Comparison of the electrical and structural properties of flash sintered yttria-stabilized zirconia
March 10-15, 2019
One of the primary conundrums in the study of field-assisted sintering techniques is distinguishing between the effects of Joule heating and the athermal electric field on both the sintering process and properties of the sintered material. This is particularly true in the case of flash sintering, in which accurate and spatially differentiated temperature measurement is difficult, complicating the removal of baseline Joule heating.
While high heating rates have been linked to rapid consolidation in the absence of an electric field1, the field is assumed to affect defect behavior during sintering and produce effects on the resulting microstructural and electrical characteristics2,3. Studying these residual properties and their relationship to flash sintering processing parameters lends insight into the degree and nature of the field contribution during flash sintering.
We present a study using impedance spectroscopy and microstructural analysis to characterize flash sintered 8 mol % yttria-stabilized zirconia (YSZ). Samples were produced using a controllable AC flash system and parameters including frequency, current ramp rate, and electrode composition were varied. Results are contextualized within the growing understanding of the thermal characteristics of flash4-6 as well as the effect of electric fields on cation7 and grain boundary mobility8 to understand the implications of observations like enhanced bulk conductivity, sensitivity of grain boundary conductivity to various processing parameters, and the temporal development of grain size. This work provides a useful perspective to the flash sintering literature with combined analysis of electrical properties and microstructure. Moreover, flash sintering via a combination of AC fields with controlled current ramps is demonstrated to be an effective route to producing more homogeneously sintered materials.
1 García, D. E., Seidel, J., Janssen, R. & Claussen, N. Fast firing of alumina. Journal of the European Ceramic Society 15, 935-938, doi:https://doi.org/10.1016/0955-2219(95)00071-2 (1995).
2 Charalambous, H. et al. Inhomogeneous reduction and its relation to grain growth of titania during flash sintering. Scripta Materialia 155, 37-40, doi:https://doi.org/10.1016/j.scriptamat.2018.06.017 (2018).
3 Carvalho, S., Muccillo, E. & Muccillo, R. Electrical Behavior and Microstructural Features of Electric Field-Assisted and Conventionally Sintered 3 mol% Yttria-Stabilized Zirconia. Ceramics 1, 2 (2018).
4 Todd, R. I., Zapata-Solvas, E., Bonilla, R. S., Sneddon, T. & Wilshaw, P. R. Electrical characteristics of flash sintering: thermal runaway of Joule heating. Journal of the European Ceramic Society 35, 1865-1877, doi:http://dx.doi.org/10.1016/j.jeurceramsoc.2014.12.022 (2015).
5 Charalambous, H., Jha , S. K., Christian, K. H., Lay, R. T. & Tsakalakos, T. Flash Sintering using Controlled Current Ramp. Journal of the European Ceramic Society 38, 3689 - 3693, doi:https://doi.org/10.1016/j.jeurceramsoc.2018.04.003 (2018).
6 Charalambous, H. et al. In situ measurement of temperature and reduction of rutile titania using energy dispersive x-ray diffraction. Journal of the European Ceramic Society 38, 5503-5511, doi:https://doi.org/10.1016/j.jeurceramsoc.2018.08.032 (2018).
7 Dong, Y., Qi, L., Li, J. & Chen, I.-W. Electron Localization Enhances Cation Diffusion in Zirconia and Ceria: A First-Principles Study. arXiv preprint arXiv:1808.05196 (2018).
8 Orrù, R., Licheri, R., Locci, A. M., Cincotti, A. & Cao, G. Consolidation/synthesis of materials by electric current activated/assisted sintering. Materials Science and Engineering: R: Reports 63, 127-287, doi:https://doi.org/10.1016/j.mser.2008.09.003 (2009).
Carolyn Grimley, Elizabeth C. Dickey, and Andre L. G. Prette, "Comparison of the electrical and structural properties of flash sintered yttria-stabilized zirconia" in "Electric Field Enhanced Processing of Advanced Materials II: Complexities and Opportunities", Rishi Raj, University of Colorado, USA Olivier Guillon, Forschungzentrum Jülich, Germany Hidehiro Yoshida, National Institute for Materials Science, Japan Eds, ECI Symposium Series, (2019). https://dc.engconfintl.org/efe_advancedmaterials_ii/69