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Gallium metal or non-metal. What metal melts in the hands




Chemistry

Gallium #31

subgroup of gallium. The content of each of the members of this subgroup in the earth's crust in the series gallium (4-10~4%) - indium (2-10~6) - thallium (8-10-7) is decreasing. All three "elements are extremely dispersed, and being in the form of certain minerals is not typical for them. 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 silver-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, °С. . . 30 157 304
Boiling point, °С... . 2200 2020 1475
Electrical conductivity (Hg = 1) . . 2 11 6

By hardness gallium close to lead, In and Ti - even softer 6-13.
Gallium and indium do not change in dry air, and thallium is covered with a gray film of oxide. When heated, all three elements combine vigorously with oxygen and sulfur. They interact with chlorine and bromine already at ordinary temperatures, with iodine only when heated. Located in a series of voltages near iron, Ga, In and Ti are soluble in acids.14 '15
The usual valency of gallium and indium is three. Thallium gives derivatives in which it is tri- and monovalent. eighteen
The oxides of gallium and its analogues - white Ga 2 O 3, yellow 1p203 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 hydroxides of Ga and In are also soluble in solutions of strong alkalis with the formation of gallates and indates similar to aluminates. They therefore have an amphoteric character, and the acidic properties are less pronounced in 1p(OH) 3, and stronger in Ga(OH) 3 than in Al(OH) 3 . So, 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 highly hydrolyzed; Of the soluble salts of weak acids, many undergo almost complete hydrolysis. While derivatives of the lower valences Ga and In are not typical for them, for thallium the most characteristic are precisely those compounds in which it is monovalent. Therefore, T13+ salts have markedly pronounced oxidizing properties.

Thallium oxide (T120) is formed as a result of the interaction of elements at high temperatures. It is a black hygroscopic powder. With water, thallium oxide forms yellow nitrous oxide (T10H), which, when heated, easily splits off water and goes back to T120.
Thallium oxide hydrate is highly soluble in water and is a strong base. The salts it forms are mostly colorless and
crystallize without water. Chloride, bromide and iodide are almost insoluble, but some other salts are soluble in water. Arbitrary TiOH and weak acids due to hydrolysis give an alkaline reaction in solution. Under the action of strong oxidizing agents (for example, chlorine water), monovalent thallium is oxidized to trivalent.57-66
In terms of the chemical properties of the elements and their compounds, the gallium subgroup is in many ways similar to the germanium subgroup. So, for Ge and Ga, the higher valence is more stable, for Pb and T1 it is lower, the chemical nature of the hydroxides in the series Ge-Sn-Pb and Ga-In-Ti changes of the same type.Sometimes more subtle "features of similarity appear further, for example, the low solubility of halide (Cl, Br, I) salts of both Pbn and Ti. For all that, there are significant differences between the elements of both subgroups (partly due to their different valence): the acidic nature of the hydroxides of Ga and its analogues is much less pronounced than that of the corresponding elements of the germanium subgroup, in contrast to PbF 2, thallium fluoride is highly soluble, etc.

Gallium Supplement

  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, the atoms of the elements of the gallium subgroup have the structure of outer electron shells 4s2 34p (Ga), 5s25p (In), 6s26p (Tl) and are univalent, i ) kcal/g-atom. Successive 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 affinity of a thallium atom for an electron is estimated at 12 kcal/g-atom.
  3. For gallium, the rare mineral gallite (CuGaS 2) is known. Traces of this element are constantly found in zinc ores. Significantly large amounts of it: E (up to 1.5%) were found in the ashes of some hard coals. However, the main raw material for the industrial production of gallium is bauxite, usually containing minor impurities (up to 0.1%). It is extracted by electrolysis from alkaline liquids, which are an intermediate product of the processing of natural bauxite into commercial alumina. The size of the annual world production of gallium is still estimated at a few tons, but can be significantly increased.
  4. Indium is obtained mainly as a by-product in the complex processing of sulfur ores Zn, Pb and Cu. Its annual world production is several tens of tons.
  5. Thallium is concentrated mainly in pyrite (FeS2). Therefore, sulfuric acid production sludge is a good raw material for obtaining this element. The annual world production of thallium is less than that of India, but is also in the tens of tons.
  6. To isolate Ga, In, and T1 in the free state, either the electrolysis of solutions of their salts or the incandescence of oxides in a hydrogen flow is used. The heats of melting 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). The heats of their sublimation (at 25°C) are 65 (Ga), 57 (In), and 43 kcal/g-atom (T1). In pairs, all three elements are composed 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 is thus an interesting case of the coexistence of molecular and metallic structures (III § 8). Ga2 molecules are also preserved in liquid gallium, whose density (6.1 g/cm) is greater than that of a solid metal (an analogy with water and bismuth). An increase in pressure is accompanied by a decrease in the melting point of gallium. At high pressures, in addition to the usual modification (Gal), the existence of two other forms of it has been established. Triple points (with a liquid phase) lie for Gal - Gall at 12 thousand atm and 3 °C, and for Gall - Galll ​​- at 30 thousand atm and 45 °C.
  8. Gallium is very prone to hypothermia, and it was possible to keep it in a liquid state down to -40 ° C. Repeated repetition of rapid crystallization of a supercooled melt can serve as a method for purifying gallium. In a very pure state (99.999%), it was also obtained by electrolytic refining, as well as by hydrogen reduction of carefully purified GaCl3. The high boiling point and fairly uniform expansion on heating make gallium a valuable material for filling high-temperature thermometers. Despite its outward resemblance 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 to Ga). Unlike mercury, liquid gallium does not dissolve alkali metals and well wets many non-metallic surfaces. In particular, this applies to glass, by applying gallium to which mirrors can be obtained that strongly reflect light (however, there is an indication that very pure gallium, which does not contain indium impurities, does not wet glass). The deposition of gallium on a plastic base is sometimes used to quickly obtain radio circuits. An alloy of 88% Ga and 12% Sn melts at 15°C, and some other alloys containing gallium (eg 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 well. Gallium can also be used as a valve seal 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 relevant, 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 (up to 0.5 of the initial value at 70,000 atm) and the melting point increases (up to 400°C at 65,000 atm). Sticks of metallic indium crunch when bent, like pewter. On paper, it leaves a dark line. An important use of indium is associated with the manufacture of germanium AC rectifiers (X § 6 add. 15). Due to its fusibility, it can play the role of 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 brilliance and prevents tarnishing in air. The addition of indium gives alloys for dental fillings increased strength. The electrolytic indium coating of other metals well protects them from corrosion. An alloy of indium with tin (1:1 by mass) solders glass well with glass or metal, and an alloy of 24% In and 76% Ga melts at 16°C. An alloy melting at 47 ° C 18.1% In with 41.0 - Bi, 22.1 - Pb, 10.6 - Sn and 8.2 - Cd finds medical use in complex bone fractures (instead of gypsum). There is a monograph on the chemistry of indium
  12. The compressibility of thallium is approximately the same as indium, but two allotropic modifications (hexagonal and cubic) are known for it, 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 by about 1.5 times in the electrical resistance of the metal (which at 70 thousand atm is about 0.3 of the usual one). Under a pressure of 90,000 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, the alloy composition of 70% Pb, 20% Sn and 10% T1 well withstands the action of mixtures of sulfuric, hydrochloric and nitric acids. There is a monograph on thallium.
  14. With respect to water, gallium and compact indium are stable, while thallium in the presence of air is slowly destroyed by it from the surface. Gallium reacts with nitric acid only slowly, while 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 noticeably dissolves in NH4OH. Volatile compounds of all three elements color a colorless flame in characteristic colors: Ga - in dark purple (L. \u003d 4171 A), almost imperceptible to the eye, In - in dark blue (L, \u003d 4511 A), T1 - in emerald green (A, \u003d \u003d 5351 A).
  15. Gallium and indium do not appear to be poisonous. On the contrary, thallium is highly toxic, and in the nature of the action it 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), excitation and sleep disturbance are observed primarily. In medicine, thallium preparations are used to remove hair (for lichen, etc.). Thallium salts have found application in luminous compositions as substances that increase the duration of the glow. They also proved to be a good remedy for mice and rats.
  16. In the voltage series, gallium is located between Zn and Fe, while indium and thallium are between Fe and Sn. The Ga and In transitions according to the E + 3 + Ze = E scheme correspond to normal potentials: -0.56 and -0.33 V (in an acidic environment) or -1.2 and -1.0 V (in an alkaline environment). Thallium is converted by acids into a monovalent state (normal potential -0.34 V). The transition T1 + 3 + 2e \u003d T1 + is characterized by a normal potential of + 1.28 V in an acidic environment or + 0.02 V - in an alkaline one.
  17. The heats of formation of E203 oxides of gallium and its analogues decrease along the series 260 (Ga), 221 (In), and 93 kcal/mol (T1). When heated in air, gallium is practically oxidized only to GaO. Therefore, Ga203 is usually obtained by dehydration of Ga (OH) h. Indium, when heated in air, forms In2O3, and thallium forms a mixture of T12O3 and T120, with the higher the content of the higher oxide, the lower the temperature. Up to T1203, thallium can be oxidized by the action of ozone.
  18. The solubility of E2O3 oxides in acids increases along the series Ga - In - Tl. In the same series, the strength of the bond between the element and oxygen decreases: Ga2O3 melts at 1795°C without decomposition, ln203 transforms into ln304 only above 850°C, and finely divided T1203 begins to split off oxygen already at about 90°C. However, much higher temperatures are required for complete conversion of T1203 to T120. Under an excess pressure of oxygen, In203 melts at 1910°C, while T1203 melts at 716°C.
  19. The heats of hydration of oxides according to the scheme E2O3 + ZH20 = 2E(OH)3 are +22 kcal (Ga), +1 (In) and -45 (T1). In accordance with this, the ease of splitting off water by hydroxides increases from Ga to T1: if Ga(OH)3 is completely dehydrated only upon calcination, then T1(OH)3 passes into T1203 even when standing under the liquid from which it was isolated.
  20. When acidic solutions of gallium salts are neutralized, 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 lp(OH)3, PR = 1 10-31 was found, and for T1(OH)3 - 1 10~45.
  21. The following values ​​were determined for the second and third dissociation constants of Ga(OH)3 according to the acidic and basic types:

H3Ga03 /C2 = 5-10_I K3 = 2-10-12
Ga(OH)3 K2“2. Yu-P / Nz \u003d 4 -10 12
Thus, gallium hydroxide is 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 pass into the corresponding anhydrous salts of the MGa02 type. Divalent metals (Ca, Sr) obtained from solutions of gallates 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 give tallates. Dry way (by fusion of 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 medium, they are apparently directly surrounded by six water molecules. Such hydrated ions are somewhat dissociated according to the scheme E(OH2)a T * 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 of Ga3+, In3* and T13*' are generally similar to the corresponding salts of A13*. In addition to fluorides, they are relatively fusible and readily soluble not only in water, but also in a number of organic solvents. Of these, only yellow Gal3 are painted

    What is 29.76 o C. If you place it in a warm palm, it gradually begins to move from a solid state to a liquid form.

    A brief excursion into history

    What is the name of the metal that melts in the hand? As noted above, such a material is known under the definition of gallium. Its theoretical existence was predicted back in 1870 by a Russian scientist, the author of a table of chemical elements - Dmitry Mendeleev. The basis for the emergence of such an assumption was his study of the properties of numerous metals. At that time, not a single theorist could have imagined that the metal that melts in the hands exists in reality.

    The possibility of synthesizing an extremely fusible material, the appearance of which Mendeleev predicted, was proved by the French scientist Emile Lecoq de Boisbaudran. In 1875, he managed to isolate gallium from zinc ore. During experiments with the material, the scientist received a metal that melts in his hands.

    It is known that Émile Boisbaudran experienced significant difficulties in isolating a new element from zinc ore. During the first experiments, he managed to extract only 0.1 grams of gallium. However, even this was enough to confirm the amazing property of the material.

    Where is gallium found in nature?

    Gallium is one of the elements that do not occur as ore deposits. The material is very dispersed in the earth's crust. In nature, it is found in extremely rare minerals such as gallite and zengeite. In the course of laboratory experiments, a small amount of gallium can be isolated from the ores of zinc, aluminum, germanium, and iron. Sometimes it is found in bauxite, coal deposits, and other mineral deposits.

    How is gallium obtained

    Currently, scientists most often synthesize a metal that melts in their hands from aluminum solutions that are mined during the processing of alumina. As a result of removing the main mass of aluminum and carrying out the procedure of repeated concentration of metals, an alkaline solution is obtained, in which there is an insignificant fraction of gallium. Allocate such material from solution by electrolysis.

    Applications

    Gallium has not found industrial use to this day. This is due to the widespread use of aluminum, which has similar properties in solid form. Despite this, gallium looks like a promising material, since it has excellent semiconductor properties. Such a metal can potentially be used for the production of transistor elements, high-temperature rectifiers, and solar batteries. Gallium looks like an excellent solution for making optical mirror coatings that will have the highest reflectivity.

    The main obstacle to the use of gallium on an industrial scale remains the high cost of its synthesis from ores and minerals. The price per ton of such metal in the world market is more than 1.2 million dollars.

    To date, gallium has found effective use only in the field of medicine. The metal in liquid form is used to slow down bone loss in people suffering from cancer. It is used to quickly stop bleeding in the presence of extremely deep wounds on the body of the victims. In the latter case, blockage of vessels with gallium does not lead to the formation of blood clots.

    As noted above, gallium is a metal that melts in the hands. Since the temperature required for the transition of the material to a liquid state is slightly more than 29 ° C, it is enough to hold it in the palms of your hands. After a while, the initially solid material will begin to melt right before our eyes.

    A rather fascinating experiment can be carried out with the solidification of gallium. The presented metal tends to expand during solidification. To conduct an interesting experiment, it is enough to place liquid gallium in a glass vial. Next, you need to start cooling the container. After a while, you can notice how metal crystals begin to form in the bubble. They will have a bluish color, as opposed to the silvery hue that is characteristic of the material in its liquid state. If the cooling is not stopped, the crystallizing gallium will eventually burst the glass bubble.

    Finally

    So we found out which metal melts in the hand. Today, gallium can be found on sale for your own experiments. However, the material must be handled with extreme care. Solid gallium is non-toxic. However, prolonged contact with the material in liquid form can lead to the most unforeseen health consequences, up to respiratory arrest, paralysis of the limbs and the entry of a person into a coma.

    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. It is designated by the symbol Ga (lat. Gallium). Belongs to the group of light metals. The simple substance gallium is a soft, ductile silver-white metal with a bluish tint.

    Atomic number - 31

    Atomic mass - 69.723

    Density, kg/m³ - 5910

    Melting point, ° С - 29.8

    Heat capacity, kJ / (kg ° С) - 0.331

    Electronegativity - 1.8

    Covalent radius, Å - 1.26

    1st ionization potential, ev - 6.00

    The history of the discovery of gallium

    The 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, outside of France, he was little known. He was 38 years old, he was mainly 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 investigated the spectrum of zinc blende brought from Pierrefitte (Pyrenees). It was in this spectrum that a new violet line was discovered. 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 was not easy 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 get a new element, but in a very small amount. So small (less than 0.1 g) that Lecoq de Boisbaudran could not fully study its physical and chemical properties.

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

    This message was read by D.I. Mendeleev recognized ekaaluminum, which he had predicted five years earlier, in gallium. Mendeleev immediately wrote to Paris. “The method of discovery and isolation, as well as the few properties described, suggest that the new metal is nothing more than ekaaluminum,” his letter said. It then repeated the predicted properties for that element. Moreover, never holding a grain of gallium in his hands, without seeing it in his eyes, the Russian chemist claimed 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 more about 5.9...6.0 g/cm3! But experience has shown the opposite: the discoverer was mistaken. The discovery of the first of the elements predicted by Mendeleev significantly strengthened the position of the periodic law.

    Finding Gaulin nature

    The average content of gallium in the earth's crust is 19 g/t. Gallium is a typical trace element with a dual geochemical nature. The only Gallium mineral, CuGaS 2 gallite, 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 enclosed in aluminum minerals. Due to the closeness 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 content of gallium 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%).

    Physical Properties Gaul

    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 (others are Bi, Ge).

    Crystalline gallium has several polymorphic modifications, however, only one (I) is thermodynamically stable, having an orthorhombic (pseudotetragonal) 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 T=20°C is 5.904 g/cm³.

    One of the features of gallium is a wide temperature range for the existence of a 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 are, 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. The surface tension measured at 30 °C in a hydrogen atmosphere is 0.735 N/m. The reflection coefficients for the wavelengths of 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 is 2.1·10 −28 m² and 5.1·10 −28 m², respectively.

    Gallium is a low toxic element. Due to the low melting point, gallium ingots are recommended to be transported in polyethylene bags, which are poorly wetted by the gallium melt. At one time, the metal was even used to make fillings (instead of amalgam fillings). This application is based on the fact that when copper powder is mixed with molten gallium, a paste is obtained, which hardens after a few hours (due to the formation of an intermetallic compound) and then can 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 because quartz (as well as most other glasses) is highly wettable by this metal. That is, gallium will simply stick to the walls of quartz.

    Chemical properties Gaul

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

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

    Gallium interacts with mineral acids with the release of hydrogen and the formation of salts, and the reaction proceeds even below room temperature:

    2Ga + 6HCl = 2GaCl 3 + 3H 2

    The reaction products 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 action is stronger than the melt of any other metal. So, graphite and tungsten are resistant to the action of a 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 zinc, scandium, and titanium subgroups. One of the gallides V 3 Ga has a rather high superconducting transition temperature of 16.8 K.

    Gallium forms polymeric hydrides:

    4LiH + GaCl 3 = Li + 3LiCl.

    The ion stability decreases in the series BH 4 - → AlH 4 - → GaH 4 - . Ion BH 4 - stable in aqueous solution, AlH 4 - and GaH 4 - quickly hydrolyze:

    GaH 4 - + 4H 2 O \u003d 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, potassium gallium alum KGa (SO 4) 2 * 12H2O.

    The interaction of gallium with sulfuric acid is interesting. 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, however, the metal is washed with hot water, the reaction will resume, and will continue until a new “skin” of sulfur grows on the gallium.

    Basic connections Gaul
    • Ga2H6- volatile liquid, t pl −21.4 °C, bp t 139 °C. In ethereal suspension with lithium or thallium hydrate, it forms LiGaH 4 and TlGaH 4 compounds. It is formed as a result of the treatment of tetramethyldigallane with triethylamine. There are banana bonds, as in diborane
    • Ga2O3- white or yellow powder, t pl 1795 °C. It 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. Obtained by heating metallic gallium in air at 260 °C or in an oxygen atmosphere, or by calcining gallium nitrate or sulfate. ΔH° 298(arr) −1089.10 kJ/mol; ΔG° 298(arr) −998.24 kJ/mol; S° 298 84.98 J/mol*K. They show amphoteric properties, although the main properties, in comparison with aluminum, are enhanced:

    Ga 2 O 3 + 6HCl \u003d 2GaCl 2 Ga 2 O 3 + 2NaOH + 3H 2 O \u003d 2Na Ga 2 O 3 + Na 2 CO 3 \u003d 2NaGaO 2 + CO 2

    • Ga(OH)3- precipitates in the form of a jelly-like precipitate during the treatment of solutions of salts of trivalent gallium with hydroxides and carbonates of alkali metals (pH 9.7). It dissolves in concentrated ammonia and concentrated ammonium carbonate solution, 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 salts of trivalent gallium.
    • GaF3- White powder. t pl > 1000 ° C, t kip 950 ° C, density - 4.47 g / cm³. Slightly soluble in water. Known crystalline GaF 3 ·3H 2 O. Obtained by heating gallium oxide in a fluorine atmosphere.
    • GaCl3- colorless hygroscopic crystals. t pl 78 ° C, t kip 215 ° C, density - 2.47 g / cm³. Let's well dissolve in water. Hydrolyzes in aqueous solutions. Obtained directly from the elements. It is used as a catalyst in organic syntheses.
    • GaBr3- colorless hygroscopic crystals. t pl 122 ° C, t kip 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 pl 212 ° C, t kip 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 t pl 1250 °C and density 3.65 g/cm³. It interacts with water, while completely hydrolyzing. Obtained by the interaction of gallium with sulfur or hydrogen sulfide.
    • Ga 2 (SO 4) 3 18H 2 O- a colorless, highly soluble substance in water. It is obtained by the interaction of gallium, its oxide and hydroxide with sulfuric acid. With sulfates of alkali metals and ammonium, it easily forms alums, 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. Obtained by the action of nitric acid on gallium hydroxide.
    Obtaining gallium

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

    With the soda-lime method of processing bauxite or nepheline ore, Gallium is concentrated in the last fractions of sediments released during carbonization. For additional enrichment, the precipitate of hydroxides is treated with milk of lime. In this case, most of the Al remains in the precipitate, and Gallium passes 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 residual anodic alloy of the Al refining process by the three-layer electrolysis method can also serve as a source of Gallium. In the production of zinc, the sources of Gallium are sublimates (Weltz oxides) formed during the processing of leaching tailings of zinc cinders.

    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.

    The use 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 an element of group III, which contributes to the enhancement of "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 elements of the V group - 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 isotope separation from a natural mixture in order to increase the sensitivity of neutrino detectors. Since the content of 71 Ga in the 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 a ton of gallium cost 1.2 million US dollars on the world market, and due to the high price and at the same time the great demand for this metal, it is very important to establish its complete extraction in aluminum production and coal processing at liquid fuel.

    Liquid gallium reflects 88% of the light falling on it, solid - a little less. Therefore, gallium mirrors are very easy to manufacture - a 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 very 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 of 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 fixing the radiation characteristic of this isotope, doctors almost accurately determine the size of foreign formations.

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

    Gallium metal is also filled into quartz thermometers (instead of mercury) to measure high temperatures. This is because gallium has a much higher boiling point than 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 Canion, Nevada, USA and in 2005 in Inner Mongolia, China - gallium is not found anywhere in the world in industrial concentrations. (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).

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

    There are not many gallium producers. GEO Gallium is one of the leaders in the gallium market. Its main facilities until 2006 consisted of a plant in Stade (Germany), which produces about 33 tons per year, a plant in Salindres, processing 20 tons / year (France) and in Pinjarra (Western Australia) - potential (but not commissioned in system) capacity up to 50 tons/year.

    In 2006, the position of the No. 1 producer weakened - the Stade enterprise was bought by the British 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. Dowa Mining's total raw material capacity is estimated at up to 20 tons/year. In Kazakhstan, the Aluminum of Kazakhstan plant in Pavlodar has a total capacity of up to 20 tons/year.

    China has become a very serious supplier of gallium. In China, there are 3 major producers of primary gallium - 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 set up a joint venture in China with a capacity of up to 40 tons/year. The American firm AXT has established a joint venture with the largest Chinese aluminum enterprise Shanxi Aluminum Factory Beijing JiYa semiconductor Material Co. with a capacity 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 the owners of gallium sites created at alumina refineries.

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

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

    The 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.

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

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

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

    The use 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. Also this material is good as a lubricant. If gallium is used together or scandium, then excellent quality metal adhesives can be obtained. In addition, metallic gallium 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 signaling systems for and fuses. Also, this metal can be found in optical devices, 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 in the production of aluminum and the processing of coal for fuel to establish its high-quality extraction, because the unique natural gallium today has become quite 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.

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

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

    As an element of group III, which contributes to the enhancement of "hole" conductivity in a semiconductor, (purity not less than 99.999%) is used as an additive to germanium and silicon.

    Intermetallic compounds of gallium with elements of the V group - 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. Therefore, gallium mirrors are very easy to manufacture - a gallium coating can even be applied with a brush.

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

    Attempts have been made to apply 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 of 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 fixing 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 has not yet been possible to use them completely due to the difficulty of obtaining gallium, an element that is quite rare (1.5-10-3% of the weight of the earth's crust) and very scattered.

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

    Usually, gallium is found in zinc, aluminum, iron ores, as well as in coal - as an insignificant impurity. And what is characteristic: the more this impurity, the more difficult it is to extract it, because there is more gallium in the ores of those metals ( , ) that are close to it in properties. The main part of terrestrial gallium is enclosed in aluminum minerals.

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

    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.

    SEARCH FOR REGULARITIES. The properties of gallium were predicted by D. I. Mendeleev five years before the discovery of this element. The ingenious Russian chemist built his predictions on the patterns of changes in properties by groups of the periodic system. But for Lecoq de Boisbaudran, the discovery of gallium was not a happy accident either. A talented spectroscopist, as early as 1863 he discovered regularities in the change 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-wavelength part of the spectrum. It was this missing line that he was looking for and found in the spectrum of zinc blende from Pierrfit.

    WORD PLAY? According to which historians of science see in the name of element No. 31 not only patriotism, but also the indiscretion of its discoverer. It is customary to believe 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 AGE, In minerals, gallium often accompanies aluminum. Interestingly, the ratio of these elements in the mineral depends on the time of formation of the mineral. In feldspars, one atom of gallium falls on 120 thousand aluminum atoms. In nephelines formed much later, this ratio is already 1:6000, and in even "younger" petrified wood - only 1:13.

    FIRST PATENT. The first patent for the use of gallium was taken at the very beginning of the 20th century. Element number 31 wanted to be used in electric arc lamps.

    SULFUR REPLACES, SULFUR PROTECTS. Interestingly, the interaction of gallium with sulfuric acid occurs. 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 the metal is washed 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. That is why contact with gallium leads many structural materials to a loss of 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! Insignificant additions of gallium oxide noticeably affect the properties of oxides of many metals. Thus, the admixture of Ga2O3 to zinc oxide significantly reduces its sintering capacity. But zinc in such an oxide is much more than in pure. And in titanium dioxide, when Ga2O3 is added, the electrical conductivity drops sharply.

    HOW GALLIUM IS GET. Industrial deposits of gallium ores in the world have not been found. Therefore, gallium has to be extracted from zinc and aluminum ores, which 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 diverse. For example, let's tell you how gallium is extracted from zinc blende - the mineral in which this element was found first.

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

    Under the action of alkali, aluminum and gallium compounds go into solution. When this solution is carefully neutralized, gallium hydroxide precipitates. But part of the aluminum also precipitates. Therefore, the precipitate is dissolved again, now in hydrochloric acid. It turns out a solution of gallium chloride, contaminated mainly with aluminum chloride. These can be separated by extraction. Ether is poured in 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 gallium. From this alkaline solution, metallic gallium is obtained. Obtained by electrolysis at a voltage of 5.5 V. Gallium is deposited on a copper cathode.