Boron

Boron is a chemical element with symbol B and atomic number 5. It is a metalloid and occurs in nature mainly in borate minerals. Boron plays a crucial role as an essential micronutrient for plants, but it has no known essential role in humans. In industry, boron and its compounds are widely used. Natural boron accounts for about 0.0018% of the Earth's crust by weight.

Physically, boron is a poor conductor of electricity and exists in several crystalline forms; elemental boron is typically dark brown to black with a very high melting point (~2075°C) and boiling point (~3927°C) and a density of about 2.34 g/cm3. As a metalloid, it forms covalent networks and a wide range of compounds, including boranes (hydroboranes), borates, boron carbide, and boron nitride.

Occurrence and production: Boron is primarily mined from borate minerals such as borax and kernite, and from boron-bearing rocks. It is refined to boron oxide and then reduced to elemental boron, often by reduction with magnesium or silicon at high temperatures, or by electrolysis. Leading producers include Turkey, the United States, and China.

Applications: Boron is used to produce borosilicate glass and fiberglass, ceramics, and ceramic glazes; boron compounds serve as agricultural micronutrients and as cleaning agents (borates). In electronics, boron is a common p-type dopant for silicon and gallium arsenide. Boron-10 is used in neutron capture therapies and shielding, and boron carbide and related materials are used in abrasives and armor.

Isotopes and safety: The stable isotopes are 10B (about 20%) and 11B (about 80%). Boron compounds vary in toxicity; many are of relatively low toxicity, but powders and dusts can be irritants or hazardous if inhaled. In plants, boron deficiency impairs growth; excessive boron can be phytotoxic.