. An alloy of indium with tin (1:1 by weight) solders glass well to glass or metal, and an alloy of 24% In and 76% Ga melts at 16°C. An alloy of 18.1% In with 41.0 - Bi, 22.1 - Pb, 10.6 - Sn and 8.2 - Cd, melting at 47 ° C, is used medically for complex bone fractures (instead of plaster). There is a monograph on the chemistry of indium
12. The compressibility of thallium is approximately the same as that of indium, but two allotropic modifications are known for it (hexagonal and cubic), the transition point between which lies at 235 °C. Under high pressure, another one arises. The triple point of all three forms lies at 37 thousand atm and 110°C. This pressure corresponds to an abrupt decrease of approximately 1.5 times in the electrical resistance of the metal (which at 70 thousand atm is about 0.3 of normal). Under a pressure of 90 thousand atm, the third form of thallium melts at 650 °C.
13. Thallium is used mainly for the manufacture of alloys with tin and lead, which have high acid resistance. In particular, an alloy with a composition of 70% Pb, 20% Sn and 10% T1 withstands the action of mixtures of sulfuric, hydrochloric and nitric acids well. There is a monograph on thallium.
14. Gallium and compact indium are stable with respect to water, and thallium in the presence of air is slowly destroyed by it from the surface. Gallium reacts only slowly with nitric acid, but thallium reacts very vigorously. On the contrary, sulfuric, and especially hydrochloric, acid easily dissolves Ga and In, while T1 interacts with them much more slowly (due to the formation of a protective film of sparingly soluble salts on the surface). Solutions of strong alkalis easily dissolve gallium, act only slowly on indium and do not react with thallium. Gallium also dissolves noticeably in NH4OH. Volatile compounds of all three elements color the colorless flame in characteristic colors: Ga - almost invisible to the eye dark purple (L = 4171 A), In - dark blue (L = 4511 A), T1 - emerald green (A, = 5351 A).
15. Gallium and indium do not appear to be poisonous. On the contrary, thallium is highly poisonous, and its action is similar to Pb and As. It affects the nervous system, digestive tract and kidneys. Symptoms of acute poisoning do not appear immediately, but after 12-20 hours. With slowly developing chronic poisoning (including through the skin), agitation and sleep disturbance are observed primarily. In medicine, thallium preparations are used for hair removal (for lichen, etc.). Thallium salts have found use in luminous compositions as substances that increase the duration of glow. They also turned out to be a good remedy against mice and rats.
16. In the voltage series, gallium is located between Zn and Fe, and indium and thallium are located between Fe and Sn. The Ga and In transitions according to the scheme E+3 + Ze = E correspond to normal potentials: -0.56 and -0.33 V (in an acidic medium) or -1.2 and -1.0 V (in an alkaline medium). Thallium is converted by acids to the monovalent state (normal potential -0.34 V). The transition T1+3 + 2e = T1+ is characterized by a normal potential of + 1.28 V in an acidic environment or +0.02 V in an alkaline environment.
17. The heats of formation of oxides E2O3 of gallium and its analogues decrease in the series 260 (Ga), 221 (In) and 93 kcal/mol (T1). When heated in air, gallium is practically oxidized only to GaO. Therefore, Ga2O3 is usually obtained by dehydrating Ga(OH)3. Indium, when heated in air, forms In2O3, and thallium forms a mixture of T12O3 and T120 with a higher content of higher oxide, the lower the temperature. Thallium can be oxidized up to T1203 by the action of ozone.
18. The solubility of E2O3 oxides in acids increases along the Ga - In - Tl series. In the same series, the strength of the bond of the element with oxygen decreases: Ga2O3 melts at 1795°C without decomposition, 1n203 transforms into 1n304 only above 850°C, and finely crushed T1203 begins to split off oxygen already at about 90°C. However, much higher temperatures are required to completely convert T1203 to T120. Under excess oxygen pressure, 1p203 melts at 1910 °C, and T1203 - at 716 °C.
19. The heats of hydration of oxides according to the scheme E203 + ZH20 = 2E(OH)3 are +22 kcal (Ga), +1 (In) and -45 (T1). In accordance with this, the ease of elimination of water by hydroxides increases from Ga to T1: if Ga(OH)3 is completely dehydrated only upon calcination, then T1(OH)3 transforms into T1203 even when standing under the liquid from which it was isolated.
20. When neutralizing acidic solutions of gallium salts, its hydroxide precipitates approximately in the pH range = 3-4. Freshly precipitated Ga(OH)3 is highly soluble in strong ammonia solutions, but as it ages, the solubility decreases more and more. Its isoelectric point lies at pH = 6.8, and PR = 2 10~37. For 1n(OH)3 it was found that PR = 1 10-31, and for T1(OH)3 - 1 10~45.
21. For the second and third dissociation constants of Ga(OH)3 according to acidic and basic types, the following values ​​were determined:

H3Ga03 /C2 = 5-10_I K3 = 2-10-12
Ga(OH)3 K2“2. S-P / NW = 4 -10 12
Thus, gallium hydroxide represents a case of an electrolyte very close to ideal amphotericity.

1. The difference in the acidic properties of gallium hydroxides and its analogues is clearly manifested when they interact with solutions of strong alkalis (NaOH, KOH). Gallium hydroxide readily dissolves to form type M gallates, which are stable both in solution and in the solid state. When heated, they easily lose water (Na salt at 120, K salt at 137 °C) and transform into the corresponding anhydrous salts of the MGa02 type. Divalent metal gallates (Ca, Sr) obtained from solutions are characterized by another type - M3 ■ 2H20, which are also almost insoluble. They are completely hydrolyzed by water.
   Thallium hydroxide is easily peptized by strong alkalis (with the formation of a negative sol), but is insoluble in them and does not produce tallates. By dry method (by fusing oxides with the corresponding carbonates), derivatives of the ME02 type were obtained for all three elements of the gallium subgroup. However, in the case of thallium, they turned out to be mixtures of oxides.
   1. The effective radii of the Ga3+, In3*, and T13* ions are 0.62, 0.92, and 1.05 A, respectively. In an aqueous environment, they are apparently directly surrounded by six water molecules. Such hydrated ions are somewhat dissociated according to the scheme E(OH2)a G * E (OH2)5 OH + H, and their dissociation constants are estimated at 3 ■ 10-3° (Ga) and 2 10-4 (In).
   2. The halide salts Ga3+, In3* and T13*’ are generally similar to the corresponding A13* salts. In addition to fluorides, they are relatively fusible and highly soluble not only in water, but also in a number of organic solvents. Only the yellow Gal3 ones are painted.

   It will not be possible to find large deposits in nature, since it simply does not form them. In most cases, it can be found in ore or germanite minerals, where there is a chance of finding from 0.5 to 0.7% of this metal. It is also worth mentioning that gallium can also be obtained by processing nepheline, bauxite, polymetallic ores or coal. First, the metal is obtained, which undergoes processing: washing with water, filtration and heating. And to obtain high quality this metal, special chemical reactions are used. A high level of gallium production can be observed in African countries, specifically in the southeast, Russia and other regions.

   As for the properties of this metal, its color is silver, and at low temperatures it can remain in a solid state, but it will not be difficult for it to melt if the temperature is even slightly higher than room temperature. Since this metal is similar in properties to aluminum, it is transported in special packages.

   Uses of gallium

   Relatively recently, gallium was used in the production of low-melting alloys. But today it can be found in microelectronics, where it is used with semiconductors. This material is also good as a lubricant. If gallium or scandium is used together, then excellent quality metal adhesives can be obtained. In addition, gallium metal itself can be used as a filler in quartz thermometers, since it has a higher boiling point than mercury.

   In addition, it is known that gallium is used in the production of electric lamps, the creation of signal systems and fuses. This metal can also be found in optical instruments, in particular, to improve their reflective properties. Gallium is also used in pharmaceuticals or radiopharmaceuticals.

   But at the same time, this metal is one of the most expensive, and it is very important to establish high-quality extraction of it when producing aluminum and processing coal for fuel, because unique natural gallium is now widely used due to its unique properties.

   It has not yet been possible to synthesize the element, although nanotechnology gives hope to scientists working with gallium.

   DEFINITION

   Gallium- thirty-first element of the Periodic Table. Designation - Ga from the Latin "gallium". Located in the fourth period, IIIA group. Refers to metals. The nuclear charge is 31.

   Gallium is a rare element and does not occur in nature in any significant concentrations. It is obtained mainly from zinc concentrates after smelting zinc from them.

   In its free state, gallium is a silvery-white (Fig. 1) soft metal with a low melting point. It is quite stable in air, does not decompose water, but easily dissolves in acids and alkalis.

   Rice. 1. Gallium. Appearance.

   Atomic and molecular mass of gallium

   The relative molecular mass of a substance (M r) is a number showing how many times the mass of a given molecule is greater than 1/12 the mass of a carbon atom, and the relative atomic mass of an element (A r) is how many times the average mass of atoms of a chemical element is greater than 1/12 mass of a carbon atom.

   Since gallium exists in the free state in the form of monatomic Ga molecules, the values ​​of its atomic and molecular masses coincide. They are equal to 69.723.

   Isotopes of gallium

   It is known that in nature gallium can be found in the form of two stable isotopes 69 Ga (60.11%) and 71 Ga (39.89%). Their mass numbers are 69 and 71, respectively. The nucleus of an atom of the gallium isotope 69 Ga contains thirty-one protons and thirty-eight neutrons, and the isotope 71 Ga contains the same number of protons and forty neutrons.

   There are artificial unstable radioactive isotopes of gallium with mass numbers from 56 to 86, as well as three isomeric states of nuclei, among which the longest-lived isotope 67 Ga with a half-life of 3.26 days.

   Gallium ions

   At the outer energy level of the gallium atom there are three electrons, which are valence:

   1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 4s 2 4p 1 .

   As a result of chemical interaction, gallium gives up its valence electrons, i.e. is their donor, and turns into a positively charged ion:

   Ga 0 -2e → Ga 2+ ;

   Ga 0 -3e → Ga 3+ .

   Gallium molecule and atom

   In the free state, gallium exists in the form of monoatomic Ga molecules. Here are some properties characterizing the gallium atom and molecule:

   Gallium alloys

   By adding gallium to aluminum, alloys are obtained that can be easily hot worked; Gallium-gold alloys are used in dental prosthetics and jewelry.

   Examples of problem solving

   EXAMPLE 1

   Exercise	Natural gallium has two isotopes. The content of the 71 Ga isotope is 36%. Find another isotope if the average relative atomic mass of the element gallium is 69.72. Determine the number of neutrons in the found isotope.
   Solution	Let the mass number of the second gallium isotope be equal to “x” - x Ga. Let us determine the content of the second gallium isotope in nature: w(x Ga) = 100% - w(71 Ga) = 100% - 36% = 64%. The average relative atomic mass of a chemical element is calculated as: Ar = / 100%; 69,72 = / 100%; 6972 = 2556 + 64x; Therefore, the second isotope of gallium is 69 Ga. The atomic number of gallium is 31, which means that the nucleus of a gallium atom contains 31 protons and 31 electrons, and the number of neutrons is equal to: n 1 0 (69 Ga) = Ar(69 Ga) - N (element number) = 69 - 31 = 38.
   Answer	The isotope 69 Ga, containing 38 neutrons and 31 protons.

   EXAMPLE 2

   Exercise	In terms of its chemical properties, gallium is similar to another element - aluminum. Based on this similarity, write down the formulas of oxides and hydroxides that contain gallium, and also create reaction equations that characterize the chemical properties of this element.
   Answer	Gallium, like aluminum, is located in group III of the main subgroup of the Periodic Table D.I. Mendeleev. In its compounds, like aluminum, it exhibits an oxidation state (+3). Gallium is characterized by one oxide (Ga 2 O 3) and one hydroxide (Ga(OH) 3), which exhibit amphoteric properties. Ga 2 O 3 + 3SiO 2 = Ga 2 (SiO 3) 3;