AskDefine | Define strontium

Dictionary Definition

strontium n : a soft silver-white or yellowish metallic element of the alkali metal group; turns yellow in air; occurs in celestite and strontianite [syn: Sr, atomic number 38]

User Contributed Dictionary

see Strontium

English

Etymology

From the name of the Scottish town Strontian

Noun

  1. a metallic chemical element (symbol Sr) with an atomic number of 38.

Translations

Translations to be checked
  • ttbc Vietnamese: stronti doesn't look right; syllables are written separately and diacritics are very common.

External links

For etymology and more information refer to: http://elements.vanderkrogt.net/elem/sr.html (A lot of the translations were taken from that site with permission from the author)

See also

Finnish

Noun

  1. strontium]]

Extensive Definition

Strontium () is a chemical element with 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. The metal turns yellow when exposed to air. It occurs naturally in the minerals celestine and strontianite. The 90Sr isotope is present in radioactive fallout and has a half-life of 28.90 years.

Notable characteristics

Due to its extreme reactivity to air, this element occurs naturally only in compounds with other elements, as in the minerals strontianite and celestite.
Strontium is a bright silvery metal that is softer than calcium and even more reactive in water, which strontium decomposes on contact with to produce strontium hydroxide and hydrogen gas. It burns in air to produce both 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 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

As a pure metal strontium is being used in strontium 90%-aluminium 10% alloys of an eutectic composition for the modification of aluminium-silicon casting alloys. The primary use for strontium compounds is in glass for colour television cathode ray tubes to prevent X-ray emission.
Other uses:
  • 89Sr is the active ingredient in Metastron, a radiopharmaceutical used for bone pain secondary to metastatic prostate cancer. The strontium acts like calcium and is preferentially incorporated into bone at sites of increased osteogenesis. This localization focuses the radiation exposure on the cancerous lesion.
  • 90Sr has been used as a power source for radioisotope thermoelectric generators (RTGs). 90Sr produces about 0.93 watts of heat per gram (it is lower for the grade of 90Sr used in RTGs, which is strontium fluoride). However, 90Sr has a lifetime approximately 3 times shorter and has a lower density than 238Pu, another RTG fuel. The main advantage of 90Sr is that it is cheaper than 238Pu and is found in nuclear waste.
  • 90Sr is also used in cancer therapy. Its beta emission and long half-life is ideal for superficial radiotherapy.
  • Strontium is one of the constituents of AJ62 alloy, a durable magnesium alloy used in car and motorcycle engines by BMW.
87Sr/86Sr ratios are commonly used to determine the likely provenance areas of sediment in natural systems, especially in marine and fluvial environments. Dasch (1969) showed that surface sediments of Atlantic displayed 87Sr/86Sr ratios that could be regarded as bulk averages of the 87Sr/86Sr ratios of geological terranes from adjacent landmasses. A good example of a fluvial-marine system to which Sr isotope provenance studies have been successfully employed is the River Nile-Mediterranean system (Krom et al, 1999; Krom et al, 2002; Talbot et al. 2000). Due to the differing ages of the rocks that constitute the majority of the Blue and White Nile catchment areas the changing provenance of sediment reaching the River Nile delta and East Mediterranean Sea can be discerned through Sr isotopic studies. Such changes are climatically controlled in the Late Quaternary.
More recently, 87Sr/86Sr ratios have also been used to determine the source of ancient archaeological materials such as timbers and corn in Chaco Canyon, New Mexico (English et al, 2001; Benson et al, 2003). 87Sr/86Sr ratios in teeth may also be used to track animal migrations (Barnett-Johnson, 2007; Porder et al., 2003) or in criminal forensics.
Strontium atoms are used in an experimental atomic clock with record-setting accuracy.

Compounds

History

The mineral strontianite is named after the Scottish village of Strontian, having been discovered in the lead mines there in 1787. Adair Crawford recognized it as differing from other barium minerals in 1790. Strontium itself was discovered in 1798 by Thomas Charles Hope, and metallic strontium was first isolated by Sir Humphry Davy in 1808 using electrolysis.
Strontium was among the radioactive materials released by the 1957 Windscale fire.

Occurrence

In 2005, China was the top producer of strontium with almost two-thirds world share followed by Spain and Mexico, reports the British Geological Survey.
Strontium commonly occurs in nature, the 15th most abundant element on earth, averaging 0.034% of all igneous rock and is found chiefly as the form of the sulfate mineral celestite (SrSO4) and the carbonate strontianite (SrCO3). 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 melted strontium chloride mixed with potassium chloride:
Sr2+ + 2 e- → Sr
2 Cl- → Cl2 (g) + 2 e-
Alternatively it is made by reducing strontium oxide with aluminium 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. The largest commercially exploited deposits are found in England.

Isotopes

The alkali earth metal strontium has four stable, naturally occurring isotopes: 84Sr (0.56%), 86Sr (9.86%), 87Sr (7.0%) and 88Sr (82.58%). Only 87Sr is radiogenic; it is produced by decay from the radioactive alkali metal 87Rb, which has a half-life of 4.88 × 1010 years. Thus, there are two sources of 87Sr in any material: that formed during primordial nucleo-synthesis along with 84Sr, 86Sr and 88Sr, as well as that formed by radioactive decay of 87Rb. The ratio 87Sr/86Sr is the parameter typically reported in geologic investigations; ratios in minerals and rocks have values ranging from about 0.7 to greater than 4.0. Because strontium has an atomic radius similar to that of calcium, it readily substitutes for Ca in minerals.
Sixteen unstable isotopes are known to exist. Of greatest importance are 90Sr with a half-life of 28.78 years and 89Sr with a half-life of 50.5 days.
  • 90Sr is a by-product of nuclear fission which is found in 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 required. The 1986 Chernobyl nuclear accident contaminated a vast area with 90Sr. 90Sr confined inside a concave silver plaque is also used for the medical treatment of a resected pterygium.
  • 89Sr is a short-lived artificial radioisotope which provides a health benefit since it substitutes for calcium in bone. In circumstances where cancer patients have widespread and painful bony metastases (secondaries), the administration of 89Sr results in the delivery of radioactive emissions (beta particles in this case) directly to the area of bony problem (where calcium turnover is greatest). The 89Sr is manufactured as the chloride salt (which is soluble), and when dissolved in normal saline can be injected intravenously. Typically, cancer patients will be treated with a dose of 150 MBq. The patient needs to take precautions following this because their urine becomes contaminated with radioactivity, so they need to sit to urinate and double flush the toilet. The beta particles travel about 3.5mm in bone (energy 0.583 MeV) and 6.5mm in tissue, so there is no requirement to isolate patients who have been treated except to say they should not have any one (especially young children) sitting in their laps for 10-40 days. The variation in time results from the variable clearing time for 89Sr which depends on renal function and the number of bony metastases. With a lot of bony metastases, the entire 89Sr dose can be taken up into bone and so the entire radioactivity is retained to decay over a 50.5 day half-life. However, where there are few bony metastases, the large proportion of 89Sr not taken up by the bone will be filtered by the kidney, so that the effective half-life (a combination of the physical and biological half-life) will be much shorter.

Precautions

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

Effect on the human body

The human body absorbs strontium as if it were calcium. Due to the elements being sufficiently similar chemically, the stable forms of strontium do not pose a significant health threat, but the radioactive 90Sr can lead to various bone disorders and diseases, including bone cancer. The strontium unit is used in measuring radioactivity from absorbed 90Sr.
An innovative drug made by combining strontium with ranelic acid has aided in bone growth, boosted bone density and lessened vertebral, peripheral and hip fractures. Women receiving the drug showed a 12.7% increase in bone density. Women receiving a placebo had a 1.6% decrease. Half the increase in bone density (measured by x-ray densitometry) is attributed to the higher atomic weight of Sr compared with calcium, whereas the other half a true increase in bone mass. It means that strontium ranelate creates new, stronger bone. Strontium ranelate (marketed under the trade names Protelos, Osseor, Protos, Bivalos, Protaxos, Ossum) is registered for treatment of osteoporosis in many countries all over the world. Strontium ranelate has been shown to strengthen bones, according to presentations given at the IOF World Congress on Osteoporosis, in June of 2006. It also reduced bone resorption.
Strontium ranelate is registered as a prescription drug in Europe and many countries worldwide. It needs to be prescribed by a doctor, delivered by a pharmacist, and requires strict medical supervision. Currently, (early 2007) it is not available in Canada or the United States.
Several other salts of strontium such as strontium citrate or strontium carbonate are often presented as natural therapies and sold at a dose that is several hundred times higher than the usual strontium intake. Despite the lack of strontium deficit referenced in the medical literature and the lack of information about possible toxicity of strontium supplementation, such compounds can still be sold in the United States under the Dietary Supplements Health and Education Act of 1994. However, their long-term safety and efficacy have never been evaluated on humans using large-scale medical trials. Such compounds should not be administered to humans before further studies are conducted. But, a recent study conducted the NY College of Dental Sciences using strontium citrate on osteoblasts showed marked improvement on bone-building osteoblasts (http://iadr.confex.com/iadr/2007orleans/techprogram/abstract_89231.htm. Biochemically, it doesn't matter what form of strontium you take as all all forms are must dissolve in the stomach, become ionized and then protein-bound in the intestinal tract to be absorbed. Servier developed strontium renalate simply as a way for them to patent a new strontium compound. In fact, strontium citrate is far more soluble than the strontium renalate and should be less toxic, all this has not been proven.
Strontium compounds have been used successfully since the 1950's to treat osteoporosis with no toxicity. It was only the hysteria created by the strontium-90 fallout and the later introduction of HRT therapy followed by the aldonterates that caused research on strontium to be halted. However, Servier has found that their strontium renalate has less toxicty, and in some cases a higher effectiveness, than many of the aldonterates used today (see Servier.com, Protelos) for their clinical trial results.
Allegedly, an attempt was made in 1968 to poison Alexander Dubček with Sr-90, but it failed.
It is thought that, contrary to popular belief, Gladiators were mostly vegetarian which ensured a greater intake of strontium leading to stronger bones and therefore more resistance to the otherwise bone-breaking and crushing attacks of other gladiators.

See also

References

  • Dasch, J. (1969). Strontium isotopes in weathering profiles, deep-sea sediments, and sedimentary rocks. Geochimica et Cosmochimica Acta, Vol. 33, pp. 1521-1552.
  • Krom et al. (1999). The characterisation of Saharan Dusts and Nile particulate matter in surface sediments from the Levantine basin using Sr isotopes. Marine Geology, Vol. 155, pp. 319-330.
  • Krom et al. (2002). Nile River sediment fluctuations over the past 7000 yr and their key role in sapropel development. Geology, Vol. 30, pp. 71-74.
  • Talbot et al., (2000). Strontium isotope evidence for late Pleistocene reestablishment of an integrated Nile drainage network. Geology, Vol. 28, pp. 343-346.
  • Barnett-Johnson, R., Grimes, C.B., Royer C.F., Donohoe, C.J. (2007) Identifying the contribution of wild and hatchery Chinook salmon (Oncorhynchus tshawytscha) to the ocean fishery using otolith microstructure as natural tags. Canadian Journal of Fisheries and Aquatic Sciences, Vol.64, pp. 1683-1692.
  • Benson, L., Cordell, L., Vincent, K., Taylor, H., Stein, J., Farmer, G., and Kiyoto, F. (2003) Ancient maize from Chacoan great houses: where was it grown?: Proceedings of the National Academy of Sciences, Vol. 22, pp. 13111-13115.
  • English, N.B., Betancourt, J.L., Dean, J.S. and J. Quade (2001) Strontium Isotopes Reveal Distant Sources of Architectural Timber in Chaco Canyon, New Mexico. Proceedings of the National Academy of Sciences of the United States of America, Vol. 98, pp. 11891-11896
  • Porder, S., Paytan, A., and E.A. Hadly (2003) Mapping the origin of faunal assemblages using strontium isotopes. Paleobiology, 29: 197 - 204.
strontium in Afrikaans: Strontium
strontium in Arabic: سترونتيوم
strontium in Azerbaijani: Stronsium
strontium in Bengali: স্ট্রনশিয়াম
strontium in Belarusian: Стронцый
strontium in Bosnian: Stroncijum
strontium in Bulgarian: Стронций
strontium in Catalan: Estronci
strontium in Cebuano: Strontium
strontium in Czech: Stroncium
strontium in Corsican: Stronziu
strontium in Danish: Strontium
strontium in German: Strontium
strontium in Estonian: Strontsium
strontium in Modern Greek (1453-): Στρόντιο
strontium in Spanish: Estroncio
strontium in Esperanto: Stroncio
strontium in Basque: Estrontzio
strontium in Persian: استرانسیوم
strontium in French: Strontium
strontium in Friulian: Stronzi
strontium in Manx: Stroinçhum
strontium in Galician: Estroncio
strontium in Korean: 스트론튬
strontium in Armenian: Ստրոնցիում
strontium in Hindi: स्ट्रोन्सियम
strontium in Croatian: Stroncij
strontium in Ido: Stroncio
strontium in Indonesian: Stronsium
strontium in Icelandic: Strontín
strontium in Italian: Stronzio
strontium in Hebrew: סטרונציום
strontium in Javanese: Strontium
strontium in Kannada: ಸ್ಟ್ರಾನ್ಶಿಯಮ್
strontium in Swahili (macrolanguage): Stronti
strontium in Haitian: Estwontyòm
strontium in Kurdish: Stronsiyûm
strontium in Latin: Strontium
strontium in Latvian: Stroncijs
strontium in Luxembourgish: Strontium
strontium in Lithuanian: Stroncis
strontium in Lojban: jinmrstronti
strontium in Hungarian: Stroncium
strontium in Malayalam: സ്ട്രോണ്‍ഷിയം
strontium in Dutch: Strontium
strontium in Japanese: ストロンチウム
strontium in Norwegian: Strontium
strontium in Norwegian Nynorsk: Strontium
strontium in Occitan (post 1500): Estronci
strontium in Uzbek: Stronsiy
strontium in Polish: Stront
strontium in Portuguese: Estrôncio
strontium in Romanian: Stronţiu
strontium in Quechua: Istronsyu
strontium in Russian: Стронций
strontium in Sicilian: Stronziu
strontium in Simple English: Strontium
strontium in Slovak: Stroncium
strontium in Slovenian: Stroncij
strontium in Serbian: Стронцијум
strontium in Serbo-Croatian: Stroncijum
strontium in Finnish: Strontium
strontium in Swedish: Strontium
strontium in Tamil: ஸ்ட்ரோன்ஷியம்
strontium in Thai: สทรอนเทียม
strontium in Vietnamese: Strontium
strontium in Turkish: Stronsiyum
strontium in Ukrainian: Стронцій
strontium in Chinese: 锶
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