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August 23, 2005

Grain of Boron Suboxide

A grain of boron suboxide (B60), synthesized by scientists at the Arizona State University (ASU) Materials Research Science and Engineering Center (MRSEC), is shown in a scanning electron microscope pseudo color image. The team at the ASU MRSEC mixed boron and boron oxide and heated them to 1,700 degrees Celsius, and at 40,000 times the atmospheric pressure at sea level, to form orange-red particles--boron suboxide (B60). Boron suboxide ranks as the third-hardest substance in the world. The ASU MRSEC was supported by the National Science Foundation at the time this research was performed. [One of four related images. See Next Image.]

More about this Image
In 1998, teams of scientists at Arizona State University (ASU) worked together to create and classify strange, new substances. Research conducted at ASU's Materials Research Science and Engineering Center (MRSEC) focused on creating super hard variations of diamond. Their final result involved synthesizing a low density compound of boron suboxide (B6O), thus creating the third hardest material in the world.

The research began when Hervé Hubert, a postdoctoral researcher at the center, began 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. During the heating and pressurization, orange-red particles formed.

Hubert consulted with electron microscopist Laurence Garvie. Garvie had been refining a technique used by scientists to analyze low weight atoms, such as boron and oxygen, called electron energy-loss spectroscopy (EELS). Using his knowledge of EELS, Garvie was able to provide detailed chemical analyses of the materials synthesized by Hubert.

A few weeks later, during an electron microscope examination, Hubert and Garvie discovered that the orange-red crystals were not a single crystal but in fact had a perfect icosahedral shape--a particle with 20 triangular faces and 12 corners, displaying 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.

After taking electron micrographs of the material, Garvie consulted with Michael O'Keeffe, a professor and expert in crystallography (the study of crystal form and structure). O'Keeffe confirmed that the material was not in fact a single crystal, but rather multiple-twinned particles. Twenty tetrahedra--a solid with four faces, each a perfect crystal--came together at a point to form a radiating pattern away from the center. This substance displayed a new way of packing atoms together to make a solid.

The boron suboxide material ranks as the third-hardest substance in the world. Only diamond and cubic boron nitride are harder than boron suboxide, which appears to have promising potential.

Since it is extremely hard, it could lead to a new class of hard-facing and wear materials, or could potentially be used as an abrasive, cutting or polishing tool. Because of its mechanical characteristics and low chemical reactivity, it could possibly replace tungsten carbide in high-wear applications. Boron suboxide may even possess special semiconductor applications. (Year of image: 1999)

Credit: Photo by Laurence Garvie, Ph.D.

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