Speaker:

Dr. Richard B. Kaner
Professor of Chemistry, Professor of Materials Science and Engineering, UCLA
Associate Director, California NanoSystems Institute

Topic: 

Metathesis Routes to Ultra-incompressible, Superhard Materials

Abstract:

Solid-state metathesis (exchange) reactions are driven by the formation of stable salt by-products.  These reactions can reach >1000°C in a fraction of a second and therefore can be used to synthesize difficult to make materials. 

Here we will explore the synthesis of refractory sulfides, nitrides and borides.  The focus will be on transition metal diborides of osmium and rhenium.  Osmium diboride will be shown to be highly incompressible with a bulk modulus comparable to that of diamond. 

Osmium diboride is relatively hard with the ability to scratch sapphire.  An even harder material can be made by substituting rhenium for osmium.  In rhenium diboride the lattice only expands 5% from that of the pure metal, while in osmium diboride the lattice expands by about 10%. 

The shorter covalent bonds in rhenium diboride lead to a highly incompressible, super-hard material.  Microindentation measurements indicate an average hardness of 48 GPa under an applied load of 0.49 N, while scratch marks left on a diamond surface confirm its super-hard nature. 

In-situ high pressure X-ray diffraction yields a bulk modulus of 360 GPa.  The incompressibility of ReB2 along the c-axis is equal in magnitude to the linear incompressibility of diamond. 

Radial diffraction experiments show that ReB2 can support the highest differential stress (17 GPa) of any material measured within the pressure regime studied (0-14

Presenter's Background:

Richard B. Kaner is Professor of Chemistry, Professor of Materials Science and Engineering and Associate Director of the California NanoSystems Institute at UCLA. He received a Ph.D. in inorganic chemistry from the University of Pennsylvania in 1984, followed by two and a half years of postdoctoral research at UC Berkeley.

He joined UCLA in 1987 as an Assistant Professor, earned tenure in 1991 and became a full Professor in 1993. He has published over 175 papers in top peer reviewed journals and holds 10 U.S. patents with 10 more pending. 

Dr. Kaner has received awards from the National Science Foundation (Presidential Young Investigator Award), the American Chemical Society (Buck-Whitney Research Award and Exxon Solid State Chemistry Fellowship), as well as awards from the Dreyfus, Fulbright, Guggenheim, Packard and Sloan Foundations for his work on new routes to materials including superhard borides, carbon nanoscrolls, graphene, fulleride superconductors, and conducting polymers nanowires.