Strontium is a chemical element with the symbol Sr and the atomic number 38. The alkaline earth metal, strontium is a very chemically reactive, gentle, silver-white metallic element. The metal forms a dark oxide layer when exposed to air. Strontium has physical and chemical properties similar to its two vertical neighbors in the periodic table, calcium and barium. This occurs naturally especially in the minerals celestine, strontianite and mined most of these first two. While the natural strontium is stable, the synthetic isotope 90 Sr is radioactive and is one of the most dangerous components of nuclear fallout, since strontium is absorbed by the body in a way similar to calcium. Stable strontium naturally, on the other hand, is not harmful to health.
Strontium and strontianite were named after Strontian, a Scottish village near the mineral discovered in 1790 by Adair Crawford and William Cruickshank; it is identified as a new element in the next year of its red-red flame test color. Strontium was first isolated as a metal in 1808 by Humphry Davy using a newly discovered electrolysis process. During the 19th century, Strontium was widely used in the production of sugar from sugar beets (see strontian process). At the peak production of television cathode ray tubes, as much as 75 percent of strontium consumption in the United States is used for faceplate glass. With the replacement of cathode ray tubes with other display methods, strontium consumption has dropped dramatically.
Video Strontium
Characteristics
Strontium is a divalent silver metal with a pale yellow color that is largely intermediate between and similar to the neighboring groups of calcium and barium. Softer than calcium and harder than barium. Melting point (777 ° C) and boiling point (1655 ° C) lower than calcium (842 ° C and 1757 ° C); barium continues this downward trend at the melting point (727 Â ° C), but not at boiling point (2170 Â ° C). The density of strontium (2.64 g/cm 3 ) is also the same between calcium (1.54 g/cm 3 ) and barium (3.594 g/cm 3 ). Three allotropes of metallic strontium exist, with transition points at 235 and 540 ° C.
The standard electrode potential for pair Sr 2 /Sr is -2.89 V, roughly halfway between Ca 2 /Ca (-2.84, V) and Couple Ba 2> /Ba (-2.92Ã, V), and close to adjacent alkaline metals. Strontium is an intermediate between calcium and barium in its reactivity to water, which reacts to contacts to produce strontium hydroxide and hydrogen gas. The strontium metal burns in air to produce strontium oxide and strontium nitride, but because it does not react with nitrogen below 380 ° C, at room temperature, it only forms spontaneous oxide. In addition to simple SrO oxide, SrO peroxide 2 can be made by direct oxidation of strontium metal under high oxygen pressure, and there is some evidence for yellow superoxide Sr (O 2 ) 2 . Strontium hydroxide, Sr (OH) 2 , is a strong base, though not as strong as barium hydroxide or alkali metals. The four dihalides of strontium are known.
Because of the large size of heavy s-block elements, including strontium, a large number of coordination numbers are known, from 2, 3, or 4 to 22 or 24 in SrCd 11 and SrZn 13 . Ca 2 ion is big enough, so high coordination number is the rule. The large size of strontium and barium plays an important part in stabilizing the strontium complex with macrocyclic polycyclic ligands such as crown crowns: for example, whereas the 18-crown-6 forms a relatively weak complex with calcium and alkali metals, the strontium and barium complex are much stronger.
The organostrontium compound contains one or more strontium-carbon bonds. They have been reported as intermediaries in the Barbier type reaction. Although strontium is in the same group as magnesium, and organomagnesium compounds are very commonly used throughout chemistry, organostrontium compounds are not widespread because they are more difficult to make and more reactive. The organostrontium compounds tend to be more similar to those of organoeuropium or organosamariums due to the same ionic radius of these elements (Sr 2 118Ã, pm; Eu 2 117Ã, pm; 2 122Ã, pm). Most of these compounds can only be prepared at low temperatures; Large ligands tend to support stability. For example, strontium dicyclopentadienyl, Sr (C 5 H 5 ) 2 , must be done by directly reacting strontium metal with mercurocene or cyclopentadiene alone; replacing C 5 H 5 ligand with bulkier C 5 (CH 3 ) 5 ligands on the other hand increase solubility, volatility, and kinetic stability of the compound.
Due to extreme reactivity with oxygen and water, strontium occurs naturally only in compounds with other elements, such as strontianite minerals and celestine. These are stored under liquid hydrocarbons such as mineral oil or kerosene to prevent oxidation; newly exposed strontium strains quickly turn yellowish with oxide formation. The fine strontium metal powder is pyrophoric, which means that it will burn spontaneously in the air at room temperature. The volatile strontium salt gives a burning red color for the flame, and these salts are used in fireworks and in the production of flares. Like calcium and barium, as well as alkaline and bivalve metal divalen europium and ytterbium, strontium metal dissolves directly in liquid ammonia to produce dark blue solution.
Isotope
Natural strontium is a mixture of four stable isotopes: 84 Sr, 86 Sr, 87 Sr, and 88 Sr. Their abundance increases with the increasing amount of mass and the heaviest, 88 Sr, constituting about 82.6% of all natural strontium, although abundance varies due to the production of radiogenic 87 Sr as princess from long-lived beta-decaying 87 Rb. The unstable isotope, the main decay mode of the lighter isotope of 85 Sr is the electron capture or positron emission for the rubidium isotope, and the heavier isotope of 88 Sr is the electron emission for yttrium isotope. Of special note is 89 Sr and 90 Sr. The former has a half-life of 50.6 days and is used to treat bone cancer due to strontium chemical similarity and hence the ability to replace calcium. While the 90 Sr (half 28.90 years) has been used equally, it is also an isotope of concern in the fall of nuclear weapons and nuclear accidents because of its production as a fission product. Its presence in bone can cause bone cancer, nearby tissue cancer, and leukemia. The 1986 Chernobyl nuclear accident was contaminated with about 30,000 km 2 with more than 10 kBq/m 2 with 90 Sr, which accounted for 5% of the core inventory 90 Sr.
Maps Strontium
History
Strontium is named after the Scottish village of Strontian (Gaelic SrÃÆ'²n an t-SÃÆ'¬thein ), where it is found in the main ore mine. Originally named strontianite by Thomas Charles Hope the name was soon after shortened to strontium.
In 1790, Adair Crawford, a physician involved in barium preparations, and his colleague William Cruickshank, acknowledged that Strontian ore exhibits properties different from those in other "heavy sparri" sources. This allows Adair to conclude on page 355 "... perhaps indeed, that the mineral scotch is a new species of earth that has not been adequately examined until now." Doctor and mineral collector Friedrich Gabriel Sulzer analyzed along with Johann Friedrich Blumenbach a mineral from Strontian and named it strontianite. He also came to the conclusion that it was different from the witherite and contained a new earth (neue Grunderde). In 1793, Thomas Charles Hope, a professor of chemistry at Glasgow University proposed the name strontites . He justified Crawford's early work and recounted: "... Considering the strange earth, I think it is necessary to name it, I call it the Strontites, from where it is found, the mode of derivation in my opinion, wholly of any quality possessed, which is the fashion of the present. This element was finally isolated by Sir Humphry Davy in 1808 by electrolysis of a mixture containing strontium chloride and mercury oxide, and announced by him in a lecture to the Royal Society on June 30, 1808. In accordance with the naming of other alkaline earth. , he changed his name to strontium .
The first large-scale strontium application is the production of sugar from sugar beets. Although the crystallization process using strontium hydroxide was patented by Augustin-Pierre Dubrunfaut in 1849, a large-scale introduction came with process improvement in the early 1870s. The German sugar industry used this process well into the 20th century. Before World War I the sugar beet industry used 100,000 to 150,000 tons of strontium hydroxide for this process per year. Strontium hydroxide is recycled in the process, but the demand for compensation during production is high enough to create significant demand that initiates strontianite mining in MÃÆ'¼nsterland. Strontianit mining in Germany ends when the mining of a celestine deposit in Gloucestershire begins. This mine supplied most of the world's strontium supply from 1884 to 1941. Although the Celestine sediments in the Granada basin were known for some time large scale mining did not begin before the 1950s.
During testing of atmospheric nuclear weapons, it was observed that strontium-90 is one of the relatively high nuclear fission products. The similarity with calcium and the possibility that strontium-90 may become enriched in bone makes research on strontium metabolism an important topic.
Genesis
Strontium is common in nature, being the 15th most abundant element in Earth (heavier barium congener being 14th), estimated to average about 360 parts per million in the Earth's crust and found mainly as mineral celestin sulphate (SrSO < sub> 4 ) and strontianit carbonate (SrCO 3 ). Of the two, celestine is more common in deposits of sufficient size for mining. Because strontium is most commonly used in carbonate form, strontianite will become more useful than two common minerals, but several deposits have been found that are suitable for development.
In strontium ground water behaves chemically like calcium. At medium pH to Sr 2 is the dominant strontium species. In the presence of calcium ions, strontium generally forms coprecipitates with calcium minerals such as calcite and anhydride at increased pH. At medium pH to acid, dissolved strontium is bound to soil particles with cation exchange.
The average strontium content of sea water is 8 mg/l. At concentrations between 82 and 90 Ã,μμol/l of strontium, the concentration is much lower than the calcium concentration, typically between 9.6 and 11.6 mmol/l. However much higher than barium, 13 g/l.
Production
The three major producers of strontium as Celestin by 2015 are China (150,000 t), Spain (90,000 t), and Mexico (70,000 t); Argentina (10,000 t) and Morocco (2,500 t) are small producers. Although strontium deposits occur widely in the United States, they have not been mined since 1959.
Most of the mined celestin (SrSO 4 ) is converted to carbonate by two processes. Either celestin is immediately washed with a solution of sodium carbonate or celestin baked with coal to form sulphides. The second stage produces a dark-colored material that mostly contains strontium sulphide. This is called "black ash" dissolved in water and filtered. Strontium carbonate is precipitated from a solution of strontium sulphide by the introduction of carbon dioxide. Sulfate is reduced to sulfide by carbothermic reduction:
- SrSO 4 2 C -> SrS 2 CO 2
About 300,000 tonnes are processed this way every year.
The metal is commercially produced by reducing strontium oxide with aluminum. Strontium is distilled from the mixture. The strontium metal can also be prepared on a small scale by electrolysis a solution of strontium chloride in potassium chloride liquid:
- Sr 2 2
e -
-> Sr - 2 Cl - -> Cl 2 2
e -
Apps
Consuming 75% of the production, the main use for strontium is in the glass for a color television cathode ray tube, where it prevents X-ray emission. This app for strontium decreases because CRT is replaced by other display methods. This reduction has a significant effect on strontium mining and refining. All parts of CRT must absorb X-rays. In the neck and tube funnel, lead glass is used for this purpose, but this type of glass shows a brownish effect due to X-ray interaction with glass. Therefore, the front panel is made of a mixture of glass that is different from strontium and barium to absorb X-rays. The mean values ​​for the glass mixtures specified for the recycling study in 2005 were 8.5% strontium oxide and 10% barium oxide.
Because strontium is very similar to calcium, it is incorporated in bone. The four stable isotopes are combined, in approximately the same proportions found in nature. However, actual isotope distributions tend to vary greatly from one geographical location to another. Thus, analyzing a person's bones can help determine his home region. This approach helps to identify patterns of ancient migration and the origin of human remains mingled on battlefield burial sites.
87 Sr/ 86 Sr ratio is usually used to determine the possibility of sedimentary sediment areas in natural systems, especially in marine and fluvial environments. Dasch (1969) shows that the surface sediment of the Atlantic shows a ratio of 87 Sr/ 86 Sr which can be regarded as the average bulk of 87 Sr/< soup> 86 Sr the ratio of geological terranes from adjacent land. A good example of the marine fluvial system that has been used by proven studies of Sr isotope is the Nile-Mediterranean River system. Due to the age of different rocks that are the majority of the Blue and White Nile, the catchment area from the change in the origin of the sediments reaching the delta of the Nile River and the Eastern Mediterranean Sea can be seen through the study of the isotope strontium. Such changes are controlled by kimari in the final quarter.
Recently, a 87 Sr/ 86 Sr ratio has also been used to determine the source of ancient archaeological materials such as wood and corn in Chaco Canyon, New Mexico. 87 Sr/ 86 The Sr ratio of teeth can also be used to track animal migration.
Strontium carbonate and other strontium salts are added to fireworks to give it a deep red color. This same effect identifies the strontium cation in the flame test. Fireworks consume about 5% of world production. Strontium carbonate is used in the manufacture of hard ferrite magnets.
Strontium chloride is sometimes used in toothpaste for sensitive teeth. One popular brand includes 10% total strontium chloride hexahydrate by weight. Small amounts are used in zinc refining to remove small amounts of lead impurities. The metal itself has limited use as a taker, to remove unwanted gases in a vacuum by reacting with them, although barium can also be used for this purpose.
Stronium radioactive
89 Sr is the active ingredient in Metastron, a radiofarmaka used for bone pain secondary to metastatic bone cancer. Strontium is processed like calcium by the body, which typically combines it into the bone in places of increased osteogenesis. This localization focuses radiation exposure on cancer lesions.
90 Sr has been used as a power source for radioisotope thermoelectric generators (RTGs). 90 Sr generates about 0.93 watts of heat per gram (lower for the 90 Sr form used in RTGs, which is strontium fluoride). However, 90 Sr has a third of life and a lower density than 238 Pu, other RTG fuels. The main advantage of 90 Sr is cheaper than 238 Pu and is found in nuclear waste. The Soviet Union deployed nearly 1,000 RTG on the north coast as a resource for lighthouses and meteorological stations.
The role of biology
Acantharea, a relatively large group of marine radiolarist protozoa, produces an intricate mineral skeleton composed of strontium sulphate. In biological systems, calcium is substituted in small levels by strontium. In the human body, most of the absorbed strontium is deposited in the bone. The strontium to calcium ratio in human bones is between 1: 1000 and 1: 2000 roughly in the same range as in blood serum.
Effects on the human body
The human body absorbs the strontium as if it were a lighter calcium congener. Because the elements are very similar, stable isotope strontium does not pose a significant health threat. The average human has an intake of about two milligrams of strontium a day. In adults, the consumed strontium tends to stick only to the surface of the bone, but in children, strontium can replace the calcium in the growing bone mineral and thus cause bone growth problems.
The biological half-life of strontium in humans has been reported from 14 to 600 days, 1000 days, 18 years, 30 years and, at the upper limit, 49 years. The published biological half-lives are explained by the metabolism of the strontium complex in the body. However, with an average of all excretion pathways, the overall biological half is estimated to be about 18 years. The level of strontium elimination is strongly influenced by age and sex, due to differences in bone metabolism.
Strontium ranelate drugs help bone growth, increase bone density, and reduce the incidence of vertebral, peripheral, and hip fractures. However, strontium ranelate also increases the risk of venous thromboembolism, pulmonary embolism and serious cardiovascular disorders, including myocardial infarction. Therefore its use is now limited. The beneficial effect is also questionable, since increased bone density is partly due to an increase in the density of strontium over the calcium it replaces. Strontium also accumulates in the body. Despite the restriction of strontium ranelate, strontium is still contained in some supplements. There is not much scientific evidence about the risk of strontium chloride when taken, those with a family history or family of blood clotting disorders are advised to avoid strontium.
Strontium has been shown to inhibit sensory irritation when applied to the skin. Topically applied, strontium has been shown to speed up the recovery rate of epidermal permeability barrier (skin barrier).
See also
References
Bibliography
- Greenwood, Norman N.; Earnshaw, Alan (1997). Chemical Elements (2nd ed.). Butterworth-Heinemann. ISBN: 0-08-037941-9.
External links
- WebElements.com - Strontium
- Strontium on Periodic Video Table (University of Nottingham)
Source of the article : Wikipedia
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