Using TTIP as a starting material, we investigated sol-gel fabrication of TiO₂-coated carbon fibers, and optimized the following fabrication parameters: coating solution composition, pulling rate and dipping time. TG measurement results indicated that no weight reduction occurred in the coated fibers air up to at a high temperature of 1000°C. From these experiments, it was concluded that the fabricated carbon fibers coated with TiO₂ were oxidation resistant.

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The problem of localization on grain growth was investigated in relation to two-sphere and uniform polysphere grain models. The new rate equations for grain growth were formulated based on Inomata's free energy theory for mass transport and Tanaka's definition of diffusion area and length. The equations included parameters for the grain size ratio, the ratio of grain boundary energy to surface energy, and the size of the system. From the equations, the growth rates were calculated as a function of the total system size. The results indicate that in the two-sphere model, the growth rate has a maximum at a certain system size meaning that grain growth was localized in the growing grain. However, in the poly-sphere grain model, the growth rate for large grains was not shown to be significantly depended on the size of the system.

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Aluminum nitride (AlN) powders were synthesized with 0.16-0.54mol% of transition metal oxides, such as TiO₂, ZrO₂, Nb₂O₅, MoO₃, WO₃, and Fe₂O₃, and characterized in terms of their powder's properties. The synthesized AlN powders were then sintered under N₂ at 1850°C for 3h with 5mass% Y₂O₃ as a sintering aid. After which, the properties, such as density, thermal conductivity and optical transmittance, of the sintered ceramics were investigated. The chemical states in which the additives exist in both of the powders and the sintered ceramics were also investigated. Little change was observed in properties of the AlN powders when synthesized with the various additives, except for a small increase in oxygen content. The additives seem to change from being oxides to being nitrides during the synthesis process. A slight reduction in the thermal conductivity of the sintered AlN ceramics was noted with the addition of 0.16mol% of the additives, but this became large as the amount was increased to 0.54mol%. The additives in the sintered AlN ceramics existed as fine particles of either one of two kinds of chemical states; the elements of group IVa existed as nitrides while the others existed as metals. The sintered AlN ceramics with transition metal additives indicated low optical transmittance, particularly for those with MoO₃ and Nb₂O₅. Consequently, shaded AlN ceramics with high thermal conductivity and virtually no optical transmittance in visible-light region were attainable.

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Changes in interface chemistry and, accordingly, in interface structure of a Si₃N₄-SiC ceramic, due to the presence of fluorine, was found to markedly affect the mechanical response of the material. Owing to a lowered cohesive interface strength, as a consequence of fluorine segregation at grain and phase boundaries, an increased fraction of intergranular fracture was monitored upon crack propagation. Moreover, in comparison to undoped specimens, fluorine-doped samples revealed markedly higher creep rates, which are related to a decrease in the apparent grain-boundary viscosity. The experimental results allow a correlation between the macroscopic mechanical properties and the atomic interfacial glass structure. A glass structure model is presented, which emphasizes the influence of broken (non-bridging) bonds on the bulk mechanical performance of Si₃N₄-SiC-based composites.

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Phase relations in the system C₃P-M₂S (abbreviations: C=CaO, M=MgO, P=P₂O₅ and S=SiO₂) were investigated by means of the quenching method at temperatures up to 1600°C. Primary crystals are tricalcium phosphate and forsterite, and an intermediate compound sc appeared coexisting with the above compounds and liquid. Two minima of liquidus are located at 1440°C between C₃P and sc, and at 1410°C between sc and M₂S. Liquid disappears below 1365°C. The original composition of sc is C₃M₂PS (50-50mol% of C₃P-M₂S) or (C_0.6M_0.4)₅PS (60-40mol% of C₅PS-M₅PS), and has a solid solution range in both sides of this composition. This sc compound decomposes to both β-C₃P and forsterite below 1365°C.

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The effects of adding a small amount of Si₃N₄ less than 0.1mass% as seed crystals on the particle size and the α-content in resulting Si₃N₄ powders were investigated. A small quantity of only 0.02mass% seed increased the α-content to more than 90%. This seems to be due to the high partial pressure of gaseous SiO evolved by reduction of SiO₂. The particle sizes of the products decreased as the amount of seed increased. Finer particles were obtained when a kind of seed powder produced through pulverization process was used, which can be ascribed to significantly finer particles in the seed. With addition of less than 0.1mass% seed, the relation between the number of seed (N) and the resultant particle size (D) was confirmed to obey the equation, D=k(1/N)^1/3, where k is a constant.

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(1) Oxidation behavior of Si₃N₄ ceramics is affected by the composition of sintering aids and the weight gain due to oxidation tends to decrease with increasing SiO₂/Yb₂O₃ ratio. In specimens with SiO₂/Yb₂O₃ ratio from about 0.07 to 0.14, the weight gain is small. In specimens with SiO₂/Yb₂O₃ ratio larger than about 0.2, the weight loss due to active oxidation occurs.
(2) In Si₃N₄ ceramics with SiO₂/Yb₂O₃ ratio smaller than about 0.2, the enrichment region of Yb and the depletion region of Yb are formed. At the initial stage of oxidation, the oxidation rate is controlled by the interface reaction. At the 2nd stage of oxidation, it is considered that the oxidation rate is affected by the rate of outward diffusion of Yb³⁺ ions. At the final stage of oxidation, oxidation rate becomes smaller than that of the parabolic behavior, which appears to be affected by the formation of Yb₂Si₂O₇ during oxidation.
(3) In order to improve the oxidation resistance, it is necessary to decrease the amount of sintering aids and to use the sintering aids with an adequate composition.

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Diamond-like carbon (DLC) thin films were deposited by the plasma CVD method in which the substrate electrode was powered by radio frequency (13.56MHz). The deposition temperature was controlled by the “plasma pulsed deposition technique”: repeated cycles of alternating 5s deposition with 3min cooling. The deposited DLC films were studied using Electron Spin Resonance (ESR) to determine the influence of both deposition and post-deposition annealing conditions. ESR spectral variations obtained in this study with spin density and linewidth are consistent with the microstructural changes observed during work reported previously, in which the film deposition conditions and the effect of post-deposition DLC film annealing were examined. When the films were deposited using more than 100W r.f. power, further progress of carbon radical reaction was observed with increase in deposition temperature. When the films were annealed, an increase in the film hardness was observed when the annealing temperature was held below about 300°C, as reported previously. The ESR study supports the hypothesis that carbon radicals remaining in the DLC films react with each other to further increase the densication of the film structural network. When the films were annealed at temperatures >300°C, the film structure was deteriorated by oxidation reactions. The ESR spectral variations obtained during annealing procedures are consistent with these conclusions. Furthermore, variations in the linewidth in ESR spectra have been discussed mainly in terms of exchange narrowing related to microstructural changes of the DLC films.

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The synthesis of fibrous mullite followed by the KDC (Knead-Drying-Calcination) process, that is used for the synthesis of potassium titanate fibers was developed. Ammonium alum was mixed with hydrated halloysite clay to make bubbles in the fired body and to control the Al₂O₃ content, then was heated at 1500°C for more than 5h. The obtained bubbled mixture was treated with hydrofluoric acid to dissolve excess glass, then fibrous mullite was obtained. The following effects of additives were determined. Ammonium alum shortened the mullite fibers. Boric acid or borix, which is simultaneously mixed with ammonium alum, produces longer mullite fibers. In addition, the fiber was grown to about 30-70μm by doping with boric acid or borix by about 5-10mass%, fired at 1500°C for 10h.

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The influence of crystalline filler such as alumina and cordierite crystals on the formation of cordierite in MgO-Al₂O₃-SiO₂ glass was investigated. The glass in which no cordierite phase is formed is smaller in Al₂O₃ content than stoichiometric cordierite. Alumina fillers were dissolved in the glass during firing, resulting in increase in alumina content in the glass. Cordierite was formed in the glass powder compact containing alumina fillers formed by firing at 950°C. On the other hand, cordierite fillers were found to play a role as the site for heterogeneous nucleation, and also to lower the precipitation temperature of the cordierite phase in the glass. Cordierite was formed in the glass containing cordierite fillers by firing at 850°C. By firing the powder compacts containing both alumina and cordierite, larger amounts of cordierite can be formed because of the combined effects of each filler.

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The characteristic of cationic polyelectrolyte adsorption on aluinosilicate particles in equilibrium and the flocculation behavior were investigated as functions of particle diameter, solid loading and polymer concentrations. The results are summerized as follows. (1) The amount of equilibrium polymer adsorption decreases with decreasing particle diameter, increasing equilibrium polymer concentration below the specified particle diameter, increasing solid loading and increasing added polymer concentration, so that the depletion flocculation occurs respectively at the specified values of the above factors. (2) The depletion flocculation occurs even in a silica stone system when the particle diameter becomes small. (3) The osmotic attraction of a polymer solution can operate over the large interparticle region from the calculation using the depletion model. (4) Plotting the amount of equilibrium polymer adsorption obtained from the above factors against the interparticle distance, a master curve is drawn. (5) Polymer adsorption depends on the interparticle region in a slurry associated with the effective polymer size, and flocculation depends on the interparticle region and on polymer concentration.

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The synthesis of alumina balloons using the microcapsulation method has been investigated, and was successful in producing a transparent balloon with a diameter of 50-80μm and a wall thickness of less than 1μm. The process is as follows. 10mass% solution of polystyrene in toluene and boehmite sots of approximately 1mol/kg concentration are mixed by a homogenizer. The resultant W/O emulsion is redispersed in water to obtain a (W/O) W emulsion which produces boehmite sols encapsulated by polystyrene in water. After keeping it for 2 days at 40°C, the products are filtered, dried and then the polystyrene crust is dissolved by toluene. The resultant balloon precursors of boehmite sols are dried, fired and then the alumina balloons are obtained. In this paper, the effects of the concentration of polystyrene or boehmite sots and the addition of ethylene glycol or tricresyl phosphate on the formation of alumina balloons were discussed in detail.

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In order to clarify the effect of the initial crack length a₀ and specimen size on the time to failure (T_f) as well as to find the most suitable condition for evaluating the minimum value of the stress intensity factor K₀ (the threshold, the slow crack growth limit), the characteristics of static fatigue tests of brittle materials were analytically discussed and the analyzed results were verified by the tests on a soda lime glass. Both by analytical and experimental works, it was clarified that the T_f for a given value of K_Ii becomes shorter as a₀ decreases (K_Ii: the initial stress intensity). This fact indicates that to use the specimens with a smaller crack is very advantageous to characterize K_Ii-T_f relations as well as the K₀ value in a shorter time.

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Agglomerates of Si₃N₄ and TiN were co-sintered to fabricate a TiN/Si₃N₄ ceramic displayed a duplex microstructure. The agglomerates-microstructure-controlled material (A) showed electrical conductivity at a lower TiN content (9.8vol%) than the theoretical value of a material with a nonuniform microstructure. This is because the ratio of R_TiN (radius of TiN agglomerates) to R_SN (radius of Si₃N₄ agglomerates) was 8, causing TiN agglomerates to be arranged around large Si₃N₄ agglomerates. It is concluded that the lower critical volume % for conductivity of this material resulted from the formation of a network of TiN spherical agglomerates with a smaller amount of additive.

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A zeolite Y was modified with aqueous solution of Fe(NO₃)₃ to improve a adsorption property of NO gas. As the result, it was confirmed that the volume of NO gas desorbed from the modified zeolites was increased at low temperature (≤100°C). Accordingly, this modified zeolites can be used as a adsobate of NO gas at the lower temperature where the deterioration of the zeolite structure is restrained. The modified zeolites were analyzed using TEM and XPS. Then, Fe compounds with thickness 1 or 2nm observed on the surface of the modified zeolite and they were dispersed like as islands. Most of the Fe compounds was estimated as Fe₂O₃.

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A sintered 0.5mass% Pd/SnO₂ sensor was coated with SiO₂ films to improve the gas-sensing properties. The SiO₂ films were prepared by a simple dip-coating method of three kinds of alkoxysilane solutions of Si(OC₂H₅)₄, CH₃Si(OC₂H₅)₃ and (CH₃)₂Si(OC₂H₅)₂, followed by calcination at 600°C. A uniform, crack-free, but still porous SiO₂ film was obtained only from CH₃Si(OC₂H₅)₃. The use of Si(OC₂H₅)₄ resulted in a film with many cracks, probably because of too much three-dimensional polymerization of the precursor up to 400°C. On the other hand, the alkoxylsilane with two methyl groups left no effective SiO₂ film behind, because a large portion of it decomposed into volatile matters upon heating. The H₂ sensitivity of the Pd/SnO₂ sensor markedly increased with the coating of a crack-free SiO₂ film from CH₃Si(OC₂H₅)₃, especially at 300°C, whereas the sensitivity to CH₄, C₃H₈ and C₂H₅OH decreased. Thus, the SiO₂ coating resulted in a highly sensitive and selective H₂ sensor, though the response and recovery time get prolonged by the coating. In contrast, the coating of a SiO₂ film with many cracks from Si(OC₂H₅)₄ showed no significant effect on the gas-sensing properties.

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Sintering behavior of the mixtures of kaolinite and basic magnesium carbonate (BMC) was investigated to obtain dense cordierite ceramics. Kaolinite and BMC were mixed by ball-milling in a molar ratio of nMgO⋅Al₂O₃⋅2SiO₂ (n=0.8-1.4). Particularly fine mixtures were prepared by beads-milling after calcination. During firing of fine mixtures, magnesia disappeared completely by reaction with metakaolin to form amorphous particles below 900°C. Since the amorphous particles were very sinterable, the pressed specimens were densified up to about 90% at 900°C, and then μ-cordierite crystallized at about 940°C. Dense α-cordierite ceramics with relative density of≥95% were obtained at 1300°C from the mixtures of n=1.0-1.4, and the lowest linear thermal expansion coefficient was 2.2×10^-6/K in the case of n=1.0, which is close to the composition of cordierite.

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This paper reports a new approach for characterization of the powder using image analysis. Through the use of image analysis for characterization the processing and properties of ceramics could be effectively controlled. Image analysis is based on the detailed particle shape analysis by SEM micrographs. We examined two kinds of SiO₂. These two SiO₂ have same particle size distribution and zeta potential, but the green sheet density and sintering behavior are different. A comparison of the results of the image analysis revealed a deference in the shape and state of agglomeration of particles. In the ball-milling process, shape factor of particles affects the behavior of breaking-up of particles into small pieces. Green sheet density was found to depend on the state of the packing of particles, that is, the state and size distribution of agglomerates. Sintering behavior was also closely connected with green sheet density.

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A thermal expansion ten times larger than that of silica glass was observed for the pressed compacts of silica glass powder, which was ground with a planetary pot mill. The extent of the thermal expansion increased with increasing the grinding time. Since quartz powder compacts did not undergo much thermal expansion after grinding, such a large thermal expansion behavior of the silica glass powders seemed to be unique for the silica glass. Solid state ²⁹Si NMR and IR spectra showed a reduction in the Si-O-Si bonding angle, which resulted due to a distortion of the silica glass network.

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The thermodynamical stability (i.e., bound strength from the solid surfaces) of water layer on the surface of differently milled silicas were evaluated by cooling DSC. The degradation in a crystallinity of silica due to milling caused the decrease in the hydrophilicity of the surface, then the bound force from the surface on the water was decreased and its long range distance force was critically decreased.

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Polycrystalline samples of GdRh₃B_x, which consists of highly reactive (Gd) and high melting (Rh, B) elements, have been successfully synthesized by arc melting method. Extreme evaporation of the constituent elements has not been observed. Compound of GdRh₃B_x has perovskite type cubic structure (space group: Pm3m). Perovskite-type GdRh₃B_x exists in the range of x=1.000 (20atom% B) and 0.444 (10atom% B). Lattice parameter of a in annealed GdRh₃B_x depends on x, and varies lineary from a=0.41331(6)nm (x=1.000) to 0.4121(1)nm (x=0.444). The TG curve indicates that the onset-temperature of oxidation for GdRh₃B_1.000 is 567.3°C and for GdRh₃B_0.706 is 611.3°C, respectively. Weight gain by heating in air up to 1200°C for GdRh₃B_1.000 (20atom% B) is 6.83% and for GdRh₃B_0.706 (15atom% B) is 8.61%, respectively. The former value for stoichiometric compound is smaller than the latter. Both samples decompose to GdBO₃ and Rh after oxidation. The micro-Vickers hardness of the annealed Gdh₃B_x increases with increasing B content in the range of x=1.333-0.444, for example hardness of the annealed GdRh₃B_1.000 (20atom% B) is 4.2(±0.10) GPa.

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A solid state electrochemical cell, (-) CO₂, O₂, Pt|0.92ZrO₂⋅0.08Yb₂O₃+Li₂O⋅Sm₂O₃⋅2SiO₂|Au, Li₂CO₃, CO₂, O₂ (+), was investigated for the monitor of carbon dioxide in air. A layer type ionic conductor prepared from Li⁺ ionic conductor and O^2- ionic conductor by the thermal treatment was used as solid electrolytes. In the range of 450 to 600°C, the electromotive force, EMF, of the sensor increased linearly with an increase in the logarithm of CO₂ partial pressure, in accordance with the Nernst law. On the other hand, the EMF was little affected by the change of O₂ partial pressure. At the detection electrode, the two-electron transfer and the four-electron transfer were found to occur for CO₂ and O₂, respectively. The four-electron transfer reaction associated with O₂ molecules was found to occur at both the detection and counter electrodes, indicating that this sensor has an excellent selectivity for CO₂. The 90% response time was within 4min. The EMF was not influenced by the introduction of water vapor.

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Two types of electrodes, sputtered Au/Ti and fired Ag, were applied to Pb[(Zn_1/3Nb_2/3)_0.91Ti_0.09]O₃ (PZNT91/9) single crystals and showed the results obtained below. These results suggest at a new method for controlling the domain structure and electrical properties of these crystals.
(1) The dielectric constant K at room temperature is 8000 for Au/Ti electrode samples. However, samples with fired Ag electrodes indicate the lower K value of 1000.
(2) The dielectric constant K_max at the Curie temperature is almost the same for both types of electrodes.
(3) After electrical poling, Au/Ti samples indicate an electromechanical coupling coefficient k_t of 52.7%, while samples with fired Ag electrodes have a relatively high k_t value of 61.4%.
(4) The lower dielectric constant in the case of the fired Ag electrodes may be due to mechanical poling. This phenomenon increases the mechanical coupling factor k_t of poled single crystals.

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Gradient PZT ceramics with a series of PbZr_xTi_1-xO₃ solid solutions in a single ceramic body were prepared by sintering a green compact composed of two different PZT layers in contact with each other. The composition of PbZr_xTi_1-xO₃ solid solution varied continuously with the distance from the interface. The dielectric and piezoelectric properties of the gradient PZT ceramics yielded the value of an intermediate composition between two single-phase PZT ceramics on both sides or the value of either of them.

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Lanthanum fluoride thin films were prepared on silica glass substrates by a sol-gel method using trifluoroacetic acid (TFA) as a fluorine source. A coating solution was produced from lanthanum acetate and trifluoroacetic acid dissolved in 2-propanol. Triuoroacetate gel films were formed by spin coating the sol, which were converted to LaF₃ thin films by heat-treatment at 300-500°C for 10min. The formation of LaF₃ is considered to result from the reaction between lanthanum ions and the fluorine species generated by the decomposition of trifluoroacetate ions at elevated temperatures. The film fired at 300°C had a smooth surface with a grain size of 30nm. Cracks and voids were only observed in the films fired at 400 and 500°C. The films fired at 300 and 400°C exhibited transmittance of greater than 90% in the visible region.

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