Scholarship & Research
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Item Biochar as a renewable carbon additive for biodegradable plastics(Montana State University - Bozeman, College of Engineering, 2022) Kane, Seth Douglas; Chairperson, Graduate Committee: Cecily Ryan; This is a manuscript style paper that includes co-authored chapters.Biochar - a carbon material produced from pyrolysis of biomass - is a promising alternative to petroleum-derived filler materials in biobased and biodegradable plastics. In this application, biochar can replace materials such as carbon black, with a material that is compatible with end-of-life degradation of bioplastics, while reducing costs and improving material properties. Specifically, high electrical conductivity biochar has the potential to be applied to create highly electrically conductive and biodegradable biochar-bioplastic composite materials. Herein, two critical gaps to development of biochar-bioplastic composites are addressed: the high variation in biochar electrical conductivity and poor thermal interactions between bioplastics and biochar that reduce the bioplastics molecular weight and mechanical properties. To this end, biochars are produced from a variety of feedstocks and their chemical structure and electrical conductivity are extensively characterized. The relationship between feedstock chemical properties, biochar chemical properties, and biochar electrical conductivity is examined. Feedstock oxygen and inorganic content are found to play a critical role in developing highly electrically conductive biochar. The impact of these biochars on the thermal behavior of bioplastics is then examined in detail, and multiple hypotheses for the reduction in thermal behavior that have been proposed in past studies are tested. Biochar moisture content is found to have a limited impact on polymer thermal degradation, while alkali and alkaline earth metals present in biochar reduce the thermal degradation temperature of common bioplastics. A simple washing method was developed to remove these metals and improve the thermal stability of biochar-bioplastic composites. Finally, the environmental benefits of biochar-plastic composites are examined with life cycle assessment methodology, and the developed biochar is examined as a conductive additive in lithium-ion batteries. This work addresses two critical issues that limited the potential of biochar to reduce environmental impacts of rapidly growing classes of materials, as well as demonstrating its applicability in critical applications of petroleum-derived materials. Biochar-bioplastic composites show a unique combination of high electrical conductivity and biodegradability, with strong potential for development of applications in diverse industries from agriculture to biomedical applications.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.