Boron

Boron is a metalloid chemical element with symbol B and atomic number 5. Produced entirely by cosmic ray spallation and supernovae and not by stellar nucleosynthesis, it is a low-abundance element in the Solar system and in the Earth's crust.^[12] Boron is concentrated on Earth by the water-solubility of its more common naturally occurring compounds, the borate minerals. These are mined industrially as evaporites, such asborax and kernite. The largest known boron deposits are in Turkey, the largest producer of boron minerals.

Chemically uncombined boron is found in small amounts in meteoroids but is not found naturally on Earth. Industrially, very pure boron is produced with difficulty because of refractory contamination by carbon or other elements. Several allotropes of boron exist: amorphous boron is a brown powder; crystalline boron is silvery to black, extremely hard (about 9.5 on the Mohs scale), and a poor electrical conductor at room temperature. The primary use of elemental boron is as boron filaments with applications similar to carbon fibers in some high-strength materials.

Boron is primarily used in chemical compounds. About half of all consumption globally, boron is used as an additive in glass fibers of boron-containing fiberglass for insulation and structural materials. The next leading use is in polymers and ceramics in high-strength, lightweight structural and refractory materials. Borosilicate glass glassware is desired for its greater strength and thermal shock resistance than ordinary soda lime glass. Boron compounds are used as fertilizers in agriculture and in sodium perborate bleaches. A small amount of boron is used as a dopant in semiconductors, and reagent intermediates in the synthesis of organic fine chemicals. A few boron-containing organic pharmaceuticals are used or are in study. Natural boron is composed of two stable isotopes, one of which (boron-10) has a number of uses as a neutron-capturing agent.

In biology, borates have low toxicity in mammals (similar to table salt), but are more toxic to arthropods and are used as insecticides. Boric acid is mildly antimicrobial, and a natural boron-containing organic antibiotic is known.^[13] Boron is essential to life. Small amounts of boron compounds play a strengthening role in the cell walls of all plants, making boron a necessary plant nutrient. Boron is involved in the metabolism of calcium in both plants and animals. It is considered an essential nutrient for humans, and boron deficiency is implicated in osteoporosis.

Contents

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• 1History
• 2Preparation of elemental boron in the laboratory
• 3Characteristics
  • 3.1Allotropes
  • 3.2Chemistry of the element
    • 3.2.1Chemical compounds
      • 3.2.1.1Organoboron chemistry
      • 3.2.1.2Compounds of B(I) and B(II)
  • 3.3Isotopes
    • 3.3.1Commercial isotope enrichment
    • 3.3.2Enriched boron (boron-10)
    • 3.3.3Depleted boron (boron-11)
      • 3.3.3.1Radiation-hardened semiconductors
      • 3.3.3.2Proton-boron fusion
    • 3.3.4NMR spectroscopy
  • 3.4Occurrence
• 4Production
  • 4.1Market trend
• 5Applications
  • 5.1Elemental boron fiber
  • 5.2Boronated fiberglass
  • 5.3Borosilicate glass
  • 5.4Boron carbide ceramic
  • 5.5High-hardness and abrasive compounds
  • 5.6Boron metal coatings
  • 5.7Detergent formulations and bleaching agents
  • 5.8Insecticides
  • 5.9Semiconductors
  • 5.10Magnets
  • 5.11Shielding and neutron absorber in nuclear reactors
  • 5.12Other nonmedical uses
  • 5.13Pharmaceutical and biological applications
  • 5.14Research areas
• 6Biological role
  • 6.1Analytical quantification
  • 6.2Health issues and toxicity
• 7See also
• 8References
• 9External links