The Synthesis and Characterization of Ultra-incompressible, Superhard BoridesRichard B. Kaner, University of California-Los Angeles, DMR 0805357 Dense transition metal borides are a growing family of superhard materials that do not require high-pressure synthesis. These compounds, which we have championed, may find applications as cutting tools and protective coatings. To address cost concerns with some of the platinum group transition metals used previously, we have recently focused our efforts on tungsten tetraboride (WB4), one of the least expensive of the superhard transition metal borides. The unique structure of WB4, consisting of a three-dimensional network of short covalent boron-boron bonds, significantly increases resistance to the movement of atoms, leading to extremely-high hardness. We have successfully synthesized phase-pure WB4 by arc melting the pure elements at ambient pressure. A Vickers microindentation hardness of 43.3 GPa was measured for this material under an applied load of 0.49 N. The zero-pressure bulk modulus, measured by high-pressure X-ray diffraction, is 326 GPa. Various ratios of rhenium (Re) were added to WB4 in an attempt to increase hardness. With the addition of 1 at.% Re, the Vickers hardness increased to ~50 GPa at 0.49 N, as we reported in the Proceedings of the National Academy of Sciences (108, 10958, 2011). Crystal structure of WB4 Vickers microindentation hardness of WB4 under loads ranging from 0.49-4.9 N. Microindentation hardness data for WB4 containing various concentrations of Re.
The Synthesis and Characterization of Ultra-incompressible, Superhard BoridesRichard B. Kaner, University of California-Los Angeles, DMR 0805357 Students in the Kaner and Tolbert groups participate in several outreach projects each year. One activity involves bringing students from Narbonne High School, located in a working class neighborhood of Los Angeles, to UCLA where the students participate in an assortment of demonstrations in which the fundamentals of many materials including metals, semiconductors and plastics, along with devices from sensors to solar cells are discussed (Prof. Kaner is pictured deflating a balloon with liquid nitrogen which re-inflates on warming). The high school students then carry out hands-on experiments designed by the graduate students such as testing solid-state thermoelectric devices. These experiments give the students a taste of what research in chemistry is all about.