The role of diffusion in ceramic processing is discussed. The utility of secondary ion mass spectroscopy (SIMS) is highlighted for the evaluation of diffusion coefficients in ceramic materials. By comparing diffusion coefficients obtained in this manner with those obtained indirectly from creep measurements, we identified the ion species that govern creep in yttrium aluminum garnet (YAG) ceramics and we showed that diffusion involving metastable defects plays an important role in ceramic processes such as sintering. The oxygen diffusion coefficients of thin films were evaluated, and the defects involved were shown to be metastable, and their origins were clarified. Furthermore, their relationship with reactivity was discussed in thin films.

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The joining of a sapphire single crystal plate to alumina ceramic tube is fabricated successfully using 34CaO·30Al₂O₃·36SiO₂ glass as an interlayer. This glass showed good adhesion performance to alumina ceramics and sapphire single crystal. The joint with no crack was obtained by heating at 1550°C for 10 min and slow cooling from 1200°C to room temperature. From the thermal shock test, the half of the specimens showed the cracks after quenching from 225°C to 0°C, but all specimens showed no cracks after quenching from 200°C to 0°C. The specimen, composed of alumina tube-sapphire plate-alumina tube showed the comparable bending strength to the specimen composed of alumina tube-alumina tube.

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Improvement of chemical corrosion resistance of silicon nitride (Si₃N₄) ceramics is strongly desired from the industry side. However, there is presently not enough information on chemical corrosion. This paper investigates corrosion resistance of two kinds of commercialized Si₃N₄-based ceramics with different additives developed for attaining high wear-resistance. One of the specimens is composed of Si₃N₄-Y₂O₃-Al₂O₃-AlN-TiO₂ (specimen A), the other of Si₃N₄-MgAl₂O₄-SiO₂-TiO₂ (specimen B). We adapted a corrosion test at 30 and 80°C in acid, basic and salt solutions. The corrosion at 30°C in acid and basic solutions in both specimens was very low in comparison with that at 80°C. Specimen A with additives of Y₂O₃ and Al₂O₃ was easily corroded by both acids and bases. In particular the specimen was strongly corroded by 5 mass% H₂SO₄, 5 mass% HNO₃ and 35 mass% NaOH solutions at 80°C. Specimen B, containing MgAl₂O₄ as an additive, was better corrosion resistant than specimen A, although specimen B was slightly corroded by a high concentration of basic solutions. The extent of corrosion by NaCl and CaCl₂ solutions was almost negligible. Solution analysis after soaking the specimens in the solutions indicated that the grain boundary phase, mainly a glassy phase, was reacting with acid. The existence of Y₂O₃ and Al₂O₃ in the glassy phase is considered to be mainly responsible for the lowered chemical corrosion resistance. Si₃N₄ grains easily reacted with bases, although the grain boundary phase was also corroded by them. These results were also confirmed by scanning electron microscopy (SEM) observation. It was concluded that an improvement of corrosion resistance against basic solutions at higher temperatures such as 80°C seems to be hardly achievable. The above data on corrosion resistance of typically commercialized Si₃N₄ ceramics are considered to be very useful to expand the application areas.

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Al₂O₃/5 vol%Ni nanocomposite materials were fabricated by pulse electric current sintering (PECS) to achieve suitable microstructures. Their mechanical and magnetic properties were investigated and related to microstructure developments. Rapid densification of nanocomposites and various microstructures was accomplished by controlling PECS temperatures. Microstructures affected mechanical properties such as fracture strength, fracture toughness and hardness. Mechanical properties of Al₂O₃ were improved by Ni; fine dispersion into Al₂O₃ matrix improves changes in various ferromagnetic properties.

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Potassium magnesium titanate (KMT) was synthesized in single-phase by calcination at 1000°C for 1 h from magnesium nitrate 6-hydrate and hydrous potassium tetratitanate fiber. For comparison, mixture of potassium carbonate, magnesium nitrate 6-hydrate and titanium dioxide powders was calcined, and KMT and small amount of an amorphous phase, which is found by TEM. Hydrous potassium tetratitanate fiber and magnesium nitrate 6-hydrate were heated at 1000°C for 1 h to obtain KMT short fibers containing small amount of magnesium oxide as a by-product. The fibers were 10-80 μm long and 1-3 μm in diameter. The fibers were soaked in water and their hydrate phases were found. The distance between its layers in crystal structure was different from the soaking condition.

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Thermal conductivity and temperature dependence of electrical resistivity of Al₄SiC₄-SiC sintered bodies at the temperature from 100°C to 1000°C were studied. Thermal conductivity of the bodies increased with the rich of SiC, and did not follow the law of mixture. Current-voltage characteristics of the bodies showed a linear relationship, and the characteristics have an ohmic region. Electrical resistivity, obtained from the current-voltage characteristics, increased with the rich of Al₄SiC₄, varied significantly depending on the temperature, and did not follow the law of mixture. Further, the difference of the electrical resistivity of the bodies was small at high temperature.

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Three-dimensional photonic crystals with periodic variations of dielectric constant were fabricated by using a stereolithography of rapid prototyping methods. Millimeter-order epoxy lattices with diamond structure were designed to reflect electromagnetic waves by forming the photonic bandgap in GHz range. Titanium-dioxide-based ceramic particles were dispersed into the epoxy lattice to control the dielectric constant. The inverse form crystals, which have a network of air holes with diamond structure in a dielectric matrix, were fabricated as well. Microwave attenuations through the normal and inverse crystals having various lattice constants were measured by using a microwave cavity and a network analyzer. These two types of the diamond structure formed a perfect bandgap which reflects electromagnetic waves along any direction. The location of the bandgap agreed with band calculations using the plane wave propagation method.

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Hollow cylinders of functionally graded materials (FGMs) composed of low-density alumina and high-density tungsten powders with two kinds of particle size were fabricated using a centrifugal molding technique. Fine and coarse particle sizes of tungsten powders were used to make continuous and gradual variations of their composition. The alumina and tungsten powders were mixed with ethanol solvent, dispersant, and binder, and rotated at 3000 rpm in a steel mold of the centrifugal molding equipment. After casting and drying the slurry, the FGM cake was sintered in a reduced atmosphere of H₂/N₂ environment at 1600°C for 3 h. Continuously gradient constituents across the thickness of the hollow cylinder were obtained with the range of the slurry viscosity from 100 mPa·s to 300 mPa·s by adjusting the mixture ratio of the two particle sizes of tungsten powders. Residual thermal stresses generated during the cooling process were also analyzed numerically for each fabricated FGM cylinder with different variation of microstructure using a multi-layered technique. The analytical results showed that tensile hoop stresses appeared on the inner surface of the hollow cylinder and compressive stresses on the outer surface, and these residual stresses were released by selecting appropriate gradients with good dispersion of particles.

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Erosion wear properties of pressureless sintered TiC/Al₂O₃ composites were measured by a collision test between Al₂O₃ or SiC particles accelerated in an air stream. TiC/Al₂O₃ composites with a different TiC fraction up to 30 mass%, which had nearly theoretical density, were used as the target materials. In the case of collision by Al₂O₃ particles, the composites including 20-30 mass% TiC had an excellent wear resistance, which wear rate was 1/20 times that of Al₂O₃ monolithic ceramics. On the other hand, in the case of collision by SiC particles, the wear rate of each composite was almost the same as that of Al₂O₃ monolithic ceramic. In order to analyze the effect of the collision particles on wear rate of each composite target material, the relation between the median crack length and the Vickers indentation load was plotted in logarithmic coordinates for both TiC/Al₂O₃ composite and Al₂O₃ monolithic ceramics. The slope of TiC/Al₂O₃ composite was larger than 2/3, which was the theoretical value estimated by indentation fracture model. Since the mean fracture strength of the SiC particles determined by a diametral compression test under quasi-static loading was 2.3 times that of the Al₂O₃ particles, the mean impact force produced by the SiC particles was much larger than that of the Al₂O₃ particles. It seems that the resistance to crack propagation of TiC/Al₂O₃ composites was reduced by collision of SiC particles.

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A compaction process of tiles consisting of two layers of powders with a rubber punch was discussed. The densification behaviors during compaction and sintering were simulated by the viscoplastic finite element method. In this method, both rubber punch and powder during the compaction were modeled as rigid porous materials. Using the rubber punch, the density distribution in the compact became more uniform, and thus the occurrence of fracture during the sintering could be prevented. The compaction process with a rubber punch is applicable to practical operations because of its easy applicability.

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Glass-ceramic composites consisting of 10SrO·50ZnO·40P₂O₅ (SZP) glass and Al₂O₃ with various particle sizes and specific surface areas were fabricated for the barrier-rib of plasma display panel. The variations of density, microstructure, bending strength and thermal expansion coefficient with Al₂O₃ contents were studied for SZP/Al₂O₃ composites. The positively or negatively charged surface state of SZP and Al₂O₃ particles was estimated from the pH of the aqueous suspensions prepared using the mixture of SZP glass or Al₂O₃ particles with 10 vol% and distilled water with pH 7 without pH adjustment. The combination of SZP glass and Al₂O₃ raw materials with similar charged surface state provides a dense SZP/Al₂O₃ sintered composite with a relatively-high bending strength and with a homogeneous microstructure.

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Mesoporous silica fibers were prepared by varying primary variables of the synthesis conditions in the static two-phase acidic system such as the hexane/Si(OR)₄ and HCl/Si(OR)₄ ratios as well as the alkyl chain length of silicon alkoxide. The morphological and structural features of the mesoporous silica materials were strongly dependent upon the hydrolysis rate of silica source used. Namely, the high fraction of well-ordered mesoporous silica fibers was achieved by a delicate balance of the hydrolysis rate of silicon alkoxide and the condensation rate of silicate species. The obtained mesoporous silica fibers consisted of hexagonally organized channels running circularly around the fiber axis. The fibers prepared with Si(OC₄H₉)₄ showed the high thermal stability because of the lower content of structural defects within the framework.

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A new fabrication route based on a solution chemistry with metal alkoxide was developed for a compound semiconductor cadmium telluride (CdTe) film. CdTe-double-alkoxide solution was prepared by the reaction of cadmium acetate with Na-alkoxide in the presence of Te-alkoxide in ethanol. Considering the moisture sensitive properties of metal alkoxides, cadmium telluride films was produced by heat-treatment at 400°C in H₂ of hydrolysis product films of the corresponding metal alkoxides, which were formed by screen printing and spin coating. Although the good CdTe film couldnot be obtained by screen printing, spin coating has yielded a dense CdTe film. A surface of the spin coating film was leveling by mechanically polishing. The produced films were characterized by X-ray diffraction, atomic force microscopy, optical absorption, and optical irradiation current-voltage measurements. Optical absorption spectra were observed the characteristic absorption in about 830nm. The optical bandgap of the films was estimated from the optical absorption versus a photon energy plots, and obtained values were 1.43±0.01eV. The measured electrical conductivities of the films varied from 10^-8 to 10^-5 (Ω·cm)^-1 with optical intensity.

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A micro-macro method for simulating a sintering process of ceramic powder compacts based on the Monte Carlo and finite element methods is proposed. Macroscopic non-uniform shrinkage during the sintering is calculated by the viscoplastic finite element method. In the microscopic approach using the Monte Carlo method, powder particles and pores among the particles are divided into many cells, and the growth of grains in the particles and the disappearance of pores are simulated by means of the Potts model. The microscopic and macroscopic approaches are combined by exchanging microscopic and macroscopic information in each step. In the Monte Carlo method, the effect of macroscopic plastic deformation on the microstructural change is taken into consideration by including plastic strain-rate calculated by the finite element method in the disappearance frequency of pore cells. The shrinkage behavior in the sintering of circular two-layer compacts is simulated by the proposed micro-macro method.

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Interests in the use of conductive whiskers for development of large-area cold emitters require fabrication of well-organized aluminum-doped zinc oxide (Al:ZnO) whiskers with uniform length and growth axis aligned in the out-of-plane direction of the substrate. In this study, a chemical-vapor deposition apparatus with a scanning nozzle, operated under atmospheric pressure was employed to achieve homogeneous growth of aggregation of Al:ZnO whiskers. The 0.5×50 mm² slit-type nozzle was designed and scanned on single crystalline substrates of (100) silicon for 7.5 h. Homogeneous Al:ZnO whiskers were grown on the substrate with an area of 50×50 mm².

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Morphological change of a large pore was evaluated for the final stage of densification in alumina ceramics. Specimens prepared at various sintering temperatures were ground to a thickness of 150 μm. The internal structures of the sintered specimens were examined with an optical microscope in transmission mode to determine the location of large pores. Detailed structures of the large pores were evaluated by scanning electron microscopy after expostion on the surface by polishing. The large pores have a crack-like shape in the specimens sintered at 1350°C. Over sintered specimens contained large porosity area consisting of many small pores.

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During the heating of cordierite (Mg₂Al₄Si₅O₁₈) glass prepared by the solidification method, many cracks were induced in the α-cordierite bulk due to crystallization of α-cordierite crystal from the glass and thermal expansion excessive mismatch between α-cordierite crystal and α-cordierite crystal. In present study, cordierite/mullite (Al₆Si₂O₁₃) composite was successfully prepared without any cracks by generating fine mullite crystals at solidification process. Rods or platelet like primary mullite phase with less than 1 μm diameter were generated in cordierite composition glass during solidification and the excessive crystallization of cordierite could be restrained. Cordierite crystal grows on primary mullite crystal.

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