Rare Earth Elements (REEs) are seventeen metallic elements with unique physical and chemical properties. These elements are foundational to many advanced technologies, powering consumer electronics and specialized defense systems. Samarium is one such element, known for its ability to form powerful, temperature-stable magnets and for its utility in nuclear and medical applications. Its identification involved a scientific race and the pioneering use of new analytical techniques.
Defining Samarium as a Rare Earth Element
Samarium (Sm), atomic number 62, is a silvery-white, moderately hard metal belonging to the Lanthanide series on the periodic table. This series is part of the larger group known as the Rare Earth Elements. The term “rare earth” is misleading, as samarium is not geologically scarce; it is more abundant in the Earth’s crust than silver or gold.
The classification stems from the historical difficulty chemists faced in separating these elements due to their similar chemical behavior. Samarium typically exhibits an oxidation state of +3 in its compounds, a characteristic shared by most Lanthanides. However, it is notable for its capacity to exist in a relatively stable +2 oxidation state, a trait useful in specialized chemical synthesis.
The Race for Spectroscopic Identification
The first observation of samarium occurred decades before its official isolation, relying on the emerging technology of spectroscopy. In 1853, Swiss chemist Jean Charles Galissard de Marignac examined the spectrum of didymia, noticing sharp absorption lines that did not correspond to any known element. This spectroscopic evidence suggested a new element was present, though de Marignac did not pursue its isolation.
The definitive identification was achieved in 1879 by French chemist Paul-Émile Lecoq de Boisbaudran, a master of spectroscopic methods. He extracted a substance from the mineral samarskite and used spectroscopy to observe the unique spectral lines of the new element’s oxide. De Boisbaudran separated the material, concentrating on a precipitate that revealed a spectral signature distinct from the other elements in the mixture.
De Boisbaudran’s work confirmed the existence of the element by isolating its oxide and identifying its characteristic light-absorption pattern. He is officially credited with the discovery and naming of the element. However, the samarium he isolated was later found to be impure, containing a comparable amount of europium. The subsequent purification of samarium oxide was accomplished by Eugène-Anatole Demarçay in 1901.
The Origin of the Name Samarium
The name “Samarium” was given by Paul-Émile Lecoq de Boisbaudran, derived directly from the mineral source from which it was isolated: samarskite. This mineral, a complex oxide, was first described in 1847 after being found in the Ural Mountains of Russia.
Mineralogist Heinrich Rose named samarskite in honor of Colonel Vasili Samarsky-Bykhovets, a Russian mining official. Samarsky-Bykhovets was the Chief of Staff of the Russian Corps of Mining Engineers and granted access to the mineral samples for study. This makes samarium the first chemical element to be named, indirectly via a mineral, after a person.
Modern Uses in Technology and Medicine
Samarium is indispensable in several high-performance applications, most prominently in the creation of Samarium-Cobalt (SmCo) magnets. These magnets are prized for their high resistance to demagnetization and their ability to maintain magnetic strength at temperatures exceeding 300 degrees Celsius. This thermal stability makes SmCo magnets the material of choice for electric motors and sensors used in aerospace, defense systems, and high-performance automotive applications.
The element also plays a significant role in nuclear technology because of the high neutron-absorption capacity of its isotope, samarium-149. This makes it a component in the control rods of nuclear reactors, where it helps regulate the fission process by absorbing excess neutrons. In medicine, the radioactive isotope samarium-153 is utilized in radiopharmaceuticals to treat pain associated with bone cancer metastases. The compound is injected to selectively target areas of increased bone turnover, delivering localized radiation.