By Ron B. Davis Jr., Georgetown University
Most people have no idea how much modern technology has been transformed by including these ultimate team players of the periodic table, the ‘rare earth’ elements. Color TV’s colors got better, thanks to europium. And the halogen lights, which actually depend on dysprosium. Magnets with neodymium have transformed everything from our headphones to the commercial turbines that make possible modern wind power farms. In short, though largely unnoticed, the so-called ‘rare earth’ elements have become indispensable in a host of modern technology applications.
Not So ‘Rare’
Although one may rarely hear about these elements, the good news is that they’re actually pretty common on Earth’s surface. Yes, they are ‘rare’ but only compared to the most common elements. In fact, calling them ‘rare’ is a bit of a misnomer.
Cerium, which most people, even today, have never heard of, is more abundant than copper. The top three most abundant members of the group are more common than tin or lead. And the entire group (with one radioactive exception) is more abundant than silver—and far more abundant than gold.
Rare earth elements are also very useful, even though they are not chemical divas, like gold. For example, an estimated 50 to 100 grams of cerium is used in every one of the millions of catalytic converters in vehicles around the world. Although, cerium isn’t the catalyst, it is, rather, a part of the heat-resistant oxide mineral that supports it.
This article comes directly from content in the video series Understanding the Periodic Table. Watch it now, on Wondrium.
The F-block Rare Earth Elements
Rare earth elements such as terbium, have made X-rays much safer and made solid-state drives possible for data storage. Hybrid and electric car batteries depend on 20-30 pounds of lanthanum. We could in fact simply call them nickel-lanthanum-hydride batteries! They save space and weight, and they’re about twice as efficient as traditional lead-acid batteries.
To understand how elements so rarely talked about can be so useful, we travel to the f-block of the periodic table, that long ‘landing strip’ of elements that’s strangely detached from the remainder of the table.
There are three f-block elements that are ferromagnetic in their pure form at room temperature, with a location on the table analogous to the iron triad, just past the mid-point of the block. Those are gadolinium, terbium and dysprosium.
Gadolinium, for example, in its 3-plus oxidation state contains seven unpaired electrons. This makes each individual gadolinium 3+ ion a powerful, atomic-sized magnet.
Radiologists take advantage of this property, formulating gadolinium 3+ containing compounds that can accumulate in certain tissues of the human body, changing how the atoms and molecules in that tissue react to applied magnetic fields. In magnetic resonance imaging, or MRI, gadolinium 3+ compounds are often used to enhance contrast in the images that are produced.
The very next three elements of the f block also have the potential to be ferromagnetic, if placed under sufficiently cold conditions. However, holmium, erbium, and thulium only become ferromagnetic at extremely low temperatures—even colder than liquid nitrogen.
And yet, the most powerful and reliable permanent magnets today, are actually created using two other rare earth elements, alloyed with elements from the ‘Iron Triad’ of magnetic elements.
Production of Ferromagnetic Materials
Samarium can be alloyed with the ferromagnetic element cobalt to produce remarkably strong permanent magnets. This made it possible to shrink electronic devices, like headphones, effectively launching the portable music player market in the 1970s.
A few Fender guitars around the start of the 21st century used this alloy in the guitar pickups that translate the vibration of strings into electrical signals.
Interestingly, the most powerful permanent magnets readily available today are so-called neodymium magnets, a mixture of neodymium with iron and boron developed by General Motors in 1982.
Neodymium magnets are the materials of choice in the design of electric motors for both cars and power tools. Tiny neodymium magnets are drivers for headphones and speakers, as well as in computer hard drives, smart phones, and many other modern technologies. Gigantic neodymium magnets are critical to the turbines of commercial wind power.
Other Uses of Rare Earth Elements
But rare earth elements have other uses beyond the production of ferromagnetic materials.
Dysprosium is combined with the halogen element iodine makes halogen lighting. The dysprosium vaporizes under intense heat and offers a wide emission spectrum, similar to natural light. Erbium is used to amplify light. This is useful both to amplify the signals carried by fiber-optic cables, and to amplify the light of lasers that dentists and dermatologists can use, without delivering a corresponding increase of heat.
Terbium is used in solid-state drives for computers and other electronics. Use of terbium in the phosphors of X-ray imaging screens made it possible for patients to receive radiation for only one-quarter of the time needed for earlier X-rays.
Gadolinium and Thulium
With six stable isotopes, Gadolinium has the greatest ability to capture neutrons of any element. In medicine, neutron radiography uses a gadolinium screen for neutron imaging. In nuclear power plants, gadolinium’s ability to absorb excess neutrons is the most powerful way to prevent a runaway chain reaction during fission.
Thulium is the second most rare, but it’s used in high-temperature conductors, the manufacture of lasers, and the manufacture of ceramic magnetic materials for microwaves.
Hence, clearly, the list of applications for rare earth elements goes on and on, making them an important strategic resource.
Common Questions about ‘Rare Earth’ Elements
Yes, rare earth elements are ‘rare’ but only compared to the most common elements. In fact, calling them ‘rare’ is a bit of a misnomer.
There are three f-block elements that are ferromagnetic in their pure form at room temperature: gadolinium, terbium and dysprosium.
The most powerful permanent magnets readily available today are so-called neodymium magnets, a mixture of neodymium with iron and boron developed by General Motors in 1982.