Herb Hubert is pictured with the high-pressure anvil at the
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Herb Hubert is pictured with the high-pressure anvil at the Arizona State University (ASU)

May 28, 2010
Herb Hubert is pictured with the high-pressure anvil at the Arizona State University (ASU) Materials Research Science and Engineering Center (MRSEC). Inside the high-pressure anvil, interlocking steel jaws compress a small crucible containing experimental mixtures. Scientists recover a small silica pellet the size of three aspirin tablets after each run. They break apart the pellet to wash out particles of material altered by extreme pressure and temperature.

Hubert and others used the anvil to synthesize boron suboxide, which ranks as the third-hardest substance in the world. This substance also exhibits a rare five-fold symmetry.

(Note: The ASU MRSEC was supported by the National Science Foundation (NSF) 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 ASU worked together to create and classify strange, new substances. Research conducted at ASU's MRSEC focused on the creation of super-hard variations on the diamond. Their final result involved synthesizing a low-density compound of boron suboxide (B6O), creating the third hardest material in the world.

The research began when Herve´ 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, who 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 provided 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 professor Michael O'Keeffe, an expert in crystallography (the study of crystal form and structure). O'Keeffe confirmed that the material was not a single crystal, but 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 diamonds 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 hardfacing and wear materials, or could potentially be used as an abrasive or 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)

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