| Description | Boron (pronounced /?b?r?n/) is the chemical element with atomic number 5 and the chemical symbol B. Boron is a trivalent metalloid element which occurs abundantly in the evaporite ores borax and ulexite.; Boron is a part of neodymium magnet (Nd2Fe14B), which is the strongest type of permanent magnet. It is found in all kinds of domestic and professional electromechanical and electronic devices, such as magnetic resonance imaging (MRI), various motors and actuators, computer HDDs, CD and DVD players, mobile phones, timer switches, speakers, etc.; Boron is a relatively rare element in the Earth's crust, representing only 0.001%. The worldwide commercial borate deposits are estimated as 10 million tonnes. Turkey and the United States are the world's largest producers of boron. Turkey has almost 72% of the world?s boron reserves. Boron does not appear on Earth in elemental form but is found combined in borax, boric acid, colemanite, kernite, ulexite and borates. Boric acid is sometimes found in volcanic spring waters. Ulexite is a borate mineral; it is a fibrous crystal where individual fibers can guide light like optical fibers.; Boron is an essential plant nutrient. Whereas lack of boron results in boron deficiency disorder, high soil concentrations of boron may also be toxic to plants. As an ultratrace element, boron is necessary for the optimal health of rats and presumably other mammals, though its physiological role in animals is not yet fully understood.; Boron is an important technological dopant for such important semiconductors as silicon, germanium and silicon carbide. Having one less valence electron than the host atom, it donates a hole resulting in p-type conductivity. Traditional method of introducing boron into semiconductors is via its atomic diffusion at high temperatures. This process uses either solid (B2O3), liquid (BBr3) or gaseous boron sources (B2H6 or BF3). However, after 1970s, it was mostly replaced by ion implantation, which relies mostly on BF3 as a boron source. Boron trichloride gas is also an important chemical in semiconductor industry, however not for doping but rather for plasma etching of metals and their oxides.; Boron is similar to carbon in its capability to form stable covalently bonded molecular networks. Even nominally disordered (amorphous) boron contains regular boron icosahedra which are, however, bonded randomly to each other without long-range order. Crystalline boron is a very hard, black material with a high melting point of above 2000 °C. It exists in four major polymorphs: ?, ?, ? and T. Whereas ?, ? and T phases are based on B12 icosahedra, the ?-phase can be described as a rocksalt-type arrangement of the icosahedra and B2 atomic pairs. It can be produced by compressing other boron phases to 12-20 GPa and heating to 1500-1800 °C; it remains stable after releasing the temperature and pressure. The T phase is produced at similar pressures, but higher temperatures of 1800-2200 °C. As to the ? and ? phases, they might both coexist at ambient conditions with the ? phase being more stable. Compressing boron above 160 GPa produces a boron phase with an as yet unknown structure, and this phase is a superconductor at temperatures 6-12 K.; Boron may be an essential nutrient for animals and humans. Physiologically, this metal/element exists as an ion in the body. Dietary boron influences the activity of many metabolic enzymes, as well as the metabolism of steroid hormones and several micronutrients, including calcium, magnesium, and vitamin D. Boron may also play a role in improving arthritis, plasma lipid profiles, and brain function.; Cosmic radiation will produce secondary neutrons if it hits spacecraft structures; and neutrons cause fission in 10B if it is present in the spacecraft's semiconductors, producing a gamma ray, an alpha particle, and a lithium ion. The resultant fission products may then dump charge into nearby semiconductor 'chip' structures, causing data loss (bit flipping, or single event upset). In radiation hardened semiconductor designs, one countermeasure is to use depleted boron which is greatly enriched in 11B and contains almost no 10B. 11B is largely immune to radiation damage. Depleted boron is a by-product of the nuclear industry.; In future manned interplanetary spacecraft, 10B has a theoretical role as structural material (as boron fibers or BN nanotube material) which would also serve a special role in the radiation shield. One of the difficulties in dealing with cosmic rays, which are mostly high energy protons, is that some secondary radiation from interaction of cosmic rays and spacecraft materials is high energy spallation neutrons. Such neutrons can be moderated by materials high in light elements such as polyethylene, but the moderated neutrons continue to be a radiation hazard unless actively absorbed in the shielding. Among light elements that absorb thermal neutrons, 6Li and 10B appear as potential spacecraft structural materials which serve both for mechanical reinforcement and radiation protection.; Magnesium diboride is an important superconducting material with the transition temperature of 39 K. MgB2 wires are produced with the powder-in-tube process and applied in superconducting magnets.; Several allotropes of boron exist: amorphous boron is a brown powder; whereas crystalline boron is black, extremely hard (about 9.5 on Mohs' scale), and a poor conductor at room temperature. Elemental boron is used as a dopant in the semiconductor industry, while boron compounds play important roles as light structural materials, insecticides and preservatives, and reagents for chemical synthesis.; The 10B isotope is good at capturing thermal neutrons. Natural boron is about 20% 10B and 80%11B. The nuclear industry enriches natural boron to nearly pure 10B. The waste product, or depleted boron, is nearly pure 11B. 11B is a candidate as a fuel for aneutronic fusion and is used in the semiconductor industry. Enriched boron or 10B is used in both radiation shielding and in boron neutron capture therapy. In the latter, a compound containing 10B is attached to a muscle near a tumor. The patient is then treated with a relatively low dose of thermal neutrons. This causes energetic and short range alpha radiation from the boron to bombard the tumor.; There is a boron-containing natural antibiotic, boromycin, isolated from streptomyces. Boron is an essential plant nutrient, required primarily for maintaining the integrity of cell walls. Conversely, high soil concentrations of > 1.0 ppm can cause marginal and tip necrosis in leaves as well as poor overall growth performance. Levels as low as 0.8 ppm can cause these same symptoms to appear in plants particularly sensitive to boron in the soil. Nearly all plants, even those somewhat tolerant of boron in the soil, will show at least some symptoms of boron toxicity when boron content in the soil is greater than 1.8 ppm. When this content exceeds 2.0 ppm, few plants will perform well and some may not survive. When boron levels in plant tissue exceed 200 ppm symptoms of boron toxicity are likely to appear.; Triethylborane is a substance which ignites the JP-7 fuel of the Pratt & Whitney J58 turbojet/ramjet engines powering the Lockheed SR-71 Blackbird. It was also used to ignite the F-1 Engines on the Saturn V Rocket utilized by NASA's Apollo and Skylab programs from 1967 until 1973. Triethylborane is suitable for this because of its pyrophoric properties, especially the fact that it burns with very high temperature. Triethylborane is an industrial initiator in radical reactions, where it is effective even at low temperatures. It is also injected into vapor deposition reactors as a boron source. Examples are the plasma deposition of boron-containing hard carbon films, silicon nitride-boron nitride films, and for doping of diamond film with boron. |
|---|
