|Name, symbol, number||samarium, Sm, 62|
|Group, period, block||n/a, 6, f|
|Standard atomic weight||150.36 g·mol−1|
|Electron configuration||[Xe] 6s2 4f6|
|Electrons per shell||2, 8, 18, 24, 8, 2 (Image)|
|Density (near r.t.)||7.52 g·cm−3|
|Liquid density at m.p.||7.16 g·cm−3|
|Melting point||1345 K, 1072 °C, 1962 °F|
|Boiling point||2067 K, 1794 °C, 3261 °F|
|Heat of fusion||8.62 kJ·mol−1|
|Heat of vaporization||165 kJ·mol−1|
|Specific heat capacity||(25 °C) 29.54 J·mol−1·K−1|
|Oxidation states||3, 2 (mildly basic oxide)|
|Electronegativity||1.17 (Pauling scale)|
|Ionization energies||1st: 544.5 kJ·mol−1|
|2nd: 1070 kJ·mol−1|
|3rd: 2260 kJ·mol−1|
|Atomic radius||180 pm|
|Covalent radius||198±8 pm|
|Electrical resistivity||(r.t.) (α, poly) 0.940 µΩ·m|
|Thermal conductivity||(300 K) 13.3 W·m−1·K−1|
|Thermal expansion||(r.t.) (α, poly) 12.7 µm/(m·K)|
|Speed of sound (thin rod)||(20 °C) 2130 m/s|
|Young's modulus||(α form) 49.7 GPa|
|Shear modulus||(α form) 19.5 GPa|
|Bulk modulus||(α form) 37.8 GPa|
|Poisson ratio||(α form) 0.274|
|Vickers hardness||412 MPa|
|Brinell hardness||441 MPa|
|CAS registry number||7440-19-9|
|Most stable isotopes|
|Main article: Isotopes of samarium|
Samarium is a rare earth metal, with a bright silver luster. Three crystal modifications of the metal also exist, with transformations at 734 and 922 °C, making it polymorphic. Individual samarium atoms can be isolated by encaspulating them into fullerene molecules.
Samarium oxidizes in air and ignites at 150 °C. Even with long-term storage under mineral oil, samarium is gradually oxidized, with a grayish-yellow powder of the oxide-hydroxide being formed. The metallic appearance of a sample can be preserved by sealing it under an inert gas such as argon.
Samarium is quite electropositive and reacts slowly with cold water and quite quickly with hot water to form samarium hydroxide:
Samarium metal reacts with all the halogens:
Compounds of Samarium include:
The most common oxidation state of samarium is +3, but +2 compounds are known too, such as SmI2.
Naturally occurring samarium is composed of four stable isotopes, 144Sm, 150Sm, 152Sm and 154Sm, and three extremely long-lived radioisotopes, 147Sm (1.06 × 1011y), 148Sm (7 × 1015y) and 149Sm (>2 × 1015y), with 152Sm being the most abundant (26.75% natural abundance).
151Sm has a halflife of 90 years, and 145Sm has a halflife of 340 days. All of the remaining radioisotopes have half-lives that are less than 2 days, and the majority of these have half-lives that are less than 48 seconds. This element also has 5 meta states with the most stable being 141mSm (t½ 22.6 minutes), 143m1Sm (t½ 66 seconds) and 139mSm (t½ 10.7 seconds).
The long lived isotopes,146Sm, 147Sm, and 148Sm primarily decay by alpha decay to isotopes of neodymium. Lighter unstable isotopes of samarium primarily decay by electron capture to isotopes of promethium, while heavier ones decay by beta minus decay to isotopes of europium
Natural Samarium has an activity of 128 Bq/g.
Samarium was discovered in 1853 by Swiss chemist Jean Charles Galissard de Marignac by its sharp absorption lines in didymium, and isolated in Paris in 1879 by French chemist Paul Émile Lecoq de Boisbaudran from the mineral samarskite ((Y,Ce,U,Fe)3(Nb,Ta,Ti)5O16). Although samarskite was first found in the Urals, by the late 1870s a new deposit had been located in North Carolina, and it was from that source that the samarium-bearing didymium had originated.
The samarskite mineral was named after Vasili Samarsky-Bykhovets, the Chief of Staff (Colonel) of the Russian Corps of Mining Engineers in 1845–1861. The name of the element is derived from the name of the mineral, and thus traces back to the name Samarsky-Bykhovets. In this sense samarium was the first chemical element to be named after a living person.
Prior to the advent of ion-exchange separation technology in the 1950s, samarium had no commercial uses in pure form. However, a by-product of the fractional crystallization purification of neodymium was a mixture of samarium and gadolinium that acquired the name of "Lindsay Mix" after the company that made it. This material is thought to have been used for nuclear control rods in some of the early nuclear reactors. Nowadays, a similar commodity product has the name "samarium-europium-gadolinium" (SEG) concentrate. It is prepared by solvent extraction from the mixed lanthanides extracted from bastnäsite (or monazite). Since the heavier lanthanides have the greater affinity for the solvent used, they are easily extracted from the bulk using relatively small proportions of solvent. Not all rare earth producers who process bastnäsite do so on large enough scale to continue onward with the separation of the components of SEG, which typically makes up only one or two percent of the original ore. Such producers will therefore be making SEG with a view to marketing it to the specialized processors. In this manner, the valuable europium content of the ore is rescued for use in phosphor manufacture. Samarium purification follows the removal of the europium. Currently, being in oversupply, samarium oxide is less expensive on a commercial scale than its relative abundance in the ore might suggest.
Samarium is not found free in nature, but, like other rare earth elements, is contained in many minerals, including monazite, bastnäsite and samarskite; monazite (in which it occurs up to an extent of 2.8%) and bastnäsite are also used as commercial sources. Mischmetal containing about 1% of samarium has long been used, but it was not until recent years that relatively pure samarium has been isolated through ion exchange processes, solvent extraction techniques, and electrochemical deposition. The metal is often prepared by electrolysis of a molten mixture of samarium(III) chloride with sodium chloride or calcium chloride. Samarium can also be obtained by reducing its oxide with lanthanum.
Uses of Samarium include:
As with the other lanthanides, samarium compounds are of low to moderate toxicity, although their toxicity has not been investigated in detail.
SAMARIUM [[[symbol]] Sm, atomic weight 150.4 (0= 16)1, a rare earth metal (see Rare Earths). The separation has been worked at by A. v. Welsbach, L. de Boisbaudran, Urbain and Lacombe (Comptes rendus, 1903, 1 37 pp. 568, 792); Demargay (ibid. 1900, 230, p. 101q); Benedicks; Felt and Przibylla (Zeit. anorg. Chem., 1905, 43, p. 202) and others. The metal may be obtained by reduction of its oxide with magnesium. It combines with hydrogen to form a hydride. The salts are mostly of a yellowish colour. The chloride, SmC1 3.6H 2 0, is a deliquescent solid which when heated in hydrochloric acid gas to 180° C. yields the anhydrous chloride. This anhydrous chloride is reduced to a lower chloride, of composition SmC1 2, when heated to a high temperature in a current of hydrogen or ammonia (Matignon and Cazes, Coupes rendus, 2906, 142, p. 183). The chloride, SmCl 2, is a brown crystalline powder which is decomposed by water with liberation of hydrogen and the formation of the oxide, Sm 2 O 3, and an oxychloride, SmOC1. The fluoride, SmF 3 .H 2 O, was prepared by H. Moissan by acting with fluorine on the carbide. The sulphate, Sm 2 (SO 4) 3.81120, is obtained by the action of sulphuric acid on the nitrate. It forms double salts with the alkaline sulphates. The carbide, SmC2, is formed when the oxide is heated with carbon in the electric furnace.