Neodymium (Nd)

• Element Symbol: Nd
• Atomic Number: 60
• Atomic Mass: 144.24
• Group # in Periodic Table: n/a
• Group Name: Lanthanides
• Period in Periodic Table: 6
• Block of Periodic Table: f-block
• Discovered by: Carl Auer von Welsbach (1885)

Neodymium is a soft, silvery-white metal. Its chemical symbol is Nd, and its atomic number is 60. This element is one of the lanthanides and is a rare earth metal. Although neodymium is classified as a rare earth, it is a fairly common element and is no rarer than nickel and copper. It tarnishes (rusts) easily when exposed to air, forming a flaky oxide coating that does not protect the metal from further oxidation (rusting). When it rusts, the element has a reddish-purple color. Neodymium compounds have numerous practical applications, playing a role in permanent magnets and lasers that are used in medicine.

Neodymium was first identified in 1885 by chemist Carl Auer von Welsbach in Vienna, Austria. It was discovered in the incorrectly classified element didymium, which Welsbach thought he had found fourteen years earlier; however, he eventually realized that he had been mistaken and that didymium was actually a mixture of two entirely new elements. Welsbach separated neodymium from the other element, praseodymium, by means of double nitrate fractional crystallization. The result was a pink salt, neodymium, and a greenish brown salt, praseodymium. In order to get these two salts, Welsbach had to run the fractional crystallization process more than one hundred times, each time lasting up to forty-eight hours. Neodymium was named for the Greek term neos didymos meaning "new twin" because of its close association with praseodymium. The pure metal of neodymium was not isolated until 1925 by American chemist H. Kremers, who also isolated lanthanum.

Physical Properties

Neodymium is a soft, bright, silvery-white metal. This rare earth metal rapidly rusts when exposed to air. When it oxidizes, it forms a flaky coating that easily peels off, thus exposing the metal to further rusting. When neodymium metal rusts, it has a reddish-purple color. As an example of just how quickly this happens, a centimeter-sized piece of neodymium completely rusts within a year. Neodymium’s standard state at 298 kelvins (K) is solid. It is, however, a soft solid because its density at room temperature is only 7.01 grams per cubic centimeter (g/cm³), as opposed to platinum, which has a density of 21.09 g/cm³ at room temperature. Like the other lanthanides, neodymium has relatively high melting and boiling points: it melts at 1024 degrees Celsius (°C) and boils at 3074 °C. Its specific heat, electrical conductivity, and thermal conductivity are unknown but are being investigated by theoretical chemists and physicists.

Chemical Properties

Neodymium metal has three oxidation states: +4, +3, and +2. The most common oxidation state is +3. This is because neodymium(III) is the most electropositive oxidation state. When an element is highly electropositive, it can react readily with any of the electronegative elements. This means that certain elements have electrons that can be donated to other elements that need them. When neodymium(III) reacts with other elements, the combination forms colored salts and other types of compounds. Neodymium(III) forms a total of thirteen different compounds altogether. This form of the element reacts with all of the halogens (fluorine, chlorine, bromine, and iodine) to form pink and purple salts. Neodymium(III) also reacts with oxygen, sulfur, nitrogen, phosphorus, and carbon and their related compounds (water, sulfates, nitrates, and phosphates). When it does, this form of the element combines with the other elements to form vividly colored compounds, which are usually pink or purple. This color change happens because neodymium has a reddish-purple color under its shiny outer coating.

Neodymium has five naturally occurring stable isotopes: neodymium-142, neodymium-143, neodymium-145, neodymium-146, and neodymium-148. The most abundant is neodymium-142 (27.2 percent). It also has two naturally occurring radioisotopes, neodymium-144 and neodymium-150. As of 2010, thirty-one total radioisotopes of neodymium have been discovered, with the two naturally occurring ones being the most stable. Neodymium-144 has a half-life of 2.29 × 10¹⁵ years, and neodymium-150 has a half-life of 7.0 × 10⁸ years. The twenty-nine other radioisotopes have half-lives ranging from less than eleven years to less than seventy seconds.

Applications

Although the word "rare" in "rare earth element" suggests that neodymium is scarce, it is actually very common. Earth’s crust contains about 33 parts per million, making it the second most abundant rare earth element after cerium. Neodymium is never found free in nature. Instead, just like the other rare earth elements, it is found in monazite and bastnaesite. These two ores contain small concentrations of every single rare earth metal currently known.

This rare earth metal is mined mainly in China, the United States, Brazil, India, Sri Lanka, and Australia. The total production of neodymium was seven thousand metric tons in 2004. The remaining reserves are estimated at approximately eight million metric tons. The bulk of the current production occurs in China.

Neodymium compounds have numerous practical applications. These compounds were first used in 1927 as reddish-purple dyes for glass, and they are still used today. Interestingly, some neodymium-laced, or "doped," glasses are used in lasers that emit infrared radiation. Infrared radiation is invisible to the naked eye because its wavelengths are much longer than those of visible light. These lasers have been used in extremely high-power applications, such as medically to treat skin cancers and for laser hair removal as well as industrially to cut and weld steel.

Neodymium alloys also have numerous applications. For instance they are used to make high-strength, powerful permanent magnets. This type of magnet is used commercially in sound-carrying products such as microphones, headphones, and loudspeakers, products in which strong magnetic fields are a requirement. Neodymium-alloy permanent magnets are also used in large-scale, environmentally friendly products such as electric motors for hybrid cars and wind turbine electric generators.

Bibliography

Cottrell, T. L. The Strengths of Chemical Bonds. New York: Academic, 1954. Print.

Coursey, J. S., et al. Atomic Weights and Isotopic Compositions with Relative Atomic Masses. NIST Physical Measurement Laboratory. Natl. Inst. of Standards and Technology, 30 Sept. 2015. Web. 13 Nov. 2015.

Emsley, John. Nature’s Building Blocks: An A–Z Guide to the Elements. 2nd ed. New York: Oxford UP, 2011.

Haynes, William M., ed. CRC Handbook of Chemistry and Physics. 95th ed. Boca Raton: CRC, 2014. Print.

"It’s Elemental: The Periodic Table of Elements." Science Education at Jefferson Lab. Thomas Jefferson Natl. Accelerator Facility, n.d. Web. 25 Sept. 2015.

Kaye & Laby Tables of Physical & Chemical Constants. Natl. Physical Laboratory, 2015. Web. 18 Sept. 2015.

"Neodymium Element Facts." Chemicool. Chemicool.com, 17 Oct. 2012. Web. 18 Sept. 2015.