Strontium (Sr) is a chemical element, an alkaline earth metal of the 2nd group of the periodic table. Used in red signal lights and phosphors, a major he alth hazard in radioactive contamination.
Discovery history
Mineral from a lead mine near the village of Strontian in Scotland. It was originally recognized as a variety of barium carbonate, but Adair Crawford and William Cruikshank suggested in 1789 that it was a different substance. Chemist Thomas Charles Hope named the new mineral strontite after the village, and the corresponding strontium oxide SrO, strontium. The metal was isolated in 1808 by Sir Humphry Davy, who electrolyzed a mixture of wet hydroxide or chloride with mercury oxide using a mercury cathode and then evaporated the mercury from the resulting amalgam. He named the new element using the root of the word "strontium".
Being in nature
The relative abundance of strontium, the thirty-eighth element of the periodic table, in space is estimated to be 18.9 atoms for every 106 silicon atoms. It is about0.04% of the mass of the earth's crust. The average concentration of the element in sea water is 8 mg/L.
The chemical element strontium is widely found in nature and is estimated to be the 15th most abundant substance on Earth, reaching concentrations of 360 parts per million. Given its extreme reactivity, it exists only in the form of compounds. Its main minerals are celestine (sulfate SrSO4) and strontianite (carbonate SrCO3). Of these, celestite occurs in sufficient quantities for profitable mining, more than 2/3 of the world supply of which comes from China, and Spain and Mexico supply most of the rest. However, it is more profitable to mine strontianite, because strontium is more often used in carbonate form, but there are relatively few known deposits.
Properties
Strontium is a soft metal, similar to lead, that shines like silver when cut. In air, it quickly reacts with oxygen and moisture present in the atmosphere, acquiring a yellowish tint. Therefore, it must be stored in isolation from air masses. Most often it is stored in kerosene. It does not occur in the free state in nature. Accompanying calcium, strontium is included in only 2 main ores: celestite (SrSO4) and strontianite (SrCO3).
In the series of chemical elements magnesium-calcium-strontium (alkaline earth metals) Sr is in group 2 (former 2A) of the periodic table between Ca and Ba. In addition, it is located in the 5th period between rubidium and yttrium. Since the atomic radius of strontiumsimilar to the radius of calcium, it easily replaces the latter in minerals. But it is softer and more reactive in water. Forms hydroxide and hydrogen gas on contact. 3 allotropes of strontium are known with transition points of 235°C and 540°C.
Alkaline earth metal generally does not react with nitrogen below 380°C and forms only an oxide at room temperature. However, in powder form, strontium spontaneously ignites to form oxide and nitride.
Chemical and physical properties
Characterization of the chemical element strontium according to the plan:
- Name, symbol, atomic number: strontium, Sr, 38.
- Group, period, block: 2, 5, s.
- Atomic mass: 87.62 g/mol.
- E-config: [Kr]5s2.
- Distribution of electrons in shells: 2, 8, 18, 8, 2.
- Gensity: 2.64g/cm3.
- Melting and boiling points: 777 °C, 1382°C.
- Oxidation state: 2.
Isotopes
Natural strontium is a mixture of 4 stable isotopes: 88Sr (82.6%), 86Sr (9, 9%), 87Sr (7.0%) and 84Sr (0.56%). Of these, only 87Sr is radiogenic - it is formed by the decay of the radioactive isotope of rubidium 87Rb with a half-life of 4.88 × 10 10 years. It is believed that 87Sr was produced during "primordial nucleosynthesis" (an early stage of the Big Bang) along with isotopes 84Sr, 86 Sr and 88Sr. Depending on thelocations, the ratio of 87Sr and 86Sr may differ by more than 5 times. This is used in dating geological samples and in determining the origin of skeletons and clay artifacts.
As a result of nuclear reactions, about 16 synthetic radioactive isotopes of strontium were obtained, of which the most durable is 90Sr (half-life 28.9 years). This isotope, produced in a nuclear explosion, is considered the most dangerous decay product. Due to its chemical similarity to calcium, it is absorbed into the bones and teeth, where it continues to expel electrons, causing radiation damage, bone marrow damage, disrupting the formation of new blood cells, and causing cancer.
However, under medically controlled conditions, strontium is used to treat certain superficial malignancies and bone cancers. It is also used in the form of strontium fluoride in chemical current sources and in radioisotope thermoelectric generators, which convert the heat of its radioactive decay into electricity, serving as long-lived, lightweight power sources in navigation buoys, remote weather stations and spacecraft.
89Sr is used to treat cancer because it attacks bone tissue, produces beta radiation, and decays after a few months (half-life 51 days).
The chemical element strontium is not essential for higher life forms, its s alts are usually non-toxic. What makes90Sr dangerous, used to increase bone density and growth.
Connections
The properties of the chemical element strontium are very similar to those of calcium. In compounds, Sr has the exclusive oxidation state +2 as the Sr2+ ion. The metal is an active reducing agent and easily reacts with halogens, oxygen and sulfur to produce halides, oxide and sulfide.
Strontium compounds have rather limited commercial value, as the corresponding calcium and barium compounds generally do the same but are cheaper. However, some of them have found application in industry. It has not yet been figured out with what substances to achieve a crimson color in fireworks and signal lights. Currently, only strontium s alts such as Sr(NO3)2 and Sr(ClO) chlorate are used to achieve this color. 3)2 . About 5-10% of the total production of this chemical element is consumed by pyrotechnics. Strontium hydroxide Sr(OH)2 is sometimes used to extract sugar from molasses because it forms a soluble saccharide from which the sugar can be easily regenerated by the action of carbon dioxide. SrS monosulfide is used as a depilatory agent and an ingredient in the phosphors of electroluminescent devices and luminous paints.
Strontium ferrites form a family of compounds with the general formula SrFexOy, obtained as a result of a high-temperature (1000-1300 °C) reaction SrCO3 andFe2O3. They are used to make ceramic magnets, which are widely used in speakers, car windshield wiper motors and children's toys.
Production
Most mineralized celestite SrSO4 is converted to carbonate in two ways: either directly leached with sodium carbonate solution or heated with coal to form sulfide. At the second stage, a dark-colored substance is obtained, containing mainly strontium sulfide. This "black ash" dissolves in water and is filtered. Strontium carbonate precipitates from the sulfide solution by introducing carbon dioxide. Sulfate is reduced to sulfide by carbothermal reduction SrSO4 + 2C → SrS + 2CO2. The cell can be produced by cathodic electrochemical contact, in which a cooled iron rod, acting as a cathode, touches the surface of a mixture of potassium and strontium chlorides, and rises when the strontium solidifies on it. The reactions at the electrodes can be represented as follows: Sr2+ + 2e- → Sr (cathode); 2Cl- → Cl2 + 2e- (anode).
Metallic Sr can also be recovered from its oxide with aluminum. It is malleable and ductile, a good conductor of electricity, but is used relatively little. One of its uses is as an alloying agent for aluminum or magnesium in the casting of cylinder blocks. Strontium improves machinability and creep resistancemetal. An alternative way to obtain strontium is to reduce its oxide with aluminum in a vacuum at a distillation temperature.
Commercial use
The chemical element strontium is widely used in the glass of color TV cathode ray tubes to prevent X-ray penetration. It can also be used in spray paints. This appears to be one of the most likely sources of public exposure to strontium. In addition, the element is used to produce ferrite magnets and refine zinc.
Strontium s alts are used in pyrotechnics because they color the flame red when burned. And an alloy of strontium s alts with magnesium is used as part of incendiary and signal mixtures.
Titanate has an extremely high refractive index and optical dispersion, making it useful in optics. It can be used as a substitute for diamonds, but is rarely used for this purpose due to its extreme softness and vulnerability to scratches.
Strontium aluminate is a bright phosphor with long-lasting phosphorescence stability. The oxide is sometimes used to improve the quality of ceramic glazes. The isotope 90Sr is one of the best long-lived high-energy beta emitters. It is used as a power source for radioisotope thermoelectric generators (RTGs), which convert the heat released during the decay of radioactive elements into electricity. These devices are used inspacecraft, remote weather stations, navigation buoys, etc. - where a light and long-lived nuclear-electric power source is required.
Medical use of strontium: characterization of properties, treatment with drugs
Isotope 89Sr is the active ingredient in the radioactive drug Metastron, used to treat bone pain caused by metastatic prostate cancer. The chemical element strontium acts like calcium, it is mainly included in the bone in places with increased osteogenesis. This localization focuses the radiation effect on the cancerous lesion.
The radioisotope 90Sr is also used in cancer therapy. Its beta radiation and long half-life are ideal for surface radiation therapy.
An experimental drug made by combining strontium with ranelic acid promotes bone growth, increases bone density and reduces fractures. Stronium ranelate is registered in Europe as a treatment for osteoporosis.
Strontium chloride is sometimes used in toothpastes for sensitive teeth. Its content reaches 10%.
Precautions
Pure strontium has a high chemical activity, and in a crushed state, the metal spontaneously ignites. Therefore, this chemical element is considered a fire hazard.
Effect on the human body
The human body absorbs strontium in the same way as calcium. These twoThe elements are so similar chemically that the stable forms of Sr do not pose a significant he alth risk. In contrast, the radioactive isotope 90Sr can lead to various bone disorders and diseases, including bone cancer. The strontium unit is used to measure the radiation of absorbed 90Sr.
