Designing Superhard Materials

Designing Superhard Materials which predicted by Richard B. Kaner was possible to be developed . Ultrahard materials are used in many applications, from cutting and polishing tools to wear-resistant coatings. Diamond remain the hardest known material, despite years of synthetic and theoretical efforts to improve upon it. However, even diamond has limitations. It is not effective for cutting ferrous metals, including steel, because of a chemical reaction that produce iron carbide. Cubic boron nitride-the second hardest material, with a structure analogous to that of diamond-can be used to cut ferrous metals. However, it does not occur naturally and must be synthesized under conditions of extreme pressure and temperature, making it quite expensive. New super hard materials are thus not only of great scientific interest, but also could be very useful.

To design new super hard materials, we must understand what makes diamond special, In diamond, tetrahedrally bonded sp3 carbon atoms form a three-dimensional, covalent network of high symmetry. Other carbon based materials have shorter and stronger carbon bonds, but not in three dimensions. Example, the trigonal sp2 bonds in graphite form sheets with shorter and stronger carbon-carbon bonds. But only weak van der Walls interaction hold the sheets together, allowing layers of graphite to cleave readily. A three-dimensional network composed of short, strong bonds is thus critical for hardness.

In thinking about new ultra hard materials, It is useful to consider the types of structural change that a material can undergo under load. These changes can be divided into elastic (reversible) and plastic (irreversible) deformation.

A material is considered stiff if it is difficult to compress elastically. A material is considered hard if it resist plastic deformation.

The effort to design super hard material can be divided into two main approaches, first, light element, including boron, carbon, nitrogen, and/or oxygen, are combined to form short covalent bonds. Second, elements with very high densities of valence electrons are included to ensure that the materials resist being squeezed together.

Toward super hard materials. By combining metals with a high density of valence electron, such as osmium, iridium, or rhenium, with small, covalent bond-forming atoms such as boron, ultra-incompressible, hard material may be created. Mixed metals, as orthorhombic structure predicted for (Os,ir)B2, can act as barriers to the movement of dislocations.