Scholarship & Research
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Item Multi-component oxide powder processing dynamics & synergy towards multi-functionality(Montana State University - Bozeman, College of Engineering, 2022) Heywood, Stephen Kevin; Chairperson, Graduate Committee: Stephen W. Sofie; This is a manuscript style paper that includes co-authored chapters.Multi-component or multi-cation ceramic oxides are particularly sensitive to processing-properties variation, in which a single defined chemical stoichiometry can embody dramatic variability in measured properties simply through the steps of synthesis and processing to reach the desired form. Hence, the tailoring of complex oxides is often convoluted by chemical doping and changes in stoichiometry when the influence of processing is not understood. Mixed conducting, multi-valent double perovskite Sr 2-x V Mo O 6-delta (SVMO) shows extraordinary electrical conductivity relative to comparable double perovskites. The technical hurdles of synthesizing and processing bulk powders of SVMO to optimize studies of fundamental electrical transport mechanisms otherwise convoluted by porosity in prior literature were overcome. The basis of various synthesis conditions via rapid microwave assisted sol-gel synthesis were discerned for their contribution to either open porosity of SVMO or enhanced densification. Enhanced resistance to particle coarsening under reducing contrast to inert atmosphere and a means to generate electrical percolation via solid-solution stability of SVMO were two key discoveries among fundamental breakthroughs understanding particle consolidation behaviors. It was discovered that SVMO's elastic modulus was well in excess of other oxide materials, approaching 300 GPa and in correspondence with the mixed V/Mo valency system provides an explanation for low thermal diffusion during sintering. The advanced solid lithium conducting garnet Li 6.25 La 3 Zr 2 Al 0.25 O 12 (LLZO) demonstrates high ionic conductivity for all solid-state batteries, however, it must be paired with an active cathode and anode to enable high energy storage capacity. The study presented here identifies methods to process LLZO materials into dense and porous constituents to satisfy the design architecture of a solid-state battery emphasizing the sensitivity of LLZO performance to lithium content and the desired cubic phase. The aim was to calibrate synthesis techniques towards minimizing sensitivity to thermal processing that contributes towards lithium loss. Studies of sintering optimization and excess lithium content in conjunction with novel freeze based tape casting methods to generate low tortuosity pores were explored. Development of these novel microstructures represents a backbone of processing methodology necessary to incorporate multivalent double perovskites in fuel-electrolysis cells and improve solid state lithium battery technologies.Item Freeze foaming: a novel process for the synthesis of foam ceramics(Montana State University - Bozeman, College of Engineering, 2018) Johnson, Nathaniel Peyton; Chairperson, Graduate Committee: Stephen W. SofieFoam is a class of materials that was developed only after World War II and ceramic foams are still in development. Many of the processes for synthesizing ceramic foam require the burning out of a polymer scaffold or the use of chemical reactions to generate pores. This thesis investigates the development of a novel synthesis approach called freeze foaming. In the freeze foaming process, pores are made by putting an aqueous solution under vacuum. The reduced pressure causes the air within the slurry to expand and form bubbles. Then once the foam is formed, it is frozen into place. Then the water is removed from the system through sublimation. Finally, the foam is densified by traditional sintering. After successfully creating ceramic foam samples, the parameters in the freeze foaming process were identified and investigated. Foam samples were characterized by taking density measurements, examining the macrostructure and microstructure with light microscopy, and determining mechanical properties through compression testing. In the end, highly porous foam samples with adjustable properties were synthesized using a novel manufacturing process.Item Manufacturing reliability for C-channel composite beams(Montana State University - Bozeman, College of Engineering, 2014) Bauer, Michael Wayne; Chairperson, Graduate Committee: Douglas S. CairnsA new manufacturing method has been developed for fabricating c-channel composite beams. The beams are to be used as test articles in four point bending tests. The motivation behind this thesis is to study the effects that specific manufacturing parameters have on the resulting amounts of porosity and fiber volume in these three-dimensional sub-scale structures. The parameters considered are number of layers of flow media, fabric architecture, flow rate of the resin, temperature of the resin, and level of vacuum pressure used. The manufacturing parameters were varied in a 1/2 factorial design of experiments where sixteen beams were manufactured, all with varying values for each parameter. A taguchi design of experiments was also formed to provide a comparison. The resulting average porosity percentages and fiber volume percentages were then determined for every beam. In addition, compression and tension tests were conducted to find the average maximum stresses for each. Once all the data had been gathered an Analysis of Variance (ANOVA) study was conducted to determine the effects and their levels of significance. It was found that the level of vacuum pressure has the most significant effect on the porosity while the fabric architecture has the most significant effect on the fiber volume. Overall, every parameter has some sort of quantifiable effect on porosity and fiber volume. There are also significant two and three way interaction effects present for each. Additionally, the 1/2 factorial design seemed to provide more accurate results compared with the taguchi design, which was inherently not comprised of data with a normal distribution and does not include interaction effects. Regression models were developed for the output levels of porosity and fiber volume. This allows manufacturers to create these beams with predetermined output levels for each and can improve testing capabilities. Also, using two layers of flow media greatly improved the consistency of the beams, while reducing porosity and slightly reducing fiber volume percentage. It is recommended to further implement the use of two layers of flow media into large sub-scale structures and potentially full scale turbine blades.