Strontium

iso	NA	half-life	DM	DE M eV	DP
⁸⁴Sr	0.56%	Sr is stable with 46 neutrons
⁸⁶Sr	9.86%	Sr is stable with 48 neutrons
⁸⁷Sr	7.0%	Sr is stable with 49 neutrons
⁸⁸Sr	82.58%	Sr is stable with 50 neutrons
⁹⁰Sr	{syn.}	28.78 y	beta^-	0.546	⁹⁰Y

SI units & STP are used except where noted.

Strontium is a chemical element in the periodic table that has the symbol Sr and the atomic number 38. An alkaline earth metal, strontium is a soft silver-white or yellowish metallic element that is highly reactive chemically. This metal turns yellow when exposed to air and occurs in celestite and strontianite. Sr-90 is present in radioactive fallout and has a half-life of 28 years.

Table of contents

1 Notable Characteristics
2 Applications
3 History
4 Occurrence
5 Isotopes
6 Precautions
7 External Links

Notable Characteristics

Due to its extreme reactivity to air, this element always naturally occurs combined with other elements and compounds, as in the minerals strontianite, celestite, etc. It is isolated as a yellowish metal and is somewhat malleable. It is chiefly employed (as in the nitrate) to color pyrotechnic flames red.

Strontium is a bright silvery metal that is softer than calcium and even more reactive in water; strontium will decompose on contact to produce strontium hydroxide and hydrogen gas. It burns in air to produce both a strontium oxide and strontium nitride, but since it does not react with nitrogen below 380°C it will only form the oxide spontaneously at room temperature. It should be kept under kerosene to prevent oxidation; freshly exposed strontium metal rapidly turns a yellowish color with the formation of the oxide. Finely powdered strontium metal will ignite 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.

Applications

At present the primary use for strontium is in glass for color television cathode ray tubes. Also:

It is also used in producing ferrite magnets and in refining zinc.
Strontium titanate has an extremely high refractive index and an optical dispersion greater than that of diamond, making it useful in a variety of interesting optics applications.
Strontium titanate has been used as a gemstone, but is very soft and so scratches easily so it is not common in this role. It does not occur naturally.
Strontium is also used in fireworks to provide color.

History

Adair Crawford recognized the mineral strontianite, named after the Scottish town of Strontian, as differing from other barium minerals in 1790. However, Klaproth and Hope discovered strontium itself in 1798 and metallic strontium was first isolated by Sir Humphry Davy in 1808 using electrolysis.

Occurrence

Strontium commonly occurs in nature, averaging 0.034% of all igneous rock and is found chiefly as the form of the sulfate mineral celestite (SrS O₄) and the carbonate strontianite (SrCOO₃). Of the two, celestite occurs much more frequently in sedimentary deposits of sufficient size to make development of mining facilities attractive. Strontianite would be the more useful of the two common minerals because strontium is used most often in the carbonate form, but few deposits have been discovered that are suitable for development. The metal can be prepared by electrolysis of the melted 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 allotropes of the metal exist, with transition points at 235 and 540°C. Strontium metal (98% pure) in January 1990 cost about $5/oz. The largest commercially exploited deposits are found in England. Isolation (* follow):'
(cathode) Sr²⁺* + 2e^- --> Sr (anode) Cl^-* �Cl₂ (gas) + e^-

Isotopes

The alkali earth metal strontium has four stable, naturally occurring isotopes: Sr-84 (0.56%), Sr-86 (9.86%), Sr-81 (7.0%) and Sr-88 (82.58%). Only Sr-87 is radiogenic; it is produced by decay from the radioactive alkali metal rubidium-87, which has a half-life of 48,800,000 years. Thus, there are two sources of Sr-87 in any material: that formed during primordial nucleo-synthesis along with Sr-84, Sr-86 and Sr-88, as well as that formed by radioactive decay of Rb-87. The ratio Sr-87/Sr-86 is the parameter typically reported in geologic investigations. Because strontium has an atomic radius similar to that of calcium, it readily substitutes for Ca in minerals. Sr-87/Sr-86 ratios in minerals and rockss have values ranging from about 0.7 to greater than 4.0.

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

Precautions

In its pure form strontium is extremely reactive with air and spontaneously ignites into flame. It is therefore considered to be a fire hazard.

The human body is not able to effectively distinguish between the chemically similar strontium from calcium and absorbs strontium as if it were calcium. The stable forms of strontium do not pose a significant health threat, but the radioactive strontium-90 can lead to various bone disorders and diseases, including bone cancer.