Cerium oxide doped with 0∼90 mol% GdO_1.5 was prepared by co-precipitation method, which was found to be much better method than solid state reaction method. The formation of solid solution at CeO₂ doped with 10 mol% GdO_1.5 was recognized even without firing the precipitate. X-ray diffraction study (50 kV, 200 mA) of sample fired at 1300°C revealed that fluorite structure existed in samples with 0∼35 mol% GdO_1.5. At composition with higher concentration of GdO_1.5, superlattice peaks were identified. This indicated the existence of a fluorite phase with superlattice or the formation of rare earth C-type structure. Density of sample fired at 1450 °C was measured by densitometer. The results show that structure of sample is a cation interstitial model with 10mol% GdO_1.5 and a anion vacancy model with 30∼50mol% GdO_1.5.

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Phase relationship and lattice constants of Ce_1-xRe_xO_2-δ(Re=Gd, Sm, Y) at high temperatures under various gas atmospheres were analyzed by using high temperature X-ray diffraction. Even though CaF₂ type cubic structure was maintained under H₂/H₂O gas mixture at temperatures less than 1000 °C, lattice expansion was observed under reductive atmospheres at temperatures more than 700 °C. By using oxygen nonstoichiometry data measured by thermogravimetry, the relationship between δ and lattice constants was estimated. It was revealed that lattice constant increased with increase of δ, however there observed was difference of expansion behavior by doping element and its amount.

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Electrochemical design of metal distribution on the alkali borosilicate glass was carried out using an ion-conducting microelectrode. Fundamental electrochemical cell consist of an anode (Ag) I Ag-β”-Al₂O₃ I alkali borosilicate glass I cathode (Ag) system, where Ag-β”-Al₂O₃ microelectrode was used as a cationic source. Ag⁺ in the Ag-β”-Al₂O₃ was substituted for Na⁺ in the glass during the electrolysis. Scanning Ag-β”-Al₂O₃ microelectrode under applying an electric field caused the micropatterned Ag-distribution in the glass surface so that the contact radius between Ag-β”-Al₂O₃ and glass was extremely small (< 10 μm).

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Highly proton-conducting glass films were prepared by controlling the pore size of the silica film. The conductivity of films with pores perpendicular to the substrate surface was high, whereby the conductivity increased with increasing water content. The high conductivity was retained at relatively low humidity due to the restriction of water movement in the pores. These porous proton-conducting materials attract considerable interest for use in small fuel cell systems.

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Conduction and diffusion of proton in nanoporous silica glasses were studied from dielectric relaxation and Pulse Field Gradient (PFG) NMR spectra. The glasses with average pore size of 2.2 nm and <1nm were prepared by the sol-gel method using different materials. The glass having large pores exhibited a high proton conductivity and high diffusion coefficient. These results were discussed to relate with the confinement effect of proton by the pores.

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Proton-conductive composites which can be utilized at intermediate temperature were fabricated using layer-structured aluminum phosphate hydrate and silicophosphate gel. The electrical conductivity of the obtained composites increased with an increase in temperature and reached an maximum value at around 110°C followed by decrease probably due to loss water. It is likely that the samples tend to recover the water leading to increase in conductivity on cooling.

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a(6H)-powder was sintered by Al-B-C additives. The powder could be densified to full density at 1900oC. Grains in the sintered specimens grew to plate-shaped grains with crystal transformation of 6H to 4H. In order to clarify the role of additives in sintering, the new models and the theory for sintering and grain growth were proposed. The theory concluded that deceasing in grain boundary energy by the additives favored sintering and densification at high temperature.

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SiC powders have been sintered with additives such as B-C, Al₂O₃, Al₂O₃-Y₂O₃ and so on. SiC single crystal is grown by vapor and deposition of SiC at high temperature near 2500°C. The spark plasma system (SPS) is characterized by a electric source of pulsed direct current and has good effects for sintering and crystal growth. A dense compact was prepared without sintering additives by SPS. The enhancement of SiC crystal growth was observed when fine SiC powders were sintered.

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The high strength of oxide eutectic composites is not lost near 1500°C. The synthesis of a eutectic composite is carried out by unidirectional solidification. This solidification is inadequate to produce large and near-net-shaped materials. Eutectic powders of Al₂O₃-Y₃Al₅O₁₂(YAG), Al₂O₃-GdAlO₃ were prepared from the eutectic composite melted by arc discharge and high-frequency induction heating. The powder was classified into 3-44, 44-64 and 64-124μm, and consolidated by the spark plasma system (SPS).

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Effect of powder characteristics on densification and grain growth of silicon nitride sintered by pulse electric current sintering was studied. Alpha- and β-type sub-micrometer and β-type fine powder were heated at about 300 K/min and kept at a sintering temperature for 5 min. Dense ceramic was fabricated from α powder at 1650°C and from β fine powder at 1580°C. Density of ceramic from β sub-micrometer powder sintered at and over 1650°C was about 95 %.

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Alumina ceramics were densified by pulse electric current sintering (PECS) using γ-alumina powders prepared from polyhydroxoaluminum-polyvinylalcohol (PHA-PVA) composite gels at sintering dtemperatures of 1250∼1550°C. PECS conditions and optimizing of calcining temperature of PHA-PVA gels were investigated. The rapid sintering by PECS was advantageous to enhance densification in the sintering of γ-alumina powders prepared from PHA-PVA gels, resulting in specimens with a relative density of more than 99% for holding time of 3 min under uniaxial pressure of 30 MPa. The use of monophasic γ-alumina powders made the sintering temperature shift to lower temperatures. The bending strength of sintered compacts fired at 1350°C reached a value as high as about 800 MPa when the sample powders were calcined at 850∼950°C.

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Pulse Electric Current Sintering (PECS) technique allows the rapid heating and cooling, thus promoting the heat and mass transfer. For preparing Al₂O₃/Co nanocomposites, in which the secondary phase should be dispersed into matrix, we used the PECS technique. The amount of the Co was restrained for fabricating the intra-granular dispersed nanocomposites. Nanocomposites fabricated by PECS technique were measured mechanical properties, such as Vickers hardness, fracture strength, and fracture toughness, and observed microstructure using SEM and TEM. Finally, we evaluated the relationship between fracture toughness and frontal process zone (FPZ) size.

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Effect of adding Y₂O₃-CaO-AlB₂ for low temperature sintering of AlN ceramics was investigated using weight loss, XRD measurements and SEM observation. Samples of AlN with Y₂O₃-CaO-AlB₂ sintered at 1650∼1700°C for 4hours were almost densified. It was found that addition of AlB₂ to AlN-Y₂O₃-CaO is effective for sintering low temperature as addition of LaB₆.

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We investigated effects of sintering additives having the eutectic point composition (1760°C) in the phase diagram of the Y₂O₃-Al₂O₃ system on sintering process of AlN ceramics. Two kinds of the sintering additives were added to AlN powder. One of these additives was Y₂O₃:Al₂O₃=2:3 wt%, another was Y₂O₃:Al₂O₃=4:6 wt%. Samples of AlN with the additives were sintered at temperatures of 1600∼1750°C for 0.5∼5h in N₂ atmosphere. Shrinkage, weight loss, density and XRD measurements and SEM observation were performed on the sintered samples. From the shrinkage and density measurements, it was found that densification of the samples drastically developed at greater than the temperature of 1750°C. The densification depends upon the eutectic point temperature.

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Silicon carbide (SiC) ceramics were sintered by hot-pressing at 1850∼2050°C for 1h under a pressure of 40 MPa in Ar flow with the addition of total 11mass% mexed rare-earths oxides and SiO₂. Dispersion of strength of the sample was remarkable. SEM micrograghs revealed the difference in microstructure between inside and outside of sintered.

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SiC/SiC composites containing 30vol.% with non-coated Tyranno SA short fibers were fabricated by tape-casting and hot-pressing at 1750°C under a pressure of 40 MPa using an Al₂0₃-Y₂0₃-CaO system as sintering additives. Fibers were mostly aligned parallel to the sheet plane of green sheets. The composite fabricated by this process achieved nearly full density after hot-pressing at 1750°C. The SiC/SiC composites showed completely brittle fracture at room and high temperatures. The reason for the brittle fracture of the composites could be mainly explained by the degradation of fiber and strength of fiber/matrix interfacial bonding.

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Nanocomposite technique and gelcasting process can be the complementary methods to achieve complex shaped harden ceramic/metal nanocomposite. To fabricate complex-shaped alumina/nickel nanocomposite, the suspension parameters of water based aqueous monomer are optimized and related process conditions (drying, debinding, and reduction-sintering) are investigated in detail.

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MgSiN₂ powder compacts with 1, 4, and 9 mol% of Si₃N₄ addition (sintering aid; 1 mol% of ytterbium oxide (Yb₂O₃) were hot-pressed at a temperature between 1550°C and 1750°C for 90 min. The relative density of MgSiN₂ compact with 4 mol% of Si₃N₄ addition hot-pressed at 1600°C for 90 min showed a maximum (94.1%) among the investigated samples. The fracture toughness value of MgSiN₂ specimen with 9 mol% of Si₃N₄ addition hot-pressed at 1600°C for 90 min was as high as 6.6 MPa·m^1/2, whereas the thermal conductivity of the MgSiN₂ specimen with 9 mol% of Si₃N₄ addition increased to 34.1 W·m^-1·K^-1 with increasing hot-pressing temperature of to 1750°C.

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Polyorganoborosilazanes with the limited B/Si/C ratios and with or without Si-H bonds were molecular-designed and synthesized. By pyrolysis of these polymers in Ar atmosphere, amorphous borosilicon carbonitrides stable at 1880°C were prepared. The amorphous structure of borosilicon carbonitride was related to the polymer structure.

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Borosilicon carbonitrides were prepared by pylorysis of polyorganoborosilazanes synthesized by co-ammonolysis of various organochlorosilanes and borontrichloride. Amorphous borosilicon carbonitride stable at 1880°C was prepared by pyrolysis of SiMe₂Cl₂-based or SiHC₂H₅Cl₂-based polyorganoborosilazane. These prepared ceramics were not only thermally stable, but the oxidation resistance is also excellent at 1700°C in dry air and at 1500°C under reduced pressure.

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AIN powders coated with nano-sized BN precursor were prepared by a chemical route. The powders were reduced in H₂ and hot-pressed to fabricate AIN/BN nanocomposites. As expected from the rule of composites, Young’ s modulus decreased with increasing BN content, the strength of the nanocomposites was significantly improved, compared with the conventional AIN/BN composites. Furthermore, the nanocomposites exhibited the excellent machinability.

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Mo(Si, Al)₂ alloy has been reported it have an excellent mechanical and oxidation properties. Mo(Si, Al)₂ powder was fabricated by carbothermal reduction method. Silica was mixed with (NH₄)₆Mo₇O₂4 aqueous solution and dried in vacuum. The powder was mixed with Al₂O₃ and carbon and heated at 1500°C in Ar + H₂. X-ray powder diffraction analysis showed MoSi₂ and Al₂O₃. For lattice constants of synthesis powder, c-axis changed by addition of Al₂O₃, indicating the substitution of Si with Al in MoSi₂.

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Slip casting and pressureless sintering process of boron carbide is made practical to the range of 99.2% relative density. Microstructure and XRD analysis of the sintered body shows its sintering mechanism that boron rich boron carbide absorbs amorphous carbon, which is converted from mainly phenoric resin and functions also as abnormal grain growth inhibitor, to almost stoichiometric B12C3 and unabsorbed carbon remains at triple point of grains to be converted to graphite.

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Mica composition glass was added to magnesia, alumina and silica powder mixture. And its reaction and sintering behaviors were investigated and the properties of obtained cordierite/mica composites were evaluated. The reaction and densification of the glass added specimens were rapidly progressed at 1050-1100°C though those of the no added specimen occurred at much higher temperatures. Such promotions of the reaction and sintering were caused by the formation of liquid phase. The mica composition glass was melted at about 1050°C. The diffusion rate of the materials became much faster through the liquid above 1050°C. The obtained cordierite/mica composites to which 40mass% glass was added could be drilled by machining tool for concrete. However, large chippings were observed.

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Material with zero-thermal-expansion is required for development and improvement of high temperature devices, electronic package and so on. One possible method to obtain zero-thermal expansion material is co-sntering of material with positive thermal expansion and one with negative thermal expansion. We have clarified that co-sintering of ZrO₂ and ZrW₂O₈ is possible below 1200 °C. Also, we have succeeded in preparation of zero-thermal-expansion material by cofiring the mixture of ZrO₂ and ZrW₂O₈ with weight ratio of 2/1.

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Fabrication of strengthened aluminum titanate (AT) could be expected by alloying with mullite to achieve a small coefficient of thermal expansion (CTE) and a high strength, simultaneously. The strength and CTE of the sintered bodies were affected strongly by the property of slurry, mixing ratio of oxides and firing temperature. The body having the strength of 100MPa and CTE of 2.5×10^-6 was obtained under the prepared condition of 70wt% AT and firing temperature of 1550°C.

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Effect of A/B ratio and ionic size of A site ion of (K_xNa_1-x)_zNb_yTa_1-yO₃ on sinterability and electric properties was studied. When A site ions existed excessively, this compound was not sintered. On the other hand, excessive existence of B site ion resulted in by-product of K₄CuNb₈O₂₃ and it improved sinterability of (K_xNa_1-x)_zNb_yTa_1-yO₃ system. When Rb was substituted for K, the crystal structures were investigated with XRD and Raman spectrum analysis. In addition sintering behavior and electric properties of Rb substituted system were also investigated.

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KNbO₃ is one of the most promising lead-free piezoelectric material for substitution of PZT family. In this study, single-crystalline KNbO₃ thin films were gorwn on single-crystalline SrTiO₃(100) substrate by LPE method. The surface morphology depended on the film growth temperature. A lot of defects due to melt-substrate reaction were observed on the film surface in the case for the melt composition of K/Nb=52.5/47.5. In contrast, the film surface obtained at a lower growth temperature from the melt composition of K/Nb=65.0/35.0 was transparent and smooth in quality. Crystallographic relationship between single-crystalline KNbO₃ film and SrTiO₃ substrate was also investigated.

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Piezoelectric properties of KNbO₃ crystals with the single domain state were investigated. Prior to piezoelectric measurements, KNbO₃ crystals were cut, polished and sized into various shapes. However, it was confirmed that these mechanical processing induced the mechanical damage into the crystals. Thus, the optimum conditions for the mechanical processing of KNbO₃ crystals were investigated, and finally, the stressed surface layers of KNbO₃ crystals were successfully removed by the chemical etching processing. It was revealed that the remove of the stressed surface layers was very effective to achieve high mechanical quality factor (Q_m). After the treatment, KNbO₃ crystals were poled by the 2-step poling method. As a result, it was confirmed that the domain state was almost single-domain state. Using this poled KNbO₃ Single-domain crystals, the piezoelectric properties with k₃₂ modes were measured using a conventional resonance method. As a result, the [110]_c poled KNbO₃ crystals exhibited the electromechanical coupling factor (k₃₂) of almost 40 %, the piezoelectric onstant (d₃₂) of almost 18.5 pC/N, the dielectric constant (ε₃₃) of almost 48 and Q_m over 7,600. This result revealed that the KNbO₃ crystals were the piezoelectrics with the low dielectric and high electromechanical coupling properties, i.e., KNbO₃ crystal is one of the promising materials for sensor application.

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The piezoelectric properties and strain of the PbNi_1/3Nb_2/3O₃-PbTiO₃-PbZrO₃ ceramic was investigated. The piezoelectric constant of the ceramic with the composition of the morphotropic phase boundary derived from the strain was 1110 pm/V. The strain of the ceramics with the tetragonal phase was 0.15% in the applied voltage at 2 kV. These excellent piezoelectric properties of this system are due to the large dielectric permittivity and electromechanical coupling coefficient as a normal ferroelectrics.

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The combination of ultrafine seed particles and seeding layer on the substrate of the precursor of PbTiO₃ was applied to decrease the crystallization temperature of lead zirconate titanate (Pb(Zr_0.52Ti_0.48)O₃: PZT) thin film by chemical solution deposition(CSD). The starting solutions were Pb(CH₃COO)₂3H₂O, Ti(C₃H₇O)₄ and Zr(C₄H₉O)₄. Mixed solution with the composition of PbTiO₃ was partially hydrolyzed and stabilized by the coating of surfactant as seed particles with 10-30nm in diameter. The crystallization temperature of PZT thin film by the addition of the ultrafine seed particles and/or the seed layer on Pt surface decreased at 450°C. The combination of the addition of seed particles and seed layer to PZT solution enabled the good ferroelectrical property even at 475°C.

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PZT thick films with composition of Pb_1+α(Zr_0.5, Ti_0.5)O₃ were prepared by a spincoating method on ITO/Corning #1737 or Pt/Ti/SiO₂/Si substrate. The coating-drying-heating procedure was repeated. As a result, thick films of about 7μm were obtained by 5 depositions. Before measurement of piezoelectricity of the PZT films, they were polled at 10kV/mm. The piezoelectric properties of the films were measured by a micro laser interferometer and lock-in amplifier. The value of d33 coefficient of the film on ITO/#1737 substrate was 50-220pm/V.

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It is known that a multiplex reflection happens in the Ultrasonic transducer of conventional type. We tried to control this multiplex reflection by using the transducer with the ceramics backing structure. We could do the single pulse of waveform by using transducer that has this structure.

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The micro-actuator was fabricated using an aerosol deposition technique. The 2∼50-μm-thick lead zirconate titanate (PZT) films were directly deposited on stainless steel or Pt/Si substrates to fabricate the micro actuators. Performance of actuators was checked using Laser Doppler interferometer.

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A new piezoelectric transformer for AC-DC converter is presented. This piezoelectric transformer, with a multilayered construction in the thickness direction, operates contour-extensional vibration mode. Output impedance of the transformer is designed to be low in order to match load impedance, approximately several tens of ohm. We fabricated a transformer whose dimensions are 14mm long, 14mm wide and 5.8mm thick and examined it. It was found that the transformer exhibited a 0.4 voltage gain and 96.3% efficiency at 135kHz, when the temperature increase was 30°C. We applied the transformer to the fabrication of an AC-DC converter. The converter showed a good line and load regulation, and the highest efficiency of 90.2% was obtained.

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Skeleton matrix W-Co bonded diamond dicing blade was fabricated by using a doctor blade method and sintered by PECS (Pulsed Electric Current Sintering) method. Fabricated dicing blade shows 2 times higher cutting speed than commercial dicing blades on 3.2 N applied force cutting test with using Al₂O₃·TiC as a cutting material. Commercial dicing blade shows decrement of cutting speed, because of the decrement of the diamond grains and their protrusion height. Fabricated dicing blade surface was kept the diamond grains and their protrusion height even though after 750mm cutting.

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In order to lower synthesis temperature of AlN by direct nitridation method, Al powder was mixed with Li salt and heated at 500-1000°C in N₂ atmosphere. Mixing of Li salt was done by a mortar, and planetary ball-mill in N₂ atmosphere for 1h. For the Al powder added 1.9mol% LiOH·H₂O, the former and later samples ware nitrided at 630 and 580°C, respectively. These temperatures were lower than a melting point of Al.

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Hollow calcium carbonates were precipitated by bubbling carbon dioxide into aqueous solution of calcium chloride in the presence of ammonia. The precipitation was carried out by control of reaction condition such as temperature, pH and impurities. Transformation of vaterite into calcite plays an important role on the precipitation of hollow calcium carbonate. It is known that concentration of magnesium ion influenced the morphology and shape of calcium carbonate precipitate. In this study was discussed the relation between hollow calcium carbonate growth and concentration of magnesium ion.

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To analyze the action mechanism of microbial-derived surfactant for the preparation of highly dispersed ultra-fine barium titanate nano-particles by sol-gel method, the adsorption behavior on the surface of prepared particles and the surface interaction between particles were characterized by using FT-IR and colloidal probe AFM etc.

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In the present study the DRIFT spectra of seven commercial Si3N4 powders produced by three different processes and nitriding media were investigated. SiHx, NHx, and OH structures could be detected in the powders. The SiHx absorption band s show the presence of tetrahedral units with different atoms (O, N, Si, H) and groups (OH, NH, NH2) combinations, which bond to the same silicon atom. Clear differences in surface layer composition could be observed.

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We present a unique technique to observe directly the large scale heterogeneity in ceramic slurry. In this technique, the slurry was thinned down to about 100μm. Then, the internal structure in slurry was successfully visualized using an optical microscopy with a transmission mode. The structural changes in slurry with regard to time, temperature and shear flow have been also observed directly.

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Particle size distributions of silica slurry with high volume fraction were characterized by ultrasonic attenuation spectroscopy (UAS). When the volume fraction was smaller than 20vol%, the mean diameters evaluated with viscous loss and scattering loss in UAS was a good agreement with those evaluated by X-ray sedimentation method at about 3vol%. For slurry with more than 20vol%, the structrual loss was additionally applied to obtain good fitting curves.

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The viscosity of dense alumina suspension containing polymer dispersant and binder(PVA) was changed by the addition of plasticizer(PEG). In order to analyze the action mechanism of each additive in dense alumina suspension, surface interaction between alumina spherical particle and substrate in solution with different additive conditions of each polymer was directly measured by using colloid probe AFM. Based on the above results, the relationship between suspension viscosity and surface interaction was discussed.

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To analyze the action mechanism of polyethyleneimine, PEI in dense alumina/ethanol suspension, the macroscopic suspension viscosity with different structure of PEI was measured and compared with the surface intraction between alumina spherical particle and flat substrate in ethanol with different structure of PEI characterized by using colloid probe atomic force microscopy (AFM). With increasing molecular weight of PEI up to 70000, the suspension viscosity decreased and short-range repulsive force between solid surface increased.

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This paper discusses the adsorption mechanism of comb-type superplasticizer and dispersion mechanism of α-TCP (Tri-Calcium Phosphate). α-TCP are widely used as main component of bone cement. The fluidity of α-TCP suspension was improved by addition of comb-type superplasticizer. As a result, it seems to be possible to produce high-strength α-TCP by using comb-type superplasticizer.

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The interaction of the SiC powder - polyacrylic acid (PAA, dispersant) - Y³⁺ ions (sintering additive) system was investigated in the pH range from 2 to 6. The amount of Y³⁺ ions adsorbed on SiC particles increased with an increase of pH because of the electrostatic attraction between negatively charged SiC surface and Y³⁺ ions. On the other hand, the amount of PAA adsorbed on SiC particles decreased with increasing pH because of the electrostatic repulsion between negatively charged SiC surface and dissociated PAA. The addition of PAA to the SiC suspension with Y³⁺ ions increased the amount of Y³⁺ ions fixed to SiC particles through the strong interaction between Y³⁺ ions and PAA adsorbed on SiC particles. The addition of PAA to the SiC suspensions with Y³⁺ ions kept the SiC particles separate during the calcination.

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Ultrafine ceria particles of equivalent diameter of 18 nm, were dispersed at 10 vol% solid in aqueous solutions with amino acid (glycine, glutamic acid or lysine) of 0.5-5.0mass% against the mass of ceria at pH 2.0. The added amino acid was adsorbed on ceria particles to enhance the zeta potential of ceria to more positive values. The increased electrostatic repulsion with addition of amino acid prevented the sedimentation of the positively charged ceria particles.

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To analyze the effect of molecular structre of polymer dispersant on aggregation behavior in SiC dense suspension and green structure prepared by slip casting, some kinds of polymer dispersant, which have different hydrophilic to hydrophobic group ratio, were synthesized from stylene and maleic acid or acrylic acid monomer. The dense SiC suspension behavior was characterized and compared with green bodies structure prepared from suspension with different polymer dispersants.

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A new direct casting method of aqueous high solids loading alumina slurries stabilized by ammonium polyacrylate has been developed. The dissolving of yittria into the alumina slurries gradually increased the ionic strength of those slurries, and then, the slurries were coagulated. As a result, the homogeneous green compact was obtained. The relative density of the sintered compact was 99.4%T.D. and 500MPa of the bending strength was achieved in that compact (heating temperature: 1550°C).

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A direct casting method of aqueous acidic high solids loading alumina and zirconia slurries stabilized by zirconium acetate (Zr-Ac) has been reported. In this study, we investigated the effects of Zr-Ac and pH on the fluidities of alumina-zirconia slurries and we found the optimum conditions of the thickening for these slurries. Complex near-net shaped alumina-zirconia composites have been obtained by the urea-urease enzyme reaction.

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