This thesis focuses on developing an appropriate cathode material throughnanotechnology as a key component for a promising alternative of renewable energygenerating systems, Intermediate Temperature Solid Oxide Fuel Cells (IT-SOFC).Aiming at a working cathode material for IT-SOFC, a recently reported capable oxideperovskite material has been synthesized through two different chemical methods.BaxSr1-xCoyFe1-yO3−δ (BSCF) with y =0.8 and x =0.2 was fabricated in nanocrystallineform by a novel chemical alloying approach, co-precipitation- as well as conventionalsol-gel method to produce oxide perovskites. The thermal properties, phase constituents,microstructure and elemental analysis of the samples were characterized by TG-DSC,XRD, SEM and EDS techniques respectively. Thermodynamic modeling has beenperformed using a KTH-developed software (Medusa) and Spark Plasma Sintering (SPS)has been used to obtain pellets of BSCF, preserving the nanostructure and generatingquite dense pellets for electrical conductivity measurements.The results show that the powders synthesized by solution co-precipitation have cubicperovskite-type structure with a high homogeneity and uniform distribution and meanparticle size of 50-90 nm range, while sol-gel powders are not easy to form a pure phaseand mostly the process ends up with large particle containing two or three phases.Finer resultant powder compared to sol-gel technique and earlier research works onBSCF has been achieved in this project using oxalate co-precipitation method. Topreserve nanoscaled features of BSCF powder which possess a significant increase ofelectrical conductivity due to decrease the electrical resistivity of grain boundaries, forthe sample synthesized through co-precipitation, ~92% dense pellet sintered by SPS atV1080 °C and under 50 MPa pressure and its electrical conductivity has been measuredfrom room temperature to 900 °C.Specific conductivity values were precisely measured and the maximum of 63 S.cm-1 at430 °C in air and 25 S.cm-1 at 375°C in N2 correspondingly are two times higher thanconventional BSCF implying a high pledge for nano-BSCF as a strong candidate ascathode material in IT-SOFC.

<p>Flash sintering was first demonstrated in 2010, where a ceramic green body was rapidly densified within seconds by applying an electric field during the heating process. The ultra-fast densification can occur as current abruptly flows through the material and self-heats by Joule heating. This process has potentials for large energy savings due to the reduction in furnace temperatures and shortened sintering time compared to conventional sintering. In addition, the ultra-high heating and cooling rates, along with the impact of electric field and current leads to the formation of unique non-equilibrium features in ceramics, which could greatly enhance their properties. Despite the potential of flash sintering, there are many challenges in moving this technique towards practical applications, such as the microstructure inhomogeneity and lack of understanding of the defects characteristics.</p> <p>In this dissertation, flash sintering was performed on ZnO to investigate the influence of various electrical conditions on the microstructure and defects. Detailed characterization was performed on flash sintered ZnO with and without a controlled current ramp, and contrasting types of current (DC and AC). These parameters show significant impact on the gradient microstructure and defects, and provide a way to tailor the desired characteristics for a wide range of applications. On the other hand, flash sintering of ZnO performed with a high electric field and low current density resulted in the growth of nanostructures. These nanostructures are unique compared to other growth techniques as they contain high density basal-plane stacking faults, and exhibit ultraviolet excitonic emission and red emission at room temperature. The nanostructure growth mechanism was investigated by varying the current density limit and revealed the formation of liquid phases which allowed growth by the vapor-liquid-solid mechanism. These findings present a new exciting route for flash sintering to produce highly defective nanostructures for device applications with new functionalities.</p>

Biological nanomaterials are defined as materials with sizes within the nanoscale range of 1 - 100 nm. The fundamental functionalities and biocompatibility of these materials can be tailored for biotechnology applications. In 1983, Ned Seeman successfully developed the first customized DNA nanostructures, Holliday junctions. Since then, the field has continued to expand rapidly and various 2D and 3D nanostructures has been designed. Although the high predictability of DNA base-pairing is essential for the design of complex DNA nanostructures, it greatly limits its functional versatility; therefore, proteins are conjugated with DNA nanostructures to compensate for that. DNA origami-protein hybrid nanostructures were introduced in 2012. However, the structural units based on DNA origami-protein hybrid nanostructures are still limited, and the majority are constructed by covalent or sequence-specific non-covalent interactions. Here we utilize the inherent, non-sequence-specific interaction between DNA and histones to present sequence-independent self-assembled DNA origami-protein hybrid nanostructures. We demonstrated using various molecular biology and imaging techniques that ssDNAs and histone proteins self-assemble into structurally well-defined complexes. We successfully assembled DNA origami–histone hybrid nanostructures using two different shapes of DNA origami: rectangular (PF-3), and rectangular with central aperture (PF-2) nanostructures. We observed precise localization of nucleosome-like histone-ssDNA nanostructures at the edge (PF-3) or the center (PF-2) of the DNA origami. In addition, we demonstrated that this DNA origami-histone interaction results in the assembly of larger DNA origami complexes, including a head-to-head type dimer and a cross-shape complex. Our results suggest the successful self-assembly of the DNA origami–histone hybrid nanostructures provide a principal structural unit for constructing higher-order nanostructures. Given the reversible nature of the geometry-based noncovalent interaction between the DNA origami and the nucleosome-like histone-ssDNA nanostructures, the self-assembly/disassembly of DNA-histones hybrid nanostructures may open new opportunities to construct stimuli-responsive DNA-protein hybrid nanostructures.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第19724号 / 工博第4179号 / 新制||工||1644(附属図書館) / 32760 / 京都大学大学院工学研究科材料化学専攻 / (主査)教授 平尾 一之, 教授 三浦 清貴, 教授 田中 勝久 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第19992号 / 工博第4236号 / 新制||工||1655(附属図書館) / 33088 / 京都大学大学院工学研究科マイクロエンジニアリング専攻 / (主査)教授 田畑 修, 教授 北條 正樹, 教授 山田 啓文 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第19999号 / 工博第4243号 / 新制||工||1657(附属図書館) / 33095 / 京都大学大学院工学研究科材料化学専攻 / (主査)教授 三浦 清貴, 教授 田中 勝久, 教授 平尾 一之 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

Consensus in scientific literature is that hyperglycemia, which is a condition that manifests in individuals with uncontrolled diabetes, causes compromised bone growth, but the exact mechanisms of are unknown. It has been estimated that 5% of dental implant failures that have previously been linked to unknown causes may be associated with undiagnosed diabetes. It is important to study the early stages of bone growth as it is accepted that they are critical in the long-term success rate of endosseous implants. This study aimed to investigate the bone healing seen in the hyperglycemic group compared to the normal (i.e. control) group, at an early time point, using high-resolution microscopy techniques. Ten young (200-250gram) male Wistar rats were used for this study with five rats assigned to the control group and the other five rats intravenously injected with 65 mg/kg of streptozotocin (STZ) to induce diabetes. An osteotomy model was used to make a 1.3mm defect in the diaphysis of the rat femurs. After five days, the femurs were removed, fixed in glutaraldehyde, dehydrated, and embedded in resin. Structural and chemical analyses were conducted on the samples using a variety of microscopy techniques to examine various factors of bone quality including: bone porosity, relative mineralization level, and the arrangement of collagen and mineral. When analyzing the micro-structure, the hyperglycemic group showed increased porosity in the newly formed bone as compared to the control group. However, no significant differences were found in the nano-structure when analyzing the arrangement of collagen and mineral.Therefore, the results in this thesis suggest that alterations in micro-architecture rather than nano-architecture may play a pivotal role in the compromised bone healing in uncontrolled diabetes at this five-day time point. Future work should investigate additional time points in the bone healing process. / Thesis / Master of Applied Science (MASc) / According to the International Diabetes Federation, 387 million people worldwide are living with diabetes of which 46.3% are undiagnosed. Uncontrolled diabetes results in hyperglycemia, which is a condition where there is an increased level of glucose in the blood. When diabetes is not regulated correctly with medication, it leads to problems in the long-term success rate of dental implants. The objective of this thesis was to investigate the early stages of bone formation, which are accepted to be critical in the long-term success rate of dental implants, in hyperglycemic animal models compared to control groups using various microscopy techniques. The different techniques used allowed for the structural and elemental compositions of bone to be studied on the micro-scale and nano-scale. It was shown that at the 5-day healing time point studied, the micro-structure, rather than the nano-structure, was negatively altered in the hyperglycemic group compared to the control group.

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