High temperature static (constant stress loading) and dynamic (constant stress rate loading) fatigue tests were conducted on hot-pressed silicon nitride and sintered silicon carbide in vacuum, and the results were treated by two types of crack growth expressions, power-law and exponential relations. The log-log representation based on the power-law relation for data on the silicon nitride produced the change in slope, suggesting effects of accelerated crack extension by rapid cavity spreading, and the semi-log representation based on the exponential relation resulted in an excellent fit with one straight line. On the other hand, data for the silicon carbide were shown to be better described by both relations. Hence, the superiority of exponential crack growth expression was suggested for life prediction as a consequence.

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SrTiO₃ ceramics were reduced both by HIP and by Ar-O₂ mixed gas at 1300°C. The degree of reduction of the specimens was characterized by optical transmittance and electric conductivity. The degree of reduction of the HIPed specimens were depended on the HIP pressure. The degree of reduction was low at high pressure, but high at low pressure. The degree of reduction of the specimens HIPed under 100MPa was equivalent to the specimen reduced under the atmospheric pressure in which oxygen partial pressure was 10¹Pa. This result was explained by the concentration of oxygen included in Ar used as a pressure medium.

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Open porous materials were produced by a Hot Isostatic Press (HIP) process. Cold-isostatically pressed powders were directly heated to a normal sintering temperature under HIPping conditions. The products were characterized by open pores and were almost free from closed pores. Those open pore materials are typically useful as filters, reactor beds, grinding materials and so on. A grind stone with silicon carbide grains with aluminium nitride bridges was discussed as an example. At the sintering temperatures of AlN above 1973K, 20 to 30% of open porosity was maintained in the HIPped samples, On the other hand, normally heated ones were almost fully densified. Since no additives for pore formation were used, uniform pore size distribution and homogeneously dispersed pores were expected by the new HIP process. Normal HIPping effects enhanced the properties of bridge parts by reducing defects and also closed pores in them. Better strength and open porosity were obtained by this method.

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Microstructural effects on the mechanical and thermomechancical properties of mullite ceramics have been investigated. The mullite ceramics were fabricated by reaction-sintering of mixture of kaolin and Al₂O₃(M-1) and by pressureless-sintering of a powder prepered from Al₂O₃ and SiO₂ sols (M-2) and Al₂O₃ sol-ethylsilicate (M-3) system from the sol-gel method. Transmission electron microscopic observation revealed that samples M-1 and M-2 contained foreign phases, but that they were much less in M-2. These showed different temperature dependence in mechanical properties such as hardness, Young's modules, fracture toughness and strength. These differences were explained by the amount of grain boundary impurity phases. Thermal shock fracture behavior was also discussed.

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The ilmenite type NaNbO₃ was prepared by low temperature hydrothermal reaction and had an endothermic phase transition at about 290°C and transformed to the perovskite type structure at about 485°C. The ionic conductivity, the lattice constants at high temperature and the latent heat were measured in order to investigate the phase transition at about 290°C. The crystal structure at 350°C was refined with the X-ray powder Rietveld method and the final R-factors were R_wp=24.1, R_p=18.4 and R_B=14.5%. The refinement indicated that partial Na⁺ ions moved to the empty octahedral sites along the c-axis. From these results the phase transition at about 290°C was concluded to be the order-disorder transition of Na⁺ ions.

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Heat resistant porous ceramics were fabricated by sintering of sol gel-derived hexaaluminate fine powders at 1200°-1600°C. Although the sintered samples showed high porosities (ca. 50%), the N₂ permeability is low because of small pore size (<100nm). The packing of planar particles of hexaaluminate formed two kinds of peaks in their pore size distribution at <10nm and 100nm. Second-stage sintering of the crushed powders significantly enhanced the N₂ permeability. In the samples after second-stage sintering, the loose packing of large agglomerates formed macropores (>10μm) besides the voids of primary particles. These macropores are effective for high gas permeation. Consequently, the second-step sintering of hexaaluminate attains the mixed structure of micropores and macropores, which is a possible microstructure for application to filtration catalysts.

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The microstructure of plasma sprayed coating of zirconia stabilized with 8wt% of yttria was analysed by the electrochemical technique. Porosity of 15.9% was mostly opened pores which consisted of cracks by cooling and the incomplete bonding of sprayed particles. The thermal properties of plasma sprayed coating of zirconia and NiCrAlY were studied by a laser flash method. The thermal conductivities measured were related to the microcracked structures described above. Also, thermal conductivities of the two-layer composites (the plasma sprayed coatings) were determined by the laser flash method using Bulmer's technique. The thermal contact resistance at the zirconia/SUS 304 interface showed a large amounts of scatter without NiCrAlY bond coating. This tendency was observed in the bonding strength of sprayed coatings. Namely, a better correlation between the thermal contact resistance and the bonding strength is obtainable.

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The effect of temperature, heating rate and addition of ZrSiO₄ seed crystals on the preparation of ZrSiO₄ powders by the sol-gel process was studied using X-ray powder diffractometry. ZrSiO₄ powders have been prepared by different precursors in Zr(OPrⁱ)₄-Si(OEt)₄, Zr(OPrⁱ)₄-SiO₂ sol, ZrOCl₂⋅8H₂O-Si(OEt)₄ and ZrOCl₂⋅8H₂O-SiO₂ sol groups. The formation rate of ZrSiO₄ was higher in Si(OEt)₄ than in SiO₂ sol. The formation rate was influenced by heating rate, and, in particular, increased remarkably below 2.5K/min. When a small amount of commercial ZrSiO₄ was added to the powder of precursor composition as seed crystals, ZrSiO₄ powder with a purity of 94-96% was formed at 1600°-1650°C. It was found that the addition of seeds results in lowering of the formation temperature of ZrSiO₄ by about 100°C. On the other hand, a ZrSiO₄ powder of 94-96% purity was obtained by heating the powder of precursor composition at 1300°C for 1h, followed by re-heating at 1600°C for 1h. The results have suggested that the preparation of ZrSiO₄ powder of nearly single phase is possible using the sol-gel process by controlling the seedings and/or the two-stage heating.

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Wetting behavior of 72Ag-28Cu-x%Ti alloys on SiC was investigated in a vacuum of 10^-3Pa, Ti-free Ag-Cu alloy did not wet SiC and the contact angle became about 160°. With more than 0.5% Ti, the alloy wetted SiC well. Wetting of SiC by Ag-Cu-x% Ti alloy was thought to proceed by the adsorption of active metal Ti at the interface. In Ag-Cu-0.2% Ti alloy, the wetting angle became about 130° in a vacuum of 10^-3Pa, but the alloy reacted with SiC. Microstructure and composition at the surface and bulk of each alloy after wetting experiment were analyzed by SEM and EDX. Non-wetting behavior of Ag-Cu-0.2% Ti alloy on SiC was thought to have resulted from the presence of atmospheric oxygen. Thus, Ti was consumed by the reaction with the atmospheric oxygen at the surface of the alloy leaving little Ti available to wet SiC. But for more than 0.5% Ti, a considerable amount of Ti for adsorption remained and wetted SiC. When the amount of atmospheric oxygen was increased, the reaction between oxygen and Ti in the brazing alloy became active and therefore the alloy could not wet SiC even in the case of Ag-Cu-2% Ti. The state that brazing alloy contacts with atmospheric oxygen is much different between the cases of wetting and joining experiments. Ag-Cu-0.2% Ti alloy could join SiC successfully, even though the contact angle was about 130° in wetting experiment, probably because it was difficult for Ti to react with the atmospheric oxygen in joining experiment and Ti could adsorb at interface.

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Strontium ferrite granules of powder particles having various fractional reactions were prepared by solid state reaction between 750° and 1250°C for 0.1 to 16h. Aggregate formation among particles was characterized by the die pressing test at 0 to 49MPa. At reaction temperatures below 1100°C, the strength of aggregates increased with reaction time and increasing temperature. At a given fractional reaction, the strength of aggregates did not depend on the reaction conditions. These results suggest that both aggregate formation and solid state reaction have the same temperature dependence. Above 1150°C, reaction was completed in a short time. Strength of granules increased as grain growth proceeded in the granule.

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The machining test with a surface grinder was carried out on new ceramics to investigate the relation among AE, grinding force and machining integrity. As a result of fundamental test, both amplitudes and continuous-times of AE signals were distinctly affected by the difference of base materials in which the AE sensor was mounted. In grinding test, the distinguishable amplitude of AE took place in coincidence with the place of the slit of test pieces, which was considerably higher than that of the bulk. In the case of new ceramics, the order of the magnitude of the amplitude of AE showed the opposite tendency compared with that of the grinding force. Especially, the integrity of sialon was superior to that of WA and 2A, in correspondence with the degree of the AE count numbers.

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A technique for precise control of shrinking rate up to high densities during sintering has been developed using a specially designed dilatometer. The detected shrinkage was periodically fed into a microcomputer system to calculate heating rate as a control parameter by a function optimized for densification behavior. By improving the accuracy of shrinkage measurement and optimizing the control function, the shrinking rate could be controlled within the accuracy of ±3% up to high densities above 95%. It was possible to reduce the grain size of sintered bodies remarkably by this precise control. This technique also contains the multi-step and functional controls of shrinking rate according to preset profiles as a function of time or shrinkage, where the accuracy was ±5% to the density more than 96%.

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This paper is concerned with the bias effect of additional DC voltage, which is applied between the reaction chamber and the substrate, on the properties of carbon films prepared by RF-plasma CVD. Hard carbon films (H_v≤2500) of 50-100nm thick were synthesized by the plasma CVD method with negative DC voltage to the substrate. The deposition rate, refractive index and microhardness of the films increased with increasing negative voltage at -140V or above. Their Raman spectra showed two broad peaks at 1350cm^-1 and 1550-1580cm^-1. These facts suggested that the additional negative bias promoted the formation of i-carbon and/or diamond like structures in the films.

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Changes in crystal phase and thermistor constant of Mn-Co-Ni oxide, a thermistor material, in cooling process below 1000°C after firing at 1400°C were studied. The starting oxide was made of nitrates of Mn, Co and Ni with a molar ratio of 3.0:1.9:1.1 by firing at 1400°C. Samples were prepared by annealing the above oxide at various temperatures between 250° and 1000°C for 24 hours followed by quenching into water. Precise X-ray diffraction analysis of quenched samples revealed the good correlation between the thermistor constant B and the fractional ratio of crystal phases, such as cubic spinel, tetragonal spinel of low-temperature form and tetragonal spinel of high-temperature form, in the sample. It seemed that, in the temperature range between 560° and 650°C, there existed very complicated crystal structures in which the fractional ratio of cubic spinel and tetragonal spinel of high-temperature form varied intricately. Therefore, it is assumed that the change in thermistor constant observed at around 550° to 650°C in the previous paper can be attributed to the very complicated changes of fractional ratio of cubic spinel and tetragonal spinel of high-temperature form in annealed samples.

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The crystallization process of the rapidly quenched glasses in the system Li₂O-K₂O-Al₂O₃-SiO₂-F has been investigated. Batches of the lepidolite composition were melted at 1773K for 10 minutes and quenched with a twin roller aparatus. Lepidolite and β-eucryptite were precipitated at 773K and 873K, respectively. However, it was requisited to keep the glass at 773K for more than 1 hour for the precipitation of lepidolite. The thermal conductivity of the glass-ceramics heated at 773K for 1hour and then at 973K for 2hours was larger than fluorphrogopite glass-ceramics, and its thermal expansion coefficient and dielectric properties were similar to those of fluorphrogopite glass-ceramics.

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Tetramethoxysilane and phenol-formaldehyde condensate, both in liquid state, were polymerized with water. The polymer was carbonized and heated at 1750°-1850°C. Thas, a mixture of fine β-SiC and C powders was obtained Hot pressing of this powder using B as a sintering aid yielded a SiC-C composite. The composite had a higher fracture toughness than sintered monolithic SiC. The crack bridging mechanism by the C particles increased the fracture toughness of the SiC-C composite.

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Bi-Sr-Ca-Cu-O ceramics with B₂O₃ additive were shynthesized. The magnetic shielding effect for the sample containing B₂O₃ was larger than that without B₂O₃. However, the XRD intensities of 2223 phase for both samples were almost the same. Therefore, it is considered that 2223 phase surrounds a non-superconductive phase in the B₂O₃-containing sample.

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