Feb. 7, 2007 Geocheminar

Wednesday, 4:00pm in Geology 4660.

In Situ Studies of Ultra-Incompressible, Superhard Materials Under High Stress Conditions

Michelle Weinberger, Jonathan Levine, Hsiu-Ying Chung, Richard Kaner, Abby Kavner, Sarah Tolbert

The need for new mechanically robust, chemically diverse materials for industrial applications has inspired and driven the quest for new material development and synthesis. To this end, we have discovered that through the optimization of two specific design parameters, valence electron density and bond covalency, it is possible to successfully design a class of ultra-incompressible, superhard metal diborides. In situ hydrostatic and non-hydrostatic high pressure X-ray diffraction and diamond anvil cell techniques were applied to investigate elastic compressibility and the limits of the elastic behavior in OsB₂ and ReB₂. From these experiments, incompressibility (bulk modulus) and the magnitudes of supported differential stresses are determined. Scratch tests show that while OsB₂ successfully scratches sapphire, ReB₂ can even scratch diamond. Microindentation experiments were also performed, resulting in knowledge about resistance to plastic deformation. These experiments reveal impressively high values of bulk modulus, remarkably high hardnesses, and some of the highest-ever measured elastically supported differential stresses.