Themes

Neodymium: structure, properties, uses

Neodymium is within the group of the most interesting and practical lanthanides. Like other of its congeners, it forms compounds that exhibit pink or purple colorations, which can color glass and ceramics sensitive to the incident light source; that is, they change color depending on which light illuminates them.

Neodymium metal sample stored in a glass vial. Source: Hi-Res Images of Chemical Elements / CC BY (https://creativecommons.org/licenses/by/3.0)

Above we have a sample of metallic neodymium. It must be stored under an inert atmosphere , otherwise it will quickly corrode by the action of oxygen. Neodymium alone is not a standout metal, as is copper or gold; however, its alloys and mixed crystals have a huge technological impact.

In this sense, neodymium is synonymous with magnets, due to the famous neodymium magnets, which are the most powerful ever created. These consist of an alloy Nd-Fe-B, whose physical properties are quite similar to those of ceramics, and which occupy an important place in endless electronic equipment.

Discovery

The discovery of neodymium began with didymium, a mixture of lanthanide oxides or salts that was mistakenly considered an element in the 19th century.

In 1885, the Austrian chemist Carl Auer von Welsbach, sought and devised a method to fractionate didymium, which by then, and thanks to spectroscopic analysis, its compound nature was already known.

Carl Welsbach completed his task after arduous fractional crystallizations of the double salts of nitrate and ammonium, obtained from the metals present in didymium: neodymium and praseodymium.

The neodymium salt was pink in color, while the praseodymium salt was greenish in color. His name, ‘neodymium’, which means ‘new twin’, derived from ‘didymium’, as it was the most abundant fraction of the didymium he worked with.

Neodymium atoms, Nd, interact strongly with each other through metallic bonding. This force, together with the atomic radius of Nd, and the way it is packed in three dimensions, ends up with settling a crystal with a compact double hexagonal structure (dhcp); its more stable and dense allotropic form.

However, when dhcp metallic crystals are heated to a temperature close to 863 ºC, neodymium undergoes a phase transition: its structure transforms to a body-centered cubic (bcc), which is less dense. Therefore, neodymium can exist as two allotropic forms: dhcp and bcc.

Electronic configuration

The abbreviated electron configuration for neodymium is as follows:

[Xe] 6s 2 4f 4

Being precisely the fourth element of the lanthanide series, the electronic filling of its 4f orbitals does not contradict the order expected and established by the Aufbau principle.

Neodymium properties

Physical appearance

Silver and shiny metal, relatively malleable and of considerable hardness, comparable to that of iron. When struck, it emits a tinkle reminiscent of bronze.

Atomic number

60

Molar mass

144.242 g / mol

Melting point

1024 ºC

Boiling point

3074 ºC

Density

At room temperature: 7.01 g / cm 3

Right at melting point: 6.89 g / cm 3

Oxidation states

Neodymium can participate in its compounds with oxidation states of 0 (Nd 0 , in alloys), +1 (Nd + ), +2 (Nd 2+ ), +3 (Nd 3+ ) and +4 (Nd 4+ ), with +3 being the most stable and common of all, as is the case with the other lanthanides.

Electronegativity

1.14 on the Pauling scale.

Ionization energies

First: 533.1 kJ / mol (Nd + gas)

Second: 1040 kJ / mol (Nd 2+ gas)

Third: 2130 kJ / mol (Nd 3+ gaseous)

Magnetic order

Paramagnetic. It is only weakly attracted to magnets. However, when doped with iron and boron atoms, it acquires magnetic saturation; that is, it reaches a maximum state of magnetization, so it will be a powerful magnet.

At temperatures below 20 K, neodymium becomes an antiferromagnetic material.

Reactivity and compounds

Neodymium is one of the most reactive metals in the lanthanide series. It must be stored out of the reach of oxygen, as it corrodes its surface quickly, since the resulting oxide cracks without being able to protect the interior of the metal from subsequent oxidation:

4 Nd + 3 O 2  → 2 Nd 2 O 3

This oxidation accelerates to 150 ° C, the neodymium burning with intensity.

It not only reacts quickly with oxygen, but also with acidic substances, such as hydrochloric acid, to release hydrogen and produce neodymium salts:

2 Nd + 6 HCl → 2 NdCl 3 + 3 H 2

The solutions of neodymium compounds show pink colorations, a characteristic that is also seen in erbium, another lanthanide. However, when illuminated with a fluorescent light bulb, they turn yellow. Note for example the image below:

a) Neodymium (III) sulfate, nitrate and chloride solutions under sunlight; b) The same solutions but illuminated with a compact fluorescent lamp. Source: W. Oelen / CC BY-SA (https://creativecommons.org/licenses/by-sa/3.0)

Aqueous solutions of the salts Nd 2 (SO 4 ) 3 , Nd (NO 3 ) 3 and NdCl 3 are pink or purple if they absorb sunlight; but they turn yellowish or even colorless (see nitrate solution) when illuminated with another light source, such as a compact fluorescent lamp.

This phenomenon is due to the electronic transitions ff, whose absorption bands interact with those of the irradiated light.

Obtaining

Neodymium is found in igneous rocks of the earth’s crust, integrating many minerals where lanthanides predominate. Among these minerals, bastnasite and monazite stand out, which, including all their families or variants, contain around 10-18% of the exploitable neodymium. Therefore, bastnasite and monazite are its main mineralogical sources.

The Nd 3+ ions must be separated from a matrix composed of other lanthanide oxides and other impurities. For this, ion exchange chromatography techniques and liquid-liquid extractions are used.

Once this is done, and depending on the selected process, neodymium ions are obtained as its oxide or any of its halides (NdX 3 ).

The oxide, Nd 2 O 3 , can be reduced with metallic sodium in the presence of calcium chloride, as indicated by the following chemical equation:

Nd 2 O 3  + 3 CaCl 2 + 6 Na → 2 Nd + 3 CaO + 6 NaCl

On the other hand, NdCl 3 can be reduced to metallic neodymium by electrolysis, or by metallothermic reduction using calcium as a reducing agent.

Uses / applications

Photography

Neodymium-doped glass is used as a yellow color filter in cameras.

Ceramics

Bulbs made of neodymium glass and illuminated by different light sources. Source: Scientific29 / CC BY-SA (https://creativecommons.org/licenses/by-sa/3.0)

Neodymium salts or oxide are used as additives to give the glass pink or purple tints. On the other hand, neodymium glasses also have the particularity, as already mentioned before, of showing different colorations depending on the incident light, as can be seen in the image below:

On the left, the bulb shows a bluish tint under fluorescent light; while on the right, it turns pink under incandescent light.

On the other hand, neodymium doped bulbs also have the characteristic of emitting whiter lights, as they absorb yellowish emissions.

Welding goggles

Welders’ goggles contain neodymium, which absorbs strong sodium emissions, thus eliminating incandescent yellow flashes.

Lasers

The beams reproduced with Nd-YAG lasers are characterized by their attractive green color. Source: Giorgio Brida from Torino, Italy / CC BY (https://creativecommons.org/licenses/by/2.0)

Neodymium oxide is used to dope the glasses used in the construction of high power lasers, capable of initiating fusion reactions.

Beams from other neodymium lasers, such as Nd: YAG (neodymium-yttrium aluminum garnet) have been used for treating skin cancer, removing body hair, and cutting or piercing steel.

Magnets

Neodymium magnet spheres fixed by strong and permanent magnetization. Source: © Nevit Dilmen / CC BY-SA (https://creativecommons.org/licenses/by-sa/3.0)

The alloy Nd-Fe-B (Nd 2 Fe 14 B) and its high magnetization, is used to create powerful magnets. These are the quintessential magnets, as they are the most powerful ever built. However, they have some disadvantages: in the pure state they lose their magnetic properties at high temperatures, and they corrode and fracture easily.

To solve these drawbacks, they are doped with other impurities and coated with layers of alloys to protect their interior and give them a metallic appearance. Thus, neodymium magnets are used in electric generators for vehicles and wind turbines, medical equipment, toys, cell phones, microphones, electric guitars, etc.

Neodymium magnets consist of the Nd-Fe-B alloy, which also contains other additives, some of which are other rare earth metals. The force with which they attract is such that it is possible to put them together to create different figures, such as the cylinder in the image above.

Likewise, these magnets serve as hobbies for those who want to test their attractiveness between two objects, observing how they are crushed in the process. See for example the following video:

Depending on the size, composition, and temperature, these magnets can even be dangerous, as they would attract massive objects towards them that could hit someone.

Related Articles

Leave a Reply

Your email address will not be published. Required fields are marked *

Back to top button