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Boron is a nonmetal with atomic number five and symbol B. It has various properties, such as capturing neutrons, extreme hardness, and several allotropes. Boron is found in nature in sodium tetraborate decahydrate and has 13 isotopes. Its strength makes it useful in aerospace and industrial abrasives, and it is used in semiconductors and nuclear reactors. Boron neutron capture therapy is being tested for treating head, neck, and brain cancers.
Boron is a chemical element with atomic number five and atomic symbol B. Notable properties of boron include its effectiveness in capturing neutrons and the subsequent effectiveness of one of its isotopes as a radiation shield; its extreme hardness, tensile strength and hardness of different boron compounds; and the existence of several allotropes and polymorphs of boron. It is a nonmetal with a standard atomic weight of 10.811. It is solid at room temperature, with a melting point of 3769°F (2349°K) and a boiling point of 7101°F (4200°K) at atmospheric pressure.
The physical properties of boron depend on its allotrope. Allotropes are different configurations of the same element, with the element’s atoms bonded together in different ways. The major allotropes of boron are called crystalline boron and amorphous boron. Amorphous boron, consisting of icosahedral boron crystals bonded together randomly without a larger overall structure, takes the form of a brown powder.
Crystalline boron is black and extremely hard. It is diamatic; in the presence of a magnetic field, it produces its own magnetic field which results in a repellent effect. Crystalline boron can be organized into four different main crystal structures, called polymorphs. Starting at pressures of about 23,206,000 pound-force per square inch (about 160 gigapascals), the properties of boron change and it becomes a superconductor.
Boron mainly forms covalent chemical bonds and can form stable molecular networks. It is a member of the aluminum family, but boron’s properties are actually closer to silicon than to aluminum. Boron is most commonly found in nature in the compound sodium tetraborate decahydrate, also known as borax. Boron carbide and cubic boron nitride are among the hardest materials known. Boron is essential to the biochemistry of plant life and ultratrace amounts are also used in animals.
Boron has 13 known isotopes, of which two, 10B and 11B, are stable. About 80% of all natural boron is 11B, with 10B making up the rest. 10B is highly effective at capturing thermal neutrons and therefore is effective as a radiation shield. The other nine known isotopes are short-lived, with half-lives of milliseconds or less.
The properties of boron give the element and its compounds numerous uses. Boron’s strength makes it valuable in the aerospace industry. Boron carbide and cubic boron nitride are useful as industrial abrasives due to their extreme hardness, and boron carbide is also incorporated into modern body armor and armored vehicles. Semiconductors made of substances such as silicon, silicon carbide and germanium are doped with boron. The 10B isotope of boron is used in control rods and shielding emergency shutdown systems of nuclear reactors and is being tested for use in a form of radiation therapy called boron neutron capture therapy to treat head, neck and brain cancers.
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