About 200 BC,Ancient Egypt、Rome、BabylonUsedboraxMaking glass and welding gold.French chemistGuy LussacUse metalpotassiumreductionboric acidThe simple boron is prepared.The content of boron in the crust is 0.001%.Boron is a black or silver gray solid.Crystalline boronThe appearance is black, and the hardness is second only todiamond, the texture is brittle.
The discovery and use of boron compounds can be traced back to ancient Egypt, for example, borax was used as a flux when making glass in ancient Egypt, and the ancient alchemists also used borax, but the chemical composition of boric acid was still a mystery until the early 19th century.
In 1808, David, a British chemist, discovered potassium by electrolysis, and then melted it by electrolysisBoron trioxideIn the same year, French chemistGuy LussacFor HetenaMetallic potassiumReducing anhydrous boric acid to produce boron.
In fact, they did not produce pure boron, and extremely pure boron is almost impossible to obtain.The purer boron is composed ofHenri MuvasanExtracted in 1892.Finally, E. Weintraub of the United States ignited the mixture of boron chloride vapor and hydrogen to produce completely pure boron.The discovered properties of boron obtained from this material are quite different from those reported previously.
Boron is named Boron, which derives from Arabic and originally means "flux".It means that the ancient Arabs have known that borax has the ability to melt metal oxides and is used in weldingFlux。It was not until 1981 that people realized that boron was an essential element not only for plants, but also for animals and humans.An early research result reported at that time suggested the necessity of boron. In this study, it was found that boron could improve bone calcification of chicks when they were fed with diets with insufficient but not completely deficient vitamin D.[2]
Content distribution
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Boron accounts for about 0.001% of the crust composition, and its main ores in nature areboraxandBoehmiteEtc.Many boron bearing salt lakes in the Tibet Autonomous Region of China have accumulated a large number of borax crystals after evaporation and drying.[3]
Boron is abundant in nature.Natural borax (NatwoBfourOseven·10HtwoO），It has been used as medicine in ancient China, called Pengsha or Basin Sand, and may have been spread from Tibet to India, and then from India to Europe.
Physical and chemical properties
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physical property
boron
The elemental boron is black or dark brown powder, with a melting point of 2076 ℃.The boiling point is 3927 ℃.There are many kinds of simple boronAllotrope, amorphous boron is brown powder,Crystalline boronIt is grayish black.Crystalline boron is inert while amorphous boron is active.The hardness of boron is similar todiamondIt has very high resistance, but its conductivity increases with the increase of temperature. It is a good conductor at high temperature.There are 14 kinds of boronisotopeOnly two of them are stable.
Weak conductor at room temperature;It is a good conductor at high temperature.In natureboric acidandborateExists in the form of.[4]
crystal structure
There are many variants of crystalline boron, all of which are BtwelveIcosahedronBasicStructural unit。The icosahedron is composed of 12 B atoms. The 20 edges of a nearly equilateral triangle intersect into 30 edges and 12 corners, each of which is occupied by a B atom.
Because BtwelveThe connection of icosahedron is different, the bond is different, and the type of boron crystal formed is also different.The most common one is α - diamond boron.
α - rhombic boron is composed of BtwelveUnitLayered structure，There are both common σ bond and α - rhombic boron crystalThree center two electronic key。The bonding electrons of many B atoms are delocalized to a considerable extent. Such crystals belong toAtomic crystalTherefore, crystalline boron has high hardness and high melting point,chemical propertyNot lively.
In α - rhombic boronlatticeEach icosahedron is connected with six adjacent icosahedrons in the same plane by three center two electron bonds through six B atoms at the waist (where the dotted triangle represents three center two electron bonds, and the bond distance is 203pm).This kind of icosahedron consists of a sheet layer. The layer bonding relies on the connection of three B atoms at the top and bottom of the icosahedron with six normal B-B covalent bonds (that is, two electron bonds at two centers, bond length 171pm) to the six nearby icosahedrons at the bottom two layers, three of which are on the upper layer and three of which are on the lower layer.
In the icosahedral structural unit of boron,BtwelveThe 36 electrons of are distributed as follows: there are 13 molecular orbitals in the icosahedron, and 26 electrons are used;Each icosahedron forms six two center two electron covalent bonds with six adjacent icosahedrons above, and six electrons are used;Six B atoms at the waist of the icosahedron and six adjacent three center two electron bonds on the same plane use 6 × 2/3=4 electrons, and the totalNumber of electronsIt is 26+6+4=36.All the electrons have been used to form complex polyhedral structures.
Bonding feature
Bonding of boron
Boron is the only non-metallic element in the third main group of the periodic table,The valence electron structure of B atom is 2stwo2poneThe valence electrons of B atom are less than the number of valence orbitals. However, compared with the metal elements lithium and beryllium in the same period, boron has smaller atomic radius, higher ionization energy and greater electronegativity, which is characterized by the formation of covalent bond molecules.
In boron atom, sptwoIn the covalent molecules formed by hybridization, the remaining empty orbital can be used asLewis acid, receiving foreign lone pair electrons to form a complex with sp ³ hybrid tetrahedral configuration.for exampleBoron trifluorideAndammoniaMolecular complexes;If there is no suitable foreign electron, it can self polymerize to form electron deficiencyMulti center keyFor example, three center two electron hydrogen bridge bond, three center two electron boron bridge bond, three center two electron boron bridge bond.
Note the difference between bridge bond and three center two electron.The boron atom in the center of the boron bridge bond is the overlap of the p orbital and the two hybrid orbitals, the hydrogen atom in the center of the hydrogen bridge bond is the overlap of the s orbital and the two hybrid orbitals, and the three center two electron boron bond is the combination overlap of the three hybrid orbitals.
Boron is easily oxidized by air, and the formation of boron trioxide film hinders the continuous oxidation of internal boron.It can react with fluorine at normal temperature and is not corroded by hydrochloric acid and hydrofluoric acid aqueous solution.Boron is insoluble in water. Powdered boron can be soluble in boiling nitric acid and sulfuric acid, as well as most molten metals such as copper, iron, manganese, aluminum and calcium.
(1) Interaction with nonmetals
B energy and N at high temperaturetwo、Otwo、Simple substance reaction such as S, for example, it can burn in air to produce BtwoOthreeAnd a small amount of BN, which can interact with F at room temperaturetwoReacts, but it does not react with Htwo, rare gas, etc.
(2) B can be converted from many stable oxides (such as SiOtwo，PtwoOfive，H2O, etc.) as reducing agent.For example, in red heat,B andsteamThe reaction generates boric acid and hydrogen:
(3) Interaction with acid
Boron does not react with hydrochloric acid, but with hot concentrated HtwoSOfour, hot concentrated HNOthreeActing to form boric acid:
2B + 3HtwoSOfour(rich)=2HthreeBOthree+ 3SOtwo↑
B + 3HNOthree(rich)=HthreeBOthree+ 3NOtwo↑
(4) Interaction with strong base
In the presence of oxidant, boron is obtained by co melting with strong alkaliMetaboric acidSalt:
2B + 2NaOH + 3KNOthree= 2NaBOtwo+ 3KNOtwo+ HtwoO
(5) Interaction with metal
At high temperature, boron can react with almost all metals to form metalsboride。They are someNon integral compoundThe more B atoms in the composition, the more complex its structure is.
Boron also causes its hydride due to its lack of electronsBoraneThe middle boron atom has an abnormally high coordination number, making it the most complex structure of all element hydrides.[1]
Preparation method
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1. First, use concentrated alkaline solution to decompose the ludwigiteSodium metaborate, replace NaBOtwoIn strong alkaline solutioncrystalCome out and make it dissolve in water to become a relatively thick solution, and inject COtwoIt is obtained by adjusting alkalinity and concentrating crystallizationSodium tetraborate。Dissolve sodium tetraborate in water, adjust acidity with sulfuric acid, and precipitate low solubilityboric acidCrystal.Heat to dehydrate boric acidBoron trioxideAfter drying, reduce B with magnesium or aluminumtwoOthreeCrude boron is obtained.Use crude boron separatelyhydrochloric acid、sodium hydroxideandHydrogen fluorideAfter treatment, brown amorphous boron with a purity of 95~98% can be obtained.[5]
2. The purest element boron is obtained by hydrogen reduction:hydrogenandBoron tribromideThe mixed gas ofTantalum wireWhen heated to 1500K, boron tribromide is reduced by hydrogen at high temperature, and the resulting boron is flaked or needle shaped on the tantalum wire.
3. It is obtained by heating magnesium powder or aluminum powder to reduce boron oxide.[4]
Main purpose
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Form life
Boron is necessary for the formation of ribonucleic acid, which is an important basic component of life.James Stephenson, a postdoctoral researcher at the Institute of Astrobiology of the Space Administration of the University of Hawaii, said: "Boron may be important for the origin of life on Earth, because it can stabilize nucleic acids, which are important components of RNA. In early life, ribonucleic acid is considered to be the information precursor of deoxyribonucleic acid."
Industrial use
Boron is a widely used chemical raw material mineral, mainly used for productionborax、boric acidAll kinds of compounds and elements of boron are important raw materials for metallurgy, building materials, machinery, electrical appliances, chemical industry, light wool, nuclear industry, medicine, agriculture and other sectors.At present, there are more than 300 uses of boron, among which glass industry, ceramic industry, detergent and agricultural fertilizer are the main uses of boron, accounting for about 3/4 of the global boron consumption.Although China is rich in boron mineral resources, its boron mineral products cannot meet the needs of domestic economic construction. In 2007, the domestic production of borax was about 400000 tons, and the import of boron mineral products was 648700 tons, relying heavily on imports. Therefore, it is very important to fully understand the world market situation of boron mineral products.
The elemental boron is used as a good reducing agent, oxidant, brominating agent, organically synthesized blending material, insulator for high voltage and high frequency electricity and plasma arc, radar transmission window, etc.
Boron is a microalloying elementaluminium alloyCombination is an effective neutron shielding material;Boron steelstayreactorUsed incontrol rod；Boron fibreUsed for manufacturing composite materials, etc;Boron containing additives can improve metallurgical industrySinterIt can reduce the melting point, reduce the expansion, and improve the strength and hardness.Boron and its compounds are also auxiliary solvents for metallurgical industry and raw materials for smelting boron iron and boron steel. Titanium boride, lithium borideNickel borideIt can smelt heat-resistant special alloy;building material.Borate and boride are important components of enamel, ceramics and glass, with good heat resistance and wear resistance, which can enhance gloss and improve surface finish.[6]
boric acid，Zinc borateIt can be used as insulating material of fireproof fiber, which is a good flame retardant, and can also be used in bleaching, mordant dyeing, etc;Sodium metaborate is used for fabric bleaching.In addition, boron and its compounds can be used as paint desiccants, welding agents, and mercury containing sewage treatment agents in the paper industry.[7]
As a trace element, boron exists in quartz ore. In the purification process of high-purity quartz sand, how to reduce the boron content as much as possible becomes the key technology.The existence of boron reduces the melting point of quartz, reduces the use times of the quartz crucible, and increases the production cost of monocrystalline silicon.
physiological function
The scientific community is not fully aware of the absorption and metabolism of boron. Boron is easily absorbed in the diet, and most of it is excreted in urine. It is combined with oxygen in the blood, which is HthreeBOthreeOr B (OH)four-, boric acid andOrganic compoundThe hydroxyl group of is used to form inorganic ester.The boron content in the blood of animals and humans is very low, and it is related to the intake of magnesium in the diet. When the intake of magnesium is low, the boron content in the blood will increase.Boron can accumulate in bone, but it is not clear what form it is.
Boron is commonly found in vegetables and fruits to maintain bone health andcalcium、phosphorus、magnesiumOne of the trace elements required for normal metabolism.It has an effect on preventing calcium loss and osteoporosis in postmenopausal women. The lack of boron will aggravate the lack of vitamin D;On the other hand, boron is also helpful to increase male testosterone secretion, strengthen muscle, and is an indispensable nutrient for athletes.Boron can also improve brain function and reaction ability.Although most people are not deficient in boron, it is necessary for the elderly to pay due attention to intake.
The physiological function of boron has not yet been determined, and there are two hypotheses to explain the obvious and different reactions when boron is deficient, as well as the known biochemical characteristics of boron.One hypothesis is that boron is a kind of metabolismRegulatory factor, viaCompetitive inhibitionsomekey enzymeTo control manyMetabolic pathway。The other is that boron has the function of maintaining the stability of cell membrane function, so it can regulateanionOr the transmembrane signal or movement of cations to affect the response of the membrane to hormones and other regulatory substances.
Plant physiology
Boron is an essential element peculiar to higher plants.Boron energy and free statesugarThe combination makes it easy for sugar to cross the plasma membrane and promote sugar transportation.The boron content in plant organs was the highest in flowers, and the highest in stigma and ovary.Boron has an important influence on the reproductive process of plants, which is closely related to pollen formation, pollen tube germination and fertilization.In boron deficiency, anthers and filaments atrophy and pollen development is poor.The phenomenon of "flower without fruit" in rape and wheat is related to the lack of boric acid in plants.When boron deficiency occurs, the growth points of root tip and stem tip stop growing, and a large number of lateral roots and buds occur, and then the growth points of lateral roots and buds die, forming clusters.Sugar beet brown rot, potato leaf curl and apple fruit shrink are all caused by boron deficiency.[8]
