Ceramic processing science across scales: The phenomenological and mean-field theory
Speaker: Assistant Professor Yanhao Dong
School of Materials Science and Engineering, Tsinghua University
Abstract: Processing science of ceramics is critical to many applications. In this talk, I shall start with the design of promoting interfacial reactive sintering in protonic ceramic electrochemical cells operated at intermediate temperature and suppressing stress corrosion cracking in oxide cathodes of lithium-ion battery used at room temperature. These efforts improve the device efficiency and stability and extend the cycle life. I will next talk about a generalized growth theory unifying the textbook knowledge of Ostwald ripening and normal grain growth. A new concept of ultra-uniformity is proposed, defined as grain size distribution narrower than predicted by the classical theory of Hillert. For curvature driven grain growth, a steady-state size distribution is analytically solvable for growth exponent n > 1 and the distribution narrows with increasing n. Experimental validation of this prediction is found in porous alumina ceramics at various intermedium and final stage sintering, which sheds light on the hidden role of porosity to self-homogenize the microstructure. When coupled with two-step sintering that freezes grain coarsening in the final stage sintering, it creates dense alumina nanoceramics with 34 nm average grain size and an extremely uniform microstructure. The new fundamental insights and rationally optimized sintering practices would enable ultra-uniform nanocrystalline ceramics with unprecedented properties and reliability.
Bio: Yanhao Dong is an assistant professor in the School of Materials Science and Engineering at Tsinghua University. He obtained his BS degree in materials science in 2012 from Tsinghua University, and his MS degree in materials science in 2014, his MS degree in applied mechanics in 2015, and his PhD degree in material science in 2017, all from University of Pennsylvania. His PhD dissertation focused on cation diffusion in zirconia ceramics, covering from experiments of sintering and grain growth to continuum-level solution of transport and growth theory to atomistic simulations of defect energetics and kinetics. He then spent five years at Massachusetts Institute of Technology as a postdoctoral researcher working on interdisciplinary materials design, processing, microstructure, and degradation mechanisms. He received Early Discovery Award, Edward C. Henry Award, Morgan Medal and Global Distinguished Doctoral Dissertation Award, and lifetime membership from the American Ceramic Society, Acta Student Award from Acta Materialia, and Sidney J. Stein Prize from University of Pennsylvania. His current research interest is on advanced ceramics for structural and energy applications.