The essential condition for glasses and glass-ceramics to bond to living bone is the formation of an apatite layer on their surfaces in the body. The apatite layer can be reproduced on their surfaces even in an acellular simulated body fluid which has ion concentrations almost equal to those of the human blood plasma. In the present study, in order to investigate the compositional dependence of bioactivity of glasses fundamentally, the apatite formation on the surfaces of glasses in the system CaO-SiO₂-P₂O₅ was examined in the simulated body fluid. Thin-film X-ray diffraction, Fourier transform infrared reflection spectroscopy and scanning electron microscopic observation were used for detecting the apatite formation. It was found that CaO-SiO₂ glasses free form P₂O₅ as well as those containing small amounts of P₂O₅ form the apatite layer on their surfaces, whereas CaO-P₂O₅ glasses free from SiO₂ as well as those containing SiO₂ do not form it. This indicates that bioactive glasses and glass-ceramics are obtained in compositions based on CaO-SiO₂ rather than CaO-P₂O₅, contrary to the general view. These results were interpreted in terms of ions dissolved from glasses.

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The crystallization process of an Fe₂O₃ 40, CaO⋅SiO₂ 60wt% glass was investigated as well as magnetic properties of the crystallized products, in order to reveal principles for obtaining ferrimgnetic and bioactive glass-ceramics useful as thermoseeds for hyperthermia of cancer. When the glass was heat-treated up to temperatures 700° to 950°C, magnetite particles were homogeneously precipitated in a CaO⋅SiO₂-based glassy and/or crystalline matrix. The diameter and content of the magnetite increased from 6 to 30nm and 10 to 36wt%, respectively, with increasing temperature of the heat treatment from 700° to 950°C. Above 1000°C, a part of the magnetite was converted into hematite (α-Fe₂O₃). The glass showed maxima in saturation magnetization and coercive force, 32emu/g and 500 Oe, respectively, when heat-treated up to 950°C. The variation of the magnetization with heat treatment temperature could be well quantitatively interpreted in terms of the content of the magnetite, whereas that of the coercive forces could be explained only qualitatively in terms of the particle size of the magnetite. The coercive forces of the magnetite-containing glass-ceramics were much higher than those of the magnetite powders of the corresponding particle sizes which were prepared from aqueous solutions.

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In the preparation of SiO₂-TiO₂ sol pillared clays, organic cations, octadecyltrimethylammonium, were added to a montmorillonite suspension, together with SiO₂-TiO₂ mixed sol solutions. The order of the addition was important; if the organic cations were added first, the effect of the addition was very small. On the other hand, if the SiO₂-TiO₂ sol solutions were added first, followed by the addition of the organic cations, a pillared clay with mesopores was obtained on calcination: the surface area increased with an increase in the amount of the addition of the organic cations. In the latter case, the organic cations probably occupy a part of the interlayer spaces of montmorillonite together with the sol particles and burning off the organic cations leaves behind mesopores in the interlayer spaces.

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Yttria-partially stabilized zirconia (Y-PSZ) coated with β-tricalcium phosphate (β-TCP) was studied for developing high-strength biomaterial. Y-PSZ substrate was first coated with a slurry of magnesium metaphosphate used as an interlayer and heated at 1120° to 1240°C. Then the product was coated with a slurry of β-TCP and heated at 1100° to 1220°C. The obtained coatings bonded well to the substrate. The β-TCP phase was retained in the coating layer of all samples. A tetragonal-to-monoclinic destabilization of the Y-PSZ was observed in the reaction layer.

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Fine powders with compositions 4mol% YO_1.5-4mol% CeO₂-ZrO₂ (4Y, 4Ce), 2.5mol% YO_1.5-4mol% CeO₂-ZrO₂, and 2.5mol% YO_1.5-5.5mol%CeO₂-ZrO₂ were prepared by hydrolysis of ZrOCl₂ solution. Using thus obtained powders, yttria- and ceria-doped tetragonal zirconia ceramics ((Y, Ce)-TZP) were fabricated by a normal sintering and a hot isostatic pressing (post-sin-tering hot isostatic pressing) and their bending strength, microstructure, and tetragonal-to-monoclinic phase transformation during low-temperature aging were studied. Mean values of the bending strength of (Y, Ce)-TZP fabricated by a normal sintering at 1500°C for 2h were 840MPa for (4Y, 4Ce)-TZP, 860MPa for (2.5Y, 5.5Ce)-TZP and 1000MPa for (2.5Y, 4Ce)-TZP. The grain size of (Y, Ce)-TZP was larger than that of 3Y-TZP. (4Y, 4Ce)-TZP and (2.5Y, 5.5Ce)-TZP showed improved thermal stability as compared with 3Y-TZP. The bending strength of (4Y, 4Ce)-TZP increased from 840MPa to 1100MPa by post-sintering HIP at 1500°C and 147MPa for 0.5h.

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Pyroelectric properties of c-axis oriented thin films with the compositions of [(1-x)PbTiO₃+xMgO], where x=0.015-0.090 prepared by rf-magnetron sputtering method were investigated. With increasing Mg content and film thickness, the relative dielectric constant, ε_r, increased and the dielectric loss, tan δ, decreased. And, the effects of film thickness on them were also seen. Results of measurement for the pyroelectric coefficient, P, showed that the direction of natural polarization is in the upward direction perpendicular to [100]-oriented Pt thin film on (100) MgO single crystal substrate. The Curie point, T_c, lowered linearly with increasing Mg content. The lowering rate was approximately 11.8°C/mol% (MgO), which gave good agreement with that of [(1-x)PbTiO₃+xMgO] [PMT] single crystals. It was found that these films have large P independent of temperature in the range from room temperature to about 300°C after heating and cooling process beyond T_c. The figure of merit, F. M., and F. M. D* on x=0.045 PMT thin film of 2μm thickness exhibited the highest values, reaching 1.5×10^-10Ccm/J and 2.1×10^-8Ccm/J, respectively. The above-mentioned values were about 2.5 and 2.6 times larger than those of the PMT single crystals, respectively. The values were about 1.5 times larger than those of Pb_1-xLa_xTi_1-x/4O₃ [PLT] thin films.

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Non-alkali multicomponent glasses in the system SiO₂-Al₂O₃-CaO-ZnO-TiO₂-B₂O₃ were prepared by the melt quenching method. The composition range was (in wt%), SiO₂=32.0-38.0, Al₂O₃=9.0-18.0, CaO=17.0-23.0, ZnO=12.0-18.0, TiO₂=10.0-19.0, and B₂O₃=2.0-7.0. Composition dependencies of glass transition temperature T_g, softening temperature T_d, thermal expansion coefficient α, and density ρ were investigated. It was found that an increase in SiO₂, Al₂O₃ or CaO content increases the T_g and T_d but anincrease in ZnO, TiO₂ or B₂O₃ content decreases these characteristic temperatures. The thermal expansion coefficient decreased with an increase in SiO₂, Al₂O₃, ZnO, TiO₂ or B₂O₃ content, but increased by the addition of CaO. It was speculated that alumina and titania are combined with CaO to produce AlO₄ or TiO₄ tetrahedra, which help SiO₂ poor compositions to form a rather stable glass network.

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ZrSiO₄ powders were prepared using a sol-gel processing from partially hydrolyzed Si(OC₂H₅)₄ and Zr(WC₃H₇)₄ solutions. The optimum conditions for obtaining precursor gels with ZrSiO₄ composition were as follows: concentration of mixed solutions; 0.25mol/l, stirring time of alkoxide solutions: 6h, pH of the hydrolysis water: 5.5, H₂O/alkoxide molar ratio: 10 and stirring time of solutions after hydrolysis: 3h. The precursor powders prepared by using these conditions were converted into ZrSiO₄ powders in about 20% yield at 1200°C for 2h by the addition of 1.5wt% ZrSiO₄ seeds. Furthermore, the formation rate of ZrSiO₄ became remarkably higher through “Hedvall effect” bringing about the transition from amorphous silica to crystalline silica at 1250°-1350°C, and the powders prepared by firing at 1500°C for 2h have become an almost single phase of ZrSiO₄ and the particle size of 0.3-0.6μm is revealed.

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The equations for the evaluation of fracture toughness by chevron notched beam, with using the bending bar whose shape is followed as JIS-R1601, are obtained analytically for five different shapes of the notch, with the method by Munz. The accuracy of the equations is tested experimentally with alumina specimens. Except one condition (stand-up type, θ=120°, α₀>0.6), scattering of the average value obtained from the experiment with every equation is within ±8%, and this scattering is almost same as the relative standard deviation of the fracture toughness of the tested alumina itself, ±7%. Then, these equations are useful if we want to evaluate fracture toughness with about this accuracy, even if the specimen is used as either stand-up or lay-down type.

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For whisker reinforced ceramic composites, many toughening mechanisms are proposed. However, it is not clear yet which mechanism mainly contributes to the toughening. In this paper, we tried to explain the toughening behavior by the pull-out mechanism. A model based on the energy balance of crack propagation and frictional energy during whisker pulling-out was constructed for analyzing experimental results. Seven types of SiC whiskers with various sizes and shapes were used for fabricating SiC whisker/Al₂O₃ composites. Mechanical properties of these composites such as frature toughness K_IC, effective fracture energy γ_eff and 4-point bending strength σ_f, were measured as a function of whisker dimension or whisker volume fraction. Fractured surfaces and crack propagation paths in these composites were observed in detail. A linear relationship between γ_eff and r²/l_w was obtained (r: radius of whiskers, l_w: length of whiskers). γ_eff also had a linear relationship with the whisker volume fraction. These results seem to support the whisker pull-out model proposed here. (K_IC)² showed linear relationships with r²/l_w and whisker volume fraction as well as γ_eff. Four-point bending strengths of these composites were not improved in spite of toughening by whisker reinforcement. It is presumed that long whiskers cause to introduce large defects into ceramic matrix.

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Powder of spherical silica particles prepared by hydrolysis of tetraethylorthosilicate was sintered by the hydrothermal hot-pressing method at low temperatures below 350°C. Densification of the powder was accelerated by the increase in reaction temperature and pressure. Formation of necks and deformation of particles were observed in fractured surface of a sintered body produced at high pressure (49MPa). Water contained in the starting powder was essential to the densification by hydrothermal hot-pressing.

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The reaction-sintered porous SiC ceramics with different particle sizes and porosities are prepared, and the effects of particle size and porosity on their gas permeability and bending strength are investigated. For porosities above 0.25, the Ergun's equation well explains the small pressure drop at large particle sizes and high porosities which were achieved by the decreased compaction pressure of raw materials. The reduction in porosity down to 0.26 by the addition of free Si under the constant compaction pressure increased the bending strength remarkably, while no change in the pressure drop was accompanied. At a porosity smaller than 0.26, an abrupt increase of the pressure drop was observed without any further increase in bending strength. These observations were examined through the analysis of morphology and pore size distribution. The abrupt change was found to occur at the point where all the smaller pores are filled with Si completely. The preferential filling of Si in smaller pores can be explained by the good wetting of SiC with Si.

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Bi-Pb-Sr-Ca-Cu-O superconductive films (T_c≥100K) were obtained by annealing films A((Bi+Pb)_1.47Sr_1.00Ca_0.92Cu_1.80O_x) at 850°C which were prepared by rf-magnetron sputtering using multi-targets. The critical current density (J_c) of the annealed films was greatly influenced by the surface roughness of the film. J_c increased proportionally with a decrease in surface roughness, indicating that the decrease of J_c was caused by the rough surface of the film, and by a liquid phase formed during the annealing process. To avoid the formation of the liquid phase and to obtain smooth surface films, low Ca content films B((Bi+Pb)_1.27Sr_1.00Ca_0.76Cu_1.37O_x) were prepared and annealed at a low temperature (835°C). The surface of the annealed film B was smoother than that of the annealed film A. The obtained films with smooth surface films showed high J_c(=27, 000A/cm²) at 77K in zero magnetic field.

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The effect of additives on Nano-structure Controlled materials has been studied. This material consists of Fe-based (Fe-Si-Al) soft magnetic metal grains completely separated from each other by insulating thin films. The synthesis process is as follows: first, a metal powder was heated to form thin uniform Al-O-N film (-10nm). Then the coated powder was compacted and hot-press sintered with additives at a high pressure. The sintered materials had electric resistivities (10⁶-10⁸Ω·m) containing B₂O₃(+5nm-+20nm) higher than that of sintered one without additives.

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Mechanical properties of pressureless sintered TiB₂ containing Ni and C were investigated. Ni and C play an important role in the densification of TiB₂. Sintered TiB₂ containing 7.5wt% (14Ni:1.5C) exhibited a bending strength of 470MPa, Vickers hardness of 17GPa and K_IC of 4.9MPa·m^1/2. The fracture surface of TiB₂ sintered containing Ni and C showed both transgranular and intergranular fracture modes. XRD analysis detected Ni₃B and TiC phases besides in addition to TiB₂ in the sintered body.

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4.5mol% yttria-partially stabilized zirconia crystals were annealed between 1500°C and 1800°C (c-ZrO₂ and t-ZrO₂ co-region) with d.c. electric current in air and microstructure and phase changes were studied using SEM, EPMA and XRD. Although no significant microstructure and phase changes were observed in samples annealed without current, an opaque tongue-shaped zone was formed at the cathode in samples annealed at high temperature with current and then cooled to room temperature without current. This zone grew through the sample toward the anode with annealing time. The opaque zone was almost the single phase of tetragonal t' phase and contained many microcracks and some large cracks. On the other hand, when annealed at 1650°C with current and cooled to about 1000°C with current and then to room temperature without current, the single crystal turned brown and did not show microstructure change and transformation to t' phase. When this sample was annealed again without current, an opaque zone of t' phase was formed at the cathode. It is presumed that the transformation to t' phase occurs when reduced samples are oxidized at high temperature.

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Mullite composite ceramics reinforced with (0-50)vol% β-silicon nitride (β-Si₃N₄) whisker were prepared by hot pressing between 1500° and 1650°C under 30MPa for 30min, and the mechanical properties (bending strength, hardness, modulus of elasticity, fracture toughness) of these composites were investigated. Fully densed composites containing up to 40vol% whisker were obtained at 1600°C. X-sialon phase, which was thought to be produced by a reaction between mullite and β-Si₃N₄, was detected in the composite fired at 1650°C. Room temperature bending strength increased with increasing whisker content and showed a maximum value (about 630MPa) at 40vol%, which was 80% higher than that of monolithic mullite. These composites had more excellent high temperature strengths than monolithic mullite. The hardness and modulus of elasticity of dense sintered bodies also increased with increasing whisker content. The fracture toughness (about 4MPa·m^1/2) of a composite with a β-Si₃N₄ whisker content of 40vol% was more than two times larger than that of monolithic mullite due to crack deflection and pull-out of whiskers in the fracture process. The β-Si₃N₄ whiskers in the composites were aligned preferentially in the direction normal to the hot pressing direction so that mechanical properties of the plane normal to the hot pressing direction were superior to those of the plane parallel to the hot pressing direction.

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Silicon carbide coating was applied to a thin high purity of alumina film which was produced from aluminum alkoxide sol by the sol-gel method. This alumina film was treated with a polycarbosilane solution and heattreated at 1200°C. The bending strength of the coated alumina film was improved, and no electrical resistivity change was observed in the thickness direction.

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High pressure sintering under the condition corresponding to the thermodynamically stable region for cubic boron nitride in a phase diagram of boron nitride was studied to demonstrate the availability of PSZ as a sintering additive of cubic boron nitride. In a specimen without additives, because of rigidity of cubic boron nitride, the sufficiently high pressure was not applied on the surface of cubic boron nitride particles effectively except for the portion of surface where the cubic boron nitride particles contacted with each other, where inversion into hexagonal boron nitride occured. In PSZ-added specimens, however, PSZ behaved as a pressure transmitting medium to the surface of cubic boron nitride particles. Consequently, phase transition into hexagonal boron nitride was prevented. On the other hand, part of partially stabilized high temperature phase t-ZrO₂ of PSZ underwent conversion into stable phase m-ZrO₂ for the specimens doped with PSZ less than 12vol%. The cubic boron nitride sintered body with PSZ of 12vol% had the highest microhardness of above Hv 2300. It was concluded that PSZ was effective as a sintering additive to obtain cubic boron nitride sintered bodies with a compact texture.

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The oxygen diffusion coefficient in Y₂O₃-containing tetragonal ZrO₂ polycrystals (Y-TZP, 2.75mol%Y₂O₃) was determined over the temperature range (600° to 800°C) by monitoring diffusion process with a microbalance. Oxygen isotope (¹⁸O) was used as a tracer. The same diffusion coefficient was obtained for specimens with different grain sizes, indicating that there was no fast diffusion along the grain boundaries in Y-TZP. The oxygen lattice diffusion was faster in Y-TZP than t-ZrO₂ doped with 14% CeO₂. This suggested that most cerium atoms in t-ZrO₂ doped with CeO₂ were in 4+ rather than 3+. The oxygen lattice diffusion coefficient in Y-TZP was almost the same as that in Ca-stabilized cubic ZrO₂, but was several orders of magnitude higher than that in m-ZrO₂ doped with 1-2% Y₂O₃.

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