Recent studies on the crystallization of a glass in the system of Na₂O-CaO-P₂O₅-SiO₂ have revealed an unknown phase. The lattice parameters were claculated from the XRD analysis; they were in agreement with the result of TEM diffraction patterns. From the evidence of TEM, EPMA, XRD and SEM analysis, the phase have been identified as (Na_0.11, Ca_0.89) (P_0.11, Si_0.89)O₃ with a P1 structure and have an isomorphic with CaSiO₃. Transition phase appeared in crystallization process was to be described; and substitutional conditions between the atoms of unknown phase were also discussed in the article.

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A method for dynamic strength evaluation of ceramic beams containing small flaws was studied. (1) The critical frequency range was obtained with evaluating the strength of beams on the basis of the static-fatigue limit. (2) The critical frequency range increased slightly, with an increase of the equivalent crack length. (3) With an increase in the ratio of the breadth and depth, the eigenvalues increased, except for the fundamental eigenvalue. The eigenvalues increased monotonically, with an increase in the slenderness ratio and the stiffness of support. (4) For an increase in the damping ratio, the critical frequency range was constant, and then decreased. The fundamental critical frequency range was not affected by the damping ratio.

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When ceramics are used as a slider material, both the wear resistance of ceramics themselves and no damage to the pair material are required. In high speed sliding, Y₂O₃-doped partially stabilized ZrO₂ adheres to pair materials and protects them, but ZrO₂ wears easily as compared with other ceramics. In this study, using Al₂O₃-ZrO₂ composites, we investigated the optimum condition to improve the wear resistance of ZrO₂ while protecting the pair materials. As results, in the combination with Si₃N₄, the optimum content of Al₂O₃ at which wear decreased to one-hundredths was detected. In this content, ZrO₂ and Al₂O₃ grain dispersed excellently with the grain size in the order of 0.1μm. It was confirmed that the microstructure and density of ceramics affected the wear properties. Furthermore, to consider the mechanism of wear resistance, the sliding surface observed by SEM and optical microscopy. It was estimated that the sliding mechanism differed from that of Al₂O₃ and ZrO₂ ceramics in the ZrO₂-Al₂O₃ composites.

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The composite plating, in which SiC particles were codeposited in Ni-P alloy coating by a chemical plating technique, was investigated with emphasis on the effects of size and dispersion of SiC particles. When fine SiC particles with an average size of 0.27μm were used, the deposition quantity of composite coating showed a maximum at a certain reaction time, and large agglomerates consisting of SiC particles and Ni-P phase were formed on the plated surface. The release of agglomerates from a substrate may cause the loss of coating in the later stage of reaction. The cleaning of SiC particles with a NaOH or HF aq. solution suppressed the formation of agglomerates and increased the quantity of composite coating remarkably. It was suggested that the surface oxide layer of SiC particles is responsible for particle agglomeration. The agglomeration was not serious for coarse SiC particles with an average size of 1.1 or 5.8μm. However, when a plating solution was vigorously agitated, the quantity of composite coating decreased significantly with an increase in particle size. On the other hand, in moderate agitation, the quantity of composite coating was increased and the content of SiC codeposited showed a maximum at the particle size of 1.1μm.

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The sintering behavior of bimodal alumina powders was investigated with reference to the change of open pore size distributions. Avarage particle sizes of fine and coarse alumina powders were 0.52μm (f particle) and 6.3μm (c particle). The coarse powder was spherical and polycrystalline. The open pore size distributions in green compacts were narrow for specimens with mixing ratios c:f=4:6-1:9, but were broad for c:f=9:1-5:5. When sintered at 1400°-1600°C, the open pore size increased with c:f=9:1-4:6, remained unchanged with c:f=3:7-1:9, and decreased with c:f=0:10. It is considered that the growth of pores was caused by the difference of sintering rates between tight and loose-packed parts, and also between c and f particles.

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The reaction between the silicon-nitride ceramics and nickel was studied in vacuum from 1373 to 1473K for up to 176.4ks. The reaction product was composed of two layers, one formed by the diffusion of silicon into nickel, and the other composed of additive oxides particles and nickel-silicon alloy. The growth of the product layer followed the parabolic law with the following rate constants (K_p): 1.2×10^-13m²⋅s^-1 at 1373K, 3.6×10^-13m²⋅s^-1 at 1423K, and 1.7×10^-12m²⋅s^-1 at 1473K. The interdiffusion coefficents (D) obtained were of the orders of 10^-15 to 10^-14m²⋅s^-1 in the temperatures range studied. These values were found to be one half to one fifth of the interdiffusion coefficients determined with a vapour-solid diffusion couple of a nickel-plate and nickel-silicon alloy powder as diffusion source of silicon vapour. The activation energy for interdiffusion (Q) was about 330kJ⋅mol^-1, independent of the Si concentration.

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Titanium nitride (TiN) whiskers was formed by heating of potassium fluorotitanate (IV) (K₂TiF₆) above 1300°C on the outer surface of graphite tube in a stream of nitrogen. It was assumed that one of the important process about the formation of TiN whisker and coating was the reaction of titanium fluorides and potassium fluoride, which were formed by thermal decomposing of potassium fluotitanate (III), with alumina tube. The shape and microstructure of the whiskers were observed by SEM and TEM. The main cross-sections of whiskers were square and regular hexagon, It was suggested that the whiskers having a square cross-section grew by layer growth mechanism on {111} tip faces of whiskers in the axial direction and on {110} lateral faces of them in the radial direction, respectively.

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A fabrication technique for surface incorporation of ZrO₂ was developed. Prefired mullite bodies with open porosities of 20-40% were infiltrated with a ZrOCl₂ solution prior to firing. Mechanical properties of the surface modified mullite were improved. The flexural strength of the composite increased by 35-40% of that of mullite at room temperature, and had the same value at 1300°C as that of mullite. The fracture toughness of the surface layer of the composite was double of that of mullite.

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Three reaction-sintered silicon carbides (RS-SiC) with different free Si contents and different porosities were heat-treated at 1780°C for 2h in Ar under a pressure of 200MPa by hot isostatic pressing (HIP) and 0.1MPa by usual heat-treatment. The capsule-free HIP-treated specimen lost 4% free Si by evaporation and exhibited a strength of 130MPa, about 72% lower than that of the as-received specimen. Nevertheless, the capsule HIP-treated specimen was free from pores, and exhibited a strength of 346MPa, about 25% lower than that of the as-received specimen. The HIP-treatment of the Si-free specimen in a capsule did not change the strength. However, the strength of the Ar-heated (0.1MPa) specimen without free Si was 270MPa, 32% higher than that before Ar-heating, showing an increase of the bonding area between grains due to mass transport by surface diffusion and/or evaportion-condensation. For the HIP-treated specimen, the decrease in the strength of the specimen with free Si may be attributed to the decrease in the bonding area resulting from penetration of liquid Si into SiC grain boundaries at elevated temperature; the unchanged strength of porous specimens without free Si may be due to the constant bonding area between grains because of no mass transport by surface diffusion and/or evaporation-condensation.

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Cr₂(C, N) was obtained by heating Cr metal powder in a mixed gas of CO and N₂. This compound is useful for high temperature structural and heat element materials since it is high melting and electronic conductive. This compound, however, is easily oxidized in an atmosphere containing oxygen at high temperatures. The oxidation resistance is enhanced by forming a densely sintered Cr₂(C, N)-ZrO₂ body. This paper described a fundamental for the development of composites in the system Cr₂(C, N)-ZrO₂. The dense Cr₂(C, N)-ZrO₂ body was obtained by heating mixtures of Cr and ZrO₂ in a gas mixture of CO and N₂ at 1500°C. For example, a dense Cr₂(C, N)-ZrO₂ body with relative density of 95% was obtained from a (60wt% Cr-40wt% ZrO₂) compact by sintering in a gas with p_co of 0.2atm and p_N2 of 0.8atm at 1500°C.

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The formation mechanism of solid particles derived from droplets by spray pyrolysis was studied. A droplet of zinc nitrate aqueous or methanol solution weighing 1 to 3mg was set on the tip of a 0.1mmφ Pt wire, This droplet was dried in a furnace at a desired temperature. Decreases in weight and diameter of the droplet by evaporation of solvent were measured with a balance and a camera system, The (droplet weight)^2/3 vs. time curve was divided into two parts: a straight portion in the first stage (part 1) and a curved one in the following stage (part 2). The critical particle size, which corresponds to the formation of hard shell on the surface of the droplet, was estimated from the droplet weight at the joint of part 1 and part 2. This critical particle size was sensitive to the drying temperature and increased when the drying temperature increased. This relationship was also confirmed in a spray pyrolysis process. For constant drying temperature, the porosity of the particles was constant even the initial concentration of droplets changed, and the particle size changed with 1/3 power of the initial concentration.

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The reaction between films and substrates was investigated by ICP-AES, SEM and XRD analyses, during the preparation of Ba₂YCu₃O_7-δ(BYCO) superconductor films from the precursor (BaCO₃-Y₂O₃-CuO) films coated on the yttria-stabilized zirconia (YSZ) substrates by the dipping-pyrolysis process. The reaction of the films with the YSZ substrates resulted in the formation of BaZrO₃ inside the substrates. Their reactivity increased (1) as the atmosphere was changed as: Ar<O₂<air, and (2) as the reaction temperature was raised. With the heat treatment above 900°C in air or O₂, the formation of BaZrO₃ caused the depletion of Ba in the films, giving rise to the changes in film phases on the substrates as: BYCO→BaY₂CuO₅+CuO→Y₂Cu₂O₅+CuO. On the other hand, poor reactivity between the films and the substrates was observed during the heat treatment in Ar at 930°C or below. However, films heated at 950°C resulted in BaZrO₃ and the mixture of Y₂O₃ and Cu₂O, inside and on the YSZ substrates, respectively.

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The slow crack growth and creep characteristic of two intered silicon nitride ceramics under tensile stress were studied. The static fatigue strength degraded with increasing temperature due to the slow crack growth and the creep deformation. In slow crack growth failure without creep deformation, the power law for crack growth rate controlled the strength degradation under constant stress and/or constant stress rate. The modified Larson-Miller parameter was applicable to life prediction under static stress in creep deformation regime. The static fatigue behavior was mainly dominated by the grain boundary nature at elevated temperature. Crystallized phases at grain boundary inhibit not only slow crack growth by stress corrosion cracking but also cavity formation during creep deformation.

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The effect of hydrolysis conditions on the structure of gels was studied on the Al-O-Si alkoxides containing up to 33mol% Al₂O₃ in the system Al₂O₃-SiO₂. The synthesized Al-O-Si alkoxides consisted of chainlike polymers, which were aggregated into three-dimensional branched polymers with increasing water content. Alkoxide solutions which were hydrolyzed with more than 4 moles of water and HCl of low concentration comprised three-dimensional branched polymers, in which Al³⁺ ions were mainly four oxygen-coordinated. And the gels were considered to consist of the aggregates of primary particles with a diameter of 70Å. On the other hand, when hydrolyzed with more than 4 moles of water and HCl of high concentration, Al³⁺ ions became six oxygen-coordinated, which resuted in disaggregation of three-dimensional branched polymers into chain-like ones. In gels from this solution, water remained even on heating at high temperature.

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AE parameters of β″-Al₂O₃ were measured during four point bending tests. Scanning electron micrographs of fractured surfaces revealed that fracture origins were divided into two classes: coarse grains and pores. Some cleavage steps were observed in the fractured coarse grains. Some micro-cracks, on the other hand, were observed around the fractured pores. AE behavior was classified into two different classes, which corresponded to different fracture origins. The K_IC values were calculated from the sizes of the fracture origin of samples. Coarse-grain-originated fractures were well predicted by the linear fracture mechanics formula using K_IC=1.7MPa√m, but no appropriate formula for pore-originated fractures were available. From the above results, it can be concluded that the fracture mechanisms of β″-Al₂O₃ differ according to the type of the defect. In coarse-grain-originated fracture, transgranular fracture occurred first, and then the final unstable fracture occurred at σc, while in pore-originated fracture, the “process zone” was made around a pore, and then the final unstable fracture occurred when micro-cracks grew up to the critical crack length.

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The pyrolysis temperature dependence of tensile strength has been studied for silicon nitride fibers produced by pyrolysis of perhydropolysilazane fibers in N₂. The tensile strength of silicon nitride fibers increased up to 4300MPa with increasing pyrolysis temperature. Catastrophic drops in tensile strength took place following crystallization of Si₃N₄. Crystalline Si precipitated at 1100°C and crystallization of α-Si₃N₄ took place at 1200°C in silicon nitride fibers (B) derived from perhydropolysilazane fibers in which the Si/N atomic ratio deviated from 3/4 in the presence of excess Si. Crystallization of α-Si₃N₄ took place at 1400°C in silicon nitride fibers (A) produced from perhydropolysilazane fibers with the near stoichiometric composition. Silicon nitride fibers (A) retained high tensile strength even after exposing above 1300°C.

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Proportion of metaphosphate, pyrophosphate, and orthophosphate in Li₂O-P₂O₅ melts containing large amounts of Li₂O were estimated by high temperature Raman spectra. The change in proportion of each structural unit with composition in melts was similar to that in rapidly-quenched glasses, though the proportions of metaphosphate and orthophosphate groups were somewhat higher in melts than in glasses.

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Tetracalcium aluminoferrite was hydrated at 25°C with acetic acid solutions. The hydration rate of tetracalcium aluminoferrite was retarded remarkably when 1.00mol/l acetic acid solution was used. When distilled water, 0.10 and 0.25mol/l acetic acid solutions were used, tetracalcium aluminate tridecahydrate was formed. However, a hydrate characterized by two X-ray diffraction peaks with spacings of 10.9 and 5.4Å appeared when 0.50 to 1.00mol/l acetic acid solutions were used. This hydrate was stable up to 150°C in air, and was a complex of organic-tetracalcium aluminate hydrate. Acetic acid molecules were probably sorbed in the interlayer region of tetracalcium aluminate hydrate.

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As a basic study on the temperature-sensitive switching element of VO₂ system, dissolution behavior of VO₂ in lead borosilicate glass was measured. X-ray diffraction intensity of VO₂ was measured by the internal-standard method. A mixed powder of VO₂ and lead borosilicate glass was annealed in nitrogen atmosphere, for 10min at 100°C steps from 600° to 900°C, and quenched into liquid nitrogen from the annealing temperature. The X-ray diffraction intensity was found to be proportional to the VO₂ concentration in lead borosilicate glass. Dissolution quantity of VO₂ was obtained as 0, 19, 38 and 46g per 100g glass at 600°, 700°, 800° and 900°C respectively.

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GaAs was thermally analyzed in air using a TG-DTA apparatus prior to the densification. Result showed that GaAs was oxidized at 550°C. Then, normal sintering at 800°C for 2h was conducted under N₂ atmosphere. The sintered body did not densify with a density of 3.93g/cm³ (relative density 74.0% T. D.). Therefore, green compacts of GaAs were encapsulated in glass containers under reduced pressure and densified by HIP treatment. Resultant densities increased with increasing temperature, pressure, and soaking time. The maximum density of 5.15g/cm³ (97.0% T. D.) was successfully achieved by the HIP treatment at 800°C and 150MPa for 2h. Microstructures of the fracture surfaces observed with a scanning electron microscope (SEM) showed little pores.

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