Surface wettability is dependent to surface energy of the material. Therefore the surface wettability basically reflects its intrinsic surface property and it has been thought that it is hard to be controlled arbitrarily. For example, inorganic materials such like metal oxides usually exhibit relatively hydrophilic property as compared with organic materials. However recent series of studies by our group revealed that photo-induced surface reaction, nanometer scale roughness, nanometer scale physical and chemical heterogeneity affect wettability greatly. This fact clearly shows that the surface wettability of a metal oxide can be controlled from superhydrophilic state to superhydrophobic state. The target of control includes not only static wettability but also dynamic wetttability. Oxide surface with high dynamic hydrophobicity can be obtained by optimizing these factors. Water repellency of developed hydrophobic ceramic surface turned out to be like a polymer surface. The novel technology to control wettability of ceramic surfaces is expected to contribute to various applications.

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The oxidation kinetics of magnesia/carbon (MgO/C) composite has been comprehensively investigated from both experimental and theoretical aspects based on current literatures, from which the shortcoming of theory has been discussed. A new kinetic model was developed to deal with the oxidation of MgO/C composite quantitatively. Effect of temperature and carbon content on the oxidation rate was especially discussed. Incorporation of the experimental data into the new model indicated that our new model could fit the experimental data very well. The kinetic parameter obtained from the new model was also compared with experimental values in literature. Besides the new model can perform a simple calculation, it can also reasonably predict the oxidation behavior based on limited experimental data.

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Noble metals addition to SnO₂ was examined in order to develop high sensitive total volatile organic compounds (T-VOC) sensors with high stability for humidity. The noble metals loaded SnO₂ thick films were prepared, and their sensor responses were measured for various kinds of VOC gases and a T-VOC test gas. The results of the measurements for various kinds of VOC gases showed that simultaneous addition of Pt, Pd and Au or simultaneous addition of Pt and Au were useful for sensitization for VOC gases giving a small response for the unloaded SnO₂ thick films. These sensors could detect 0.056 ppm of the T-VOC test gas, and the sensor responses increased with increasing the concentration of the T-VOC test gas. The series of additives with Pd was effective to improve the stability for humidity. The sensor loaded with Pt, Pd and Au simultaneously satisfied both high sensitivity to the T-VOC test gas and sensor-response stability for humidity. The results of X-ray photoelectron spectroscopy of the sensor showed that most of loaded palladium exists as PdO. In addition, it was suggested by the shift of binding energy of a Sn3d orbit and an O1s orbit that the electronic sensitization was dominant in the sensor. It was supposed that the electronic sensitization was effective for the sensor response stability for humidity. From these results, the combination of the chemical sensitization by Pt-Au addition and the electronic sensitization by Pd addition gives high sensitivity to the T-VOC test gas and stability for humidity to the Pt-Pd-Au loaded SnO₂ thick films, and it is expected that the SnO₂ thick film with Pt, Pd and Au will be applicable to T-VOC gas sensor.

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Submicron-sized α-Si₃N₄ and nanosized amorphous Si₃N₄ powders were sintered by spark plasma sintering at 1700°C for holding times of 60 to 120 s at heating rates of 1.7 to 6.1°C/s with Y₂O₃ and Al₂O₃ sintering additives. The nanostructure control of liquid-phase sintered Si₃N₄ ceramics was achieved by selecting optimum heating schedules such as temperature, holding time and heating rate. Fully dense nanostructured β-Si₃N₄ ceramics with grain size of 150 nm were prepared using nanosized amorphous Si₃N₄ starting powder. The transformation to β-phase in Si₃N₄ ceramics obtained from the nanosized amorphous Si₃N₄ powder was more greatly accelerated than that from submicron-sized α-Si₃N₄ powder.

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It was found that oxide-ion conductivity of Nd-doped CeO₂ (Ce_1-xNd_xO_2-x/2) increased with an increase in Nd content x up to x = 0.2, showing a maximum value at x = 0.2, and then decreased with x. In order to clarify the origin of the decrease in the conductivity of the heavily Nd-doped CeO₂, Rietveld analyses of the X-ray diffraction and neutron diffraction data were carried out, assuming two phases with oxygen deficient fluorite-type and rare-earth C-type structures (0.45 ≤ x ≤ 0.7). The oxide-ion conductivity of the heavily Nd-doped CeO₂ is discussed in relation to the formation of the rare-earth C-type structure, which derives from the oxygen ordering of the defect fluorite-type structure.

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Bi-based glass powders with nanometer size as the additive of conducting paste were directly prepared by flame spray pyrolysis. The mean size of the powders increased from 37 to 52 nm as the concentration of spray solution was changed from 0.05 to 1 mol/L. The nano-sized glass powders prepared by flame spray pyrolysis had broad peaks at around 28° in the XRD patterns. The glass transition temperature (T_g) of the nano-sized glass powders was 365°C. The glass layer formed from the glass powders obtained from spray solution with low concentration of 0.05 mol/L had clean surface at a firing temperature of 400°C. On the other hand, the glass layers formed from the nano-sized glass powders obtained from spray solutions of 0.5 and 1 mol/L had smooth surfaces at a firing temperature of 450°C. Deviation of composition of nano-sized glass powders obtained from the spray solution with low concentration of 0.05 mol/L occurred in the flame spray pyrolysis process. Therefore, crystallization of the glass powders occurred after firing.

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Redox potentials of Fe³⁺/Fe²⁺ in silicate liquids measured by voltammetry were evaluated by comparison with those obtained by other analytical methods. Differential pulse voltammetry was carried out for 20Na₂O·80SiO₂ and 18K₂O·82SiO₂ (mol%) melts doped with 0.5 or 3 wt% Fe₂O₃ and 15Na₂O·9CaO·76SiO₂ and 25CaO·16MgO·9Al₂O₃·50SiO₂ melts doped with 1 wt% Fe₂O₃. Observed half wave potentials (E_1/2) agreed with those of previous voltammetry experiments, however, systematically smaller than E_1/2 calculated from redox ratios measured by wet chemistry and Mössbauer spectroscopy and redox potentials estimated from calorimetric data by about 0.1-0.3 V. The Fe³⁺/Fe²⁺ ratios calculated from the E_1/2 by the voltammetry were always overestimated compared with those by other analytical methods. We could not explain the reason for discrepancy of the E_1/2. It is expected that at least the discrepancy can not result from reduction of oxygen in working electrode, ohmic drop effect and difference between diffusivities of Fe²⁺ and Fe³⁺ in the liquids.

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In this paper, we present the photoluminescence (PL) characteristics of plasma display panel (PDP) phosphors under Xe-He-Ne gas discharge. Under high Xe-content gas discharge, PL intensity of the phosphors significantly enhanced due to the increased 173-nm excitation light. By analyzing the PL properties of the phosphors, it was shown that the luminescence saturation phenomenon greatly influences the PL intensity of PDP phosphor under high Xe-content gas discharge.

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Microstructure control of BaTiO₃/Ag composite was examined from the preparation stage of Ag-deposited BaTiO₃ particles. Uniform BaTiO₃ particles were prepared by hydrothermal treatment of a hydroxide gel. Then Ag nanoparticles were deposited uniformly on the BaTiO₃ particle surface by the reduction of diamminesilver (I) ions using glucose. Dense BaTiO₃/Ag composites were obtained respectively via pressureless sintering and spark plasma sintering of the Ag-deposited BaTiO₃ particles. Although the BaTiO₃ and Ag particles grew well after pressureless sintering, their grain growth was suppressed by spark plasma sintering. The Vickers hardness and dielectric constant of the composites were much higher than those of the monolithic BaTiO₃ sintered body.

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Organic-inorganic hybrid aerogels with polymethylsilsesquioxane (PMSQ, CH₃SiO_1.5) composition have been synthesized by a modified two-step sol-gel process. The precursor alkoxysilane is hydrolyzed in a weakly acidic condition, and subsequently allowed to undergo polycondensation in a weakly basic condition which is brought up by the hydrolysis of urea. Two kinds of surfactant (nonionic and cationic) have been utilized to suppress macroscopic phase separation. The resultant porous morphology could be modified by the kind of surfactant used. Small angle X-ray scattering (SAXS) and nitrogen adsorption have been employed to assess the porous morphology and it is found that the obtained PMSQ aerogels consist of aggregated particles and each particle contains micropores. Compressive mechanical properties have also been discussed based on the obtained information on porous morphology.

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The present investigation reports the application of four different types of filler materials (Al₂O₃, Y₂O₃, SiC and Si₃N₄) for the preparation of particulate-reinforced composites (PRC) by precursor impregnation and pyrolysis (PIP) method. In the oxide filler systems, deterioration by crack formation was observed during repeated processing cycles. The large difference of the coefficient of thermal expansion between the oxide fillers and Si-C-N matrix is considered as the reasons for the deterioration. The PRC made with SiC filler showed the highest values of relative density, strength, Young's modulus, hardness, and fracture toughness among the four types of PRC. The SiC-based PRC also offered the highest thermal mass stability and creep resistance.

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We synthesized a perovskite-type oxynitride, LaTiO₂N, by nitridation of the oxide precursor under NH₃ atmosphere at low temperature and flow rate. We successfully synthesized LaTiO₂N at 1023 K (750°C) under flowing NH₃ gas at a rate of 18 dm³/h using a handmade rotary furnace form the amorphous oxide precursor prepared by a sol-gel technique-polymerizable complex method. The average particle size of the LaTiO₂N sample prepared at 1023 K (750°C) (LTON-750) was smaller than for the LaTiO₂N sample prepared by a conventional solid-state reaction method at 1223 K (950°C) (LTON-SS). The smallest particle size of LTON-750 was estimated at 20-30 nm. The BET surface area of LTON-750, calculated from the N₂ adsorption isotherm, was 35.0 m²/g. This is approximately 2 times greater than that of LTON-SS. Furthermore, LTON-750 and LTON-SS demonstrated the ability to adsorb H₂ at 77 K.

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