Factors limiting the strain rate available to superplastic deformation in oxide ceramics are discussed from existing knowledge about high-temperature plastic deformation and cavitation mechanisms. Simultaneously controlling these factors is essential for attaining high-strain-rate superplasticity (HSRS). This is shown in monolithic tetragonal zirconia and composite materials consisting of zirconia, α-alumina and a spinel phase: at strain rates higher than 10^-2 s^-1, tensile ductility reached 300-600% in the monolithic material and 600-2500% in the composite materials. Post-deformation microstructure indicates that certain secondary phases should be effective in suppressing cavitation damage and thereby enhancing HSRS.

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Ceramic materials have been a promising candidate for structural materials under sever conditions. In 1994, the authors published a review paper on impact damage of ceramic materials. In/before that period, the main topics of published papers were on erosion behavior of ceramics impacted by small objects at relatively low velocities and on postmortem observation/measurements. In this decade, however, progressive improvements of in situ observation/measuring techniques provided many important and useful visible/numerical results concerning the impact on ceramics. Therefore, this paper summarizes achieved results that mainly appeared in the last decade, concerning following topics; Impact damage, fracture and/or strength of ceramics including glasses and graphites. This survey reveals that the trends on research topics seemed to change in this decade: Papers on low-velocity erosion decreased, those on high-velocity were published, and results based on scientifically quantitative analyses were presented. Most important thing is that a concept of “fracture wave” and the wave itself was found out. The mechanisms and the modeling, however, remain unclear because of insufficient number of precise measurements associated with their detailed observation of the related phenomena for ceramics. Precise and detailed observation on damage/fracture behavior, based on a time-place sequence of damage/crack initiation and propagation, is necessary in the whole specimen's response.

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The simple polymerization of methyltriethoxysilane (MTES) has been achieved by the co-hydrolysis with chemically modified tantalum or niobium alkoxides, at room temperature, within 0.5 h and under a slight catalyst. The addition of the transition metal alkoxides into MTES is found to accelerate the formation of siloxane bonds, which was confirmed by ²⁹Si- nuclear magnetic resonance measurement. The siloxane condensation degree of the obtained sol was found to be approximately 80%. The self-supported crack-free hybrid films could be obtained by using this solution. Crack-free ceramic films of 90 mm diameter and 0.2 mm thickness were also obtained by the pyrolysis of the above-described hybrid films. The solutions could also be used as coating precursors, allowing smooth and homogeneous coating films without cracks or pores to be obtained by the dip coating of sol to the various substrates. The adhesion between the coating films and substrates showed large values even for organic substrates, which was evaluated by a cross cut tape test. Scratch hardness was also high.

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A new tellurate, BaTiTe₃O₉, was found in the BaO-TiO₂-TeO₂ ternary system. Using conventional solid state reaction, the new single phase compound, BaTiTe₃O₉ phase was synthesized and sintered over the very low temperature range of only 625-700°C. In addition, different calcinations routes, including the effect of TiTe₃O₈ precursor in the phase formation, were examined. The dielectric properties of BaTiTe₃O₉ ceramics were determined in the microwave region as well as at low frequencies. The relative dielectric permittivity (ε_r) and the temperature coefficient of permittivity (TCε) of BaTiTe₃O₉ at 1 MHz were measured as 30 and 790 ppm/°C, respectively. The dielectric properties were maintained up to microwave region without degradation. The dielectric permittivity and Q×f product obtained were 29 and 1,700 GHz at 7.6 GHz, respectively. The temperature coefficient of resonance frequency (TCF) showed a large negative value of -372 ppm/°C.

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Zinc oxide thin films were fabricated via a sol-gel method using zinc acetate as a starting reagent. The precursors used were modified with ethanolamines and/or α-hydroxyketones, and their derivatives. Oriented films with the c-axis perpendicular to the substrate were obtained from the sols modified with monoethanolamine and co-modified with monoethanolamine and acetoin. The co-modified specimens exhibited higher degrees of orientation. The film from the sol modified with monoethanolamine crystallized at the low temperature of 400°C and had an unusual plicated structure. The co-modification with acetol and hydrazine was also applicable to the sol-gel zinc oxide film. The c-axis orientation and the plicated structure of the films from the sol modified with monoethanolamine were discussed on the basis of the thermal analysis.

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Polyhydroxoaluminum (PHA)-lactic acid (LA) composite gels were prepared from PHA-LA mixed solutions. Phase transition behavior of the composite gels under heat-treatment was studied. The gels transformed into transition aluminas and/or α-alumina, depending on the heat-treatment conditions. Composite gels containing 3-10 mass% LA were found to yield α-alumina when heat-treated at low temperatures of around 500°C. The low-temperature formation of α-alumina was promoted at low heating rates. The fraction of α-alumina formed in the heat-treated products increased with temperature, reaching 40 mass% at ~800°C. The low-temperature formation of α-alumina is induced by the transformation of a partially formed diaspore-like structure, which is enhanced with reducing heating rate. The formation of 6-coordinated Al from 4-coordinated Al via the intermediate 5-coordinated Al during heat-treatment seems to be key to the formation of the diaspore-like structure, leading to the low-temperature formation of α-alumina.

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The purpose of the present experiments is to consider the relations between colour-change and crystalline phases of hard oxidizing fire iron red glaze by quenching temperature during firing. The colour of fired samples was analyzed by UV-vis spectrometer and compared with the values of L^*a^*b^*. The result of the experiments showed that the values of L^*a^*b^* had changed remarkably at 1050-950°C, without any observed radical change. Changes in crystalline phases with quenching temperature, whitlockite-type crystals already appeared with firing at 1050°C. Magnesioferrite crystal that was related to the red colour appeared at 950°C upon cooling process and became more clear at 850°C. However, because fine red spots were observed on the surface of sample quenched at 1050°C, it could be considered that the main reaction influencing on coloration had occurred at 1050-950°C. Therefore it is desirable soaking or annealing at 1050-950°C to obtain a prompt crystallization.

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Oxide-ion conductivity of pyrochlore-type solid solution was measured for the compositions of (Yb_1-xNd_x)₂(Ce_1-0.88xZr_0.88x)₂O₇ (YbNd system), which had various average cation radius ratio, r(A³⁺)/r(B⁴⁺), but constant lattice parameters and oxygen content. The crystal structure of the YbNd system were assigned to rare-earth C-type (x=0), fluorite-type (0.2≦x≦0.8) and pyrochlore-type (x=1.0) phases, depending on the average cation radius ratio of r(Yb_1-xNd_x)/r(Ce_1-0.88xZr_0.88x). The oxide-ion conductivity of the YbNd system decreased with an increase in the ordering of oxygen vacancy. These results were supported by the results of Raman spectra of the YbNd system.

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Hydroxyapatite powders (HAp; Ca₁₀(PO₄)₆(OH)₂) hybridized with 0-5 mass% Al₂O₃ were prepared from calcium hydroxide and di-ammonium hydrogenphosphate by a wet chemical synthesis. Ethylacetoacetate Aluminum Diisopropoxide (Al(OC₃H₇)₂(C₆H₉O₃)) was used as a source for aluminum oxide. The obtained powders were characterized by X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) specific surface area measurement, and magic angle spinning-nuclear magnetic resonance spectroscopy (MAS-NMR). The X-ray diffraction patterns showed no Al₂O₃-peaks irrespective of Al₂O₃ content, suggesting that the Al₂O₃-hybridized HAp powders were single phase. The Al₂O₃-hybridized HAp powder had larger specific surface area. According to MAS-NMR analysis, it was considered that the aluminum element existed as aluminum oxide, it was not substituted for the Ca²⁺, PO₄ ^3-, or OH^- ions.

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Porous calcium-phosphate films were formed on alumina ceramics by a spray-pyrolysis technique, using two kinds of starting solutions having Ca/P ratios of 0.50 and 1.67. A β-tricalcium phosphate (β-TCP) phase was present in the resulting films with a thickness of about 50 μm. The films were porous and the median pore size was about 105 μm. After Scotch^® tape (#810) adhering to the films was removed from the substrates, the films were still present on the substrate. The biocompatibility of the alumina ceramics coated with β-TCP (simply referred to as coated specimen) was examined using MC3T3-E1 cells as an osteoblast model. The cells on the coated specimen well proliferated in a similar manner to those cultured polystyrene dish and on uncoated alumina ceramics. The alkaline phosphatase activity of the cells cultured on the coated specimen for 17 d was significantly higher than that of the uncoated alumina ceramics. The present porous β-TCP films have good cellular responses with respect to cell proliferation and differentiation.

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A novel CO₂ separation technique that employs the chemical reaction of lithium-containing oxides with CO₂ has been developed. Since this method is effective in the temperature range of 450°C to 700°C, it has the advantages of enabling CO₂ separation in power plants without lowering the temperature and of absorbing CO₂ from the steam-methane reforming process at the same time. Because the absorption is exothermic and the steam reforming is endothermic, the energy loss is expected to be significantly reduced by combining the reactions. Hydrogen yields are expected to be higher because the equilibrium may be shifted by the removal of the CO₂ by-product. We have therefore proposed a pre-combustion CO₂ capture system using lithium silicate and steam reforming. Bench-scale experiments were performed to measure the methane conversion and CO₂ removal efficiency in order to evaluate the feasibility of the pre-combustion CO₂ capture system. At temperatures of less than 650°C, the methane conversion in the case of mixture of catalyst and absorbent was higher than that in the case of catalyst alone. In addition, the CO₂ removal efficiency is almost 90%. These results appear to indicate that pre-combustion CO₂ capture combined with steam reforming is feasible.

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Zinc oxide (ZnO) and magnesia (MgO) powders were made by flame spray pyrolysis of zinc acetate and magnesium acetate, respectively, dissolved in methanol-water mixture. The product powders were characterized by nitrogen adsorption, infrared adsorption (IR), X-ray diffraction (XRD) and transmission electron microscopy. The effects of solvent on powder characteristics were examined by changing methanol content (X=1-0.4) in the solvent. Polyhedral aggregates of nanoparticles were formed from the precursor solution with X=1-0.6 for both ZnO and MgO syntheses, suggesting complete evaporation of the metal species and particle formation in the gas phase. Decrease of the methanol content to X=0.4 lowered the spray flame temperatures, suppressing complete evaporation, resulting in a mixture of nanoparticles and large (e.q.>100 nm) particles for both ZnO and MgO synthesis. On the other hand, the XRD and IR spectra indicated partial hydroxide formation for MgO synthesis, differed from ZnO synthesis. The reaction with water vapor in the combustion gas can be enhanced for MgO because of the larger Gibbs energy change for hydroxylation in MgO than in ZnO.

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Polycondensation reaction of 70PhSiO_3/2•30Ph₂SiO_2/2 (Ph=C₂H₅) polysiloxane has been almost completed by treating the corresponding gel with a diethyl ether-aqueous NaOH immiscible two phase liquids. The phenyl-modified siloxane gel is dissolved in diethyl ether phase which is immiscible with an NaOH aqueous solution. After stirring the immiscible solution vigorously, the glass-ether phase is extracted and then subjected to evaporation to leave glass precursor. The phenyl-modified siloxane glass is prepared by melting the precursor at 200°C over 1 h, in which the polycondensation reaction of siloxane network is almost completed. It is found that the obtained siloxane glass shows a softening temperature around 80°C and this value remains unchanged even after heat-treatment over 200 h at 200°C.

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