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Infrared light microscopy with liquid immersion technique was applied to examine the internal structure of the granules and green compact of ZrO2 nano-powders, whose refractive index is 2.14. Internal structure could be observed clearly even for their high refractive index by this microscopy. Granule deformation is directly observed with this method for green compacts made at various pressures.

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Surface of commercial Silicon Nitride Powders will be disscuss.

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RBSN(Reaction Bonded Silicon Nitride) is manufactured by reaction sintering of silicon powder by nitrogen. This process is useful industrially for two reasons. At first, cheap silicon powder can be utilized to compare with expensive silicon nitride powder. And secondly, shrinkage by sintering is almost zero. RBSN is porous material, so silicon infiltration had been tried to make it dense like RBSC(Reaction Bonded Silicon Carbide). But this trial had not been successful because wettability between silicon nitride and silicon is not so good. In this study, we succeeded in manufacturing silicon infiltrated RBSN by improvement of raw material formula and infiltration process. And we also attained prevention of silicon burst in cooling process, which is a general problem when manufacturing various silicon infiltrated composites.

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The thermal conductivity of silicon nitride ceramics prepared with varying oxide sintering additive compositions was studies. The oxide sintering additives promote formation of liquid phase to enhance densification. After cooling down, liquid phase may be remains as a glassy or partially crystallized grain-boundary phase. The grain-boundary phase reduces thermal conductivity of Si₃N₄ ceramics due to lower thermal conductivity of oxides. An Y₂O₃-Al₂O₃ system is one of the most popular additives for densification of Si₃N₄ because low temperature for sintering and the resulted ceramics show excellent mechanical properties. But Al₂O₃ will promote to form SiAlON phase which has also low thermal conductivity. To improve the thermal conductivity of Si₃N₄ ceramics, eliminating of glassy phase by post-sintering heat treatment at difference nitrogen gas pressure at varying temperature was examined in this study. Y₂O₃- Al₂O₃, Y₂O₃-SiO₂, and Y₂O₃-MgO systems were used as additives for the sintering of silicon nitride ceramics. The SiO₂ and MgO have high vapor pressure which can be eliminated from the ceramics by the vaporization. Effects of heat treatment conditions on the microstructure, chemical composition, and thermal conductivity of silicon nitride ceramics were observed.

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b-SiAlON nano ceramics were fabricated by spark plasma sintering using the ultra fine powder synthesized through carbothermal reduction-nitrogen method, and its aqueous and gas corrosion resistance were evaluated. As a result of TEM observation,the devoloped b-SiAlON ceramics were composed of nano-sized grains and the glassy phase was hardly found at the grain boundary. It showed much higher aqueous corrosion resistance than commercialized Si3N4 ceramics. We also obtained valuable information of corrosion surface from SPM observation.Furthermore, the b-SiAlON nano ceramics possessed high corrosion resistance to air and air-SOXgas mixture at high temperature. It is considered excellent thermal and chemical durability of b-SiAlON but also very little glassy phase in their grain boundary.

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Usually, in the system of AlN with Y₂O₃ additive, first of all, yttrium aluminate is produced as a grain boundary phase. And, by further heat treatment in nitrogen-reducing atmosphere, it is found that yttrium aluminate at grain boundary is transformed into YN from the surface. As a result, fortunately, we found AlN containing YN as a grain boundary phase showed electrical conductivity. The purpose of this study is to fabricate electrically conductive AlN ceramics with high thermal conductivity, and to control the electrical conductivity by addition of a small amount of CeO₂, which is easily reduced compared with Y₂O₃.

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A micro-Raman spectroscopic investigation has been performed to observe structural disorder in each grain of aluminum nitride ceramics as semiconductor equipment parts. A selective thermal oxidation treatment normalizes a different rate of a corrosion reaction depending on a crystal face and improves consequently the corrosion resistance. With thermal oxidation treatment, line widths of Raman bands more increased in grains including mainly crystals with (100) preferred orientation than in those of (002), indicating that (100) faces oxidize preferentially rather than (002) faces. According to Raman shift from the oxidized sample, oxidation induces residual compressive stress for grains including a large number of (100) prefer-oriented crystals. On fluorination of the oxidized sample, an increase of line widths was not observed in both kinds of grains, suggesting that prior anisotropic thermal oxidation treatment of (100) faces, which is more sensitive to corrosion than (002) faces, inhibits the progress of a decay reaction.

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Boron-rich compounds consisting of B12 icosahedra are of potential interest for applications to their remarkable physical and chemical properties, which in many cases are of potential interest for applications to thermoelectric and photodetectors. However, there is very little information about the physicochemical and mechanical properties of aluminum magnesium higher borides. Crystals of AlMgB22 are obtained by adding relatively little amount of Mg metal. But, owing to the high vapour pressure of Mg at high temperature, optimum conditions for growing AlMgB22 crystals are not established. In this paper, we report the optimum experimental conditions for growing relatively large crystals of AlMgB22 from Mg compounds (MgO2, MgC2O4, Mg(OH)2, Mg(CH3COO)2, MgF2, MgI2 other) and crystalline boron powders as the starting materials using and Al self-flux under an argon atmosphere. The size, morphology crystallographic data of the crystals were determined. Oxidation resistance in air up to 1473K, Vickers microhardness and magnetic susceptibility measurements at low temperatures of AlMgB22 crystals were studied.

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To be high purity is often required for the oxide films deposited by the chemical vapor deposition technique due to effect of residual impurity on the morphology and crystalinity of the films. This study reveals that desorpted species from the oxide film sample measured using thermal desorption spectroscopy under high vacuum conditions. The molecules H₂,H₂O,N₂ and CO₂ were detected at high temperature.The relationship between residual species and microstructure in the film will be discussed.

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The amorphous alumna films deposited by the chemical-vapor depositionmethod were annealed at 600 ﾟC. After anneal treatment, microcracking was recognized on the surface of the films. The microcracking occurred at 300 ﾟC. In addition, desorption of water was observed at 300 ﾟC and higher. The microcraking occurs by the volume reduction of the film with desorption of water.

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The amorphous alumna films deposited by the chemical-vapor deposition method produces microcracking on the surface at 300 ﾟC. To avoid formation of microcracking, molecular design of starting materials was conducted. Optimum starting material avoids microcracking of the films during the annealing treatment. No desorption of water was observed on crack-free film.

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Electron beam-physical vapor deposition (EB-PVD) is a widely used technique for depositing thermal barrier coatings (TBCs) on metal substrates for high temperature applications, such as gas turbines, in order to improve thermal efficiency. As particularly, it is necessary to evaluate how the thermal conductivity of yttria-stabilized zirconia (YSZ) coatings is affected by processing conditions during EB-PVD. In this work, we calculated the thermal conductivity of YSZ coating layers deposited on dense YSZ substrates based on theory. This work also addresses the influence of processing conditions (especially substrate rotation speed) on microstructure during EB-PVD and its influence on the thermal conductivity of zirconia coating layers.

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