A new technology to fabricate low-to-zero shrinkage Al₂O₃-based composites, Reaction Bonding of Aluminum Oxide (RBAO), is presented: Al and Al₂O₃ precursor powder mixtures are intensively milled, compacted, and heat-treated in air, such that Al fully oxidizes to Al₂O₃. The volume expansion associated with the oxidation partially compensates for the sintering shrinkage. The process can be modified by incorporating other metals or ceramic phases to change the final composition, to enhance the mechanical properites, and to further compensate for the sintering shrinkage. Interesting characteristics of this technology are easy green machining without binders, superior mechanical properties of reaction-bonded bodies without final machining (also when green machined), superplastic formability, near-net-shape capability, and broad microstructural and compositional versatility.

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Chemical states of Mn in BaTiO₃ and interactions between Mn and other dopants were studied mainly by chemical analysis and ESR spectroscopy. Chemical analysis showed that the average valency of Mn doped into BaTiO₃ was about 3.4, indicating the occurrence of a significant concentration of oxygen vacancy. The average valency of Mn was scarcely affected by codoping of an equimolar amount of La with Mn, but was markedly lowered by addition of Si. It was assumed that stabilization of La segregated to the grain-boundary region due to La-Mn interaction resulted in suppression of the cation vacancy formation and eventually in protection of adsorbed oxygen ions at the grain boundaries. ESR analysis showed that La³⁺-Mn³⁺ associate was a strong trap center compatible with Mn⁴⁺. The mean valency of Mn in the grain-boundary region of Mn- and La-codoped BaTiO₃ was significantly lower than that in the grain interior.

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Bi₂Sr₂CaCu₂O_x glass and glass fibers were prepared by a conventional melt-quenching method and fiber drawing from a glass plate respectively, and grain orientation behavior of superconducting glass-ceramics and fibers obtained by annealing was examined. At the surface and in the interior of the glass-ceramic fiber, all c-axes oriented parallel to the direction of fiber length. In the bulk glass-ceramics, the oriented grains grew from the surface to the interior of the bulk and the morphology and thickness of the oriented layer were very sensitive to the annealing atmosphere. It is concluded that the oriented layers at the surface were formed by precipitation of the Bi₂Sr₂CaCu₂O_x phase with release of oxygen absorbed during heating.

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Region of α′- and β′-sialons in the Si₃N₄-Yb₂O₃-AlN system, glass forming region of the Yb₂O₃-AlN-SiO₂ system, phase relation of the Si₃N₄-(Yb₂O₃)_0.4(AlN)_0.6-SiO₂ system and properties of oxynitride glasses have been studied. The results are summarized as follows.
(1) In the Si₃N₄-Yb₂O₃-AlN system, region of α′- and β′-sialons has some width.
(2) Lattice parameters of α′- and β′ -sialons tend to increase with increasing amount of additives.
(3) α′- and β′ -sialons coexist with liquid phase at temperatures higher than about 1460°C. Solubility of Si₃N₄ in the liquid of Yb₂O₃-AlN-SiO₂ system is small.
(4) Glass transition temperature and softening temperature of oxynitride glasses in the Yb₂O₃-AlN-SiO₂ system are in a range from 830 to 925°C and from 970 to 995°C, respectively.

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Six kinds of powders in the CaO-P₂O₅-SiO₂-B₂O₃ system were prepared by a sol-gel process. The powders consisted of various Ca/P ratios: 1.50, 1.67 and 2.00. The composites were fabricated by firing the compressed powders at 1100°C for 1h. The relative densities (bulk densities/true densities) of the composites without B₂O₃ were only 65%, whereas those of the composites with 10 mol% of B₂O₃ were as high as 98%. When these composites with B₂O₃ were hydrothermally treated at 160°C for 4-24h in NH₃ solution at a pH of -10, the surfaces of the composites were homogeneously coated with whisker-like hydroxyapatite (HAp) particles. However, no HAp was found from the composites without B₂O₃. The bending strengths of the composites with B₂O₃ remained unchanged after the hydrothermal treatment.

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Dissolution behavior of high-purity α-alumina particles was studied in acidic solutions (pH 2.6-5.5) and basic solutions (pH 7.2-9.3) containing Mg²⁺ ions at room temperature. The amount of dissolved α-alumina was dominated by the solubility limit of aluminium hydroxide formed on the surface of α-alumina. The α-alumina in an acidic suspension of 5 vol% solids dissolved to increase pH of the suspension and to produce a supersaturated solution of Al³⁺ ions in which nucleation and growth of aluminium hydroxide proceeded until the Al³⁺ concentration reached the solubility limit of aluminium hydroxide. Little adsorption of Mg²⁺ ions onto the positively charged alumina surface (<0.5μmol/m²) was examined in the acidic suspensions at pH 4.1-4.3. The amount of alumina dissolved in the basic suspensions was less than that in the acidic solutions. Weakly charged negative alumina surface of 1m² in the basic suspension at pH 7.9 adsorbed Mg²⁺ ions of 1.9μmol.

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Isothermal sintering reaction of a sialon composite containing Y-α′-sialon and β′-sialon has been investigated in the system Si₃N₄-Y₂O₃-AlN. Y-α′-sialon and β′-sialon were formed at temperature≥1450°C. The amount of Y-α′-sialon increased with increasing the holding time at 1450 and 1550°C, while the lattice constant decreased. On the other hand, the amount of Y-α′-sialon increased first and then decreased and accordingly, its lattice constant decreased first and then increased with increasing the holding time at temperatures≥1650°C. These changes are estimated to be closely related to the formation reaction and the thermal stability of Y-α′-sialon.

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The effect of additives on BaTiO₃-based PTC thermistor has been investigated by using metal alkoxides as a molecular precursor. Fine grain PTC thermistor was obtained via alkoxide route. In alkoxide route, the range of Y addition to obtain semiconductive BaTiO₃ was wider than that in a conventional solid state reaction route. Silicon which promotes densification and reduces the sintering temperature was added in the form of silica sol or Si alkoxide. In both cases, an addtion of Si reduced the resistivity of the Y-added BaTiO₃. Generally, Mn was added as a barrier layer modifier and enhances the PTC effect. Thus an addition of Mn increase the resistivity of thermistors. However, in the present experiments, it was observed that the addition of a small amount of Mn lowered the resistivity. This was due to the homogeneous dispersion of a small amount of additives via alkoxide route, which can not be achieved in the conventional solid state reactions.

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High figure of merit, 2.6×10^-3K^-1 at 25°C, was achieved in p-type bismuth telluride ceramics fabricated by hot-isostatically pressing the pulverized metallic powder mixtures. Pulverization behavior of the metallic powders obeyed the Rittinger's low and the resultant thermoelectric properties depended on the pulverizing conditions. Dissolution-condensation mechanism for densification gave rise to the isotropic microstructure and hence isotropic thermoeletric characteristics.

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Preparation of hydroxyapatite (HAp) with elongated diopside grains was studied. Diopside powder with a composition of CaO 23.3 mass%, MgO 14.2 mass%, SiO₂62.5 mass% was added to HAp powder (BET value was 65m²/g) and sintered at 1280°C for 2h. These powders were selected to control the reaction of HAp and diopside and to obtain composites with elongated diopside grains. The bending strength of HApdiopside composite containing 60 vol% diopside was 265 MPa and the fracture toughness was 3.2 MPa·m^1/2. These values were about 2 or 3 times higher than those of HAp. The increase in bending strength of the composite was attributed to an increase in fracture toughness. It was proved that diopside has no general toxicity in cell culture. It is expected that HAp-diopside composite ceramics are useful for artificial bone and dental root.

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Joining of Si₃N₄ to Si₃N₄ was carried out using Ag-Cu filler metal containing Ti, Zr, V and Nb as an active metal. Bonding treatment was performed at 1173 to 1473K for 1h in a vacuum. The shear strengths of the joints brazed at 1173 to 1473K using active filler metals containing Ti and Zr were 150 to 250 MPa. The fracture position of the joints after shear test was the filler metal or mixture of the filler metal and Si₃N₄. On the other hand, the average shear strengths of the joints brazed at 1373K using active filler metals containing V and Nb were 144 and 163 MPa, respectively. The fracture position of the joints using these filler metals was the interface between filler metal and Si₃N₄ in all cases. The active filler metals containing Ti and Zr yielded TiN and ZrN fine grains close to the Si₃N₄. No fine grains were observed in the joint using active filler metal containing V and coarse columnar grains of V₃Si were observed. Therefore, it is concluded that the fine grains of the nitrides formed close to the Si₃N₄ is responsible for the substantial bonding between filler metal and Si₃N₄.

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BaNd₂Ti₅O₁₄ dielectric capacitor materials were pulverized by ball-milling, and the properties of pulverized powders and their sinterability have been studied by XRD, SEM, BET and electrical measurements. The properties of the pulverized powders were largely affected by the material and size of the milling balls. Milling with SiO₂ or ZrO₂ balls improved the sinterability and especially the powders milled by SiO₂ balls were densified at 1000°C that is 150°C lower than the normal sintering tempeature. On the other hand, the powders milled by Al₂O₃ balls exhibited poor sinterability. Dielectric properties of the resulting ceramics made from these powders were also varied according to the milling media. These results indicated that the properties of the powders and of the ceramics can be ascribed to the media wear in pulverized powders.

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Dense barium metaplumbate (BaPbO₃) (BPO) thin films with good metallic conduction have been produced by a metal-alkoxide method. Addition of a small amount of triethyleneglycol was effective to obtain smooth films. Thin films were deposited on either cleaved MgO (100) single crystal substrates (MgO (100)) or oxidized single crystal Si (100) wafers (SiO₂/Si) by spin coating. Single-phase BPO films were obtained by firing at 500°C in O₂ flow when a combination of Ba(OCH₂CH₂OCH₃)₂, Pb(OCH₂CH₃)₂ and CH₃CH₂OH was used as the raw materials and solvent. Dense BPO thin films deposited on MgO (100) and SiO₂/Si substrates had a room-temperature resistivity of about 2.6 and 0.7mΩ·cm, respectively, comparable to a typical value of 0.5mΩ·cm in bulk BPO ceramics produced by powder processing. The electrical property of the obtained films is indicative of their potential use as an electrode material for ferroelectric thin film devices.

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End member and solid-solution single crystals of alkali halides were prepared by Bridgman method, using sodium chloride (NaCl), potassium chloride (KCl), sodium bromide (NaBr) and potassium bromide (KBr). Transparent and crack-free specimen was obtained in each end member single crystal. As a result of X-ray diffraction experiment in solid-solution single crystals, it was found that maximum content is 20 to 25mass%. Lattice parameter in each solid-solution single crystal was satisfied with Vegard's law. The solid-solution single crystals without cracks also were obtained in wider solid-solution region in anion (Cl^- or Br^-)-replacement type than in cation (Na⁺ or K⁺)-replacement type. This result in cation-replacement appears to be attributed to difference between two cationic radii. Single crystal in KBr-KCl system indicated increment of Vickers hardness with adding the alkali halide. On the other hand, in NaBr-NaCl system, adding NaBr to NaCl caused solid-solution hardening, while adding NaCl to NaBr caused solid-solution softening. Curves of density and refractive index versus the content had a downward convex shape. This result corresponds to Lorentz-Lorenz relationships, which connects density with refractive index.

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Effects of particle size and addition of BN on the fracture energy (γ_s) as well as effective fracture energy (γ_eff) of pressureless sintered β′-Sialon-BN composites have been studied, and porosity, flexural strength, Young's modulus and fracture toughness were evaluated. Results obtained are as follows; comparison of the effect of particle size of BN revealed that the deterioration of mechanical properties is smaller for the fine particles of BN. Similarly, γ_s is insensitive to BN content, while maximum γ_eff was observed at 30mass% addition of fine BN particles. The contribution of nonlinear fracture energy γ_R(=γ_eff-γ_s) is related to the presence of bar-like crystals in the microstructure of β′-Sialon-BN composite.

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Using Mg(OH)₂ powder, Al-sec-butoxide and Zr-n-butoxide as the raw materials, ZrO₂ dispersed MgO-Al₂O₃ ceramics were prepared by calcining at 1000°C for 2h and sintering at 1600°C for 1h. The relationship between the properties and the content of ZrO₂ was investigated. The relative density of the sintered bodies was improved when ZrO₂ content exceeded 1.4vol%. The bending strength increased with increase in the ZrO₂ content above 6.6vol%, while the fracture toughness improved by 12.5 to 15.1vol% ZrO₂. The sinterability of spinel between 1200 and 1400°C was also enhanced by the ZrO₂ addition. The bending strength was improved with increase in the content of tetragonal-ZrO₂ transformed to monoclinic-ZrO₂ by fracture. The fracture toughness was improved with the total content of tetragonal-ZrO₂ in the matrix.

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The composite ceramics of the TiN-TiB₂ system, which have high electrical conductivities and can be used for electric discharge machining, were sintered at 2100°C for 3.6 ks in the ambient Ar gas of normal pressure. The mechanical and electrical properties of the ceramics were characterized. The TiN-TiB₂ composite ceramics, which contained 20-60 mass%TiB₂, had higher relative densities of about 87%. Vickers hardness, flexural strength, fracture toughness, Young's modulus and shear modulus of the composite ceramics were about 1.2-2.3 times higher than those of pure TiN or TiB₂ ceramics having relative densities of about 83 and 74%, respectively. The mechanical properties of the ceramics depended principally on the relative densities, while the electrical conductivity was dependent on the contents of TiN and TiB₂.

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The packing density of the cakes prepared by slip casting of the alumina powder mixtures with a wide particle size distribution ranging from 0.1 to 10μm has been studied. More effective particle packing was achieved for powder mixtures consisting of two discrete size components, in which the fine particles can fill the void spaces between the coarse particles. The entire range of distribution can be divided into two regions so as to constitute a binary packing system. The ultimate packing density depended on the fraction of the finest component rather than the variety of the size distributions. The packing behavior was discussed in terms of the two different types of the packing mode.

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Dissolution process of CaMoO₄ in aqueous suspension containing H-R, a strongly acidic ion exchange resin with hydrogen form, was studied mainly by chemical analysis of the liquid phase. Several analytical methods such as titration using NaOH solution or H-R suspension, calorimetry, thermal analysis and XRD were carried out in order to confirm the dissolution mechanism. CaMoO₄ does not dissolve according to the equation, CaMoO₄+2(H-R)→Ca-R₂+H₂MoO₄ owing to the aggregation to polyanion by the acidification of MoO₄^2-. By considering the experimental results, it is concluded that CaMoO₄ dissolves to yield an acid having a composition to be H₄Mo₈O₂₆. The dissolution process of CaMoO₄ and alkali titration for the resultant acid are summarized as follows: (1) The dissolution process of CaMoO₄ as a function of H-R (g) is expressed by the following two-stages reactions, 8CaMoO₄+12(H-R)→Ca₂Mo₈O₂₆(aq)+6(Ca-R₂)+6H₂O Ca₂Mo₈O₂₆(aq)+4(H-R)→H₄Mo₈O₂₆(aq)+2(Ca-R₂). With increasing the amount of H-R, the concentrations of Ca and Mo increase at the initial stage which is followed by the decrease in Ca²⁺ concentration at the final stage. The formation of the intermediate, Ca₂Mo₈O₂₆(aq), is proved by the experimental fact of ca. 4 of Mo/Ca molar ratio. (2) The neutralization between the final acid product, H₄Mo₈O₂₆(aq) and NaOH solution proceeds according to the following two-stage reactions, H₄Mo₈O₂₆(aq)+4NaOH(aq)→Na₄Mo₈O₂₆(aq)+4H₂O, Na₄Mo₈O₂₆(aq)+12NaOH(aq)→8Na₂MoO₄(aq)+6H₂O.

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β″-Al₂O₃ has been developed as a solid state electrolyte for the sodium-sulfur battery. Generally, raw material β″-Al₂O₃ was prepared by the wet-mixing process such as zeta-process. In this study, the dry-mixing process as a new safety procedure for the β″-Al₂O₃ raw material was investigated. Homogeneous mixtures were obtained by mixing 1-3mass% dispersing agent. However, anomalous grain growth was observed in this system during the sintering process. Seed crystal methods were also investigated for depression of anomalous grain growth during the sintering. Microstructure of sintered products was changed considerably by addition of more than 3mass% seed. The electrical resistivity of β″-Al₂O₃ thus obtained was significantly reduced by the addition less than 5mass% seed. It is considered that the electrical resistivity of β″-Al₂O₃ is governed by the number of grains and density of sintered products. The mechanical strength of seeded products was markedly higher than unseeded one's.

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The films of hydroxyapatite-calcium phosphate were coated on alumina ceramic substrates by electrophoretic deposition technique. Homogeneous films were obtained by using a mixed solution of ethanol and 2, 4-pen-tanedione (acetylacetone). The calcium phosphate compound with low melting point played a role of binder between HAp and alumina substrate. The apatite phase of coated layers was decomposed to α- and β-tricalcium phosphate, on sintering at 1300°C.

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The elemental distribution in BeO-doped pressureless sintered SiC ceramics, with high thermal conductivity (270W/m·K) and high electrical resistivitiy (4×10¹¹Ω·m) was investigated by secondary ion mass spectroscopy (SIMS). Intense image of oxygen was observed at the grain boundaries and weak image of Be was detected very close to the positions of oxygen. The intensity contrast of these two elements do not always coincide at all positions. These results suggest that the additive BeO exists at grain boundaries as BeO and/or nonstoichiometric Be oxide.

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