The formation of the high-T_c phase in Bi-Sr-Ca-Cu-O films fabricated using metal alkoxides has been investigated. Pb-doping, addition of excess Ca and Cu, change of heating and cooling rates and firing under low oxygen partial pressure were studied to increase the volume fraction of the high-T_c phase. The Pb-doping and the firing under low oxygen partial pressure were not effective, but addition of a proper amount of excess Ca and Cu under the firing condition at high heating and cooling rates was effective. The film with a nominal composition of Bi₂Sr₂Ca₃Cu₄O_x fired at 850°C for 48h in air at heating and cooling rates of 30°C/min showed superconductivity with T_c (onset)=125K and T_c (zero)=115K.

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Effects of various kinds of rare earth oxides (Y₂O₃, Er₂O₃, Sm₂O₃, La₂O₃ and CeO₂) addition on the sintering of mullite and the precipitation behavior of secondary phases in the mullite sintered bodies were investigated. The sintering of the mullite compacts, to which a small amount of these rare earth oxides was added, was performed at 1500°-1600°C. The morphologies of the rare earth silicates precipitated and remained on the grain boundaries of the sintered bodies could be classified into three categories, i.e., crystalline, glassy and decomposed substances, depending upon the kinds of the rare earth oxides added. The microstructures of the mullite sintered bodies changed as the amount of the additives varied. The three point bending strength of the sintered mullite increased with the addition of 0.5wt% of Y₂O₃ or CeO₂. On the other hand, excessive amount of these additives would result in the decrease of the three point bending strength. It was found that the maximum value of three point bending strength was evidently related to the melting point of the secondary phases existed in the sintered bodies of muilite.

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The creep deformation in 72wt%Al₂O₃-mullite (72A), 74wt%Al₂O₃-mullite (74A) and those containing 10vol%ZrO₂ (72A-10Z and 74A-10Z, respectively) has been studied. Stress exponent n's for creep in 72A-10Z and 74A-10Z were 1.1-1.2 and 1.0-1.2, respectively, slightly smaller than those in 72A (1.2-1.3) and 74A (1.3-1.5). Activation energies for creep in 72A-10Z and 74A-10Z were 157 and 158kcal/mol, respectively, slightly smaller than those in 72A and 74A (171 and 169kcal/mol, respectively). Creep rate in 74A was increased more than that in 72A by addition of 10vol% ZrO₂. It was estimated that the enhanced creep rate of mullite ceramics by the addition of ZrO₂ was ascribed to the relaxation of the stress at grain boundary triple points by the creep deformation of ZrO₂ grains.

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The proof-test and non-destructive inspection (N. D. I.) are used to assure the reliability of structural ceramics. Especially, the proof-test has widely been applied to guarantee the safety of the structural materials. On the other hand, N. D. I. is not yet adopted independently, because of no available theoretical analysis. In this paper, the statistical theory and effective execution method of N. D. I. are presented. By calculating the flaw-size distributions for uni-axial tensile stress field after N. D. I., the effect of screening-size (d_p) is analysed theoretically. It is concluded that the stress field in N. D. I. must be the same as the stress field in real loading.

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PbTiO₃ single crystals with SrO additive (<0.5wt%) were grown by a flux cooling technique. The electrical measurements were carried out by using as-grown crystals of PbTiO₃ with 0.4wt% SrO. In summary, (1) The addition of SrO remarkably effected on the crystal size and the yield of PbTiO₃. Especially, it was available for improving the crystal perfection of PbTiO₃. (2) The resulting crystals was platelet (1.6×1.6×0.2mm) in shape and yellow-brown with highly transparent. (3) According to the X-ray diffraction, little change of axial ratio c/a was observed with increasing SrO content. (4) The arrhenius plot of σ_dc indicated that the conductivities were represented as the following equations; σ=3.1×10³exp(-0.2/κT) [25°-150°C], σ=3.1×10³exp(-1.5/κT) [150°-500°C]. (5) Above 300°C, the nonohmic behaviour was observed in the I-V characteristic curves. And the threshold value V_H decreased with increasing temperature.

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Composite ceramics of α-alumina mixed with up to 40vol% β-silicon nitride whisker were fabricated by hot-pressing at 1400°-1700°C under 30MPa for 30min. The properties (bending strength, fracture toughness, thermal shock resistance, and oxidation resistance et al.) of the hot-pressed bodies were investigated. Dense alumina-Si₃N₄ whisker composite ceramics were obtained in the region of whisker contents up to 30vol% at the sintering temperatures above 1600°C. The composite mixed with 20vol% whisker and fired at 1600°C showed the highest bending strength (about 610MPa), which is lower than the maximum strength of alumina (about 630MPa). These composites had more excellent high temperature strength, hardness and thermal shock resistance than monolithic alumina. The fracture toughness (about 4.7MPa·m^1/2) of a composite with a whisker content of 30vol% was 1.7 times as large as that of monolithic alumina. The weight gain by oxidation at 1400°C increased with increasing oxidation time and whisker content, but decrease in strength was not observed after oxidation.

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A 6H→3C transformation, which does not commonly occur at high temperatures, was observed in SiC. A 6H-SiC and TiN powder mixture was hot-pressed in a flowing Ar atmosphere. The starting 6H-SiC powder was completely transformed to 3C polytype above 2200°C, although 3C-SiC was not stable at this temperature. It was found that coexistence of N was essential for this 6H→3C transformation, and a small amount of Ti was detected in the transformed SiC grain. The results suggest that a solution of N or TiN in the SiC grain would transform the 6H-SiC to the 3C form.

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A modulated structure of a low-temperature form of zirconium titanate (ZrTiO₄) was analyzed with an X-ray diffractometer. Superstructure spots were indexed by introducing a modulated wave vector of k=0.58. Intensities for normal and superstructure spots measured along the a* axis were used for the calculation of electron densities. The results indicated the existence of a modulation of scattering amplitude of cations as well as a displactive modulation of oxigen ions. The estimated ordered arrangement of metal ions along the a-axis was Zr-Zr-Ti-Ti-Zr-Zr-.

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The grinding process induces residual stresses and scratch cracks near the surfaces of ceramic work-pieces. In order to reduce the influences of the surface damage layers, the effects of annealing on the bending strength of alumina specimens ground with a #170 diamond wheel were investigated. Surface residual stresses were measured by the X-ray diffraction method and the effects of residual surface stresses on the bending strength were discussed using a simplified model. As a result, the annealing process restored the surfaces damage layers and bending strengths of ground alumina specimens to the initial condition. The compressive residual stress influenced the micro-cracks perpendicular to the grinding direction and consequently the bending strengths increased slightly, however, they hardly influenced the deep scratch cracks parallel to the grinding direction.

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Oxidation resistance and oxidation mechanism of a carbon/carbon composite (C/C composite), on which inner layer of TiC and outer of SiC were coated by chemical vapor deposition, were investigated. The CVD conditions used were, TiCl₄-CH₄-H₂ or SiCl₂-CH₄-H₂ system, deposition temperatures ranging from 1050° to 1350°C and total gas pressures ranging from 40 to 100 Torr. TiC coating was 7-50μm thick and SiC coating was 70-270μm thick. The oxidation resistance of the coated C/C composite was estimated from room temperature to 1300°C in air using several heating programs. In two layers-coating, the number of thermal cracks which generated on the surface of the coated layer decreased and the oxidation resistance improved depending on the thickness ratio of TiC to SiC coating as compared with SiC monolayer-coating. It is recognized that large compressive stress generated in the outer layer of SiC and TiO₂ (rutile) formed along the thermal cracks in the coated layers after the oxidation.

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The effect of alumina content and composition of tetragonal zirconia (TZP) on the fracture strength and hydrothermal stability of (Y, Ce)-TZP/Al₂O₃ composites HIPped at 1400° to 1600°C under 147MPa for 0.5h in Ar were studied. (Y, Ce)-TZP/Al₂O₃ composites HIPped at 1400°C exhibited the maximum density and maximum bending strength. The mean values of bending strength of HIPped (Y, Ce)-TZP/Al₂O₃ composites were 1800MPa for (4Y, 4Ce)-TZP/25wt%Al₂O₃ composites, 1700MPa for (2.5Y, 4Ce)-TZP/25wt%Al₂O₃ composites, and 1600MPa for (2.5Y, 5.5Ce)-TZP/25wt%Al₂O₃ composites. The phase stability of HIPped (Y, Ce)-TZP/Al₂O₃ composites under hydrothermal conditions at 180°C and 1MPa increased with increasing alumina content. Dispersion of Al₂O₃ into (Y, Ce)-TZP was useful to enhance the bending strength, to suppress the tetragonal→monoclinic phase transformation and grain growth of zirconia and to improve the resistance to low-temperature degradation.

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The mechanism of pyrolysis of two types of amorphous Si-Ti-C-O fibers (Tyranno fiber T-1 containing 17.8%O and T-2 containing 13.3%O) was studied in an argon atmosphere at temperatures from 1673K to 1973K. The pyrolysis rate was measured with a thermobalance, and the pyrolysis products were investigated by X-ray diffraction and TEM observation. The amorphous fiber T-1, in which the atomic arrangement was disordered in comparison with that in T-2, evolved both SiO and CO to crystallize to β-SiC and TiC rapidly. TEM observation showed three-dimensional growth of SiC crystallites. At the same fractional decomposition of the fiber, the crystallite of T-1 was smaller than that of T-2. The pyrolysis rate was described with an Avrami-Erofeev equation. The exponent m of this equation was 1.4 for both fibers. The rate constant k for T-1 was larger than that for T-2. The activation energies were 413kJ/mol for T-1 and 368kJ/mol for T-2. The pyrolysis rate was determined by the crystal growth of SiC controlled by the diffusion of carbon in the fiber.

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To investigate the sintering behavior of reaction bonded ceramics containing good self-sintering ceramic powders as starting materials, Al₂O₃ and Si powder mixtures were heated to 1350°C in a 0.88MPa nitrogen gas atmosphere. Shrinkage of abouf 0.3% was observed for the samples containing 20 to 70vol%Al₂O₃. This value was a few times larger than that of Si₃N₄ bonded ceramics containing non-self-sintering powders such as SiC, TiN and ZrN. It was proved that the grain growth of Al₂O₃ powders by self-sintering increased the shrinkage. TEM observation of the sintered body showed that micro-cracks were present at the grain boundaries of Al₂O₃ and Si₃N₄ grains. These cracks seemed to form due to stress of the Al₂O₃ sintering on the Si₃N₄ skeleton formed from the Si powders. This skeleton might depress the free sintering shrinkage of Al₂O₃ powders. The TEM observation also showed that Si₃N₄ grains grew epitaxially on the Al₂O₃ surface, which meant Si₃N₄ could be bonded to inorganic compounds with ionic bond character.

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Electroconductive ceramics were machined by a wire electro-discharge machining method. The machining rate and surface roughness for various pulse durations were evaluated as a function of duty factor. It is obvious that there exists an optimum duty factor from a standpoint of machining rate, and that the optimum duty factor increases with increasing pulse duration, specially in machining zirconia ceramics. But, the maximum machining rate did not depend so much upon duty factor. The machined surface roughness increased generally with an increase in duty factor. This indicates that the roughness of the machined surface did not always increase with an increase in machining rate.

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This report describes the results of VAMAS international round robin test for evaluating fracture toughness of ceramics. Thirteen laboratories in Japan, France, Germany, UK, Canada, Belgium and CEC (JRC Petten) took part in the test. The values of fracture toughness obtained by the SEPB, the IF and the IS methods were compared with one another for gaspressure sintered silicon nitride (GPSSN) and zirconia-alumina composites (ZAC). Also examined were indentation load dependence of fracture toughness measured by the IF and the IS methods and loading rate dependence of fracture toughness by the SEPB method. The results showed that the toughness values evaluated by the SEPB method have relatively wide scatter among the participants, suggesting some difficulty with this technique; the IS method gave the smallest scatter and the IF method the largest scatter. Fracture toughness measured by the SEPB method was dependent on the loading rate, especially for ZAC. This may have been caused by stress corroson cracking. The values measured by the IF and IS methods depended apparently on the indentation load.

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The structural change of silicate ions in 11Å tobermorite with carbonation of ALC was studied by solidstate high resolution ²⁹Si NMR spectroscopy. It was found that the tobermorite in ALC is an anomalous Alsubstituted type and that the silicate ions have double chain structure with Si-O-Si bridges. In addition, it was suggested that the silicate ions in tobermorite change from the double chain structure to three-dimensional cross-linked framework with the carbonation of ALC.

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Electrical properties of an YBa₂Cu₃O_7-x/metal film/indium interface were examined by the DC four-probe technique. Contact resistance in the order of 10^-6Ω·cm² was achieved with gold, silver and copper, while a high-resistive and non-ohmic junction was formed with indium. Evaporation of Ib metals was very effective in decreasing the contact resistance and such a technique will be of experimental or practical use in large current carrying applieations of YBa₂Cu₃O_7-x.

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The surface roughness of SiC whiskers is changed by heat treatment in an inert gas atmosphere. Taking advantage of these phenomenon, SiC whisker/Al₂O₃ composites containing whiskers with different surface roughness were fabricated and their mechanical properties were evaluated. Composites using whiskers with smooth surface showed higher fracture toughness K_IC and higher effective fracture energy γ_eff than those with rough surface It is suggested that smoothing of whiskers' surfaces leads to decrease in frictional force at whisker/matrix interfaces and that pullingout of whiskers which becomes easy to occur toughens the composites.

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