Piezoelectric crystals are used as actuator, sensors and transducers in a great number of devices. In specially, high temperature applications are very important to use for pressure, force, acceleration and vibration sensors. Many kind of piezoelectric crystals, such as Lithium Niobate, Lithium Tantalate, Quartz and so on, have been applied for high temperature devices. But the most fundamental limitations are phase transitions and twinning occurrence with elevated temperature. A₃BC₃D₂O₁₄-type crystals, unlike above crystals, did not undergo a phase transition up to the melting temperature. They do not appear a phase transition and twinning with increasing temperature up to melting point. Thus, it is expected that A₃BC₃D₂O₁₄ -type crystals will be proposed possible solution to solve a problems for high temperature applications. A₃BC₃D₂O₁₄ -type crystals were investigated and grown for high temperature piezoelectric properties.

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Gibbsite, as-received as a precursor from a surface coating process, was used in this study as starting powder to study its phase transformation to gamma alumina. The powder was first washed, dried, ground and then calcined in an electric furnace at a controlled heating rate, to the holding temperature, held at temperature for a fixed time and cooled at a predetermined rate to produce a high surface area of the powder for use as a catalyst support. The results of this study have shown that the heating rate of calcination has affected and can be used to control the BET surface area of the powder. A faster heating rate for the calcination treatment can promote a higher surface area and porosity of the powder. XRD patterns and TEM micrographs have been used to show the phase transformation from gibbsite to gamma alumina.

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NiAl₂O₄ spinel has a high electric conductivity and a good stability in high-temperature; hence it becomes a promising candidate as anode material in aluminum electrolysis. The self-propagating high-temperature synthesis technique was employed to produce NiAl₂O₄ spinel by using Al and NiO as reactants, the synthesized powders were studied by using SEM and XRD. The XRD results show that different products were obtained when molar ratio (R) of NiO/Al changed, while NiAl₂O₄ spinel could only be formed when the ratio was higher than 1.5. The amount of the NiAl₂O₄ spinel reaches maximum when R was 2. The XRD results also show that the lattice constant of the spinel synthesized by the SHS was slightly smaller than the published data, which means that a lot of defaults might exist in the crystalline lattice. The reaction chemistry and the reaction mechanism were also studied in the present work.

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Abstract: Ceramic Phase transformation in laser melting zone on composite bed of Zn-Al based Al2O3 ceramic is reported in this paper. A12O3(99%)layer was sprayed on the surface of parent material by plasma spraying equipment, and the sprayed layer was melten by transverse flowing CO2 laser . The microstructure, composition and distribution of the ceramic phase were studied Through these researches, we get three conclusions: 1. Two layers are formed on the basal body after sprayingα-A12O3 ceramic. The superficial layer is ceramic phase and the transition layer is binder layer of ceramic phase and basal body; 2.Superficial layer is formed mainly byα-A12O3 with littleγ-A12O3 after sprayingα-A12O3;3. Theα-A12O3 and γ-A12O3 ceramic phases in superficial layer transform intoδ-A12O3 ,which is body-centred tetragonal (bct). Ceramic-phase grains in molten pool are mainly distributed in superficial layer, and there are also some ceramic grains in subsurface and transition layer.

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Mesoporous crystalline titania with large surface area was obtained with polymer templating. The wet gels, prepared by hydrolysis of Ti-alkoxide in ethanol, were immersed in a solution of triblock-copolymer, poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) [Pluronic], dried under ambient atmosphere, and annealed at 500°C. After annealing, diffraction peaks of anatase were found. Pore size, pore volume and BET surface area of the annealed gels depended on the concentration of Pluronic. The micelle-like aggregates of Pluronic, which consisted of hydrophobic and hydrophilic blocks, were incorporated in the wet gel, and the shrinkage of gels during drying was restricted. Thus, the pore size and the surface area of annealed gels increased.

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Directionally solidified composites from eutectic melts were known as superior materials which keep high mechanical strength up to very high temperature just below melting points. In these composites, two phases are coexisted as a phase-separated glass or eutectic solid and both phases formed three dimensional network. Whereas they exhibits excellent properties, the process needs very high temperature and shape and composition of materials are strictly limited. In this study, we try to form composites with the same structure with eutectic solids but from usual ceramic processing methods. First fine alumina raw powder was calcined at moderately lower temperature to obtain highly porous materials. Then a nitrate solution with YAG composition was immersed into open pore of calcined specimens. After decomposition of nitrate salt, they were hot-pressed at higher temperature to obtain dense composites. Mechanical properties of obtained composites were evaluated and compared with the composites prepared from powder mixtures.

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Small whiskers of indium, In, were observed self-extruding from grain boundaries of the ternary carbide, Zr₂InC, after several weeks at room temperature. Using a heating stage in the scanning electron microscope, the In structures growth rate was accelerated for real time observation. At temperatures below the melting point of In (157 °C), whiskers form; as temperature is slowly increased to above 157°C, a transformation occurs from whiskers to spheres. Some whiskers transform directly into spheres; others shrink back into the Zr₂InC matrix. Once formed, the sphere population coarsens and is monitored in real time, with larger spheres growing at the expense of smaller ones. The whisker growth rates depend on temperature and are linear with time; the sphere growth rate is virtually instantaneous. Applications such as nanowires, quantum dots and interconnects in micro-devices may be possible if the location and rate of growth of the whiskers/spheres can be controlled.

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Perovskite-type divalent cations substituted rare-earth metal manganese oxides with a formula of Ln_1-xA_xMnO₃ have been extensively investigated during the past forty years, due to their particular electrical and magnetic properties. Followed by the discovery of giant magnetoresistance (GMR), preparations of this class of materials attracted more attentions. However, most of the preparations are concerned to high-temperature solid-state reactions and sol-gel processes. Herein, we report a mild chemical route to these materials. Giant magnetoresistance materials La_0.5A_0.5MnO₃ (A=Ba, Sr, Ca) and La_1-xBa_xMnO₃ (x≥0.5) were hydrothermally prepared and characterized by means of XRD, TG-DTA, SEM, ICP, and iodometry. The system alkalinity and initial molar ratio of Mn(VII)/Mn(II), associated with reaction temperature, were observed dominating the crystallization of the products. Hydrothermal route exhibited obvious advantages in terms of lower synthesis temperature, short reaction time, ready chemical operation for adjusting mixed valence, and high purity and crystallinity of products.

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Reproducible ceramic component manufacturing requires controlling ceramic materials and processing. Sintering is a key process in ceramic manufacturing, as it largely determines the microstructure and properties of a finished part. The master sintering curve (MSC) represents a science-based technology to predict and control densification during sintering. MSC theory has been validated on systems that densify by solid-state, liquid-phase, and viscous sintering. Additionally, MSCs have been determined for systems that undergo isotropic and anisotropic densification. The concept of the MSC is simple enough to be easily implemented on the manufacturing floor, yet it is firmly rooted in fundamental sintering science. MSC theory has been used to design time-temperature profiles to reliably achieve a given sintered density, and as a quality control tool to verify materials and processing reproducibility. The master curve concept also has been applied to the decomposition of organics, which provides the potential to optimize the entire firing process.

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Sintering of translucent polycrystalline alumina involves grain-boundary diffusion, and the retardation of grain growth has been ascribed to drags due to solute and/or spinel second phase particles. Magnesia solubility in alumina was proposed as grain-size dependent. We will report that the solid solubility of magnesia in alumina is indeed a function of grain size. During grain growth and sintering of magnesia-doped alumina, the enriched dopant level at grain boundaries and the equilibrium dopant content in the lattice undergo dynamic evolution. Recent advancements have converted alumina to sapphire through abnormal grain growth, in which magnesia-doped alumina is heat treated to first achieve a state of equiaxed grain structure followed with out-diffusion of the dopant so as to give a high rate of grain growth to result in sapphire. Nucleation can start from the interior of the wall, which is ascribed to a gradient in the magnesia level of the green body.

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We have proposed a ″holographic encoding technique by an interfered infrared femtosecond laser pulse″. In this technique, holographic gratings are encoded on the surface of various nonphotosensitive materials such as dopant-free silica glass and diamond as a consequence of the interference of two femtosecond pulses split from a single pulse. Varying the angle between the two crossed pulses changed the encoded periodic spacing. A minimum periodic spacing of ~ 430 nm was achieved for a laser wavelength of 800 nm. Furthermore, we have succeeded in encoding refractive index-modulated volume-type gratings deep inside pure silica glass and sapphire crystals if we use a single chirped (0.2 ∼5 ps duration) laser pulse. The present technique provides a fast method applicable for encoding volume-type gratings inside any nonphotosensitive transparent dielectric materials and for fabricating optical devices such as distributed-feed-back lasers and multilayered memories.

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Compacts of spherical alumina particles with and without c-axis orientation were prepared in high magnetic field and were employed to separate the shape and crystalline factors for the anisotropic sintering in alumina compacts. The compact of the spherical particles showed markedly anisotropic shrinkage in sintering when they are oriented. Isotropic shrinkage was noted when the particles were randomly oriented. Clearly, the crystalline factor plays an important role in the anisotropic shrinkage in sintering. The shape factor also plays a role in the anisotropic shrinkage in alumina compacts made of industrial grade powder.

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When a huge number of particles is in mutual contact at elevated temperatures, the evolutionary formation of grain boundary network and the morphological change of pore channels take place in the process of sintering. While the complicated morphological change of interfaces occurs microscopically, the sintering is macroscopicaly described as the densification, i.e., the increase of bulk density by the decrease of pore volume. In the macroscopic continuum theory of sintering the shrinkage rate of porous material is expressed as a response to the external stress and the driving force of sintering, i.e., sintering stress. Here we propose an exact method to determine the sintering stress tensor of porous materials from the interfacial energies of pores and grain boundaries. This method is applicable to calculate the sintering stress of materials with anisotropic complex microstructures in non-equilibrium state. The realistic simulation of sintering of particles in three dimensions will be demonstrated.

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Grain growth behaviors of Al₂O₃ grains, intragranular as well as intergranular ZrO₂ grains were systematically investigated for Al₂O₃/ZrO₂ composites with nano-sized ZrO₂ dispersions, in order to find favorable processing conditions for preparing nanocomposites in Al₂O₂/ZrO₂ system. The starting materials were ultra-fine α-Al₂O₃ powder (average particle size 140 nm) and classified fine ZrO₂(3Y) powder (average particle size 89 nm). The composites were prepared by centrifugal slip casting method, and sintered at 1400, 1550, 1650 and 1750 ^oC for 2, 12, 24 and 48 hours. Influences of sintering temperature and time, volume fraction of ZrO₂ dispersions in the composites, on the grain growth behaviors, size distributions and relative amount of intragranular and intergranular ZrO₂ grains were studied.

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Yttria-rare earth co-doped tetragonal zirconias were prepared by high temperature hydrolysis of at 200°C for 1 h. Different contents of Sm₂O₃, Gd₂O₃ and Nd₂O₃ were separately used as co-dopants. The obtained powders were tested for their stability as a function of heat treatment up to 1200°C. The powders were investigated by DTA, XRD, IR, BET surface area and TEM techniques. Amorphous-like zirconia powders having noticeably high BET surface areas, around 300 m²/gm, were obtained. IR investigations showed metastable tetragonal spectra for all the samples. Semi-rounded and rod-like nanosized particles were observed by TEM for most of the as-prepared powders. The calcined powders displayed patterns and spectra of the stabilized tetragonal phase. 100% stable tetragonal zirconias are obtained for Gd-Y and Nd-Y co-dopings, while about 98% of the tetragonal phase is obtained for the Sm-Y co-doping. The relationship between the conditions of preparation and the obtained results are briefly discussed.

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Pure zirconia powder of 0.2 micron was prepared as aqueous slip and compacted under high centrifugal force of about 10,000 g. The phase stabilizer of yttria was infiltrated in pre-sintered body as aqueous solution of yttrium nitrate. There was a difference in sintering performance with slip concentration. The compact with dilute slip (55 mass%) deformed and cracked during sintering, whereas that of thick slip (72 mass%) sintered without deformation. The yttria was successfully added by above mentioned technique which inhibited cracking during sintering. A compact of 99 % in relative density was obtained at 1623 K. The hardness and fracture toughness (IF method) increased with amount of yttria, and reached Hv 1270 and 9.1 MPa • m^1/2, respectively, with yttria addition of 2.7 mol%.

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Sintering enhanced by centrifugal force has been proposed. The application of centrifugal force during sintering enables to promote material transfer via plastic deformation, creep, and diffusion enhancement, resulting in higher density at lower temperature compared with conventional sintering. Further, this process is advantageous for diffusion bonding and thick film sintering, in which free of solid-contact contamination during the process is achieved. In terms of diffusion bonding, contact pressure more than several Mpa generated by the acceleration of 100 km/s² can be applied for the specimens with a thickness of a few mm, which leads high tensile strength being identical with that of diffusion bonding via hot pressing. Hence, production of miniaturized ceramics-metal parts can be available by this process. Several demonstrated results of centrifugal sintering will be presented.

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Microwave sintering is a sintering process in which objective materials absorb microwave and heat themselves from the inside. When microwave energy is effectively absorbed to the material, energy consumption for the sintering can be reduced. In this work, a domestic microwave oven was employed for sintering ceramics. However, it is difficult to absorb them effectively for the long wave. Then, the method of efficiently absorbing the microwave is needed. In general, dielectric loss of ceramics is low at room temperature, but it is high at high temperature. The material which dielectric loss is high at room temperature was used as a susceptor. we were investigated include optimization of heating system set up, determination of maximal densification level, influence of SiC susceptor on temperature distribution, comparison of microwave and conventionally sintered specimens regarding their density. They were examined by using the ZnO as a model material.

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In the last decade, the fast development of high power laser systems has stimulated a variety of industrial applications in which lasers act as well defined local energy sources. In this context, the Institute for Nonmetallic Materials of the Technical University Clausthal together with the Wacker Chemie GmbH, both in Germany, have developed techniques for the laser sintering of high purity SiO2 preforms under clean-room conditions: SiO2 preforms have been sintered with CO2 laser systems providing an output power of up to 12 kW (cw.). It could be shown that, regarding their efficiency, state of the art CO2 laser systems are an alternative to heat sources commonly used for sintering. Moreover, laser systems have the advantage that a contamination of the material to be sintered can virtually be excluded. With the laser as a local energy source large SiO2 preforms can be sintered to graded structures without changing their geometry.

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Compaction curves were studied by direct observation of internal structure of the compact made from spray-dried granules. Compaction curves have been widely believed to occur in three stages, compaction by granule rearrangement, compressive fracture of granules and compaction by primary particle rearrangement in each granule. However, the behavior was not observed directly. In this study, we tried to observe the internal structure of the compact for each stage. Some kinds of alumina granules were fabricated by spray drying with changing slurry conditions. The characteristics of granules were measured for relative density, shape, flowability, and compression strength. The green compacts were made from each granule with uni-axial pressing method. The compaction curves in uni-axial pressing were measured by compression testing machine from 0 to 100MPa. Observation result showed that granule rearrangement occurred in first stage. The granule fracture and rearrangement of primary particle in granule was started simultaneously in second stage.

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Hard metals are commonly produced following a powder metallurgy route, which involves powder production, mixing, granulation, pressing and sintering. Granulation is commonly done by spray-drying. A polymeric binder is added to the suspension prior to spray-drying to impart a sufficient strength to the granules. The amount of binder will largely affect granule properties such as granule strength, density, and friction behaviour and thus the pressing of the powder body. In this presentation, we will present results on direct measurements friction and adhesion of the granules using the atomic force microscope (AFM). Measurements can easily be performed between two single granules or a granule and a flat substrate. We will describe how the granule friction and adhesion varies with binder content, applied load and relative humidity. The results will be related to the binder distribution in the granules.

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Particle packing structure was evaluated using a polarized microscopy for tape cast alumina green body. Alumina particles of elongated shape were aligned with their long axis parallel to the tape casting direction. The overall particle packing structure was consistent with what was expected from the slurry flow under a blade. The sintering of the green body revealed a greater shrinkage in the thickness direction, which strongly related to the particle packing structure in the greeb body.

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The occurrence of cracks in a drying process of slip-cast hollow green bodies for large potteries was investigated. In the slip casting process, the flow of the poured slurry was observed, and a weld line was formed in the green body by contact between the side surfaces of slurry. In the drying process, the moisture content of the green body in the weld line was lower than that in the neighboring parts, and thus cracks occurred at the weld line. Vibration of the plaster mold during the slip casting was proposed to prevent the occurrence of cracks in the drying process. It was found that the vibration is effective in preventing the cracks.

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Excessive grinding forces generate defects on surfaces of a ground material. A new grinding system was proposed to minimize the excessive forces by maintaining the feeding force constant, instead of the feeding rate. This new system was evaluated in this study. Sintered Al₂O₃ was ground, and grinding-forces and table-feeding rate were measured for different feeding depths. The surface roughness and fracture strength of ground Al₂O₃ were measured to evaluate ground defects. Table-feeding rate decreased as the feeding depth increased on constant force feeding method. Specific grinding energy showed constant values for different feeding depths. Surface roughness showed no change with feeding depths from 1 to 50 μm. Fracture strength of specimens by a conventional constant feeding rate method decreased with feeding depths increased while that by the new proposed method showed no change for any feeding depths. It was found that the constant force feeding grinding system minimizes defects.

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A strong holding force of abrasive-grains in a grinding stone is of great importance to accomplish efficient ceramic-grinding. Laser dressing is a novel method that achieves the selective removal of a matrix material with a minimal damage on abrasive-grains by selecting a certain wavelength of laser. For a porous cast-iron matrix diamond grinding stone, laser irradiation can simultaneously enhance diamond-holding strength by the chemical reaction between diamond and cast-iron matrix. In this study, it has been confirmed that carbide, Fe₃C, forms after laser irradiation at the interface between cast-iron and diamond by Auger electron spectroscopy analysis. This carbide forms dimples on diamond surfaces and holds diamond grains with an anchor effect. As a consequence, through ceramic grinding, a laser dressed diamond grinding stone can retain higher number of diamonds with higher abrasive-grain protrusion heights due to an enhanced grain-holding strength than a grinding stone dressed by a conventional mechanical method.

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The b-sialon materials converted through the simultaneous carbothermal reduction and nitridation process varies with the characteristics of the starting materials of the local kaolin of Malaysia. The presence and amount of the b-sialon phase was observed to depend on the alumina/silica ratio, the content of kaolinite, particle size and the impurities that was present in the kaolin such as free silica and mica. The investigations of the phase development was carried out at temperatures from 1000oC to 1550oC at nitrogen flow rate of 10ml/cm3 and activated carbon of 10% in excess. The phase development was analysed using X-Ray Diffraction technique while its microstructure through Scanning Electron Microscope. Apart from b-sialon, other phases such as mullite, aluminium nitride, X-phase sialon and alumina was also observed during the phase development of the different kaolin.

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Colemanite, Datolite, and kurnakovite are some of important industrial borate minerals, which have chemical compositions as Ca₂B₆O₁₁•5H₂O, CaBSi₄(OH), and Mg₂B₆O₁₁•5H₂O. They are commonly used as the source of glass or glass fiber. However, they have a limitation because of cations in the composition. The colemanite ore has been processed to separate out boron component in the form of boric acid. The effect of process parameters, such as concentration of sulfuric acid, heating temperature, recrystallization and drying condition on the boric acid crystal phase, purity, and shape of particle was studied. Boron and calcium in colemanite have been dissolved in sulfuric acid solution and calcium has been separated out as a calcium sulfate solid, which has very small solubility in hot water, while boric acid has been fully dissolved. Finally the boric acid has been crystallized using solubility difference by lowering temperature.

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Porous carbon materials have been sealed perfectly with a molten silicate glass, where the wettability of the carbon to the molten glass was improved by infiltration and pyrolysis of perhydropolysilazane. The interfacial structure between the carbon and glass depended on the N₂ partial pressure during sealing. Cristobalite was produced at the interface under lower N₂ partial pressures. Transformation of cristobalite during cooling after sealing led to formation of many cracks at the interface. Therefore, the transformation is though to decrease adhesion of the glass layer to the carbon substrate. Coating of the glass at higher N₂ partial pressures did not followed by the cristobalite production. The structural changes occurring as a result of variation in N₂ partial pressures related to thermodynamic calculations. The coating remarkably improved the oxidation resistance of the carbon.

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Lithium titanate (Li₂TiO₃) pebbles are considered to be the candidate material of the tritium breeders for fusion reactor from viewpoints of good tritium recovery, chemical stability, etc. As a part of the fusion blanket development, an irradiation test of Li₂TiO₃ pebbles will be performed in the testing reactor. In the present study, the fabrication test of ⁶Li enriched Li₂TiO₃ pebbles was carried out for this irradiation test by the wet process. Using the results of fabrication test, various TiO₂ doped and undoped Li₂TiO₃ pebbles (1 mm diameter) were developed with nearly the same microstructure (density, grain size in the region of 5μm, porosity). Sphericity of the Li₂TiO₃ pebbles, which is the ratio of the longest diameter to the shortest diameter, was less than 1.1. Chemical and mechanical properties such as hydrogen reduction rate and collapse strength were evaluated.

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Ceramic evaporator of concentrated sulphuric acid of over 90% for thermo chemical Iodine-Sulphuric(IS) hydrogen and oxygen production plant coupled with 200MWt High Temperature Gas cooled reactor was designed. This IS plant of hydrogen was designed to product 25000 Nm3/h hydrogen ant 63MW heat energy is to be loaded to evaporator to produce 1950 kmol/h sulphuric vapor at 759K under 2MPa. However, this evaporator is exposed to sulphuric acid at high temperature and pressure and material choice for this design is very limited. From the erosion test result of refractory metals and ceramics under high temperature and pressure in concentrated sulphuric acid, SiC and Si3N4 exhibit good acid proof behavior. Therefore these ceramics was selected for he evaporator and R&D including large scale ceramic tube fabrication test and ceramic/ceramic bonding test has been carried out. This paper present recent R&D results of the ceramic evaporator.

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The traditional methods to fabricate Al₂O₃ catalyst supports are direct sintering of the transitional Al₂O₃ phases (γ-, δ- and θ- Al₂O₃) with addition of some inhibiting agents and sol-gel processing, etc. In this work, an Al/Al(OH)₃ powder mixture was used to fabricate Al₂O₃ support at a temperature of 600°C in vacuum by pressureless sintering. A high surface area was retained due to the transitional Al₂O₃ phases produced by the decomposition of Al(OH)₃, which have grain sizes less than 10 nm. At the same time, the Al₂O₃ support has superior mechanical properties, because a metal Al network was formed after sintering. Moreover, a definite conductivity was kept for the Al₂O₃ support, which is of significance for electro-catalyses. The present approach provides a new way of fabricating porous Al₂O₃ supports in industrial applications.

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Nuclear magnetic resonance (NMR) is powerful tool for characterizing porosity and its evolution during consolidation and sintering.The open porosity is filled with NMR sensitive liquids or gases and signal intensity and relaxation times are used as probes of the porosity. Gas phase imaging allows non-destructive characterization of density, and spatially resolved measurements of pore size, surface area, and adsorption isotherms. Images obtained as a function of pressure provide a map of adsorption isotherms that compare well to results obtained using conventional N2 BET adsorption. Measurements on samples with a range of densities and on samples fabricated with deliberate density gradients demonstrate a variety of pore characterization measurements and the utility of the NMR technique for assessing microstructural homogeneity and for following changes as sintering occurs. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under Contract DE-ACO4-94AL85000.

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Floc-casting method was investigated for fabricating green body free from large pores. Floc-casting method is a consolidation-forming method based on a flocculation phenomenon in concentrated slurry induced by temperature change. A merit of this method is ease to make homogeneous structure. However, the bubble in the slurry remained as large pores in the green body even with de-airing in vacuum. The large pores was quantitatively investigated in green body with optical and confocal laser fluorescent microscope. The green body was made from slurries with various powder contents. The porosity of slurry was measured from weight and volume of slurry before and after de-airing. The porosity of slurry was about 0.5-1.5vol% and increased with increasing powder content. In consolidated body, the pore size in the body increased with increasing powder content in the slurry. The shape of pore was spherical and its size was several hundreds micrometer in diameter.

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Structure of alumina green body was examined by a novel optical method to discuss the deformation mechanism during sintering for alumina compacts prepared by slip casting method. The novel method applied in this study is based on polarized light microscopy, with which even the minor particle orientation can be detected easily in the green body made by slip casting. The alumina compact was fabricated by slip casting in gypsum molds. Alumina powder particles have two forms, i.e., elongated and spherical shapes. Degree of particle orientation was evaluated from the retardation in green body relation to that of single crystal. The green body was sintered at 1673 to 1873K, and the deformation in sintering was discussed in terms of the density and degree of particle orientation.

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The purpose of this study is to elucidate the relation between alumina particle shapes and the firing deformation of the large body formed by slip casting. Two different shapes of alumina powders with the same particle size were used to cast the large green bodies with the size of 200×200×30mm. The slurries were filled into the mold set vertically. The body was taken out from the mold and stored for a week in the dry room at 35°C. The bodies were fired at 1600°C by electric furnace. Consequently, the large firing deformations were observed on the sintered bodies with the tabular alumina, but not on the bodies with the globular one.

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Machining damage was examined using industrial alumina ceramics with several grain sizes. Alumina ceramics were formed by dry-pressing method with spray-dried granules, and sintered at 1570 degree C for 2-27 hours. Grain size of the sintered body was 3-9μm. Flexural specimens with 3×4×40mm were prepared by the cutting and grinding process. Grinding direction was perpendicular to longitudinal direction of the specimen. Specimens were impregnated in fluorescent dye, then, fracture strength was measured by 4-point bending test. The fracture surface was observed with a confocal scanning laser fluorescence microscope (CSLFM). Depth of machining damage and fracture origin were easily characterized by the fluorescent dye. The result showed that machining damages were spread deeply and widely in the specimen with small grain size. The fracture started from the region of the machining damage. The fracture strength depended remarkably on the depth of the machining damage.

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The field of catalytic process requires ceramics supports with rigorous properties and a wide variety of shapes, this implies the generation of new materials with well geometric specific shapes. Extruded monolithics ceramics are actually being used extensively in catalytic reactors. The present work describes the fabrication of monolithic ceramics with diferent geometric shapes by direct extrusion of ceramic pastes. In this way monolithics ceramics with triangular, hexagonal, honey-rod and tubular cross section have been produced. The shape of some of these monolithic let its pilling for bulding some big catalytic reactors. After extrusion and sintering all ceramics present good physical properties such as: textural, density and porosity as well as good mechanical properties such as: hardness. These suggest their use in different kind of catalytic applications. Aspects of the monolthic ceramic fabrication process will be here analyzed.

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Patterned ceramic structures composed of two different materials with a feature resolution in the micrometer range have been generated by microfluidic lithography. Micro-channels made of poly(dimethylsiloxane) were filled with well-dispersed slurry of high solid loading followed by solidifying suspension upon solvent evaporation. The cross-inserted comb-type ceramic structures with 50 μm and 100 μm width were fabricated in a relatively large area of 2×2 cm² for alumina dyed with red and blue colors. It was found that controls of suspension characteristics and its drying play an important role in determining of pattern quality. Micro-channel filling was significantly influenced by viscosity and surface tension of suspension and interfacial interaction of suspension with surfaces of the substrate and poly(dimethylsiloxane). Once filled, a proper drying condition must be met. Otherwise, the micro-channels were disconnected due to capillary stress, resulting in a poor pattern generation.

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Floating-type reduction-nitridation of flake-like TiO₂ powder in N₂-NH₃ and N₂-NH₃-C₆H₁₄ was investigated at 800 to 1550 °C.Flake-like titanium nitride powder containing unreacted TiO₂ (rutile-type) and titanium oxynitride was synthesized at above 1200 °C. The color of resultant powders, which were nitrided in N₂-NH₃-C₆H₁₄ gas mixture at above 1300 °C, was brown. The specific surface areas and particle size distribution of resultant powders were almost same as the raw TiO₂ powder for all reaction temperature. Following floating-type reduction-nitridation of flake-like TiO₂ powder, packed-bed nitridation was carried out at 1000 to 1550 °C. The electrical resistivity of compacted resultant powder decreased with increasing reaction temperature, and had smallest value of 0.008Ω•cm by packed-bed nitrided at 1550 °C.

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The sinterability of lithium aluminum silicate (LAS) with silicon nitride added was investigated. The sinterability of LAS improved by the addition of silicon nitride. It is considered that the melting point of LAS was lowered by the addition of silicon nitride, and this liquid phase promoted the densification of LAS. The lattice constant of LAS with silicon nitride added was measured by XRD and it was found that the a-axis was longer and the c-axis was shorter than LAS with no additive. It is supposed that this phenomenon is due to the substitution of nitrogen for oxygen in LAS lattice, and the decreased melting point of LAS with silicon nitride added is also supposed to be influenced by this melting of nitrogen.

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Development of ceramic materials for high-voltage insulators tends to substitute the quartz portion with alumina in order to achieve greater product reliability. However, compositions with high alumina content require additional processing or increasing sintering temperature. This results in economic disadvantages for the alumina porcelain. The introduction of alumina-mullite porcelain is an alternative material to reduce structural stresses induced by quartz and, meanwhile, lessen the operating cost caused by alumina. The works will present the compositions and effect of changing the amount of feldspar, kaolin and ball clay on the fired strength, as well as, phase and microstructure evaluation. The results will give practical guidance for the manufacturers who would like to improve their products for high-voltage applications with a slight change in their sintering condition.

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Self-consistent isothermal barriers are introduced to sinter ceramics using 2.45GHz microwave as heat source. To design a high temperature industrial kiln using microwave, characteristics of heat generation by microwave is studied in fired products and lining materials. By selecting the lining materials which show equivalent or little high heat generation comparing with the products, and good insulation, the kiln structure was developed to utilize the microwaves to the full. The microwave kiln introducing self-consistent isothermal barriers shows less temperature gradient in a product than conventional electric kiln firing, because it can heat the products internally and externally. Accordingly, microwave can shorten the firing period especially in large-sized products without cracking. The fired products using microwave at 50oC lower than the conventional firing show the equivalent density and microstructure. Their texture becomes uniform and the strength is improved. Thus, the energy cost of microwave firing becomes one half of the conventional firing.

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Sintering of thick film and multi-stacked film have been possessed great interest to develop highly integrated functional devices. So far, an enhancement of sintering is mainly carried out by applying external pressure as seen in HP or HIP. However, those processes can not directly apply to the sintering of films from the industrial point of view. In this work, centrifugal sintering equipment was designed and produced. Furthermore, advantageous effects of centrifugal pressure on sintering were investigated by several examinations. We introduce new concept about centrifugal sintering method with high pressure and without pressure medium, and some experimental sintering data will be shown.

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Cerium compounds were prepared from aqueous solution of cerium nitrate by homogeneous precipitation methods. Urea and hexamethylenetetramine (HMT) were used as chemicals that produce NH₃ and consequently NH₄OH when heated to about 80^oC in aqueous solution. When urea was used, the precipitates with uniform in size, larger than 1 μm, were obtained. However, the products were not oxide. They were confirmed by x-ray diffraction to be cerium oxide carbonate hydrate. When HMT was used, the precipitates were very fine in size, less than 0.1 μm and they were cerium oxide. These products were compared with the precipitates which formed when NH₄OH was directly used. These products were also sintered to find the effect of preparation method on the density of bulk sample. CeO₂ prepared by HMT exhibited the highest sintered density.

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A thermoelectric element is produced by the joining of p- and n-type semiconducting materials. Both types of Si_0.8Ge_0.2 powders were prepared with boron or phosphorous added as a dopant into a mixture of Si and Ge by a gas-atomizing method, and then, the dense bodies were formed from these two types of Si-Ge powders by pulse-current sintering separately. The thermoelectric properties; i.e. thermal conductivity, resistivity and Seebeck coefficient of the dense bodies were determined at a temperature from room temperature to 1073 K, followed by the evaluation of the power factor and figure of merit. The effect of ball-milling on sinterability and thermoelectricity of these powders was further discussed

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The ultrasonic irradiation differs from traditional energy sources in duration, pressure, and energy per molecule, and it is a unique means on the interaction between energy and matter The ultrasonic irradiation differs from traditional energy sources in duration, pressure, and energy per molecule, and it is a unique means on the interaction between energy and matter. In this study, enigmatic docomposition behaviors of noble nano metal oxide were investigated for ultrasonic cavitation at room temperature. By choosing suitable conditions, it is reasonable to expect that these simple sonochemical processes can be extended to obtain nano-sized metal particles. Thus applications by using these reactions were investigated to prepare the nano-sized metal particles on various materials at ecology, and mechanisms and applications were investigated.

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Sintering aids for porous alumina ceramics are usually organic materials, e.g., polyvinylalcohol (PVA) as a binder and acrylic resin spheres as fugitive material. The organic sintering aids are thermally decomposed during its firing and sintering processes. The pyrolysis behavior is important for better conditioning of the process and better property of the final product. The analysis of the pyrolysis behavior usually requests Evolved Gas Analysis-Mass Spectrometry (EGA-MS), well-known as TG-MS. In this study, Ion Attachment Mass Spectrometry (IAMS) has been applied for EGA-MS to obtain spectra with no cracking by the ionization. Peaks of characteristic fragments with higher mass have been observed in IAMS spectra during the pyrolysis, since the IAMS presents soft ionization. The comparison with Electron Impact (EI-MS) spectra which allows fragment ions with smaller mass due to the ionization is also presented.

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Fine silicon nitride powder was prepared by mechanical grinding. Commercial submicrometer powder with sintering additives was ground with aluminium metal. Peaks of silicon nitride broadened after grinding in XRD analysis. This suggested that particle size of silicon nitride decreased. The powder was hot-pressed in nitrogen at 30MPa for 5 minutes. Heating rate was about 300 K/min to prevent grain growth. Dense material was obtained by sintering at 1550 ^oC. Crystalline phases of the material were silicon nitride and sialon. Fractured surface was observed by SEM. Fine grains of 100-200 nm were observed.

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