Three types of carbon fibers, PAN-based HSCF, pitch-based HMCF with low graphitization degree, and pitch-based CF70 with high graphitization degree, were used to prepare unidirectional carbon fiber reinforced SiC composites (CF/SiC) by multiple impregnation of polycarbosilane and subsequent pyrolysis at 1200°C for 5-9 times. The experimental results showed that pyrolytic product of polycarbosilane at 1200°C in N₂ consisted of β-SiC phase in a nearly amorphous state and impurity oxygen. The impregnation behavior of polycarbosilane for CF70/SiC was different from those of HSCF/SiC and HMCF/SiC. CF70/SiC showed a flexural strength of 700MPa, which was markedly higher than those of HSCF/SiC and HMCF/SiC. Moreover, CF70/SiC exhibited non-catastrophic fracture behavior, whereas HSCF/SiC and HMCF/SiC showed brittle fracture behavior. Scanning electron microscope (SEM) and transmission electron microscope (TEM) observation of these composites clarified that HSCF/SiC and HMCF/SiC had a strong fiber/matrix interface bonding, whereas CF70/SiC had a weak interface bonding. It was concluded that highly graphitized CF70 was the most suitable reinforcement for the CF/SiC composite.

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Use of microwave heating for sintering of silicon nitride ceramic is being actively investigated. Sintering of seeded and non-seeded Silicon Nitride with Y₂O₃, Al₂O₃ and MgO as sintering aids was carried out in an applicator fed by a 28GHz Gyrotron source at 1600, 1700 and 1750°C for 2h. Microstructure of the specimens was analyzed by SEM, and flexural strength and fracture toughness measured. All seeded specimens showed complete α-β transformation and a bimodal microstructure with a high proportion of elongated and thick grains. Flexural strength of seeded specimens decreased (from 910 to 800MPa) as the sintering temperature increased, due to the increase in size of elongated grains, as well as to interlocking of these grains. In non-seeded samples, strength increases as it does the sintering temperature, achieving a level of 960MPa. Fracture toughness increased up to 7.0MPa⋅m^1/2 in non-seeded specimens, and up to 8.1MPa⋅m^1/2 in seeded specimens. Suitable combination of strength and toughness can be obtained applying seeding and microwave heating techniques.

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Diamond films have been deposited by hot filament chemical vapor deposition on hot-pressed silicon nitride substrates using a mixture of hydrogen and methane with a CH₄/H₂ volume ratio fixed to 0.5%. Scratching with diamond paste of the as-received substrates was necessary to obtain high nucleation densities (10⁸-10⁹cm^-2) in the 750-1000°C deposition temperature range, while, on scratched substrates, the nucleation density decreased at 1050°C. The diamond deposition rate has its maximum at around 850-900°C. The film texture was {111} ‹100› at the low deposition temperatures, while became {111} {100} ‹110› at temperatures higher than 750°C. A careful analysis of the Raman spectra allowed us to identify the best deposition conditions for the growth of high quality diamond. Silicon nitride as a substrate for diamond CVD is better than cemented tungsten carbide due to the lower level of residual stress and to the higher phase purity of the coating.

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The mechanical properties of hot-pressed, low-temperature-calcined α-alumina powder made from commercial aluminum hydroxide by seeding of wet grinding abrasion powder were investigated. The microstructure of samples sintered at low temperature is composed of very fine equiaxial grains and its bending strength is higher than 800MPa. As the sintering temperature increases, the grains become large and uniaxially elongated, the bending strength of sintered bodies decreases, and the fracture toughness increases. A sample sintered at 1400°C shows a bending strength of 600MPa and a fracture toughness of 7.9MPa⋅m^1/2 (SEPB method). A maximum fracture toughness of 9.0MPa⋅m^1/2 is achieved in a sample sintered at 1600°C. This high fracture toughness is caused by a uniform and elongated grain structure, and by increment of grain boundary fracture.

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The microstructure of hot-pressed SiC added with AlB₂-C was analyzed by the microstructural observation and elemental analysis. According with the results of such analysis, the mechanical properties at high temperature were discussed. AlB₂-C mainly reacted to form Al₂O₃ and B₄C. A minor fraction on Al-Si-(B)-C-O phase, in which O was thought to be supplied from impurity SiO₂ in the raw SiC powder, was observed by transmission electron microscope. Al-C-O phase was detected as an intergranular phase. The flexural strength decreased from 60MPa at room temperature to 530MPa at 1450°C and the fracture toughness with SEPB method increased from 4.5MPa⋅m^1/2 at room temperature to 10.9MPa⋅m^1/2 at 1500°C. The intergranular phase of Al-C-O is thought to cause strength degradation because of the phase softening at high temperature. From fracture surface observation after fracture toughness test, a fibrous texture on the fracture surface was observed. Auger electron analysis revealed that the fibers were composed of Al-C-N-O. The Al-C-O intergranular phase may become a highly viscous Al-C-N-O phase during toughness test at 1500°C in N₂, enhancing the crack-face bridging effect.

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Spherical porous zirconia and titania particles were synthesized by the sol-gel process from zirconyl chloride, zirconium tetrapropoxide and titanium tetraisopropoxide in W/O emulsion, respectively. Zirconia particles are obtained by addition of urea and hexamethylenetetramine in a starting solution. When the molar ratio of zirconyl chloride, calcium chloride, urea, hexamethylenetetramine, N, N-dimethyl formamide and H₂O is 1:0.2:1.1:0.9:1.4:45, spherical porous zirconia particles could be synthesized. The particles occurred cubic and monoclinic form at 600°C, respectively. Peak pore-diameter of the particles was 4nm. The pore volume increases with increase in calcium content. After the extraction of calcium by hot water, the specific surface area of the particles is enhanced 110m²/g. SiO₂-ZrO₂ binary particles are synthesized by using zirconium tetrapropoxide and 2-methoxyethanol. When the molar ratio of tetramethoxysilane (TMOS), zirconium tetrapropoxide, 2-methoxyethanol, H₂O and HCl is 0.7:0.3:5.25:20:3.6×10^-4, the specific surface area of the particles was 260m²/g. After the extraction of SiO₂ parts by 1M NaOH aqueous solution, the weight loss of the particle was 10mass%. Titania particles are obtained by addition of diethanolamine or 2-methoxyethanol in starting solution. Peak pore-diameter of the particles is 4nm when the molar ratio of diethanolamine to titanium tetraisopropoxide was 1.5. By calcination at 500 and 700°C, the particle occurred anatase and rutile type, respectively. TiO₂-SiO₂ binary particles are synthesized by using 2-methoxyethanol. When the molar ratio of titanium tetraisopropoxide, TMOS, 2-methoxyethanol, H₂O and HCl is 0.4:0.6:4:20:1.8×10^-3, the specific surface area of the particles was 180m²/g after the extraction of SiO₂ parts by 0.1M NaOH aqueous solution.

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Crack growth behaviors in continuous fiber-reinforced ceramic matrix composites have been analyzed in termes of stress intensity factors using the finite-element method. Namely, the effects of Young's modulus ratio, E_m/E_f, and fiber volume fraction, V_f, on the stress intensity factors have been investigated. As a result, it was confirmed that the stress intensity factor increased with increasing the Young's modulus ratio and decreasing the fiber volume fraction. Also, the results showed that a matrix with a low Young's modulus and a low thermal expansion coefficient is effective for preventing crack growth from the matrix through the fiber.

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The TiB₂-ZrB₂ ceramic system, which has a range of high hardnesses and electrical conductivities, was sintered by the hot-pressing method from mixed powders of TiB₂ and ZrB₂. The mixed powders calcined at 1450°C for 5.4ks with compositions from 100mol% TiB₂ to 100mol% ZrB₂ (20mol% step) were preformed at a pressure of 98MPa, and then hot-pressed at 2000°C for 3.6ks under a pressure of 31.2MPa in an ambient Ar gas. The system was found to form solid solutions between TiB₂ and ZrB₂ crystal structures. (TiB₂)_0.6(ZrB₂)_0.4 ceramics, for example, had a relative density of 96.5%, hardness of 30.4GPa, flexural strength of 354MPa, fracture toughness (K_IC) of 3.87MPa⋅m^1/2, Young's modules of 449GPa, fracture energy of 16.5J⋅m^-2 and electrical conductivity of 6.8MS⋅m^-1. The ceramics is expected to be used as a ceramic mold material that can be machined by electrical discharge and as electro-conductive high-temperature structural materials.

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An extensive and systematic study of heat treatment for the synthesis of the 2223 phase has been performed. Results of X-ray diffraction (XRD), scanning electron microscopy (SENT) and energy dispersive X-ray micro-analysis (EDX) are presented. It is found experimentally that the most efficient heat treatment temperature to obtain the specimen having a high volume fraction of 2223 phase is 1133K. The formation of the 2223 phase begins substantially in only one hour after the reaching to 1133K. In addition, the thermal hysteresis is essential. Once the specimen is calcined below 1133K, for example at 1073K, impurities such as Ca(Sr)-Cu oxides are inevitably included in the final product, even though the firing is made subsequently at 1133K. The forming of the Ca(Sr)-Cu oxides, which arise from the intermediate step in the heat treatment process, influences strongly and prohibits to grow the 2223 phase. It is stressed that the calcining at 1133K is important and key technique.

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The changes in the pore structures of compacts of ironstone china during a heating process were investigated using mercury intrusion porosimeter. A rollerhead-machine was used to form the compacts of ironstone china. The compacts were heated at 400-1280°C for 2h. Pore volume and pore size distribution of the samples were measured by means of mercury intrusion porosimeter. The results obtained were as follows: (1) The pores existed in the ironstone china body are within the range of pore diameter which can be measured by means of mercury intrusion porosimeter, then, the changes in the pore structures of compacts during a heating process can be discussed by the results of mercury intrusion porosimetery. (2) Pore volume of green compacts measured by means of mercury intrusion porosimeter was 157mm³/g, which was agreed with the results of apparent porosity value of 30% measured by means of Archimedes methods. (3) The pore diameter at maximum mode of distributions was 0.2μm, and almost of pores were existed in the range between 0.02 and 0.35μm in diameter. (4) Pore volume of the compact increased during the heating process at 800-1000°C. Pore volume heated at 800-1000°C was 190mm³/g, and then it decreased with heating temperature after 1000°C. (5) The pore diameter at maximum mode of distributions became large with the heating temperature and small pore was decreased. The pore diameter at maximum mode of distributions was about 0.7μm in the sample heated at 1220-1240°C, and then it decreased with the temperature after 1240°C.

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This study deals with the shape forming mechanism of granules spray-dried from alumina slurries whose dispersing system has been systematically controlled by adding nitric acid. Both the micro structure of granules and the slurry characteristics have been attentioned, in order to identify the main parameter governing the formation mechanism of granules. It is shown that the structure of spray-dried granules strongly depends on the degree of flocculation in the prepared slurry. Granules prepared from dispersed slurry are irregularly shaped and the majority of them are dimpled, while flocculated slurry results in essentially spherical and homogeneous granules. It is also shown that the shape forming process can be reasonably explained with invoking a shrinkage process of sprayed droplets.

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Simulation of surfaces and grain boundaries of α-alumina were carried out by the molecular dynamics method using an ionic pair potential. Simulation of five different surfaces, (1101), (1104), (1102), (1120), (0001), showed that, although a distorted structure formed at the surface, the calculated surface energies (γ_sv) were similar to each other. Simulations of five grain boundary misorientations (general, near Σ11, basal twin, Σ7, Σ3 grain boundaries) showed that both the structure and calculated grain boundary energy (γ_gb) were markedly different for each boundary. The values of γ_sv. and γ_gb were similar to those reported in previous simulation studies, but were larger than the experimentally measured values. The energy ratios, γ_gb/γ_sv, were in the range 0.07 to 1.11, which was comparable to experimental values previously determined. The molecular dynamics simulation of surfaces and grain boundaries is shown to be a useful technique for the microstructural design of ceramics on the atomic scale.

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Thermal reactions of mixtures of kaolinite and magnesium compounds in the mole ratio of MgO: Al₂O₃: SiO₂=1:1:2 were investigated to obtain uniform amorphous materials containing magnesia below 900°C. B₂O₃-added mixtures of kaolinite and ultrafine particles of synthesized magnesium hydroxide with an average width of about 0.1μm resulted in the amorphous state at about 800-850°C after decomposition of the starting materials. Addition of B₂O₃ promoted the crystallization of μ-cordierite from amorphous state and then the crystallization of α-cordierite. Addition of B₂O₃ more than 1mass% appeared to accelerate the direct crystallization of α-cordierite from the amorphous state. The complete transformation to α-cordierite was obtained by firing at 900°C for 1h. On the other hand, uniform amorphous materials were not obtained from mixtures of kaolinite and reagent-grade magnesium compounds with an average particle size of about 1μm by firing at 900°C, because of insufficient diffusion reaction of mixtures.

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Pore-size distributions and the microstructure of clay-water and alumina-water system were determined by mercury porosimetry and SEM observation to consider the relation between plasticity and packing structure of the dough. Bimodal distributions of pores were observed in size with submicron (s-pore) and several-micron (l-pore) regions for the extrudable dough of clay-water system. Submicron pore group (s-pore) corresponded to inter-particle pores which exist among the primary particles. And the several-micron pore group (l-pore), which vanishes during drying process at 100°C, would be corresponded to inter-aggregate pores. The l-pore has strong relation with extruding behavior of the dough: in the dough with higher extrudability, a larger amount of l-pore was included and the l-pore was obviously observed even at water contents lower than the plastic limit. On the other hand, monomodal distributions of pores by s-pore were characteristic for the unextrudale doughs of alumina-water system. It was estimated that the l-pore, which is filled with water under wet condition, acts as the free space among the aggregate during extrusion to promote the deformation of a dough.

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The crystal structure of hydrous-zirconia fine particles, produced by the hydrolysis of ZrOCl₂ in aqueous solutions with and without an addition of NH₄OH or HCl, was investigated using X-ray diffraction (XRD) and Raman spectroscopy. Main emphasis was placed to clarify the effects of pH on the crystal formation. The XRD patterns of hydrous zirconias synthesized at pH-values below about 1 were similar to those observed for monoclinic crystalline zirconia. At pH-values greater than about 1, the diffraction line assigned to the 111 reflection of the tetragonal or cubic phases was observed, in addition to those of the monoclinic phase. Raman spectra measurements revealed that the diffraction line agreed with that of tetragonal crystalline zirconia. The fraction of the tetragonal phase showed a tendency to increase as the pH increased. When the pH was attained to around neutrality, amorphous hydroxide formed. These experimental results indicated that the crystal phase in hydrous zirconia is primarily governed by the concentration of H⁺ ions (pH) produced during hydrolysis. The crystal-formation mechanism for hydrous-zirconia fine particles was determined on the basis of the present experimental results.

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Samples having various compositions were prepared in air by solid phase reaction at 1700K in order to investigate the presence of compounds in the CaO-SiO₂-Y₂O₃ system. The quaternary oxides obtained were Ca₂Y₈Si₆O₂₆ (hexagonal, P6₃/m, a=0.93429 (2), c=0.67393 (1) nm, apatite-type structure), Ca₂Y₂Si₂O₉ (monoclinic, P2₁/c, a=0.74470 (3), b=1.04926 (3), c=1.09666 (5) nm, β=110.179(3)°, cuspidine-type structure), Ca₃Y₂Si₃O₁₂ (orthorhombic, Pnma, a=0.65420(3), b=1.56280 (6), c=1.00331(4)nm, silico-carnotite-type structure) and Ca₃Y₂Si₆O₁₈ (monoclinic, C2/c, a=1.33422 (5), b=0.77320 (3), c=1.47959 (6) nm, β=90.263(3)°). Reversible phase transformation of Ca₂Y₂Si₂O₉ was suggested from the examination of samples annealed at 1900K (orthorhombic) and at 1700K (monoclinic). The crystal structure of Ca₂Y₃Si₆O₂₆ was refined by Rietveld analysis for the X-ray powder diffraction pattern.

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The addition of polyethyleneglycol (PEG) to polynuclear hydroxoaluminum (PHA) ion solutions having high [OH/Al] ratios led to transparent composite gels on drying. PHA-PEG composite gels having high content of PEG were transformed into a single phase of γ-alumina upon heating above 850°C, while PHA gels were transformed into mixed phases γ- and χ-alumina. The addition of PEG suppressed the phase transition and shifted the transition temperature to higher temperatures, resulting in a high surface area and monomodal pore size distribution for γ-alumina. The grains of γ-alumina thus obtained exhibited transparency and a sharp and homogeneous pore size distribution around 3.4nm in diameter. The state of incorporated PEG phase may control pore distribution of γ-alumina because the interaction between PHA and PEG, through OH and ether groups, promotes the formation of clustered domains of loosely oriented PHA ions. The domains homogeneously dispersed in the matrix of PEG probably resulted in homogeneous precipitation of γ-alumina having a narrow particle distribution, leading to a sharp monomodal pore size distribution for γ-alumina. The addition of polyvinylalcohol (PVA) to PHA solutions had similar effects to that of PEG.

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A coprecipitate of the carbonate was first obtained by the titration of sodium carbonate into solution in which MnO, SrCO₃, and La₂O₃ were dissolved by hydrochloric acid. Heating the coprecipitate for 1h at 600°C, 7h at 1000°C, and successively 10h at 1300°C produced a sintered body of (La_1-xSr_x)MnO₃, which was observed by electron microscopy and analyzed by X-ray powder diffratoetory. As a result, it was clarified that the coprecipitation method enables to obtain the single phase in the range of x=0.4-0.6, which is not possible by the dry process. Even in the range x=0.2-0.4, where both the methods enable to obtain the single phase, the samples prepared by the coprecipitation method had better homogeneity and smaller compositional fluctuation than these prepared dry method.

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MgO-ZnO solid solution powders were synthesized by heating at 1400°C for 3h in air. A single phase with cubic type structure was obtained in the mass ratio (MgO/ZnO) of 4.0 and 1.5, but the ratio of 0.67 resulted in a ZnO phase in addition to MgO-ZnO solid solution. After milling the solid-solution powders by planetary ball mill, powders with average particle size of 0.1μm were obtained and used in the test of growth-inhibition of bacteria. From the results of these tests, it was found that the effect of growth inhibition against Escherichia coli and Staphylococcus aureus decreased with increasing the dopant amount of ZnO in MgO-ZnO solid solution.

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Highly-oriented Si nanoparticles (SNP) were precipitated in amorphous SiO₂ using separation by implanted oxygen (SIMOX) method and showed visible luminescence at room temperature. In order to investigate the microstructure of the SNPs, we observed the Si/SiO₂ interface by cross-sectional high-resolution transmission electron microscopy (HRTEM). The three-dimensional shape of the SNPs observed from different directions is an {111}-surrounded octahedral structure, each apex of which has an {100} facet. The upper (surface-side) interface of SiO₂/Si(100) contains missing atomic rows, while the lower (substrate-side) interface of Si(100)/SiO₂ is atomically flat except for the steps at the intersection with (111) plane. Similar atomically sharp structures were observed at the Si{111}/SiO₂ interfaces. Image-simulation of the interfaces well reproduced the microstructures observed by HRTEM and proved that the interfaces are those of amorphous SiO₂ and single-crystal Si without any intermediate layer.

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