Boron (chemical element)
BORON, B (from the Latin word "Borum" * EN: boron; DE: Bor; FR: bore; ES: boro; RU: бор), is the chemical element of the group III of the periodic table by Mendeleev, the atomic number is 5, the atomic mass is 10.811. Natural boron has two stable isotopes: 10B (19.6%), and 11B (80.4%). It has been isolated by the French chemists J. Gay-Lussac and L. Thénard during the 1808. It forms dark gray crystals.
There are known 3 modifications of boron: alpha-rhombohedral with the density of 2460 kilograms per cubic metre, tetragonal with the density of 2370 kilograms per cubic metre, and beta-rhombohedral with the density of 2300 kilograms per cubic metre; the temperature of the melting point is 2200 degrees Celsius, the temperature of the boiling point is approximately 3700 degrees Celsius; the specific heat of fusion is 4.5 megajoules per kilogram; the specific heat capacity of the amorphous boron is 2.3 kilojoules per kilogram-kelvin (at the temperature of 20 degrees Celsius), the thermal coefficient of linear expansion is 1.1x8.3 • 10^-6 per degree (within the 20-750 degrees Celsius interval of temperatures). Crystalline boron is semiconductor. Boron is diamagnetic. The oxidation state of boron is 3; the chemical bonds B - O, B - Cl, and others are polar. Boron is the complex-forming element, the coordination number is 4. Boron is amphoteric, and chemically quite inert (especially the crystalline boron). It burns within the air at the temperature of 700 degrees Celsius, with the forming of the boron anhydride B2O3, which is dissolving within water with the forming of the boric acid H3BO3. The major compounds of boron are borates (the salts of boric and polyboric acids); there have been obtained boranes, halides, nitrides, carbides, sulfides, and selenides of boron. With metals, boron forms borides. Boranes are toxic. The average content of boron within the Earth's crust is 3 • 10^-4% by mass.
Within the nature, boron has not been found in the free state. It forms approximately 80 minerals: natural borates, borosilicates (datolite, danburite), and boroaluminosilicates (tourmaline, axinite). As isomorphic impurity, it is the part of the rock-forming aluminosilicates, and in the form of adsorbed impurity, it is the part of the iron hydroxides. Geochemical migration under endogenous conditions is performed in the form of the fumes of boric acid within the gases of volcanoes, or in the form of the hydroxyfluoride-borate complex compounds of potassium and sodium under hydrothermal conditions, and within the zone of supergene processes, the migration is performed in the form of the soluble salts of polyboric acids. The excess of boron within the soils and nutritional products causes the emergence of the series of endemic diseases. On the major genetic types of deposits of boron, see within the "Boron ores" article.
They obtain the amorphous boron using the method of the reduction of the boric anhydride by magnesium, and the pure crystalline boron using the thermal decomposition of boron halides on the tungsten or tantalum wire (at the temperature of 1300 degrees Celsius), and using the reduction of them by hydrogen (at the temperature of 1000-1600 degrees Celsius), and also using the electrolysis of borates.
The usage of boron is diverse. They mostly use boron within the production of glass, ceramics, rubber products, enamels, fertilizers, and herbicides. Small quantities of boron within steels and bronzes increase their strength and resistance against corrosion. Within the nuclear energetical industry, there is used the ability of the 10B isotope to absorb thermal neutrons: of boron carbide and its alloys, there are manufactured the control rods for nuclear reactors. They use the cements with the addition of natural borates within the external concrete protection against neutronic radiation, and they use the beta-boron carbide as abrasive material; of boron nitride, they manufacture the highly refractory materials, and its alpha-form is used as the dry lubricant within bearings.
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