We continue to review some of the most important materials in heat treatment and metallurgy.
Samarium (chemical symbol: Sm)
Samarium (Fig. 1) is a bright, yellowish-silvery metal that has a density and hardness similar to that of zinc. It is stable in air at room temperature but will ignite when heated to 150ºC. Samarium is considered paramagnetic at room temperature, meaning that it is very weakly attracted by the poles of a magnet, but it will not retain any permanent magnetism. Despite never being found freely in nature, it is found alongside other lanthanide metals in a variety of minerals such as monazite (Fig. 2) and bastnasite. Within these minerals, samarium can be isolated from the other components by ion exchange and solvent extraction.
Samarium was first observed in 1853 by Swiss chemist Jean Charles Galissard de Marignac when he viewed spectroscopic lines of the mineral dydimia he was studying that matched no known element. It wasn’t until 1879 that French chemist Paul-Emile Lecoq de Boisbaudran isolated the new element from the mineral samarskite. The new element was named after the mineral from which it was found. Lecoq also discovered the element gallium in 1875 and later isolated both gadolinium and dysprosium.
One of the most common applications for samarium is in samarium-cobalt magnets (Fig. 3), which have high permanent magnetization of about 10,000 times that of iron and second only to that of neodymium magnets. In addition to their high resistance to demagnetization, they keep their magnetism at temperatures up to 700ºC, making them ideal for use in precision-guided weapons.
Other uses for these magnets range from small motors and headphones to high-end magnetic pickups for guitars and other musical instruments. Samarium also sees use as a catalyst and chemical reagent to assist in the decomposition of plastics, the de-chlorination of pollutants, and for dehydration and dehydrogenation of ethanol. As with other lanthanides, samarium is also commonly used in carbon-arc electrodes for film studio lighting and projection lights.
Here are a few important facts about samarium.[2,5]
- Atomic number: 62
- Atomic weight: 150.36
- Melting point: 1347 K (1074°C or 1965°F)
- Boiling point: 2067 K (1794°C or 3261°F)
- Density: 7.52 grams per cubic centimeter
- Phase at room temperature: Solid
- Element classification: Metal
- Period number: 6
- Group number: none
- Group name: Lanthanide
- Electron configuration: [Xe] 4f66s2
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