Variety of functional porous materials in metal oxide, metalloxane polymer and even pure organic polymer compositions obtained by a sol-gel process are reviewed. Specifically, processes including polymerization-induced phase separation have been extensively introduced from theories to practices. The basic concept of hierarchical pore architecture in monolithic materials is explained, together with several examples of successful applications. Depending on the hierarchy, single, double and triple, unique family of materials can be fabricated. Existing and prospective applications and future challenges of the materials are also shown.

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In order to obtain materials with a tailored thermal expansion, in particular zero-thermal-expansion between -50~100°C, the possibility of preparation, thermal expansion behavior and phase transition of Al_2-xM_x(WO₄)₃ (M: Y, Ga and Sc) have been examined. Y was not substituted for the Al site in Al₂(WO₄)₃. Al_2-xGa_x(WO₄)₃ single phase could be prepared in x range as high as 0.4. The phase transition temperature involving abrupt expansion increased with an increase of Ga content, resulting in no phase transition for Al_1.6Ga_0.4(WO₄)₃ between -50~100°C. However, zero-thermal expansion could not be obtained in Al_2-xGa_x(WO₄)₃ at the temperature range. Al_2-xSc_x(WO₄)₃ single phase was obtained for the whole x range. The temperature of the phase transition decreased with an increase of Sc content and the abrupt expansion due to the phase transition disappeared above -50°C for the specimen with x larger than 0.3. The thermal expansion coefficient could be controlled with Sc content and zero-thermal-expansion was observed for the specimens with x around 0.1 and 1.5.

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To investigate the appropriate particle size and addition amounts of BaTiO₃ for developing thin-film Ni electrodes, the effects of the changes in the particle size and addition amounts of BaTiO₃ in Ni electrode paste film was studied. From the relationship between particle sizes of Ni and BaTiO₃ to increase dry film density, it was found that BaTiO₃ with a particle size 0.225 times as large as Ni particles could be tolerated from theoretical considerations and measured data. From the relationship between addition amounts and dry film density where Ni powder with a particle size of 0.4 μm and BaTiO₃ with a particle size of 0.1 μm were used, addition amounts up to 7.5 mass% could increase dry film density without decreasing Ni density. The Ni density invariably decreased with different addition amounts (7.5 mass% to 20 mass%). It was also found that BaTiO₃ addition considerably suppressed shrinkage and that the suppressing effect of the addition amount of 7.5 mass% was slightly smaller, while the effect was mostly invariable with larger addition amounts.

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On two SiC ceramics and a standard fused silica specimen, depth-sensing indentation tests with a Berkovich indenter were carried out at several peak loads. The loading part of the load-displacement curves were statistically analyzed and it was shown that the loading exponent of the relation P ∝ hⁿ was lower than the expected value of 2 in most of the cases. Factors affecting the loading exponent have been considered and evaluated. It was demonstrated that their effect was minimal on the fitting results.

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The extrusion behavior of hydraulic alumina (HA) pastes prepared by hydration of the HA was studied in order to fabricate the porous alumina ceramics by an extrusion technique. While all the HA paste samples cured for over 8 h were hardened by hydration, different extrusion behaviors were observed. In the early stage of hydration (<24 h), water separation from the hardened HA paste was remarkable and the paste was not extruded clearly. On the other hand, even without the addition of an organic plasticizer, the hardened HA pastes cured for a long period (>48 h) showed good extrusion behavior. Furthermore, the water acted as a fugitive material in the extruded green bodies. Consequently, the open porosity of the sintered (at 1400°C for 2 h) alumina ceramics could be controlled over a range of 66.9-71.7% by the addition of water (ratio of water to HA powder: 0.8 to 1.4 by weight) without the use of organic fugitive materials.

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Oxidation behavior of spark plasma sintered (SPS) magnesium aluminum oxynitride (MgAlON) was investigated in this study. Monophase MgAlON without pores was easily obtained and evaporation was sufficiently limited by the utilization of the SPS process. The MgAlON powder was oxidized above 750°C, and a detectable mass gain of the MgAlON plate could not be obtained below 1200°C, because the oxidation reaction was of a very low level and occurred only on the surface. High temperature were favorable to oxidation reaction. According to the isothermal mass gain and evolution of oxidized morphology of the plates oxidized at different temperature, it could be deduced that the oxidation of MgAlON was limited by interface reaction. To analyze more profoundly, an oxidation model was proposed.

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In order to achieve fine phosphor materials with high efficiency, phase-separated glasses and glass-ceramics in Mn-doped ZnO-SiO₂ system, of which composition was xZnO-(100-x)SiO₂ mol% (x=10, 20, 30) in the immiscibility region, were prepared by melting and subsequent heat-treatment process. All the melt-quenched glasses were phase-separated into two phases, i.e. a ZnO-rich phase and a SiO₂-rich one. The SiO₂-rich particles were formed into the ZnO-rich phase in the composition of x=20 and x=30, while the ZnO-rich particles were formed in the SiO₂-rich phase in the composition of x=10. The melt-quenched glass showed the orange-emission at around 625 nm of its peak wavelength. After the heat-treatment on the melt-quenched glasses, the Zn₂SiO₄ (willemite) phase were precipitated, and the glass-ceramics gave strong green-emission at around 525 nm. The intensity of the green-emission of the glass-ceramics in the composition of x=10 was higher than those in the composition of x=20 and x=30 in spite of the same amount of precipitated Zn₂SiO₄ phase.

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Blood proteins have been shown to be effective for osteoconduction and for biomaterial applications. The blood coagulation system progressed rapidly after biomaterial implantation. The interaction of biomaterials with blood coagulation proteins is considered to play an important role in osteoconduction. The purpose of this study was to evaluate the in vitro interaction of the coagulation factor with hydroxyapatite (HA) and the interaction of the coagulation factor with osteoblast-like cells cultured on HA. After 0.2 U/ml thrombin stimulation, the proliferation, alkaline phosphatase (ALP) activity, adherent morphology, and tyrosine phosphorylation of the osteoblast-like cells cultured on HA samples were investigated. Incubation with 0.2 U/ml thrombin stimulation induced an increase in cell number and inhibition of ALP activity. The thrombin stimulation resulted in changes in the morphology of the adherent osteoblast-like cells and static bands recognized as tyrosine phosphorylated proteins lysed from adherent osteoblast-like cells in blot analysis. These results of this study indicated that the thrombin promoted the proliferation, changes of cell morphology, and inhibition of ALP activity. It was suggested that thrombin could affect the cell morphology and proliferation near the HA.

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The microstructure and crystal phase in 2.8 mol% yttria-stabilized zirconia polycrystals were investigated. Starting powders were prepared by wet dispersing and mixing using an agitator mill or by the liquid phase precipitation method. The composites powders were sintered at 1275-1600°C and then analyzed. Solid phase method (SPM) powders showed higher sinterability than those of the liquid phase precipitation method (LPM) powders, and high density samples consisting of fine grains could be obtained at lower sintering temperatures than from LPM powders. Unlike the LPM sample, the cubic and tetragonal phase was formed in the SPM sample at low sintering temperature, because there was the region of high and low Y³⁺ ion concentration in the material. As the sintering temperature increased, the cubic phase decreased and tetragonal phase increased by the progress of the diffusion of Y³⁺ ions. And then, Y³⁺ ions segregated at grain boundaries, and tetragonal grains containing cubic phase at grain boundary regions were formed. The thermal expansion curve for the SPM sample samples sintered at 1275°C exhibited a monoclinic to tetragonal transformation during the heating stage; however, the expansion was linear during the cooling stage, as was the case for both SPM samples sintered at higher temperatures and the LPM samples. The thermal expansion behavior of the SPM sample suggested that the monoclinic phase was essentially not present within the sample, although the transformed monoclinic phase in a surface layer by grinding stresses was exist.

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The effect of additives has been studied to improve the strength of machinable glass-mica ceramics. Titania, Y₂O₃-doped partially stabilized zirconia (Y-PSZ) and celsian (Ba_1-xSr_xAl₂Si₂O₈, x=0, 0.1 and 0.2) powders (10 mass%) were mixed to the previously prepared glass-mica powder (content of F-flogopite: 45 vol%) by using a ball mill. The ball-mill grinding without additives improves the strength from 144 to 172 MPa through the size reduction of mica grains and the increase in sintered density. The addition of TiO₂ and Y-PSZ is more effective to the microstructural refinement and the strengthening (190 MPa/TiO₂, 220 MPa/Y-PSZ). Y-PSZ particles are segregated to the longitudinal ends of mica grains and suppress their longitudinal growth. It is expected that the Y-PSZ particles act as the reinforcements to the glass matrix to enhance the strength. The growth of titania particles under sintering results in the limited effect to structural refinement and the smaller strength than that for Y-PSZ-doped materials. The addition of celsians is further effective to the size reduction of mica grains and related densification to improve the strength (203-241 MPa) markedly. The celsian particles do not show their coarsening as well as Y-PSZ, and dissolve to the glass phase during sintering gradually. It is considered that the dissolution of celsians suppresses the growth of mica grains by changing the chemical composition of the glass phase. The increase of Young's modulus of the celsian-doped glass phase should also contribute to the strengthening.

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To achieve the recycling of the used toner carrier particles, which are ferrite sintered particles coated with polymer film, the hydrothermal treatment of the used toner carrier powder in pure water or H₂O₂ aqueous solution was investigated. The polymer films coated on the ferrite core particles could be mostly removed by the sonication after the hydrothermal treatment in pure water. However, the polymer resin was not completely decomposed by the hydrothermal treatment in pure water, and large amount of pure water (liquid/solid ratio is more than 50 cm³/g) was required for decreasing the carbon content (<0.1 mass%) sufficiently. On the other hand, the polymer films could be completely removed by the hydrothermal treatment in 5.4 mass% H₂O₂ aqueous solution without sonication. In this case, H₂O₂ will effectively work as oxidizer for the polymer resin during the hydrothermal treatment. The recovered ferrite core particles obtained by the present hydrothermal treatment exhibited the same magnetic and/or electric properties as the virgin ferrite core particles. Therefore, it is found that the present hydrothermal treatment in the presence of H₂O₂ oxidizer (5.4 mass%) can be one of efficient recycling processes for toner carrier particles for the electrophotographic machine.

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Co_xFe_3-xO₄ thin films have been prepared on glass substrates by a new aqueous solution-based sol-gel method without involving any organic additives or solvents. This process consists of (1) deposition of precursor (α-FeOOH) thin films in an aqueous solution, (2) adsorption of Co²⁺ on the precursor film and (3) heat-treatment of the Co-bearing precursor film at 673 K in a flow of 55%CO+45%CO₂. The value of x in the resultant thin films fell around 0.73. The crystalline phases, microstructure, thickness, and magnetization behavior were characterized on the cobalt ferrite films.

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The slow cooling of NaCl-TiO₂ mixtures easily grew colorless and transparent Na₂Ti₆O₁₃ whiskers. The whisker growth was conducted by heating a mixture of TiO₂ and NaCl at 1100°C for 10 h, followed by cooling to 500°C at a rate of 5°C•h^-1. Whiskers having average sizes of approximately 450×10 μm were grown from high-temperature solutions containing Ti of 0.3-13 mol%. The whiskers, which were hexagonal prisms, elongated in the <010> directions.

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Hierarchically ordered porous materials composed of imogolite with macro-, meso- and microporous systems were fabricated via colloidal templating. The monodispersed polystyrene particles used as templates were assembled into a close-packed structure on Si substrates. An imogolite sol was infiltrated into voids of polystyrene particles to form composite films. The ordered macropores as well as micro- and mesopores originating from imogolite were confirmed after the removal of templates by either extraction with toluene or calcination. The films were stable in organic solvents, such as acetone, ethanol, and hexane. Although the extracted film was unstable in water, the stability was improved by calcination. Imogolite is found to be a quite useful building block to fabricate hierarchically ordered porous materials with a wide range of porosities without using surfactants as templates.

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Particle oriented strontium bismuth titanate ceramics with high density and oriented structure was successfully developed by a novel processing involving a high magnetic field and reaction sintering. The mixed powder of bismuth titanate and strontium titanate were dispersed in slurry and set in high magnetic field. The a,c-axes bismuth titanate particles were oriented to the applied magnetic field in the green compact. The subsequent reaction sintering resulted in the a,b-axes strontium-bismuth titanate ceramics of obtained structure. The microstructure was highly anisotropic and dense.

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