Erbium (Er)

• Element Symbol: Er
• Atomic Number: 68
• Atomic Mass: 167.259
• Group # in Periodic Table: n/a
• Group Name: Lanthanides
• Period in Periodic Table: 6
• Block of Periodic Table: f-block
• Discovered by: Carl Gustaf Mosander (1843)

Erbium is a soft, silvery-white metal. It is part of the lanthanide series, which includes elements with atomic numbers between 57 and 71 in the periodic table. Like the other elements in this series, erbium is a rare earth element. It is a component of a variety of minerals in Earth’s crust, including bastnaesite, euxenite, gadolinite, monazite, and xenotime. Erbium metal is not found in its pure form in nature.

Erbium was discovered in 1843 by Swedish chemist Carl Gustaf Mosander. He extracted oxides containing rare earth elements from ore minerals mined near the village of Ytterby, Sweden. The element in the erbium oxide he extracted was initially named "terbia," which represented the element terbium. However, the differences between erbium and terbium were later sorted out.

Limited technologies in the mid-1800s as well as the similarities between all of the rare earth elements made identification of each distinct element difficult. In fact, the oxide identified by Mosander was later found to contain multiple rare earth elements. In 1878 Swiss chemist Jean-Charles Galissard de Marignac extracted the new element ytterbium from a sample that was previously thought to contain only erbium oxide.

A pure sample of erbium metal was isolated in 1934 by Wilhelm Klemm and Heinrich Bommer. These scientists heated erbium chloride with potassium to produce the pure metal.

Physical Properties

Erbium is a silvery-white element with a metallic luster that is a solid in its standard state—that is, its state at 298 kelvins (K). It is a relatively soft, malleable metal. Erbium has a density of 9.066 grams per cubic centimeter (g/cm³) at standard state. Its melting point is 1497 degrees Celsius (ºC). Its boiling point is 2868 ºC. The specific heat of erbium is 168 joules per kilogram-kelvin (J/kg·K). Erbium is a good conductor of both heat and electricity. Its thermal conductivity is 15 watts per meter-kelvin (W/m·K). Its electrical conductivity is 1.2 × 10⁶ siemens per meter (S/m). Its resistivity is 8.6 × 10⁻⁷ meter-ohms (m·Ω).

Erbium has different magnetic properties at different temperatures. Above 85 K, erbium is paramagnetic. This means it has only a small response to a magnetic field. Below 20 K, it is ferromagnetic. This means it can strongly attract other materials even though it is electrically uncharged. Erbium is antiferromagnetic between 20 and 85 K. This means that it shows little external magnetism at these temperatures.

Chemical Properties

Erbium has a simple, closely packed, hexagonal crystal structure. This element is reactive with air and water. A sample of erbium tarnishes slowly in air. Erbium dust can catch fire easily or explode. This element reacts with all halogens and dissolves in most diluted acids to form solutions. Erbium that is dissolved in dilute sulfuric acid forms a rosy red solution. Erbium does not dissolve in hydrofluoric acid. It instead forms a protective erbium trifluoride layer on the acid’s surface.

The electron affinity of erbium is 50 kilojoules per mole (kJ/mol). Erbium has three valence electrons. Its ionization energies are 589.3, 1150, 2194, and 4120 kJ/mol. Its electronegativity is 1.24.

Erbium has six naturally occurring stable isotopes. The most common of these is erbium-166, which represents one-third of the erbium on Earth. The other natural isotopes, in order of abundance in Earth’s crust, are erbium-168, erbium-167, erbium-170, erbium-164, and erbium-162. There are thirty known radioactive isotopes of erbium. The half-lives of these isotopes are very short. Its one-second half-life gives erbium-145 the shortest half-life of all erbium isotopes. Erbium-169’s 9.4-day half-life is the longest. This element has an electron configuration of [Xe]4f¹²6s².

Applications

Erbium can be found in a variety of minerals in Earth’s crust. Its overall crustal abundance is 2.8 parts per million. This makes erbium a relatively abundant rare earth element. Its abundance is similar to that of the elements tantalum and tungsten.

The major minerals containing erbium include euxenite, xenotime, and laterite ionic clays. Large deposits of ionic clays exist in southern China. Therefore, China has become the main global commercial source for erbium.

Erbium is obtained by first subjecting crushed minerals to liquid-liquid solvent extraction. At the end of the extraction process, ion exchange is used to isolate erbium salts. These salts are then heated with calcium at high temperatures in an argon atmosphere to produce pure erbium metal.

Erbium ions emit photons in the presence of infrared light. This property makes erbium useful as an amplifier of signals within a fiber-optic network. A fiber-optic network uses long glass fibers covered with protective plastic tubes in order to transmit light signals. Erbium is added to these glass fibers through a process called doping. As the light signal moves through the fiber, the erbium emits photons and increases the strength of the signal. Fiber-optic technology is used to transmit Internet, television, and phone data over long distances via cables.

Erbium’s ability to emit photons also makes the element useful in lasers. Erbium lasers are often used in dermatological and dental procedures. These lasers allow doctors to perform accurate surgical procedures on the top layers of skin and on sensitive tooth enamel.

When combined with nickel to form the alloy Er₃Ni, erbium becomes useful as a regenerator in cryocoolers. Cryocoolers are small, freestanding coolers designed to bring objects down to cryogenic temperatures. They are used to cool infrared sensors in security systems, magnets in MRI systems, and biological specimens. The high magnetic heat capacity of the erbium-nickel alloy effectively exchanges heat within the cryocooler at extremely low temperatures.

Erbium oxide has a pink color. This makes it useful for a variety of applications. Erbium oxide is added to zirconium to make synthetic pink gemstones. It is added to glass to make pink sunglasses or safety glasses that absorb infrared light. It is also added to ceramic glazes to decorate clay vessels, such as jars, cups, and plates.

Bibliography

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"Technical Data for Erbium." The Photographic Periodic Table of the Elements. Element Collection, n.d. Web. 8 Sept. 2015.