Chemical Fact Sheet
Strontium
| Chemical Abstract Number (CAS #) | 7440-24-6 |
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| Analytical Methods | 200.7 - 200.8 - 6010 - 6020 |
| Molecular Formula | Sr |
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Synopsis
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Strontium - (Strontian, town in Scotland), Sr; at. wt. 87.62(1); at. no. 38; m.p. 777 deg C; b.p. 1382 deg C; sp. gr. 2.54; valence 2. Isolated by Davey by electrolysis in 1808; however, Adair Crawford in 1790 recognized a new mineral (strontianite) as differing from other barium minerals (baryta). Strontium is found chiefly as celestite (SrSO4) and strontianite (SrCO3). 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 540 deg C. Strontium is softer than calcium and decomposes water more vigorously. It does not absorb nitrogen below 380 deg C. It should be kept under mineral oil 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. Twenty six other unstable isotopes and isomers, 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 Auxiliary Power) devices. These devices hold promise for use in space vehicles, remote weather stations, navigational buoys, etc., where a lightweight, long-lived, nuclear-electric power source is needed. 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 it is very soft. It does not occur naturally. Strontium metal (99% pure) costs about $1/g while the metal, 99.95% pure, sells for about $10/g. |
| Use | In fireworks, red signal flares, on tracer bullets Added to alloys of tin & lead to add hardness & durability, deoxidizer in copper & bronze "Getter" in electron tubes Igneous coloring agent, material for condenser, optical glass, lead removing Source of electric power |
| Apparent Color | Silvery-white metal; Face-centered cubic structure |
| Boiling Point | 1366 deg C |
| Melting Point | 757 + OR - 1 deg C |
| Molecular Weight | 87.62 |
| Density | 2.6 g/cu m |
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Chemical and Physical Properties |
Natural strontium is a mixture of four isotopes; twelve other unstable isotopes are known to exist Alkaline earth metal; valence of 2; Isotopes: 88 (82.56%), 86 (9.86%), 87 (7.02%), 84 (0.56%); Heated metal combines with hydrogen to form strontium hydride & with nitrogen to form strontium nitride. Three allotropic forms exist, with transition points at 235 & 540 deg C Strontium will displace hydrogen from water (90)Sr has a half life of 28 yr & is a high energy beta emitter /(90)Sr/ Lattice constant: 6.05; latent heat of fusion: 104.7 kJ/kg; electrical resistivity: 22.76 uohms/cm Specific heat: 0.0719 cal/g/K @ 25 deg C Entropy of formation: 12.5 cal/deg mole @ 298.15 K (25 deg C); heat capacity: 6.3 cal/deg mole @ 298.15 K (25 deg C) & std pressure Its common cationic salts are water-soluble; it forms chelates with compounds such as EDTA; strontium coordination compounds are not common. Yellowish white, upon exposure to air. |
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Environmental Impact |
World wide sampling of soils revealed strontium cmpd contents around 300 mg/kg. |
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Environmental Fate |
Strontium occurs in nature in celestite (strontium sulfate) use strontianite (strontium carbonate). In earth's crust total amt is est to be 430 g/ton; in sea water 10 ppm. Found in small quantities associated with calcium or barium minerals. |
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Atmosphere |
A relatively high concn of strontium in air dust (600 ug/cu m) was reported. Metal fumes generated during welding of steel gave 3 ug strontium/cu m. Metal fumes generated during welding of steel |
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