Ultrafine powders of β-SiC containing 15wt% free Si, which were produced by the gas evaporation method, were pres surelessly sintered. The behavior of SiC crystal growth during the sintering was observed by scanning electron microscopy (SEM). When the sintering was carried out under the condition that the upper side of the sample is free surface, granular crystals only grew up until 2200°C. On the other hand, under another condition that sample surfaces are sandwiched by graphite plates, plate-like crystals began to grow at 1850°C, and these crystals grew remarkably with the increase of the sintering temperature. X-ray diffraction analysis showed that the granular crystals were β-SiC, the same as that of raw powders. Plate-like crystals were α-SiC and the flat surface of the plate was the basal plane, (001). Sintered bodies were not densified when the granular and plate-like crystals remarkably grew. The pressureless sintering of SiC containing free Si at the temperature above the melting point of Si is considered to be liquid phase sintering. The migration of constituent atoms by diffusion becomes easy when free Si existed as liquid phase. Hence the growth of large plate-like crystals could occurred easily at the position existing such liquid phase. Therefore the existence of free Si is not favorable to obtain a dense sintered body.

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Adding silicon carbide particles to silicon nitride and subjecting the mixture to hot-isostatic-pressing process after pressureless sintering increases both bending strength and Young's modulus, although fracture toughness remains at almost the same. This is because that the added SiC particles inhibit excess grain growth of β-Si₃N₄ resulting in reducing flaw size for fracture. The SiC particles of less than 0.2μm in diameter are trapped within the β-Si₃N₄ grains through hot-isostatic-process with microcracks which reduce imposed stress resulting in further contribution in high strength. SiC particles, however, do not alter the fracture characteristics for fracture toughness.

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The sintering mechanism of Si₃N₄-bonded SiC ceramics produced by sintering compacts of powder mixtures of SiC and Si in a nitrogen atmosphere is discussed based on the microstructural analyses by scanninig electron microscopy (SEM) and transmission electron microscopy (TEM). SEM observations showed that amorphous whiskers and fine Si₃N₄ grains grew on the SiC particles surfaces at the initial stage of sintering, and that amorphous whiskers disappeared to form fine Si₃N₄ grains when heated to the final sintering temperature of 1350°C. TEM observations showed that Si₃N₄ grains grew epitaxially on the SiC lattice and no foreign elements such as oxygen were detected at the SiC-Si₃N₄ interface, and that grain growth of Si₃N₄ seems to be suppressed by the presence of oxygen.

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The effect of Cr₃C₂ additive was investigated on the sintering process of TiB₂. The 5-7.5wt% of Cr₃C₂ well functioned to improve the relative density, the bending strength and Vickers hardness. According to the X-ray diffraction data, TiC and CrB were formed at the grain boundaries of TiB₂, Also, the solid solution between TiB₂ and Cr₃C₂ was recognized. The SEM observation supported that a liquid phase was significantly concerened in the sintering of TiB₂. The sintering behaviour of TiB₂ was discussed on the microstructural and compositional viewpoints.

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Ammonium aluminum carbonate hydroxide (ARCH) as starting material to obtain α-alumina fine powders was synthesized between aqueous solutions of ammonium hydrogen carbonate (AHC) and ammonium alum (AA). The effects of pH of the AHC aqueous solution and reaction temperature on the formation of AACH were discussed. Three products, amorphous aluminum hydroxide, pseudoboehmite (=low crystalline boehmite) and AACH were formed depending on pH. AACH was mainly formed in alkaline aqueous solutions. The optimum synthetic condition of AACH was discussed in terms of the relation between pH and concentration of species calculated by the master variable technique of ionic equilibrium in AHC and AA aqueous solutions. NH₄⁺, AlO(OH)₂^- and HCO₃^- species were neccessary to form AACH. Crystallite size of AACH decreased with increasing concentrations of ionic species, [NH₄⁺]⋅[AlO(OH)₂^-]⋅[HCO₃^-] and decreasing reaction temperature. Homogeneous, spherical α-alumina particles with a particle size of 0.2μm were obtained by firing at 1050°C for 6h from the AACH with a crystallite size of 50Å synthesized at a pH of 10.0 at 5°C.

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Feromagnetic amorphous oxides were prepared by rapidly quenching the molten antiferomagnetic ferrite BiFeO₃ containing lithium oxide. The composition range giving an amorphous phase in the system of Bi₂O₃-Li₂O-Fe₂O₃ was found to contain more than 30mol% Bi₂O₃. Composition within this range gave X-ray amorphous phase on quenching were confirmed to be an amorphous by X-ray diffraction analysis. Especially, the crystallization temperature of the composition 20Li₂O⋅30Bi₂O₃⋅50Fe₂O₃ was observed 430°, 580°, and 730°C by differential thermal analysis. The saturation magnetization and coercive force of this amorphous oxide were about 13emu/g at 15k Oe and about 100Oe at room temperature, respectively. The thermomagnetic curve showed irreversible change and the curve was slanted near the Curie point. Extrapolation gave the Curie temperature at 563°C. ⁵⁷Fe Mossbauer absorption spectra indicated that the amorphous phase is composed of two phases paramagnetic and ferromagnetic having small particles, X-ray photo spectroscopy spectra showed that Fe³⁺ ions exist in both states of 6-coordinate site and 4-coordinate plus 6-coordinate sites.

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The cyclic fatigue properties of three kinds of toughened Al₂O₃ composites doped with SiC whisker, TiC and partially stabilized ZrO₂ particle were compared with results of four kinds of Al₂O₃ ceramics with different purities. The effects of stress amplitude and initial crack size on fatigue properties were investigated by using polished and pre-cracked samples. Furthermore, the accelerated phenomena on initiation and propagatation velocities of fatigue crack under cyclic loading condition were quantitatively assessed by the estimatation method using an experimental relation based on subcritical crack growth velocity and static fatigue data. As results, in the case of polished sample, the accelerated effect on fatigue that 99.99% and 99% Al₂O₃ ceramics typically showed was restrained in Al₂O₃ composites. The cyclic fatigue properties of Al₂O₃ composites used in this paper can be successfully estimated under wider condition of stress application from the data on static fatigue than the case of Al₂O₃ ceramics. On the condition that a sample was pre-cracked by Knoop indenter, Al₂O₃ composites hindered the accelerated effect on fatigue crack propagation under cyclic loading as well. Especially, the cyclic fatigue data of pre-cracked ZrO₂/Al₂O₃ composite agreed well with the estimated value from static fatigue properties.

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TeO_x-Pd thin films were studied for optical recording. Te₄₈Pd₂₄O₂₈ in the system TeO_x-Pd had a high crystallization temperature and showed a large difference in transmittance between the amorphous and crystalline states. The crystallization of Te₄₈Pd₂₄O₂₈ thin films took place stepwise in 4 stages at 150°, 270°, 326°, and 365°C. The activation energies for the crystallization were 4.17, 2.84, 5.39, and 1.79eV, respectively. The crystallization which plays a key role in the optical memory by laser irradiation was shown to be the first stage crystallization. The threshold laser power for crystallization was 9mW for 50ns irradiation. The Te₄₈Pd₂₄O₂₈ thin films were found to be good optical memory materials of the so called “write-once” type showing high speed response and high stability.

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As a candidate for solid blanket material of fusion reactor, porous particles of lithium stannate Li₂SnO₃ was prepared by the decomposition of lithium hexahydroxystannate Li₂Sn(OH)₆ at a relatively low temperature of 600°C. Sintering of these porous particles at 1000°C resulted in blocks with bulk densities as low as about 50% theoretical. Densification of the block was found to be accelerated by either grinding of the starting powder or addition of Li₂O. The present process has advantages of low temperature synthesis of lithium compounds, and small size and high porosity of primary particles. Release of tritium generated by neutron irradiation and stored in the block occurred up to 600°C, much lower temperature than with Li₂O. This result is reasonably explained as due to the small size of primary particles of Li₂SnO₃ and also due to the high porosity of the sintered block.

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Series of Al-substituted fluorine micas, KMg_2+xLi_1-x(Al_xSi_4-x-yGe_yO₁₀)F₂ and KMg_2+xLi_1-x(Al_xGe_4-x-ySi_yO₁₀)F2; x=0.0-1.0, y=0, 1, 2, 3, were synthesized and variations of infrared spectra and lattice constants with Al-substitution were studied and compared to those with Ga-substitution reported previously. The infrared spectra of the synthesized micas varied sensitively with composition. Continuous changes in lattice constants with increasing Al-contents proved that there were complete series of solid solutions between the end member micas, Lattice constants a and b increased almost linearly with increasing Al-content in all series. However, c·sinβ (basal spacing) remained almost unchanged or slightly increased in the case of Al-for-Si substitution while it decreased linearly in the case of Al-for-Ge substitution, These complicated changes of cell dimensions were explained in terms of the tetrahedral rotation angle α, the octahedral flattening angle ψ, and the change in interlayer conformation. Linear relationships between c·sinβ and average radius of tetrahedral cation were obtained for Al-and Ga-micas having an x-value of 1.0 and for micas having x-value of 0.0., respectively, showing that the cell dimension and structural deformation depend essentially on both the charge balancing and the size of tetrahedral cations.

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The conditions for direct preparation of fibrous II-gypsum anhydride having the lowest solubility in gypsum modifications by the reaction in CaCl₂-H₂SO₄-CH₃OH system were reported in a previous paper. Studies were made on investigate the relationship between the incorporation of phosphate ion and the decrease of both solubilities of needle-like form (produced by the reaction of CaCl₂-Na₂SO₄-Na₂HPO₄ system) and fibrous form (produced by the reaction of CaSO₄-Na₂HPO₄-CH₃OH system) of gypsum hemihydrate. Phosphate ion into the needle-like hemihydrate was incorporated by adding a CaCl₂ solution to a mixed solution (pH 8) of Na₂SO₄ and Na₂HPO₄ at 100°C. Changes in lattice constants caused by the substitution of SO₄^2-→HPO₄^2- in gypsum hemihydrate crystal were found by X-ray diffraction. The upper limit of the incorporation was 7 per cent (HPO₄^2-/SO₄^2- molar ratio 0.07). This finding was also supported from data of TG-DTA, IR spectra and scanning electron microscopic observation. However, the upper limit was raised up to 15 per cent (HPO₄^2-/SO₄^2- molar ratio 0.15), if pH of the mixed solution was adjusted to 9 from 8 by adding NaOH solution.
On the other hand, the fibrous hemihydrate was incorporated with phosphate ion by the reaction on between Na₂HPO₄ solution and gypsum organogel which was produced by adding methanol to a saturated solution of gypsum dihydrate at 65°C. The upper limit of the incorporation of phosphate ion was also 15 per cent. This fibrous solid solution had a very high water-resistivity as 0.4×10^-3 Ca²⁺ mol dm^-3 after dipping in water for 1h retaining the original fibrous form, Moreover, fibrous II-anhydride produced by heating this fibrous solid-solution showed a good water-resistivity as decreasing to about 1/50 against that of gypsum dihydrate (1.52×10^-2 Ca²⁺ mol dm^-3 after dipping in water for 1h).

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The present study deals with the relationship between the microstructures and the fatigue failure mechanisms in five different kinds of sintered silicon nitride ceramics. Static fatigue test and cyclic fatigue test were conducted with a stress ratio (R) condition of 0.1 using flex specimens at room temperature, as a means to determine the effects of microstructures on crack propagation. Also, the accelerative effects upon the propagation velocity of fatigue cracking in cyclic loading conditions were discussed quantitatively using the estimation method applied to the empirical equation for subcritical crack growth.
The results indicated that the accelerative effects on propagation velocity under cyclic fatigue conditions were observable in samples in which the matrix was composed of microcrystalline grains of the sintered silicon nitride ceramics, but not in those with a matrix composed of amorphous materials. Thus, under cyclic loading, the fatigue crack propagation was found to be governed by the microstructure of the sample, in particular by the matrix filling the gaps between the coarse grains.

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A composite iron powder coated with TiB₂ and TiN double layers was prepared by the continuous rotary powder bed chemical vapor deposition in the reactant systems of TiCl₄-B₂H₆-H₂ and TiCl₄-N₂-H₂. TiN was coated on to spherical iron powder with a particle diameter of 70-120μm under the following deposition conditions; temperature: 1000°C, reaction time: 0-120min, flow rate: TiCl₄ 3ml/min, N₂ 200ml/min, H₂ 300ml/min, Ar 20ml/min, and the rotation speed of specimen cell: 90rpm. Crystalline or amorphous TiB₂ was subsequently coated on to TiN coated iron powder under the conditions: temperature: 600°-850°C, reaction time: 60-240min, flow rate ratio of B₂H₆ to TiCl₄, R=0.16, H₂ 300ml/min, Ar 140-300ml/min. The composite iron powder covered with uniform and adherent double layers of TiB₂ and TiN was oxidation-resistant up to 700°C in air.

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Effect of glaze on the bending strength of high strength whiteware bodies containing 30% Alumina was investigated. The significant increase of the bending strength by the applied glaze is due to the reduced size of fracture origin at the surface of body. Compressive stress in the glaze is necessary to avoid fracture initiation within glaze. Coarse quartz grains in the glaze act as the fracture origin and reduce the bending strength. Raw materials for glaze must be milled well not to create fracture origins in the glaze. By glazing, bending strength could be raised by about 1.4 times of that of unglazed bodies; bending strength of unglazed and glazed test bars were 24.0kg/mm² and 33.5kg/mm² respectively.

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A relation between PTC (Positive Temperature Coefficient) characteristics and oxygen diffusion coefficients in BaTiO₃-PTC thermistors was studied. As a result, PTC behavior was not obtained unless the annealing temperature exceeded 900°C. Both coefficients of oxygen volume diffusion with and without PTC behavior were equal to each other and of 2×10^-14cm²/s at 850°C. But, the coefficient of oxygen boundary diffusion with PTC behavior was much larger than that without PTC behavior.

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An alumina green body was made transparent by immersing a liquid which has a refractive index close to that of alumina. Its internal structure was examined directly with an optical microscope.

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A model for two-dimensional compaction of cylinders is proposed. The equation ln(P₂/P₁)=κ₁κ_sN_t(1/Z_s2-1/Z_s1) based on the model well described an experimental relation between the applied pressure P_a and the number of propagation sources of rearrangement, Z_s, where κ₁ is a constant, κ_s is a coefficient of friction, N_t is the total number of contacts among cylinders, Z_s1, and P₁ are the initial value of Z_s and that of P_a, and Z_s2 and P₂ are the final ones, respectively. The equation indicates that ln(P₂/P₁) is roughly proportional to 1/Z_s2 under the condition P₁<<P₂ because of Z_s2<<Z_s1, which means that a feature in the initial packing structure vanishes on compaction. The κ_s value, on the other hand, has appreciable influence on the Z_s2 value, i.e., the final packing structure.

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