Strontium (Sr) is a chemical element, alkaline earth metal of the 2nd group of the periodic table. Used in red flashing lights and phosphors, it poses a major threat to health from radioactive contamination.
Discovery story
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 Kruykshenk in 1789 suggested 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 Humphrey Davy, who electrolyzed a mixture of wet hydroxide or chloride with mercury oxide using a mercury cathode, and then mercury was evaporated from the amalgam obtained. 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 as 18.9 atoms for every 10 6 silicon atoms. It is about 0.04% of the mass of the earth's crust. The average concentration of an element in seawater is 8 mg / l.
The chemical element of strontium is widely found in nature, and, according to experts, is the 15th most common substance on Earth, reaching a concentration of 360 parts per million. Given its extreme reactivity, it exists only in the form of compounds. Its main minerals are celestin (SrSO 4 sulfate) and strontianite (SrCO 3 carbonate). Of these, celestite is found in sufficient quantities for cost-effective production, more than 2/3 of the world supply comes from China, while Spain and Mexico supply most of the remainder. However, it is more profitable to extract strontianite, because strontium is often used in carbonate form, but its deposits are relatively few.
The properties
Strontium is a soft metal, like lead, which shines like silver at the site of the 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. In a free state in nature does not occur. Accompanying calcium, strontium is a part of only 2 main ores: celestine (SrSO 4 ) and strontianite (SrCO 3 ).
Among the chemical elements magnesium – calcium – strontium (alkaline earth metals), Sr is in group 2 (formerly 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 strontium is similar to the radius of calcium, it easily replaces the latter in minerals. But it is softer and more reactive in water. Upon contact with it forms hydroxide and hydrogen gas. Three strontium allotropes with transition points of 235 ° C and 540 ° C are known.
The alkaline earth metal usually does not react with nitrogen below 380 ° C and forms only oxide at room temperature. However, in the form of a powder, strontium spontaneously ignites with the formation of oxide and nitride.
Chemical and physical properties
The characteristic of the chemical element strontium according to plan:
- Name, symbol, atomic number: strontium, Sr, 38.
- Group, period, block: 2, 5, s.
- Atomic mass: 87.62 g / mol.
- Electronic configuration: [Kr] 5s 2 .
- Electron distribution over the shells: 2, 8, 18, 8, 2.
- Density: 2.64 g / cm 3 .
- Melting and boiling points: 777 ° C, 1382 ° C.
- The oxidation state: 2.
Isotopes
Natural strontium is a mixture of 4 stable isotopes: 88 Sr (82.6%), 86 Sr (9.9%), 87 Sr (7.0%) and 84 Sr (0.56%). Of these, only 87 Sr is radiogenic - it is formed during the decay of the radioactive isotope of rubidium 87 Rb with a half-life of 4.88 × 10 10 years. It is believed that 87 Sr was produced during the “primary nucleosynthesis” (early stage of the Big Bang) along with the isotopes 84 Sr, 86 Sr and 88 Sr. Depending on the location, the ratio of 87 Sr to 86 Sr 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
90 Sr (half-life of 28.9 years) is the most durable. This isotope produced by a nuclear explosion is considered the most dangerous decay product. Due to its chemical similarity with calcium, it is absorbed in bones and teeth, where it continues to eject electrons, causing radiation damage, damaging the bone marrow, disrupting the formation of new blood cells and causing cancer.
However, under medical conditions, strontium is used to treat some superficial malignant neoplasms and bone cancer. It is also used in the form of strontium fluoride in chemical current sources and in radioisotope thermoelectric generators, in which the heat of its radioactive decay is converted into electricity, serving as long-lived, light sources of energy in navigation buoys, remote weather stations and spacecraft.
89 Sr 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 of strontium is not necessary for higher forms of life; its salts are usually non-toxic. What makes 90 Sr dangerous is 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 an exceptional oxidation state of +2 in the form of an Sr 2+ 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, since the corresponding calcium and barium compounds, as a rule, do the same, but are cheaper. However, some of them have found application in industry. We have not yet figured out with the help of what substances to achieve raspberry color in fireworks and signal lights. Currently, in order to obtain this color, only strontium salts, such as Sr (NO 3 ) 2 nitrate and Sr (ClO 3 ) 2 chlorate, are used. 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 sugar can be easily regenerated by the action of carbon dioxide. SrS monosulfide is used as a depilator and ingredient in phosphors of electroluminescent devices and luminous inks.
Strontium ferrites form a family of compounds with the general formula SrFe x O y obtained as a result of the high-temperature (1000–1300 ° C) reaction of SrCO 3 and Fe 2 O 3 . Ceramic magnets are made from them, which are widely used in speakers, car wiper engines and children's toys.
Production
Most of the mineralized celestine SrSO 4 is converted to carbonate in two ways: either celestine is directly leached with a solution of sodium carbonate, or it is heated with coal to form a sulfide. In the second stage, a dark substance is obtained, containing mainly strontium sulfide. This "black ash" is dissolved in water and filtered. Strontium carbonate is precipitated from a sulfide solution by introducing carbon dioxide. Sulfate is reduced to sulfide by carbothermic reduction of SrSO 4 + 2C → SrS + 2CO 2 . An element can be obtained by cathodic electrochemical contact, in which a cooled iron rod acting as a cathode touches the surface of a mixture of potassium chloride and strontium, and rises when strontium solidifies on it. Reactions at the electrodes can be represented as follows: Sr 2+ + 2e - → Sr (cathode); 2Cl - → Cl 2 + 2e - (anode).
Metallic Sr can also be reduced from aluminum oxide. It is malleable and ductile, a good conductor of electricity, but relatively little is used. One of its applications is an alloying agent for aluminum or magnesium in casting cylinder blocks. Strontium improves machinability and creep resistance of the metal. An alternative way to obtain strontium is to restore its oxide with aluminum in vacuum at a distillation temperature.
Commercial application
The strontium chemical element is widely used in the glass of cathode ray tubes of color TVs to prevent the penetration of x-rays. It can also be part of aerosol paints. This, apparently, is one of the most likely sources of strontium exposure on the population. In addition, the element is used for the production of ferrite magnets and for the purification of zinc.
Salts of strontium are used in pyrotechnics because they burn the flame red when burned. And the alloy of strontium salts with magnesium is used as part of incendiary and signal mixtures.
Titanate has an extremely high refractive index and optical dispersion, which makes it useful in optics. It can be used as a replacement for diamonds, but is rarely used for this purpose because of its extreme softness and vulnerability to scratches.
Strontium aluminate is a bright phosphor with long-term phosphorescence stability. Oxide is sometimes used to improve the quality of ceramic glazes. The
90 Sr isotope 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 generated by the decay of radioactive elements into electricity. These devices are used in spacecraft, remote weather stations, navigation buoys, etc. - where a light and long-lived nuclear-electric energy source is required.
Medical use of strontium: characterization of properties, treatment with drugs
The 89 Sr isotope is an active ingredient in the radioactive drug Metastron, used to treat bone pain caused by metastatic prostate cancer. The chemical element of strontium acts like calcium, mainly included in the bone in places with increased osteogenesis. This localization focuses the radiation exposure on the cancerous lesion.
The 90 Sr radioisotope is also used in cancer therapy. Its beta radiation and long half-life are ideal for surface radiation therapy.
An experimental preparation obtained by combining strontium with ranelinic acid promotes bone growth, an increase in bone density and a decrease in 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%.
Precautionary measures
Pure strontium has high chemical activity, and in the ground state, the metal spontaneously ignites. Therefore, this chemical element is considered fire hazard.
Effects on the human body
The human body absorbs strontium in the same way as calcium. The two elements are so chemically similar that the resistant forms of Sr do not pose a significant health hazard. In contrast, the radioactive isotope 90 Sr can lead to various bone disorders and diseases, including bone cancer. A strontium unit is used to measure the radiation absorbed by 90 Sr.