A large magnitude of pressure was hydrostatically applied on silica glass. After removing the compression pressure, the silica glass shows an increase in refractive index and also in density, which is corresponding to the pressure. X-ray photographs of the densified specimens indicate that the profile of scattering intensities of haloes are different from those of the normal silica glass. The position of the strongest intensity shifts toward the higher angle with increasing the compression pressure. The manner of the structure changes of silica glass with increasing the compression pressure is discussed based on the ring structure-model of the SiO₄ tetrahedra and the radial distribution functions calculated from the profiles of the scattered intensities.

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Interaction energy between charged particles in submicron size range was calculated as a function of distance between particles or solid content for an aqueous colloidal system of monosize spherical particles. This calculation revealed the surface potential effect and particle size effect on the interaction energy. A metastable phase diagram for one-component colloidal system was constructed on the basis of the interaction energy between two charged particles. This phase diagram suggests that nature of colloidal suspensions of smaller particles approaches colloidal solid at lower solid contents.

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Silicalite, considered to be a polymorph of SiO₂, was prepared hydrothermally using amorphous silica, tetrapropylammonium bromide (TPA-Br) and NaOH. Silicalite was synthesized in a quartz glass ampoule under the following conditions; [NaOH]/[SiO₂]=0.2 and [TPA-Br]/[SiO₂]=0.1. With an increase of [NaOH]/[SiO₂] ratio quartz precipitated gradually instead of silicalite; thus, at 0.9 of [NaOH]/[SiO₂] ratio, the main product was quartz irrespective of the presence of TPA⁺ ion. Several ppms of aluminium and boron ions were always detected in the crystals. The extra addition of either of the two ions in the starting materials facilitated the formation of silicalite. Silicalite (or ZSM-5 of extra high silica content) is formed in a Pyrex glass ampoule or under the presence of Pyrex glass rods in a silica ampoule, though serious contamination (50-200ppm) by both ions is unavoidable.

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A computer simulation of a Cold Isostatic Press (CIP) densified bodies was carried out to estimate the initial relative density and the coordination number which are important factors to elaborate HIP maps. First, the mean coordination number and the packing fraction of CIPped bodies were calculated.
Secondly, these values were compared to those of other simulations for unidirectional packing model. Two assumptions were used to simulate CIPped bodies. They were (a) all particles were rigid spheres of the same size, and (b) they were moved initially toward the center to contact three other particles.
The results were as follows:
(1) The relative density and the mean coordination number of simulated CIPped bodies are 0.56 and 6.5, respectively. The coordination number is higher than the value obtained for an unidirectional packing model.
(2) The present model gives a reasonable relative density and coordination number for a CIPped body.
(3) The relative density and the mean coordination number of simulated CIPped bodies give good agreement with the initial state used in the HIP maps.

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The initial setting time of Portland cement containing sodium gluconate is quickly than that of cement without sodium gluconate. Such a behavior of early hydration is due to an action of the formation of ettringite. The formation process of ettringite from hydration of synthesized C₃A and CaSO₄⋅2H₂O with the addition of sodium gluconate was investigated from the changes in composition of liquid phase within several minutes with standing time. The results are summarized as follows. Calcium and sulfate contents in liquid phase increase by the addition of sodium gluconate, and the solubility of CaSO₄⋅2H₂O is also enlarged. The time shown high concentration of calcium and sulfate contents is longer than that without additives. It is resulted to form Ca complex with gluconic acid and Ca²⁺ in liquid phase. Ettringite was produced in this period and unreacted CaSO₄⋅2H₂O was disappered. The concentration of calcium content in liquid phase immediately increased after contact with water, and decreased after their, That is, the phenomenon of deposition happens rapidly after the dissolution. After the formation of Ca complex, gluconic acid was adsorbed on the surface of unhydrated particles. CaSO₄⋅2H₂O depressed the adsorption of gluconic acid on C₃A.

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Porous mullite ceramics were prepared from New Zealand kaolin with transition metal oxide (TiO₂, Fe₂O₃, CuO, CoO, or ZnO), fired at 1300°-1600°C, by leaching the glassy matrix with a 5N sodium hydroxide solution at 153°C under 5atm. Addition of the transition metal oxides was effective on the densification of the kaolin. Leaching rate evaluated by the depth of the leached layer of the sintered body decreased with an increase in firing temperature. However, formation of spinel phase in the ZnO- or CoO-containing sample suppressed the leaching rate. The growth of the needle mullite crystals became remarkable with an increase in the amount of the additives as well as sintering temperature, resulting in the enlargement of the average pore size in the range of 500 to 5100Å. Purity of the porous mullite ceramics was highest (99.6 wt%) for the sample with 5 wt% of CuO, fired at 1500°C for 1h.

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Corrosion of Si₃N₄ sintered bodies against blast furnace slags, converter slags and main components of these slags such as CaO, FeO and MnO₂ has been studied at 1200°-1400°C for 1-12h in air, Ar, N₂ and O₂-N₂ atmospheres. For Si₃N₄ sintered bodies containing small amounts of Y₂O₃ and Al₂O₃ additives, the corrosion rate increased with increasing pores and glass phase in sintered bodies. The corrosion behavior of Si₃N₄ sintered bodies against the various salts in Ar, N₂ and O₂-N₂ atmospheres, except for FeO salt, was very stable. In case of less corrosive salts such as blast furnace slag and CaO, the corrosion rate of Si₃N₄ sintered bodies in O₂-N₂ atmospheres increased with increasing O₂ partial pressure up to the air composition, the corrosion rate decreased extremely then above the air composition. In the corrosion of the Si₃N₄ sintered bodies against the various salts, the oxidation of Si₃N₄ seems to have occurred, and the corrosion proceeded continually by the reaction of SiO₂ with the salts.

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Mechanical properties of pressureless sintered TiB₂ with Cr₃C₂ additive was investigated. Cr₃C₂ plays an effective role in the densification of TiB₂. TiB₂ sintered with 5wt% Cr₃C₂ exhibited a bending strength of 320MPa and Vickers hardness of 24GPa. The fracture surface of TiB₂ sintered with Cr₃C₂ showed both transgranular and intergranular fracture modes. CrB and TiC phases were detected besides TiB₂ in the sintered body by XRD analysis and Cr₃C₂ disappeared.

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Highly pure β-sialon powders (z=2 and 3) derived from silicon-diimide were sintered by HIP without additives. The sintering behavior was compared with that of mixed powders of Si₃N₄, AlN and Al₂O₃. In synthesized powders, full density was attained after HIPing under 160MPa at 1500°C (z=3) and 1600°C (z=2) for 2h, respectively. These temperatures were found to be 100° to 300°C lower than that required to complete the sialon formation in mixed powders. After HlPing at the lowest temperature necessary for full densification, little grain growth was observed and maximum hardnesses of 16.5GPa (z=2) and 15.0GPa (z=3) were obtained. Fracture toughness was 3 to 4MPa⋅m^1/2 by the indentation method. Flexural strength was as low as 250 to 300MPa.

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Rod-like particles of Al₂TiO₅-MgTi₂O₅ solid solutions were synthesized by heating mixed powders of MgO, Al₂O₃ and TiO₂ above 1050°C in the presence of 10atom% mixed fluoride of MgF₂ and AlF₃. The rod diameter decreased with decreasing synthesis temperatures while the aspect ratio increased. At a certain temperature the rod diameter increased with increasing MgTi₂O₅ contents while the aspect ratio decreased. A sinterable powder composed of rod-like particles, in which rod diameter and aspect ratio were about 2μm and about 4, respectively, was obtained by heating the raw materials containing 50% MgTi₂O₅ at 1200°C. Using the rod-like particles, a sintered body of a highly oriented solid solution with the Lotgering's index f_//a of 0.76, was obtained. Thermal expansion anisotropy was observed, and the hysteresis of the expansion-shrinkage behavior was smaller than that of the sintered body without preferred orientation.

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Recently, Ri, Hamano and Nakagawa have experimentally revealed adsorption effect transistor characteristics of ZnO sinters [Yogyo-Kyokai-Shi, 93, 230-36 (1985); Yogyo-Kyokai-Shi, 94, 419-24 (1986)]. These results are computationally simulated for the sinters having the local states of bulk donors, grain boundary interface acceptors, surface acceptors and thermally desorbable surface donors in conformity with Fermi-Dirac's law for electron occupation, Poisson's equation for potential distribution and charge neutrality condition. Each parameter of the local states is concurrently obtained within the reasonable value. The potential barrier at necks with radius larger than the surface Debye length is weirlikely formed because of the interface and so independent of the surface states (open-out necks). The potential barrier at necks with radius smaller than the surface Debye length is formed in the shape of a saddle because of both the surfaces and the interfaces and so depends on the neck radius and the surface states in addition to the interface states. The bulk resistivity of sinters is obtained by the effective medium approximation for random networks in consideration of the neck radius distribution. The clusters bonded by the open-out necks percolate always through the sinters above 85% in the relative density. On the basis of the above, the hysteresis of bulk resistivity and adsorption effect transistor responses to admission of propane gas are analyzed.

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Mullite (3Al₂O₃⋅2SiO₂) has a low thermal expansion coefficient and low dielectric constant, so it is a favorable material for substrate applications. It is difficult, however, to sinter pure mullite ceramics even above 1700°C. Thus, mullite ceramics containing glass additives (Al₂O₃-MgO-SiO₂ glass) which could be sintered at about 1600°C were fabricated and their properties were investigated. At about 90wt% of silica content in glass, the mullite ceramics has a low dielectric constant (5.9), high bending strength (210MPa) and low thermal expansion coefficient (3.5×10^-6/°C). From electron diffraction analysis, sillimanite (Al₂O₃⋅SiO₂) crystals were observed at boundaries of these ceramics. These ceramics showed little grain growth, responsible for their high bending strength. Substrate of mullite ceramics are suitable for mounting silicon devices.

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Crystal structures of ilmenite type NaNbO₃ and LiNbO₃, which were prepared by low temperature hydrothermal and ionexchange reactions respectively, were refined by the X-ray powder Rietveld method. Final R-factors were R_wp=16.9, R_p=12.2, R_B=6.1% for NaNbO₃ and R_wp=13.9, R_p=11.1, R_B=5.7% for LiNbO₃. The mean Nb-O distances of both ilmenite type compounds agreed with those of their corresponding stable phases. The mean Na-O distance of the ilmenite type NaNbO₃ was as large as that of the spinel type Na₂WO₄, while, the mean Li-O distance in the ilmenite type LiNbO₃ was slightly larger than that of the LiNbO₃ type LiNbO₃ or other compounds containing LiO₆ octahedra. Structural refinement of other ilmenite type compounds of MgTiO₃, CdTiO₃, NaSbO₃, NaBiO₃ and KSbO₃ was also carried out by the X-ray powder Rietveld method. Stability field of ilmenite type compounds, ABO₃, was discussed on the basis of volumes of the AO₆ and BO₆ octahedra.

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The defect size distribution of the monofilament in which several types of defects coexist, was theoretically derived using the competing risk theory and the fracture location theory. The defect size distribution indicated a similar form of the multimodal Weibull distribution. This was because the defect size had the one-to-one correspondence to the fracture stress. To apply this theory in practice, we conducted tensile tests of PAN-based carbon fibers. Observed defect sizes of PAN-based carbon fibers coincided with the theoretical distribution as a first approximation.

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An investigation was made on the factors which affect the accuracy of the K_IC value for structural ceramics at high temperature region by single edge precracked beam (SEPB) method. A sharp pop-in precrack was introduced in a rectangular specimen of a polycrystalline alumina and silicon carbide by bridge indentation technique. The precracked specimens were fractured by three points bending with a cross-head speed of 0.5mm/min at a temperature from 800° to 1500°C in air. The precracked specimens were also fractured at room temperature after annealing at a temperature from 800° to 1600°C in air or vaccum. By comparing the K_IC values thus obtained, effects of crack healing and crack tip blunting on the K_IC values were discussed. The effect of healing and blanting on the K_IC values for an alumina measured at high temperatures was small owing to the weakened healing strength and active slow crack growth at these temperatures. On the other hand, the K_IC value for a silicon carbide increased remarkablly due to the effect of oxidation products formed at high temperature.

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Three kinds of high strength β-tricalcium phosphate (β-TCP) ceramics(β-TCP ceramic, β-TCP ceramic with solute magnesium content, and β-TCP-AIPO₄ composite ceramic) were prepared. Their biocompatibility was tested by a tissue culture method by use of a line cell derived from Chinese hamster (V79). Initial cell attachment of β-TCP ceramics was smaller than that of polystyrene tissue culture dish, because the surface of β-TCP ceramics was too hydrophilic for the attachment of cell. However, the rate of cell growth on β-TCP ceramics was faster than that of the polystyrene tissue culture dish. It was confirmed by the present tissue culture method, that the biocompatibility of β-TCP ceramics was not decreased by MgO or Al₂O₃-SiO₂ additive which was used for improving the strength of sintering body.

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The effects of whisker diameter and carbon coating to whiskers on the mechanical properties of SiC-whisker-reinforced cordierite composites were studied. The flexural strength of cordierite reinforced with whiskers of a small diameter was stronger than that with a large diameter. The fracture toughness of cordierite reinforced with whiskers of a small diameter was slightly larger than that with a large diameter. No significant effect of coating of whisker with carbon was observed on the flexural strength and fracture toughness of SiC-whisker reinforced cordierite composite.

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High-purity polycrystalline magnesia with different microstructures were prepared, and the effects of grain size on their bending strength and thermal shock damage resistance were investigated. The bending strength (δ_B) increased with decreasing grain size (D: μm), and expressed by following equationn. δ_B=403D^-0.26 (MPa). On the other hand, the thermal shock damage resistance increased linearly with increasing grain size, which was explained by the damage resistance parameter, R′′′=E/σ_T²(1-ν), where E is Young's modulus, ν is Poisson's ratio and σ_T is tensile strength. E and ν are unchanged and σ_T(σ_B×0.6) decreased with increasing grain size, so R′′′ increased with increasing grain size. Consequently, thermal shock damage resistance increased with increasing grain size.

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