Conference Dates
September 17-20, 2017
Abstract
Oxidation of carbides-based ultra-high temperature ceramics is the main limiting factor for its use for aerodynamic surfaces. Experimental thermodynamic and structural data for refractory oxides above 2000 °C are mostly absent. The following techniques applied to fill this gap will be discussed: i) Commercial ultra-high temperature differential thermal analyzers (DTA) allow investigation of phase transformations and melting in inert environment to the temperatures up to 2500 °C; ii) Combination of laser heating with splittable nozzle aerodynamic levitator allow splat quenching and drop calorimetry from temperatures limited only by sample evaporation; iii) Synchrotron X-ray and neutron diffraction on laser heated aerodynamically levitated oxide samples allow in situ observation of phase transformations in variable atmosphere, refinement of high temperature structures and thermal expansion. The recent experimental findings include anomalous thermal expansion of defect fluorite structure of YSZ before melting [1] and measurement of fusion enthalpy of Y2O3, which can be used for sensitivity calibration for DTA at 2430 °C [2]. These methods provide temperatures, enthalpies and volume change on phase transformations above 2000 °C which are complementary experimental data for optimization of CalPhaD databases.
[1] Structure and Thermal Expansion of YSZ and La2Zr2O7 Above 1500 °C from Neutron Diffraction on Levitated Samples, S.V. Ushakov, A. Navrotsky, R.J.K. Weber, J.C. Neuefeind, Journal of the American Ceramic.Society 98(10), 3381 (2015)
[2] A combined experimental and theoretical study of enthalpy of phase transition and fusion of yttria above 2000 °C using “drop-n-catch” calorimetry and first-principles calculation, D. Kapush, S.V. Ushakov, A. Navrotsky, Q.-J. Hong, H. Liu, A. van de Walle, Acta Materialia 124, 204 (2017)
The work was supported by the National Science Foundation Award DMR-1506229.
Recommended Citation
Sergey V. Ushakov and Alexandra Navrotsky, "Phase transformations in oxides above 2000°C: Experimental technique development" in "Ultra-High Temperature Ceramics: Materials for Extreme Environment Applications IV", Jon Binner, The University of Birmingham, Edgbaston, United Kingdom Bill Lee, Imperial College, London, United Kingdom Eds, ECI Symposium Series, (2017). https://dc.engconfintl.org/uhtc_iv/58