DEFINITION
Cobalt- a chemical element located in the fourth period in the VIIIB group of the Periodic Table D.I. Mendeleev.
The serial number is 27. The structure of the atom is shown in fig. 1. Metal of the d-family.
Rice. 1. Scheme of the structure of the cobalt atom.
Under normal conditions, cobalt is a white substance with a yellowish tint, it glistens. Able to exist in the form of several modifications, each of which is stable in a certain temperature range. Up to 430 o C, α-cobalt with a hexagonal close-packed lattice is stable, above 430 o C - β-cobalt with a face-centered cubic lattice.
The molar mass of cobalt is 58.9332 g/mol. This value indicates the ratio of the mass of a substance (m) e number of moles of a given substance (n), denoted by M and can be calculated by the formula:
In other words, the molar mass of a substance is the mass of 1 mol of a given substance, expressed in g/mol or kkmol.
Cobalt cannot exist in the form of a gas, only in the form of a solid, therefore, to find the value of its molar mass, you cannot use the value of the molar volume or make calculations using the Mendeleev-Clapeyron formula.
Examples of problem solving
EXAMPLE 1
| Exercise | Cobalt weighing 2.95 g was dissolved in hydrochloric acid, and a cobalt (II) salt was formed, hydrogen sulfide was passed through the resulting solution. Determine the mass of the precipitate formed. |
| Decision | Let's write the reaction equations, which are mentioned in the condition of the problem: Co + 2HCl dilute = CoCl 2 + H 2 (1); CoCl 2 + H 2 S = CoS↓ + 2HCl (2). Let's find the amount of cobalt substance that reacted (molar mass - 59 g / mol): n(Co) = m(Co) / M(Co); n (Co) = 2.95 / 59 = 0.044 mol. According to equation (1) n (Co): n (CoCl 2) \u003d 1: 1, therefore, n (Co) \u003d n (CoCl 2) \u003d 0.044 mol. Then, the number of moles of cobalt (II) sulfide (precipitate) will also be equal to 0.044 moles, since n (CoCl 2) : n (CoS) = 1:1. The mass of cobalt (II) sulfide is (molar mass - 91 g / mol): m(CoS)=n(CoS)×M(CoS); m (CoS) = 0.044 × 91 = 4.004 g. |
| Answer | The mass of cobalt (II) sulfide is 4.004 g |
EXAMPLE 2
| Exercise | The standard electrode potential of nickel is greater than that of cobalt (E 0 Co 2+ / Co 0 \u003d -0.27 V, E 0 Ni 2+ / Ni 0 \u003d -0.25 V). Will this ratio change if we measure the potential of nickel in a solution of its ions with a concentration of 0.001 mol / dm 3, and the potential of cobalt - in a solution with a concentration of 0.1 mol / dm 3? |
| Decision | Let us determine the electrode potentials of cobalt and nickel under given conditions using the Nernst equation: E ’ Ni 2+ / Ni 0 \u003d E 0 Ni 2+ / Ni 0 - 0.059 / n ×lg (a Ni 2+ / a Ni 0); E ’ Ni 2+ / Ni 0 \u003d -0.25 + (0.059 / 2) × lg10 -3; E ’ Ni 2+ / Ni 0 \u003d -0.339 V. E ’ Co 2+ / Co 0 \u003d E 0 Co 2+ / Co 0 - 0.059 / n × lg (a Co 2+ / a Co 0); E ’Co 2+ /Co 0 \u003d -0.27 + (0.059 / 2) × lg10 -1; E ’Co 2+ /Co 0 \u003d -0.307 V. |
| Answer | Under given conditions, the potential of cobalt is greater than the potential of nickel |
Powdered cobalt is mainly used as an additive to steels. This increases the heat resistance of steel, improves its mechanical properties (hardness and wear resistance at elevated temperatures). This metal is part of hard alloys, from which high-speed cutting tools are made. One of the main components of the hard alloy - tungsten or titanium carbide - is sintered in a mixture with cobalt metal powder. It is Co that improves the toughness of the alloy and reduces its sensitivity to shocks and impacts. So, for example, a cutter made of supercobalt steel (18% Co) turned out to be the most wear-resistant and with better cutting properties compared to cutters made of vanadium steel (0% Co) and cobalt steel (6% Co). Also, cobalt alloy can be used to protect against wear of the surfaces of parts subjected to heavy loads. Hard alloy is able to increase the service life of a steel part by 4-8 times.
It is also worth noting the magnetic properties of cobalt. This metal is able to retain these properties after a single magnetization. Magnets must have high resistance to demagnetization, be resistant to temperature and vibrations, and be easy to machine. The addition of cobalt to steels allows them to retain their magnetic properties at high temperatures and vibrations, and also increases their resistance to demagnetization. For example, Japanese steel containing up to 60% Co has a large coercive force (resistance to demagnetization) and only loses its magnetic properties during vibrations by only 2-3.5%. Cobalt-based magnetic alloys are used in the production of electric motor cores, transformers and other electrical devices.
It is worth noting that cobalt has also found application in the aviation and space industries. Cobalt alloys are gradually beginning to compete with nickel alloys, which have proven themselves and have been used in this industry for a long time. Alloys containing Co are used in engines where a sufficiently high temperature is reached, in aircraft turbine designs. Nickel alloys lose their strength at high temperatures (at temperatures from 1038°C) and thus lose to cobalt alloys.
Recently, cobalt and its alloys have been used in the manufacture of ferrites, in the production of "printed circuits" in the radio engineering industry, and in the manufacture of quantum generators and amplifiers. Lithium cobaltate is used as a high-performance positive electrode for the production of lithium batteries. Cobalt silicide is an excellent thermoelectric material and allows the production of thermoelectric generators with high efficiency. Co compounds introduced into glasses during their melting provide a beautiful blue (cobalt) color to glass products.
SUBJECT: "Cobalt is a chemical element"
Performed:
Student of biological and chemical
faculty Savenko O.V.
Checked:
Professor Maksina N.V.
Ussuriysk, 2001
PLAN :
Element of the Periodic Table…………………………….……3
Discovery history…………………………………………………...3
Being in nature……………………………………………...3
Getting……………………………………………………………4
Physical and chemical properties………………………………..4
Application…………………………………………………………..7
Biological role…………………………………………………….7
Radionuclide Cobalt-60……………………………………………..8
List of used literature…………………………………9
Element of the periodic system
The name of the element "cobalt" comes from the Latin cobaltum.
Co, a chemical element with atomic number 27. Its atomic mass is 58.9332. The chemical symbol for the element Co is pronounced the same as the name of the element itself.
Natural cobalt consists of two stable nuclides: 59Co (99.83% by weight) and 57Co (0.17%). In the periodic system of elements of D. I. Mendeleev, cobalt is included in group VIIIB and, together with iron and nickel, forms in the 4th period in this group a triad of transition metals with similar properties. The configuration of the two outer electron layers of the cobalt atom is 3s 2 p 6 d 7 4s 2 . It forms compounds most often in the +2 oxidation state, less often in the +3 oxidation state, and very rarely in the +1, +4 and +5 oxidation states.
The radius of the neutral cobalt atom is 0.125 Nm, the radius of the ions (coordination number 6) Co 2+ is 0.082 Nm, Co 3+ is 0.069 Nm and Co 4+ is 0.064 Nm. The successive ionization energies of the cobalt atom are 7.865, 17.06, 33.50, 53.2, and 82.2 eV. On the Pauling scale, the electronegativity of cobalt is 1.88.
Cobalt is a lustrous, silvery-white, heavy metal with a pinkish tint.
Discovery history
Since antiquity, cobalt oxides have been used to color glass and enamels deep blue. Until the 17th century, the secret of obtaining paint from ores was kept secret. These ores in Saxony were called "kobold" (German: Kobold - brownie, an evil gnome who prevented miners from extracting ore and smelting metal from it). The honor of discovering cobalt belongs to the Swedish chemist G. Brandt. In 1735, he isolated a new silvery-white metal with a faint pinkish tint from the insidious "impure" ores, which he proposed to call "kobold". Later this name was transformed into "cobalt".
Being in nature
In the earth's crust, the content of cobalt is 410 -3% by weight. Cobalt is part of more than 30 minerals. These include carolite CuCo 2 SO 4 , linneite Co 3 S 4 , cobaltite CoAsS, spherocobaltite CoCO 3 , smaltite CoAs 2 and others. As a rule, cobalt in nature is accompanied by its neighbors in the 4th period - nickel, iron, copper and manganese. In sea water, approximately (1-7) 10 -10% cobalt.
Receipt
Cobalt is a relatively rare metal, and the deposits rich in it are now practically exhausted. Therefore, cobalt-containing raw materials (often these are nickel ores containing cobalt as an impurity) are first enriched, and a concentrate is obtained from it. Further, to extract cobalt, the concentrate is either treated with solutions of sulfuric acid or ammonia, or processed by pyrometallurgy methods into a sulfide or metal alloy. This alloy is then leached with sulfuric acid. Sometimes, to extract cobalt, sulfuric acid "heap" leaching of the original ore is carried out (crushed ore is placed in high heaps on special concrete platforms and these heaps are watered with a leaching solution from above).
Extraction is increasingly being used to purify cobalt from accompanying impurities. The most difficult task in the purification of cobalt from impurities is the separation of cobalt from nickel, which is closest to it in chemical properties. A solution containing cations of these two metals is often treated with strong oxidizing agents - chlorine or sodium hypochlorite NaOCl; cobalt thus passes into the precipitate. The final purification (refining) of cobalt is carried out by electrolysis of its sulfate aqueous solution, to which boric acid H3BO3 is usually added.
Physical and chemical properties
Cobalt is a hard metal that exists in two modifications. At temperatures from room temperature to 427°C, the a-modification is stable (hexagonal crystal lattice with parameters a=0.2505 Nm and c=0.4089 Nm). Density 8.90 kg / dm 3. At temperatures from 427°C to the melting point (1494°C), the b-modification of cobalt is stable (face-centered cubic lattice). The boiling point of cobalt is about 2960°C. Cobalt is a ferromagnet, Curie point 1121°C. Standard electrode potential Co 0 /Co 2+ -0.29 V.
In air, compact cobalt is stable; when heated above 300°C, it becomes covered with an oxide film (highly dispersed cobalt is pyrophoric). Cobalt does not interact with water vapor contained in the air, water, solutions of alkalis and carboxylic acids. Concentrated nitric acid passivates the surface of cobalt, just as it passivates the surface of iron.
Several oxides of cobalt are known. Cobalt(II) oxide CoO has basic properties. It exists in two polymorphs: the a-form (cubic lattice), which is stable at temperatures from room temperature to 985°C, and the b-form (also cubic lattice) that exists at high temperatures. CoO can be obtained either by heating cobalt hydroxorcarbonate Co(OH) 2 CoCO 3 in an inert atmosphere, or by careful reduction of Co 3 O 4 .
If cobalt nitrate Co (NO 3) 2, its hydroxide Co (OH) 2 or hydroxocarbonate is calcined in air at a temperature of about 700 ° C, then cobalt oxide Co 3 O 4 (CoO Co 2 O 3) is formed. This oxide is chemically similar to Fe 3 O 4 . Both of these oxides are relatively easily reduced by hydrogen to free metals:
Co 3 O 4 + 4H 2 \u003d 3Co + 4H 2 O.
When calcining Co (NO 3) 2, Co (OH) 2, etc. at 300 ° C, another cobalt oxide appears - Co 2 O 3.
When an alkali solution is added to a cobalt(II) salt solution, a precipitate of Co(OH) 2 precipitates, which is easily oxidized. So, when heated in air at a temperature slightly above 100°C, Co(OH) 2 turns into CoOOH.
If aqueous solutions of divalent cobalt salts are treated with alkali in the presence of strong oxidizing agents, then Co (OH) 3 is formed.
When heated, cobalt reacts with fluorine to form CoF 3 trifluoride. If gaseous HF acts on CoO or CoCO 3, then another cobalt fluoride CoF 2 is formed. When heated, cobalt reacts with chlorine and bromine to form, respectively, CoCl 2 dichloride and CoBr 2 dibromide. By reacting metallic cobalt with gaseous HI at temperatures of 400-500°C, cobalt diiodide CoI 2 can be obtained.
By fusing powders of cobalt and sulfur, silver-gray cobalt sulfide CoS (b-modification) can be prepared. If, however, a current of hydrogen sulfide H 2 S is passed through a solution of a cobalt (II) salt, then a black precipitate of cobalt sulfide CoS (a-modification) precipitates:
CoSO 4 + H 2 S \u003d CoS + H 2 SO 4
When CoS is heated in an H 2 S atmosphere, Co 9 S 8 is formed with a cubic crystal lattice. Other cobalt sulfides are also known, including Co 2 S 3 , Co 3 S 4 and CoS 2 .
With graphite, cobalt forms carbides Co 3 C and Co 2 C, with phosphorus - phosphides of the compositions CoP, Co 2 P, CoP 3. Cobalt also reacts with other non-metals, including nitrogen (nitrides Co 3 N and Co 2 N appear), selenium (cobalt selenides CoSe and CoSe 2 are obtained), silicon (silicides Co 2 Si, CoSi CoSi 2 are known) and boron ( among the known cobalt borides are Co 3 B, Co 2 B, CoB).
Metallic cobalt is able to absorb significant amounts of hydrogen without forming compounds of constant composition. Two stoichiometric cobalt hydrides CoH 2 and CoH were synthesized indirectly.
Water-soluble cobalt salts are known - CoSO 4 sulfate, CoCl 2 chloride, Co(NO 3) 2 nitrate and others. Interestingly, dilute aqueous solutions of these salts have a pale pink color. If the listed salts (in the form of the corresponding crystalline hydrates) are dissolved in alcohol or acetone, then dark blue solutions appear. When water is added to these solutions, their color instantly turns into a pale pink.
Insoluble cobalt compounds include phosphate Co 3 (PO 4) 2 , silicate Co 2 SiO 4 and many others.
Cobalt, like nickel, is characterized by the formation of complex compounds. Thus, ammonia molecules NH 3 often act as ligands in the formation of complexes with cobalt. Under the action of ammonia on solutions of cobalt(II) salts, ammine complexes of cobalt of red or pink color appear, containing cations of composition 2+. These complexes are rather unstable and are easily decomposed even by water.
Ammine complexes of trivalent cobalt, which can be obtained by the action of ammonia on solutions of cobalt salts in the presence of oxidizing agents, are much more stable. Thus, hexammine complexes with the 3+ cation are known (these yellow or brown complexes are called luteosalts), red or pink aquapentammine complexes with the 3+ cation (the so-called roseosalts), etc. In some cases, ligands around the cobalt atom can have different spatial arrangement, and then there are cis- and trans-isomers of the corresponding complexes.
Cobalt
COBALT-a; m.[German] Kobalt]
1. Chemical element (Co), a silvery-white metal with a reddish tint, harder than iron.
2. The paint is dark blue, which includes this metal.
◁ Cobalt, th, th. K-th ores. K-th steel. K paint.
cobalt(lat. Cobaltum), a chemical element of group VIII of the periodic system. The name is from the German Kobold - brownie, gnome. Silvery white metal with a reddish tint; density 8.9 g / cm 3, t pl 1494ºC; ferromagnetic (Curie point 1121ºC). At normal temperatures in air, it is chemically stable. Minerals are rare, mined from nickel ores. Basically, cobalt is used to obtain cobalt alloys (magnetic, heat-resistant, superhard, corrosion-resistant, etc.). The radioactive isotope 60Co is used as a source of γ-radiation in medicine and technology. Cobalt is important for the life of plants and animals, it is part of vitamin B 12.
COBALTCOBALT (lat. Cobaltum), Co, chemical element with atomic number 27, atomic mass 58.9332. The chemical symbol for the element Co is pronounced the same as the name of the element itself. Natural cobalt is composed of two stable nuclides (cm. NUCLIDE): 59Co (99.83% by weight) and 57Co (0.17%). In the periodic system of elements of D. I. Mendeleev, cobalt is included in group VIIIB and, together with iron (cm. IRON) and nickel (cm. NICKEL) forms in the 4th period in this group a triad of transition metals with similar properties. The configuration of the two outer electron layers of the cobalt atom 3 s 2
p 6
d 7
4s 2
. It forms compounds most often in the oxidation state +2 (valency II), less often in the oxidation state +3 (valency III) and very rarely in the oxidation states +1, +4 and +5 (valencies, respectively, I, IV and V) .
The radius of the neutral cobalt atom is 0.125 nm, the radius of the ions (coordination number 6) Co 2+ - 0.082 nm, Co 3+ - 0.069 nm and Co 4+ - 0.064 nm. The successive ionization energies of the cobalt atom are 7.865, 17.06, 33.50, 53.2, and 82.2 eV. On the Pauling scale, the electronegativity of cobalt is 1.88. Cobalt is a lustrous, silvery-white, heavy metal with a pinkish tint.
Discovery history
Since antiquity, cobalt oxides have been used to color glass and enamels deep blue. Until the 17th century, the secret of obtaining paint from ores was kept secret. These ores in Saxony were called "kobold" (German: Kobold - brownie, an evil gnome who prevented miners from extracting ore and smelting metal from it). The honor of discovering cobalt belongs to the Swedish chemist G. Brandt (cm. BRANDT Georg). In 1735, he isolated a new silvery-white metal with a faint pinkish tint from the insidious "impure" ores, which he proposed to call "kobold". Later this name was transformed into "cobalt".
Being in nature
In the earth's crust, the content of cobalt is 410 -3% by weight. Cobalt is part of more than 30 minerals. These include carolite CuCo 2 S 4 , linneite Co 3 S 4 , cobalt (cm. COBALTIN) CoAsS, spherocobaltite CoCO 3 , smaltite CoAs 2 and others. As a rule, cobalt in nature is accompanied by its neighbors in the 4th period - nickel, iron, copper. (cm. COPPER) and manganese (cm. MANGANESE (chemical element)). In sea water, approximately (1-7) 10 -10% cobalt.
Receipt
Cobalt is a relatively rare metal, and the deposits rich in it are now practically exhausted. Therefore, cobalt-containing raw materials (often these are nickel ores containing cobalt as an impurity) are first enriched, and a concentrate is obtained from it. Further, to extract cobalt, the concentrate is either treated with solutions of sulfuric acid or ammonia, or processed by pyrometallurgy methods into a sulfide or metal alloy. This alloy is then leached with sulfuric acid. Sometimes, to extract cobalt, sulfuric acid "heap" leaching of the original ore is carried out (crushed ore is placed in high heaps on special concrete platforms and these heaps are watered with a leaching solution from above).
Extraction is increasingly being used to purify cobalt from accompanying impurities. The most difficult task in the purification of cobalt from impurities is the separation of cobalt from nickel, which is closest to it in chemical properties. A solution containing cations of these two metals is often treated with strong oxidizing agents - chlorine or sodium hypochlorite NaOCl; cobalt thus passes into the precipitate. The final purification (refining) of cobalt is carried out by electrolysis of its sulfate aqueous solution, to which boric acid H 3 BO 3 is usually added.
Physical and chemical properties
Cobalt is a hard metal that exists in two modifications. At temperatures from room temperature to 427°C, the alpha modification is stable (hexagonal crystal lattice with parameters a=0.2505 nm and c=0.4089 nm). Density 8.90 kg/dm 3 . At temperatures from 427°C to the melting point (1494°C), the beta modification of cobalt is stable (face-centered cubic lattice). The boiling point of cobalt is about 2960°C. Cobalt is a ferromagnet, (see Ferromagnetism (cm. FERROMAGNETISM)), Curie point (cm. CURIE POINT) 1121°C. Standard electrode potential Co 0 /Co 2+ -0.29 V.
In air, compact cobalt is stable; when heated above 300°C, it becomes covered with an oxide film (highly dispersed cobalt is pyrophoric (cm. PYROPHORIC METALS)). Cobalt does not interact with water vapor contained in the air, water, solutions of alkalis and carboxylic acids. Concentrated nitric acid passivates the surface of cobalt, just as it passivates the surface of iron.
Several oxides of cobalt are known. Cobalt (II) oxide CoO has basic properties. It exists in two polymorphic modifications: the alpha form (cubic lattice), stable at temperatures from room temperature to 985 ° C, and the beta form that exists at high temperatures (also cubic lattice). CoO can be obtained either by heating cobalt hydroxorcarbonate Co(OH) 2 CoCO 3 in an inert atmosphere, or by careful reduction of Co 3 O 4 .
If cobalt nitrate Co (NO 3) 2, its hydroxide Co (OH) 2 or hydroxocarbonate is calcined in air at a temperature of about 700 ° C, then cobalt oxide Co 3 O 4 (CoO Co 2 O 3) is formed. This oxide is chemically similar to Fe 3 O 4 . Both of these oxides are relatively easily reduced by hydrogen to free metals:
Co 3 O 4 + 4H 2 \u003d 3Co + 4H 2 O.
When calcining Co (NO 3) 2, Co (OH) 2, etc. at 300 ° C, another cobalt oxide appears - Co 2 O 3. When an alkali solution is added to a cobalt (II) salt solution, a precipitate of Co (OH) 2 precipitates, which is easily oxidized. So, when heated in air at a temperature slightly above 100°C, Co(OH) 2 turns into CoOOH. If aqueous solutions of divalent cobalt salts are treated with alkali in the presence of strong oxidizing agents, then Co (OH) 3 is formed.
When heated, cobalt reacts with fluorine to form CoF 3 trifluoride. If COO or CoCO 3 is acted upon by gaseous HF, then another cobalt fluoride CoF 2 is formed. When heated, cobalt reacts with chlorine and bromine to form, respectively, CoCl 2 dichloride and CoBr 2 dibromide. By reacting metallic cobalt with gaseous HI at temperatures of 400-500°C, cobalt diiodide CoI 2 can be obtained. By fusing powders of cobalt and sulfur, silver-gray cobalt sulfide CoS (beta modification) can be prepared. If, however, a current of hydrogen sulfide H 2 S is passed through a solution of a cobalt (II) salt, then a black precipitate of cobalt sulfide CoS (alpha modification) precipitates:
CoSO 4 + H 2 S \u003d CoS + H 2 SO 4
When CoS is heated in an H 2 S atmosphere, Co 9 S 8 is formed with a cubic crystal lattice. Other cobalt sulfides are also known, including Co 2 S 3 , Co 3 S 4 and CoS 2 . With graphite, cobalt forms carbides Co 3 C and Co 2 C, with phosphorus - phosphides of the compositions CoP, Co 2 P, CoP 3. Cobalt also reacts with other non-metals, including nitrogen (nitrides Co 3 N and Co 2 N appear), selenium (cobalt selenides CoSe and CoSe 2 are obtained), silicon (silicides Co 2 Si, CoSi CoSi 2 are known) and boron ( among the known cobalt borides are Co 3 B, Co 2 B, CoB).
Metallic cobalt is able to absorb significant amounts of hydrogen without forming compounds of constant composition. Two stoichiometric cobalt hydrides CoH 2 and CoH were synthesized indirectly. Water-soluble cobalt salts are known - CoSO 4 sulfate, CoCl 2 chloride, Co(NO 3) 2 nitrate and others. Interestingly, dilute aqueous solutions of these salts have a pale pink color. If the listed salts (in the form of the corresponding crystalline hydrates) are dissolved in alcohol or acetone, then dark blue solutions appear. When water is added to these solutions, their color instantly turns into a pale pink.
Insoluble cobalt compounds include phosphate Co 3 (PO 4) 2, silicate Co 2 SiO 4. Cobalt, like nickel, is characterized by the formation of complex compounds. So, as ligands (cm. ligands) in the formation of complexes with cobalt, ammonia molecules NH 3 often act. Under the action of ammonia on solutions of cobalt(II) salts, ammine complexes of cobalt of red or pink color appear, containing cations of composition 2+. These complexes are rather unstable and are easily decomposed even by water.
Ammine complexes of trivalent cobalt, which can be obtained by the action of ammonia on solutions of cobalt salts in the presence of oxidizing agents, are much more stable. Thus, hexammine complexes with a 3+ cation are known (these yellow or brown complexes are called luteosalts), aquapentammine complexes of red or pink color with a 3+ cation (the so-called roseosalts). In some cases, the ligands around the cobalt atom can have different spatial arrangements, and then there are cis- and trans-isomers of the corresponding complexes.
Anions CN - , NO 2 - can also act as ligands in cobalt complexes. By reacting a mixture of hydrogen and CO with cobalt hydroxocarbonate at elevated pressure, as well as by reacting under pressure with CO and metallic cobalt powder, binuclear dicobalt octacarbonyl of the composition Co 2 (CO) 8 is obtained. When it is gently heated, carbonyl Co 4 (CO) 12 is formed. Carbonyl Co 2 (CO) 8 is used to produce highly dispersed cobalt, which is used to apply cobalt coatings on various materials.
Application
The main share of the obtained cobalt is spent on the preparation of various alloys. Thus, the addition of cobalt makes it possible to increase the heat resistance of steel, improves its mechanical and other properties. Cobalt is a component of some hard alloys, from which high-speed tools (drills, drills) are made. Especially important are magnetic cobalt alloys (including the so-called magnetically soft and magnetically hard). Cobalt-based magnetic alloys are used in the manufacture of electric motor cores, they are used in transformers and other electrical devices. For the manufacture of magnetic recording heads, cobalt soft magnetic alloys are used. Cobalt hard magnetic alloys such as SmCo 5 , PrCo 5 , characterized by high magnetic energy, are used in modern instrumentation.
For the manufacture of permanent magnets, alloys containing 52% cobalt and 5-14% vanadium or chromium (the so-called wicalloys) are used. (cm. VIKALLOY)). Cobalt and some of its compounds serve as catalysts (cm. CATALYSTS). Cobalt compounds introduced into glasses during their melting provide a beautiful blue (cobalt) color to glass products. Cobalt compounds are used as pigments in many dyes.
Biological role
Cobalt is one of the trace elements (cm. MICROELEMENTS), that is, it is constantly present in the tissues of plants and animals. Some land plants and algae are able to accumulate cobalt. Entering the molecule of vitamin B 12 (cobalamin), cobalt is involved in the most important processes of the animal body - hematopoiesis, the functions of the nervous system and liver, and enzymatic reactions. Cobalt is involved in enzymatic processes of atmospheric nitrogen fixation by nodule bacteria. The body of an average person (body weight 70 kg) contains about 14 mg of cobalt. The daily requirement is 0.007-0.015 mg, daily intake with food is 0.005-1.8 mg. In ruminants, this need is much higher, for example, in dairy cows - up to 20 mg. Cobalt compounds are necessarily included in microfertilizers. However, an excess of cobalt is harmful to humans. MPC dust of cobalt in the air is 0.5 mg/m 3 , in drinking water the permissible content of cobalt salts is 0.01 mg/l. The toxic dose is 500 mg. Particularly toxic are the vapors of cobalt octacarbonyl Co 2 (CO) 8 .
Radionuclide cobalt-60
Of great practical importance is the artificially produced cobalt radionuclide 60 Co (half-life T 1/2 5.27 years). The gamma radiation emitted by this radionuclide has a sufficiently powerful penetrating ability, and "cobalt guns" - devices equipped with 60 Co, are widely used in flaw detection, for example, gas pipeline welds, in medicine for the treatment of oncological diseases and for other purposes. 60 Co is also used as a radionuclide label.
encyclopedic Dictionary. 2009 .
Synonyms:Scientific and technical encyclopedic dictionary
- (Cobaltum), Co, chemical element of group VIII of the periodic system, atomic number 27, atomic mass 58.9332; metal, mp 1494shC; ferromagnet, Curie point 1121shC. Cobalt is a component of magnetic, high-strength, hard and other alloys; ... ... Modern Encyclopedia
- (lat. Cobaltum) Co, a chemical element of group VIII of the periodic system, atomic number 27, atomic mass 58.9332. The name is from the German Kobold brownie, gnome. Silvery white metal with a reddish tint; density 8.9 g / cm³, mp 1494 .C; ... ... Big Encyclopedic Dictionary
Husband. grayish metal, in various fossils, which, by appearance, are called: cobalt white, red, etc. Cobalt, containing cobalt, related to it. Cobalt flowers, arsenic cobalt red. Dahl's Explanatory Dictionary. IN AND. Far... ... Dahl's Explanatory Dictionary
Cobalt- (Cobaltum), Co, chemical element of group VIII of the periodic system, atomic number 27, atomic mass 58.9332; metal, mp 1494°C; ferromagnet, Curie point 1121°C. Cobalt is a component of magnetic, high-strength, hard and other alloys; ... ... Illustrated Encyclopedic Dictionary
Cobalt- (Co) hard silvery metal. It is used: for the production of special alloys, parts of turbojet aircraft engines, cutting tools, magnetic materials; when welding; in the ceramic and glass industry; in rural ... ... Russian encyclopedia of labor protection
COBALT- COBALT, Cobaltum (chemical sign Co), a shiny white metal with a reddish tint, belonging to the VIII group and the 4th row of the periodic system of Mendeleev. In its typical compounds, K. is bivalent and trivalent, forming two series of salts: oxides ... ... Big Medical Encyclopedia
COBALT- chem. element, symbol Co (lat. Cobaltum), at. n. 27, at. m. 58.93; heavy silvery-white metal with a reddish tint, density 8900 kg/m3, tmelt = 1493 °C. K. refers to ferromagnets. Cobalt minerals are rare and do not form industrial ... ... Great Polytechnic Encyclopedia
Co (from German Kobold brownie, gnome * a. cobalt; n. Kobalt; f. cobalt; i. cobalto), chem. element of group VIII periodic. Mendeleev systems, at. n. 27, at. m. 58.9332. Natural K. consists of 2 stable isotopes 59Co (99.83%) and 57Co (0.17%) ... Geological Encyclopedia
An ordinary person who is not associated with chemistry and medicine, as a rule, has a vague idea of the importance of cobalt for his life and health. Another reason why we find it difficult to explain what cobalt is is its poor distribution in nature. Only 0.004% - this is its content in the earth's crust. However, the metal and its compounds are actively used in metallurgy, agriculture and medicine. In our article, we will expand our understanding of the role of cobalt in industry, as well as dwell on its functions in the human body.
Place of an element in the periodic system
What place does cobalt occupy in the periodic table? The properties of chemical elements, including the metal we are considering, depend on their position in the table of D. I. Mendeleev. It is located in group VIII b (in the short form of the table - in the iron triad of group VIII). Like iron and nickel, in its atom at the last energy level there are two electrons, which indicates that the metal belongs to d-elements and determines its main characteristics. The metal has two valences - II and III. It is also characterized by the phenomenon of allotropy, metal modifications can have a cubic or hexagonal structure.
What is cobalt?
What are the physical properties of the element? In appearance, it has high hardness and magnetic properties. Silvery sheen, malleability and thermal stability are some of the physical features of the element, which are also inherent in its other two neighbors in the periodic system - nickel and iron. Neither oxygen nor water acts on cobalt at ordinary temperatures. Its compounds, such as smalt, have been known since ancient times as substances used to obtain blue stained glass and color ceramic products.
Cobalt is a typical metal, similar in chemical properties to iron. What are the features of its oxides, bases and salts?
Compounds of divalent and trivalent cobalt
The ability to form complex salts is the main distinguishing feature of Co (III) atoms. unstable, the coordination number of cobalt in them is always equal to six. They have a high oxidizing power. Medium salts, for example, CoCL 3 or Co 2 (SO 4) 3 easily transform into salts in which cobalt is already a divalent metal. Its anhydrous compounds are blue in color, and crystalline hydrates and solutions are pink. Unlike other bases, trivalent cobalt hydroxide, when interacting with hydrochloric acid, does not form salt and water, but releases free chlorine from it. The base of the divalent metal in the form of a blue precipitate is obtained by direct reaction of the corresponding salt with an alkali. Let us give a description of the properties of cobalt, which is part of the solid solutions of metals in each other - alloys.
It gives the material exceptional technical parameters of resistance to high temperatures, hardness, resistance to abrasion and corrosion. Alloys containing cobalt are used in the defense industry, rocket science and in closed-loop chemistry. In the production of tool grades of steel, materials with magnetic properties, cobalt is also used as an alloying additive. The characteristics of the properties of such iron alloys are very different from conventional stainless steels containing only chromium or nickel.
The use of cobalt in technology
About a third of all metal produced in the world goes to the production of cermets - artificial composite materials. Tungsten carbide serves as a solid base in them, and cobalt acts as a binding and fixing component. It is also a strategic raw material for the production of engine turbines in the aircraft industry.
In its pure form, the metal is practically not used, but the use of cobalt in a mixture with other elements (iron, copper, tungsten and chromium) is widespread in various industries. The stellite alloy, containing up to 60% cobalt, is characterized by increased heat resistance and hardness; it is an indispensable material for the manufacture of cutters and drills in tool production. Such as tungsten and molybdenum enhance its characteristics. Vitalium alloy, which has a high resistance to plastic deformation, also contains cobalt. connection is as follows: heat-resistant and acid-resistant, used in the manufacture of chemical equipment: synthesis columns, distillation apparatus. The role of alloys in counteracting various types of corrosion is great, for example, parts and mechanisms made of stellite resist destruction during oscillatory and rubbing movements of mechanical surfaces in internal combustion engines.
Methods for obtaining cobalt
Various sectors of the economy require the use of materials containing cobalt. This contributes to an increase in the extraction of ores and minerals, namely: cobalt spice and gloss. The composition of these rocks also includes arsenic, which forces the use of increased safety measures in the processes of metal smelting. The main method for obtaining cobalt is pyrometallurgy, and the method of treating the ore with sulfate acid is also used. The most promising are deposits of silicate-oxide ores, pyrite and pentlandite in China, Russia (on the Kola Peninsula, in the Republic of Tuva and the Krasnoyarsk Territory), as well as in Canada.
The use of metal in agriculture and medicine
Certain important properties that the trace element cobalt possesses contribute to its use, for example, in crop production to increase the vegetative mass of plants. In alfalfa, lupine, clover and other valuable forage grasses of the legume family, it is included in the enzymatic reactions of nitrogen fixation, which occur with the help of nodule bacteria. The lack of a microelement is manifested by such symptoms as discoloration of leaf blades and their loss of the ability to photosynthesis, slowing down growth processes and disruption of the entire plant development cycle. Excessive content of cobalt is possible due to violation of the norms for the introduction of microfertilizers. Since its compounds are highly soluble in water, they immediately enter the xylem and through the conductive elements (vascular-fibrous bundles) enter the leaf mesophyll, causing their discoloration and wilting. Cereal crops are most sensitive to an excess of a microelement: oats, barley, rice.
Biochemistry about the role of cobalt compounds
The branch of biology that studies living matter at the molecular and cellular level has established the important function of this chemical element. It is part of the non-protein part of biologically active substances - enzymes and hormones. For example, cobalt in the human body is found in thyroxine molecules produced by the thyroid gland and controlling metabolic processes. Another vital hormone that regulates blood glucose levels is insulin. It is secreted by the β-cells of the islets of Langerhans of the pancreas and also contains cobalt compounds. Insufficient intake of the element into human cells and organs is observed during the transition from mixed nutrition to vegetarianism, with helminthic invasions and diseases of the digestive system. As you can see, cobalt is a trace element that seriously affects the level of homeostasis in the human body.
The value of a chemical element in metabolism
Hematopoiesis, carried out by the red bone marrow, occurs with the participation of cobalt-containing substances - activators of the corresponding enzymes. One of the main B vitamins - cyanocobolamin (B 12), participating in the formation of red blood cells in the hematopoietic organs, protects the body from anemia. Proper and balanced nutrition, containing liver, beef, seafood, dried apricots, beets, will provide the necessary level of cobalt in the human body (about 40 mg per day) and protect it from diseases of the immune, cardiovascular and endocrine systems.