Development of measures to deal with the shortage of high-quality clays and advancement of new uses for traditional ceramics have been matters of great importance for ceramic industries. As a solution to these problems, this review focuses on the recent development of kaolinite clay synthesis and the use of kaolinite as a humidity conditioning material. (1) Kaolinite clay synthesis has been investigated. During investigations, a spherical-shaped kaolinite, which is crystallographically novel, was discovered. A new reaction vessel was also developed for efficient hydrothermal synthesis of clayey materials. The conditions for the synthesis of fine grain size, high plasticity, and reduced iron content kaolinite were optimized for a bench-scale process as one measure against clayey resource shortage. (2) Materials which autogenously regulate humidity without using electric energy have been studied, and model substances have been developed for porous materials with fine pore size of several nanometers based on the capillary condensation theory. Selectively leached kaolinite showed suitable properties as a humidity conditioning material and synthesis conditions were optimized for a material with uniform pore size and high pore volume. Natural nanoporous materials were also developed as low-cost humidity conditioning materials. It was concluded that elucidation of the relation between water and materials is important for synthesis and application of clays as an environmentally friendly material.

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Anatase of good crystallinity has been developed on titanium substrates by soaking in a 30 mass% hydrogen peroxide solution at 80°C for 8h, soaking in distilled water at ambient temperature for 12h, and subsequently aging in distilled water at 80°C for 3d. The anatase layers exhibit good bioactivity as inducing apatite deposition in Kokubo's simulated body fluid within 2d.

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Copper indium disulfide thin films were successfully formed from water-ethanol (1:1) solutions of nonchlorinated compounds on glass substrates by an intermittent spray pyrolysis deposition method. The adequate conditions were determined to be as follows: spraying rate 1.0ml/s, spraying time 0.5 s, substrate temperature 350°C, and S/(Cu+In) ratio of the spray solution 1.25, with which the yield of the thin films was ca. 3.7%. The CuInS₂ thin film was dark brown and composed of grains 1-3μm in diameter, with a direct band gap of 1.48 eV. The heterojunctign of CuInS₂ and CdS fabricated by this method presents the possibility of the application to a solar cell after the improvement of the short circuit current.

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SnO₂ thin film heteroepitaxially grown on a rutile (100) TiO₂ single crystal substrate exhibits high-density interfacial misfit dislocations and related planar defects. The misfit dislocation network formed on the heterointerface consists mainly of two types of partial edge dislocations with Burgers vectors of 1/2[101] and 1/2[110], to fully relieve the lattice mismatch, and the dislocations inevitably involve inclined (101) and vertical (010) planar defects extending toward the film surface, respectively. Some of the (101) planar defects form wedge-shaped defects, and frequently accompany a single or multiply stacked (101) nanotwin lamellae. Another (011) type of planar defect originating at fused threading dislocations with 1/2[011] Burgers vectors is also detected by plan-view observation, showing the same crystallographic feature as (101) planar defects observed in the cross-sectional (010) projection. The dominant relaxation mechanism through partial edge dislocations suggests the low interfacial energy of the defect plane in the rutile structure, hindering the control of high crystallinity in rutile oxide thin films.

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Cordierite/ZrO₂ nano-composite powders were prepared by a colloidal coating process. Cordierite particles are embedded within a continuous layer of fine amorphous ZrO₂ that was provided by the colloidal processing after drying. Tetragonal ZrO₂ was first formed at 650°C and monoclinic ZrO₂ phase was identified at the calcination temperature of 800°C. After calcination at 850°C, crystallized ZrO₂ particles with the size from 10nm to 30nm homogeneously covered the surface of cordierite particles. Cordierite/ZrO₂ nano-composite powders prepared by a colloidal coating process show better sinterability than that of cordierite/ZrO₂ powder mixtures prepared by a conventional mixing method, and were sintered to a density of over 96% at a low temperature of 1300°C.

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Crystalline thin films of lead chromates, Pb_1+xCrO_4+x(0≤x≤1) could be prepared by RF-magnetron sputtering using a PbCrO₄ target under the atmosphere of 3Pa Argon and 1Pa oxygen. The chromates formed were composed of PbCrO₄ and Pb₂CrO₅, and the relative compositions of the two phases changed rather sensitively with a change in RF power and substrate temperature. A single phase of PbCrO₄ (x=0) was formed when both the power and the temperature were low, (eg; 100W and 300°C), while that of Pb₂CrO₅ (x=1) was under the opposite conditions (eg; 200W and 550°C), with the mixture being obtained under the intermediate conditions.

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In order to decrease the cost of β-alumina for solid electrolytes of AMTEC (alkali metal thermo-electric converter), it is desirable to use low purity starting materials. In this paper, we investigated the influence of impurities such as SiO₂ and Fe₂O₃, which are usually contained in low purity alumina, for several hundreds ppm, on properties and microstructure of β″-alumina. The content of β″-alumina phase and the density decreased with the addition of SiO₂, and the resistivity of β″-alumina increased even with the addition of amounts of SiO₂ as small as 500ppm. Additional SiO₂ formed as a glassy phase at multiple grain junctions, but no secondary phase was observed at boundaries between two adjacent grains. Si segregated along the grain boundaries. It was suggested that the segregated Si suppressed the sintering and increased the resistivity. The addition of Fe₂O₃ did not affect the properties such as content of β″-alumina phase, density and resistance, but the addition of Fe₂O₃ in ≥0.5 mass% resulted in grain growth. Because Fe ions were suggested dissolved in spinel block of β″-alumina, it was considered that Fe₂O₃ did not influence the properties of β″-alumina.

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Ba_6-3xSm_(8+2x)(1-y)Ti₁₈O_54-δ{δ=3y(x+4)} ceramics were developed in this study to lower the sintering temperature as well as to maintain the excellent microwave dielectric properties of tungsten-bronze-type like Ba_6-3xSm_8+2xTi₁₈O₅₄ solid solutions. Ba_6-3xSm_(8+2x)(1-y)Ti₁₈O_54-δ ceramics were prepared by a slight change in the mixing composition from the solid solutions area to Ba₂Ti₉O₂₀ direction on the BaO-Sm₂O₃-TiO₂ ternary phase diagram. Effects of compositional parameters x and y on the density of the sintered body and the microwave dielectric properties were investigated. Ba₄Sm_9.15Ti₁₈O_53.72(x=2/3, y=0.02) ceramics sintered at 1350°C demonstrated the excellent properties including a high relative permittivity (ε_r=81), high quality factor (Q⋅f=10000GHz) and low temperature factor of resonant frequency (τ_f=-13ppm/°C). These properties are almost equivalent to those obtained in Ba₄Sm_9.33Ti₁₈O₅₄(x=2/3) solid solutions which need higher fabricating temperatures than 1460°C. It was also shown that a ball-milling technique strongly affected the density of sintered body and the resulting relative permittivity.

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We have investigated the influence of the sputtering target material on the crystallinity and crystal orientation of aluminum nitride (AIN) thin films. It was found that the type of sputtering target material affects the crystallinity and orientation of AIN thin films. The crystallinity and c-axis orientation of thin films deposited with an aluminum target are higher than those of thin films prepared with a sintered AIN target. The fullwidth at half maximum of the X-ray diffraction (XRD) rocking curves of thin films deposited with aluminum and AIN targets were 3.1 and 8.5°, respectively. From the results of X-ray photoelectron spectroscopy (XPS) analysis, the thin film deposited with an aluminum target contained 2 atom% oxygen, and the thin film deposited with an AIN target contained 8 atom% oxygen. Furthermore, the AIN target contained 3.1 atom% oxygen by fusion extraction analysis. This suggests that the oxygen included in the AIN target disarranges the crystallinity and orientation of the AIN thin films.

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Porous materials of AlOOH-Al₂O₃ were prepared by precipitation of aluminium chloride solution using aqueous ammonia, and by heating at various temperatures below 400°C. The obtained porous materials showed steep increase of water vapor adsorption in the relative humidity range of 55-90%. This porous material is, thus, considered to be a candidate for intelligent humidity control materials (Humidity Self-controlled materials). Pores formed by sublimation of coexisting ammonium chloride in the sample contribute to the improvement of the humidity conditioning property.

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To develop a humidity self-control material, mesoporous powder was prepared from kaolin by a selective leaching method and a porous fired body was formed upon firing after pressing with adding organic binders. The humidity conditioning ability was evaluated by the B-value method. The B-value, specific surface area, total pore volume, pore size distribution, and water vapor adsorption of the selectively leached kaolin ceramics were compared with commercially available humidity conditioning ceramics. The selectively leached kaolin ceramics showed the highest B-value among the humidity conditioning ceramics investigated and this result is considered to be obtained because of a narrow pore size distribution at around 1-4nm in pore radius. The pore size necessary to show capillary condensation at relative humidity of 60% was calculated to be about 1.5nm in radius based on the Kelvin's capillary condensation theory. This confirmed the importance of a narrow and fine pore distribution.

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The function of oxygen storage capacity (OSC) is very important to improve a performance for an automobile exhaust catalyst. CeO₂-ZrO₂ solid solution has an excellent OSC, and is available for a catalytic promoter. In this paper, OSC of the CO reduced CeO₂-ZrO₂ solid solution having various composition loaded with Pt was estimated by thermo gravimeter, and the phases and the crystalline structure of the reduced CeO₂-ZrO₂ solid solution were studied by X-ray diffraction method. The maximum total OSC-value of the reduced material occurs at the composition of 50mol% CeO₂-50mol% ZrO₂. The maximun value is about 753μmol O₂/g-solid solution, which is about twice the value (416μmol O₂/g-solid solution) of the attritionmilled CeO₂-ZrO₂ solid solution, and 5 times higher than that (150μmol O₂/g-solid solution) of the material synthesized by conventional impregnation. The reduced material consists of Ce₂Zr₂O₈ and CeO₂ solid solution in the composition range from 30 to 50mol% ZrO₂. The reduced material consists of the mixture, Ce₂Zr₂O₈ and ZrO₂ in the composition range from 50mol% ZrO₂ to 100mol% ZrO₂. The presence of Zr⁴⁺ near Ce⁴⁺ makes the expansion easier enhancing further valence change, because Zr⁴⁺ is very small in volume. Regular distribution of Ce and Zr ions would make it possible to place Zr⁴⁺ in the nearest position to Ce ion. This would be the reason why the partial OSC of Ce₂Zr₂O₈ is much higher than the complete solid solution.

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Phosphosilicate (P₂O₅-SiO₂) gels with a P/Si molar ratio of 1.0 heat-treated at 150°C were found to retain a high conductivity of 1.5×10^-2S·cm^-1 even after holding at a temperature of 130°C at a relative humidity of 0.7% for about 400 min. On the other hand, the conductivity of the porous silica gels impregnated with 5M H₃PO₄ largely decreased from 1×10^-2 to 6×10^-6S·cm^-1 during holding under the same conditions for about 400 min. The difference in the changes of conductivities between phosphosilicate gels and H₃PO₄-impregnated porous silica gels with holding time indicates that the former can retain larger amounts of adsorbed water at 130°C than the latter. Condensed structural units with Si-O-P-OH groups in the phosphosilicate gels are expected to enhance the retention of the adsorbed water in the gels aiid improve the proton conductivity even at relatively high temperatures and low humidity conditions.

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The effect of various experimental conditions on deposition efficiency (D.E.), i.e., the ratio of the deposited to flowed amount of powder in electrophoretic deposition (EPD), was investigated using α-Al₂O₃ powder dispersed in ethanol. The flowed amount was estimated with a simple equipment, i.e., a suspension container with a barrier and shutter which separated it into two parts. The effect of applied voltage, the amount of added HCl solution in disperse medium and the particle size distribution of the powder on the D.E. were studied. All D. E. values obtained in this study did not exceed 100%. This means that all of the flowed particles did not immediately deposit on the electrode. The fast flow, caused by a high electric field or a high zeta potential of the particles, slightly decreased the D. E. value. A slight change of dispersion state by addition of HCl solution to the suspension largely affected the D. E. value. Furthermore, the existence of a critical limit in the particle size distribution of starting powder for large D. E. was suggested.

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