Graduate Student Seminar
March 21, 2025
10:00 a.m. ET
McConomy Auditorium, First Floor Cohon University Center
Thermophysical and Thermochemical Properties of Transition Metal Diborides up to and above 3000˚C
Metal diborides (MB2 | M = Ti, Zr, Nb, Hf, Ta) are considered an ultra-high temperature refractory ceramic due to their relatively low reactivity and high melting point. While these properties are appealing, they also make it difficult to fully characterize their thermochemical and thermophysical properties up to melting. This work will discuss high temperature levitation methods using a conical nozzle levitator system equipped with lasers to investigate the melting points and thermal expansion of the metal di-borides in addition to drop solution calorimetry methods to measure formation energies.
The melting point will be investigated using a cooling trace experiments in conjunction with a 400 W CO2 laser and a 500 W Yb laser to melt metal di-boride samples up to ~3400 ˚C. The thermal expansion will be investigated by coupling the levitation system with X-ray diffraction at Argonne National Laboratories Advanced Photon Source. The high temperature X-ray diffraction data was used to calculate anisotropic coefficients of thermal expansion. The coefficients were compared amongst the five diborides (MB2 | M = Ti, Zr, Nb, Hf, Ta) up to ~3000 ˚C. Drop solution calorimetry using a lead borate solvent was used to dissolve the di-borides to measure enthalpies of formation.
It was found that all diborides at low temperatures exhibited larger thermal expansion along the c-axis. As the temperature increased, the thermal expansion in the a-b plane increased at higher rate, leading to higher thermal expansion in the a-b plane at high temperatures. The anisotropy in TiB2, ZrB2 and HfB2 varied on the order of a33 / a11 ~ -0.94, while NbB2 and TaB2 varied on the order of a33 / a11 ~2.4-0.25. It was found that the anisotropy could be related to the atomic displacement parameters of the metal cations. The melting point and formation enthalpy measurements corroborated with literature values last collected in the 1970s. The validation of the laser melting and drop solution techniques has set the McCormack laboratory up to explore fundamental thermodynamics in multi-component boride systems in the future.
These thermophysical and thermochemical measurements will be critical in developing ultra-high temperature material systems for applications in nuclear fission/fusion reactors, and aerospace vehicles. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under contract DE-AC52-07NA27344, and the National Science Foundation (NSF) in the Directorate for Mathematical and Physical Sciences (MPS), under the Division of Materials Research (DMR), in the Ceramic (CER) program. Award number: 2047084.
Scott J. McCormack
Assistant Professor, Materials Science and Engineering
University of California, Davis
McCormack grew up in the small fishing village of Eden on the Far South Coast of Australia. He completed a Bachelor of Engineering with First Class Honors (H1), majoring in Materials Engineering at the University of Wollongong, NSW, Australia in 2013. He then completed his Ph.D. in Materials Science and Engineering from the University of Illinois at Urbana-Champaign, IL, USA in 2019. He is now an Assistant Professor of Materials Science and Engineering at the University of California, Davis, CA, USA. He holds a visiting scholar/professional status at Lawrence Livermore National Laboratory (LLNL). He was a recipient of the Nuclear Regulatory Commission (NRC) Faculty development award in 2020, National Science Foundation (NSF) Early Career Award in 2021, received an Excellence in Teaching Award in 2023 and the Outstanding Young Faculty Award in 2024 from UC Davis’ College of Engineering. He is passionate about STEM outreach and has been leading the American Ceramic Societies (ACerS) Northern California (NorCal) Section since 2020 and is an Associate Editor for the Journal of The American Ceramic Society (JACerS). His research focuses on ultra-high temperature thermochemistry for materials in extreme environments for applications in hypersonic platforms, nuclear fission/fusion and space exploration. More information can be found at: https://mccormacklab.engineering.ucdavis.edu.
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