COBALT: STRUCTURE, PROPERTIES, APPLICATIONS - CHEMISTRY - 2025

The cobalt is a transition metal belonging to the group VIIIB of the periodic table and whose chemical symbol is Co. is a solid blue - gray (depending impurities) found throughout the earth 's crust; although its concentration hardly represents 25 ppm or 0.001% of it.

This metal is an essential trace element in the nutrition of ruminants. It is also part of the nucleus of vitamin B ₁₂, necessary for the maturation of erythrocytes. Vitamin B ₁₂ has a structure similar to that of the heme group of hemoglobin; but with Co instead of Faith.

Metallic cobalt sample. Source: Hi-Res Images of Chemical Elements

In nature, cobalt is not usually found pure, but within complex mineral matrices such as: cobaltite, skutterudite, erythrite, etc. In these minerals, cobalt is usually combined with nickel, iron or arsenic.

The name 'cobalt' comes from the German kobalt, which in turn derived from kobolt, a name that miners gave to mineral ores that produced blue dyes and had few metals that they knew; Ores that, it is worth mentioning, caused them poisoning.

Cobalt is found in ores along with nickel, iron, and copper, among other metals. Therefore, it cannot be obtained pure, and requires intense refining work to purify it until its use is practical.

It was discovered by the Swedish chemist Georg Brandt, between 1730 and 1740. It was the first metal discovered since prehistory. Brandt pointed out that cobalt was responsible for the blue tint of ceramics and glass; and not bismuth, as was believed until then.

Cobalt has 29 isotopes. The ⁵⁹ Co is stable and represents almost 100% of the isotopes of cobalt; the remaining 28 are radioisotopes. These include ⁶⁰ Co, used in the treatment of cancer. It is a magnetic element, conserving its magnetism at high temperatures. This property has allowed it to form alloys such as the so-called Alinco, used in loudspeakers, microphones, radio horns, etc.

History

Antiquity

Cobalt was used as far back as 2,000 to 3,000 years BC. The Egyptians, Persians, and Chinese dynasties used it in the making of their sculptures and ceramics. It provided the blue coloration so appreciated in works of art and articles of use.

The Egyptians (1550 - 1292 BC) were probably the first people to use cobalt to give glass its blue color.

Cobalt is not isolated in ores, but in the presence of minerals with nickel, copper and arsenic.

When trying to melt copper with nickel, arsenic oxide was produced, a very poisonous gas that was the cause of the poisoning suffered by the miners.

Discovery

Cobalt was discovered, approximately, in the year 1735 by the Swedish chemist Georg Brandt, who realized that cobalt, precisely, was the metal that contributed the blue coloration of ceramics and glass.

It was the first metal discovered since ancient times. Since this time, man used numerous metals such as iron, copper, silver, tin, gold, etc. In many cases it is unknown when they began to be used.

Mining production

The first cobalt mining in the world began in Europe, with Norway being the first producer of cobalt blue; a compound of alumina and cobalt, as well as enamel (powdered cobalt glass), used as a pigment in ceramics and in paint.

The preponderance in the production of cobalt moved to New Caledonia (1864) and Canada (1904), in the Ontario region due to the discovery of deposits in those countries.

Later, the current Democratic Republic of the Congo (1913) became the world's leading producer of cobalt due to the discovery of large deposits in the Katanga region. Currently this country, together with Canada and Australia, is one of the main cobalt producers.

Meanwhile, the ROC is the world's leading producer of refined cobalt, importing the metal from the Democratic Republic of the Congo for refining.

In 1938, John Livinglood and Glenn Seaborg achieved production in a ⁶⁰ Co atomic reactor; A radioactive isotope that is used in medicine to treat cancer.

Structure and electron configuration of cobalt

Cobalt, like other metals, holds its atoms together through the metallic bond. The force and compression is such that they establish a metallic crystal, where there is a tide of electrons and conduction bands that explain their electrical and thermal conductivities.

Microscopically analyzing cobalt crystals, it will be found that they possess a compact hexagonal structure; there are triangles of Co atoms arranged in ABAB… layers, forming triangular prisms with interleaved layers, which in turn, represent one sixth of a hexagon.

This structure is present for most cobalt samples at temperatures below 450ºC. However, when the temperature rises, a transition begins between two crystallographic phases: the compact hexagonal (hcp) and the face-centered cubic (fcc, for its acronym in English: face-centered cubic).

The transition is slow, so not all hexagonal crystals turn cubic. Thus, at high temperatures cobalt can exhibit both crystalline structures; and then its properties are no longer homogeneous for all metal.

Crystal beads size

The crystal structure is not completely perfect; it can harbor irregularities, which define crystalline grains of different sizes. The smaller they are, the lighter the metal or sponge-like. On the other hand, when the grains are large, the metal will become solid and solid.

The detail with cobalt is that not only the grains modify the external appearance of the metal: also its crystalline structure. Below 450ºC, the hcp structure should predominate; but when the grains are small, as in spongy cobalt, the dominant structure is the fcc.

The opposite occurs when the grains are large: the fcc structure dominates over the hcp. It makes sense since large grains are heavier and put greater pressure on each other. At higher pressures, the Co atoms compact more and choose to adopt the hcp structure.

At high temperatures (T> 1000ºC), the transitions just described occur; but in the case of spongy cobalt, a small portion of its crystals become hexagonal, while most continue to be cubic.

Stable hcp nanocrystals

In a Spanish research work (Peña O'shea V. et al., 2009), it was demonstrated that it was possible to synthesize hexagonal cobalt nanocrystals capable of withstanding temperatures close to 700ºC without undergoing transitions to the fcc phase.

To do this, the researchers reduced samples of cobalt oxides with CO and H ₂, finding that the hcp nanocrystals owed their stability to a coating of carbon nanofibers.

Electronic configuration and oxidation states

The electron configuration of cobalt is:

3d ⁷ 4s ²

It can therefore theoretically lose up to nine electrons from its valence shell; but this does not happen (at least under normal conditions), nor is the Co ⁹⁺ cation ^formed.

Its oxidation states are: -3, -1, +1, +2, +3, +4, +5, with +2 and +3 being the main ones.

Properties

Physical appearance

Solid, lustrous, blue-gray metal. Polished cobalt is silvery white with a bluish hue.

Atomic weight

58.933 g / mol.

Atomic number

27.

Periodic table

It is a transition metal that belongs to group 9 (VIIIB), period 4.

Melting point

1,768 K (1,495 ° C, 2,723 ° F).

Boiling point

3,200 K (2,927 ° C, 5,301 ° F).

Density at room temperature

8.90 g / cm ³.

Heat of fusion

16.06 kJ / mol.

Heat of vaporization

377 kJ / mol.

Molar caloric capacity

24.81 J / mol K

Speed ​​of sound

4,720 m / s (measured on a metal rod).

Hardness

5.0 on the Mohs scale.

Magnetism

It is one of the three ferromagnetic elements at room temperature. Cobalt magnets retain their magnetism at temperatures as high as 1,121ºC (2,050ºF).

Electronegativity

1.88 on the Pauling scale.

Ionization energy

First level of ionization: 740.4 kJ / mol.

Second ionization level: 1,648 kJ / mol.

Third level of ionization: 3,232 kJ / mol.

Atomic radio

125 pm.

Atomic volume

6.7 cm ³ / mol.

Reactions

Cobalt slowly dissolves in dilute mineral acids. It does not combine directly with hydrogen or nitrogen, but it does combine with carbon, phosphorus, and sulfur by heating. It binds to the oxygen present in water vapor at high temperatures.

Reacts vigorously with 15 M nitric acid, forming cobalt nitrate, Co (NO ₃) ₂. Reacts weakly with hydrochloric acid to form cobalt chloride, CoCl ₂. Cobalt does not form hydrides.

Both Co ⁺² and Co ⁺³ form numerous coordination complexes, being considered one of the metals with the highest number of these complexes.

Applications

Alloys

Cobalt alloys are used in the manufacture of jet engines and gas turbine engines. An alloy called Alinco, made up of aluminum, nickel, and cobalt, has strong magnetic properties. Alinco magnets are used in hearing aids, compasses and microphones.

The so-called cutting tools are made with stellite alloys, made of cobalt, chromium and tungsten. Superalloys have a melting point close to that of cobalt, and are characterized by their great hardness, being used in the manufacture of low expansion tools.

Ceramics, sculptures and glass

Glasses glasses with cobalt. Source: Pxhere.

Since ancient times, cobalt has been used by numerous cultures to give their art and decorative works a blue tint. In this sense, oxides have been used: cobalt, CoO, and cobalt, Co ₃ O ₄.

In addition to their use in the manufacture of ceramics, glasses and enamels, cobalt oxides are used in the preparation of catalysts.

Doctors

Cobalt-60 (⁶⁰ Co), a radioactive isotope that emits beta (β) and gamma (γ) radiation, is used in the treatment of cancer. Γ radiation is electromagnetic radiation, so it has the ability to penetrate tissues and reach cancer cells, thus allowing their eradication.

Cancer cells are cells that divide rapidly, which makes them more susceptible to ionizing radiation that strikes their nucleus, damaging genetic material.

The ⁶⁰ Co, like other radioisotopes, is used in the sterilization of materials that are used in medical practice.

Likewise, cobalt is used in the manufacture of orthopedic implants, along with titanium and stainless steel. A large portion of hip replacements employ cobalt-chrome femoral stems.

Alternative energy

Cobalt is used to improve the performance of rechargeable batteries, playing a useful role in hybrid vehicles.

Electroplating

Cobalt is used to provide metal surfaces with a good finish that protects them against oxidation. Cobalt sulfate, CoSO ₄, for example, is the main cobalt compound used in this regard.

In labs

Cobaltous chloride, CoCl ₂.6H ₂ O, is used as a moisture indicator in desiccators. It is a pink solid that changes to a blue color as it hydrates.

Biological role

Cobalt is part of the active site of vitamin B ₁₂ (cyanocobalamin) that is involved in the maturation of erythrocytes. Its absence causes an anemia characterized by the appearance in the blood circulation of large erythrocytes known as megaloblasts.

Where is it located

Earth crust

Cobalt is widely distributed throughout the earth's crust; although its concentration is very low, estimating that it constitutes 25 ppm of the earth's crust. Meanwhile, in the Solar System as a whole its relative concentration is 4 ppm.

It is found in small amounts in the nickel-iron complexes, being native to the Earth and to meteorites. It is also found in combination with other elements in lakes, rivers, seas, plants and animals.

Vitamin B

In addition, it is an essential element for the nutrition of ruminants and is present in vitamin B ₁₂, necessary for the maturation of erythrocytes. Cobalt is not usually isolated in nature, but is found in different minerals combined with other elements.

Minerals

Cobalt minerals include the following: cobaltite, in combination with arsenic and sulfur; erythrite, formed by arsenic and hydrated cobalt; the glaucodot formed by cobalt, iron, arsenic and sulfur; and the skutterudite formed by cobalt, nickel and arsenic.

In addition, the following additional cobalt minerals can be noted: linnaelite, enamel and heterogenite. Cobalt is accompanied in minerals mainly by nickel, arsenic and iron.

Most of the time, cobalt is not extracted from the ores that contain it, but is a by-product of the mining of nickel, iron, arsenic, copper, manganese and silver. A complex process is required to extract and isolate cobalt from these minerals.

References

1. Wikipedia. (2019). Cobalt. Recovered from: en.wikipedia.org
2. A. Owen and D. Madoc Jone. (1954). Effect of Grain Size on the Crystal Structure of Cobalt. Proc. Phys. Soc. B 67 456. doi.org/10.1088/0370-1301/67/6/302
3. Víctor A. de la Peña O′Shea, Pilar Ramírez de la Piscina, Narcis Homs, Guillem Aromí, and José LG Fierro. (2009). Development of Hexagonal Closed-Packed Cobalt Nanoparticles Stable at High Temperature. Chemistry of Materials 21 (23), 5637-5643. DOI: 10.1021 / cm900845h.
4. Anne Marie Helmenstine, Ph.D. (February 02, 2019). Cobalt facts and physical properties. ThoughtCo. Recovered from: thoughtco.com
5. The Editors of Encyclopaedia Britannica. (June 08, 2019). Cobalt. Encyclopædia Britannica. Recovered from: britannica.com
6. Lookchem. (2008). Cobalt. Recovered from: lookchem.com
7. Ducksters. (2019). Elements for kids: cobalt. Recovered from: ducksters.com