Porous ceramics incorporate pores to improve material properties, including thermal insulation, while maintaining inherent ceramic properties such as corrosion resistance and high mechanical strength. Conventional porous ceramics are usually fabricated by insufficient sintering that excludes pores; thus, it must be terminated in an early stage to maintain high porosity. The premature termination leads to degraded strength and durability. We developed a superplastic-foaming method to fabricate ceramic foams in the solid state. In this method, the inserted foam agent evaporates after full densification of the matrix at the sintering temperature. Closed pores expand by superplastic deformation driven by the gas pressure. The pores are introduced after sintering the solid polycrystal. Then, only closed pores are introduced, improving the insulation of gas, sound and heat. The pore walls are fully densified for high mechanical strength. Compared to the melt-foaming method, this technique is practical because the fabrication temperature is far below the material’s melting point, and it does not require moulds. In addition, the size and location of the pores can be controlled by the amount and position of the foam agent.

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The interaction between solid surfaces was evaluated by scanning probe microscopy using a colloidal probe. The dispersant provided a repulsive force between the solid surfaces at less than 30 nm. On the other hand, the binder provided a bridging force between the solid surfaces for retraction at less than 500 nm. Because of the complicated nature of the forces acting between the surfaces, the separation distance between ceramic particles (SDP) was calculated. Moreover, the relation between the agglomeration/dispersion of Al₂O₃ particles and the calculated SDP were discussed. As an extension of these results, Al₂O₃ pastes were prepared for tape casting from a viewpoint of the SDP. The tape casting of nanoparticles, which is generally difficult, was successful. On the basis of these fundamental studies applied to environmental functional materials, porous ceramics having oriented pores were prepared by an extrusion method. The obtained porous ceramics demonstrate high capillary action and are used for the relaxation of an urban heat island. Porous ceramics having nano-sized pores were prepared by a slip casting method. The porous filter has CO₂ gas separation ability by using surface diffusion.

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Phosphosilicate glasses were prepared using both sol–gel and conventional melting methods, and proton conductivity of these glasses was investigated. Glasses prepared by sol–gel method are porous, and proton conductivity increases significantly by absorption of water. The pore structure, especially pore size, is a crucial factor in order to obtain high proton conductivity in wide temperature/humidity ranges. On the other hand, in the case of glasses prepared via conventional melting method, proton incorporation into the glasses as well as decreasing alkali cation conductivity by utilizing the mixed-alkali effect are indispensable. Proton conduction mechanisms in these glasses are discussed.

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Three solid solutions [(1 − x)LNN-xBaTiO₃ (BT), xBaZrO₃ (BZ) and xK_0.5Ba_0.5Ti_0.5Nb_0.5O₃ (KBTN)] based on (Li_0.12Na_0.88)NbO₃ (LNN) with the rhombohedral symmetry were prepared by conventional solid state reaction and their dielectric property was investigated. In the LNN-BT system in x ≤ 0.6 a secondary phase was observed as well as the perovskite-type phase and the psudo-cubic and tetragonal single phases were observed in 0.7 ≤ x ≤ 0.94 and 0.95 ≤ x ≤ 1.0, respectively. In LNN-BZ and LNN-KBTN systems single phases of the compounds with the rhombohedral symmetry were formed in x ≤ 0.05. The length of the a-axis increased with content of BZ or KBTN and that of the c-axis was almost unchanged except x = 0.1 for LNN-BZ. The secondary phase with the tetragonal tungsten bronze-type (TTB) structure was observed in wide composition range of these solid solutions, and Li_xBa₂NaNb_5−xM_xO₁₅ (M: Ti, Zr) with the TTB-type structure was prepared and their crystal structure and dielectric property were investigated.

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Randomly-oriented and b-axis oriented mordenite seed layers, which were pre-fabricated out of and in a strong 12 T magnetic field, were hydrothermally treated in clear reaction solutions with molar ratios of 6Na₂O:Al₂O₃:30SiO₂:xH₂O (x = 1500, 3500 and 10000). Crystal growth of the seed particles only slightly occurred in the solution of x = 10000, but occurred in the solutions of x = 1500 and 3500, giving rise to densified films. However, the films treated with x = 1500 were composed of two layers with different morphologies; i.e., the precipitation of crystals from the solution was considered to induce the upper layer in the bi-layered films. Homogenized films were formed in the solutions of x = 3500. The initial orientation of the seed layer was retained in the continuous films treated at x = 3500. Thus, dense, continuous mordenite films with random and b-axis orientations were successfully fabricated from random and b-axis oriented seed layers by hydrothermal treatment in the clear reaction solutions at the molar ratio of 6Na₂O:Al₂O₃:30SiO₂:3500H₂O.

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Micrometric 2D arrays of Ba(NO₃)₂ were spontaneously produced on a glass substrate through crystal growth induced by evaporation of water from viscous solutions containing polyvinyl alcohol (PVA). Specific trigonal microarrays were formed when the {111} face of Ba(NO₃)₂ was parallel to the substrate. Aligned triangles, honeycomb frames, and thin rod arrangements were obtained by adjusting the concentrations of Ba(NO₃)₂ and PVA. The formation of the particular microarrays is achieved through zigzag growth of the cubic crystal in the thin polymer matrix.

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In order to develop non toxic magnetic beads, influence of Fe addition to the hydroxyapatite was investigated, and Fe doped hydroxyapatite was prepared by hydrothermal process at 423 K. The crystal phase of obtained samples had a hydroxyapatite related structure, and α-Fe₂O₃ phase generated as a second phase at the ratio of Fe more than 5 mol % additions. The ratio of α-Fe₂O₃ phase increased depending on the ratio of Fe, and 40 and 73% of added Fe existed as α-Fe₂O₃ phase at 5 and 10 mol % addition, and the estimated doped amount of Fe is about 2.1 mol % for 5 mol % addition and 2.7 mol % for 10 mol % addition, respectively. All samples showed paramagnetic property, and magnetization of sample increased depending on the ratio of Fe. The maximum magnetization of 0.63 Am²/kg was obtained at the Fe ratio of 10 mol %.

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We prepared titanium dioxide (TiO₂) photocatalysts sensitive to visible light, namely copper(II) [Cu(II)]-grafted tungsten and gallium co-doped TiO₂ (Ti_1−3xW_xGa_2xO₂, x value is up to 0.12), based on the concept of narrowing the band gap of TiO₂ by positively shifting its conduction band (CB) edge to a lower energy level and the catalytic multi-electron reduction of oxygen by Cu(I) ions [H. Yu, H. Irie, K. Hashimoto, J. Am. Chem. Soc., 132, 6898 (2010)]. Using this approach, the optical band-gap energy of TiO₂ was decreased to ~2.8 eV, and band-gap narrowing was confirmed by measuring the action spectrum for oxygen evolution from water in the presence of iron ions [Fe(III), from FeCl₃]. The Cu(II)-grafted Ti_1−3xW_xGa_2xO₂ (x = 0.12) photocatalyst effectively decomposed 2-propanol to carbon dioxide (CO₂) via acetone under visible light (400–530 nm, 1 mW/cm²) with a CO₂-generation rate of 0.30 µmol/h. Grafting Cu(II) ions after the hydrochloric acid treatment of Ti_1−3xW_xGa_2xO₂ (x = 0.12) increased the CO₂-generation rate to 0.40 µmol/h.

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MgO-doped Al₂TiO₅ ceramics were reactively sintered from commercial α-Al₂O₃, TiO₂ anatase and MgCO₃ (basic) powders. Powder mixtures with molar ratio of Al₂O₃:TiO₂:MgO = 1:1:0, 1:0.95:0.05, 1:0.90:0.10, and 1:0.85:0.15 were prepared by wet ball-milling with ZrO₂ media. The green pellets were sintered at 1300–1500°C for 2 h in air to obtain dense samples. With changing the MgO doping amount, Al₂TiO₅/Al₂O₃, Al₂TiO₅/MgAl₂O₄/Al₂O₃, Al₂TiO₅/MgAl₂O₄ composites were synthesized. MgO doping was effective to reduce the Al₂TiO₅ matrix grain size and to reduce the strong anisotropy of Al₂TiO₅, which resulted in fewer microcracks. The maximum strength of samples sintered at 1400 and 1500°C were 106 and 32 MPa (15 mol % MgO), respectively.

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Mono-tungsten carbide (WC) and tungsten (W) have been successfully synthesized and classified by controlling organic–inorganic hybrid precursors. Tungstic acid (H₂WO₄) was dissolved into ammonium water and then citric acid (C₆H₈O₇) as a carbon source was dissolved into the H₂WO₄ solution. The precursors, which were obtained by drying the chemical complex solutions, were heated at 1473 K for 1 h with Ar gas flow by a conventional electric furnace. Classification of WC and W was achieved by controlling the precursor processing conditions. In terms of making WC only, two important processing factors were revealed. One, the C/W molar ratio of an organic–inorganic hybrid precursor should be more than 4.0, and two, the obtained chemical complex should be re-dissolved and aged for more than 24 h. Tungstic ions in the re-dissolved chemical complex solution may be changed into polyanions. The sizes of the obtained WC particles and W metal were approximately 100 nm and 2 µm, respectively.

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We synthesized pure-silica ZSM-48 zeolite with cheap and conventional amphiphilic organic cation, dodecyltrimethyl ammonium cation, as structure-directing agent. Although severe hydrothermal conditions are usually required to utilize organics possessing anisotropic charge distribution, by controlling the water content of the reactant gel, the crystallization was completed within 5 days at 160°C. This approach enabled the ZSM-48 zeolite synthesis with lower synthesis temperature, shorter synthesis period, and higher productivity. Smaller size of the obtained crystals reflected the enhanced nucleation from the concentrated reactant gel. These results suggested that the concentrated system has an advantage in the synthesizing zeolite with an amphiphilic organic cation as structure-directing agent.

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