MadSci Network: Chemistry

Re: Boron and its applications in Materials science

Date: Mon Jul 27 14:37:24 1998
Posted By: David Ellis, Researcher, NASA Lewis Research Center
Area of science: Chemistry
ID: 899173848.Ch

The element Boron (chemical symbol B, atomic number 5) is a semiconductor. It is closely related to Silicon (chemical symbol Si, atomic number 14).

Boron has been used as a stiff, lightweight fiber in aerospace applications much like carbon and graphite fibers. Composites of boron fibers in an aluminum matrix have been tested at NASA Lewis Research Center as fan blades for jet engines. There are a few other applications in sports such as bicycling that have started using the boron fibers as well. Elemental boron also finds use in the nuclear industry. However, most commercial usage of boron is in boron compounds.

If you look at the periodic table of elements, Carbon (chemical symbol C, atomic number 6) lies between boron and Nitrogen (chemical symbol N, atomic number 7). The hardest substance is diamond, a form of carbon. It turns out that by combining boron and nitrogen you can form boron nitride (BN). BN is second only to diamond in hardness. The BN is used to make abrasive cutting tools. They typically replace diamond and carbide tooling. Abrasive Technology and other companies provide tooling to a wide variety of industries. The Abrasive Engineering Society can provide further information.

Boron carbide (BC) is also becoming more popular as a thin film coating. Thin film coatings are typically only a few micrometers thick or less. In the case of BC, BN and diamond, the films are generally used to provide a very hard, scratch resistant surface. Glass, for example, can be coated to make eyeglasses more scratch resistant. DiamondBLACK Technologies, Inc. is one of many companies that produce BC thin film coatings.

Many other boron compounds find use in our everyday life. Borax (Na2B4O7 10H2O) is used as a water softener. Remember the "40 mule train" laundry detergent? Various boron compounds are used in enamels for appliances. Borosilicate glasses have been used for centuries. Boric acid is used as an insecticide.

Diamond also has another interesting feature. It is the substance with the highest thermal conductivity. BN also has a high thermal conductivity. It can be used in applications where it is necessary to dissipate heat or to move heat through a part quickly. BN is also a good electrical insulator. That makes BN useful in many electronic applications as well. An example would be surface mount electronics where an insulating substrate is needed but the substrate also needs to be used to cool the chips. Companies such as Carborundum and AEE make BN powders that can be added to plastics and metals to increase their thermal conductivity. Aremco is an example of a company that makes BN ceramics.

Finally, like graphite, BN is a good solid lubricant. That means it can be used at very high temperatures. Jet engines, industrial furnaces and satellites are some examples where BN might be used. Carborundum's Tres BN line of BN powders are in fact used in cosmetics to make them go on easier and more smoothly.

Additional reference: Ullmann's Encyclopedia of Industrial Chemistry, 5th Edition

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