Date of Award

5-14-2023

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Mechanical and Aerospace Engineering

Advisor(s)

Jeongmin Ahn

Keywords

Bilayer Shrinkage, Ceramics, Combustion, Energy, Self-Shaping, Solid Oxide Fuel Cells

Abstract

This thesis investigates advanced techniques to control multilayer ceramic composite (MCC) 3D geometry and layer architecture. MCCs have tremendous potential to significantly change a variety of fields due to their ability to withstand extreme environments. However, our limited ability to shape them into complex objects impedes these efforts. To address this issue, two techniques have been introduced: fill coating and bilayer shrinkage driven self-shaping. Central to both techniques is the control of residual stresses experienced by MCCs during sintering. In the case of fill coating and the control of layer architecture, these residual stresses needed to be reduced to prevent the fracture of the novel internal cathode tubular solid oxide fuel cell (IC-tSOFC). This was achieved with the adoption of extended sintering procedures which promoted plastic deformation processes like creep stress relaxation. The novel fill coating technique used to produce IC-tSOFCs was then investigated using scanning electron microscopy (SEM) to ensure that the deposited films were highly uniform and comparable to films deposited using the more mature dip coating technique. The electrochemical performance of the IC-tSOFC was then thoroughly evaluated on a variety of fuel streams including pure hydrogen, dilute hydrogen, simulated exhaust from a boiler, and simulated exhaust from a two-stroke internal combustion engine. The second focus of this thesis takes advantage of the residual stresses that complicated IC-tSOFC development rather than dissipating them. By using the mismatch in the thermal expansion coefficient between adjacent layers within planar MCCs, curvature may be introduced. Substrates were produced using tape casting and a thin film was then added to this substrate using aerosol spray deposition. By controlling the thickness of the substrate and film, as well as the 2D shape of the substrate and pattern of the applied film, the curvature and shape of the final self-formed part was controlled. Beyond demonstration of this novel manufacturing technique, investigation into curvature and shape prediction using analytical and finite element method (FEM) modeling enabled the development of a methodology to design parts using self-shaping. Initial investigations focused on predicting curvature. Though a disagreement between modeling and experiment was observed, an experimental TEC was introduced to replicate experimental results in FEM modeling. This understanding of the 2D curvature was then extended to three dimensions to analyze shape. Predictions regarding bifurcation between cap-like and tube-like deformation modes was applied to the ceramic system using FEM modeling and experiment. These predictions were shown to be consistent with theoretical understanding. Similarly, bending direction for tube-like deformation was shown to be generally consistent with theoretical understanding, but here FEM modeling struggled to reliably predict the final 3D geometry of shapes with high degrees of symmetry, and experimental samples experienced misorientation of bending, indicating that models may need to be expanded to include a greater variety of forces controlling deformation. Overall, this thesis shows successful development of novel manufacturing techniques to enable wider application of ceramic materials. While the IC-tSOFC introduces new combined heat and power-SOFC systems to be explored, self-shaping ceramics introduces a variety of fundamental questions regarding the underlying mechanism driving bilayer shrinkage within MCCs as well as full understanding of the interaction between 2D substrate shape and film pattern at any scale.

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