The intermetallic compound, MoSi₂, has great potential as an elevated-temperature structural material but it exhibits some undesirable properties such as low fracture toughness and low strength at elevated temperatures. Improvement of these properties can be achieved by reinforcing MoSi₂ with the addition of SiC particles or whiskers, or by alloying it with Mo₅Si₃. The preparation of MoSi₂ composites from powders gives rise to an oxidation problem since SiO₂ covers the raw powder. To avoid this problem, the material must be prepared in situ. In this work, multiphase composites based on the Mo-Si-C system have been prepared using a solid-state displacement reaction between Mo₂C and Si. Samples were prepared from a mixture, containing different proportions of Si and Mo₂C powders, which was pelletized under vacuum at 40MPa and heat-treated in argon. The pieces obtained exhibit different proportions of SiC, MoSi₂ and Mo₅Si₃. The microhardness obtained ranges from 12 to 14GPa, and K_c is over 8MPa·m^1/2, which is higher than that of pieces made of MoSi₂ only.

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Polyhydroxoaluminum (PHA) solutions produced transparent gels on drying. These gels were transformed into activated aluminas upon heating. To obtain activated alumina having uniform pores, various amounts of tetramethylammonium chloride (TM) were added to the PHA solutions followed by drying to form PHA-TM composite gels. The γ-alumina obtained from the composite gels having ≥30% TM content showed a sharp monomodal pore size distribution in the range of 3 to 4nm, depending on the heating temperature in the range of 400 to 900°C. The γ-alumina gave the highest pore volume of 0.25cm³·g^-1 at 400°C. On the other hand, the γ-aluminas obtained from the composite gels having TM content below 20% showed a bimodal pore size distribution in the range from 3 to 8nm. These results indicate that pore sizes of γ-alumina can be precisely controlled by the heating temperature for composite gels having ≥30% TM content.

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The products of reaction between Pb(Zr_0.53Ti_0.47)O₃ (PZT) and PbO-B₂O₃ glasses at 850°C were studied using powder and bulk PZT samples. PZT dissolved in glass phase and solid products were precipitated. The reaction zone composed of glass phase and solid products was formed between bulk PZT and glass. As the B₂O₃ content in the glass increased, the amount of dissolved PZT and the thickness of reaction zone increased. When glasses with 40 and 60mol% B₂O₃ were used, the solid products were Ti-rich PZT and ZrO₂ (ZrO₂-TiO₂ solid solution), which were expected from the phase diagram of the PbO-ZrO₂-TiO₂ system. When a glass with 80mol% B₂O₃ was used, the solid products were ZrO₂ and TiO₂, which were supposed to be formed by non-equilibrium reaction sequences. The microstructure of the reaction zone depended on the chemical composition of glass, indicating that the solubility of constituent oxides of PZT was dependent on glass composition.

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The formation process of 60Li₂S⋅40SiS₂ lithium ion conducting materials prepared by mechanical milling was investigated by X-ray diffraction (XRD), ²⁹Si magic angle spinning nuclear magnetic resonance (MAS NMR), X-ray photoelectron spectroscopy (XPS), and scanning electron microscope (SEM) observation. Upon mechanical milling for only 1h most SiS₂ particles reacted with Li₂S crystals to form partially amorphous materials. Such material reacted with the residual Li₂S crystals by further mechanical milling treatments, until the composition of the amorphous part became the nominal one. Since the fully amorphous part became dominant in a continuously percolated structure, the ion conductivity could be greatly improved from 10^-10 to 10^-4S·cm^-1 at room temperature.

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This paper describes the friction properties of cluster diamond/glassy carbon (CD/GC) composites and graphite cluster diamond/glassy carbon (GCD/GC) composites as self-lubricating materials. CDs and GCDs in the shape of superfine particles are intended as solid lubricants. Friction tests were performed on several friction surfaces by varying sliding velocity and load. Testing was carried out in three friction environments (i.e., ambient air, mineral oil and distilled water). The results of these tests revealed that the friction behavior of CD/GC and GCD/GC composites is mainly influenced by both load and CD (or GCD) content in the composites. Their friction coefficients decreased as the load decreased under low load and low sliding velocity in ambient air. In addition, little influence of the friction environments was observed in the friction properties. Consequently, CD/GC and GCD/GC composites are promising as self-lubricating materials, particularly under low-load conditions.

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Rare-earth-doped ceria powders (Ce_0.8R_0.2O_1.9, R=Yb, Y, Gd, Sm, Nd and La), prepared by oxalate coprecipitation, were sintered at 1600°C in air. All X-ray diffraction patterns of the samples could be indexed as those of a cubic fluorite structure. The measured lattice parameter and density were well explained by the oxygen vacancy model associated with the substitution of a rare-earth-dopant for cerium. The observation of rare-earth-doped ceria ceramics by high-resolution transmission electron microscopy indicated that no crystalline or amorphous secondary phase formed in the grain interior or at grain boundaries. The rare-earth-dopant elements dissolved uniformly in the bulk and at grain boundaries.

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Imperfectly ordered KAlSiO₄ shows a greatly increased uptake of Ni²⁺ from solution which motivated this study of the state of Ni²⁺ in Ni-exchanged KAlSiO₄ using X-ray photo-electron spectroscopy (XPS), X-ray fluorescence (XRF), powder X-ray diffraction (XRD), extended X-ray absorption fine structure (EXAFS) and solid state nuclear magnetic resonance spectroscopy (NMR). The imperfectly ordered KAlSiO₄ was synthesized by solid-state reaction of kaolinite with K₂CO₃ at 550°C for 24h. The Ni-exchanged KAlSiO₄ samples were obtained by treatment in a solution containing 10^-3-10^-1M NiCl₂ buffered with 0.5M NaCl at 60°C. Comparison of the surface and bulk chemical compositions analyzed by XPS and XRF indicated that the Ni²⁺ sorbed on the KAlSiO₄ is largely concentrated at the surface. The XRD pattern of the Ni-exchanged KAlSiO₄ showed weak broad peaks corresponding to a phase with a layered structure and a change in the halo pattern of the KAlSiO₄. EXAFS analysis confirmed the presence of a Ni-containing layered double hydroxide (LDH; Ni_1-yAl_y(OH)₂X_y⋅nH₂O) as indicated by the interatomic Ni-Ni distance and Ni coordination number. The ²⁹Si MAS NMR showed shift and peak splitting corresponding to an increase in the degree of polymerization of the SiO₄ tetrahedra forming the framework of the tridymite-type structure and the ²⁷Al MAS NMR showed an increase of six coordinated Al in the Ni-exchanged KAlSiO₄. It is concluded, from all these results, that the Ni²⁺ in Ni-exchanged KAlSiO₄ forms a Ni-Al LDH-like phase on the surface of the KAlSiO₄. This is considered to be the main reason for the higher Ni²⁺ uptake compared with various other cations adsorbed on imperfectly ordered KAlSiO₄.

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Hg-based superconductors, Hg_0.8M_0.2Ba₂Ca₂Cu₃O_y (Hg (M) 1223; M=Cr, Mo, W, In, Ru and Sn) were prepared using a high pressure technique and their superconducting properties, T_c and B_irr, were investigated. Nearly single-phase samples of Hg (M) 1223 (M=Cr, Mo, In and Ru) were obtained by heating at 1000-1100°C for 1-4h under 6GPa. T_c of the substituted samples was lower than 135K. Enhancement in B_irr was observed in Hg (Ru) 1223. A possible explanation for this phenomenon was proposed.

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A photoreactive [Pb-Ti] precursor was successfully synthesized by chemical modification of metallo-organics with alkanolamine. The synthesized precursor showed strong absorption at wavelengths shorter than 350nm, being effective for the absorption of ultra-violet light. Photolithographic patterning of [Pb-Ti] precursor film on MgO (100) substrate could be prepared by UV-irradiation. The patterned precursor film yielded highly oriented lead titanate (PbTiO₃) of perovskite single phase by rapid heating at 550°C. PbTiO₃ films with a thickness of about 100nm could also be synthesized on a Pt/quartz substrate using cyclic treatments of coating/UV-irradiation. Compared with the conventional method, this synthetic method was found to be useful from the following viewpoints: (1) preparation of thicker film was possible within short time; and, (2) synthesis of PbTiO₃ single phase with a uniform microstructure could be obtained.

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Emission and excitation spectra of X₂-Y₂SiO₅ doped with Ce³⁺ ions have been investigated at room temperature, in which Ce³⁺ ions were added by using different starting materials of CeO₂ (IV) or Ce(NO₃)₃⋅6H₂O (III). The emission spectra were analyzed on the base of a Gaussian function to investigate the detailed optical characteristics of Ce³⁺. Y₂SiO₅ doped with CeO₂ exhibited a broad spectrum with a tail in the range from 500 to 600nm. On the other hand, Y₂SiO₅ doped with Ce(NO₃)₃ gave a relatively sharp spectrum shorter than 500nm. With using fitting parameters based on Gaussian function, Y₂SiO₅ doped with CeO₂ was found to show an additional Gaussian band around 430nm in contrast to the Ce(NO₃)₃ doped one. Furthermore, the fluorescence spectra under the excitation at 330nm indicated that a broad spectrum with a peak at 430nm is only observed in Y₂SiO₅ doped with CeO₂. Such an emission spectrum is similar to the new Gaussian band at 430nm estimated from the parameter fitting. This implies that the new band actually exists, contributing to the tail of the emission spectra. These results give a new information on the occupation site of Ce³⁺ in the X₂-Y₂SiO₅ matrix.

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Adsorption property and surface reactivity on the top and the bottom faces of float glass were compared, and factors governing these properties were investigated. It was found that both the adsorption property with organic substances and the reactivity with silane coupling reagents were higher on the bottom face compared with the top face. It was also revealed by time-of-flight secondary ion mass spectrometry (TOF-SIMS) measurements that the difference in these properties was attributed to the density of surface OH group as adsorptive and reactive sites. The high density of surface OH group on the bottom face was explained in terms of the large surface concentration of tin penetrated into the glass during float process. The reason for the surface OH group density dependence on the tin concentration can be explained by X-ray photoelectron spectroscopy (XPS) O1s peak analysis: the SnOH group easily forms as compared with the SiOH group because of the high reactivity with water due to high Lewis basicity. Furthermore, it was found that the surface reactivity of various metal oxide materials was also explainable on the basis of Lewis basicity governing the formation of surface OH group. The analytical results leading to the successful control of the adsorption property and surface reactivity were discussed in detail.

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Polycrystals of ErRh₃B_x are synthesized by arc melting. The compounds of ErRh₃B_x have a perovskite-type cubic structure (space groups Pm3m). The nonstoichiometric phase exists for the boron content from x=1.000 (20mol% B) to 0.61 (13.3mol% B). The lattice parameter of a depends on x, and varies linearly from a=0.4151nm (x=1.000) to 0.4063nm (x=0.61). The micro-Vickers hardness of the ErRh₃B_x compaunds increases with increasing their B content. The hardness of ErRh₃B_1.000 (20mol% B) sample is 8.6±0.3GPa. The thermo gravimetric curve indicates that the onset-temperature of oxidation for ErRh₃B_1.000 is 1303K. The weight gain of ErRh₃B_1.000 during heating in air to 1473K is 0.7%.

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Coating films prepared from methyltriethoxysilane (MTES) showed flexibility and good adhesion to stainless steel sheets (SUS). However, it is necessary for the coated SUS substrates to have more flexibility in the practical use, because these materials are usually subjected to the vigorous forming processes in the practical use. In this study, organic-inorganic hybrid coatings were prepared by the incorporation of the blocked isocyanate into the sol prepared from MTES. It was found that the thermally altered blocked isocyanate, and free N=C=O groups were regenerated, which were successfully cross-linked to the inorganic network derived from MTES during the firing process. Elongation of the hybrid films was increased with an increase in the content of incorporated blocked isocyanate. Adhesion of the MTES-derived coating films to SUS substrates was drastically improved by the hybridization. The good adhesion of the hybrid films was achieved by suppression of the crack formation at the bent portions.

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Excellent transparent YAG (Y₃Al₅O₁₂) ceramics containing Ce additives of 0.06 to 3.8mol% and small amount of Si as sintering aids were fabricated by a simple solid-state reaction method using high-purity powders of Y₂O₃, Al₂O₃ and CeO₂. Ce: YAG ceramics, after vacuum sintering at 1750°C for 10h, became fully transparent. Ce: YAG ceramics obtained was confirmed optically perfect isotropy in the dark field image under crossed nicols using a polarizing microscopy. When the electron beam irradiated to Ce: YAG ceramics with perfect optically isotropy and pore-free structure, the fluorescent image for the electron beam became extremely homogeneous and clear.

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To investigate the possibility of developing a humidity self-control material, mesoporous-powder prepared by selective leaching method was pressed and fired with adding organic binders. A comparison was carried out with a material fired with clay binder. The specific surface area, total pore volume, pore size distribution, and water vapor adsorption of the fired bodies were measured for samples prepared at various firing temperatures, to evaluate the humidity controlling properties. The amount of water vapor adsorbed by the fired bodies decreased with increasing the firing temperature of the bodies. The amount of water adsorption on the body fired at 900°C (GK33-900) at a relative humidity between 30 and 60%, and between 60 and 90% was, however, similar to that of the original powder. It was found that the dry pressing process with organic binders was more suitable than that with clay binders and it was possible to manufacture the fired body preserving the humidity self-control property.

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Translucent Al₂O₃ ceramics could be successfully produced by slip casting using a gypsum mold, provided that CaSO₄ impurities, which had penetrated into the green compacts from the gypsum mold, were removed by the wash of calcined compacts with HCl aqueous solution. Al₂O₃ ceramic samples were sintered at 1350°C for 2h under vacuum. The relative densities of the sintered Al₂O₃ ceramic compacts with the HCl treatment were slightly higher than those of the untreated samples. Grains in the HCl-treated samples grew homogeneously with about 1μm in diameter. The sintered Al₂O₃ ceramics with the HCl treatment were translucent. Transmittance values were measured by spectroscopy. Transmittance values in the HCl-treated samples increased from 0 to 12% as the wavelength increased from 300 to 900nm.

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Structural change of OH-free fused quartz tube by blowing with hydrogen-oxygen flame was investigated by optical adsorption. The blowing increased the OH content within _??_500μm from the surface. The maximum OH content was ca. 1100ppm.

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Growth enhancement of the bone-like layer on electrically polarized hydroxyapatite was investigated. Dense hydroxyapatite ceramics were electrically polarized in a dc field. For estimation of the bone-like grown layer on the polarized hydroxyapatite ceramic surfaces, polarized specimens were immersed not only in a simulated body fluid (SBF) with the inorganic ion-concentrations equal to those of human blood plasma, but also in minimum essential medium (MEM), and in MEM supplemented with 10% foetal bovine serum. After several days of immersion, the grown crystal layers were observed by scanning electron microscopy, and analyzed by X-ray diffraction and IR spectroscopy. As a result, the bone-like hydroxyapatite crystals grew rapidly on the negatively polarized surface, while the growth was restricted on the positively polarized surface both in SBF and MEM. The morphology of the grown layers on the polarized surface was different among the immersion fluids. The growth enhancement of the bone-like layer on the polarized HAp was demonstrated in multiple ions based on inorganic and organic groups. It was considered that the charged surfaces of the polarized HAp ceramics accelerated the growth of the bone-like layer on the negatively polarized surface, but was inhibited on the positively polarized surface.

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The success of traditional glass industry depends on the flexibility in shaping the products by using the viscous flow of glass. The metal industry also utilizes various type of plastic forming, for example, forging, extrusion, and drawing. On the other hand, ceramics are very hard and brittle materials that fracture with almost no plastic deformation. The ceramic components have been usually fabricated by powder processing and by precise grinding after the sintering.
Fulrath, Rice, and Nishikawa performed their pioneering works on deformation processing of ceramics in 1960s. The concept of “superplasticity” appeared in metallurgical field in those days, and attracted the interests of many materials scientists. The superplasticity refers to extraordinarily large elongations of polycrystalline solids at elevated temperatures. The search for superplasticity in ceramics has been made by Morgan, Bradt, Raj, and Evans. However, it remained as a dream of ceramists to realize the superplastic elongation as an intrinsic nature of polycrystalline solids without the help of viscous flow of intergranular glass phase.
The finding of superplasticity of Y₂O₃-stabilized tetragonal ZrO₂ polycrystals (Y-TZP) by Wakai and a series of subsequent reports triggered the intensive research on ceramics superplasticity internationally: “Superplasticity of Yttria-Stabilized Tetragonal ZrO₂ Polycrystals, ” Advanced Ceramic Materials, 1, 259 (1986), “Superplasticity of TZP/Al₂O₃ Composite, ” Advanced Ceramic Materials, 3, 71 (1988), “A Superplastic Covalent Crystal Composite, ” Nature, 344, 421 (1990).
Wakai and coworkers demonstrated that the superplasticity is a common nature of micro grain ceramics that could be observed not only in zirconia, but also in composites, hydroxyapatite, silicon nitride and silicon carbide. The superplasticity can be applied to forming components (superplastic forming), strengthening and toughening (superplastic forging), shaping components concurrent with densification (superplastic sinter forging), and superplastic bonding. Furthermore the superplastic deformation plays an important role in stress assisted densification processes such as hot isostatic pressing and hot pressing. The researches on ceramics superplasticity in the last decade of 20th century are summarized in several reviews; Jimenez-Melendo and Dominguez-Rodriguez, J. Am. Ceram. Soc., 81, 2761 (1998) on zirconia, Wakai, Kondo, and Shinoda, Current Opinion in Solid State & Materials Science, 4, 461 (1999) on silicon nitride and silicon carbide.
The paper, which is selected in this issue, is one of the early papers on superplasticity of zirconia. The relationship between flow stress and strain rate was necessary for superplastic foming in compression. The flow stress was a function of grain size, and it showed that the grain refinement was essential for superplastic deformation. This was the first paper which pointed out that the major mechanism of superplasticity in zirconia was the grain boundary sliding of submicron grains.

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