Browsing by Author "Tsakalakos, Thomas"

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Citation - WoS: 2
Citation - Scopus: 2
Anatomy of Flash Sintering in Yttria-Stabilized Zirconia Solid-State Electrolyte: High Temporal Resolution Energy-Dispersive X-Ray Diffraction Using a 200 Kev Synchrotron Probe
(Springer Heidelberg, 2023) Savkliyildiz, Ilyas; Degnah, Ahmed; Biçer, Hülya; Salur, Emin; Tsakalakos, Thomas; Akdoğan, Enver Koray
High-energy synchrotron X-ray diffraction enables ultra-rapid data collection to determine unit cell volume evolution of 8YSZ under thermal and electric field (30 V/mm). Such an approach provides unprecedented insight into the anatomy of 8YSZ's flash sintering in the 797-810 & DEG;C interval. The densification due to flash sintering occurs in 40 s during which X-ray spectra were collected every 2 s. The densification of 8YSZ was accompanied by 0.55% anelastic peak shift on (220) reflection. Concomitantly, the applied thermal and electric field led to anelastic expansion of the cubic lattice parameter (+ 0.55%) and unit cell volume (+ 1.57%). Besides, an irreversible increase in the peak intensity (+ 22.6%), a decrease in peak width (- 18.3%), and integrated peak (- 13.6%) are determined. The observed anomalies are attributed to the response of oxygen vacancy generation and redistribution to the combined electric and thermal fields.
Citation - WoS: 9
Citation - Scopus: 10
Multicycle Flash Sintering of Cubic Y2o3-Stabilized Zro2: an in Situ Energy Dispersive Synchrotron X-Ray Diffraction Study With High Temporal Resolution
(Elsevier Ltd, 2022) Biçer, Hülya; Degnah, Ahmed; Salur, Emin; Şavklıyıldız, İlyas; Tsakalakos, Thomas; Akdoğan, E.Koray
The current induced unit cell volume changes, (111) Bragg peak full width at half maximum (FWHM) and its integrated intensity in 8 % Y2O3 stabilized ZrO2 (8 %YSZ) solid state electrolyte was monitored during a triple-flash sintering experiment by in situ energy dispersive x-ray diffraction using a polychromatic synchrotron probe (max, photon energy 200 keV) with 2 second temporal resolution. The first spontaneous singularity in the unit cell volume (+0.54 %) was observed at 899 °C under 15 V/mm applied field intensity, which was associated with 13 mA/mm2 current draw and an increase in density to 97 %. Following anelastic relaxation of the unit cell volume under open circuit conditions, the same applied field was applied twice in a row which resulted in additional induced singularities at 925 °C (+0.48 %) and 944 °C (+0.42 %). A floating baseline, which was above the thermal expansion baseline, was observed from 833 to 969 °C and was attributed to Joule heating. The singularity at 899 °C is associated with a sharp change in (111) FWHM and a 34 % decrease in integrated peak area that was attributed to changes in the distribution of oxygen vacancies and the changes in their concentration as induced by the applied field in the spontaneous transient stage of flash sintering. © 2022 Elsevier Ltd
Citation - WoS: 12
Citation - Scopus: 11
Thermal Expansion of Nano-Boron Carbide Under Constant Dc Electric Field: an in Situ Energy Dispersive X-Ray Diffraction Study Using a Synchrotron Probe
(CAMBRIDGE UNIV PRESS, 2020) Biçer, Hülya; Akdoğan, Enver Koray; Şavklıyıldız, İlyas; Haines, Christopher; Zhong, Zhong; Tsakalakos, Thomas
The thermal expansion coefficient (TEC) of nano-B4C having 50 nm mean particle size was measured as a function of applied direct current (DC) electric field strength varying from 0 to 12.7 V/mm and over a temperature range from 298 K up to 1273 K. The TEC exhibits a linear variation with temperature despite being measured over a range that is well below 50% of B4C's normal melting temperature. The zeroth- and first-order TEC coefficients under zero-field condition are 4.8220 +/- 0.009 x 10(-6) K-1 and 1.462 +/- 0.004 x 10(-9) K-1, respectively. Both TECs exhibit applied DC electric field dependence. The higher the applied field strength, the steeper the linear thermal expansion response in nano-B4C, which suggests that the applied field affects the curvature of the interatomic potentials at the equilibrium bond length at a given temperature. No anisotropic thermal expansion with and without applied electric field was observed, although nano-B4C has a rhombohedral unit cell symmetry. The rhombohedral unit cell angle was determined as delta(R) = 65.7046 degrees (0.0007), and it remains unaffected by a change in temperature and applied electric field strength, which we attribute to B4C nanoparticle size and its carbon saturation.