Abstract
This review paper focuses on the phenomenon of thermochemical expansion of two specific categories of conducting ceramics: Proton Conducting Ceramics (PCC) and Mixed Ionic-Electronic Conductors (MIEC). The theory of thermal expansion of ceramics is underlined from microscopic to macroscopic points of view while the chemical expansion is explained based on crystallography and defect chemistry. Modelling methods are used to predict the thermochemical expansion of PCCs and MIECs with two examples: hydration of barium zirconate (BaZr1−xYxO3−δ) and oxidation/reduction of La1−xSrxCo0.2Fe0.8O3−δ. While it is unusual for a review paper, we conducted experiments to evaluate the influence of the heating rate in determining expansion coefficients experimentally. This was motivated by the discrepancy of some values in literature. The conclusions are that the heating rate has little to no effect on the obtained values. Models for the expansion coefficients of a composite material are presented and include the effect of porosity. A set of data comprising thermal and chemical expansion coefficients has been gathered from the literature and presented here divided into two groups: protonic electrolytes and mixed ionic-electronic conductors. Finally, the methods of mitigation of the thermal mismatch problem are discussed.
Highlights
The expansion of a solid upon the exposure to heat is a phenomenon known to mankind for centuries
Issues That Can Lead to Cell Failure. Results on both Solid Oxide Fuel Cells (SOFCs) and Proton Ceramic Fuel Cells (PCFCs) studies are used for the following list, as work on the PCFCs is scarcer
The chemical expansion upon reduction observed in typical SOFC cathodes (BSCF and LSCF) is much lower at 500–600 °C than at 800–1000 °C and should pose much less of a problem
Summary
The expansion of a solid upon the exposure to heat is a phenomenon known to mankind for centuries This process is called thermal expansion and examples of scientists studying thermal expansion can be dated back as far as 1730, when Petrus van Musschenbroek [1] measured the expansion of metals used in pendulum clocks. This posed a significant problem for time measurements at the time, as the length of the pendulum would change with small temperature variations, inducing a change in the period of the oscillating pendulum of up to ±0.05% [2].
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
