Theses and Dissertations at Montana State University (MSU)
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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 Sintering in ceramics and solid oxide fuel cells(Montana State University - Bozeman, College of Engineering, 2017) Hunt, Clay Dale; Chairperson, Graduate Committee: Stephen W. Sofie; David Driscoll, Adam Weisenstein and Stephen W. Sofie were co-authors of the article, 'Nickel nitrate and molybdenum oxide as a yttria-stabilized zirconia sintering aid' in the journal 'Processing, properties, and design of advanced ceramics and composites' which is contained within this thesis.; Marley Zachariasen, David Driscoll and Stephen W. Sofie were co-authors of the article, 'Current degradation rate quantification of solid oxide fuel cells with and without aluminum titanate' which is contained within this thesis.; David Driscoll and Stephen W. Sofie were co-authors of the article, 'Constant rate of heating definition of the undefined function of density of the Wang and Raj equation for 8YSZ' which is contained within this thesis.; David Driscoll and Stephen W. Sofie were co-authors of the article, 'Constant rate of heating definition of undefined density function for 8YSZ with a sintering aid' which is contained within this thesis.; David Driscoll and Stephen W. Sofie were co-authors of the article, 'Constant temperature definition of the undefined density function for 8YSZ' which is contained within this thesis.; David Driscoll and Stephen W. Sofie were co-authors of the article, 'Constant temperature definition of the undefined density function of 8YSZ with a sintering aid' which is contained within this thesis.Nature's propensity to minimize energy, and the change in energy with respect to position, drives diffusion. Diffusion is a means by which mass transport resulting in the bonding of the particles of a powder compact can be achieved without melting. This phenomenon occurs in powdered materials near their melting temperature, and is referred to as 'sintering'. Because of the extreme melting temperature of some materials, sintering might be the only practical means of processing. The complexity and subtlety of sintering ceramics motivated the evaluation of empirical data and existing sintering models. This project examined polycrystalline cubic-zirconia sintering with and without transition-metal oxide additions that change sintering behavior. This study was undertaken to determine how sintering aids affect the driving force, and activation energy, the energy barrier that must be overcome in order for an atom or ion to diffuse, of the densification occurring during sintering. Examination of commercially-available cubic-zirconia powder sintering behavior was undertaken with dilatometry, which allows monitoring of the length change a material undergoes as it sinters, and with scanning electron microscopy, which facilitates the study of sintered-sample microstructure. MATLAB algorithms quantifying sintering results were developed. Results from this work include proposed definitions of a 26-year-old undefined function of density factor in a well-accepted mathematical model of sintering. These findings suggest activation energy is not changing with density, as is suggested by recent published results. The first numerical integration of the studied sintering model has been performed. With these tools, a measure of the activation energy of densification of cubic-zirconia with and without the addition of cobalt-oxide as a sintering aid has been performed. The resulting MATLAB algorithms can be used in future sintering studies. It is concluded that sintering enhancement achieved with cobalt-oxide addition comes from reduction in activation energy of densification of cubic-zirconia. Further, it is suggested that the activation energy of densification does not change with material density. This conclusion is supported by the sensitivity of the numerical integration of the aforementioned sintering model to changes in activation energy.Item Development of porous ceramics with graded columnar pore structures via freeze-tape casting(Montana State University - Bozeman, College of Engineering, 2008) McCrummen, John Drew; Chairperson, Graduate Committee: Stephen W. SofieFreeze-tape casting is a new processing technology that can generate continuous columnar-graded pore structures utilizing a wide variety of ceramic and/or metallic powders. The uni-directional solidification and subsequent freeze drying of yttria stabilized zirconia (YSZ) based aqueous cast tapes is being evaluated for various applications including fuel cells, filtration/separation membranes, and catalyst supports. The degree of pore divergence, pore packing, and pore orientation can be actively tailored by altering the solids loading, freezing rate, and tape pulling speed. The effects of solids loading and freezing rate is discussed with respect to morphology of ice growth. SEM and density data is reported to establish the breadth of tailorability and extent of anisotropy in the frozen tapes. The freeze cast structure of ceramic materials is highly porous. The production of freeze cast, YSZ-based tapes include tap casting techniques and high temperature sintering steps. SEM analysis is displayed at varying angles relative to casting direction to provide further insight of the morphology of these materials. Results of varying solids loading and freezing temperature studies are discussed in detail. Compressive strength data by ASTM standard methods was resultant of concentric ring-on-ring testing and is further explained. Freeze cast structures appear to be potentially desirable over traditional pore formers for various applications.