Nowadays, oxygen sensors attached to gasoline and diesel engines are required their downsizing, fast responsibility and high accuracy, in order to make exhaust gas clean and reduce the air pollution. The objective of this study is an application of porous oxide semiconductor which is prepared through phase separation of high temperature oxide melts to the oxygen sensors. CeO₂ was selected as a candidate of semiconductor, of which electronic conduction changes with oxygen partial pressure; furthermore CeO₂-SiO₂ binary system has stable immiscibility region at high temperature. Al₂O₃ was also added because it makes phase separation structure much finer and more homogeneous. The phase separation texture, crystallization behavior, and the electron conductivity of the melted samples have been investigated.

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Porous particles consisting of nanograins and nanosheets of crystalline tin dioxide were prepared from aqueous solutions of tin (II) at 60 degree C. The shapes of the primary and secondary particles were controlled by adjusting the concentration and pH. The highest value of specific surface area, 240 m²/g, was obtained by subsequent hydrothermal treatment. Addition of urea into the solutions promoted the formation of porous films of tin dioxide on a glass substrate.

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This work reports sensing properties of SnO₂ particle layers deposited by the electrospray pyrolysis method from SnCl₂ ethanol solution. Thediscriminating properties for several gases are examined with dynamic response which occurs when the temperature was changed during sensing.

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We have succeeded in fabricating micropatterns of a metal oxide film with an arbitrary regulated thickness onto polymer substrate through a liquid phase process. In this study, polyimide (PI) sheet was employed. Oxide nanoskin (ONS) was first formed onto the PI substrate to achieve good adherence between the metal oxide film and the PI surface. Photolithographically micropatterned octadecyltrimethoxysilane (ODS) layer on the ONS was used as an ultrathin molecular template. Although the metal oxide film was homogeneously deposited onto entire surface of the template, the deposits on the ODS-covered regions were completely eliminated by solution lithography using absolute toluene, resulting in the formation of the well-defined microstructures of the metal oxide.

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Nanocomposite pressure sensor has been developed by dispersing inorganic conductive phase and nano-sized particles into elastomer matrix. Good mechanical and relaiability for pressure sensing capability have been achieved by optimizing of percolation volume of dispersant as well as anisotropic structure of them. Relationship between novel processing, structure and performance will be discussed.

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The PTCR and temperature sensing properties of the textured vanadium oxide (V₂O₃) ceramics doped with chromium are mainly discussed. Ultra-fine V₂O₃ powder prepared by urea homogeneous precipitation method is used as a starting material and the obtained sintered compacts show superior PTCR properties depending on their sintering conditions. Highly dense sample with smaller grain size exhibits rapid and larger PTCR jump (over 10³) at T= T_MI: the metal-insulator (M-I) re-transition temperature. It is also appeared that by texture controlling, T_MI at elevated temperature can be independently controlled without any variation in T_MI at reduced temperature.

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The self-temperature control type humidity sensor is a sensor which does not need a temperature compensation circuit. Until now, We have reported that sensing element which showed the possibility as such sensor was produced and obtained from combining lead chromate (PbCrO4) with 0.3 mol of iron oxide (Fe 2O3). However, The improvement in reliability is needed and to be necessary for the practical application of this kid of elements. Therefore, This experiment was curried out for the purpose of obtaining a highly reliable element that keeps having a stable characteristic. It was possible to drastically change the heat treatment condition of device fabrication by using either gold or platinum as electrode material. As a result, elements of desirable characteristic were got.

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In the area of photo communication, Glass-ceramics including ferroelectric crystals which show second order optical non-linearity are expected for photonic devices, e.g., wavelength shift. And it is expected that these glass-ceramics have higher second order optical non-linearity.
Crystal orientation is one of the methods that improve several properties of ceramics. In this research, 30BaO-15TiO₂-55GeO₂ glass-ceramics were prepared in a high magnetic field of 10T. And then crystal orientation and second order optical non-linearity were measured. In the result, the crystal orientation and second optical non-linearity of the samples heat-treated in a high magnetic field are improved compared with the samples heat-treated in no magnetic field.

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Tellurite glass is expected very much as optical control glass with a large refractive index and the efficient optical nonlinearity. It was reported that nanometer-scale glass particles were successfully produced by ultraviolet laser irradiation on the surface of tellurite (TeO2) based glasses and whose diameters and heights are able to control by condition of UV laser irradiation. Such particle structure of nano-size turns into important structure for realization of the nanometer-scale optical circuit exceeded diffraction limit operating the new photon propagation system. However, the formation mechanism of a nano particle is not clear yet at present. To modify any desired patterns and size of ordered nano-particles, it is quite important to understand the formation mechanism of UV-induced nano particles. In this research, to clarify that, we applied UV laser irradiations with heating assistance. The diameter of a particle did not change but particle height grew greatly. This result has suggested that the thermal effect is participating in particle formation.

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When a silicon nitride (Si₃N₄) ceramics is fabricated with yttrium oxide (Y₂O₃) as a sintering aid, the compounds in the Si₃N₄-SiO₂-Y₂O₃system are formed. The typical compounds of the Si₃N₄-SiO₂-Y₂-O₃- system are Y₂Si₃O₃N₄(melilite), YSiO₂N(wollastonite), Y₄Si₂O₂N₇(cuspidine) and Y₅(SiO₄)₃N(apatite). In order to improve high temperature strength of silicon nitride ceramics, it is necessary to control the composition of grain boundary phase and important to make clear the properties of the compound in the Si₃N₄-SiO₂-Y₂O₃ system. In the present study, we fabricated the dense sintered body in the Si₃N₄-SiO₂-Y₂O₃ system and found that (1) the hot pressing of the high purity compounds made the fabrication of high density ceramics with over 98 % of relative density possible, and (2) the flexural strength of the ceramics was arranged as: YSiO₂N>Y₂Si₃O₃N₄>Y₄Si₂O₇N₂>Y₅(SiO₄)₃N.

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The aim of this work is to develop novel functional ceramics by Spark Plasma Sintering (SPS) of powders composed by metastable amorphous phases. An amorphous Alumina/Silica (molar ratio 1:1) powder obtained by rapid quenching of the melt was sintered by SPS and compared to the pressureless sintering method results. Unique amorphous bulks with promising functionality are expected. It was found that although the amorphous phase could be maintained by SPS at 850degC (100degC/min, 0sec), the relative density was low (80%). The densification proceeded (95%) at 900degC but abrupt mullite crystallization leaded to cracking. However, since densification did not proceed (50%) by pressureless sintering at 900-1100degC, the present process was found to be a potential method to produce unique amorphous bulks and improve sinterability.

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alph(6H) and beta(3C)-SiC powders were sintered with the addition of AlB2 and C. SiC powders could be densified to approximately 98% of theoretical density over a wide range of temperature from 1900 to 2150^oC. The sintering temperature was about 200^oC lower than that of the industrial method. 6H and 3C plytypes in alph- and beta-SiC grains were partially transformed into 4H. The partial transformation grew SiC grains from spherical-shaped to plate-shaped grains at 2000^oC. The low temperature sintering made it possible to utilize a hot-isostatic-pressing(HIP). alph-SiC powder was firstly pre-sintered at 1850^oC to the nearly full density and the subsequent post-HIP at 1850^oC completed densification resulting almost the 100% theoretical density.

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Nano-crystalline beta-Si3N4 powder has been prepared by high-energy mechanical milling. A systematic study of various sintering parameters, namely temperature, holding time, heating rate, etc. was conducted to investigate their effect on the densification, grain-growth and mechanical properties of the nano-crystal beta-Si3N4 powder. The objective is to obtain a dense beta-Si3N4 ceramics with grains as small as possible.

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We demonstrated the glass strengthening technique by femtosecond laser beam irradiation. Effect of laser irradiation conditions on strength improvement of the glass, and this mechanism was investigated. A shade of density was observed at laser-irradiated areas by various analyses. Bending strength of laser-irradiated glass was improved to over 1.7 times under the optimum irradiation condition. From the results of bending test, we confirmed that the shade of density at 75mW irradiated power and that the narrow scanning line periods suppress the propagation of microcracks effectively.

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