The Knoop microhardness profiles were determined on the (100) of MgO⋅1Al₂O₃ and MgO⋅3Al₂O₃ single crystals. The ‹100› were the hardness maxima and the ‹110› the hardness minima for both compositions. The nonstoichiometric spinel was the most anisotropic, but the stoichiometric MgO⋅1Al₂O₃ crystal had the larger load-independent “true” hardness for all indentation orientations on the (100). The hardness profiles were found to be dominated by the {111}‹110› primary slip systems from comparison with the calculated ERSS diagrams for the crystals, although differences in the profile shapes were evident. The nonstoichiometric spinel exhibited the greater indentation load/size effect in terms of the Meyer's Law exponent.

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Composites with several compositions in TiC-SiC system were fabricated by chemical vapor deposition and several properties were measured. The CVD conditions used were, TiCl₄-SiCl₄-CH₄-H₂ system, deposition temperature of 1350°C and total gas pressure of 60Torr. The TiC-SiC composites with various compositions were fabricated by stepwise change in the Ti/(Ti+Si) ratio in the feed gas on the basis of thermodynamic calculation for the system. The obtained composites were fully dense with columnar structure perpendicular to the substrate plane and had (220) orientation on parallel there to. Thermal expansion coefficients of the TiC-SiC composites parallel to substrate ranged from 4.5 to 7.4×10^-6K^-1 and Young's Modulus perpendicular to the substrate ranged from 220 to 467GPa depending on the composition. These measured values agreed with that calculated from some rules of mixture in composite.

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Porous SiO₂-ZrO₂ glass was prepared from a sol containing polyethylene glycol (PEG) by the sol-gel method. After air-drying at room temperature, the gel was baked at 600°C. The ZrO₂ content in the porous glass was 30wt%. The median pore diameter of the porous glass was 2nm regardless of the molecular weight and amount of PEG added. The reproducibility of the pore size distribution was good, and the pore volume and surface area were linearly proportional to the amount of PEG added. Alkali resistance of the porous glass was much larger comparing to the porous SiO₂ glass.

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By measuring shrinkage and bulk density of the specimens at 900°-1700°C, sintering of three kinds of high purity ZrSiO₄ powders prepared from 0.2-0.8M ZrOCl₂ and colloidal silica was studied. The flexural strength of their sintered bodies at room temperature to 1400°C was also evaluated to investigate the effect of sintering conditions. In the initial stage of sintering of high purity ZrSiO₄ powders with an average particle size of 0.5μm, grain boundary diffusion was a dominant factor. The apparent activation energy for sintering in the initial stage was 81kJ/mol. On the other hand, when the average diameter of the particles is greater than 0.7μm, the bulk diffusion seemed to be overwhelming, and the apparent activation energy for sintering was higher than 130kJ/mol. In the intermediate and final stages of sintering, the powders with relatively large sizes have resulted in high bulk density. However, the strength of the specimen obtained using powders with large grain sizes was low since the grain growth proceeded significantly. The sintered bodies of high-purity ZrSiO₄ with excellent flexural strength at high temperature were obtained by sintering the powder with the average particle size of less than 0.5μm up to more than 98% of theoretical density.

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In order to strengthen and toughen Si₃N₄ ceramics by addition of SiC-whiskers, we tried the control of interfacial properties between whisker and matrix and of orientation of whiskers. For interfacial control, the effects of Al₂O₃, ZrO₂ and carbon coating to the surface of whiskers were studied. The flexural strength and the fracture toughness of Si₃N₄ composite containing Al₂O₃-coated whiskers by decomposition of aluminum stearate, were stronger (1107MPa) and larger (10.2MPa·m^1/2) than those of the composite with noncoated whiskers. TEM observation revealed that Al₂O₃-coated whiskers in the composite had smoother surface than non-coated whiskers and that a film-layer was formed at the interface between whisker and matrix. For orientation control, the flexural strength and the creep rupture resistance at 1250°C of Si₃N₄ composite, reinforced with uni-directionally oriented whiskers by the doctor-blade method, were much stronger (1180MPa) and much larger than those of monolithic Si₃N₄ ceramics. After creep testing, the new stacking fault and dislocation in the whiskers were observed by TEM. On the basis of these results, the mechanisms of toughening and high-temperature strengthening of SiC(w)/Si₃N₄ have been discussed.

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Effect of coarse quartz grains on mechanical properties of triaxial porcelain body was examined. Bodies composed of 50 kaolin, 25 potash feldspar and 25wt% fine quartz, which was replaced in turn with 74-149μm coarse ones, were fired at 1400°C for 1h. Their bulk density was about 2.38g/cm³ and hardly changed with the amount of coarse quartz. Bending strength of the fired specimens was markedly decreased from 1350kgf/cm² for the body free from the coarse quartz grains to about 900kgf/cm² by addition of only 0.03% of the coarse grains, and further decreased with an increase in the amount of coarse grains. Weibull coefficient of the bending strength increased with increase in the amount of the coarse quartz grains. Scattering in the bending strength values and also mean deviation of starting point of failure from the maximum stressed point decreased with increase in the content of the coarse quartz grains. From these relations, it was inferred that most failures of the specimens were started at the origin associated with the coarse quartz grains. The results clearly shows that not only the control of the quartz grain size within an appropriate range but also the prevention of the contamination by coarse quartz grains are indispensable for the increase in the mechanical strength of a porcelain body.

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The frost susceptibility of inorganic porous building materials was discussed from a viewpoint of quantitative analysis of internal pore structures. The analysis was undertaken on the basis of a couple of black-and-white image data, such as two dimensional pore-size distribution and three dimensional pore-connecting texture being constructed by a computer from original SEM photographs. The results were summarized as follows. The frost susceptibility showed excellent correlations with factors obtained by the quantitative analysis of pore-connecting texture. They are (a) an averaged shape factor (S) of the deviation from the perfect circle, a variance and a standard deviation about (S); (b) a distribution of (S) along with the polishing direction and a branching degree in a three dimensional connecting texture of pores; and (c) a fractal dimension calculated from the data of an accumulated pore-size distribution which was measured by the mercury-intrusion method. It is suggested that they should be used as promissing factors for the indirect evaluation of the frost susceptibility of inorganic building materials.

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The distribution of electric resistance in dielectric semiconductive ceramic can be observed using optical microscope and scanning electron microscopes by electrolytic etching in dilute acid. Using this method, insulating layers of BaTiO₃ surface semiconductive ceramic capacitor and SrTiO₃ boundary layer capacitors can be successfully observed. It is considered that the latter insulating boundary layers are different from Bi diffused layers.

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High temperature oxidation tests were carried out in a flowing O₂-N₂ mixture for gas-pressure-sintered Si₃N₄ containing Y₂O₃ and Al₂O₃ as sintering aids. The oxidation temperature and time were 1400°C and 15h, respectively and O₂ concentration in the gas mixture ranged from 1 to 100vol%. The oxidation reaction was monitored every minute by measuring of the evolved N₂ and NO gases with a quadrupole mass spectrometer. The oxidation rate expressed as the N₂ evolution rate was in the order 1%O₂>21%O₂≥100%O₂. In oxidation in high O₂ concentration, oxidation kinetics obeyed the parabolic law and a good conformity was obtained between the amount of N₂ evolved and the weight gain of the Si₃N₄ sample after the oxidation. At a low O₂ concentration (1vol%), the oxidation rate was partly expressed by the first-order kinetics and a poor conformity was observed between the amount of N₂ evolved and the weight gain. It should be noted that the conformity improved when the gas flow rate was greatly increased.

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Nicalon-SiC fibers were coated with C, SiC at 1200°C and 1300°C by chemical vapor deposition to improve the thermal stability of the fibers and to modify fiber-matrix interface. A coating layer having thickness of 0.1-25μm was obtained by controlling the CVD conditions. According to the AES and SEM analyses, a carbon rich layer (0.1-0.5μm) was deposited on the fiber surface initially. Nuclei of silicon carbide were formed on the surface of the carbon rich layer and finally whiskers or domed grains of silicon carbide were grown. The deposition rates of the carbon rich layer and silicon carbide layer were about 0.02μm/min and 0.65μm/min, respectively. It was observed by XRD and TEM that domed grains, which were the mixtures of β-SiC and small amount of α-SiC, consisted of subgrains and contained stacking faults in high density.

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New piezoelectric mechanical dampers have been fabricated using composites of piezoelectric ceramic: polymer: carbon black. Significant vibrational damping was observed in the composites with a ceramic volume fraction more than 50%. Damping characteristics are contlollable by changing the conductivity through the carbon black concentration.

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ZSM-5 zeolite with the molar ratios SiO₂/Al₂O₃=61-75 was synthesized hydrothermally at 220°C from silica stone containing Al₂O₃ component of 1.40wt% (occurred in Ioh island, Kagoshima Prefecture, Japan), with tetra-n-propylammonium bromide (TPABr) and NaOH solution. The formation ratio, yield, and morphology of ZSM-5 were strongly affected by the concentration of NaOH solution. Increasing NaOH concentration decreased the yield and SiO₂/Al₂O₃ ratio of ZSM-5. ZSM-5 zeolite formed from the silica stone smaller than 44μm in NaOH solutions of concentrations higher than 1.0mol/l consisted of rectangular particles of about 5μm. The Al₂O₃ and Fe₂O₃ components in the silica stone remained in the formed ZSM-5. It was possible to control the SiO₂/Al₂O₃ ratio of ZSM-5 from 44 to 431 by adding NaAlO₂ or amorphous SiO₂ to the Ioh island stone. Roles of Na and TPA ions in the formation of ZSM-5 were also discussed.

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The crystallization behavior of a glass in the SiO₂-Al₂O₃-CaO-ZnO-TiO₂-B₂O₃ system with additives was investigated by means of DTA, XRD and SEM observation. The additives were wollastonite, silica, lime, Fe₂O₃, alumina, zirconia, zircon, 36.6CaO⋅63.4SiO₂ glass, titania, montmorillonite, kaolin, talc, zeolite. The main results are as follows. (1) The most effective additives that reduced the double peaks of DTA curve into a single one were wollastonite, TiO₂ and 36.6CaO⋅63.4SiO₂ glass. Among them, only external addition of wollastonite shifted the peak temperature downward. (2) Crystal precipitation was enhanced on the wollastonite contacted glass surface. (3) The precipitated crystalline phase was speculated to consist of tiny particles of anorthite, gehlenite, willemite and titanite crystals.

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The leaching behavior of Y₂O₃-Al₂O₃-SiO₂ glasses was studied in connection with the hydrothermal corrosion of Si₃N₄-Y₂O₃/Al₂O₃ ceramics. Leaching tests were conducted with the glass blocks under hydrothermal conditions at 300°C for 1 to 10 days. It was found that the weight loss of the glasses is less than 0.8mg/cm² after 10 days and the durability of the glasses is higher than that of SiO₂ glass, Corning-1723 glass and Si₃N₄-Y₂O₃/Al₂O₃ ceramics. It was considered that the higher durability of the glass under hydrothermal conditions is due to the lower leach rates of Y₂O₃ and Al₂O₃.

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The thermal shock resistance of high thermal conductive SiC ceramics by the water quench method was studied in comparison with other SiC ceramics. The critical temperature difference (ΔT_C) of the flexural strength was dependent on the kinds of SiC ceramics. The high thermal conductive SiC ceramics had the highest ΔT_C value of 680°C. The hot-pressed SiC and pressureless-sintered SiC ceramics with smaller thermal conductivities had the ΔT_C values of 450° and 350°C, respectively. The thermal shock fracture resistance parameters (R′) calculated from the thermal conductivities at 500°C were 22kW/m for high thermal conductive SiC, 16kW/m for hot-pressed SiC and 12kW/m for pressureless-sintered SiC ceramics, which agreed qualitatively with the ΔT_C values. The ratio of the calculated stress intensity factor (K_I) for the crack initiation at the water quenching to the critical stress intensity factor (K_IC) obtained from the flexural strength was in the range of 60-80%, and were approximately constant in any examined SiC ceramics.

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A SiC/Al₂O₃ composite sheet was prepared from a green sheet composed of polycarbosilane (PCS) and Al₂O₃ powder with the weight ratio of 2:1. The green sheet was fired in the temperature range of 1200° to 1400°C under N₂ gas atmosphere, and three point bending strength of the composite was examined. The strength in room temperature increased with firing temperature and showed the maximum value of 333MPa at 1300°C. Dispersion of Al₂O₃ particles in the SiC matrix was effective to increase the strength of monolithic SiC sheet derived from PCS. When the composite was fired at 1400°C, however, the bending strength dropped rapidly in a similar manner as PCS-derived SiC fiber.

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Preparation of SiC-Si₃N₄ composite fine powders from chlorosilanes, C₂H₄ and NH₃ by R. F. thermal plasma was studied. SiC-Si₃N₄ composite fine powders were prepared by injecting chlorosilanes (SiCl₄, SiHCl₃, SiH₂Cl₂), C₂H₄ and NH₃ to the tail flame of R. F. plasma. When the powder was prepared from SiH₂Cl₂, C₂H₄ and NH₃, the powder composition depended on the C₂H₄ and NH₃ flow rate. When C₂H₄ flow rate was low, the powder contained SiC, Si, Si₃N₄ and amorphous phases. As the C₂H₄ flow rate increased, crystalline SiC, C and amorphous phases were present. The surface area of the powder was from 46.6 to 100m²/g and the particle size was from 0.02 to 0.2μm. TEM and SAED observation showed that these composite powders contained Si, SiC, Si₃N₄, C and amorphous particles. Si2p XPS spectra of the powder were separated into SiC, Si₃N₄, SiO₂ component. These composite powders were considered to be a mixture of SiC, Si₃N₄, C and amorphous particles. After heat treatment at 1773K for 1h in Ar, amorphous phase disappeared and the crystalline phases in the powder were SiC and Si₃N₄.

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A novel method for controlling the microstructure of a ceramic green body has been proposed. In this method, spherical granules with uniform size were placed mechanically in a regular array on a mesh, and then moved to a substrate (Micro mechanical processing). To demonstrate the potential of this method, alumina granules with size range 77-85μm were used as a model, and a hexagonal close packed structure was made. Uni-axial pressing of this array can create a uniform and orderly structured green body (Ordered structure).

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The contact angle θ of the melt with the SiO₂-MgO-Al₂O₃ ternary eutectic composition on W substrates and the penetrating behavior of the melt into W powder compacts were studied in the temperature range from 1350° to 1650°C in N₂/H₂ atmosphere. θ decreased with increasing temperature and θ in a wet H₂ atmosphere was about 20° smaller than that in the dry H₂ atmosphere. No time dependence of θ or no reaction between the melt and W was observed at 1600°C. The shrinkage of W compacts after the penetration of the melt was observed when θ was below 40°.

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(Pb, La) (Zr, Ti)O₃ films were prepared by CVD using Pb(DPM)₂, La(DPM)₃, Zr(O⋅t-Bu)₄, Ti(O⋅i-Pr)₄ and O₂ as starting materials. PLZT films were grown with almost complete epitaxy on (100) MgO substrates. The deposition rate of the film was about 50-100nm/min. Some optical properties were almost the same as those of PLZT ceramics.

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