Neodymium – facts and properties

Position in the periodic table

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Occurrence and extraction

Together with cerium and lanthanum, neodymium is among the most abundant lanthanides, and in the Earth's crust it is more common than cobalt or tin. So quantity is not the problem. The problem is availability: ores such as monazite and bastnaesite are spread over a few deposits, and China mines most of the rare earths. Even more concentrated are the separation of the elements and the manufacture of the magnets. When China restricted exports in 2010, prices shot up. Since then other countries have expanded mines and processing plants.

Production burdens the environment. Breaking down the ores produces acidic wastewater and residues that, as with monazite, can contain thorium. That is why recycling is gaining importance. Neodymium can be recovered from the magnets of old hard disks, motors and generators, but so far this happens only on a small scale.

The element owes its name to didymium. In 1885 Carl Auer von Welsbach split this supposed element into two, one of which became neodymium, Greek neos didymos, new twin. The full story is on the praseodymium page.

Properties and reactions

Neodymium is the fourth lanthanide, in period 6. Praseodymium lies to its left and promethium to its right. Its electron configuration is [Xe] 4f⁴ 6s² and its electronegativity is 1.14. The metal has a density of 7.01 g/cm³, melts at 1021 °C and boils at 3074 °C. It is soft, shiny and tarnishes in air. The oxide layer flakes off, so the metal keeps corroding. With water it forms hydrogen and neodymium hydroxide, slowly when cold and faster when warm. It is therefore kept under oil or protective gas.

In compounds it is mostly a triply charged ion. Neodymium salts are pink to violet, and neodymium oxide is bluish grey.

The magnets consist of the compound Nd₂Fe₁₄B. Their strength comes from the interplay of the partners: iron provides a high magnetisation, and neodymium makes that magnetisation hard to reverse. The magnet therefore keeps its direction even against strong external fields. As drawbacks, the magnets lose strength when hot and rust easily. Magnets for motors therefore have some of the neodymium replaced by dysprosium, and they get a protective nickel coating.

Uses in everyday life and technology

The magnets were developed in the early 1980s and have made many devices smaller and lighter. They are found in the drive motors of electric cars, in the generators of many wind turbines, in headphones and loudspeakers, in the actuators of hard disks, in electric bicycles and in magnetic catches.

A second large field is laser technology. The Nd:YAG laser uses a crystal of yttrium aluminium garnet in which a small share of the yttrium ions is replaced by neodymium ions. It emits infrared light with a wavelength of 1064 nanometres. If the frequency is doubled the light turns green. Green laser pointers work the same way, usually with a related neodymium crystal. Such lasers cut, weld and engrave metal, treat clouding after cataract surgery in ophthalmology and measure distances. Neodymium glass lasers produce extremely short, energetic flashes of light in fusion research.

Neodymium glass is violet, and its colour depends on the light source. In daylight it looks bluish, in incandescent light reddish violet.

Neodymium magnets demand care. Large ones snap together and can crush fingers. They can disturb data carriers and medical devices such as pacemakers. If a child swallows several small magnets, they can attract each other through the gut wall and injure it. That is a medical emergency.

Quick question

What is the atomic number of neodymium (Nd)?

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