Silica glass is an important optical material in deep-ultraviolet (DUV, λ≤300 nm) and vacuum-ultraviolet (VUV, λ≤200 nm) spectral regions. However, DUV-VUV transparency of silica glass is significantly influenced by the presence of structural imperfections (point defects). This article describes point defects in silica glasses of low metallic impurity contents (“synthetic” silica glasses), and optical and chemical properties of these point defects. It is shown that controlled doping with specific point defects can improve the transparency and radiation hardness of silica glass in DUV-VUV spectral region. Such doped species include network modifiers that relax the glass structure and mobile interstitial hydrogen molecules. Utilization of these techniques in developing photomask substrates for F₂ laser photolithography and DUV optical fibers for ArF laser transmission is presented.

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This article reviews our research into artificial microstructures made of inorganic oxides and their optical functions. The described microstructures, which are potential ingredients of the emerging optical devices, include oxide nanowires and photonic crystals. Chemical solution methods were used to fabricate zinc oxide nanowire ultraviolet laser arrays and two-dimensional oxide photonic crystals with photonic band gaps at visible wavelengths. The dimensions of these microstructures were determined by considering the calculated results of the guided modes in nanowires and the band structures in photonic crystals. Current issues in fabrication and the applications of these oxide microstructures as optical devices are discussed.

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We suggested liquid phase patterning (LPP) of ceramics and fabricated nano/micropatterns of ceramic thin films in the solutions. Molecular recognitions of functional groups of self-assembled monolayer (SAM) were utilized for site-selective deposition (SSD) of oxides based on crystallography, interfacial chemistry and the solution chemistry for inorganic materials. The processes should contribute to the development of future environmentally friendly processes.

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Glass is an attractive material as a solid electrolyte and an electrode for all-solid-state lithium secondary batteries. In the present paper, the preparation and characterization of Li₂S-based oxysulfide glasses and sulfide glass-ceramics as solid electrolytes are reviewed. In particular, two strategies of enhancing Li⁺ conductivity are proposed; one strategy is the utilization of “mixed-anion effect” by combining sulfide and oxide anions (in oxysulfide systems) and the other is the precipitation of superionic metastable crystals by careful heat-treatment of glasses. The superior Li⁺ conducting solid electrolytes with the highest conductivity and the lowest activation energy for conduction have been achieved in the Li₂S-P₂S₅ glass-ceramics. For the SnO-based glasses as a negative electrode in a lithium ion cell, the relationship between electrochemical performance and local structure is also discussed. All-ceramic electrochemical cells using the oxysulfide glassy electrolytes and the SnO-B₂O₃ glassy electrodes were fabricated and then characterized as a lithium secondary battery.

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The continuous increase of the turbine inlet temperature in gas turbines necessitates new thermal barrier coatings (TBCs) with enhanced temperature capability and longer lifetime. This paper reviews our recent challenges to develop new plasma-sprayed TBC systems for the next generation of land-based gas turbine engines. It is shown that the addition of small amounts of La₂O₃ is effective in reducing the thermal conductivity of Y₂O₃-stabilized ZrO₂ plasma-sprayed top coats. It is also revealed that precise control of the oxygen partial pressure of the pre-oxidation atmosphere leads to an improvement of the oxidation resistance of MCrAlY bond coats. The newly-developed TBCs show much longer thermal cycle life than that of conventional coatings.

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The formation process of inorganic crystals in biological systems (biomineralization) is the fruitage of an extended period of fine-tuning by evolution and is replete with material scientific key considerations. In this article, our recent attempts to elucidate the mineralization mechanism of hydroxyapatite (HAp) in natural bodies are described. It has been known that inorganic crystals precipitate onto organic matrix surfaces in biomineralization processes. Amphiphilic organic molecules assembled to monolayer films were employed to reproduce the organic matrices and the HAp precipitation process onto the monolayers were subjected to spectroscopic and structural analyses. We also determined the interfacial atomic structure of HAp {100} facet by using high-resolution transmission electron microscopy. A mechanism of HAp mineralization was proposed in view of the experimental results to determine the underlying reasons for refinement in structures of biominerals.

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Spherical polyphenylsilsesquioxane particles were prepared by a two-step acid-base catalyzed sol-gel process, in which various amounts of ethanol were used as a solvent to vary the concentration of phenyltriethoxysilane (PhSi(OEt)₃) used as a starting alkoxide. The decrease in the PhSi(OEt)₃ concentration led to the decrease in the average molecular weight and glass transition temperature of the polyphenylsilsesquioxanes. Thus, the change of the PhSi(OEt)₃ concentration in the preparation of polyphenylsilsesquioxane particles by the two-step acid-base catalyzed sol-gel process is an effective means to control the glass transition temperature of the particles.

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Particle packing structure in alumina green tape was studied by optical microscopy with a special focus on the direction of alignment and the degree of orientation. The effect of processing conditions on the packing structure was also examined. Non-uniformity of the c-axes orientation of alumina particles and variation of its orientation degree existed in the tape thickness direction (z-axis). The tape cast with a narrow blade exit length and low casting speed showed a relatively large non-uniform structure. The c-axes of alumina particles aligned more strongly along the z-axis at the upper surface than the lower surface, where the orientation deviated from the z-axis. A moderate local c-axes orientation at the lower surface was developed after the increases of either the blade exit length or the casting speed, however, the orientation degree varied from the upper to the lower surfaces.

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Precursors for silicon carbide spherical particles were prepared from liquid mixtures of spherical carbon black, phenolic resin and ethyl silicate. After the gelation, drying and pyrolysis at 1273 K, carbon-silica hybrids were obtained with C/SiO₂ ratios in 2.77-2.98. In these pyrolyzed materials, a part of the carbon existed as carbon black dispersed in the matrix. The other carbon, which originated from phenolic resin, was located in the surrounding matrix area. These C-SiO₂ hybrids were heat-treated at 1838 K in an Ar gas flow to obtain SiC particles with carbothermic reduction process. The conversion process of the hybrids to SiC was monitored by thermo-gravimetric analysis. The influence of the carbon black content on conversion rates, residual amounts of excess carbon and the resulting SiC particle morphology were investigated.

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A silicon nitride (Si₃N₄)-boron nitride (h-BN) composite is utilized for brazing jig, since it shows low-wettability for brazing metals. Combination of green machining and reaction bonding (RB) is a potential process to reduce machining cost. However, precision is a problem. Thus, in this work, the composite was fabricated by uniaxial die-pressing followed by cold isostatic pressing, green machining and reaction bonding. Precision of green machining and dimensional change (i.e., expansion) after RB were investigated. Green machining was successfully done, and dimensions of the specimen were within the acceptable error range of 100 μm. After RB, the specimen was slightly expanded. Expansions were about 0.5% and 0.9%, respectively, for perpendicular and parallel to the die pressing direction. Ununiform expansion seemed to be due to the alignment of h-BN caused by uniaxial die pressing.

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An acid resistant fluoroapatite coated titanium dioxide (FAp-TiO₂) was synthesized by adding a fluoride ion (F^-) to hydroxyapatite (HAp), in order to avoid dissolution of the HAp at an acidic atmosphere. In this study, the optimization of synthetic conditions of FAp-TiO₂ was investigated in terms of the amount of the fluorine (F^-) added to the simulated body fluid, the reaction temperature and the time. The addition of F^- to simulated body fluid was performed after coating HAp on the surface of TiO₂ surface. The crystallinity of FAp phase generated on the TiO₂ was strongly affected by changing the reaction conditions. The optimized synthetic conditions of FAp-TiO₂ as photocatalyst were the addition of 0.25 mM-0.5 mM F^- in the fluid and then the reaction time for 3 h at 60°C. The adsorptivity and the photocatalytic activity of the FAp-TiO₂ in the optimum conditions were investigated using the butyric acid and trimethylamine as model solutions. Consequently, the FAp-TiO₂ could obtain higher adsorptivity and photocatalytic activity for trimethylamine, rather than the uncoated TiO₂.

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We fabricated porous alumina ceramics from a technique for making a cake. Polyvinyl alcohol (PVA), methyl cellulose (MC), and granulated sugar (SUGAR) were used as additives to give the alumina slurry the foaming property and the foam stability. The alumina slurry with PVA, MC, and SUGAR became creamy by mixing for 2.5 min by an electric mixer at 940 rpm. The creamy alumina slurry was able to be extruded by a forcing bag and smoothed by a blade. The creamy alumina slurry dried at 45°C, and then was sintered at 1600°C to a density of about 20%. The pore sizes in the sintered porous alumina ceramics were 0.2 mm or less. The flexural strength of sintered porous alumina ceramics with 78% porosity was 12 MPa.

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Porous materials were prepared by stacking needle-like titania particles. The uniform, needle-like titania particles were synthesized by hydrothermal treatment of titanium hydroxide gel containing ethylenediamine. A seeding technique controlled the particle size of them. The obtained particles were dispersed in aqueous solutions with various pH values and vacuum-filtered to form bulk materials. Porous materials with uniform microstructure were obtained when the pH of the suspension was adjusted to the value suitable for generating electrostatic repulsion between dispersed titania particles. Changing the size of component particles also controlled the pore size of the porous titania.

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A H⁺-form lepidocrocite-like layered titanate H_1.07Ti_1.73O₄ was exfoliated in a n-propylamine solution to prepare a colloidal solution of the titanate nanosheet. The nanosheet colloidal solution shows a very high reactivity with Ba(OH)₂ in the formation reaction of BaTiO₃. The sub-micrometer BaTiO₃ sheet-like and spherical particles can be obtained by reacting the nanosheet colloidal solution with Ba(OH)₂ at 80°C. This reaction provides a novel low temperature process for the preparation of BaTiO₃.

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