Freeze-Cast Porous Ceramics: Tailoring Chemistry and Porosity for Functionality

Citation

Quinn, Laura Katherine (2024) Freeze-Cast Porous Ceramics: Tailoring Chemistry and Porosity for Functionality. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/nj6y-4315. https://resolver.caltech.edu/CaltechTHESIS:06012024-040012207

Abstract

Porous ceramics have been created and utilized in applications ranging from the automotive industry to biomedical research, with the chemical and pore characteristics of these ceramic structures crucial to their function and design. In this work, these intertwined factors are explored for a variety of applications by controlling the chemistry through precursor preparation and heat treatments, and the porosity controlled through freeze casting, a tunable and facile pore-forming technique yielding a range of pore sizes and morphologies. First, shape memory and superelastic behaviors in ceria-doped zirconia are observed by creating porous honeycomb structures that can accommodate the volume change of the martensitic transformation enabling such performance. By controlling dopant concentration, powder morphology, and freezing rate, the martensitic transformation is tracked over multiple cycles and collection volumes in these bulk-scale, polycrystalline zirconia ceramics. Next, transparent porous model sediments are created through heat treatments of freeze-cast synthetic cryolite (Na3AlF6) powder. Fluorescent beads the same size as many bacterial cells are visualized in a range of pore morphologies over both depth and time, and these porous ceramics are deployed in a sedimentary environment and the imaging of the microbial communities contained within and are found to colonize the porous cryolite structures. Alternate porous habitats for bacterial colonization are further created using materials such as iron oxides and carbon nanotubes to produce structures that can act both as electron acceptors and as microbial habitats. Finally, thermally anisotropic Si-based porous ceramics are developed with a potential use in optical devices. Using two contrasting preceramic polymers and both traditional and UV-assisted freeze-casting techniques, porous SiOC is produced from preceramic polymers with differing carbon contents. Together, these examples explore how the chemistry and porosity of porous ceramics can be manipulated to affect the chemical, optical, mechanical, and thermal properties of ceramic structures to best suit the intended function.

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