12CaO·7Al₂O₃ (so called C12A7) has been known as mayenite, which is a component of alumina cement. As the crystal is composed of positively charged nano-cages, it can clathrate several different anion species and show different outstanding properties, e.g., high oxidizing ability, high conductivity maintaining its optical transparency, catalytic reactivity for producing ammonia from nitrogen and hydrogen gases, etc., depending on the chemical species clathrated in the cates. In the present study, we focus on the newly obtained C12A7 prepared by solution plasma process and examined its phase stability and crystal structures of the unknown C12A7. TEM, XRD, TG-DTA analyses revealed the unknown C12A7 phase has large lattice parameters and small crystallite size compared to the standard (normal) C12A7 phase and is unstable in O₂ containing atmosphere, whereas is stable in H₂ atmosphere.

Xerogels of large specific surface area have been successfully prepared by optimizing sol-gel process without any templates. It was found that the optimum solvent to obtain gels of large specific surface area is 1-propanol and the optimum molar ratio of solvent to alkoxide is 10. It was also clarified that the consecutive addition of water to reaction system by introducing humidified air is critical to specific surface area and that with humidified air the less initial content of water can provide gel of larger specific surface area. Consequently silica gel with specific surface area of 1869 ‍m²/g could be obtained. Titania gel with specific surface area of 597 ‍m²/g was successfully prepared by using ammonium acetate as catalyst together with above mentioned strategy.

Obtained titania gel was used as support material of Ni nanoparticle and the catalytic activity was tested then compared with commercially available non-porous titania fine particle and commercially available silica gel. As a result, the significance of catalyst-support interaction and improvement of loading amount of catalyst nanoparticles attributed to porosity were confirmed.

We have investigated the wet classification of a submicron silica particle using the counter- and orthogonal-electrophoresis method. The counter-electrophoresis method is a classification technique to move particles in the opposite direction with respect to their gravitational settling direction using electrophoresis. In contrast, the orthogonal-electrophoresis method is a technique to move particles using electrophoresis in the orthogonal direction with respect to the flow direction of the slurry. In order to examine the effectiveness of these two methods, two types of slurry were prepared: an ultrasonicated silica slurry with a constant electrophoretic mobility regardless of the particle diameter and a bead-milled silica slurry in which the absolute value of the electrophoretic mobility increases with the increase in the particle size. The results revealed that understanding the electrophoretic characteristics of the slurry and selecting a suitable classification method are important parameters for conducting wet classification using electrophoretic phenomena.

Periodic structures of colloidal particles have attracted considerable interest because they are promising for a wide range of potential applications. Convective self-assembly of colloidal particles is a possible candidate because it is capable of fabricating ordered arrays in a simple manner at low-cost without any templates. We have succeeded in fabricating stripe pattern parallel to the air-solvent-substrate contact line and dot array pattern by using this technique. In the present study, we newly revealed the formation of stripe patterned structures perpendicular to the contact line by controlling the particle concentration and particle size. We found out that the vertical stripe pattern is formed when the particle size of 500 ‍nm is used under the concentration region between those for the horizontal stripe and dot array patterns. The width of the vertical stripes increases with the particle concentration, while the spacing between stripes remains unchanged against the concentration. Furthermore, we fabricated a peculiar hybrid pattern composed of vertical stripes and dot arrays by using a two-step convective self-assembly method, in which a vertical stripe pattern of 570 ‍nm silica particles was first prepared on a substrate, and the vertical stripe pattern was then immersed in a suspension of 120 ‍nm silica particles.

Aluminum doped zinc oxide (AZO) was synthesized with various pH adjustments reagent (ammonia, TMAH, TEAH and TPAH) by hydrothermal reaction. Regardless of the pH adjustment, the main product of the synthesized powders with 5 ‍mol% Al was zinc oxide. However, the diffraction peaks of gahnite (ZnAl₂O₄) were detected in the sample prepared from the precursor solutions with TMAH, TEAH and TPAH as pH adjustment. The excellent absorption property in near-infrared (NIR) region was obtained in the synthesized powder with about 2 ‍mol% Al using ammonia. Based on these results, the initial state of Zn and Al ion in precursor solution is thought to affect the crystal phase of the product in hydrothermal synthesis. The NIR absorption property was highly enhanced by using urea as the pH-shift reagent during hydrothermal reaction process.

Ce³⁺-doped Y₃Al₅O₁₂ (Y_2.97Al₅O₁₂:Ce_0.03³⁺, YAG:Ce³⁺) phosphors have been widely used for white light emitting diodes (LEDs). Here, we report on the effect of Al(OH)₃ powder addition on the mechanical synthesis of YAG:Ce³⁺ phosphor. The YAG:Ce³⁺ phosphors were synthesized by the mechanical method using an attrition-type mill. When Al(OH)₃ was added at 12.5 ‍mass% to the raw powder materials and milled, the synthesis of YAG:Ce³⁺ phosphor was achieved at the vessel temperature of 438°C. The crystalline, structure, luminescence spectra and internal quantum yield of YAG phosphor were evaluated by X-ray diffraction, scanning electron microscopy, photoluminescence spectroscopy and a quantum yield measurement device, respectively. The synthesized YAG:Ce³⁺ phosphor revealed the maximum internal quantum yield of 27%.

This manuscript described the development of core-shell type micro-encapsulated phase change materials (MEPCM) using Al-based alloy as a phase change material (PCM) for high temperature applications. Al-25 ‍mass% ‍Si microspheres (diameter: 75~90 ‍μm, melting temperature: 577°C) was used as core material (=PCM). The MEPCM was prepared in two steps. First step is the formation of AlOOH precursor shell on the PCM microspheres in boiling distilled water. Second step is heat-oxidation treatment in an O₂ atmosphere to form a stable Al₂O₃ shell. The effects of heat-oxidation temperature (1150–1350°C) on the shell morphology and heat storage performance, were mainly investigated. As results, MEPCMs were successfully prepared and the shell compositions were single α-Al₂O₃ phase regardless of different heat oxidation temperature. The heat capacities of the as prepared MEPCMs were over 4 times higher than that of conventional heat storage materials. The MEPCM developed in this study has great promise in future energy utilization processes.

Tailoring the crystallographic orientation in ceramics is very useful for improving their properties. A magnetic field is shown to be very effective in controlling the crystallographic orientation in bulk ceramics. The particles were rotated to an angle minimizing the system energy by a magnetic torque generated from the interaction between the magnetic anisotropy and the applied magnetic field. This processing was applied to control the microstructure in lanthanum silicate oxyapatite (LSO) for SOFC and LiCoO₂ for Li ion secondary battery. Electric conductivity parallel to the c-axis in the c-axis oriented LSO was higher than that perpendicular to the c-axis. The battery performance of the ideal textured cell fabricated using a rotating magnetic field has a significantly higher performance than a oriented cell prepared by a static magnetic field.