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Dysprosium: structure, properties, obtaining, uses

Dysprosium is, along with holmium, the metal with the highest magnetic force, making it an essential component for the manufacture of magnets and data storage equipment. Although its name is preceded by the prefix dis-, the truth is that it represents one of the metals with the largest and most promising technological applications.

Ultra pure and dendritic sample of metallic dysprosium. Source: http://images-of-elements.com/ / CC BY (https://creativecommons.org/licenses/by/3.0)

Dysprosium usually participates as a Dy 3+ cation in many of its compounds, having up to five unpaired electrons in its 4f orbitals, which explains the origin of its unusual magnetic properties. Its compounds, yellowish or greenish in color, are luminescent, emitters of infrared radiation, and are good dopants for magnetic materials.

Discovery

Dysprosium was discovered in 1886 by the French chemist Paul Èmile Lecoq, who studied rare earth mineral samples and identified it spectroscopically by analyzing different fractions extracted from holmium oxide. Lecoq carried out more than 30 precipitations of metal hydroxides using ammonia, followed by obtaining their respective oxalate salts.

Because of the extensive work, Lecoq named this metal ‘dysprosium’, whose etymological origin comes from the Greek word ‘dysprositos’, which comes to mean ‘difficult to obtain’.

Structure of dysprosium

The dysprosium atoms, Dy, are held together in their crystals by the action of the metallic bond. As a result of these interactions, its atomic radii, and the mode of its packing, dysprosium ends up adopting a compact hexagonal crystalline structure (hcp), which characterizes its hardness, and which corresponds to the α-Dy phase.

At low temperatures, the hcp structure undergoes orthorhombic (β-Dy phase) distortions, caused by magnetic transitions between the ferromagnetic (below -188.2 ºC) and antiferromagnetic states.

Meanwhile, at high temperatures (above 1381 ºC), the structure of dysprosium transforms to body-centered cubic (bcc), corresponding to the γ-Dy phase or allotrope.

The electronic and abbreviated configuration for dysprosium is as follows:

[Xe] 4f 10 6s 2

Being the tenth member of the lanthanide series, there is a correspondence between this fact and its ten electrons in the 4f orbitals.

When oxidized and loses three electrons, the resulting Dy 3+ cation has a configuration:

[Xe] 4f 9 6s 0

Where up to five unpaired electrons remain in their 4f orbitals. This characteristic explains the unusual magnetic properties of dysprosium and its compounds.

Properties of dysprosium

Physical appearance

Dysprosium is a grayish metal that darkens even more when oxidized. It has considerable hardness, the surface of which, when filed with a wheel, gives off sparks of greenish yellowish tones.

Atomic number

66

Molar mass

162.5 g / mol

Melting point

1407 ºC

Boiling point

2562 ºC

Density

At room temperature: 8,540 g / cm 3

Right at the melting point: 8.37 g / cm 3

Oxidation states

Dysprosium has the following oxidation states or numbers in its compounds: 0 (Dy 0 in alloys or organo compounds), +1 (Dy + ), +2 (Dy 2+ ), +3 (Dy 3+ ) and +4 (Dy 4+ ). Of all of them, the most stable and predominant is +3, since Dy 3+ cations have a distinctive electronic stability.

Electronegativity

1.22 on the Pauling scale

Ionization energies

First: 573 kJ / mol

Second: 1130 kJ / mol

Third: 2200 kJ / mol

Magnetic order

It is strongly paramagnetic above 300 K. Not even a powerful neodymium magnet attracts it with remarkable force; unless it freezes in liquid nitrogen and reaches its ferromagnetic state. Then it will be attracted very strongly.

Reactivity

Metallic dysprosium oxidizes slowly or quickly in a flame to transform into its respective oxide:

4 Dy + 3 O 2  → 2 Dy 2 O 3

This oxide, Dy 2 O 3 , has the particularity that it possesses magnetic properties of greater magnitudes than those of iron oxide, Fe 2 O 3 (both sesquioxides).

Also, metallic dysprosium reacts easily with cold or hot water to produce its hydroxide:

2 Dy + 6 H 2 O → 2 Dy (OH) 3  + 3 H 2

And also directly with the halogens to form a series of halides whose solids are white or yellowish green.

Dysprosium is capable of reacting at high temperatures with any of the non-metals, to produce compounds where it participates with oxidation states of +3 or +2. Its oxalate salts, Dy 2 (C 2 O 4 ) 3 , are insoluble in water, a property on which Lecoq relied to be able to separate it from holmium oxide where it was present.

Obtaining

Raw material

Dysprosium is part of many rare earth minerals, including: xenotime, monazite, bastnäsite, euxenite, gadolinite, lateritic clays, etc. It is found with an appreciable abundance (7-8%) in the yttrium-rich versions of these minerals, also accompanied by the ions of the metals erbium and holmium.

However, monazite sands and rare earth phosphate minerals are the main mineralogical and commercial source for the production of dysprosium.

Production

Dysprosium is a by-product of yttrium extraction and metallurgical processing. Its Dy 3+ ions are separated by magnetic methods during a flotation process, so that a concentrate of lanthanide ions remains, which in turn end up being separated by applying ion exchange chromatography techniques.

Dy 3+ ions react with different halogens to obtain their halides, which are finally reduced using alkali or alkaline earth metals as reducing agents:

3 Ca + 2 DyF 3  → 2 Dy + 3 CaF 2

Said metallothermic reduction is carried out in a tantalum crucible under an inert helium atmosphere .

The purification of dysprosium is achieved by separating it from the cooled mixture, and distilling it under vacuum to remove impurities from other salts, thus obtaining increasingly pure metal samples.

Uses / applications

Infrared spectroscopy

The compounds formed between dysprosium and chalcogenides (O, S, Se, etc.) are emitters of infrared radiation, which is used in spectroscopic analysis for the elucidation of structures, characterizations, and the monitoring of chemical reactions.

Nuclear reactors

Dysprosium is an excellent neutron absorber, which is why it makes up part of the control rods in nuclear fission reactors, in such a way that it disperses or neutralizes an excess of the energy released.

Cinetamography

Lamps containing dysprosium iodide, DyI 3 , mixed with cesium iodide and mercury bromide, are used in film studios , characterized by their intense luminescence.

Computers

Both dysprosium and its ions are very susceptible to magnetization, a property that makes them ideal components for the manufacture of hard disk drives for computers, and data storage devices in general.

Magnets

Dysprosium atoms also serve as additives for powerful neodymium magnets (Nd-Fe-B), used primarily for wind turbine power generators.

Dosimetry

Likewise, dysprosium ions are combined with some salts to grant them luminescence, which is activated by the least exposure of ionizing radiation, therefore being used in dosimetric devices.

Terphenol-D

Dysprosium is the essential component of the Terphenol-D alloy, which also contains erbium and iron atoms. It is a magnetostrictive material, which means that it changes shape (expands or contracts) when it interacts with different senses of a magnetic field. Terphenol-D has applications in sonar systems, transducers, speakers, sensors, etc.

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