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Erbium: structure, properties, obtaining, uses

Erbium participates with an oxidation state of +3 in the vast majority of its compounds, a fairly common chemical characteristic among lanthanide elements. When these compounds, like ErCl 3 , are dissolved in aqueous solutions, they show a pink coloration; as well as several of its solids, used as additives to color glass, jewelry or ceramics.

Metallic erbium sample. Source: Hi-Res Images of Chemical Elements / CC BY (https://creativecommons.org/licenses/by/3.0)

The popularity of erbium is not very remarkable, even among chemistry students. However, those who work in telecommunications and with fiber optic cables will know how important it is to amplify the signals that travel between all continents.

Discovery

Erbium was discovered in 1843 by the Swedish chemist Carl Gustaf Mosander, who was studying samples of the mineral gadolinite, collected in the quarries of Ytterby, a village located in Sweden.

From gadolinite he isolated yttrium oxide, Y 2 O 3 , and after a series of precipitations with ammonium hydroxide and heating, he obtained two new precipitates: erbia and terbia oxides.

However, in 1860, after spectroscopic studies, the identities of the respective oxides were exchanged: erbia corresponded to terbium oxide, while terbia was erbium oxide.

Chemical structure of erbium

Erbium atoms interact with each other using the valence electrons from their 4f and 6s orbitals, thus establishing a strong metallic bond. As a result of this bond, its atomic radii, and the manner of its packing in crystals, erbium adopts a compact hexagonal structure, hcp, of a dense character.

Electronic configuration

The abbreviated electron configuration for erbium is:

[Xe] 6s 2 4f 12

It has 12 electrons in its 4f orbitals, which indicates that this electronic configuration does not correspond to any irregularity or exception to the order of filling (Aufbau’s principle).

Physical appearance

Silvery-white, soft, malleable metal that slowly oxidizes when exposed to air. When roughly filed, it gives off sparks and greenish glints.

Atomic number

68

Molar mass

167.26 g / mol

Melting point

1529 ºC

Boiling point

2868 ºC

Density

At room temperature: 9.066 g / cm 3

At melting point: 8.86 g / cm 3

Oxidation states

The preferred oxidation state for erbium, as well as for other lanthanides, is +3 (Er 3+ ). It can also have oxidation states of 0 (Er 0 ), +1 (Er + ) and +2 (Er 2+ ), these being however less common.

Magnetic order

Paramagnetic at room temperature. It is weakly attracted by magnets.

Electronegativity

1.24 on the Pauling scale.

Ionization energies

-First: 589.3 kJ / mol

-Second: 1150 kJ / mol

-Third: 2194 kJ / mol

Reactivity and compounds

Erbium reacts to form compounds participating with an oxidation number of +3. For example, when a metallic piece of erbium loses its shine, it is because a layer of its oxide covers its surface:

4 Er + 3 O 2  → 2 Er 2 O 3

It also reacts with hot or cold water to form its hydroxide:

2 Er + 6 H 2 O → 2 Er (OH) 3  + 3 H 2

And directly with all the halogens to give rise to their respective halides, whose general formula is ErX 3 (ErF 3 , ErCl 3 , etc.). These halides, like many of the erbium (III) compounds, are distinguished by the fact that their solids present pink or purple colors, like their aqueous solutions, where we have the complex aqueous [Er (OH 2 ) 9 ] 3+ .

Interestingly, erbium compounds retain their pinkish coloration only if they are kept exposed to the open air, receiving UV radiation from the sun . Otherwise, they exhibit matte colors.

Obtaining

Erbium sample 99.99%

Raw material

Erbium is found in nature as part of many rare earth minerals, including monazite, lateritic clays, bastnasite, xenotime, and euxenite.

The latter two, together with the clays of southeast China, are the main raw materials for the production of erbium. China is the country that leads, and by far, the supply and market of lanthanides.

Production methods

The Er 3+ ions , from the oxide Er 2 O 3 , must be separated from the rest of the mineralogical matrix, composed of other lanthanides (Eu 3+ , Sm 3+ , etc.). Doing this was a cumbersome and expensive process; however, with the development of ion exchange chromatography techniques, the production of erbium and other metals was possible.

Then dissolving the xenotime or the selected mineral in an acid medium (HCl or H 2 SO 4 ), and separating the Er 3+ ions as Er 2 O 3 or any of its salts, a reduction is carried out using potassium or potassium vapors. calcium, as reducing agents, under an inert argon atmosphere . It was not until 1934 that the first considerably pure erbium sample was produced.

Uses / applications

Jewelers

The color of erbium oxide is used in synthetic gems and glass objects to tint them pink.

Photography

Erbium atoms absorb infrared radiation, which is why they are used in photographic filters.

Lasers

Erbium is part of yttrium and aluminum garnets (YAG), used to reproduce lasers with which the skin is rejuvenated and scars, blemishes or wrinkles are eliminated in dermatological treatments.

Optical fibers

Erbium atoms are also used as dopants in optical fibers, acting as light amplifiers every 50 kilometers of cable on ocean floors. This allows the signal to travel enormous distances, thanks to which it is possible, for example, to play YouTube videos from different parts of the world.

The photons excite the erbium atoms in the glass, losing energy and releasing more photons, causing the intensity of the light traveling through the fiber to double.

Welding goggles

The ability of erbium atoms to absorb light is exploited in welding goggles, which contain erbium salts that absorb glaring flashes, thus preventing the worker from injuring their eyes or going blind while welding.

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