ChEMS Seminar: Ionic Substitution in Apatite: From Biologic Structures to Non-stick Turbine Blades
University of California, Santa Barbara
Abstract: Through coupled ionic substitutions, the apatite crystal structure accommodates a wide range of compositions enabling diverse structural and functional applications. This seminar will introduce the structure, typical cation and anion substitutions, and varied applications of apatite-based materials. We will then focus on the important role that apatite crystallization plays in mitigating the degradation of ceramic thermal and environmental barrier coatings (T/EBCs) in turbine engines caused by molten silicate deposits. In this application, rare-earth (RE) cations from the coatings react with SiO2 and CaO in the deposit to form apatite. This process consumes the melt and can block further infiltration into the coating. However, the effectiveness of these reactions to mitigate T/EBC degradation is strongly dependent on both the identity of the coating material and the composition of the deposit. We will discuss these effects in the context of the underlying apatite-phase equilibria and the reaction dynamics. To address the open-ended nature of this problem, new computational tools have been developed to improve and accelerate life prediction. The application of these tools has provided guidance for the design of future coating systems.
Bio: David L. Poerschke earned his B.S. and M.S. in Materials Science and Engineering from Case Western Reserve University. As an NDSEG fellow, he completed his Ph.D. at the University of California Santa Barbara in 2014, and is currently a postdoctoral scholar at UCSB. His research focuses on understanding the interrelated roles of thermodynamics and kinetics in the structural evolution of multiphase ceramic systems. Recent activities include the development of phase equilibria-based models of thermal and environmental barrier coating degradation by molten silicates, oxidation of ultra-high-temperature ceramics, and processing of SiC-based ceramic matrix composites to prevent oxidative embrittlement.
Host: Prof. Daniel Mumm