The microwave joining of Al₂O₃ to MgO was attempted with a single mode cavity furnace as an example of joining of different kinds of ceramics. The joining was possible under the following conditions; joining temperature: 1850-2150K, joining pressure: 0.03-0.5MPa and heating time: 2-10min. Samples joined at 2150K and 0.5MPa for 4min had a maximum bending strength of 90MPa which was about 60% of the MgO specimen. An MgAl₂O₄ layer was formed by the reaction between Al₂O₃ and MgO at the interface. A crack which developed during the bending test propagated along the interface of the MgAl₂O₄ phase and the MgO one. The hardness of the joined region was higher than that of the other region without heating.

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PbTiO₃(PT)-PbO-B₂O₃ ferroelectric glass-ceramic thin films were produced by a sol-gel process. A pin-hole free thin film was obtained when it was prepared in a way that small PT crystals developed in a glass matrix using the RTA technique. The achievement of high PT content (>50mol%) at levels unattainable by the conventional glass-ceramics preparation methods was semiquantitatively shown. PT crystallized at a temperature below 500°C. The dielectric properties of the 0.6PT-0.4(PbO⋅B₂O₃) film fired at 600°C were ε=143, and tanδ=0.04.

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Anatase films for a photocatalyst have been prepared on substrates by a dip-coating technique using peroxotitanic acid (PTA) solution and peroxo-modified anatase (PA) sol. The as-dried film prepared from PA sol had already crystallized to anatase phase, while the film prepared from PTA solution crystallized above 300°C. Adhesion strength of the films at 300°C was over 60MPa, and their relative density was over 80%. Photocatalytic efficiency of the film prepared from PA sol for the degradation of acetic acid was higher than that of the film prepared from PTA solution. The films obtained above 300°C from PA sol exhibited the highest catalytic activity. However, the film less than 0.70μm thick resulted in decrease of photocatalysis.

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Large transparent specimens of polycrystalline zinc oxide with c-axis orientation prepared by the vapor transport method are submitted to open-aperture Z-scan measurement at 532nm. The effective two-photon absorption coefficient β_eff of the polycrystalline ZnO is determined to be 8.6±1.4cm/GW. Optical power-limiting behavior associated with the two-photon absorption is observed clearly in the polycrystalline ZnO of 0.95mm thick under the incident beam irradiance of interest.

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Syntheses, sinterings and vaporizations of double oxides of Li₂O⋅WO₃(1/1), 2Li₂O⋅WO₃(2/1) and 3Li₂O⋅WO₃(3/1) in the system Li₂O-WO₃ were investigated. 1/1 mixture changed to 3/2 compound at 100°C and 1/1 formed above 500°C. Sinterings of 1/1 were made at 700°C for 4h with relative density (RD) of 89-91%. 2/1 mixtume changed to α-2/1 from 100 to 700°C and β-2/1 appeared in the temperature range from 740 to 1000°C. Sinterings were made at 800 to 1000°C with RD of 45-47%. 3/1 mixture began to form 3/1 at 600-700°C and maximum yield of 3/1 compound was obtained at 1000°C. Sinterings were made at 900-950°C for 3h with RD of 62-80%. Vaporization experiments on pellets (1.37cm in dia.) were made in air flow (1cm·min^-1) at temperatures from 700 to 1000°C, and straight lines with slopes from 0.2 to 1.0 were obtained on a log-log graph of both vaporization and time. These slope values increased approaching to 1 with increasing vaporization time. From the vaporization rates at early stages, an activation energy of 170kJ·mol^-1 was obtained for 3/1 compound. Products after the vaporizations of 3/1 compound were mixtures of 2/1 and 3/1. The vaporization experiments for pure WO₃ were also made at 700-1100°C and the slope values were almost 1. The amount of vaporization was lower than those for 3/1 and 2/1. Effect of porosity on the vaporization was confirmed using NaCl compacts with various porosities. The maximum increase of the vaporization rate against the specimen with 0% porosity was 14% for that with 30% porosity.

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Effects of radiation of 28MeV electrons, fast neutrons, 0.5-2.5MeV ions such as H⁺, He⁺, O⁺, Ar⁺ and Ni²⁺ on YBa₂Cu₃O_7-δ thin films were investigated. The normal resistivity and c-axis lattice constant increased with fluence. Below a threshold fluence for each irradiation the critical temperature (T_c) was constant, while above this fluence T_c decreased with fluence. On the other hand, the transport critical current density (J_c) increased in the low fluence range with a maximum value of 4-30% in enhancement ratio at an optimum fluence, and decreased in the high fluence range. The decrease in J_c was supposed to come from the degradation of grain boundaries as well as intragrains. The threshold fluence φt decreased with the mass A of incident ions in the relation, φt/cm^-2=10¹⁷(A/amu)^-2.5. For each case of irradiation the threshold fluence and the optimum fluence gave 10^-2 and 10^-4-10^-5dpa, respectively, and at the latter fluence cascade damage regions begin to overlap.

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The crystal structure of melamine diborate (C₃N₆H₆⋅2H₃BO₃), well known as raw material of boron nitride, was determined by single crystal X-ray analysis. Molecules are packed in a monoclinic crystal system, space group P2₁/c, with a=0.3596(1)nm, b=2.0111(2)nm, c=1.41092(9)nm, β=92.12(2)°, Z=4 and crystal density is 1.627g/cm³. Molecules in the crystal are linked together by hydrogen-bonds, and form spirally stacked quasi-sheets parallel to a-axis. Bond lengths of hydrogen-bonds range from 0.181(2)nm to 0.209(2)nm. The crystal shows needlelike habit and its longitudinal direction is also parallel to a-axis. The preferred orientation, which was elucidated from powder X-ray diffraction pattern, is presumably due to the needlelike habit and is attenuated by grinding.

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Compressive creep behavior of Si₃N₄-3.62mol%Y₂O₃-6.04mol%Al₂O₃ hot-pressed at 1900°C for 0, 1.5 and 6h was investigated in the temperature range of 1250-1350°C under 30-100MPa, respectively. The relationship between the steady state creep rate and the grain size was discussed in relation to the grain growth mechanism during sintering. The grain size increased and then the creep rate decreased with increasing sintering time. The stress exponent of the creep rate was determined to be nearly unity. The apparent activation energy was measured to be about 700kJ/mol. In addition, the microstructural observation revealed that no cavity appeared at grain boundaries during creep test. These results confirmed that the creep deformation in the apparent steady state creep regime is due to the diffusion-controlled solution/precipitation. Moreover, the grain size exponent in the creep equation was determined to be 2.4-3.1 and also found to be approached to 3 when the average of the smallest grains was selected. These findings indicate that the creep deformation is controlled by the diffusion through the grain boundary glassy phase, and that the solution/precipitation is mainly due to the small grain.

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The surface of relatively large-sized spherical fine HAP particles (D_m=9.32μm) were coated with smallsized fine PSZ particles (D_m=0.12μm) by a dry impact blending method. The surface of the HAP particles were found to be coated completely with the fine PSZ particles. The HAP/PSZ composite particles were sintered. The fracture toughness, microstructure and crystal phases of the sintered body were investigated. The fracture toughness of the sintered body consisting of 100% HAP was 1.1MPa·m^1/2, although those of the sintered bodies with HAP/PSZ weight ratios of 10/2, 10/5 and 10/10 (made by hot pressing) were 1.8, 1.8 and 2.8MPa·m^1/2, respectively. Direct particle connections were seldom observed, electron-microscopically, among the fine HAP particles in the sintered body of the composite particles. The sintered body comprises a three-dimensional and continuously-reticulate PSZ phase in which the spherical fine HAP particles are scattered. X-ray diffractometry revealed that the sintered bodies with HAP/PSZ molar ratios of 10/2, 10/5 and 10/10 made by the hot pressing consisted of HAP and PSZ (tetragonal zirconia) only. It could be understood, from these observations, that toughening by PSZ still remain effective in the sintered body of the composite particles.

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Iron oxide thin films were deposited from 400 to 600°C by CVD from iron acetylacetonate (Fe(acac)₃) using N₂ as the transporting gas and separately introduced O₂ as oxidation gas. β-Fe₂O₃ tended to be formed independent of O₂ flow rate at 400°C. At 500 and 600°C, spinel-type Fe₃O_4+x was formed under low O₂ flow rates. With increasing O₂ flow rate, mixture of β-Fe₂O₃ and spinel-type Fe₃O_4+x was formed and the amount of β-Fe₂O₃ phase increased. Further increase in O₂ flow rate resulted in the formation of β-Fe₂O₃ as a single phase. Fourier transformation infrared spectroscopy (FT-IR) measurement suggested that iron acetyl-acetonate vapor changed the molecular form by decomposition under certain condition. It was supposed that the change in molecular form influences the deposited phase of iron oxide films.

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High-purity mullite was sintered in oxidizing (air) and reducing (N₂=H₂=50%) atmospheres, and effects of the firing atmosphere and V₂O₅ addition on the sintering behavior and bending strength of mullite ceramics were investigated. The firing atmosphere did not affect the bulk density of the undoped mullite ceramics sintered at below 1650°C. SiO was formed by the reaction between mullite and H₂ in the reducing firing. Higher bulk densities of the undoped mullite ceramics sintered at 1700°C in the reducing atmosphere than those sintered in the oxidizing atmosphere were assumed to be caused by the formation of glass phase in pores from the reaction between SiO and H₂O. Addition of 0.1mass% V₂O₅ yielded mullite ceramics with the highest bulk density irrespective of the sintering atmosphere. High-temperature bending strength of the undoped mullite ceramics sintered in the reducing atmosphere showed a maximum at a lower temperature than that in the case of the ceramics sintered in the oxidizing atmosphere probably because of the presence of the glass phase.

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Fine powders in CeO₂-ZrO₂ system have been prepared from the precipitate mixtures of cerium (III) nitrate solution, zirconium oxychloride solution and an excess amount of ammonia under hydrothermal conditions at 180°C, and their changes in crystal phase and surface area by calcination, sinterability, the crystal phase and the microstructure of the sintered bodies have been investigated. Twelve mol% CeO₂-doped fine zirconia powders hydrothermally synthesized showed metastable cubic zirconia phase without monoclinic phase and they gradually transformed into tetragonal phase by calcining at above 600°C. The samples except for 12mol% CeO₂-ZrO₂ consisted of two phase mixtures of zirconia and ceria. The crystallite size of 12mol% CeO₂-doped zirconia particles and CeO₂ particles in the 70mol% CeO₂-ZrO₂ powder was about 6nm and 20nm, respectively. Dense CeO₂-ZrO₂ ceramics were obtained by sintering these powders at above 1400°C for 1h. The sinterability of the powders increased with increasing CeO₂ concentration. The calcined 80mol% CeO₂-ZrO₂ powders pressed at 98MPa reached a maximum density with single cubic CeO₂ solid solution at 1300°C for 1h. The average grain size of 12mol% CeO₂-doped tetragonal zirconia ceramics sintered at 1500°C was 1.5μm. Although the grain size of the sintered body in the two-phase region (tetragonal zirconia and cubic CeO₂ solid solution) was below 1.0μm, it increased with increasing CeO₂ concentration within the single phase region of cubic CeO₂ solid solution.

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Hollow glass microspheres named Shirasuballoons have been prepared from nitric volcanic materials named Shirasu or Hakudo. Fine Shirasuballoons were desired to improve their physical and chemical properties. Preparation conditions of fine Shirasuballoons are examined for five kinds of vitric volcanic materials (Shinjo-Shirasu, Kakuto-Shirasu, Yoshida-Shirasu, Biei-Hakudo and Nakano-Hakudo). Fine Shirasuballoons with particle sizes under 20μm and bulk densities under 0.5g/cm³ were prepared by heating rapidly the milled powders except Shinjo-Shirasu using a fluidized bed furnace. Foaming conditions are discussed by water contents and foaming temperatures. Evolved gases from the raw materials on heating in vacuum were almost water. Two water desorption peaks are observed; a large amount of water desorption peak at temperature ranges of 200-300°C and a small amount of water desorption peak around 700°C, where the latter peak was not observed for the Shinjo-Shirasu with a low water content. Existence states of water are interpreted by infrared absorption spectrum. The shell thickness of fine Shirasuballoons produced is closely related to the water content of the raw material, which was interpreted by the phenomenon that an increase in water content of glass results in a decrease in viscosity at a foaming temperature.

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Sintering behavior of (Ni, Co)O ceramics with 2mass% Al₂O₃ having various characteristics was investigated. Characteristics of Al₂O₃ powder was changed by heating of a raw Al₂O₃ powder consisting of α and γ phases from 200 to 1200°C for 5h. The fraction of γ phase in the Al₂O₃ powder decreased remarkably at temperatures between 900 and 1100°C, the specific surface area of the Al₂O₃ powder decreased, and the particle size increased remarkably at temperatures between 1000 and 1100°C. The shrinking behavior of (Ni, Co)O doped with these Al₂O₃ powders was measured from 800 to 1400°C by TMA. In the temperature region 800 to 1100°C, the shrinkage of CN I, which was defined as (Ni, Co)O with Al₂O₃ treated below 1000°C, was smaller than that of CN II, which was defined as (Ni, Co)O with Al₂O₃ treated above 1100°C. The CN I, however, shrank drastically above 1120°C, and more extensively than CN II above 1200°C. The relative density of CN I sintered at 1300°C for 10h was more than 98%, while that of CN II was less than 95%.

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The stable crack growth in Al₂O₃ monolithic and Al₂O₃ matrix composites dispersed with 10-30vol% SiC particles is examined in strength tests in both air and vacuum using Knoop-indented specimens. The crack growth exponent n, 33 for the Al₂O₃, increases with the volume fraction of SiC particles to 88 for the 30vol% SiC composite. The increase of n-value with the additon of SiC particles is concluded to result from the increased tendency of transgranular fracture. Due to the thermal expansion mismatch between SiC particles and Al₂O₃ matrix, the residual tensile stress in the matrix is generated in the circumferential direction around the particles, resulting in the particles which attract the crack. The residual stress-induced deviation of the crack path within the polycrystalline Al₂O₃ matrix increases the percentage of transgranular fracture and the n-value. The relation between the n-value and the R-curve is also discussed qualitatively. When the Knoop-indented specimen is broken under vacuum, a stable crack growth region is found on the fracture surface for the Al₂O₃-SiC composites, but not for the Al₂O₃ monolithic. It is expected that the n-value has a strong correlation to the rising R-curve behavior.

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Finite element analysis was performed to investigate the shear stress distribution in double notched isotropic and orthotropic specimens under compressive loading. The shear stress distribution between the notches in the orthotropic material was found to be relatively uniform except at the notch roots where a distinct stress concentration was predicted at both for the isotropic and the orthotropic materials. In brittle orthotropic materials, microcracks initiate in the adjacent regions to the notch roots and may relax stress concentration. Static and dynamic tests were performed on double notched specimens of continuous carbon fiber-reinforced silicon nitride ceramics. The shear strength in the fiber direction is much lower on the perpendicular plane than on the parallel plane to the hot pressing direction. The strain rate dependencies of the shear strength were clarified through the present method. It is found that the shear strength evaluated by this method was much lower than that evaluated by conventional tests, such as the short beam or the compression tests.

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The slip casting of silicon carbide was studied to develop a forming method for the fabrication of engineering ceramics. In this study, α-silicon carbide powder produced by the Acheson method was used. The isoelectric point of α-silicon carbide powder was determined to be pH 3.5 from zeta-potential measurement. By using styrene-maleic acid copolymer as a deflocculant, high density green bodies were obtained from a slurry containing 60mass% solids. The SiC sintered at 2200°C for 4h in Ar atmosphere showed a high density of 3.10g·cm^-3, flexural strength of 400MPa and Weibull modulus of 9.4.

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In order to improve the frost durability of the vinylon fiber-reinforced cement board (FRCB), surface-carbonation of the board was studied to control the pore structure near the surface. The carbonation precipitated fine crystalline calcite on the surface of the FRCB and reduced the water absorption by decreasing fine pores from about 0.02 to 0.8μm in diameter. Thus, it was experimentally confirmed that the frost durability of the FRCB was effectively enhanced by surface carbonation.

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Beta-silicon carbide whiskers (β-SiCw) were synthesized by heating powdered “silica black” ore, which consisted mainly of SiO₂, carbon, Al₂O₃, Fe₂O₃, in a closed graphite crucible in argon at 1673K for 3.6×10⁴s. When the samples were dispersed in cotton fibers before heating, a large concentration of whiskers resulted, which formed agglomerates several hundred microns in size. The individual whiskers were on average 0.3μm in diameter and 30μm long with an aspect ratio of 100. A droplet of composition, Fe_2.5Si, was formed on a tip of each whisker, suggesting the VLS growth mechanism.

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