Figure 3 is a schematic flow diagram for a reliability analysis of ceramic structural components. First, the strength of a number of specimens (at least 50) is measured under inert test conditions, i.e. in absence of subcritical crack growth. From a Weibull analysis of this data base and a stress analysis of the component, the fast fracture reliability can be calculated. The fatigue reliability is then calculated based on the fatigue parameters determined by measuring the strength of a group of specimens (at least 100) as a function of stressing rate in a simulated service environment. If the calculated reliabilities are too low, the design of the component can then be modified iteratively until an acceptable level of reliability is reached or proof testing can be used to assure aginst failure in service.

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Phase transformations of clay containing iron oxide, by firing under various atmospheric conditions up to 1250°C, were studied by X-ray diffraction and ESR. Under reducing conditions and at low temperature (1100°C), hercynite was formed but dissociated at high temperature. Iron oxide was reduced to metallic iron under strongly reducing conditions. The stable phase of hematite appeared when fired in oxidizing atmospheres at 1250°C. Three types of color were observed in the fired products, such as, red in oxidative firing, black in neutral or strongly reductive firing, and yellowish brown in mild reductive firing. Mechanical property was found to be weakest when fired at air ratio of 0.9, that was, under mild reducing condition. This paper describes the effect of atmospheric conditions on firing properties of Japanese clay containing iron oxide for industrial applications.

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Reaction of titanium metal with high temperature-high pressure water were studied in a closed system and in an open system under the conditions of 400°-700°C, 10-150MPa and 0-120h. Titanium hydride (TiH_x), rutile and anatase phases were produced from α-titanium. Reactions proceeded above 450°C and almost finished at 650°C under 100MPa for 3h. Titanium was changed into rutile, anatase and titanium hydride at 500°C under 100MPa for 8h, and then anatase and titanium hydride were changed into rutile beyond 120h. The pressure had little effect in these reactions. Crystal growth of rutile was observed in the open system where high temperature-high pressure water acted as a solvent. The crystallite size of rutile was increased for about 3h but stopped at about 65nm in the closed system, while it was gradually increased about 85nm in the open system at 500°C under 100MPa for 120h.

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Fine powders of the SiO₂-Al₂O₃ system, co-precipitated by hydrolysis of solutions containing silicon tetraethoxide and aluminum isopropoxide, were mixed with carbon and heated at 1430°C in N₂ atmosphere for the carbothermal reduction and nitridation. Among the resultant sialon powders of different Si/Al ratios, only the powder prepared from the starting powder with Si/Al=1 composition gave single phase sialon. The sialon powder consisted of fine particles of 0.05-0.3μm in diameter. The processes of carbothermal reduction and nitridation were investigated for a Si/Al=1 composition on the basis of chemical analysis of the resultant sialon powders. The chemical reactions included not only the substitution of O by N but also the evaporation of SiO vapor. Accordingly, the Si/Al ratio in the sialon powder decreased with increasing heating time.

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The preparation of β-sialon from a powder mixtures of Si₃N₄, Al₂O₃ and AlN was studied with respect to the media and duration of ball milling and the particle size of Al₂O₃. The mechanical properties of hot-pressed β-sialon with z=1, 2, 3 and 4 were measured. The distribution of flexural strength was smallest after 72h milling. The effect of the average particle size of Al₂O₃ (<1μm) on the flexural strength was not clear. The flexural strength and Vickers hardness of β-sialon decreased from about 50kg/mm² to about 38kg/mm² and from about 2100kg/mm² to about 1300kg/mm², respectively, with increasing z-value from 1 to 4. Young's modulus decreased from 2.91×10⁶kg/cm² to 2.34×10⁶kg/cm² with increasing z-value from 1 to 3, howerver, it increased slightly to 2.37×10⁶kg/cm² at z=4. Fracture toughness decreased from about 3.6MN/m^3/2 to about 2.4MN/m^3/2 with increasing z-value from 1 to 3, and it was almost constant from z=3 to z=4.

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Diopside (CaO⋅MgO⋅2SiO₂) crystals have been grown in molten alkali halides. Natural dolomite (CaCO₃⋅MgCO₃) and α-quartz were found to be the best starting materials, NaCl being the most suitable flux. Characterization has been made with crystals obtained under the following conditions: R₁=α-quartz/dolomite (molar ratio), R₂=starting material/flux (weight ratio), soaking temperature and soaking period. When soaked at 1100°C for 12h with R₂=0.02, the following results were obtained.
(1) Monticellite (CaO⋅MgO⋅SiO₂) was synthesized with 0.25≤R₁≤1.00, åkermanite (2CaO⋅MgO⋅2SiO₂) with 0.75≤R₁≤1.75 and diopside, with 1.25≤R₁≤3.00.
(2) The well grown diopside crystals had a maximum size of 2.0×1.5×0.5mm (plate), 1.0×1.0×0.8mm (polyhedron), φ0.3×4.0mm (needle).

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Fine titanium dioxide powder having spherical particles was prepared by ultrasonic spray pyrolysis of alcoholic solution of metal alkoxide (Ti(i-OC₃H₇)₄) in an infrared-image furnace heated at 600°-1000°C. Particles prepared were spherical and have two peaks in the size distribution; one with a mean diameter of 0.2-0.3μm and the other ultrafine particles of about 0.01μm. General characteristics of powders were similar for all reaction temperatures. Microstructural examination by TEM shows clearly that the spherical particles prepared at 1000°C were composed of primary particles of about 0.01μm. With decreasing reaction temperature the microstructure becomes indistinct and it is undefined at 600°C. The change of primary particle size with experimental conditions was examined through the BET specific surface area measurement. The mechanism of pyrolysis was discussed based on these results.

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TiCl₄ was hydrolyzed, vacuum distilled and partially neutralized with alkaline solution to give 0.25-2.0M (M=mol/l) TiO₂ hydrosol. The TiO₂ hydrosol was dialyzed against water buffer for 24-120h for gelation. The resultant TiO₂ hydrogel was put into a polyethylene cylinder and unidirectionally frozen by lowering the cylinder into a -78°C cold bath at a rate of 1.1-8.1cm/h (Fig. 1). The resultant product was allowed to thaw at room temperature. A bundle of porous TiO₂ fibers of about 10cm in length and 20-100μm in diameter was obtained when the partial neutralization was sufficient, the concentration of the hydrosol was 1.0-2.0M, the time of the dialysis was 48-120h, and the lowering rate of the cylinder was 2.2-4.5cm/h. Under other conditions TiO₂ granules were formed. The cross section of the fibers was polygonal (Fig. 2). Their diameter (d) increased with increasing distance from the bottom of the cylinder and with decreasing lowering rate of the cylinder (Fig. 3). Both the freezing rate (R) and the thermal gradient (G) at the frozen front during unidirectional freezing decreased with increasing distance from the bottom of the cylinder (Figs. 6 and 7). The diameter of the fibers was related to the freezing rate and the thermal gradient by the equation d=a/(RG)+b, where a and b are constants (Fig. 11). The approximate composition of the fibers dried at 120°C was TiO₂⋅0.3H₂O. The fibers contained numerous fine pores with diameters less than 6.0nm and dominant at 3.0nm (Fig. 8). The specific surface area measured by a BET method using N₂ was 350cm²/g. The fibers contained also small anatase crystals, which were grown with an increase of heating temperature and then transformed to rutile crystals at about 670°C (Figs. 9 and 10). From consideration of formation of the TiO₂ hydrogel (Eqs. (1)-(6)) and freezing processes (Fig. 11), it was concluded that the high degree of polymerization of TiO₂ hydrogel and cellular growth of ice crystals from gel are essential for obtaining long TiO₂ fibers by unidirectional freezing of gel.

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The hydrolysis behavior of Si₃N₄ powders was studied to find its relation to the crystallinity, which was controlled by the heating conditions of amorphous Si₃N₄ prepared by the imide decomposition method. In the 0.5N NaOH aqueous solution heated at 100°C, amorphous Si₃N₄ was hydrolyzed completely in a short time, whereas crystalline Si₃N₄ was stable and hardly hydrolyzed. In the hydrolysis of partially crystallized Si₃N₄, amorphous fraction estimated from the amount of evolved NH₃ was in good agreement with that determined by X-ray diffraction measurement. It was proved that hydrolysis testing was a conventional method to determine the crystallinity of Si₃N₄ powder accurately. In this study, the grain morphology of Si₃N₄ powders before and after hydrolysis testing was also observed by a scanning electron microscopy. It seemed that Si₃N₄ powder with low crystallinity was a inhomogeneous mixture of ultrafine amorphous and idiomorphic crystalline particles and that any of the single particle in the powder was not in the partially crystallized state.

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The machining of grinding wheel is an important research subject related to wheel finishing process in grinding wheel manufacturing factory, In this study, a turning experiment of grinding wheels has been performed by the use of single-point carbide cutting tools. The work-wheel was 100mm dia. white alumina vitrified wheels of different hardness values, while the cutting tool was P 20, K 10, and K 01 cemented carbide tools. The cutting speed ranged from 30 to 150m/min, the maximum depth of cut was 1.0mm, and the feed was 0.2 to 0.6mm/rev. Thus, the tool wear and cutting force were measured under various cutting conditions, and the optimum cutting condition was determined. The results showed that grinding wheel can be easily cut by using a proper carbide cutting tool, such as K 01 or K 10, and by selecting relatively low cutting speeds. The effect of wheel grade on the tool wear and cutting force was specially evident.

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