The characteristics of three chemical solution processes, evaporation and spray pyrolysis method, co-precipitation method and sol-gel method, were discussed in the preparation of raw materials for oxide superconductors. There were two ways to produce superconductors: one involves the formation of barium carbonate in the course of producing superconductors, while the other does not. In the latter path, the temperature to form superconductors is about 200°C lower than in the former. In order to prevent formation of barium carbonate, it is important that barium nitrates or their similar salts are used as precursors. Synthesis of 123 and 124 by the sol-gel method at low temperatures demostrated the following points concerning the formation and phase stability of these superconductors. At lower temperatures, 124 is more stable than tetragonal 123. Orthorhombic 123 is a meta-stable phase and is produced through tetragonal 123 formed at temperature high enough to transform to orthorhombic phase.

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Blast furnace slag containing CaO, MgO, Al₂O₃ and SiO₂ as major components was used as the raw material for β-spodumene glass-ceramics. The batch compositions were modified by mixing blast furnace slag with SiO₂, Al₂O₃, Li₂CO₃ and nucleating agent TiO₂. The crystallization processes of the glasses based on the blast furnace slag were investigated using differential thermal analysis (DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM) and electron diffraction (ED). It was found that the major crystalline phase was β-spodumene (Li₂O⋅Al₂O₃⋅4SiO₂) and the average thermal expansion coefficients between 25° and 700°C were 40.1 and 47.2×10^-7°C^-1 for two different samples.

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Platelike β-alumina particles with an average size of 0.3μm were formed at 1100°C from alkoxide-derived amorphous powder with the chemical composition (wt%) 9.3 Na₂O, 1.0 MgO, and balance Al₂O₃. No β″-alumina formed from the gel of mixed alkoxides. The particle size of the β-alumina increased with increasing MgO content. Aggregation of the platelike particles in green compacts caused a tendency toward the formation of pores surrounded by flat planes, and pores of this type remained in the sintered samples. Densification of the β-alumina powders was inhibited by MgO, and Al₂O₃ dissociated from the β-alumina during sintering in an Na₂O-poor atmosphere. The Na₂O loss from green compacts in a semi-closed Pt container reached a constant value after a short sintering time and was suppressed in an Na₂O-rich atmosphere. In addition, the evaporation behavior of MgO, measured during sintering at 1600°C, followed Henry's law in the MgO-Al₂O₃ system of β-alumina.

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(1) In order to control the concentration of nucleation agents in the melt of the domestic scoria, 1-2wt% sucrose were added. When the ratio of FeO/Fe₂O₃ ranges between 0.93 and 1.32, the optimum crystallization was obtained with the crystal size of about 0.1μm and the homogeneous microstructure.
(2) The impurities, FeO, Fe₂O₃, and TiO₂ affect the formation of magnetite and ulvospinel which are the nucleation agent of the all specimens in this study. Not only the FeO/Fe₂O₃ ratio but also the absolute amount of iron oxides are important factors in the nucleation process. When 1-2wt% sucrose were added, the ratio of FeO/Fe₂O₃ increased from 0.18 to 0.93-1.32.
(3) The temperature and holding time for the nucleation and crystallization as well as the activation energy for crystallization were determined by DTA. The nucleation temperature varied from 625° to 760°C and that for crystallization from 800° to 850°C depending on the amounts of additives.
(4) The crystalline phases after the heat treatment were diopside, alkermanite, and gehlenite as a major phases and also α-quartz, spinel and grossular were found as the minor phases.
(5) The scoria glass with the addition of 20wt% SiO₂, 7wt% CaO, 5wt% MgO, and 1wt% sucrose shows the lowest activation energy and also developes fine and uniform crystal particles.
(6) The thermal expansion coefficients of the glass-ceramics are higher than those of parent glasses.

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The structure and distribution of hydrolysis and polycondensation products of methyltriethoxysilane present in aqueous solutions containing sodium ions have been investigated with the trimethylsilylation technique and by ²⁹Si n. m. r. spectroscopy. It has been found that the polymerization of hydrolysis products of methyltriethoxysilane in aqueous solutions containing sodium ions takes place randomly and a variety of the species with different structures is present. However, the degree of polycondensation of the species in the aqueous solutions at a certain Si concentration is much lower than that of silicate species, which may be attributed to the difference in the functionality of silane in the species formed from methyltriethoxysilane and silicate anions or the repulsion between methyl groups in the species from methyltriethoxysilane. In addition, ²⁹Si n. m. r. peaks due to the monomeric, dimeric, and linear and cyclic trimeric species consisting only of the CH₃SiO₃^3- unit have been assigned.

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The piezoelectric composite-bar method was applied to elastic modulus measurement of ceramics (zirconia, alumina, silicon nitride and silicon carbide). The procedure of measurement was simplified by using quartz vibrators with various resonant frequencies and grease as the adhesive. The resonant frequency f_s of the specimen was observed to depend on the resonant frequency f_q of the vibrator. The value of f_s was maximum at f_s=f_q. The most probable value of f_s (f_s0) is obtained at f_s=f_q, and was determined by plotting f_s against f_q. The experimental error in f_s was evaluated by the plot of f_s vs. f_q (f_s/f_s0 vs. f_q/f_s0) and was smaller than 0.1%, when the difference between f_q and f_s0 was 10%. The value of Q^-1 was observed to be minimum at f_q/f_s0=1.

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Dissolution behavior of synthetic ettringite in an aqueous suspension containing a strongly acidic ion exchange resin, hydrogen-form (H-R) was investigated by monitoring the variations in pH and specific conductivity and by analyzing the fraction of dissolved ions using ion chromatography. The results obtained are summerized as follows;
(1) Initial cation exchange reaction between ettringite and H-R in aqueous media produces a hydrous alumina gel incorporated with small amounts of calcium and sulfate ions (Eq. 1).
Al₂Ca₆(OH)₁₂(SO₄)₃+6(H-R)→3CaSO₄(aq)+3(Ca-R₂)+6H₂O+2Al(OH)₃ (1)
(2) In the final stage, the released H₂SO₄ produced by the subsequent ion exchange reaction between CaSO₄ (aq) and H-R reacts with the gel to be dissolved accompaning with the complete dissolution of the ettringite.

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Dried gels prepared by the sol-gel method from a mixture of tetramethoxysilane (TMOS), water using a variety of solvents. The structure of dried gels was remarkably varied with the solvent used. The bulk density of dried gels decreased with decreasing vapor pressure of solvents except for 1, 4-dioxane. The bulk density of dried gel is closely related to the pore radius and pore volume. A dried gel with a small bulk density has a large pore radius and a large pore volume. Solvents with a long linear chain and a functional group which is exchangable with a silanol group were effective to prepare the dried gel with small bulk density and a large pore radius.

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Preparation of mullite from a mixture of kaolin and gibbsite by dry-grinding has been investigated by XRD, DTA and SEM. The structure of the mixture transformed to an amorphous structure by dry-grinding for 240h and the spherical particles 0.2-0.3μm in diameter were obtained. The mixture ground for 240h formed the spinel phase and mullite after firing at 950°C. It was therefore considered the dry-grinding was effective to promote the formation of mullite. The activation energy for the mullite formation from 240h ground specimen decreased to 544kJ/mol from 1047kJ/mol in no grinding specimen. The lattice parameters of mullite formed from the specimens ground various time and fired at 1500°C for 1h were similar values with those of mullite with 3Al₂O₃⋅2SiO₂ composition.

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A well-crystallized LaCrO₃ powder with a primary particle size of about 1μm was synthesized through the complex precipitation process; obtaining the precipitate of complex hydroxide from an NaOH aqueous solution of Cr(NO₃)₃ by adding LaCl₃ and then heating the precipitate up to 700°C. The LaCrO₃ single-phased powder was prepared from the precipitate obtained by adding less amount of La³⁺ than the equimolar ratio, but an excess adding of La³⁺ resulted in La₂CrO₆ with LaCrO₃. From density measurements and SEM observations, the powder thus prepared has no remarkable sinterability. However, the electrical conductivity (about 0.069S/cm) of the specimen, of which relative density was as low as 57%, was comparable with those reported on the dense specimens. The temperature dependence of conductivity of the present specimen showed a break around 180°C. The activation energy was determined as 0.20 and 0.23eV above and below 180°C, respectively.

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The trajectories of silica and germania fine particles in the flow fields of combustion gases were simulated to find optimum conditions for producing the optical fiber soot preform by the VAD method. The proposed model simulates two-dimensional flow of combustion gases and the particle trajectories by considering the interactions between the gas and the particles in given temperature fields. The obtained results are summarized as follows: (1) Thermophoresis influences the particle trajectories in the vicinity of the preform surface and draws the particles toward the surface. The temperature gradient in the combustion gas, to which thermophoresis velocity is proportional, must be kept large in that region. (2) Optimum distributions of silica and germania particles in the soot preform, contrary to expectation, is attained not by the difference in particle properties such as density and thermal conductivity but by the spatial distribution of both metallic oxides in the flame and the combustion gas flow. Then it is important to analyze the flame structure and chemical reactions producing these particles, and hence to control the distribution of the reaction zone and also the flow field of the flame.

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Shear stress of sericite suspensions was measured against shear rate in the range of 16 to 650s^-1 using a rotational viscometer. Mineral compositions of two kinds of clay particles (AT-S, AT-K), which were obtained by elutriation from two different kinds of powdered Amakusa pottery stones, were mainly sericite and a few amount of kaolin mineral and quartz. Rheological properties of these sericite suspensions were approximated as Bingham body and analysed using DLVO theory of coagulation and dispersion. The results were summarized as follows;
(1) Bingham yield stress (BYS) values obtained from the relation between shear stress and shear rate became higher with increasing the volume fractions of AT-S and AT-K suspensions from 1.8% to 6.9%. BYS values of two suspensions were nearly zero at pH 7, increased from pH 6 to pH 5, and decreased at pH 4.
(2) Total potential energy of interaction between two flat clay particles and Bingham yield stress (BYS) of clay suspensions were calculated using the estimated edge and face potentials of sericite on the basis of DLVO theory and the equation of total energy dissipation rate. The calculated results showed that BYS values of both sericite suspensions became zero at pH 7, then had finite values at pH 6 and pH 4, and had a maximum at pH 5 because these calculated values were brought about from the different association modes such as face to edge and edge to edge. These changes of calculated BYS values with pH explained well those of measured ones. It was also made clear that the thickness of sericite gave a great effect on BYS values.

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The metallizing of high-Al₂O₃ ceramics (purity>99%) with W or Mo was investigated by painting W, Mo, H₂WO₄ or H₂MoO₄ powder on the Al₂O₃ substrate and heating at 1400°C in H₂ or Ar. When heated in H₂, where H₂WO₄ and H₂MoO₄ were reduced to W and Mo, the bonding of W and Mo coatings to Al₂O₃ was very weak for all metal sources. This may be explained by the insufficient amount of glass component, mainly SiO₂, in Al₂O₃ substrate to bond metal phase. When heated in Ar, on the other hand, H₂WO₄ gave W coating tightly bonded to Al₂O₃, although H₂MoO₄ did not form Mo coating. The metallic W may be produced by the thermal decomposition of W-oxide in Ar and bound to the substrate with a glass phase formed by the reaction between W-oxide and Al₂O₃. When Ni was joined to the substrate above the melting point, a large gap was observed at the interface between Ni and non-metallized Al₂O₃ substrate. On the other hand, Ni adhered tightly to W-metallized Al₂O₃ substrate, indicating that W phase played a role as an intermediate bonding layer between Ni and Al₂O₃.

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Cutting tools of Ti(C, N)-Cr₃C₂ ceramics have better wear resistance than those of TiC-TiN cermets and WC-Co alloy tools for carbon steel. Sintered bodies of this system have the fracture toughness K_1C of 2.5MPa⋅m^1/2. Higher fracture toughness is necessary for wider application. Therefore, addition of Al₂O₃ to Ti(C, N)-Cr₃C₂ system is tried. The main results are as follows:
(1) Ti(C, N)-5wt% Cr₃C₂-Al₂O₃ sintered bodies containing 30-50wt% Al₂O₃ have the porosity of 0.1vol%, K_1C of 4.2MPa⋅m^1/2, transverse rupture strength of about 700MPa, and Vickers hardness of 1850Hv.
(2) These sintered bodies consist of (Ti, Cr) (C, N, O) and Al₂O₃.
(3) It is thought that high K_1C is due to high toughness of Al₂O₃ grains and grain boundaries between (Ti, Cr) (C, N, O) and Al₂O₃.

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The preparation of β-spodumene powder from alumina sol, silica sol and lithium nitrate solution by the sol-gel process, its sintering condition and properties of sintered bodies have been investigated. The crystallization temperature of the β-spodumene powder was estimated to be about 720°C by TG-DTA, and also it was confirmed by XRD that the crystallization temperature of β-spodumene in the firing process corresponded to this temperature. A sintering characteristic of powders obtained from different preparation conditions showed remarkable differences to the progress of densification and the thermal stability. Moreover, the microstructure of sintered bodies was influenced by preparation conditions of powder and firing temperature. In particural, the sintered bodies formed above 1100°C by using the powder, which was prepared at 600°C for 4h, incorporated large pores (ca. 10μm) in the grains. The thermal expansion and contraction curves showed reversible behavior in the process of heating and cooling, and the average thermal expansion coefficient was 1.4×10^-6°C^-1 (RT-1000°C).

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A metal acetate gel as a precursor of YBa₂Cu₃O_7-y superconductor bloats in the range of 200°-300°C during heat treatment for conversion of the gel into a superconducting ceramic, becoming a porous and deformed product, when the heating rate is 5°C/min. In order to minimize the pore formation and deformation, the mechanism of bloating and the change of microstructure of the gel were investigated by thermal analysis, X-ray diffraction technique, infrared spectroscopy and mass spectroscopy of evolving gases. It was confirmed that the gel is composed of weak bonds between metal ions through acetate ions and that the sintering process includes elimination of water, thermal decomposition of metal acetates and reaction of precipitated intermediate species. It was also found that the bloating is caused mainly by abrupt thermal decomposition of acetate ions bonding with copper ions. Lower heating rates such as 0.0833-0.167°C/min(5-10°C/h) for the heat treatment of gel fibers were found to be effective in converting them into dense ceramic fibers by lowering the rate of thermal decomposition of acetate ions and by suppressing severe bloating.

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Using the isothermal method, the densification process of the quartz-feldspar-kaolinite system, representative of ceramics used for building construction, was investigated at various packing ratios (65-69%). The Arrhenius equation can be established between the temperature and the time necessary for densification before the vitrification point. In addition, the particles show a rhombic dodecahedron orientation, as described by Sallam et al., irrespective of the packing ratio at forming. A linear relation can be established between the logarithm of the packing ratio and the logarithms of the gradient and intercept of the Arrhenius equation. The apparent activation energy necessary for vitrification is 104-117kcal/mol, and the apparent activation energy decreased with increasing packing ratio. This indicates a possibility that the body possesses a specific coefficient for densification which is extremely important industrially.

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Tritium, a fusion reactor fuel, is produced by neutron-irradiation of Li-containing ceramics. The container for Li-containing ceramics is made of zirconium alloys, which are embrittled by tritium. Ceramic coating was applied to the zirconium alloy to prevent the hydrogen embrittlement, and the tension and collapse tests, and the acoustic emission measurement during these tests were conducted to understand the mechanical properties of the ceramic coating film and the underlying zirconium alloys. Results of these tests revealed that the coated zirconium alloys have a sufficently high strength for the container. Furthermore, the acoustic emission signal and the stress change were observed and associated with the peeling and cracking of the ceramic coating film.

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α-Al₂O₃ and three hydrated aluminas were studied by photoacoustic spectroscopy (PAS).
Hydrargillite (α-Al(OH)₃), boehmite (α-AlO(OH)) and bayerite (β-Al(OH)₃) showed different absorption patterns in the -OH stretching and bendings.
(1) PAS data for hydrargillite, boehmite and bayerite in the wave length region from 400 to 4000cm^-1 are relatively consistent with previously reported data.
(2) The spectrum of hydrargillite consists of five main -OH stretching bands at 3620, 3525, 3446, 3393 and 3379cm^-1. These bands shifted slightly from the reported IR spectroscopic data, suggesting some diferrences in OH band length.
(3) The spectrum of η-Al₂O₃ obtaine by heating bayerite at 700°C in good agreement with that of boehmite.
(4) PAS is a useful tool for the characterization of dehydrated and hydrated aluminas.

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The compressive and bending strength of SiC whisker preforms were improved by heating at 1723K in nitrogen atmosphere. Addition of silica sol before heat treatment was found to increase the mechanical strength of SiC whisker preforms. Chemical reactions at high temperature were discussed relating to the boundary phase. Fracture mechanism of SiC whisker preforms was also discussed.

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The effect of the bias pressure of Cyclic-CIP. on the bulk density of alumina compact was examined, and the following results were obtained.
(1) When the maximum pressure is constant, the high bulk density can be obtained with decreasing bias pressure.
(2) Relative bulk density of 74.2% was obtained under the condition of 100MPa in maximum pressure, 0MPa in bias pressure and 10000 cycles.
(3) In order to obtain the same bulk density, the maximum pressure of C-CIP can be decreased over one-tenth of that of static-CIP.

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