Dysprosium – facts and properties

Position in the periodic table

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Occurrence and extraction

Dysprosium is one of the heavy rare earths, which are introduced on the lanthanum page. In the Earth's crust it is more common than bromine. It occurs in xenotime, in small shares in monazite and above all in ion-adsorption clays in southern China and Myanmar. In these clays the rare earths sit loosely on the surface of the mineral grains and can be washed out with salt solutions. That is cheap, but it often leaves damage to soil and groundwater.

The dependence on China is greater for dysprosium than for neodymium. Most of it is mined in China or Myanmar and separated in China, and other countries are only now building their own separation plants. Recycling from old magnets and new processes that need less dysprosium come on top of that. The metal itself is made by reducing the fluoride with calcium.

The French chemist Paul-Émile Lecoq de Boisbaudran found the element in 1886 in a sample that was thought to be pure holmium oxide. He had to work the material up again and again in more than thirty precipitations before a new fraction became visible. That gave the element its name. Pure dysprosium did not exist until the 1950s, when ion exchange made it easier to separate the lanthanides.

Properties and reactions

Dysprosium is the tenth lanthanide. In period 6, terbium is on its left and holmium on its right. It has the electron configuration [Xe] 4f¹⁰ 6s² and an electronegativity of 1.22. Its density of 8.55 g/cm³ is among the higher ones in the row. It melts at 1412 °C, boils at 2567 °C and has an atomic radius of 178 pm. The metal is soft enough to cut and tarnishes only slowly in air. It reacts sluggishly with cold water and faster with warm, giving hydrogen. In compounds it is triply charged. The salts are yellowish and the oxide is yellowish white.

Magnetically, dysprosium is an extreme. Together with holmium it has the largest magnetic moment of any element. At room temperature the metal is only paramagnetic and becomes ferromagnetic only below about minus 190 degrees Celsius. Its strength therefore shows in alloys and compounds.

That explains its role in neodymium magnets. In heat, an opposing field can more easily flip the magnetisation of a magnet, and the loss is permanent. In the compound Nd₂Fe₁₄B, neodymium holds the magnetisation in one preferred direction. If some dysprosium is built in instead of neodymium, this anchoring holds more strongly, and the magnet resists demagnetisation even at a hundred degrees Celsius and more.

Uses in everyday life and technology

The main consumer is neodymium-iron-boron magnets for drives. In the motors of electric cars and the generators of wind turbines, the magnets get hot and are exposed to strong opposing fields. An addition of a few per cent of dysprosium makes them fit for the job. To cut demand, dysprosium is now placed only at the grain boundaries of the magnet grains, where it does the most good, and it is partly replaced by terbium. Other motor designs manage entirely without these elements.

Dysprosium is also part of Terfenol-D, the alloy with terbium and iron that deforms especially strongly in a magnetic field. More on this is on the terbium page.

Metal-halide lamps often contain dysprosium iodide. The salt evaporates in the arc and emits a broad spectrum that resembles daylight. Such lamps light film sets, sports grounds and stages.

In nuclear engineering dysprosium absorbs neutrons and is suitable as a material for control rods. Dosimeters made of calcium sulfate doped with dysprosium store energy from radiation and give it off as light when heated, which is how the radiation exposure of workers is measured.

Dysprosium compounds are only slightly toxic. As with other metals, the fine powder can burn.

Quick question

What is the atomic number of dysprosium (Dy)?

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