The precipitates with TiO₂/K₂O molar ratio=4 were obtained by hydroysis of KOH-Ti(iso-C₃H₇O)₄ ethanol solution. The dried product was amorphous, and changed to a crystalline intermediate by heat-treating at about 600°C. The well grown submicron crystals of K₂Ti₄O₉ were obtained by heat-treatment at 1000°C for 1h.

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The electrophoretic deposition method was used to form an alumina layer with a thickness of about 1mm. Alpha alumina powders with average diameters of 0.2 and 0.6μm were dispersed in water at pH 2.5 to provide positive charge. Positively charged alumina particles in the aqueous suspension of 15vol% solid were deposited on a cylindrical carbon electrode by passing direct current of 5-200mA at 50-300V. The weight of the alumina layer was proportional to the deposition time and applied voltage. Electrolysis of the HCl solution occurred together with the electrophoretic deposition of alumina particles. The deposition efficiency calculated from the deposition rate of alumina particles was in the range of 0.13 to 0.15. The density and thickness of the formed alumina layer increased periodically with deposition time. The alumina layers with relative densities of 56-62%, formed from the 0.6μm-alumina powder, were sintered at 1100°-1500°C in air. The densification rate was reduced above 1400°C by large pores (200-500μm).

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Fracture stress (σ_f) of tetragonal zirconia ceramics containing 4mol% Y₂O₃ was measured as a function of stressing rate (σ) (dynamic fatigue). Linear relationships were obtained between log σ_f and logσ at room temperature. Crack growth parameters N obtained from the slopes of the linear relationships were 32 for grain size of 0.47μm (Z4Y-Ia), 33 for 0.62μm (Z4Y-Ic) and 46 for 1.34μm (Z4Y-II). A linear relationship was observed between log σ_f and log σ for Z4Y-Ic at 250°C, and the N value was 41. Log σ_f for Z4Y-II at 250°C was constant at stressing rates above 30.2MPa/s. The N value obtained for stressing rates below 3.02MPa/s was 8.7. The time to failure t_f under several applied stresses σ's measured for the specimen with a grain size of 1.34μm (Z4Y-II) at 250°C (static fatigue) was similar to the life time predicted from dynamic fatigue data. A linear relationship was observed between logt_f and logσ, and the N value obtained from the slope was 7.3.

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Using a radio-frequency (rf) thermal plasma torch with a water cooled nozzle, the diamond film was synthesized at the maximum rate of 880μm/h on a molybdenum substrate from CH₄ and H₂ at a torch pressure of 517 Torr. The deposition rate was studied as a function of following parameters: diameter of the nozzle (6 to 24mm), diameter of the plasma torch (50 and 60mm), plate power (44 to 81kW), torch pressure (740 to 400 Torr), and CH₄/H₂ feed ratio (4 to 5%). The deposition rate increased with decreasing the nozzle diameter from 24 to 8mm but decreased at 6mm. The columnar-like films were obtained after one hour deposition with the nozzles of 12, 10, and 8mm in diameter.

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To improve the thermal stability of Y-TZP, the fabrication and properties of yttria- and ceria-doped tetragonal zirconia ((Y, Ce)-TZP)/alumina (Al₂O₃) and Y-TZP/Al₂O₃ composites using fine powders prepared by a hydrolysis technique were studied. The mean values of the bending strength of the composites consisting of 25wt% Al₂O₃ and (Y, Ce)-TZP with compositions 4mol% YO_1.5-4mol% CeO₂-ZrO₂, 2.5mol% YO_1.5-4mol% CeO₂-ZrO₂ and 2.5mol% YO_1.5-5.5mol% CeO₂-ZrO₂ were 1000-1100MPa. (Y, Ce)-TZP/Al₂O₃ composites showed no t→m phase transformation on aging at 250°C in air for 1500h. (4Y, 4Ce)-TZP/25wt% Al₂O₃ and (2.5Y, 5.5Ce)-TZP/25wt%Al₂O₃ composites showed no structural degradation and superior stability under the hydrothermal conditions at 180°C and 1MPa as compared with 3Y-TZP, (Y, Ce)-TZP and Y-TZP/Al₂O₃ composites.

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Conditions of the operation (impregnation method) of the impregnation-dehydration-heating (under 800°C) of the CrO₃ saturated aqueous solution to Al₂O₃ compacts and the filling process of Cr₂O₃ to the basic materials have been investigated utilizing DTA-TG, XRD, SEM, and a Vickers hardness meter. In the heating operation of the Al₂O₃ compacts to which CrO₃ is impregnated, CrO₃ has produced only finely-powdered Cr₂O₃(≤0.5μm) at a temperature of more than 500°C and the said fine powders of Cr₂O₃ has caused increase of the filling weight to the compacts. In case of more than the number of the times of impregnation where the filling weight or Cr₂O₃ to the fired bodies is almost saturated, a densification layer of Cr₂O₃ was formed in the vicinity of the surface of the fired bodies. The densification layer in question exerts remarkable influence upon the hardness values of Al₂O₃-Cr₂O₃ fired body surface, and the fired body surface hardness has been determined in accordance with the degree of densification layer.

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The densification and grain growth of high purity Al₂O₃ and Al₂O₃-15vol% ZrO₂ were examined in the final stage of sintering. Both densification and grain growth took place much faster in Al₂O₃ than in Al₂O₃-15vol% ZrO₂. The densification rate of Al₂O₃ was explained by the rate equation proposed by Ashby et al., which was slightly modified by taking into account the actual distribution of pores. On the other hand, the densification rate of Al₂O₃-15vol% ZrO₂ was much sluggish than that estimated from the modified rate equation. The grain-boundary diffusion of constituent ions might be retarded by the zirconia addition.

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Post-indentation slow crack growth in soda-lime-silica glass in various aqueous RNO₃ (R⁺; Li⁺, Na⁺, K⁺, Rb⁺) solutions was investigated in order to understand the mechanism of stress corrosion of glass. The crack growth was found to depend on both the concentration and the nature of the supporting electrolytes. The crack growth was enhanced by the change in the concentration of alkali metal ions from 10^-4-1M, and also by the nature of alkali metal ions in the order of Hofmeister series Li⁺<Na⁺<K⁺<Rb⁺ at the ion concentration of 10^-2M. These behaviors showed that the results obtained can be interpreted in terms of the molecular structure of the glass/electrolyte interface based on the charged states.

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Hot presseed Ti (C, N)-30wt% TiB₂ ceramics have an average bending strength of 900MPa, but have a wide distribution of bending strength. The additive effects of carbide, namely ZrC, HfC and NbC, were examined in order to improve the distribution, Addition of these carbides caused that the recommendable sintering temperature is lower than that of Ti(C, N)-30wt% TiB₂ system. The addition of 5wt% HfC improved the Weibull coefficient from 8 to 12. Ti(C, N)-30wt% TiB₂-5wt% HfC materials had the Vickers hardness of 2100 and the fracture toughness K_IC of 4MPa·m^1/2. The hardness and K_IC values were same as those of Ti(C, N)-30wt% TiB₂ materials. These phenomena can be explained by the following facts. Added HfC particles react with the Ti(C, N) particles to form Ti rich or Hf rich solid solution of (Ti, Hf) (C, N). These solid solutions limit the grain growth of Ti(C, N). The lower sintering temperature of this system is also effective to suppress the grain growth. The limited grain growth makes higher transverse rupture strengths and their minimized distribution. However, no change in hardness and K_IC occurred because of the formation of Ti rich or Hf rich solid solution of (Ti, Hf) (C, N).

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Trimagnesium phosphate hydrate was synthesized by mechanochemical reaction of a slurry of magnesium hydrogen phosphate trihydrate and magnesium oxide with the molar ratio of 2:1 in a pot mill for a few hours. Mg₃(PO₄)₂⋅8H₂O was obtained by using a slurry with more than 60wt% water; Mg₃(PO₄)₂⋅22H₂O, with 40wt% water. The anhydrate of trimagnesium phosphate was obtained by heating Mg₃(PO₄)₂⋅8H₂O or Mg₃(PO₄)₂⋅22H₂O above 700°C.

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The effect of grain size of quartz on mechanical strength of porcelain body was examined. The bending strength of the fired body increased with an increase in interplanar spacing of quartz in the fired body, which indicates that the quartz is under a tensile stress. Con-sequently, the glassy matrix surrounding the quartz grains is a compressive stress which acts as prestress, improving mechanical properties. The strength of the body depends on the grain size of quartz, and maximum strengths were obtained at 10-20, 5-10 and <5μm, respectively, fired at 1400°, 1350°-1250°C and 1200°C. Smaller and larger quartz grains gave lower strength, probably because of extensive dissolution and crack generation, respectively.

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The dielectric properties of Pb(Mg, Nb)O₃ ceramics with various B-site ratios (Mg/Nb=M/N ratio) were investigated. With changing M/N ratio from 0.30 to 1.00 (stoichiometric ratio=0.50), the dielectric constant changed largely. Particularly, it showed the maximum of 20000 at T_c at a non-stoichiometric ratio (M/N) of 0.66. The resistivity ρ, tanδ and T_c were a most independent of the M/N ratio. Crystal phase analysis, in the case of small M/N ratio (0.3) showed that the main phase was pyrochlore with low dielectric constant. Samples with M/N ratios higher than the stoichiometric one had a perovskite phase. Moreover, it was observed that the lattice constant at M/N ratio=0.66 was larger than that of the stoichiometric one. The change of dielectric constant seems to be associated with the crystal structure and the lattice constant.

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Both an anomalous broad dielectric peak above the Curie temperature and a normal sharp dielectric peak at the Curie temperature were observed in Pb_1-XLa_2X/3 TiO₃ (X=0.05-0.20) ceramics. The broad dielectric peak shifted toward higher temperatures with increasing frequency, associated with a decrease in its peak value. The complex impedance loci consisting of two semicircles were found for the materials above the Curie temperature indicating that the dielectric property can be analyzed using an equivalent circuit with a series connection of two RC parallel circuits. The origin of the broad peak has been tentatively interpreted to be an interfacial polarization at the grain boundaries.

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Viscometers capable of measuring a wide range of viscosity covering 1-10¹²Pa·s were developped and tested for some alkali silicate glasses. For the range of 10³-10⁸Pa·s, a conventional viscometer was used with a 5mm wide and 10mm long penetration tip of alumina tube, which lowered the measurable viscosity range maintaining the precision. For the range of 10⁸-10¹²Pa·s, the beam-bending principle was utilized. By applying load to a sheet glass specimen with an alumina tube, and by heating at 3°C/min, viscosities in the range of 10⁸-10¹²Pa·s were measured in a single run. It was shown that these viscometers can be applied to Li₂O-Na₂O-2SiO₂ glasses. It was demonstrated that glass transition temperature T_g agrees well with the temperature at which a viscosity of 10¹²Pa·s was attained. It was also found that the viscosity vs. temperature relationship can be described by the Fulcher's type equation over the wide range temperature with good accuracy.

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To determine the content of o′-phase in β′-o′sialon ceramics, green compacts of a Si₃N₄ powder and boehmite sol were oxidized at 900°-1050°C, followed by sintering and HIPing. The ratios of O/N in the prepared sialons were changed at a fixed ratio of Si/Al. X-ray diffractometry, optical and scanning electron microscopy, electron-probe microanalysis were used for examination. Optical and electronmicrographs coupled with image analysis showed that, with increasing oxidation temperature, the amount of o′-phase increased and its grain size decreased. The o′-phase contents determined were well correlated to that calculated from the XRD results. These results explained the densities of sialon ceramics.

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Preparation of SiO₂-TiO₂ fibers containing various TiO₂ contents by a new method was investigated. In order to obtain polytitanosiloxanes (PTS), a precursor, partially hydrolyzed tetraethoxysilane (TEOS) was brought into reaction with bis (2, 4-pentanedionato) titanium diisopropoxide (PTP) in methanol in various molar ratios of TEOS/PTP from 1 to 15. Concentration of the resultant methanol solutions of PTS gave sols with spinnability, from which SiO₂-TiO₂ ceramic fibers containing 5-50 TiO₂ mol% were prepared.

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Mechanical properties of a commercial SiC-fiber/CVI-SiC composite were examined. The composite showed high fracture toughness (12.5MPa·m^1/2) and low strength (162MPa in tensile strength) comparing to those far other engineering ceramics, resulting from fracture behavior dependent on the microstructure. The high fracture toughness is a result of fiber debonding and pull-out effects, however, the low strength is associated with porous microstructure.

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Hydrolysis of aluminum secondary-butoxide was studied in various solvents. Mixtures of n-octanol and organic solvents affected the properties of the final products. Gel was formed when hydrophobic solvents were added, whereas sol was formed in case of hydrophilic solvents. The mixed solvent of n-octanol and acetonitrile was found to be optimum in the preparation of monodispersed spherical powders. In addition, the influences of water, acetonitrile, dispersant, hydrolysis temperature and aging time on the preparations of monodispersed aluminum oxide particles were investigated.

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