A rapid quench hydrothermal apparatus with a large volume has been newly designed. The apparatus has advantages in quenching the sample and in having a large sample space with small temperature differences. To determine the optimum operation conditions, the temperature gradients inside the vessel were measured at the water pressure of 100MPa, the temperatures of 300°, 500° and 700°C and for the following variables: the angle of inclination of vessel, the length of vessel inserted into the furnace and the temperature gradient of the furnace. The flat temperature gradient over the range of 10cm is successfully obtained with the temperature difference of 2°C at the temperature of 700°C. The characteristics of the operation modes are as follows: the vessel is inclined at -10° for the horizontal and is inserted to the furnace with “steeper” temperature gradients. A reacted sample is quenched within only 1 minute when the vessel is removed from the furnace. The apparatus and its operations described offer a new method for hydrothermal experiments.

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The process and technique for direct measurement of current-voltage characteristics of a single grain boundary and a grain in silicon carbide ceramics containing beryllia were discussed. Discharging between two tips of aluminum micro-pattern electrodes by applying pulsed voltage caused melting of the tips of electrodes. As the results, aluminum-rich alloy layers were formed along the discharge path and also at the tip section of micro-pattern electrodes resulting in the breakdown of the Schottky barriers and the formation of the ohmic contacts at the interfaces of SiC and electrodes. The formation of the ohmic contacts made it possible to measure the current-voltage characteristics of a grain and a grain boundary directly.

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Pressureless sintered silicon nitride was joined to molybdenum with metallic interlayers by hot-pressing and by hot-isostatic-pressing. The interfacial strengths of niobium and molybdenum was 400MPa. With increasing metal thickness, the residual stress in a joint increased resulting in a decreased strength. Lamination of molybdenum and tungsten layers reduced the residual stress. The highest tensile residual stress appeared at the corners of the square bond face joint. The magnitude of the residual stress depended on the dimension of the joint and increased with increasing size. When the side of the bond face was 20mm, the joint collapsed without any applied load. The joint with the molybdenum/tungsten laminate interlayer had the strength of 240MPa at 1173K and was resistant to thermal cycles between 673K and 1273K.

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The pressureless bonding of 3Y-TZP and Ti metal using a bonding agent containing Cu₂O-added 5 wt% activated carbon as a reductant has been investigated. The test specimen consisting of two kinds of the materials in question with the bonding agent interposed between the two has been heat-treated at 1000°C for 0min to 8h, exposed in an argon stream. The average strength of the test specimens bonded under the conditions of 4°C/min of heating rate and 30min of treatment time was 53MPa. An observation of the interfacial composition and an analysis of the micro-constituents have been performed with the bonded body thus obtained, employing EPMA and SEM with an energy-dispersive-type X-ray analyser. As the result, Cu produced by the carbon reduction of Cu₂O is diffused into the Ti metal to form CuTi₂. It has been made known that the structure of the bonded interface comprised of plural layers is as shown below. The reaction layers from 3Y-TZP sequential to Ti metal are titanium oxides layer (TiO, Ti₂O)/Ti-rich layer (Ti with scanty Cu)/Cu-Ti alloy layer (CuTi₂). The most effective parameters affecting the bonding strength are surface roughness of TZP and heating rate when heat-treatment is conducted. The bonding strength obtained by utilizing a specimen of TZP with 3μm of surface roughness and 20°C/min of heating rate for 30min of treatment time was higher than 110MPa. None of strength degradation has been noticed at all with the bonding strength of the bonded bodies thus obtained in Ar gas, N₂ gas, and the air up to 1000°, 800° and 400°C, respectively. The result implies that the bonded bodies are thermally stabilized.

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Ultrafine Y₂O₃ powder was produced from metallic yttrium powder by a radio frequency (RF) plasma method, and used as an additive to aluminium nitride in normal sintering. The average particle size (Microtrack method), shape (TEM), specific surface area (BET method) and crystalline structure (X-ray diffraction) of the ultrafine Y₂O₃ powder were evaluated. Density and thermal conductivity were measured for the sintered aluminium nitride containing the ultrafine or commercial Y₂O₃ powders as additive. Grain boundaries of the sintered aluminium nitride were also examined by X-ray diffraction and SEM. Yttrium distribution in the sintered aluminium nitride was analyzed by EPMA. The results are summarized as follows:
(1) The ultrafine Y₂O₃ powder contained two allotropic forms. The average particle size and specific surface area of the ultrafine Y₂O₃ powder were 1.63μm and 14.2m²/g respectively. Particles were spherical. One of the commercial powders tended to form agglomerates, and had a higher specific surface area with bigger effective particle size.
(2) The aluminium nitride powder was densified with the ultrafine Y₂O₃ powder more extensively than the one of the commercial Y₂O₃ powders at 1700°C.
(3) Thermal conductivity of the sintered aluminium nitride with the ultrafine Y₂O₃ powder was higher (120W/(K·m)) than that with the commercial Y₂O₃ powders (about 50W/(K·m)). Both of them were sintered at 1700°C.
(4) Yttrium ions of the sintered aluminium nitride with the ultrafine Y₂O₃ powder were distributed throughout the sintered bodies compared with the one with the commercial Y₂O₃ powders.
(5) The sintered aluminium nitride with the ultrafine Y₂O₃ powder shows a lower oxygen content than the one with the commercial ones.

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Silicon oxynitride ceramics were prepared by hot-pressing an equimolar Si₃N₄/SiO₂ mixture with a small amount of CeO₂. The formation of Si₂N₂O occurred not in the solid state but via the liquid phase in which the reactants dissolve. The chemical composition of the intergranular phase (liquid phase) changed during the reaction. CeO₂ additive gave a liquid phase with a portion of SiO₂ and Si₃N₄ above the eutectic temperature. The liquid phase promoted the formation of Si₂N₂O with increasing temperature. SiO₂ content in the liquid phase increased with increasing temperature and time, until residual SiO₂ particles dissolved completely in the liquid. After all of the residual SiO₂ particles dissolved in the liquid, SiO₂ component in the liquid was consumed for the formation of silicon oxynitride, and the Ce₂O₃/SiO₂ ratio in the liquid increased. When the ratio reached a certain value, the liquid crystallized during cooling. Fracture toughness K_IC of hot-pressed specimens increased by increasing soaking time and the amount of CeO₂. Since the intergranular phase in the specimen with a high K_IC value was crystalline and silicon oxynitride grains were larger, probably the residual strains and microcracking were induced on interfaces between the silicon oxynitride grain and the intergranular crystalline phase due to thermal expansion mismatch, resulting in interfacial bonding weakened to some extent. Consequently, crack deflection by rod-shaped silicon oxynitride grains efficiently occurred in the specimen. Flexural strength and its temperature dependence also changed by increasing the soaking time and the amount of CeO₂. This result was also attributed to the difference in thermal and mechanical properties (e.g. softening temperature) of intergranular phases.

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Needle-like mullite was prepared from New Zealand kaolin at temperatures from 1300° to 1700°C, and some properties of a porous ceramics sheet composed of needle-like mullite produced by leaching out the silica glass from the fired kaolin were examined. The fine needle-like mullite began to grow at 1500°C and crystals 10 to 20μm long and 1 to 2μm thickness were obtained above 1650°C. The growth direction was identified to be [001] of mullite. Most of the alumina component contained in the raw material was converted into mullite above 1650°C, and the product was composed of 59 to 60wt% of mullite, 39 to 40wt% of glass and approximately 0.6wt% of corundum. Leaching out 39.3wt% of glass from the kaolin fired at 1650°C provided a porous sheet with the porosity approximately 60% and the pore diameter of 0.5 to 0.6μm. With thoroughly leaching out the glass, the ratio of Al₂O₃/SiO₂ and the apparent density of the porous sheet approached those of the theoretical mullite. Furthermore, the specific surface area of the porous sheet increased with increasing amount of glass leached and did not decrease by reheating in the temperature range from 1200° to 1650°C.

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A synthetic method of fine powders of sodium hexatitanate was developed. First, Na₂O⋅3TiO₂ was prepared by calcining a 3:1 mixture of TiO₂ and Na₂CO₃, followed by dispersion in boiling water to convert to (Na⋅H₃O)O⋅3TiO₂. Heating of this material at 400°C or above yielded fine powders of sodium hexatitanate. The prepared Na₂O⋅6TiO₂ powders with satisfactory dispersibility in paint were subjected to the test as heat insulating paint. Properties of the paint with sodium hexatitanate was excellent in infrared reflectance, infrared emissivity as well as thermal conductivity, as compared to that of the paint with aluminum flakes or rutile type TiO₂ pigments widely used as heat insulating paint.

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The frost durability of autoclaved light weight concrete (ALC) was enhanced by heat treatment of surface modified ALC using inorganic chemicals (lithium-silicate sol with or without Ag₂O). By surface modification with the lithium-silicate sol containing a small amount of Ag₂O, the effective mold-proofing of ALC was realized. Several physical and chemical properties of surface modifying chemicals and the surface modified ALC were characterized under different heating conditions.

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First, sintering of two spheres of isotropic material which causes shrinkage is analyzed geometrically. The relation among the sphere radii, intersphere shrinkage and neck radius is expressed independently of ratio between the sphere radii. On the other hand, the larger ratio between sphere radii gives the larger selfexpansile pressure on the neck. Second, the sintering of crystallites of irregular shape as ZnO powder is considered within the initial stage, and P(r_p), the probability density of distribution of grain size r_p and P(r_n), that of neck radius r_n are deduced statistically. If r_p is given by the mean value of three elemental lengths independent of each other, P(r_p) conforms to the χ²-distribution of 3 degrees of freedom and the average value r_p represents the distribution of r_p. Because r_n depends on the linear intergrain-shirinkage Δr as well, P(r_n) conforms to the χ²-distribution of 4 degrees of freedom. The average value r_n represents the distribution of r_n. Thus, the sintering of the actual grains can be equated to that of spheres of isotropic material with the same radius r_p which cause the relative shrinkage of Δr/r_p. Ultimately, r_n and P(r_n) are derived from the observed values of r_p and the relative density of sintered bodies. Third, the major grains construct the skeleton of sintered body and merge the minor grains in openings among the major grains during sintering. The arrangement of major grains through which electric current flows hardly varies. The decrease in electric resistance as sintering progresses is caused by the growth in each neck radius and each grain size. The arguments as above support the process for Hamano et al. to derive the dependence of bulk resistivity on the neck radius from the experimental results.

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A ceramic coating material was developed by using saponite/acriflavine complex as a filler and aluminum phosphate as a binder. This material coated on the soft steel plate was heated below 773K in air, followed by examination of some properties. Good ceramic coating was obtained from a material consisting of 80% filler and 20% binder, after heating at 573 and 673K. This coating consisted of the layered structure oriented parallel to the substrate surface and exhibited 9H in the pencil hardness and 90/100 in the cross-cut test. According to the taber abrasion tast, its abrasion resistivity was relatively low. Based on these results, a possiblity to use the complex as a filler for the ceramic coating is discussed.

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K₂Ti₆O₁₃ fibers and its related composite fibers were prepared as derivatives of K₂Ti₂O₅ fibers having a layered structure by a compositional-structural change technique. The K₂Ti₂O₅ fibers were prepared by crystallizing from a melt using a mixture of the natural rutile (95% TiO₂) or anatase (90% TiO₂) ores and K₂CO₃ powder in an attempt to reduce the fabrication cost. The composition of K₂Ti₂O₅ fibers was controlled by extracting K⁺ in interlayers with water, boiling water and treating with dilute acid solution, and then the structural change was carried out by heat-treatment above 1000°C. The water-treatment is essentially to produce K₂Ti₆O₁₃ fibers, and the boiling water-treatment, to produce K₂Ti₆O₁₃-TiO₂ (rutile)-K_1.5Fe_1.5Ti_6.5O₁₆ (priderite) composite fibers, and the dilute acid solution-treatment, to make anatase or rutile fibers. The melting temperature of K₂Ti₆O₁₃ phase of the obtained fibers was measured by DTA. The K₂Ti₆O₁₃ single phase from rutile ore melted congruently at 1352°C, that in the composite fibers from the same ore at 1316°C, and that in the composite fibers from anatase ore at 1332°C. Thermal conductivities of sintered disk prepared from the obtained fibers are estimated at a temperature range from 300K to 1100K, and the K₂Ti₆O₁₃ and composite fibers were found to be good heat-inshulators.

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Tetragonal zirconia polycrystals containing 3.0mol% Y₂O₃ were rapidly quenched from melts and their low temperature degradation phenomena were examined at 250°C in air. As-quenched material showed a high stability against OH^- trigger which was considered as an agent of the degradation.

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