Structure ceramics with good mechanical properties, for example zirconia, are electrical insulators. We have succeeded to add electric conductive properties to zirconia ceramics. In this study, Bi₂O₃-CuO-V₂O₅ glass was used as a conductive phase and OY, 3Y, and 8Y zirconia as matrix ceramics. Sintered by PECS, we have investigated the electric conductive properties of zirconia ceramic obtained by nanoscale modification of its grain boundary. The TEM observation revealed that electric conductive glass phase was formed in grain boundary and that nanoparticle precipitated within glass phase.

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In recent years, ceramic/metal nanocomposites such as alumina/nickel exhibited unique mechanical properties and peculiar magnetic functions. These materials are usually fabricated by hot-press method using chemically prepared nanocomposite powders. However, the mechanical machining is one of the difficulties to expand wide range of practical application because its expense is generally very high. Gelcasting is one of the novel methods for fabricating complex-shaped ceramic green bodies from high-solids-loaded suspensions. However, the mechanical properties of gelcasting products show relatively lower than that of general sintering processes. From these points of view, nanocomposite technique and gelcasting process can be the complementary methods.

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Al2O3/ Cu nanocomposites were sintered by PECS (Pulse Electric Current Sintering) method in a vacuum of 4.5 X 10-5 Torr. We measured mechanical properties of nanocomposites with changed sintering temperature. Relative densities of all samples sintered over 1250°C were larger than 98% of the theoretical density. The maximum values of fracture strength were improved from 807MPa to 901MPa due to annealing in 5 vol% Cu content specimens. But, the values of fracture toughness were decreased due to decrease of frontal process zone size in annealed specimen.

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Al2O3/ Ni nanocomposites were sintered by PECS (Pulse Electric Current Sintering) method in a vacuum of 4.5X10-5 Torr. We were carried out annealing 800°C, 1000°C, and 1200°C. Relative densities of all samples were larger than 95% of the theoretical density. The values of fracture strength were decreased with increase annealing temperature. However, the values of fracture toughness of annealed specimens at 800°C are higher than that of without annealing specimen.

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In order to synthesize AlN powder at lower temperature, Al raw powder was mixed with Li salt by planetary ball-mill in N2 atmosphere and heated at 500 - 800°C in N2 atmosphere. The Al powder adding 1.9 mol% LiOH H2O and milling for 1h was the best condition for AlN synthesis examined in this study. Single phase AlN powder was obtained at 580°C form this sample and this temperature was about 80°C lower than melting point of Al.

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Floating-type direct-nitridation of Al in N₂-NH₃ was investigated at 1350 to 1550°C. Following the floating-type direct-nitridation, the resultant powders containing unreacted Al were heated at 1200 °C and 1400 °C for 3600s in N₂ (call to combined nitridation) again. All of the powders containing unreacted Al, which were obtained by flowting-type direct-nitridation, changed to perfect conversion by the combined nitridation. Those AlN powder had good sinter ability, and high thermal conductive AlN ceramics of 200 W/mK could be obtained by sintering with aid of Y₂O₃.

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AlON ceramics were prepared by using the powder mixture of AlN and Al2O3 powder. AlON single phase was obtained in the range of 20 to 35mol% AlN at 1900°C. Translucent AlON ceramics were prepared by pressureless sintering and HIP sintering at 1850°C for 120 min under 180MPa.

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AlN fibers were prepared by Gas-Reduction-Nitridation Method which keeps the original morphology of the raw alumina fibers and has a single-step synthesis process utilizing NH3-C3H8 gas mixture. And its microstructure and particle size were evaluated by AFM and SEM. SEM analysis showed that the morphologies of nitrided fibers were the same as that of the alumina raw material and retained its smooth surface and regular shape, whereas it was confirmed that the particle size of nitrided fibers were about twice as big as that of the raw material by AFM observation.

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We investigated effect of MgO as the sintering additive on sintering behavior of AlN. Powder pellets of the AlN with the MgO, and AlN without additive were sintered at temperatures of 1600∼1750°C for 2 ∼ 4 h in N2 atmosphere. Shrinkage, weight loss, density and XRD measurements, and SEM observation were performed on the obtained samples. From the SEM observation, it was found that particle growth was hardly found in both the samples. By the XRD, grain-boundary phase of the AlN with MgO samples was MgAl2O4 with high melting point (≥2000°C). From the results, no effect of the MgO additive on the sintering behavior of the AlN seems to depend on physical state (liquid or solid) of the grain-boundary phase.

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An AlN ceramic was sintered with a dopant of Y2O3 under a reducing nitrogen atmosphere with carbon. The ceramic exhibited a high thermal conductivity, 272 W/mK. The value was equivalent to the experimental value of its single crystal (285 W/mK). The oxygen content of the sample was very low, 0.05 mass%. The microstructure was characterized by a high-resolution transmission electron microscope (HR-TEM).

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The tribological properties of hot-pressed the B₄C-metal boride ceramics were investigated by Block-on-Ring test method, compared with B₄C without additives and other ceramics. The wear rate and friction coefficient of the B₄C-TiB₂ ceramic were lower than that of Si₃N₄ ceramic. In addition, the friction coefficient of this composite was lower both than that of Si₃N₄.

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Carbon nitride thin film was prepared on Si (100) substrate by PECVD. Optical emission spectroscopy was used to survey the plasma composition during preparation. Structure and composition were investigated using AFM, XRD, XPS and Raman spectroscopy. Depositions of α- and β-C₃N₄ were confirmed by XRD. Raman spectra also support the existence of α- and β-C₃N₄.XPS analyses indicate the presence of sp² and sp³ C-N bonds in carbon nitride. It was demonstrated that HMTA could be used as a promising precursor for CVD to deposit carbon nitride.

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Floating-type reduction-nitridation of flake-like titanium oxide in N2-NH3 or N2-NH3-C6H14 was investigated at 800 to 1550°C. Flake-like titanium nitride powder was synthesized by 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. The electrical resistivity of compacted resultant powder decreased with increasing reaction temperature.

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Silicon carbide powders with Y2O3 and SiO2 additives were sintered by hot-pressing at 1950°C for 1h under a pressure of 40 MPa in 1.0MPa of Ar atmosphere. Bending strength, microstructure and oxygen content of sintered specimens were evaluated. Oxygen content was equivalent between inside and outside of the sintered body. Volatilization of SiO2 was strongly restricted by higher gas pressure, and the uniform distribution object of sintering additives was achieved.

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SiC ceramics sintered with B, C and metal borides/OH. Tanaka, N. Hirosaki and T. Nishimura (NIMS)/ SiC powders mixed with metal borides were sintered at 1800-2200°C. MoB, NbB2, TaB2, TiB2, VB2, WB and ZrB2 promoted densification of SiC powder. Adding a fairly large amount of borides, such as 2-6 vol% WB, 0.8-2.5 vol%B and 3 vol%C, enabled us to control grain growth and densify SiC powder at 2000°C. The sintered SiC materials with a large amount of metal borides, B and C had high fracture toughness.

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We have developed the silicon carbide fabricated using silicon infiltration. In this study, in order to develop the practical use, we are considered to form the green body that consists of charcoal. "Bincho-tan" charcoal that contained 35% of porosity was used for porous carbon and was reaction-sintered by silicon infiltration. The property of relative emissivity was evaluated.

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We newly developed the RS-SiC that had excellent strength property in comparison with present commercial RS-SiC. In this study, in order to develop the practical use, joining process for the high-strength RS-SiC was investigated. A porous carbon was inserted between the green bodies, and then it was reaction-sintered. The bending strength and the microstructure at the joined RS-SiC were evaluated.

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Nuclear heat IS process is consisted of HI and H2SO4 decomposition-recycling reactions and expected to be hydrogen mass production plant with couple of HTGR. Conceptual design study on ceramic evaporator of concentrated sulphuric acid for IS process has been carried out in Japan atomic research institute. The paper reports the results of erosion test of ceramics under high temperature sulphuric acid and conceptual design of full scale evaporator of suiphuric acid in nuclear heat IS plant.

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Thermal conductivity of BeO-doped SiC ceramic was measured at temperatures from 4 to 1000K. Low conductivity below 60 K is due to phonon scattering by grain-junction or presence of grain boundary, because the conductivity decreased according to klemens's T³ law.

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Thermal shock fracture test using an infrared radiation heating (IRH) technique was performed on porous silicon carbide ceramics, which have various porosities (40-80vol%) and pore sizes (5-30 micrometer), for the diesel particulate filter (DPF). The thermal shock strength, R1c, of these materials were estimated experimentally, which were termed experimental R1c was measured by the IRH technique. It was possible to quantitatively evaluate the relationship between thermal shock resistance and microstructure of porous ceramics using R1c. Thermal shock strength, R1c, was decreased with the increase in porosity and pore size, and it was strongly dependent on the pore size.

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SiC ceramics with resistivity of higher than 10¹⁰Ωm and large size(φ370mm) has been found. The resisitivity of hot pressed SiC with BN addition increased by annealing. We researched the influence of annealing temperature on microstructures and electric properties. This result indicated that annealing process affected the diffusion of boron and nitrogen in SiC matrix.

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Chemically vapor deposited (CVD) SiC was oxidized by electron cyclotron resonance (ECR) plasma in N₂-O₂ and Ar-0₂ atmospheres in the temperature range between 473 and 1073 K. The effects of temperature, oxygen partial pressure and crystal surface (i.e. Si face and C face) on the oxidation rates were investigated. The oxide thickness on the C face was larger than that on the Si face in both N₂-O₂ and Ar-0₂ atmospheres. The structure of oxide films was amorphous SiO₂. The oxide formation in Ar-O₂ atmosphere proceeded at lower oxygen partial pressures than that in N₂-O₂ atmosphere. The ECR plasma oxidation for CVD-SiC was significantly effective to produce oxide films at low temperatures.

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Strengthening of machineable glass-mica composites has been attempted by the reduction of the longitudinal size of mica grains and the dispersion strengthening of the glass phases. Grinding the starting material improves the strength from 147MPa to 186MPa by reducing the average length under 1.08μm. Precipitation of MgTi₂O₅ and the dispersion of YTZ particles raise the strength to 226MPa(TiO₂) and 241MPa(YTZ). Celsian-doped materials show almost full density and the refinement of mica grains to 0.9μm. This material have high elastic modulus and high strength of 204∼265MPa.

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Mica composition glass was added to magnesia and alumina powder mixture. And its sintering behaviors and mechanical properties were investigated. The reaction and densification of the glass added specimens were rapidly progressed at 1150-1200°C though those of the no added specimen occurred at much higher temperatures. Such sintering behaviors were caused by the liquid phase formed at 1000-1100°C. The obtained spinel/mica composites to which 40mass% glass was added could be drilled by super hard machining tool without fatal chippings. Mechanical strength of that was about 225MPa.

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Hollow alumina microspheres were successfully fabricated by a mechanofusion method. High fracture strength could be achieved with the hollow alumina microspheres, probably due to its mechanically uniform shell structure, in comparison with commercially available hollow ceramics microspheres, such as alumina bubble, fry ash and shirasu balloon. An aluminum-based composite with hollow alumina microspheres showed higher three-point vending strength than those prepared with other ceramic microspheres. Hollow alumina microspheres remained unfractured at the fracture surface of the composite, suggesting the propagation of fracture along with the interface between the aluminum and the hollow alumina microspheres.

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Two kinds of liquid-phase coating method, vacuum enhanced dip-coating and in-situ reaction deposition, was applied to coat LaPO4 on alumina fibers for improving the coating uniformity. Coating was characterized for thickness, microstructure and composition by SEM and XRD. The influence of the coating precursor concentration on coating uniformity and mechanical property of composites with the coated fibers by two coating methods was investigated and compared. The composites using the fiber coated by in-situ reaction deposition method showed better mechanical properties.

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The corrosion behavior of PAN-based carbon fiber and pitch-based carbon fiber by high temperature-high pressure various solutions has been studied at 400-800°C under 100 MPa for 24 h. Below 500°C carbon fibers exhibited good corrosion resistance in both acid and alkaline solutions, but above 700°C especially in alkaline solution, their weights drastically decreased. As the reaction temperature increased, the Raman peaks which represent sp3- or sp2- carbon network became sharp. We concluded that the corrosion started first from the external disordered part, and then the internal ordered part was corroded with the increase of the temperature.

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Fatigue properties of C/C composites under shear stress was investigated in air, water and vacuum pump oil. Crack propagation rates of C/C composites were increased in water and decreased in vacuum pump oil. Consequently one of the fatigue crack growth mechanism seems to be SCC (Stress Corrosion Cracking) by the water molecules in air.

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2-step reaction bonding method is effective way to fabricate fiber reinforced SiC composites because it doesn't need to make BN coating on reinforcing fiber. The influences of the fabricating conditions (concentration of solutions and layered pattern etc.) on the mechanical properties of SiC composites by 2-step reaction bonding method were investigated here. It turns out that the properties vary with combination of conditions.

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SiC long-fiber-reinforced SiC composites was made by using carbon-coated SiC fiber (Tyranno SA). The carbon coating was formed by a heat-treatment at 1700°C-1800°C under vacuum for 0.5h-2h. SiC/SiC composites were fabricated by hot-pressing at 1700°C under a pressure of 40MPa using Al2O3-Y2O3-CaO system as sintering additives. Effects of fiber coating on mechanical properties of obtained composites were evaluated.

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Si-based oxide coating on Hi-Nicalon Type S SiC fiber was fabricated by sol-gel method. Si(i-C3H9)4 was dissolved in 2-propanol to prepare the coating solution. SiC fiber was dipped in this coating solution. After dipping, the coated layer was hydrolyzed at room temperature in air and then heated up to 1400°C. The fiber was coated with oxide layer well by 2times dipping. The coating by 5times dipping was smoother than that by 2times dipping. The coating layer was amorphous phase measured by XRD. The relative tensile strength of coated fiber was almost same as that of uncoated fiber.

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SiC fiber reinforced SiC composite was fabricated by filament winding method and PIP method. α-Al₂O₃ powder, γ-Al₂O₃ powder and Aluminum triisopropoxide were coated on the surface of SiC fiber. The fiber was infiltrated in suspension composed with SiC powder and polycarbosilane/hexane solution, and wound as sheet shape. Green body was formed with these sheets. The green body was synthesized at 1473 K for 1.8 ks in Ar atmosphere. The composite showed typical non-brittle fracture manner and large work-of-fracture. The composite with coarser Al₂O₃ interface layer showed slightly higher bending strength and fracture toughness.

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Green sheets of the composites using Tyranno SA short fibers with Al₂O₃-Y₂O₃-CaO and ZrO₂-Y₂O₃-Al₂O₃ sintering additives were prepared by tape-casting, and then there were stacked and hot-pressed at 1650-1750°C. The short fibers were mostly aligned along sheet forming direction and long axis of bend bars, i. e., perpendicular to the hot-press direction. From SEM observation, the SiC matrix was found to have a relatively uniform microstructure composed of fine SiC grains with smaller size than 1 mm.The pullout of short fibers was observed in the case of the composites used ZrO₂-Y₂O₃-Al₂O₃ additives, however fracture behavior of the composites was catastrophic. Bending strength of the composites with Al₂O₃-Y₂O₃- CaO additives was higher than that of the composites with ZrO₂-Y₂O₃-Al₂O₃ additives.

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The densified SiC/SiC composites were fabricated by reaction bonding (RB) process. Two kinds of SiC fiber fabrics were used; (1) Hi-Nicalon, and (2) Hi-Nicalon type S. Both of SiC fiber fabrics were coated with pyrolitic C andβ-SiC by the chemical vapor deposition (CVD) treatment. The densities of the SiC/SiC composites attained relative densities of 90% or higher. The SEM microstructure observation showed that the CVD treatment used in this study prevented adhering the fibers to the matrix. This effect allows the pull-out phenomenon in the both specimens, and therefore the both specimens exhibited non-catastrophic failure behavior and have a high fracture energy. The bending strength of the specimen using Hi-Nicalon type S was higher than that using Hi-Nicalon. The reason is that the strength degradation of Hi-Nicalon type S is smaller than that of Hi-Nicalon.

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Highly thermal conductive Tyranno SA fiber reinforced 3D SiC/SiC composites were fabricated by Chemical vapor infiltration (CVI) and polymer impregnation and pyrolysis (PIP). The 3D textures (X:Y:Z= 1:1:0.09, 1:1:0.2, 1:1:0.45, 1:1:1.23) were directly woven from Tyranno SA fiber. Their Z-directional thermal diffusivity and conductivity show high values as expected. The effect of fiber configuration on the thermal diffusivity/conductivity was observed but became small at high temperature and obscure when the densities of composites were scattered.

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Mechanism of the electric charge emission from the single crystal of LiNbO₃ by changing the temperature was investigated. The emission rate was dependent of the pressure, the kinds of atmospheric gas and became maximum at the gas pressure of approximately 5Pa. The direction of current was dependent on the electric surface from which the electric charges are emitted. The integrated value of the dc current is proportional to the Boltzmann factor concerning to the first ionization energies for the atmospheric gases for stainless steel sample stage. The single crystal of LiNbO₃ and stainless steel sample stage is bonded then current was not detected.

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LaCrO₃ is a candidate material for interconnecter of Solid Oxide Fuel Cell (SOFC). Authors have already reported about effect of Ti substitution of Cr site of La CrO3 on sintering property. In this paper, We will show the effect of Ti substitution on the thermal and electrical property. LaCrO₃ has phase transition from orthombic to rombohedral at 550K. When amount of Ti substitution is increased, the phase transition temperature is decresed. Above 20% Ti substitution, phase transition is not observed. The Electric conductivity is reduced by Ti substitution. Hopping conduction mechanism of LaCrO₃ is influenced, because of activation energy of Arrhenius plot is changed according to Ti substitution.

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The gray oxide phase with the perovskite type structure of (Ba,Sr)(U,Pu,Zr,RE,Mo)O₃ has been observed in irradiated oxide nuclear fuels. The thermal and mechanical properties of the fuels will be affected by the precipitated oxide phase. In the present study, the physical properties of the perovskite type oxides have been examined and the relationships between the properties have been discussed.

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BaMO₃ (M:U, Zr, Ce) were prepared by solid state reaction of BaCO₃ and MO₂ (M:U, Zr, Ce) powders. The X-ray diffraction measurements showed that the samples were a perovskite structure, respectively. The samples for the measurements were prepared from the sintered body. The thermal properties of BaMO₃ (M:U, Zr,Ce) were evaluated from room temperature to 1400 K.

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The mechanical properties such as the Young's modulus and Vickers hardness of BaUO₃, BaZrO₃, Ba(U, Zr)O₃, BaCeO₃ have been measured and the relationships between the properties have been studied. The mechanical properties of BaZrO₃ and BaCeO₃ show typical characteristics of the perovskite type oxides, while those of BaUO₃ show glass-like characteristics.

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Polycrystalline Cd_3-xMn_xTe0₆(0.0≤x≤0.65) has been prepared by solid-state reaction process. A stoichiometric mixture powder of CdO, TeO₂ and MnO was ground thoroughly. This powder was calcined in air at 750°C for 9 h. A calcined powder was pressed into pellets and sintered at 1080°C for 2 h. From the results of powder X-ray diffraction, samples show a single phase within a range of x from 0.0 to 0.65. Avobe room temperature, dielectoric constant and dielectric loss increase rapidly with increasing temperature.

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Hole doping into Cd₃TeO₆ with a 1:1 ordered perovskite structure was carried out by alkali-metal substitution. The sign of the Seebeck coefficient in Cd_3-xA_xTeO₆ (A=Li⁺, Na⁺) was negative which show that major conduction carriers are electron, indicated that hole doping was not realized. Furthermore, the introduction of 3d orbital was carried out by Cu²⁺ substitution for Cd²⁺.The sign of the Seebeck coefficient in partially Cu²⁺-substituted Cd_3-xCu_xTeO₆ was negative which show that major conduction carriers are electron, while that in Cd_3-x-yCu_xA_yTeO₆ (A=Li⁺, Na⁺) was positive,indicated that major conduction carriers was changed from electron to hole by alkali-metal substitution.

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The monoclinic perovskite type oxide Cd3TeO6 is n-type semiconductor (P21/n), and electron-doped single crystal sample show high thermoelectric power. However, the seebeck coefficient of electron doped compound decreased with decreasing resistivity. We tried to synthesize solid solution crystal CaxCd3-x TeO6 in order to prevent decrease of seebeck coefficient. CaxCd3-xTeO6 single crystals ware prepared by heating mixture of CdO, CaO, and TeO2. The Lattice Parameter a, b increased and c decreased with increasing x. The electric resistivity and Seebeck coefficient of single crystals will be measured from 20K to 320K.

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T1 :The molecular dynamics (MD) calculation has been performed for BaUO₃ in the temperature range from 300 K to 2000 K to evaluate the physical properties viz., the lattice parameter, thermal expansion coefficient, compressibility, heat capacity, and thermal conductivity.

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SrTiO₃ based perovskite is prospective material as the thermoelectric material. However, the high thermal conductivity decreases the performance, figure of merit. In this study, the thermoelectric properties: the electrical conductivity, Seebeck coefficient, the thermal conductivity, of La-doped BaTiO₃ and (Ba, Sr)TiO₃ have been evaluated in the temperature range from room temperature to 1073 K.

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Gallium nitride (GaN) films were grown on zinc oxide (ZnO) single crystals with 0001 orientation using MBE method. The results of XRD and x-ray pole figure measurement indicate that the GaN films are grown epitaxially on the ZnO 0001 substrates. The optical properties of these films were investigated by photoluminescence spectra. In these films, strong band-edge emission in the UV region was observed, and the intensity of visible emission was very low.

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By the PLD method, thin films in which ZnO was made to add Mg, Al is fabricated and it were investigated at X-ray diffraction, PL measurement, etc. When substrate temperature was as low as 300°C, the formation of a super-lattice in which satellite peaks peculiar to super-lattice films are observed clearly, and have a steep interface was suggested. By the film of substrate temperature 600°C, the peak wavelength of PL waveform had shifted to the low wavelength side from the peak of non-doped ZnO thin film. This is considered that Al and Mg diffuse between layers in fabrication, and it is because non-doped layers were polluted with Al or Mg.

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The effects of film growth rate on the quality of the PLD grown ZnO films were investigated by varying the process parameters of a laser pulse repetition rate and geometry around substrate and target. The grown films were characterized by XRD, AFM, Hall, and PL in order to clarify the relationship between the process parameters, growth rate and quality of the grown films.

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ZnO thin films and those doped with Al were fabricated by MBE process. Zn and Al metals were evaporated by K-cells and oxygen radicals generated by an RF-plasma gun were irradiated during the film growth on sapphire substrates. The condition of radical oxygen spectrum was extremely important to obtain thin films with high quality. The carrier concentration increased, when the intensity of radical oxygen increased. However the mobility was independent of the intensity of radical oxygen. This result shows decreasing the oxygen vacancy in the cause of radical oxygen.

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An optical readable hydrogen sensor consisting of palladium / stearic acid (SA) thin films was prepared on a glass substrate. SA layer was deposited on glass substrate by vacuum evaporation. Pd was prepared on SA by R. F. magnetron sputtering technique. The sensor without SA showed the increase in optical transmittance after hydrogen exposure. In case of sensor with SA layer, the optical transmittance decreased when the sample was exposed to hydrogen.

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