Fibrous silica was prepared by drying a silica suspension. Under the experimental conditions, it was possible to prepare a fibrous silica of 7cm in length and 40-200μm in width. The surface morphology of the silica fibers consisted of almost close-packed silica particles. When the suspension concentration was low or the contact angle of the meniscus was large, the film thickness was small and no fibers were generated. The direction of the silica fiber generation was always perpendicular to the water level.
The formation mechanism of the fibers was elucidated as follows:
(1) Formation of closely-packed homogeneous SiO₂ film.
(2) Generation of cracks by shrinkage of the film.
(3) Formation of fibers by propagation of cracks.
Some experimental conditions affected the fiber width. A concentrated silica solution (i.e., thick film), large silica particles, and low drying temperature gave a wide fiber. The particle diameter and drying temperature also influenced the fiber width. The larger silica particles and the lower drying temperature gave wider fibers.
As prepared fibers were translucent and fragile, however, they became strong by calcination at 800°C for 1h. A measurement of the pore diameter distribution revealed that they have homogeneous pores with a diameter around 20nm. After calcination at 1000°C, they became transparent and the strength was much higher than that at RT. The pores observed until at 800°C disappeared at 1000°C.

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The phase transformation and densification behavior of (Pb_1-X²⁺La_2X/3³⁺)₅Nb₁₀O₃₀ (X=0.00-0.20) tungsten bronze (TB)-type compounds were studied with respect to La³⁺ ion substitution for Pb²⁺ ion in Pb₅Nb₁₀O₃₀. Analysis of the phase identification shows that the phase transformation temperature (low temperature rhombohedral form ↔ high temperature tetragonal form) decreases along with the increase of La³⁺ amount. The decrease of phase transformation temperature limits excessive grain growth, which usually occurs from the co-proceeding of phase transformation and sintering in Pb₅Nb₁₀O₃₀ and, as a result, the density after sintering is effectively improved. Furthermore, two different densification models for Pb₅Nb₁₀O₃₀ and (Pb_1-X²⁺La_2X/3³⁺)₅Nb₁₀O₃₀ were described and discussed.

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AlON-BN composite was prepared by heating a mixed powder compact with Al₂O₃-AlN-20mass% BN-3mass% Y₂O₃ (Al₂O₃/AlN=2.4 in molar ratio) at 1850°C for 2h in N₂. The relative density of the heated compact was 70%. Oxidation characteristics of AlON-BN composite were investigated over the temperature range of 1000-1500°C in air. AlON and BN were oxidized to form Al₂O₃ and B₂O₃ at the initial stage, respectively. The reaction between the formed B₂O₃ and Al₂O₃ yielded Al₄B₂O₉ and Al₁₈B₄O₃₃. Below 1200°C, oxygen penetrated into the composite through the open pores and oxidation occurred since the surface layer was porous owing to an insufficient amount of the formed B₂O₃ liquid. At 1100 and 1200°C, volume expansion accompanied by the formation of Al₁₈B₄O₃₃ caused the occurrence of cracks in the composite. At 1300°C, a relatively dense layer with B₂O₃ liquid surrounded the composite and suppressed the penetration of oxygen into it. At 1500°C, oxidation was promoted to cause the deformation of the composite.

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An Y-doped ceria powder with composition of Ce_0.8Y_0.2O_1.9 was prepared by heating oxalate coprecipitate at 600°C in air. The calcined powder was milled with α-alumina ball of 3mm diameter. The Y-doped ceria films were formed by doctor blade method applied to aqueous suspensions of 23-35vol% Y-doped ceria powder with a median size 0.9μm. The thickness of the formed films depended strongly on the blade clearance. The density of the sintered films was affected by the solid content of the suspension. This result was discussed with the sintering model associated with the shortest distance between particles. Upon heating, a lot of closed pores were formed at the initial stage of sintering. The densification process and microstructures of the films were discussed in relation to the properties of powder compacts consolidated by isostatic pressing.

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An alumina substrate forms a dense and uniform layer of bone-like apatite on it, when it is soaked in a simulated body fluid, provided that it is faced to a glass of composition, MgO 4.6, CaO 44.7, SiO₂ 34.0, P₂O₅ 16.2 and CaF₂ 0.5mass%, placed at a distance of 0.2mm. Effect of the ion concentrations, pH and temperatures of the fluid on the apatite formation on the substrate were investigated. The bone-like carbonate apatite was formed even in fluids lacking in calcium or phosphate ion, since those ions and carbonate ions are supplied from the glass and the surrounding fluids, respectively. An apatite was formed in fluids with pH 6.53 to 7.48 but not in those with pH less than 5.00, because the apatite is stable only in neutral to basic environment. Apatite formed in fluids at 30 to 60°C but not below 20°C, since only a small amount of silicate ions is released from the glass at lower temperatures.

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Shaped body of quartz bonded by tobermorite was fabricated by adding small amount of CaO and by autoclaving at 180°C for 24h. The specimen was fired at various temperatutes and a porous body of quartz bonded by wollastonite was obtained. In specimens fired <1000°C, the bonds between quartz particles mainly provided by β-wollastonite formed by topotactic reaction of tobermorite. On the other hand, in specimens fired >1130°C, quartz particles were connected by both crystobalite and β-wollastonite, and the bond provieded by the latter being stronger than that of the former.

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Diffusion of scandium, gallium and ytterbium ions into single- and poly-crystalline yttrium aluminum garnets has been studied. Volume diffusion coefficients of gallium ions in single crystals were larger than those of scandium and gallium ions. On the other hand, the diffusion coefficients of scandium and ytterbium ions took almost the same values. The cations diffusion exhibited an extrinsic behavior. Cation ratio of Y/Al influenced the diffusivity of scandium and ytterbium diffusion. The yttrium-rich YAG had a smaller concentration of yttrium vacancies than that with a stoichiometric composition. The scandium and ytterbium ions preferentially diffused along grain boundaries.

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A new class of critical temperature resistor (CTR) was fabricated from metal/silica glass composites. The electrical resistivity of the composite with 20vol% of Ag filler suddenly decreased from 10⁵ to 10¹Ω·m at about 300°C, in analogy with the CTR characteristic observed in VO₂ ceramics. It was assumed that this phenomenon was due to the high thermal expansion of the conducting filler in a low-thermal-expansion matrix: as the temperature increased, the conducting filler particles expanded to come into contact with one to another, resulting in a drop of resistivity at a critical temperature. The critical temperature varied with both the kind and the amount of metal filler.

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The relationship between mechanical properties and oxidation of ALON-based composite ceramics at high temperature was investigated. The flexural strength of ALON-based composite ceramics at 600-800°C decreased by 10-30% compared to the strength measured at room temperature. The flexural strength at 1000°C was about one half of the room temperature strength; however, the strength at >1000°C increased again. Investigation based on X-ray diffractometry (XRD) and thermogravimetry-differential thermal analysis (TG-DTA) clarified that in the ALON-based composite ceramics, formation of γ′-ALON and B₂O₃ by oxidation of γ-ALON, BN phases in the ceramics occurred by heating up to 800°C in air, then at 1000°C α-Al₂O₃ formed from γ′-ALON and finally 9Al₂O₃⋅2B₂O₃ formed on the surface of the ceramics containing BN contents higher than 10vol%. Decreasing of flexural strength at elevated temperature was caused by oxidation of γ-ALON and BN phases.

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Our recent investigation established a method for quantifying the amount of amorphous silicon nitride by ²⁹Si MAS NMR technique, which involved the full relaxation of the ²⁹Si nuclear spin system between pulses in order to make the signals proportional to the number of nuclei in each phase. In this work, solid-state NMR study of the crystallizing behavior of silicon nitride powder, synthesized by the thermal decomposition method of imide, has been attempted. Because the crystalline and amorphous phases of Si₃N₄ have different thermal expansion and oxidation susceptibilities, this difference strongly affects sinterability and the mechanical properties of the final sintered body. In view of the effects of crystalline vs. non-crystalline phases on sinterability and mechanical properties, it is crucial to establish a reliable method for measuring the quantities of α-, β-, and amorphous Si₃N₄ in the batches of Si₃N₄ powder before carrying out the sintering process. Moreover, because remains of hydrogenous products generally exist on the surface of the silicon nitride powder, this affects the characteristic of slurry and sinterability of the Si₃N₄ powder. Thus, the quantification of the amount of hydrogenous products in the silicon nitride powder is also required. According to ²⁹Si MAS NMR spectra of silicon diimide (Si(NH)₂) during thermal decomposition at a series of temperatures, the crystalline phase increased as calcination temperatures increased. The integrated intensities of ¹H MAS NMR spectra varied directly as specific surface areas. The bands near 1630 and 3300cm^-1 arising from adsorbed molecular water and the unknown band near 1400cm^-1 were observed in IR spectra. This result can be interpreted as indicating that there exists a proportional amount of compound consisting of hydrogen to specific surface area on the surface of silicon nitride powder, which was measured by ¹H MAS NMR.

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The sedimentation behavior of particles during high-speed centrifugal compaction process (HCP) was investigated. Slips of alumina powders with various particle sizes (0.2-0.54μm) were put into a glass tube and mounted in a high-speed centrifuge with a rotor radius of 120mm. Then they were rotated at 3000-5000rpm for 0.25-4ks. The color change of slip was observed and the profiles of slip concentration in the glass tube was measured. During HCP, the slip divides into three zones with clear boundaries regardless of the compacting conditions. The upper part is merely water (clear zone), the middle is the slip (falling zone), and the lower is an unmovable sediment (compacted zone). Growing velocity of clear zone increases as the initial concentration of slip decreases. However, growing velocity of compacted zone is almost unaffected by the initial concentration. The growing velocity of the compacted zone, on the other hand, increases in proportion to the centrifugal force and to the square of particle size. This tendency is nearly the same as the Stokes' sedimentation law. Under various conditions, the concentration of slip at the boundary between the falling zone and the compacted zone is rather constant at around 50vol%. This constancy is considered to be the main reason for the above mentioned characteristics of compacting velocity.

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A model for the oxidation kinetics and mechanisms of Si-Ti-C-O fiber-bonded ceramics was newly developed to evaluate the oxidation behavior quantitatively at temperatures ranging between 773 and 1473K in air. The model considers the geometry changes of pores resulting from consumption by oxidation of the free carbon layer, and the oxygen consumption due to oxidation of the pore walls. A differential equation for the oxygen concentration profile along the pore was derived and solved numerically. For materials with very thin carbon layer, the geometry change of the pore has a significant effect on the oxygen concentration profile. The relative mass changes due to oxidation of (1) the external surface, (2) the carbon layer and (3) the pore walls were respectively calculated and thermogravimetric analysis (TGA) curves of the material derived from their sum. The calculated TGA curves well agreed with the experimental data. The length of carbon layer consumed by oxidation was calculated as a function of time and temperature. At low temperatures, the rates of the carbon consumption were low, but pores took place proceeded for long time. At high temperature, in contrast, the oxidation of the carbon layer was inhibited in a short time due to the quick sealing of the pore entrance by silica layer. Thus, the oxidation damage is limited only in the vicinity of the material surface.

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In the process starting from fabrication of sintered PZT bulk target to its thin-film synthesis on Pt/Ti/SiO₂/Si substrates by pulsed laser deposition technique, the precise composition analysis has been carried out by X-ray fluorescence (XRF) measurement. The coexistent elemental effect was calibrated by a multiple regression analysis of normalized PZT specimens. As a result, an excellent XRF table for precise quantitative analysis of PZT system in the vicinity of the morphotropic phase boundary (MPB) around Zr/Ti=53/47 was prepared. X-ray diffraction (XRD) and its modeling calculation supported XRF results and evaluated Pb stoichiometry in the perovskite structure during sintering process of PZT bulk ceramics. Under the variation of the partial oxygen pressure from 1 to 10Pa in the PLD conditions, 5Pa was the most suitable for PZT film growth highly oriented to perovskite (111) direction, and the composition deviation between bulk target and thin film was also investigated. Further effects of target degradation by laser-beam irradiation on the film stoichiometry and crystallinity were discussed.

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Synthesis of novel composite adsorbent composed of phillipsite-type zeolite (Na₃Al₃Si₅O₁₆⋅6H₂O) and sepiolite (Mg₈Si₁₂O₃₀(OH)₄⋅12H₂O) with high adsorbing abilities for ammonium ion and water, respectively, has been attempted from coal fly ash (FA) i.e. one of the major industrial wastes and sepiolite as natural resources. Although three kinds of zeolites i.e. phillipsite, hydroxysodalite and A-type were formed by hydrothermal treatment of fly ash with NaOH solution, only phillipsite was able to be synthesized selectively by judicious control of all the conditions of reaction temperature, and NaOH concentration and amount. Phillipsite-sepiolite composite was successfully synthesized with similar treatment conditions favorable for phillipsite formation. Thus obtained composite not only retained both the original adsorbing abilities of phillipsite for ammonium ion and sepiolite for water but also had a good molding-ability due to sepiolite. This novel composite adsorbent could be useful for effective usage of industrial wastes and/or natural resources as well as for ammonium ion adsorption under wet environments.

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Synthesis and applicability for biomedical use of barium rare earth oxide silicates were studied. Barium rare earth oxide silicates (Ba_2+xLn_8-x(SiO₄)₆O_2-x/2; Ln=La, Ce, Pr, Nd, Sm, Eu, Gd, Dy) were synthesized by solid state reaction at 1400°C in air for 2h. Except for Ln=Ce, Dy, the synthesized powders were identified single phase of barium rare earth oxide silicates (Ba₂Ln₈(SiO₄)₆O₂) by XRD. The samples were including OH^- and CO₃^2- in O^2- site of the lattice by IR analysis. The powders with Ba₄La₆(SiO₄)₆O type (x=2) compositions were sintered at 1400°C in air for 2h, and the maximum relative density was 96%. Biocompatibility of the barium rare earth oxide silicate ceramics was estimated by in vitro and in vivo tests. Osteoblast-like (MC3T3-E1) and fibroblast (L929) cells were cultured on the obtained ceramics. After cultivation, cell proliferation and many gap junctions between the cells were observed on all the barium rare earth oxide silicate ceramics. It was confirmed that barium rare earth oxide silicates had an affinity to cultured cells. Ba₄Eu₆(SiO₄)₆O is the most biocompatible material for cell proliferation and adhesion in the obtained ceramics, and the compatibility was equal to that of HAp ceramics. The sintered Ba₄Eu₆(SiO₄)₆O was implanted under the skin of Wister rats for 7d. The tissue reaction, observed in the hematoxylin-eosin stained section, indicated that barium europium oxide silicates had a good biocompatibility.

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To clarify the effect of packing powder on densification and translucency of Si₃N₄ ceramics, a Si₃N₄ ceramic doped with Al₂O₃ and Y₂O₃ was fabricated by pressureless-sintering at 1650-1850°C under N₂ atmosphere using a carbon heating-element furnace and a graphite crucible. Three different packing powders were used: BN+Al₂O₃, Si₃N₄+Al₂O₃ and (a raw powder for sintering)+BN. Density measurement, color of sintered body evaluation, optical absorption measurement from 200 to 2500nm of wavelength, X-ray diffraction analysis, oxygen content analysis, scanning electron misroscopy, and transmission electron microscopy coupled with energy dispersive X-ray spectroscopy were conducted. The specimen sintered with BN+Al₂O₃ packing powder at 1750°C kept its original oxygen content after sintering, and reaches almost full density. This specimen was more translucent than the others at its wavelength longer than 800nm. In the case of sintering with (a raw powder for sintering)+BN or without packing powder at 1750°C, the oxygen content in the sintered bodies decreased with the starting mixture and the color of sintered bodies changes to a more black one. The low translucency and black coloring could be attributed to pores and to a change in the microstructure or to Si, respectively. The reaction/decomposition of both Si₃N₄ and SiO₂ was effectively suppressed by sintering using the BN+Al₂O₃ packing powder, without changing composition.

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Graded Ba_1-xSr_xTiO₃ (BST) ceramics, which had a continuously varying graded composition from one surface toward the other of the specimen, were examined with respect to their dielectric property. Specimens were prepared by sintering superposed layers of green compacts of BST solid solutions with different values of x. The electric relative permittivity of a single-phase BST ceramic showed a peak at the Curie temperature, which shifted to lower temperatures with increasing x. On the other hand, the profile of relative permittivity vs temperature of the graded BST ceramic experienced a linear characteristic. Furthermore, its slope could be controlled by changing the volume fraction of each layer. The relative permittivity was 4000-5500±5% in the temperature range from 30 to 110°C.

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Advanced new ceramic materials are expected to be available for use as new energy and information materials, on which devices for solving energy and information problems will be based. The properties of these new materials will be strongly dependent on the atomic arrangements, the direct atomic analysis of which will have been contributed to by HREM. In addition to such direct atomic observation, information from such methods as nano-electron diffraction, electron energy-loss spectroscopy (EELS), energy dispersive X-ray spectroscopy (EDX) and electron holography has being combined recently by progress with the electron gun. It will soon be possible to clarify atomic arrangement, composition, electronic state and magnetic structure of the nano-regions in these advanced materials.

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We researched the realization of novel optical functions of glass by combining an external electromagnetic field induced electronic structure and rare-earth-ions. We reviewed the phenomena, mechanisms, and the applications of photostimulated luminescence induced by X-ray, long-lasting phosphorescence by ultra-violet light, space-selective manipulation of the valence state of rare-earth-ion, and the formation of rare-earth-ion-doped optical waveguide for light amplification by a focused infrared femtosecond laser. The proposed concept will lead to a new possibility in the realization of novel optical functions for rare-earth-ion-doped glasses.

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