Frank Herbert works in space DuneA precious natural substance called aromatic melange gives humans the ability to navigate vast expanses of the world to build an intergalactic civilization.
In real life, here on earth, a group of natural metals, known as rare earths, have made our society’s power technology possible. The demand for these crucial components in almost all modern electronics is skyrocketing.
Rare earths fill thousands of different needs; cerium, for example, is used as a catalyst to refine petroleum, and gadolinium captures neutrons in nuclear reactors. But the most outstanding of these abilities lie in their light and magnetism.
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We rely on rare earths to color our junk shelves, glow as a sign of authenticity on Euro banknotes and provide signals via optical fibers across the board across the seas. They are also necessary to build some of the world’s strongest and most reliable magnets. They generate sound waves in your headphones, boost digital information through space and transfer the trajectories of heat-seeking missiles. Rare earths are also driving the growth of green technologies, such as wind energy and electric power, and are also giving rise to new components for quantum computers.
“The list just goes on and on,” says Stephen Boyd, a synthetic chemist and independent consultant. “They are everywhere.”
Earth’s rare superpowers come from their electrons
The rare earths are the lanthanides — lutetium and all 14 elements between lanthanum and ytterbium across one row of the periodic table — plus scandium and yttrium, which tend to be deposited in the same region and have similar chemical properties to the lanthanides. This gray to silver metal is often ductile with sharp points and melts.
Their hidden powers are placed in their electrons. All atoms have a nucleus surrounded by electrons, which are called orbital zones. The electrons in the orbitals farthest from the nucleus are the electrons that participate in chemical reactions and form bonds with other atoms.
Most of the lanthanides have another heavy pair of electrons called “f-electrons”, which reside in the Goldilocks zone located near the valence electrons, but a little closer to the nucleus. “These are ambers that have both the magnetic and luminous properties of rare earth elements,” says Ana de Bettencourt-Dias, an inorganic chemist at the University of Nevada, Reno.
Rare earths add color and light
Along certain beaches, the sea sometimes turns blue at night, as the bioluminescent layer is washed away by the waves. Rare earth metals also glow when excited. The trick is to tickle their f electrons, Bettencourt-Dias says.
Using an energy source such as a laser or a lamp, scientists and mechanics can collide one of the f-electrons of the rare earth into an excited state and then fall back into its lethargic or ground state. “When the lanthanides return to earth,” he says, “let them shine.”
Each rare earth emits specific wavelengths of light when excited, says de Bettencourt-Dias. This precise accuracy allows engineers to carefully tune the electromagnetic radiation in many electronics. Terbium, for example, emits light at a wavelength of about 545 nanometers, making it good for building green phosphors in television, computer and smartphone screens. Europium, which has two common forms, was usually constructed from red and blue phosphorus. All together, these phosphor screens can be painted with many shades of the rainbow.
Rare earths also emit useful invisible light. Yttrium is the key ingredient in yttrium-aluminum carbuncle, or YAG, the synthetic crystal that forms the core of many high-power lasers. Engineers plan to make these lasers by lacing YAG crystals with other rare earths. The most popular variety are neodymium YAG lasers, which are used for everything from cutting steel to removing tattoos to laser-reinvention. Erbium-YAG laser beams are preferred for minimally invasive surgeries because they are easily absorbed by the water in the flesh and thus cannot cut too deep.
Beyond lasers, lanthanum is used to make infrared glass absorbing goggles in night vision. “And our internet is doing our homework,” Tian Zhong, a molecular engineer at the University of Chicago. Much of our digital information travels through optical fibers as light with a wavelength of about 1,550 nanometers — the same wavelength that erbium emits. Fiber optic signals darken as they travel far from the source. Because those cables can stretch for thousands of kilometers across the ocean floor, erbium fibers are used to boost signals.
Rare earths make magnets
In 1945, scientists built ENIAC, the world’s first programmable, general purpose digital computer (SN: 2/23/46, p. 118). Nicknamed the “Giant Brain,” ENIAC weighed more than four elephants and had a footprint roughly two-thirds the size of a tennis court.
Less than 80 years later, the ubiquitous smartphone — boasting far more computing power than ENIAC ever did — fits snugly in the palms of our hands. Society owes this miniaturization of electronic technology in large part to the exceptional magnetic properties of rare earths. Small rare earth magnets can do the same job as larger magnets without rare earths.
But those f-electrons are a myth. The rare earths have many electron orbitals, but the f-electrons inhabit a specific group of seven orbitals called the 4f-subshell. In each subshell, the electrons try to diffuse themselves between the orbitals inside. Each orbital can be home to two electrons. But since the 4f-subshell contains seven orbitals, and the rare earths contain fewer than 14 f electrons, the elements tend to have more orbitals with only one electron. Neodymium atoms, for example, have four of these ions, while dysprosium and samarium have five. Crucially, these unpaired electrons tend to point — or spin — in the same direction, Boyd says. “This is what creates the north and south poles as we classically understand magnetism.”
Since these single f electrons fly behind the valence shell electrons, their spiny synchronisers are relatively safe from demagnetizing forces, such as heat and magnetic fields, which makes them great for building permanent magnets, Zhong says. Permanent magnets, like those that make up pictures on refrigerator doors, passively generate magnetic fields that arise from atomic structure, unlike electromagnets, which require an electric current and can be bent.
But even rare earth targets have their limits. Pure neodymium, for example, corrodes fractures easily, and its magnetic pull begins to lose strength above 80° Celsius. So manufacturers mix some rare earths with other metals to make the magnets softer, says Durga Paudyal, a theoretical scientist at Ames National Laboratory in Iowa. And it does this well because some rare earths can orchestrate the magnetic fields of other metals, he says. Just as a weighted lottery ticket lands preferentially on one side, some rare earths, such as neodymium and samarium, exhibit stronger magnetism in certain directions because they contain unequally filled orbitals in their 4f-subsits. This directionality, called magnetic anisotropy, can be transferred to the fields of other metals such as iron or cobalt to compose robust, extremely powerful magnets.
The most powerful rare earth alloy magnets are neodymium iron-boron magnets. A three-kilogram neodymium alloy magnet can lift objects that weigh over 300 kilograms, for example. More than 95 percent of the world’s permanent magnets are made from this rare earth alloy. Neodymium-iron-boron magnets generate vibrations in smartphones, create sounds in earbuds and headphones, read and write data on hard drives, and generate magnetic fields used in MRI machines. And adding some dysprosium to these magnets can increase the resistance to heat shock, making it a good choice for the rotors that spin in the hot interiors of many electric vehicle motors.
Samarium-cobalt magnets, developed in the 1960s, were the first popular rare earth magnets. Although slightly weaker than neodymium-iron-boron magnets, samarium-cobalt magnets have superior heat and corrosion resistance, so they work in motors, generators, speed sensors in cars and airplanes, and in moving parts. some heat missiles that Samarium-cobalt magnets also form the heart of most waveguide tubes that boost signals from communication systems and satellites. Some of these tubes transmit data from Voyager 1—the most distant human-made object ever—over 23 billion kilometers away (SN: 7/31/21, p. 18).
Because they are strong and reliable, rare earth magnets support green technologies. They are in motors, drivetrains, power steering and many other components in electric vehicles. Tesla’s use of neodymium alloy magnets in its latest Model 3 vehicles has stirred up a lot of concern chains; China supplies most of the world’s neodymium (SN: 1/11/23).
Rare earth magnets are also removed in many turbines to replace gearboxes, which boosts efficiency and reduces maintenance. In August, Chinese engineers introduced the world’s first maglev line based on rare earth magnets, which allow trains to float without consuming electricity.
In the future, they may advance the calculation of the quantity of rare earths. While conventional computers use binary bits (those 1s and 0s), quantum computers use qubits, which can occupy two states at once. As it turns out, the crystals containing the rare earths yield qubits, when f-electrons are clipped and can store information over a long period of time, Zhong says. One day, computer physicists might even be able to flatten the properties of rare earths by sharing information in qubits between quantum computers and the Internet’s quantum delivery, he says.
It’s too early to predict exactly how rare earth metals will continue to influence the expansion of these growing technologies. But it’s probably safe to say: We need more rare earths.
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