Strontium, an alkali earth metal, was first isolated by Davey by electrolosis in 1808; however, Adair Crawford in 1790 recognized a new mineral (strontianite) that differed from other barium minerals. He called this mineral strontium, after Strontian, a town in Scotland, Ireland. Strontium has an atomic number of 38, and its atomic mass is 87.62.
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 540 degrees Celsius.
Strontium is softer than calcium and decomposes in water more vigorously. It does not absorb nitrogen below 380 degrees Celsius. 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.
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., 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. As previously mentioned, strontium is used in fireworks and flares because it produces a striking crimson color. It has also been used as a gemstone, but is very soft. It does not occur naturally.
Like other minerals, strontium exists naturally in food, plants and seawater. It's present, too, in our bodies although no one's determined that we need it. A danger exists because strontium can replace calcium in bones. The strontium that had everyone on red alert in the 1950s, however, was radioactive strontium 90, which aboveground nuclear explosions rained down upon us. It showed up in grass, silage, in cow's milk and ultimately those who drank that milk. Once absorbed into the bones, strontium 90, with a half-life of twenty-eight years, continues to assault the body with internal radiation. Even small doses of it can cause leukemia and bone cancer, particularly in children less than ten years old. The Federal Radiation Council quickly set acceptable levels of strontium 90. As a result, estimates suggest that internal radiation (by strontium 90 and other radioactive substances in food or drink) now accounts for only 0.3 percent of the fatal cancers in the United States.