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Strontium

Author: Robert Husted, Mollie Boorman

Atomic Number 38
Atomic Symbol Sr
CAS ID No. 7440-24-6
Atomic Weight 87.6200 amu
Electron Configuration [Kr] 5s2
Melting Point 768.0 C
Boiling Point 1377 C
Density 2.600 g/cm3
History

(Named after Strontian, a town in Scotland.) Isolated by Davey by electrolysis in 1808, however, Adair Crawford  recognized a new mineral (strontianite) as differing from other barium minerals in 1790.

Forms

Strontium is found chiefly as celestite and strontianite. The metal can be prepared by electrolysis of the fused chloride mixed with potassium chloride, or is made by reducing strontium oxide with aluminum in a vacuum at a temperature at which strontium distills off. Three allotropic forms of the metal exist, with transition points at 235 and 540C.

Properties

Strontium is softer than calcium and decomposes in water more vigorously. It does not absorb nitrogen below 380C. It should be kept under kerosene to prevent oxidation. Freshly cut strontium has a silvery appearance, but rapidly turns a yellowish color with the formation of the oxide. The finely divided metal ignites spontaneously in air. Volatile strontium salts impart a beautiful crimson color to flames, and these salts are used in pyrotechnics and in the production of flares. Natural strontium is a mixture of four stable isotopes.

Isotopes

Sixteen other unstable isotopes are known to exist. Of greatest importance is 90Sr with a half-life of 29 years. It is a product of nuclear fallout and presents a health problem. This isotope is one of the best long-lived high-energy beta emitters known, and is used in SNAP (Systems for Nuclear Auxilliary Power) devices. These devices hold promise for use in space vehicles, remote weather stations, navigational buoys, etc., and where a lightweight, long-lived, nuclear-electric power source is needed.

Uses

The major use for strontium at present is in producing glass for color television picture tubes. It has also found use in producing ferrite magnets and in refining zinc. Strontium titanate is an interesting optical material as it has an extremely high refractive index and an optical dispersion greater than that of diamond. It has been used as a gemstone, but is very soft. It does not occur naturally.




Last Update: 2011-02-16