Thermal Properties of ZrB 2 Ceramics William Fahrenholtz, Missouri University of Science and Technology, DMR % C ZrB 2 + pores 1% C Graphite inclusions Outcome: The thermal conductivity of ZrB 2 was increased by reducing the carbon content of the final ceramics. Impact: No previous studies have examined the effect of carbon on the thermal properties of ZrB 2. Higher thermal conductivities are needed to mitigate thermal shock failures in extreme heating environments such as those encountered in hypersonic flight and rocket propulsion. Explanation: Carbon is incorporated in ZrB 2 during synthesis (reduction of ZrO 2 and B 2 O 3 using carbon) and densification (graphite heating elements and graphite crucibles). Intentional carbon additions affect ZrB 2 in two ways. In the “low” C regime, C reacts with and removes surface oxide impurities and any residual C forms a Zr(B,C) 2 solid solution. In the “high” C regime, excess C forms graphite inclusions in the ZrB 2 matrix (plus ~1 vol% pores). Above: Measured C content in ZrB 2 ceramics as a function of C added to the starting powder showing two regimes. Left: Room temperature thermal conductivity of ZrB 2 ceramics as a function of C added during processing. Low C Regime: C removes surface oxides, but thermal conductivity (k) decreases as C content increases due to solid solution formation. No graphite inclusions were observed in the ceramics. High C Regime: Graphite inclusions are observed in the microstructure, but the value of k stabilizes due to the presence of high k graphite inclusions.

Boride Ceramics as an Outreach and Education Focus William Fahrenholtz, Missouri University of Science and Technology, DMR Artist depiction of the hypersonic concept vehicle X-51. To date, the length of hypersonic flights has been limited to just a few seconds due to factors such as lack of materials for robust leading edges. Image from NASA Image Exchange web archive Left: High school students in the UHTC lab for a demo. Right: Melting point demo by a graduate student from the UHTC group. Outcome: Transition metal boride and carbide ceramics, also known as ultra-high temperature ceramics or UHTCs, are a focus for outreach and education activities at Missouri S&T. Impact: More than 1/3 (22 out of 61) of the sophomores in Materials Science and Engineering at Missouri S&T listed participation in activities such as summer camps or laboratory tours as an important factor in choosing their major. Strong visual images and memorable demonstrations excite students and capture their interest. Explanation: The UHTC research group is among the most active at Missouri S&T for participation in summer camps for high school students and visits from K-12 groups or individual students. Visitors experience interactive demonstrations on melting temperature, thermal conductivity, and thermal shock that combine strong visual images with information about the education and career opportunities in the field of materials for use in extreme environments.