In the carbothermal reduction-nitridation method of producing silicon nitride powder, the effects of addition of silicon nitride seeds on the particle size and α-content in the resulting silicon nitride powder were investigated. The ratio of carbon to silica was determined to be 2.2, which is somewhat higher than the stoichiometric ratio. The ratio was fixed in the subsequent experiments. Adding a small amount of seeds caused a steep increase of α-type in the resulting silicon nitride powder regardless of the types of seeds. However, as the amount of seeds increased, the powder began to reflect the original crystal form. The seed prepared through a pulverizing process yielded fine silicon nitride particles of 0.5 to 0.6μm, equal to the mean diameter of the seed. It is inferred that this was due to the existence of a large numbers of very fine particles in the seed powder. The seed made by the silicon-imide decomposition method produced relatively large particles because of the lack of very fine particles, the size being twice of the mean diameter of the seed. The relation between the numbers of seeds and resultant particle size (D) could be described by the equation D=k(1/N)^1/3, where N is the numbers of seeds and k is a constant.

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The reactions between ethoxytrimethylsilane and alkali ions were investigated by ²⁹Si NMR to evaluate the formation of Si-O-M (M: alkali metal) linkage. The difference in the reactions among alkali species was also discussed. The formation of the linkage was influenced by the pH of reaction mixture. The shift of NMR signal to higher magnetic field, which can be ascribed to linkage processes, was observed in the solution with pH greater than 13.1. The magnitude of the shift arising from the addition of alkali ions increased in the order of Na⁺, K⁺ and Li⁺. In the solution containing alkali ions, the efficient shielding of Si nuclei also increased in this order, which confirmed the strong Si-O-M linkage. However, little difference in the formation rates between Si-O-Na and Si-O-K was observed and the formation processes of Si-O-Li, Si-O-Na and Si-O-K were considered to be identical.

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Surface treatment is one of the most efficient ways to improve the water wettability, flowability and oxidation resistance of graphite powders used in castable refractories. In this study, the above properties of graphite powders coated with TiO₂ (formed by heating Ti(OCH₂CH₂CH₂CH₃)₄ at 120°C in air) were investigated. The results showed that the wettability and flowability of the graphite powders were greatly improved when the amount of TiO₂ coated was more than 0.5mass%, and the oxidation resistance increased with increasing amount of TiO₂ coated. The above improvement in the properties of the graphite powders was considered to be related to the changes in the size, shape and surface state of the powders.

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The improvement of the pyroelectric properties of Pb(Zr, Ti)O₃ (PZT) ceramics by means of compositional and morphological modification was realized. A compact body consisting mainly of equimolar PbZrO₃ (PZ) and PZT raw powders was encapsulated within a petri dish, followed by Ar-HIP under the conditions of 900°C-98MPa-2h. The dense body obtained was probably composed of the two raw powders and their serial solid solutions, of which the temperature dependence of the pyroelectric coefficient of 9.4×10^-4C·m^-2·°C^-1 at 25°C was almost flat over a wide temperature range of 15-70°C. Furthermore, the figure of merit (FM1) of this dense body was 199×10^-14C·m·J^-1 which was sufficient for practical applications.

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Phase relations in the system tricalcium phosphate (3CaO⋅P₂O₅=C₃P)-enstatite (MgO⋅SiO₂=MS) have been investigated in the temperature range 1100 to 1600°C by means of the quenching method. C₃P takes β-type (whitrockite) in a wide region by dissolution of MgO, and diopside (d) appeared in the composition range more than 40mass% C₃P by a reach in between MgSiO₃ and liberated CaO. The enstatite transfers to iron-free pigeonite (pi) by taking CaO in an MS-rich region, where pi coexists with protoenstatite, MgSiO₃ (pr). Primary crystals which appeared in a wide region are β-C₃P and pi, and primary diopside appears in a narrow region at a minimum temperature (1265-1305°C). In the subsolidus region below 1245°C, β-C₃P coexists with d, pi or pi-pr mixture. The system is not binary and it should be discussed from the ternary system C₃P-M-S and the quaternary system C₃P-CMS₂-MS-S.

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Residual stresses in Al₂O₃ and Si₃N₄-matrix nanocomposites (added with β-SiC or WC phase) have been measured by piezo-spectroscopy. The highest residual stress value was found in Al₂O₃-matrix materials. Machining procedures have been found to play a minor role in the formation of residual stresses. Analyses of both spectroscopic and strength data suggest that, when the coefficient of thermal expansion of the matrix material is much higher than that of the added dispersoid, an apparent strengthening effect may arise in nanocomposite materials. However, this effect does not arise from an actual enhancement of the inherent material toughness, since it is proved that any strength enhancement vanishes in presence of externally introduced flaws≥30μm.

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This paper shows that silica sol derived from silicon alkoxide is an excellent additive for resin. Silica disperses into the matrix of resin by using emulsion type phenol resin, and it can mix in resin homogeneously by using resol type phenol resin. It is well known that silica sol derived from silicon alkoxide consists of ultra fine particles. In the present study, a clear colorless silica sol has been prepared by hydrolysis of tetraethyl orthosilicate (TEOS) using p-toluenesulfonic acid monohydrate as a catalyst. The silica sol was mixed well in resol type phenol resin, and the contents of silica in coatings was higher in the case of resol type phenol resin than that of emulsion type phenol resin. The coatings were evaluated on the degree of surface-cracks, on chemical resistance (acidic and basic aqueous solutions) based on peeling from substrate, on hardness and on resistance to fire. Emulsion type phenol resin and resol type phenol resin were used. Both of the coatings up to 30mass% silica-contents in the former and 45mass% silica-contents in the latter were crack-free. Chemical resistance was not degra-dated by the addition of silica. Hardness and resistance to fire were remarkably improved by the addition of silica sol.

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Effect of suction pressure p_cap and permeability K_m of plaster mold on the slip casting of a high concentrated alumina slurry of 58.8vol% was investigated. Three cylindrical plaster molds were fabricated from the slurries having water-to-plaster mass ratios of 0.55, 0.63 and 1, and designated as the 55%-mold, 63%-mold and 100%-mold. The 55%, 63% and 100%-molds were characterized by low p_cap and low K_m, high p_cap and low K_m, and low p_cap and high K_m, respectively. Casting rate at an early stage increased with increasing p_cap×K_m or K_m, and average bulk density of cast body increased with increasing p_cap. Local green density increased from the center toward the wall of mold because of consolidation of the compressible cake. High p_cap×K_m and low p_cap enhanced percolation effect, and resulted in remarkable segregation of fine particles near the mold wall. Green body with a high relative density of 66.3% and a homogeneous density distribution was obtained from the 63%-mold showing high p_cap and low K_m.

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The reaction of silicon carbide (SiC) particles with molten carbon-saturated iron was studied to find the optimum conditions for SiC application to refractories in the iron- and steel-making process. When compared with C brick, C-SiC brick dipped into carbon-saturated iron at 1500°C under 0.2-0.5MPa for 1h was less penetrated by iron. Optical microscope and scanning electron microscope observations showed morphological changes of SiC grains at the hot face of C-SiC brick as well as adhesion of Fe-Si metal to the SiC grains. The reaction mechanism was discussed using phase diagrams and thermodynamic data. In conclusion, the iron which penetrates the brick causes a breakdown of SiC in which Si dissolves into the iron. C of SiC and C in the iron precipitate on the surface of SiC grains. Moreover, the increase of Si in the iron raises its viscosity. This result shows that SiC grains act to inhibit iron penetration into carbon-based refractories.

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A new hybridized process for preparing optical fibers has been developed. The process consists of overcladding a VAD-derived core rod with commercial silica powder by cold isostatic pressing (CIP) technique. Single-mode optical fibers were fabricated by the process which used the core rod having a ratio of core to cladding radius of 3 and silica powder of average particle diameter of 10μm. The losses were 0.36dB/km at 1.3μm and 0.23dB/km at 1.55μm. The points for the process are following; (1) Silica powder was granulated by spray dryer from slurry containing poly-vinyl-alcohol (PVA) to be packed uniformly into a rubber mold for CIP forming. (2) To prevent the core rod from breaking in the compression, a rubber mold with a structure in which both ends of the core rod were pressed by hydrostatic pressure was used. This CIP process provided the hybridized soot preform which consisted of the core rod and a porous body around it from silica powder in one step. (3) It was very important that 10μm silica powder was used because it was easy to purify into high-purity glass. (4) To remove PVA which was added in granulating, heat treatment was carried out at 500°C in an atmosphere of dry air. The heat-treated porous body containing 25ppm carbon was consolidated into the overcladding glass for low-loss optical fibers. Further, a relation between the pore diameter and purification of the porous body was studied. As a result, pores with more than 0.2μm diameter were presumed to be required for making high-purity glass by chlorine purification.

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The effect of temperature and applied stress on the ferroelastic behavior of partially stabilized zirconia pseudo-single crystals doped with 3mol% yttria was studied using a uniaxial compression method at high temperature. X-ray diffraction patterns showed that the ferroelastic domains were rearranged to orthogonal two directions. The amount of domain switching increased with increasing applied stress but remained with loading time. The critical stress required to induce the ferroelastic domain switching decreased with increasing temperature; 200MPa at 700°C, 160MPa at 800°C, 125MPa at 1000°C and 100MPa at 1200°C. The activation energy of domain switching was calculated to be about 16kJ/mol using critical stress vs. temperature plot. The model for explaining a domain switching mechanism was proposed on the basis of the displacement of ions.

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Silicon-nitride ceramics were joined to metal with an 80mass% Ni-20mass% Cr alloy sheet as an insert material. Joining was performed between 1323 and 1473K in vacuum. Microstructures and growth behavior of reaction layers and the influence of annealing after joining were investigated with a scanning electron microscope and an electron probe microanalyzer. On the joints bonded at 1323-1423K, the reaction layers including a large ammount of Ni solid solution were formed, whereas the reaction layers bonded at 1473K primarily consisted of fine chromium nitrides. Growth of reaction layers obeyed the parabolic law and rate constants (k_p) for the growth were 9.6×10^-16-2.5×10^-14m²/s at 1323-1473K. The activation energy for the growth of reaction layers (Q_kp) was 305kJ/mol. The fracture bending strength of Si₃N₄/Inconel couples showed the maximum of 590MPa at room temperature. The joints bonded at 1343 and 1473K were annealed at 1073K for 720ks in vacuum. Variations in microstructure and composition of the reaction layers of joints bonded at 1343K were observed, and the fracture bending strength showed large degradation. On the other hand, those of joints bonded at 1473K remained almost unchanged on annealing.

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The effects of the concentration of titanium (IV) chloride solution, aging temperature and time, and the pH of solution on the morphology and size of hydrous titanium (IV) oxide fine particles formed by a colloid aging method were studied in detail. Cube-shaped particles of 0.20μm in size were formed by aging 2.5×10^-2mol·dm^-3 titanium (IV) chloride solution at room temperature for 5d. The cube-shaped particles were easily attained by decreasing the titanium (IV) chloride concentration and/or increasing the aging temperature. The aging of 5.0×10^-2mol·dm^-3 titanium (IV) chloride solution with urea at 90°C for 20h gave needlelike-shaped, cube-shaped, and spherical particles in the ranges of pH<1, 1≤pH<2 and 6<pH, respectively. Cube-shaped particles of 0.24μm in size used as seeds were successively grown to 0.38μm in size under the same aging conditions described above except without urea. It is concluded that both the chloride ion and the pH of solution play an important role on the formation of cube-shaped hydrous titanium (IV) oxide fine particles.

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Bulk densities and their sintering shrinkages of different radius compact disks cut from a CIP compact were measured to investigate the influence of compressibility of granules in compression test on density distribution in a CIP compact. Two kinds of granules, Al₂O₃ and SiC, with different compressibility were used. Bulk densities of compact disks increased with increasing the radius of disks and sintering shrinkages decreased with increasing the radius. All these things made it clear that there was density distribution in radial directions of CIP compacts. SiC compact by CIP produced much lager difference of density in radial direction, compared with Al₂O₃ compact. It seemed reasonable to suppose that the compressibility and surface condition of granules had an influence on producing differences of density in radial direction.

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Two kinds of composites of MoSi₂ and ZrO₂ stabilized with 8mol% Y₂O₃ (8Y-ZrO₂) were fabricated by sintering at 1873K for 90min under a vacuum of 2-8×10^-3Pa and subsequent HIPing at 1873K for 60min in Ar. The mechanical properties for both bodies were determined at room temperature. No new compound was produced in the MoSi₂/ZrO₂ composites by firing up to 1873K for 90min under a reduced pressure. Young's modulus of MoSi₂/8Y-ZrO₂ composites decreased linearly with an increase in the amount of 8Y-ZrO₂. On the other hand, Vickers hardness of the composites increased with an increase in the amount of 8Y-ZrO₂ and the effect of HIPing for sintered bodies on these values was clearly noticed. The bending strength of composites increased and then decreased with an increase in the amount of 8Y-ZrO₂. The bending strength of HIPed bodies was higher than that of as-sintered bodies over the 8Y-ZrO₂ content range of 0-60vol%. The 8Y-ZrO₂ content dependence of fracture toughness for composites was almost the same as that of bending strength, although the amount of 8Y-ZrO₂ at which the bending strength and fracture toughness for composites take a maximum values, were different.

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Main process of the powder particles' assembly, proposed for creation of multi-functional materials, consists of drawing electrified patterns on substrates and introducing electrified powder particles onto the substrates. In the process, the powder particles are arranged along with the patterns by electrostatic force. In the present paper, electrification behaviors on ceramic substrates was studied. Electrified images were formed on calcium titanium oxide (CaTiO₃) substrates using electron beam. The substrates were positively electrified by 1kV electron beam, while the substrates were negatively electrified by electron beams with 3kV and higher voltages. Electrified images were observed by the voltage contrast method using 2kV electron beam scanning. Sharpness of electrified images were influenced by the condition of electron exposure. Sharp images were obtained by the electron beams with dose electron density of 0.2pC/μm² and accelerating voltage of 5-15kV. The electrified images disappeared after 1h in air, but were maintained for 62h in vacuum.

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The effect of microstructure on the fatigue behavior at room temperature in air was studied using sialon ceramics with different microstructures prepared by selecting starting raw materials and sintering conditions. Dynamic, static and cyclic fatigue tests were carried out on smooth specimens by the 3-point bending method. Oxide content in the intergranular phase and grain size affectted the dynamic fatigue behavior. Remarkable slow crack growth attributable to the stress corrosion by humidity in air was observed in the sample with elongated grains. In static fatigue tests, the observed lifetime of each sample was in agreement with that predicted from dynamic fatigue properties, and the crack propagated through the intergranular phase. The acceleration of fatigue was observed under cyclic loading. The accelerative effects on cyclic fatigue was significant in the sample with coarse grains. Sialon ceramics with elongated grains prepared by HIP showed both high fracture toughness and high strength, but the fatigue parameter “n” was low and the acceleration of fatigue under cyclic loading was significant because of its coarse grains.

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To examine the microstructure development in alumina ceramics, green bodies made by injection molding were densified under various conditions and examined by X-ray diffraction analysis and scanning electron microscopy coupled with image analysis. Although a previous paper showed that powder particles were oriented slightly, conventional characterization method used in the present study showed that the particles were randomly packed. Pronounced grain orientation occurred in the densification/grain growth process from the minor particle orientation in the green body. In the final ceramics, grains were aligned along the flow direction in the injection process.

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Softening and sintering behavior of Al₂O₃-SiO₂(AS), Al₂O₃-SiO₂-ZrO₂(ASZ) and Al₂O₃-SiO₂-Cr₂O₃(ASC) glass fibers that are generally called ceramic fibers were investigated by dilatometric measurement. Thermal linear change of a single fiber was measured with an optical microscope with a hot stage. All the fibers showed sharp shrinkage at about 1000°C due to crystallization. Glass spheres that have the same composition as the glass fibers and compacted bodies of the crushed glass fibers showed shrinkage at about 1200°C in addition to the shrinkage at about 1000°C. The shrinkage at 1200°C for the glass spheres was governed by softening, and the shrinkage of the compacted body of crushed glass fibers was governed by sintering and softening. Softening of the glass spheres was in the order of ASC≥AS>ASZ and sintering of glass fiber was in the oder of ASZ=AS>ASC at 1400°C. Sintering of glass fibers was governed by the viscous flow mechanism and its apparent activation energy changed at about 1300°C.

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It is well known that solid solution is formed in the SiC-AlN system over a wide compositional range. However, the proposed composition range for homogeneous alloy formation is hardly obtained by conventional sintering of powder mixtures of SiC and AlN due to the low diffusivity in the two covalently-bonded compounds. The present study was focused on the preparation of SiC-AlN solid solutions by in-situ HIP-sintering of premixed powder of Si, C and AlN, which was considered to be a handy and less-complicated process as compared to existing ones. It was found that the formation of SiC from Si and C occurred remarkably above the melting point of Si, and fully dense SiC-AlN ceramics could be obtained under the HIP-sintering condition of 2123K and 200MPa. The HIP-sintered compacts showed fine-grained microstructures consisting of SiC-rich and AlN-rich solid solutions with approximate compositions shown in the phase diagram. The mechanical properties, in particular, the fracture strength and hardness of the HIP-sintered SiC-AlN solid solutions and/or mixed composites were better than those of the monolithic SiC and AlN.

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