Polyborosilazane with a low oxygen content was synthesized by reacting perhydrosilazane with tris (dimethylamino) borane. The chemical structure of this polymer was investigated by infrared and nuclear magnetic resonance spectroscopies. The borazine ring structure was observed in the polymer. Amorphous silicon nitride was obtained by pyrolysis of this polymer in a stream of N₂ at 1000°C with about 80mass% ceramic yield. The pyrolysis product remained amorphous after further heating to 1700°C under N₂. The oxygen content in the pyrolysis product was 1.1mass%. Crystallization to β-Si₃N₄, β-SiC and α-Si₃N₄ took place on annealing in N₂ at 1800°C for 1h. These results indicate that this polyborosilazane is a good precursor for amorphous silicon nitride-based materials with low oxygen content.

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As a first step to clarify the influence of Peltier effect on the temperature and electrostatic potential distributions as well as heat and electric current flow in a composite thermoelectric material, basic equations to describe the heat and electric current have been numerically solved for typical configurations of two thermoelectric energy conversion materials, a series and a parallel configuration. Above distributions and flows have been visualized for several dimensionless coefficients related to thermoelectricity. Peltier effect brings about less energy conversion efficiency in case of a series configuration of the phases with different Seebeck coefficients from each other than that in case of a parallel configuration. When no electric current is taken out from a composite thermoelectric material, Seebeck coefficients of the materials of a series and a parallel configuration are the same and given by the volume average of those of composing materials, as is expected.

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A sialon composite consisting of Y-α′-sialon and β′-sialon is obtained by hot-pressing mixtures of Si₃N₄, Y₂O₃ and AlN powders. In this study, the effect of the presence of a small amount of SiO₂ on the reaction during sintering, especially on the formation of Y-α′-sialon, is investigated. The sinterability of mixtures of Si₃N₄, Y₂O₃ and AlN powders was remarkably improved by the addition of a small amount of SiO₂. The amount of Y-α′-sialon after sintering decreases with increasing amounts of SiO₂ added to the starting mixtures, while the lattice constants, hence the solubility of Y-α′-sialon and β′-sialon, remain unchanged.

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The precipitation of gelatinous aluminium hydroxide from aqueous solutions of aluminium sulphate and ammonium, potassium and sodium slums with sodium hydroxide solution was investigated under different conditions. The resulting precipitates were examined by X-ray diffraction study, infrared spectroscopy and thermal analysis (TG and DTA). It was determined that the composition of the precipitates depends on experimental conditions, in particular the pH value of aqueous solutions: this composition varied in the order of amorphous aluminium hydroxide, pseudoboehmite and bayerite as the pH of aqueous solutions in their formation increased, although the precipitation behavior was influenced by aluminium salts containing sulphate. The results obtained are discussed in comparison with the precipitates from aqueous solutions of chloride or nitrate of aluminium with alkali.

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Barium titanate fine particles were prepared by a hydrothermal method using titanium tetrahydroxide gel and barium hydroxide. In particles with an average size of 89.62nm, the crystal structure changed from cubic to tetragonal accompanied with a decrease in the amount of lattice defects such as lattice hydroxyl groups, without a change in particle size. This result revealed that a physical quantity with size much smaller than the particle size could determine the crystal structure of barium titanate. To explain this phenomenon, we proposed a new model based on the stability of lattice vibrations, in which the amount of the lattice defects can determine the correlational size of barium titanate dipoles, and the tetragonality (c/a) is dependent on the correlational size. Moreover, the model can be used to explain the size effect on relative permittivity and Curie temperature in barium titanate.

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Two of the fundamental properties of carbon-containing refractories with Al, hydration resistances and reactions with CO of Al₄O₄C and Al₂OC formed in the refractories at high temperatures were investigated. Al₄O₄C is formed from a mixture of Al₂O₃:Al:C=4:4:3 (molar ratio) above 1300°C. Al₂OC is formed from a mixture of Al₂O₃:Al:C=1:4:3 (molar ratio) above 1400°C. The hydration resistances of Al₄O₄C and Al₂OC are much better than that of Al₄C₃. Al₄O₄C and Al₂OC react with CO to form Al₂O₃ and C at temperatures above 900°C.

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Apatite formation on the surfaces of various silica gels prepared in different media and silica glass was investigated in SBF1.5Ca. After the soaking in SBF1.5Ca for 7d, the bonelike apatite was formed on the surfaces of all the silica gels having abundant silanol groups. It was not, however, formed on the surface of the silica glass having little silanol groups even after the soaking for 2 weeks. From the results, it can be concluded that all the kind of silanol groups developed on the silica gels can induce the apatite nucleation, although there is some differences in their nucleating abilities. It is interesting to know what type of the silanol groups is most effective for the apatite nucleation. Unfortunately, however, Raman spectra in Fig. 1 give no information about difference in surface structure among the gels. Further study is needed for revealing the most effective structural unit.

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The critical cooling rate for 30Na₂O⋅10MgO⋅60SiO₂ glass, which exhibits low Rayleigh scattering, was evaluated based on viscosity. To this end, the viscosity and thermal expansion coefficient of this glass were measured using a thermomechanical analyzer. The beam bending and parallel plate methods were effective in measuring the viscosities in the range of interest of higher than 10⁴dPa·s. The critical cooling rate was determined as the cooling rate at which the density of the glass melt became identical to that of solid glass at the glass transition temperature when the melt was cooled from the liquidus to the glass transition temperature. The obtained value for this glass was 2.6°C/min.

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Porous thin films of SnO₂ were prepared on an alumina substrate using hydrothermally synthesized SnO₂ sol, to investigate the influences of film-preparation conditions on the microstructure and H₂S sensing characteristics of the thin films obtained. The sensitivity and response transient to 5ppm H₂S in air depended significantly on calcination temperature, operating temperature and film thickness. The 0.6μm-thick SnO₂ film calcined at an optimum temperature of 700°C exhibited gas sensitivity (the ratio of electrical resistance in air to that in gas) as high as 550 together with good response transient characteristics to 5ppm H₂S in air at 200°C. The crystallite size of SnO₂ as well as the pore size increased uniformly with a rise in calcination temperature, growing to 17.4nm and 21nm, at 700°C, respectively. The formation of well-defined large mesopores appears to be responsible for the excellent H₂S sensing characteristics.

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The surface properties of copper oxide (CuO) were discussed for considering the working mechanism of a CuO/ZnO heterocontact gas sensor having carbon monoxide (CO) gas selectivity. We focused on p-type semiconducting CuO, using sodium as a dopant, which is a key material for selective CO gas sensing and its surface properties were characterized by XPS, TPD and FT-IR analyses. It was found that the Cu/O ratio of the 1mol% Na₂CO₃-added CuO surface was higher than that of pure CuO surface by XPS analysis. By TPD analysis, it was found that CO was adsorbed more strongly on 1mol% Na₂CO₃-added CuO than on pure CuO. By the in situ IR measurement of CO adsorbed on the surface of 1mol% Na₂CO₃-added CuO specimen under 300°C, we found two asymmetric bands of CO, whereas an asymmetric streching CO₂ band was found on IR measurement of pure CuO specimen. It was confirmed that Cu atoms on pure CuO surface exposed to CO at 300°C changed from Cu²⁺ to Cu¹⁺ or Cu⁰, in contrast to Cu atoms on 1mol% Na₂CO₃-added CuO surface, which changed to Cu²⁺. The electrical conductivity was measured as a function of temperature for pure CuO, CuO with 1mol% Na₂CO₃ and ZnO specimens. The resistivity of ZnO was larger than that of pure CuO and CuO with 1mol% Na₂CO₃ by three and six orders of magnitude at 250°C, respectively. A working mechanism of CuO(Na)/ZnO heterocontact gas sensor was elucidated in order to explain its high CO selectivity.

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The structure of spinnable solution of triethylaluminium and ethylsilicate-40 and calcination process of drawn alumina gel fiber were investigated. In spinnable solution there were no Al-O-Si bonds between polyaluminoxane, whose average polymerization degree was about 24, and ethylsilicate-40. The Al-O-Al and Al-O-Si bonds and five-coordinated aluminium atoms were formed during calcination process until γ-alumina was crystallized in the fiber around 960°C, due to elimination of alcohol and water. With the crystallization of γ-alumina, the amorphous silica was segregated, and located between alumina crystals.

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Fluorine muscovite KAl₂(AlSi₃O₁₀)F₂ was synthesized through solid state reaction at 600°C for about 100h from stoichiometrical batches. Fluorine muscovite was not formed by heating these raw batches at higher temperatures above 700°C. It was indispensable for mica formation to use γ-Al₂O₃ as raw materials. Appropriate forming pressure for green bodies was found to be 37.5-75MPa for obtaining crystal aggregates of fluorine muscovite with well-developed interlocking house-of-cards microstructure, which gave machinability to the sintered bodies. Thermal durability of fluorine muscovite crystals in air was relatively high due to the formation of a protective vitrified phase on the surface upon decomposition. Changes in lattice constants and IR spectra suggestes the formation of fluorine muscovites having variable layer charges between 1.0-0.9.

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Sr_0.2Ba_0.8Nb₂O₆ ceramics with 1mol% V₂O₅ addition were fabricated by liquid phase sintering. A compact sintered at 1300°C for 100h had the spontaneous polarization of 6.1×10^-2C/m² at 50°C. The sharp permittivity peak was observed at 293°C, corresponding to the Curie temperature. The crystal structure had the orthorhombic symmetry with a₀=1.7654, b₀=1.7662 and c₀=0.7961nm at room temperature. The orthorhombic-tetragonal phase transition was found at about 120°C.

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Composite ceramics of alumina mixed with up to 50vol% titanium carbide whiskers were fabricated by hot-pressing at 1600°C under 30MPa for 30min. The mechanical properties and the cutting perfomance for cast iron or carbon steel of the hot-pressed bodies were studied. Dense composites with relative densities above 98% were obtained at whisker content with up to 40vol%. The composite containing 20vol% whiskers showed the highest bending strength of around 560MPa. Increasing whisker content decreased the elastic modulus, but increased the Vickers hardness and the fracture toughness. The composite mixed with 20vol% or 30vol% titanium carbide whiskers was found to be capable of having the cutting performance similar to the available ceramic composite cutting tools such as titanium carbide particle/alumina composite and silicon carbide whisker/alumina composite.

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Carbon dioxide reforming of CH₄ was investigated over Ni catalyst supported on ceramic foam, which was a macro-porous medium. The catalyst showed a stable activity, and the pressure drop in a continuous flow reactor did not increase. On the other hand, the pressure drop increased on an industrial Ni catalyst by the carbonaceous deposition. The experiment was carried out in a pure CH₄ flow in order to accelerate the carbonaceous deposition rate. The ceramic foam catalyst suppressed the increase in pressure of the reactor even though carbon deposited to a certain extent. It was revealed that the performance of the ceramic foam catalyst was due to its high porosity.

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In this study, using spherical alumina powder with a narrow particle size distribution as the coarse powder, slips were prepared from a bimodal size distribution alumina powder mixture, of which the particle size ratio of the coarse to the fine powder was about nine and the mixing ratio of the coarse and fine powders was 7:3, and cast. A green compact which had a high packing density of about 78% and a uniform packing structure was obtained when slips in which the particles were sufficiently dispersed and the alumina content was about 49vol%, were cast.

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Pyrolytic behavior of Si-C-O fiber (Nicalon) in the alumina matrix composite was investigated. The composites with high densities of 93-94% were obtained by hot-press treatment at 37.5MPa at 1573-1773K. The pyrolysis of Nicalon in the composite was suppressed during sintering. Furthermore, Nicalon underwent little pyrolysis on reheating at 1973K.

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Three-dimensional Tyranno fiber reinforced SiC composites were fabricated by repetitive infiltration of molten polycarbosilane into 3-dimensional textile preforms (volume fraction 35-39%) with different fiber orientation ratio, followed by a pyrolysis process up to 1200°C in flowing argon. The composites displayed both high fracture toughness and work of fracture. In addition, a semistable fracture behavior was maintained even at 1200°C in air. Bending strength, fracture toughness, and work of fracture of the composite were strongly affected by the fiber orientation ratio and fiber diameter of the preform. This study suggested that the volume fraction of fiber along the tensile direction was the critical parameter for increasing the mechanical properties of the composite, and that the use of thin fibers involved higher values of work-of-fracture.

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An alumina-zirconia (AZ) composite powder was prepared by thermal decomposition of organic precursors synthesized from ethyl acetoacetate aluminium di-isopropylate and zirconium n-butoxide. The specific surface area of AZ was higher than that of alumina-zirconia (ALK) prepared from aluminium sec-butoxide and zirconium n-butoxide. The true density of AZ was lower than that of ALK. Selective reduction of nitrogen oxide with propylene in oxygen-rich atmosphere on AZ was superior to that on ALK.

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The effect of seed crystal properties on the microstructure of Si₃N₄ ceramics was investigated. Three β-Si₃N₄ powders with average grain size of 0.74, 5.84 and 21.66μm and β-Si₃N₄ whiskers were used as seeds. Seeds (2mass%) were added to the mixture of α-Si₃N₄ and sintering aids, and the mixture was hot-pressed at 1850°C for 8h. Growth of large rodlike-grains was enhanced by the micron-sized single-crystalline β-Si₃N₄ particle. Crushed β-Si₃N₄ whiskers were similarly effective in growing rodlike-grains. On the contrary, polycrystalline β-Si₃N₄ particles and submicron-sized β-Si₃N₄ particls did not affect greatly the final microstructure.

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The effect of TiO₂, ZrO₂ and P₂O₅ as nucleating agents was discussed in a SiO₂-Al₂O₃-MgO-CaO-Na₂O glass system. Crystallization study of glass system containing these oxides indicated that only surface crystallization and not volume crystallization occurred. The crystals that were formed were wollastonite and a small amount of diopside. It was found that these oxides suppressed surface crystallization and reduced the crystal growth rate. The reason for this suppresion was explained by the crystal growth theory. These oxides were considered to stabilize the glass system by incorporating into the glass network.

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Aluminum hydroxide was precipitated by a conventional chemical reaction between alum and NH₄OH in aqueous solution. The wet precipitates concerned were dispersed into alcohols such as ethyl alcohol, n-propyl alcohol and isobutyl alcohol, evaporated to dryness, and calcined at 1250°C for 2h. These treatments resulted in porous and weak agglomerates in the calcined alumina, which was well-sinterable.

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