Ce³⁺-doped garnet materials have attracted a great deal of attention in w-LEDs and scintillators applications because of their various optical properties. In 2011, we reported intense photocurrent by blue light excitation in Y₃Al_5−xGa_xO₁₂ (Yttrium Aluminum Gallium Garnet, YAGG):Ce³⁺ phosphors with high Ga content. With increasing Ga content in YAGG:Ce, the energy gap between the lowest excited 5d level (5d₁) and the conduction band (CB) decreases because the crystal filed splitting of Ce³⁺ becomes much smaller and the CB energy decreases. Based on the photoconductivity results, we concluded that Y₃Al₂Ga₃O₁₂:Ce³⁺ luminescence is quenched by thermal ionization. Utilizing the thermally assisted photoionization by blue light excitation, we tried to prepare a blue light chargeable persistent phosphor. In 2013, we found that Cr³⁺ ions act as suitable electron traps for persistent luminescence at room temperature in YAGG:Ce³⁺, and successfully developed the blue light chargeable persistent phosphors. In YAGG:Ce³⁺–Cr³⁺ persistent phosphors, the charging process (thermal ionization process) and detrapping process were controlled by CB energy engineering.

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The radioactive decontamination of water, soil and other materials requires cheap and effective adsorbents. Artificial zeolites synthesized from an industrial waste (coal fly ash: Na-P1 type zeolite) and a natural material (diatomite: mordenite type zeolite) have a high Cs⁺ adsorptivity in the adsorption experiments using 0.1 g of the zeolite and 50 mL of up to 7.5 mM CsCl. The coexisting cation suppressed the Cs⁺ adsorption onto the zeolites, and the effect of the suppression was in the order, K⁺ > Na⁺ > Ca²⁺ > Mg²⁺. A thermodynamic analysis proved that the Cs⁺ adsorption onto the two zeolites was exothermic favoring a lower temperature. The artificial mordenite showed a greater Cs⁺ adsorption strength, higher distribution coefficient and lower ΔG°, especially at low Cs⁺ concentrations. Adsorption isotherm analysis by the Langmuir, Freundlich, Temkin and Dubinin-Radushkevich models showed a greater Cs⁺ adsorption selectivity for the artificial mordenite even at a low pH.

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In order to analysis the hydration reaction of fly ash cement, extended Tomozawa’s equation which considers the particle size distribution was applied to the reaction process of mixed system consisting of fly ash and ordinary Portland cement. By measuring the pozzolanic reaction of fly ash and the hydration reaction of ordinary Portland cement, the interaction between each reaction in fly ash cement was quantitatively analyzed. We also derived an equation to analyze the theoretical porosity of the fly ash cement based on the hydration reaction of the mixed system, and applied it to calculate the time dependence of porosity of the fly ash cement. Comparison of the simulated porosity with experimental values revealed that the porosity tend to increase with fly ash content, and after one year of aging, has almost no dependence on the vitrification rate of the fly ash.

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In this study, the effects of Co²⁺ substitution for Mg²⁺ on the sintering behavior and dielectric properties of Ca(Mg_0.92−xCo_xAl_0.08)(Si_0.96Al_0.04)₂O₆ ceramics were investigated. The main phase transformed from Ca(Mg,Co,Al)(Si,Al)₂O₆ to CaCoSi₂O₆ as the x value varied from 0.1 to 0.92. Meanwhile, the sintering temperature decreased from 1250°C (x = 0.1) to 1150°C (x = 0.8 and x = 0.92), and both the dielectric constant and the τ_f value increased with the increase of the x value. Typically, the coexistence of the two phases resulted in a relatively porous structure that lowered the Q×f value of the ceramic system when the x value was 0.4 and 0.5. Sintered at the temperature of 1150°C, a Q×f value of 60,125 GHz with dielectric constant of 8.46 and τ_f value of −49.26 ppm/°C was obtained for the Ca(Mg_0.92−xCo_xAl_0.08)(Si_0.96Al_0.04)₂O₆ ceramics with the x value of 0.92.

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The template ion exchange of chromium cations into FSM-16 (#16 Folded Sheets Mesoporous Materials) for 247 h resulted in a 2.89 wt % incorporation of those cations into the FSM-16, although only a 0.3 wt % incorporation had previously been reported. The XRD pattern of the resultant solid (Cr-FSM-16) showed that the hexagonal structure characteristic of FSM-16 remained after the 2.89 wt % incorporation of chromium cations. XPS could be used to detect the Cr³⁺ and Cr⁶⁺ species on the surface of Cr-FSM-16. A pre-edge peak that was due to a tetrahedrally coordinated Cr⁶⁺ species was confirmed in the XANES spectrum of the Cr-FSM-16, which showed that the coordination state around some Cr species was similar to that around the Si species in FSM-16. With the increase in the amount of chromium cations in FSM-16, its catalytic activity and stability during the oxidative dehydrogenation of isobutane were evidently improved.

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The effect of oxide layer formation on the emissivity of Si–Zr–C–O fibers was examined in this study. In order to form a uniform oxide layer on each fiber surface, the Si–Zr–C–O fiber felt was exposed to air at a high temperature. The oxide layer consisted of SiO₂ (cristobalite) and dispersed 10–25 nm ZrO₂ particles. Whereas, the fiber core itself exhibited no microstructural changes crystallographically or morphologically despite the exposure. The total emissivity of the exposed fiber felt calculated at 1000°C was 87.6 ± 4.1% and exhibited a similar value to the initial total emissivity (89.2 ± 4.2%). These results indicated that the emissivity of the Si–Zr–C–O fiber felt was unchanged irrespective of the formation of the oxide layer when the layer thickness was less than 5–6 µm. Furthermore, the radiation heat transfer performance was theoretically evaluated taking into consideration the diameter degradation of the fiber core itself. This suggests that the decrease in size of the diameter of the fiber core do not have a significant effect on heat transfer in this study range.

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The densification behavior of the green pellets with different densities prepared from hydroxyapatite powders consisting of plate-like particles was investigated. The green pellets were prepared by two methods, hydrothermal hot-pressing and uniaxial pressing, at different compression pressures. The hydrothermal hot-pressing gave the green pellets with densities higher than those using with uniaxial pressing. The shrinkage of the green pellets was observed by calcination at temperature above 800°C. The green pellets with higher bulk density gave the sintered compacts with higher density. When the calcination temperature was increased, densification proceeded with the increase in pore diameter and the decrease of pore volume. Even at temperature below 700°C, the size of pores increased with the increase in calcination temperature without shrinkage of the green pellets. Thus, the green compacts of the same density but with different pore sizes distribution prepared by hydrothermal hot-pressing and uniaxial pressing, had similar pore size distribution after calcination at 700°C, As a result, they had the same densification behavior by calcination at high temperature above 800°C. The densification behavior was found to be dependent on the density of green pellets, but not on the method of preparation of green pellets.

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Platinum nano particles dispersed tungsten trioxide (Pt/WO₃) is a promising hydrogen gas sensor material which can detect it by the change of color. Hydrogen gas sensing properties of Pt/WO₃ thin film strongly depend on its film structure. Particularly, the porosity and the particle size of WO₃ are very important for obtaining good hydrogen sensitivity. The morphology of Pt/WO₃ thin film prepared by sol–gel process can be modified by the heat-treatment temperature and the Ti-doping to WO₃. Pt/WO₃ thin films consisting of small particles and porous structure were obtained by Ti-doping. Especially, Ti-doping was very effective to obtain the small WO₃ particle in spite of a high temperature heat treatment. It was considered that Ti-doping produced oxygen vacancy in WO₃ lattice and this disturbed the densification of the film and the grain growth of WO₃. This sample showed a good response to hydrogen gas exposure, compared with that of non-doped sample. Therefore, it was found that the surface modification by Ti-doping can enhance the optical hydrogen gas sensing property of Pt/WO₃.

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Macro-porous silicon carbide with high porosity around 70 vol %, comprising micrometer-sized spherical porosities and a relatively denser surface layer, was fabricated by a direct blowing and reaction bonding method. The macro-porous Si/phenolic composites with the denser surface layer were prepared through a one-pot process of blowing of novolac resin which changes to the phenolic resin by thermal curing to form macro-porous body and forming the denser surface layer. The composite was then converted into porous SiC by reaction bonding at 1450°C under vacuum. It was found that the bending strength of the macro-porous silicon carbide increased by 30% due to the denser surface layer. This study proposed a novel fabrication method to provide macro-porous ceramics with high porosity and improved strength in simple one-pot process.

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