- Samarium (Sm) is a moderately hard, silvery metal with atomic number 62, belonging to the lanthanide series of the periodic table.
- It has an electron configuration of [Xe] 4f⁶ 6s² and typically forms the Sm³⁺ ion, its most stable oxidation state, although the +2 state can also occur in some compounds.
- Its atomic structure contains sixty-two protons, generally eighty-eight or ninety neutrons, and sixty-two electrons arranged in six shells.
- Naturally occurring samarium consists of seven stable isotopes, with samarium-152 (¹⁵²Sm) being the most abundant at about 26.8%, followed closely by ¹⁵⁴Sm, ¹⁵⁰Sm, and ¹⁴⁹Sm. One isotope, samarium-149 (¹⁴⁹Sm), is notable for its extremely high neutron absorption cross-section, making it important in nuclear technology.
- Samarium is not found in nature as a pure metal but occurs in minerals such as monazite ((Ce,La,Nd,Th)PO₄) and bastnäsite ((Ce,La)(CO₃)F), often alongside other rare earth elements. Significant deposits are located in China, the United States, Australia, Brazil, and India. It is extracted through a series of complex chemical processes involving solvent extraction and ion-exchange separation from other lanthanides.
- The element was discovered in 1879 by French chemist Paul-Émile Lecoq de Boisbaudran, who isolated it from the mineral samarskite ((Y,Fe,U)(Nb,Ta)O₄). Samarium is named in honor of the Russian mining engineer Colonel Vasili Samarsky-Bykhovets, marking the first time a chemical element was named after a person.
- Samarium has diverse and significant applications. One of its most important uses is in samarium–cobalt (SmCo₅ and Sm₂Co₁₇) permanent magnets, which are known for their high strength, excellent thermal stability, and resistance to demagnetization—qualities that make them ideal for use in aerospace, defense systems, and high-performance motors. In nuclear reactors, samarium-149 is employed as a neutron absorber (control material) due to its ability to capture thermal neutrons efficiently. Samarium compounds, such as samarium(III) oxide (Sm₂O₃), are used in ceramics and specialized glass to absorb infrared radiation. Additionally, samarium is used in carbon arc lighting for the film industry, in laser crystals, and as a catalyst in certain organic chemical reactions, such as the samarium diiodide (SmI₂)-mediated reduction.
- Chemically, samarium is reasonably stable in air compared to some other lanthanides, developing a slow-growing oxide layer. It reacts slowly with cold water but more rapidly with heated water, producing samarium hydroxide and hydrogen gas. It also reacts readily with acids, forming colorless Sm³⁺ solutions, and with halogens to form samarium halides.
- Biologically, samarium has no known essential function in living organisms. Most of its compounds are of low to moderate toxicity, but safety precautions are necessary, especially when handling finely divided metal or radioactive isotopes like ¹⁵³Sm, which is used in targeted cancer therapy for bone pain palliation.
- From an environmental perspective, samarium in its mineral form is stable and poses little risk. However, the environmental impact of mining rare earth ores that contain samarium can be significant due to the production of chemical waste and possible release of radioactive by-products from associated thorium and uranium in the minerals.
