Monodispersed spherical Ta₂O₅nH₂O particles have been prepared by hydrolyzing Ta(OEt)₅ with water and basic catalyst in ethanol. The particle size was controlled within the range between 0.05 and 1μm by adjusting the amount of water and catalyst. The results of change in particle size and of ζ potential measurement suggested that the particles grew by the coagulation mechanism. Particles were amorephous, transforming to crystalline Ta₂O₅ at 740°C without appreciable shape change.

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An analysis of the high temperature internal friction pertinent to polycrystals has been conducted. The analysis indicates the important influence of the grain size, the grain boundary diffusivity and the elastic modulus on the magnitude of the bachground level of the internal friction. The background is shown to exhibit three regimes: quasi-static behaviour at low frequencies; short-range diffusion, grain boundary sliding dominated internal friction at high frequencies (at temperatures above the sliding peak); and long range diffusive behaviour at intermediate frequencies. Experimental data for Al₂O₃ and Si₃N₄ exhibit the trends anticipated by the analysis.

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The isotherms in ion exchange equilibrium between alkali silicate glasses and molten salts have been determined for Na⁺-K⁺ ion exchange reactions. The distribution equilibria for alkali were obtained for some glasses with different alkali fractions in a series of mixed alkali glasses. The distribution curves at 500°C were almost the same for all glasses. However, at 350°C the distribution data were not represented by a single curve probably due to the fact that the exchange distribution is influenced by the starting composition. Thermodynamical approach was made on the basis of the exchange isotherms according to the Ekedahl analysis. The activity coefficient of each alkali ion at 500° and 350°C was derived from the experimental data, and the heat of mixing was calculated for an imaginary mixed system of two end-members (Na-glass/K-glass). Thermodynamical behavior of the glass is regarded as that of a regular solution above T_g. Then, alkali ion mobitity in mixed alkali glasses was discussed in term of mixing enthalpy, and the ion exchange kinetics was analyzed using activity coefficients of alkalis and other data.

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The elastic moduli and their pressure and temperature derivatives of lead silicate glasses were measured by the cubic resonance method and pulse superposition method. Thermal expansion coefficients and heat capacities were also measured The sound velocities, Young's modulus, shear modulus decreared monotonously with increasing PbO content, but the bulk modulus increased with increasing PbO content up to its maximum at about 50mol% PbO and then decreased remarkably. The compositional dependence of bulk modulus was interpreted based on the change in the role of Pb²⁺ ions in glass structure. That is, Pb²⁺ ions behave as a network modifier for PbO content<50mol% and as a network former for PbO content>50mol%. The short- and medium-range structures in lead silicate glasses were discossed in terms of the three-band theory using characteristic temperatures obtained from the specific heats. It was found that the medium-range order in lead silicate glasses increased with increasing PbO content. The elastic anomaly in fused silica with negative pressure and positive temperature derivatives disappeared with increasing PbO content. Lead silicate glasses with PbO content>40mol% showed no elastic anomaly. The characteristic temperature representing the intermolecular bonding of the glass network was found to affect the pressure and temperature derivatives of elastic moduli.

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Crack configurations beneath Vickers indentation in 3mol% Y₂O₃-partially stabilized zirconia ceramics with average grain sizes of 0.4μm (Z3Y-I) and 1.0μm (Z3Y-II) were examined and their fracture toughness was measured. Crack configurations were assessed by the dye penetrant technique and observations of the flaw distribution on the fracture surfaces by using scanning electron microscopy. The crack configurations of partially stabilized zirconia were found to be of Palmqvist type even at a high indentation load (50kg). However, the Palmqvist type cracks were well-developed in the direction of indentation depth and appeared to be different in shape from the typical Palmqvist type cracks like those observed in WC-Co. Fracture toughnesses K_IC measured by the controlled surface flaw technique and the chevron notch technique were 7.13-7.26MPa·m^1/2. K_IC values were also measured by the indentation fracture technique using Niihara et al. equation, Lankford equation and Evans equation based on polynominal curve fitting. K_IC values obtained by using Niihara et al. equation were the lowest and those obtained by Lankford equation were the largest in three equations. The K_IC's obtained by using Evans equation were intermediate between them, and 6.58MPa·m^1/2 for Z3Y-I and 7.25MPa·m^1/2 for Z3Y-II.

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Tensile and three-point-bending tests were conducted at room and elevated temperatures on hot-pressed Si₃N₄ containing Y₂O₃ and Al₂O₃ to obtain information on characteristics of tensile strength and its relation to bending strength in ceramics. At room temperature, Weibull modulus in tensile tests was lower than that in bending ones. At 1200°C, strength decreased but Weibull moduli increased in both tests, and the increase in Weibull modulus of tensile tests was so remarkable that no significant difference was observed between tensile and bending tests. The tensile strength calculated from the results of bending tests using effective volume was lower than and almost equal to the observed value at room temperature and 1200°C respectively. Therefore, it is considered that the degree of dispersion of crack size in tensile specimens is different from that in bending ones at room temperature, and that the effect of crack size on the failure strength becomes less significant due to softening of the glassy phase at grain boundaries at 1200°C. Though the temperature dependence of tensile strength was similar to that of bending strength, it was difficult to obtain the precise failure stress by bending tests at 1400°C, because of plastical deformation.

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Crystals of α-quartz were obtained from a silica gel in alkali halides. We found that the addition of LiCl to NaBr provides the most suitable flux. The gel was heated to 850°C, and cooled slowly near the transition temperature. By this treatment β-quartz was converted to α-quartz. The following results were obtained.
(1) The NaBr-LiCl system provides the best flux for the crystallization of α-quartz. The best flux molar ratio R₁ (=NaBr/LiCl) for obtaining α-quartz was 9.7/0.3.
(2) The crystal size decreased with decreasing ratio R₂ (=silica gel/flux, molar ratio) from 0.1 to 0.01, and reached a maximum (0.5×0.5×1.2mm).
(3) When 1wt%-CaCO₃ was added to the flux under conditions (1) and (2), an α-quartz crystal with a maximum size of 0.5×0.5×2.5mm were obtained.

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One t/d test plant facilities of the shaft kiln for calcination of coal ash pellets is designed and constructed. Experimental studies are carried out with this test plant to examine the relationship between reactor behavior and product properties and to clarify the technical problems of the shaft kiln necessary to attain the stable operation. It is found that the most important factor is smooth movement of the pellets supllied from the top of the kiln. Steady and smooth discharge of the pellets could be achieved by applying a forced discharger like a ram feeder. The maximum temperature level of the moving bed in the shaft kiln is governed by not only operational conditions but green pellet composition such as carbon and moisture content. The position of the maximum temperature is affected by an air flow rate as well as discharge rate. The calcined pellets are tested according to JIS A 5002 (Light-weight concrete for structure) and Anouncement No. 13 of Environmental Agency (Industrial Waste Disposal Regulation) and tested properties satisfy the specification and regulation values. Especially, the compressive concrete strength shows 550kgf/cm² which is about 40% stronger than that of JIS value. Conceptual design of a 50t/d pilot plant and cost estimation of the developed process are performed based on the studies conducted up to now. In case of a 1000t/d plant, production cost is estimated under 3000yen/m³.

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Physico-chemical properties of Si₃N₄ powders were investigated with reference to grain growth behavior. The results obtained are as follows:
(1) The heat of immersion, one of the measures for the surface activity of powder, had no connection with the grain growth.
(2) The powder having a large lattice strain showed a large heat of immersion.
(3) Migration of surface atoms occurred from ca. 1450°C, and the rearrangement of particles took place, resulting in the crystallite growth.
(4) The rate of β phase formation was independent of the β content in the original powder.

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Silicon Nitride containing 5wt% MgO was hot-pressed at 1800°C and 300kg/cm², and physical and tribological properties of sintered bodies were measured as a function of hot-pressing time. The bulk density increased with hot-pressing time up to 60min. The fracture toughness increased and the Vickers hardness decreased with increasing hot-pressing time, but these values remained essentially constant after 60min sintering. The coefficient of friction on a hot-pressed silicon carbide disk did not change, but the specific wear rate decreased rapidly with hot-pressing time up to 60min, and approached a constant value, 5×10^-8mm²/kg. The bodies hot-pressed up to 30min consisted of mixed small and relatively large grains. But the grain growth occurred and fibrous microstructures were fully developed after 60min sintering, and only β-phase was detected by X-ray diffraction. As a conclusion, the physical and tribological properties of sintered silicon nitride were almost constant after 60min hot-pressing, which was consistent with the change of microstructure accompanied by α→β phase transformation.

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Normally sintered silicon carbide was joined with a Si₃N₄-Y₂O₃-La₂O₃-MgO mixture having a composition, Si₃N₄:Y₂O₃+La₂O₃=35-65:65-35 (mol%), at 1600°-1800°C for 30-90min in argon (provided that Y₂O₃/La₂O₃ molar ratio is unity and MgO content equals to 20wt%). The highest room temperature joining strength, 397MPa, was obtained by joining at 1700°C for 60min with a composition, Si₃N₄:Y₂O₃+La₂O₃=55:45 (mol%). The strength measurement at high temperature (holdihg time: 10min) showed that the strength of the same specimen was more than 300MPa up to 1000°C, but decreased rapidly above 1000°C. The joining strength decreased with holding time above 900°C. The thickness of the joining layer was about 20μm. No diffusion into silicon carbide matrix of Y, La and Mg, ingredients in the joining agent, was observed, and the joining agent formed a glassy phase after joining. These results imply that joining of silicon carbide ceramics occurred only by the wetting of oxynitride of Si₃N₄-Y₂O₃-La₂O₃-MgO system (the bending strength: about 280MPa). The lowering of jointing strength at high temperature was attributed to the softening above T_g and to the brittleness due to crystallization of oxynitride glass.

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The influence of size and diameter/thickness (D/T) ratio on the homogeneity of cylindrical silicon carbide powder compacts formed by cold isostatic pressing has been studied. The degree of inhomogeneity was estimated by the measurement of spatial distribution of bulk density, Vickers microhardness and pore size distribution for the specimens cut out from the compacts. The degree of inhomogeneity in the density and hardness was relatively smaller than that in uniaxially die-pressed compacts. However, the distribution patterns of the density and hardness which were similar to each other showed the presence of high density and high hardness layer near the surface of the compacts. Furthermore, inhomogeneity was found locally in the inner part of the compacts. A considerable decrease in volume fraction of the smaller sized pores was recognized at the corner edge of the cylindrical compacts. The volume of the inhomogeneous layer near the upper surface in the compacts with a larger D/T ratio tends to be reduced with decreasing D/T ratio. For the same D/T ratio, however, the homogeneity did not depent on the size of the compacts. This behavior could be explained by the difference in damping behavior of the applied pressure between the radial and axial directions.

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A method has been developed for analyzing priderite type ceramics with good acuracy and precision. A sample was dissolved in dilute sulfuric acid after disintegration by fusion with potassium pyrosulfate or potassium sodium carbonate. When a sample contained niobium, it was dissolved in a mixture of sulfuric and hydrofluoric acid. Titanium and niobium in the solution were determined gravimetrically with cupferon, and barium was determined with sulfuric acid. Magnesium, zinc, aluminium and gallium were determined by direct or bach titration with CyDTA or EDTA. Ion exchange chromatography and solvent extraction were required to separate each element from titanium before the determination. Potassium, rubidium, cerium and magnesium were determined by atomic absorption spectrophotometry after the dissolution of a sample in a mixtuts of sulfuric and hydrofluoric acids.

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Osmic acid (2 to 4% solution of OsO₄) has been used for a long time as a fixing reagent of bio-speciments for electron microscopy. The treatment procedure of waste osmic acid has not yet been established due to its harmful effect. This note describes a technique to stabilize chromic acid as a substitute for osmic acid by alkoxide-gel formation.

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Rockwell and Vickers hardnesses of silicon nitride, silicon carbide and partially stabilized zirconia were determined. Rockwell superficial hardness decreased linearly when the load increased. A table of the relation between Rockwell hardness and Vickers hardness for high strength ceramics has been obtained by comparing Vickers hardness with Rockwell surface stress calculated from the Rockwell indented diameter and the shape of the indenter.

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Cylindrical specimens of fused silica refractories were rotated in molten manganese steel, and the changes of manganese and silicon content in the steel were pursued, in order to clear up the mechanism of the corrosion. The results are as follows; (1) The manganese content decreased and the silicon content increased as the reaction proceeded. The molar ratio of the change of manganese content to that of silicon content in the steel was about 2. The reaction layer formed on the surface of the specimen was manganese silicate containing a small amount of iron oxide. And the molar ratio of MnO/SiO₂ was about 1. (2) The overall reaction was expressed as follows; 3(SiO₂)_ref+2Mn=2(MnO⋅SiO₂)+Si (3) The apparent activation energy of the reaction was 14kcal/mol, which suggests that the reaction was controlled by the diffusion of manganese in molten steel.

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The effect of (CH₂)₆N₄ concentration on the particle shape of zinc oxide is discussed with reference to the properties of solutions. Results are as follows: formation rate of ZnO precipitate increases with increasing temperature and with increasing concentration of (CH₂)₆N₄. At a given temperature, rapid formation of ZnO results in globes, while slow formation results in needles. However, needles are formed at a faster rate at 100°C than globes formed at 80°C. With an increase, in (CH₂)₆N₄ concentration, the viscoisty and pH of the solution increase, while the electric conductivity decreases. In the plots of viscosity vs. (CH₂)₆N₄ concentration, two regions with different slopes were observed, each of which corresponds to different shapes of product particles.

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