This paper describes the delayed fracture behavior under tensile loading at elevated temperatures of three engineering ceramics: silicon nitride, silicon carbide and alumina/silicon carbide nanocomposites. There are two regions in the delayed-fracture mechanism map of silicon nitride; slow crack growth and creep damage rupture. The creep lives, which are mostly governed by facet-sized cavity formation, reasonably follow the Monkman-Grant relation. Silicon carbide, which generally does not contain glassy phase at grain boundaries, shows excellent creep resistance even at very high temperatures. The creep lives are well described by a diffusive crack growth model. Creep resistance of alumina/silicon carbide nanocomposite is markedly improved compared with that of alumina with an equivalent grain size, due to pinning effect of intergranular silicon carbide particles. The interface between the intergranular particles and the alumina matrix is much stronger than the alumina/alumina interface. This rigid bonding causes the inhibition of vacancy nucleation and annihilation at the interface, which results in threshold stress of creep.

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Ln₂Mn_xM_2-xO₇ (Ln=rare earth or Y, M=Mo, Ta, Nb or W) was synthesized under ordinary pressure and various atmospheres with the expectation of achieving various symmetries and properties. These compounds are analyzed as similar structures of rhombohedrally distorted pyrochlore structures by X-ray diffraction (XRD). However, transmission electron microscope (TEM) images reveal differences between structures: Ho₂Mn_2/3Nb_4/3O₇ and Er₂Mn_2/3Mo_4/3O₇ possessed a monoclinic structure, while Ho₂Mn_2/3Ta_4/3O₇ and Ho₂MnTaO₇ possessed a trigonal structure with an incommesurate nature. The differences in the structures were caused by the stacking sequence along the c-direction of a pair of A cation and B cation layers, where B cations formed a hexagonal tungsten bronze (HTB)-type layer that is a characteristic frame-layer in the pyrochlore-related structure. In the case of Er₂MnWO₇, however, different types of structures with a trigonal cell show that no pair of A-cation and B-cation layers existed along the c-direction in the crystal.

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The possibility of preferential recovery of lead from lead zirconate titanate (PZT) ceramics by wet ball milling with aqueous H₂SO₄ solution was investigated. The wet ball milling was performed using a pot mill apparatus in air for 0-96h at room temperature with the rotational speed fixed at 300rpm. Untreated PZT was dipped in aqueous H₂SO₄ solution for comparison with the wet-ball-milled specimen. The diffraction lines of the PZT crystallites disappeared completely from the XRD results, and only the diffraction lines of PbSO₄ were confirmed by the wet ball milling for more than 48h. For all the dipped specimens, the diffraction lines of PZT were identified even when the specimens were treated in 4.5mol/dm³ H₂SO₄ solution for 96h. According to ICP analysis of the dissolved components into the H₂SO₄ filtrate, the amounts of zirconium and titanium dissolved in the solution were found to increase with increasing treatment time, and the leaching behavior of both ions conformed closely to the collapsing behavior of the PZT crystal structure. As for lead ion in the solution, the dissolution amount was below 0.1% compared with the initial lead content in PZT ceramics under all the ball milling conditions. These results indicated that more than 99.9mass% of lead in PZT can be recovered as PbSO₄ by wet ball milling for more than 48h. The purity of the recovered PbSO₄ calculated from the ICP results was approximately 98mass%.

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The dispersibility of aqueous BaTiO₃ slurries with poly ammonium acrylate-based dispersant has been investigated. BaTiO₃ particles were well-dispersed in the high pH region and the adsorption behavior of dispersant strongly depended on the slurry pH. The dispersion of BaTiO₃ particles at various pH was also elucidated by characterizing the sedimentation density, viscosity of slurries, amount of adsorbed dispersant and tape-casted green sheets. The microstructures of green sheets fabricated using aqueous BaTiO₃ slurries were found to depend greatly upon the dispersion state of BaTiO₃ particles in the slurries.

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Optimum conditions for the synthesis of non-agglomerated barium strontium titanate (BST) nanoparticles were examined. The effects of salt concentration, operating temperature, and droplet/particle residence time in the hot zone as a function of carrier gas flow rate and heating zones on particle size, crystallinity, and chemical composition of BST nanoparticles were investigated. Highly crystalline, dense BST nanoparticles in a size range of 17-60nm with a narrow size distribution (σ_g=1.2) were prepared using a salt-assisted spray pyrolysis (SASP) method without the need for post-annealing or for controlling of initial excess of barium and strontium in the solution, relative to titanium. The particle size decreased with decreasing salt concentration, operating temperature and droplet/particle residence time in the hot zones. The chemical homogeneity of the resulting particles was analyzed using Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES). The chemical composition of the resulting powder completely reflected the initial solution composition. SASP can be used to produce highly crystalline (Ba_1-x, Sr_x)TiO₃ (x=0.5) nanoparticles in sizes as small as 30nm in a single step.

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The machinability and contact damage of Al₂O₃/BN nanocomposites fabricated through the chemical method were investigated in the present work. The Al₂O₃/BN microcomposites indicated considerably low fracture strength by adding BN particles, although machinability was improved. However, the nanocomposites showed both high fracture strength and good machinability. Hertzian contact test were performed to evaluate the contact damage. From the result of SEM observation of the samples after this test, it was found that the damage of the monolithic Al₂O₃ and Al₂O₃/BN microcomposites have a classical Hertzian cone fracture and many large cracks, respectively, whereas the damage observed in the nanocomposites appeared to be quasi-plastic deformation.

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In order to solve environmental problems, such as the shortage of dump yards and the exhaust of toxic gases by incineration of the industrial solid wastes (ISW), the development of a new method to prepare porous adsorbents from ISW's was investigated. Sludge from gravel plants and sawdust from wood plants were used as ISW'. A mixture of the sludge, sawdust, and clay minerals added as caking additive was kneaded together with an appropriate amount of waster or activator aqueous solution. The kneaded mixture was molded in a cylindrical shape by extrusion, and then calcined for 1h under N₂ atmosphere. The prepared calcined bodies had a porous structure with pore sizes of micron order. It was found by the methylene blue adsorption measurement in aqueous media that relatively high adsorption capacity (ca. 70mg/g) was attained in case of the carbon-ceramics porous composite, which was calcined at 850°C with 14.5mequiv./g-sawdust of K₂CO₃ as activator and potter's clay as caking additive. These results indicate that porous ceramic materials dispersed with activated carbon can be prepared from ISW, and an appropriate amount of activator and caking additive with low cation exchangeable ability are effective to enhance the adsorbability for methylene blue.

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The crystal structure and the electrical properties for Al-doped ZnO films have been investigated with a parameter of a substrate's arrangement in the RF magnetron sputtering system. The samples faced to inside of the target area (0-40mm) shows lower conductivity in comparison with samples arranged at outside of the target area (50-70mm). The electrical properties of the ZnO films are strongly affected by the damage due to collision of sputtered particles and recoiled Ar ions. The experimental mobility of the samples arranged at outside the target area (50-70mm) shows good agreement with the value calculated by the Brooks and Dingle theory assuming that the carrier scattering is mainly originated from the ionized impurities scattering.

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Mo₅Si₃ particle reinforced silicon nitride and silicon oxynitride composites were fabricated by sintering green compacts of silicon nitride, added with the molybdenum powder or a precursor for molybdenum oxide powder, at 1850°C in nitrogen atmosphere. During the sintering process, molybdenum powders reacted with Si₃N₄ to form the Mo₅Si₃ particles at grain boundary junctions in Si₃N₄, and MoO₃ reacted with Si₃N₄ to generate Mo₅Si₃ particles and Si₂N₂O grains simultaneously. However, because a small amount of oxygen was included in the molybdenum powder, a little amount of Si₂N₂O grain generated in the Mo₅Si₃-Si₃N₄ composite. The Si₂N₂O grains were needlelike crystals in Mo₅Si₃-Si₃N₄ composite, but the shape changed into the tabular in the Mo₅Si₃-Si₂N₂O composite. The flexural strengths of Mo₅Si₃-Si₃N₄ and Mo₅Si₃-Si₂N₂O composites improved slightly by incorporating the Mo₅Si₃ particles, and were 946 and 712MPa, respectively. Because of pulling-out of elongated Si₂N₂O grains during fracture and the effect of fracture toughening by internal stresses due to the Mo₅Si₃ and matrix thermal expansion coefficient mismatch, the fracture toughness of Mo₅Si₃-Si₃N₄ composite was 6.9MPa·m^1/2, -6% higher than that of normal Si₃N₄. However, the fracture toughness of the Mo₅Si₃-Si₂N₂O composite was affected by the tabular crystal Si₂N₂O which has a low value of fracture toughness, and reached the same valu as Si₂N₂O.

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Fe₂O₃-added magnesia-spinel brick, in replacing magnesia-chrome brick, has been recently used as a basic refractory for the burning zone in cement rotary kiln. According to the system MgO-Fe₂O₃ phase diagram, the phase change and the separation with temperature fluctuation in the kiln may damage the microstructure of the magnesia-spinel brick, which leads to the quality deterioration. The MgO-rich region of this system has been investigated by using a high-temperature X-ray diffraction (XRD) apparatus in air. The change from MgOss to MgO accompanied by the exsolution of Fe³⁺ occurs possibly around 1010°C based on the phase diagram. However, MgOss was found to still exist at room temperature in this study. Also, it was proved that the formation temperature of the solid-solution including 5-20mass%Fe₂O₃ shifted to a higher temperature compared to the conventional result. The unknown edge of the boundary line between MgOss and MgOss+MgFe₂O₄ on the MgO-Fe₂O₃ composition line was estimated in the system MgO-FeO-Fe₂O₃ phase diagram by considering the oxygen partial pressure of the atmosphere as 0.1MPa. The lattice constant of MgOss was altered by the change of the electronic spin state of Fe³⁺ from low-spin state to high-spin state around 1100°C on a temperature-elevated process, together with the solution quantity of Fe³⁺ and heating temperature. Furthermore, the crystal strain of MgOss and MgFe₂O₄ increased remarkably upon this spin alternation. However, the reverse-change of the spin state could not be recognized on a cooling process, then MgOss was considered to be metastable due to this slow reverse-change. The existence of MgOss single phase in the system MgO-Fe₂O₃ became clear under expanded conditions, which certainly contributes to the realization of the long life time of magnesia-spinel bricks.

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Sodium ionic conductors such as NASICON (Na₃Zr₂Si₂PO₁₂) have been used as a solid electrolyte for electromotive force (EMF) CO₂ sensor. However, it has been difficult to obtain a sufficiently high quality for this type of sensor. In general, when the EMF CO₂ senser is left in an atmosphere having a high water concentration, such as a high-humidity atmosphere or condensation atmosphere, the EMF of the sensor greatly decreases. For the purpose of improving the humidity-resistance of the CO₂ sensor, Li₂TiSiO₅ is employed as a solid electrolyte. It is composed of the following electrochemical cell: CO₂-Air/Au-Li₂CO₃/Li₂TiSiO₅/Au/CO₂-Air. The electrochemical reaction is in good agreement with the Nernst equation, and reacted electron is calculated as 2.04. The sensor fabricated with Li₂TiSiO₅ shows good linearity when it is exposed to an atmosphere of 90% relative humidity at 60°C. However, the EMF of the sensor decreases slightly as compared to its initial value. In order to obtain a high humidity-resistance for the sensor, NiO-Li₂CO₃ is used as the sensing electrode. In this case, the reaction constant, 2.04, is preserved and the EMF of the sensor does not change after exposure to high humidity atmosphere. Au-NiO-Li₂CO₃/Li₂TiSiO₅/Au can be considered to serve as a high humidity-resisting system for solid electrolyte CO₂ sensors.

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Diesel engine, which is widely used as a power plant for trucks and buses, is most efficient internal combustion engine. However, it generates a large amount of particulate matter (PM) and NOx. Diesel particulate filter (DPF) system is expected to be an effective tool to reduce PM and NOx emissions, but it is far from practical use because of clogging and low heat-resistance. In this work, ZrO₂/SiC felt which supported perovskite oxide catalyst is employed as a filter material, and the performances of the new DPF system to reduce PM and NOx emissions were evaluated. As a result, La_0.9K_0.1CoO₃ supported by alkoxide method exhibited promising performance to reduce PM and NOx emissions, and Pt on the perovskite oxide enhanced the PM oxidation performance at about 500°C.

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The pyrolysis behavior of organic-inorganic hybrids with Si-O-Nb/Si-O-Ta oxygen bridged heterometallic bonds was investigated. The easy cleavage of Si-O-Nb bonds was confirmed by infrared (IR) spectra, and Si-O-Ta bonds were broken at higher temperatures, suggesting the difference in energy between Si-O and O-M (M=Nb and Ta). The decomposition from T unit to D and Q units was analyzed by ²⁹Si-nuclear magnetic resonance (NMR). The redistribution due to the exchange reactions between Si-O and Si-C bonds was confirmed, which was also supported by thermogravimetric analysis-mass spectroscopy (TG-MS) results. Disiloxane and silane from the hybrid with Si-O-Nb bonds were detected at lower temperatures than those from the hybrids with Si-O-Ta or without Si-O-Nb bonds. The evolution temperature of these gases was close to the cleavage temperature of Si-O-Nb/Si-O-Ta bonds, which indicates that the cleavage of Si-O-Nb/Si-O-Ta bonds affects the redistribution.

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Water vapor corrosion resistance of titanium aluminate (Al₂TiO₅) was examined at 1500°C in 30wt% H₂O flow. The weight loss rate of this substance was 8.6×10^-6g/cm²·h during a 100-h test. No phase change occurred during the corrosion test, but anisotropic corrosion behavior was observed. In the X-ray diffraction patterns of the sample surface following the corrosion test, the relative intensities of 230 and 420 peaks were drastically decreased compared with that of the sample prior to corrosion. Geometrical patterns as like to sand ripples or terraced fields were observed on the sample surface after testing corresponding to the anisotropic water vapor corrosion.

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Porous silicon oxycarbide (SiOC) ceramic with a porosity of 60% and a cell density greater than 10⁴cells/cm³ was fabricated from a mixture of a polysiloxane and a chemical blowing agent by simple compression molding and subsequent pyrolysis of the polysiloxane. Optimization of processing parameters and selection of appropriate chemical blowing agent for each system will provide a simple processing route for producing highly porous ceramics.

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