Boron (B)
Boron (B) is a chemical element with the atomic number 5, classified as a metalloid. It is relatively scarce in the Earth's crust, found at approximately 9 parts per million, making it the thirty-eighth most abundant element. Major deposits of boron are located in California and Turkey, with additional occurrences in parts of China and South America. Boron is utilized in various applications, primarily in the production of heat-resistant borosilicate glass, such as Pyrex, and in fiberglass and porcelain enamels. Furthermore, boron plays a role in the formulation of detergents, soaps, and agricultural products like fertilizers and herbicides.
The element exists in several allotropic forms, with crystalline boron appearing dark red and powdered boron being black. Although essential for some higher plants, boron is not necessary for animal life and can be toxic in high concentrations. Historically, boron compounds have been used since ancient times, with borax being traded as early as 4000 years ago. The modern isolation of boron began in the early 19th century, leading to its diverse applications in various industries, including construction, agriculture, and medicine.
Boron (B)
Where Found
Boron is not abundant. There are about 9 parts per million of boron in the Earth’s crust, which makes boron the thirty-eighth element in abundance. Commercially valuable deposits are rare, but the deposits in California and Turkey are very large.
Primary Uses
The main uses of boron are in heat-resistant glasses, glass wool, fiberglass, and porcelain enamels. It is also used in detergents, soaps, cleaners and cosmetics, and synthetic herbicides and fertilizers.
Technical Definition
Boron (abbreviated B), atomic number 5, belongs to Group III of the periodic table of the elements and resembles silicon in many of its chemical properties. It has two naturally occurring isotopes: boron 10 (19.8 percent) and boron 11 (80.2 percent). Boron exists in several allotropic forms. The crystalline forms are a dark red color, and the powdered forms are black. The most stable form has a melting point of 2,180° Celsius, a boiling point of 3,650° Celsius, and a density of 2.35 grams per cubic centimeter.
Description, Distribution, and Forms
Boron is found primarily in dried lake beds in California and Turkey. Isolated deposits also occur in China and numerous South American countries. The major deposits of borate minerals occur in areas of former volcanic activity and in association with the waters of former hot springs. Searles Lake in southeastern California has layers that are 1.6 percent and 2.0 percent borax. Boron is found naturally only as borate minerals such as ulexite [B5O6(OH)6]·5H2O and borax Na2[B4O5(OH)4]·8H2O or as borosilicates. Boron is more concentrated in plants than in animal tissue.
The use of borax laundry detergents, the burning of coal, and mining have filled the atmosphere and irrigation waters in some areas with boron compounds. Although there have been some reports of damage to grazing animals, boron is not considered a danger unless it is in the form of a pesticide, an herbicide, or fiberglass, which is carcinogenic.
Boron is an essential element only for higher plants. The amount needed by those plants and the amount that is toxic are only a few parts per million apart, so toxicity effects can easily occur. Boron is not known to be necessary to animal life, and it is quickly excreted in urine. In high concentrations toxicity effects can occur, especially in the brain, before all the boron is excreted.
History
Borax was used in ancient times to make glazes and hard glass and was traded by the Babylonians four thousand years ago. However it was not isolated in pure enough form to be characterized as an element until 1808. The isolation was achieved by Joseph-Louis Gay-Lussac and Louis-Jacques Thénard and independently by Sir Humphry Davy. Boron was isolated from boric acid through a heated reaction with potassium. The first pure (95 to 98 percent) boron was isolated by Henri Moissan in 1892.
Obtaining Boron
The four main methods of isolating boron are reduction by metals at high temperature, electrolytic reduction of fused borates or tetrafluoroborates, reduction by hydrogen of volatile compounds, and thermal decomposition of hydrides or halides. About 3.8 million metric tons are produced annually. Boron will form compounds with almost every element except the noble gases and a few of the heavier metals. It is said to have the most diverse chemistry next to carbon and is characterized as a metalloid by some properties and as a nonmetal by others. This rich chemistry leads to a wide range of uses.
Uses of Boron
One of the most common uses of boron is in the production of borosilicate glass (Pyrex glass). Borosilicate glass does not expand or contract as much as regular glass, so it does not break with temperature changes as easily as regular glass. Pyrex cooking vessels and most laboratory glassware are made of borosilicate glass. Boron improves the tempering of steel better than other alloying elements. Boron carbide is one of the hardest substances known and is used in both abrasive and abrasion-resistant applications as well as in nuclear shielding. Lighter elements are better shields for neutrons than are heavy elements such as lead. Boron-10 neutron capture therapy is one of the few ways to treat a nonoperable brain tumor. The boron-10 isotope collects in the tumor. When a neutron hits the boron, a reaction produces radiation to kill the cancer cells.
Borate is used in the production of glass fiber thermal insulation, the principal insulating material used in construction. Another glass application is as a thin, glassy coating fused onto ceramics and metals. Examples include wall and floor tiles, tableware, bone china, porcelain, washing machines, pots, and architectural paneling. Boron is also used in algicides, fertilizers, herbicides, insecticides, and water treatments. Sodium polyborate can be used to control fleas, and boric acid has been used in the control of cockroaches. Fire retardants include zinc borate, ammonium pentaborate, and boric oxide. These are used in chipboard, cellulose insulation, and cotton mattresses. Boron compounds are also used in metallurgical processes such as fluxes and shielding slags and in electroplating baths. Borax is a water-softening agent, while boron is used as a bleaching agent. Perborates in water form hydrogen peroxide to act as a bleach. Boron is also used in cosmetics, pharmaceutical and hygienic products, pH adjusters, emulsifiers, stabilizers, and buffers.
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