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 	   Grains of boron suboxide loom like boulders in this
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Grains of boron suboxide loom like boulders in this scanning electron microscope view.

May 11, 2010
Grains of boron suboxide loom like boulders in this scanning electron microscope view. The grains are actually submicroscopic. They are also tough--only diamond and cubic boron nitride are harder--and they exhibit a rare five-fold symmetry. Boron and oxygen atoms form 20-sided icosahedra that pack together into the larger crystalline icosahedra, shown.

More about this Image Arizona State University postdoctoral researcher Herve Hubert synthesized the material by mixing boron and boron oxide and heating them at high pressure--up to 1,700 degrees Celsius--and at 40,000 times the atmospheric pressure at sea level. Tiny orange-red particles form during the heating and pressurization. They have a perfect icosahedral shape, each particle with 20 triangular faces and 12 corners displays five-fold symmetry. A crystal, which contains atoms packed in a regular repeating pattern, cannot have five-fold symmetry. Icosahedral particles in nature are rare. Some viruses pack in this way, but they are much smaller in size. Twenty tetrahedra--a solid with four faces, each a perfect crystal--come together at a point to form a radiating pattern away from the center. This substance displays a new way of packing atoms together to make a solid.

This boron suboxide material ranks as the third-hardest substance in the world. It appears to have promising industrial potential. Since boron suboxide is extremely hard, it can be used as an abrasive or as a cutting or polishing tool. Its mechanical characteristics and low chemical reactivity make it a candidate to replace tungsten carbide in high-wear applications. Boran suboxide may possess special semiconductor applications as well. (Year of image: 1999)


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