Direct oxidation behavior of MgO-C refractories has been investigated at 1000°C in air. The amount of graphite burnout during isothermal oxidation has automatically been recorded every 1min using a thermo gravimeter (TG). In this regard, the effect of Al and/or alumina addition as well as graphite fraction on the oxidation rate has been examined. An increase in alumina content or graphite fraction enhanced oxidation rate, while an increase in Al content retarded it. X-ray diffractometry and various porosity analyses were conducted on the samples before and after oxidation test to explain the oxidation results.

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Synthesis of the Ce_0.9Gd_0.1O_1.95(CGO) powder by polymeric precursor solution with mixing of nitrates, nitric acid and ethylene glycol was investigated with emphasis on the effect of polymerization of the precursor solution on the crystallization and morphology of the derived solid intermediate and the final oxide powder. It is first evidenced that the solid intermediate derived from the polymerized solution exists in the form of well-crystallized cerium-gadolinium formate solid solution, Ce_1-xGd_x(HCOO)₃, exhibiting the polycrystalline and anisotropic growth morphology. Moreover, the intensive polymerization of the precursor solution results in the direct formation of the loosely agglomerated nano-scaled CGO oxide powder at the temperature as low as 130°C. The effects of nitric acid and nitrates on the polymerization of the precursor solution are identified experimentally, based on which, a polymerization mechanism of the ethylene glycol process is proposed.

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The apatite-forming ability of zirconia gels with different structures was investigated in a simulated body fluid (SBF) with ion concentrations nearly equal to those of human blood plasma. Zirconia gels with amorphous, tetragonal, or monoclinic structure were prepared by a sol-gel process and subsequent heat treatment at various temperatures. Zirconia gel with an amorphous structure formed only a small amount of apatite on its surface, even after 14 d of immersion in SBF, whereas gels with tetragonal or monoclinic structures formed quite a large amount of apatite on their surfaces after 3 d of immersion, and their surfaces were fully covered with apatite within 14 d of immersion. This result indicates that specific arrangements of Zr-OH groups in tetragonal or monoclinic zirconia are effective in inducing apatite nucleation.

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β-tricalcium phosphate (β-TCP) is usually prepared by burning a mixture of dicalcium hydrogenphosphate anhydride (DCPA) and calcium carbonate (CaCO₃) above 1100°C. However, hydrothermal synthesis may be a more effective process for energy-saving. In addition, amorphous calcium phosphate (ACP) is very useful as a raw material for the morphological control of crystalline calcium phosphates. The present work investigated about the hydrothermal synthesis of β-TCP from ACP. ACP (Ca/P atomic ratio of 1.25-1.55) as starting material was obtained by a hydrolysis reaction of a calcium dihydrogenphosphate monohydrate (MCP) solution. Hydrothermal synthesis of β-TCP occurred under the following conditions: liquid/solid weight ratio, 30; carboxylic acid (formic acid, acetic acid, propionic acid, butyric acid and valeric acid) concentration, 0-1.5mol·dm^-3; temperature, 160-260°C; time, 0-72h. ACP crystallized into DCPA in hydrothermal conditions at 160°C, and was transformed into two phases, β-TCP and DCPA, above 200°C. Single-phase β-TCP formed at 220°C. Hydrothermal synthesis of β-TCP occurred under the following optimum conditions: formic acid solution, 1.0mol·dm^-3; temperature, 220°C; time, 3h. Ca/P atomic ratio of the hydrothermal synthesized β-TCP was 1.48±0.01 and the product was quantified as Ca_2.98(HPO₄)_0.04(PO₄)_1.96.

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The microstructure and chemical changes in the composite working electrode of electrochemical cells ((Composite working electrode)|Pt(Cathode)|YSZ|Pt(Anode)) for NO decomposition were observed and investigated. It was found that the NiO/YSZ interface is not stable at the electrochemical cell operating temperature of 600°C. Structure evolution was studied by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The formation of a small amount of Ni phase and of small size NiO grains with a size of about 10-100 nm in the NiO/YSZ interface region was observed and investigated. The reduction of NiO into Ni phase in the near surface region under the external voltage applied between the cathode and anode is proposed. The oxidation of small Ni grains into NiO grains as a result of NO and O₂ gas adsorption at the NiO/YSZ interface is discussed.

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The thermoelectric device of oxide p-n coupled element of NaCo_1.7Cu_0.3O₄ and Ba_0.2Sr_0.8PbO₃ has been fabricated using direct joining between p-type and n-type. Because of unwanted reaction between the two p- and n-type oxides, the diffusion barrier of Au foil was used and the device was stable and showed no appreciable contact resistance at the junction after the thermal cycle at 1000 K in air. The TE maximum power from the device was 12.5 mW when the temperatures of the hot and cold side of the device were 1045 K and 539 K, respectively. The device showed neither appreciable contact resistance at the junction nor changes in thermopower, after the high-temperature durability test in air.

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The high temperature Vickers microhardness of 12 mol% ceria-doped tetragonal zirconia polycrystals (12Ce-TZP) was measured in the temperature range of 25°C to 1000°C in a vacuum. The measurements were carried out in successive stages of heating and then cooling. The hardness of the 12Ce-TZP abruptly decreased from 8.2 GPa at 25°C to 4.5 GPa at 400°C, above which it began to gradually decrease, followed by saturation at 1000°C. Upon subsequent cooling from 1000°C to 25°C, the hardness began to increase back to the original hardness upon heating and it always surpassed the former. The increase in hardness upon cooling was found to be based on the reduction from Ce⁴⁺ to Ce³⁺ in 12Ce-TZP (CeO₂-ZrO₂) during the high temperature indentation measurements in a vacuum. Also, for the 12Ce-TZP (CeO_1.5-ZrO₂) sufficiently reduced by heat-treatment in hydrogen, the reduction-induced hardening did not occur because the Ce cation had been stabilized in a trivalent state during the measurements. Cracking occurred over the entire temperature range measured for the 12Ce-TZP (CeO_1.5-ZrO₂). On the contrary, the 12Ce-TZP (CeO₂-ZrO₂) showed pseudo-ductile→brittle transition characteristics; that is, indentation cracks were not observed at all up to 400°C, whereas they were remarkably recognized upon further increasing temperature.

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The refractive index distribution shape of SiO₂-TiO₂-BaO-K₂O systems r-GRIN lens can be controlled by the kind of solvent used for providing of concentration distribution process of barium. The expansion of the concentration difference of barium was also examined. The kind of solvent used in providing of concentration distribution process has a significant influence on the refractive index distribution shape in terms of Δn or N₂₀′. Solvents which enable to large Δn was aliphatic ether, having an ether bond as a functional group. In this case, the dielectric constant of these solvents was between 3 and 6. A mixture solvent of methanol and di-isopropyl ether was suitable as a solvent to expand the Δn of r-GRIN lens.

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Three types of structural ceramics, Al₂O₃/SiC, mullite/SiC and Si₃N₄/SiC having excellent crack-healing ability were sintered. A semi-elliptical surface crack of 75-110μm in surface length was made on each specimen with a Vickers indenter. The basic crack-healing behavior was studied systematically on Al₂O₃/SiC as a function of crack-healing temperature and time. Three point bending tests were carried out to investigate the strength of crack-healed samples. The specimens containing the semi-elliptical surface crack were healed under static or cyclic bending stress on mullite/SiC and Si₃N₄/SiC. It was shown that a crack could be healed completely either under a static or a cyclic stress. The competition between self crack-healing rate (S_CHR) and crack growth rate (C_GR=da/dt) determines the crack-healing behavior under stress: (i) In case of S_CHR>C_GR, a crack can be healed completely even under stress and recover of strength is complete. (ii) In case of S_CHR≅C_GR, a crack cannot be healed completely and recover of strength is insufficient. (iii) In case of S_CHR<C_GR, the specimen fails due to crack growth under stress.

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Zirconia balloons were synthesized from zirconium tert-n-butoxide in F/B/F (formamide/benzene/formamide) emulsion. Zirconium tert-n-butoxide in benzene ranging from 0.5 to 2.0mol·l^-1 was dispersed in formamide. The formed droplets of zirconium tent-n-butoxide in benzene could be solidified in formamide because solvent benzene was extracted by formamide; these solidified droplets were hydrolyzed with water in order to obtain zirconia precursor balloons. Zirconia precursor balloons were successfully obtained from a 1.2mol·l^-1 solution of zirconium tert-n-butoxide in benzene. Diameter of zirconia precursor balloons was 150 to 450μm. Zirconia precursor balloons could be heat-treated at 1300°C to form zirconia balloons without damage of the balloon structure. The diameter of zirconia balloons was in the range between 100 and 400μm. Weight loss and shrinkage observed during heat-treatment were 34.5mass% and 45vol%, respectively. Zirconia balloons consisted of grains 0.2μm in diameter. Pores 50nm in diameter existed on their surface and wall cross section.

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This paper reports about synthesis and fluorescence properties of Ce (III) and Tb (III) codoped vaterite phosphor emitting by black light irradiation. Ce³⁺ and Tb³⁺ codoped vaterite was synthesized by a liquid phase reaction by adding 0.1mol·dm^-3 (NH₄)₂CO₃ solution into 0.10mol·dm^-3 CaCl₂ solution including CeCl₃ and TbCl₃ at 35°C. The formation ratio of vaterite included Tb³⁺ increased by adding glutamine. The emission wavelengths of the vaterite phosphor excited with 275nm light were 490, 545 and 580nm. However, the emission intensity of 545nm by codoping Ce³⁺ and Tb³⁺ into vaterite host increased by 50 times. Emission of Ce³⁺ and Tb³⁺ codoped vaterite phosphor observed at about 545nm and the emitted color was green. The largest emission was observed in the vaterite phosphor prepared by synthetic conditions with a (Ce+Tb)/Ca atomic ratio 0.04 (Ce/Ca atomic ratio: 0.02, Tb/Ca atomic ratio 0.02).

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Nano-size γ-Al₂O₃ particles of four different sizes were synthesized by MOCVD (Metal Organic Chemical Vapor Deposition) method and then translucent nano-structured γ-Al₂O₃ ceramics are pelletized under a pressure of 2.5 GPa by a uniaxial compaction-method. Although these nano-structured γ-Al₂O₃ ceramics showed low density, they were fairly translucent. The relationship between transmittance and thickness of these specimens can be described by Lambert-Beer's law. The nano-structured γ-Al₂O₃ ceramics with different particle diameter and thickness have been prepared in order to clarify the dependence of particle size on the optical transmittance. The optical transmittance decreased with increasing initial particle diameter. In the case of 0.20mm thickness samples, the γ-Al₂O₃ with 5.6nm initial particle diameter showed an optical transmittance of about 60%. However, the optical transmittance decreases less than 5% when initial particle diameter is increased to 34.4nm. This phenomenon could be explained by Rayleigh scattering, which is the scattering due to the particle diameter being much smaller than the wavelength of light. In these visible regions (500-800nm), a scattering coefficient related with Rayleigh scattering was inversely related to the fourth power of the wavelength and directly proportional to the square of the grain size.

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A polycrystalline Pb((Zr, Ti)O₃/ (Pb, Sr) ((Zr, Ti)O₃ (PZT/PSZT) multilayer films have been synthesized on a titanium substrate by hydrothermal method in order to increase the density. This method consisted of two steps of hydrothermal reaction. The first step was the fabrication of a PSZT layer on the titanium substrate at 160°C for 12 h. The second step was the fabrication of PZT layer on the PSZT layer at 130°C for 4 h. The density, the breakdown electric field and young's modulus of the PZT/PSZT multilayer were 7.2g·cm^-3, 6.7 V·μm^-1 and 7.1×10¹⁰ N·m^-2, respectively. These values were larger than those of PZT/PZT multilayer.

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The fracture behavior of alumina and carbon fibers was investigated by using the loop test. The fracture surfaces of these fibers indicated a typical pattern containing a line shape, which appeared on the compression side of alumina fibers and on the tension side of carbon fibers. These fracture morphologies are interpreted as being locations of crack initiation (tension side in alumina and compression side in carbon), propagation following by bend-breaking. The loop test proved to be a useful and simple method to identify the fracture process.

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Fiber-reinforced ceramics were fabricated by using pehrydropolysilzane (PHS), polyborosilazane added PHS (PHS-B) or methylhydropolysilazane (MHS) as matrix precursors, and their mechanical properties were investigated with respect to the crystallinity of the matrix. By firing at 1523 K, MHS and PHS-B formed amorphous matrix and gave composites with the flexural strength of 820 and 920 MPa. PHS formed a crystalline matrix and gave a composite with a flexural strength of 450 MPa. The high strength composites may be brought by the lower elastic modulus of amorphous matrix as compared to the crystalline one. Because the low-elastic matrix decreases the stress concentration on fiber due to matrix-cracks. The heat resistance of the composite was tested upon heat exposure at 1523 K for 720 ks. The amorphous composite, fabricated by MHS at 1623 K, endured the heat exposure and retained 77% of its initial strength.

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Deposition of dense 8mol% Y₂O₃-stabilized ZrO₂ (YSZ) electrolyte thin-films with and without Ce_0.9Gd_0.1O_1.95 (CGO) interlayer by spin coating of polymeric precursor solutions on a porous La_0.6Sr_0.4Co_0.2Fe_0.8O₃ (LSCF) substrate and the electrical properties of the constructed thin-film cell were investigated. Anisotropic crystal growth in the YSZ thin films annealed at 1150°C was confirmed by XRD and SEM. The high-temperature chemical reaction between YSZ and LSCF was depressed by coating a CGO interlayer on the porous LSCF substrate before coating YSZ thin film. The impedance measurements of the electrochemical cell constructed by the LSCF electrode-supported YSZ thin-film electrolyte with CGO interlayer showed a lower electrode reaction resistance.

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α′-SiAlON containing Sr, having a large ionic radius, was obtained by hot-pressing. Sr was accommodated in α′-SiAlON in conjunction with Y. The effect of adding Sr to Y-α′-SiAlON on thermal conductivity and mechanical properties was studied. Thermal conductivity decreased from 11.9W/m·K to 6.2W/m·K with increasing addition of Sr, due to increasing of phonon scattering both in the lattice and at the grain boundary. Bending strength increased from 460MPa to 860MPa with increasing addition of Sr. The increase in bending strength can be associated with grain size refinement and fracture toughness. Fracture toughness also increased with increasing addition of Sr.

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