Superconductive BYCO ceramics with the transition temperature of 95K have been obtained by sintering in oxygen gas flow at 950°C, and the relationships between the superconductive properties and the texture have been studied. With increasing the apparent density of the BYCO ceramics, T_c decreased. The crystallite boundary and lattice defect, studied with a transmission electron microscope, also degraded the transition temperature. By adding CuO to the calcined BYCO powder, well aligned flaky particles in which the a-b planes preferentially grow were formed, and much sharp transition, as well as some increase in critical current, has been recognized in comparison with normal BYCO ceramics.

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The structure of solid solutions formed in Co₂GeO₄-Mg₂GeO₄-Zn₂GeO₄ and Ni₂GeO₄-Mg₂GeO₄-Zn₂GeO₄ systems was studied by means of X-ray diffraction diagrams and visible reflectance spectra. The color of the solid solutions was examined.
(1) Spinel [Sp I], olivine and phenacite solid solutions were formed around Co₂GeO₄ (Ni₂GeO₄), Mg₂GeO₄ and Zn₂GeO₄, respectively, in two ternary systems. Another spinel [Sp II] solid solutions were formed around Co_1.2Zn_0.8GeO₄ and Ni_0.8Zn_1.2GeO₄ in each system.
(2) From the change of the value of lattice constant, the Sp I solid solution was found to be the normal-type spinel solid solution containing 4-coordinated Ge⁴⁺ ion. Reflectance spectra revealed the presence of 6-coordinated Co²⁺ and Ni²⁺ ions.
(3) The results of the structure refinement by X-ray pattern fitting method and the change of the value of lattice constant suggested that the Sp II solid solution was the inverse-type spinel solid solution containing 6-coordinated Ge⁴⁺ ion.
By annealing some specimens of the Sp II solid solution, the tetragonal spinel solid solution containing the 1:1 order of Ge⁴⁺ and divalent cation on octahedral sites was formed. These results supported that the Sp II solid solution was the inverse-type spinel solid solution.

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Ba-ferrite with controlled particle size was synthesized by the hydrothermal attrition mixing, a new method which was a combination of conventional hydrothermal treatment and attrition mixing using balls. Under hydrothermal conditions, attrition mixing influenced the nucleation process in crystallization. The nucleation rate increased with increasing number of balls and/or increasing rotation speed. The Ba-ferrite fine particles thus obtained showed a snake like hysterisis curve, different from Ba-ferrite fine particles synthesized at high temperatures. This is probably due to the lattice distortion enhanced by the OH^- ions incorporated during the hydrothermal synthesis.

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Glass-forming regions were determined in the MgO-Ga₂O₃-B₂O₃ system by melt quenching method. Phase separation occured for B₂O₃ rich compositions. Raman spectroscopy and IR spectroscopy measurements revealed that boroxol ring groups exist in the B₂O₃ rich compositions and that diborate groups of 4-fold coordinated boron exist at MgO rich but Ga₂O₃ poor compositions. Pyroborate or orthoborate groups of 3-fold coordinated boron were found at MgO rich compositions in the ternary system. With the increase in Ga₂O₃ content the concentration of diborate group decreased and GaO₄ tetrahedra were formed together with di-tiborate and metaborate ring groups. Hence, MgO-Ga₂O₃-B₂O₃ system as well as GaO-Ga₂O₃-B₂O₃ system forms a continuous network of 6-membered rings consisting of GaO₄-tetrahedra. A possibility that Ga⁺³ ion might partially be incorporated in these groups was pointed out from the shifts of the Raman scattering peaks associated with Pyroborate or orthoborate groups. The smooth variation in density and refractive index of the glass with composition indicates that the structural change of glass with composition is continuous.

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Kaolinite mixed with 10 to 30wt% CuO was fired at 900°-1000°C and the phase transformation during firing was studied by powder diffraction analysis. The addition of CuO markedly promoted formation of mullite and cristobalite from kaolinite. The copper spinet was formed at 950°-1000°C and the quartz solid solution was formed at 950°C. The lattice constants were precisely determined for the quartz solid solution. Of the two lattice constants of the quartz solid solution (c₀ and a₀), the value of c₀ agreed with that for α-quartz, while the value of a₀ was larger than that for α-quartz and was between that for α-quartz and that for β-quartz. Thus, the quartz solid solution has a structure in which a-axis is expanded. The value of a₀ for the quartz solid solution decreased and the amount of copper spinel formed increased with an increase in CuO content. This results suggested that the amount of Cu²⁺ ion in the quartz solid solution did not change but the amount of Al³⁺ ion decreased with an increase in CuO content.

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The influence of applying pressure on structural homogeneity such as density and microhardness distribution in CIP-ed powder compacts of silicon carbide has been investigated at the pressure from 100 to 900MPa. The green density of thin disks (φ10mm×3mm) varied according to Cooper's relation, which showed that the compaction of powders performed through two processes with different pressure dependence. A compaction process in the low pressure region (<200MPa) was packing which accompanies the deformation of agglomerated particles (Process I). and the following process in the high pressure region (>300MPa) was the rearrangement of primary particles (Process II). Vickers microhardness increased remarkably in the later process. As for larger powder compacts (φ52mm×25mm). inhomogeneous surface layer formed as the result of reduction of applying pressure by friction among particles and bridgings. The degree of the inhomogeneity varied de-pending on the applying pressure. Microhardness decreased gradually toward the center of compact at the pressure of 100MPa. where only Process I was predominant in the surface and also the center of compact during CIP-ing. At 200MPa, the difference in microhardness between the surface and center of compact increased because the pressure reduced to the level where Process I was predoninant at the center, on the contrary, Process was predominant near the surface. Above 500MPa. a homogeneous zone with almost constant microhardness values was formed in the compacts. The homogeneous zone developed with increasing applying pressure. At 900MPa, the compact showed the most homogeneous structure covered with a high hardness thin surface layer. Highly dense and homogeneous powder compacts could be formed by applying high CIP-ing pressure.

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Formation of Cr-metallized layer on the surface of SiC ceramics by the vapor-diffusion method was studied The metallization was carried out at 1273K up to 360ks in an evacuated chamber. As a vapor source, pure Cr powder was used. The kinetics of layer growth was described by the parabolic law with the rate constant of 4.2×10^-16m²/s at 1273K The metallized layer was composed of four layers; double carbide: Cr_5-xSi_3-zC_x+z at the bottom layer, chromium silicide: Cr₅Si₃ at the middle layer, a transition layer from chromium silicide to chromium cabides which consist of a Cr₇C₃ and Cr₃C₂ at the surface layer.

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The anisotropic deformation formed in Y-PSZ crystals by Vickers indentation was discussed on the base of an analysis of the surface texture. Needle-like texture appears around the indentation and is related to occurrence of the transformed monoclinic phase. The appearance region of this texture differs from one another in the crystal direction of ‹010› and ‹011›, and changes with angle between the crystal orientation and the direction of pyramidal indentor. This morphological change on the surface results mainly from the crystal anisotropy of the slip systems and the orientation of the pyramidal form of the indentation. Observation of fracture surfaces indicated that the needle-like texture appeared in the slip plain less frequently than in other places. Polarized micrographs showed that the strain region around the indentation below the surface was the same region where the needle-like texture was observed.

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The main objective of this study is to characterize the prominent features of a thermal plasma CVD, and to investigate the principal deposition mechanism in this method. The materials chosen in this study were SiC, Si₃N₄ and BN. The deposition rate achieved was from 5 to 27μm/min. The relationships between the structures of the coatings and the dwell time of reactants (t_d) were investigated under reactant partial pressure of about 1 Torr, substrate temperature of 850° to 1300°C, and t_d of 50 to 400μs. In SiC, columnar, flat dense, or powder-like coatings were deposited at t_d of 80 to 200, 200 to 400, or over 200μs, respectively. In Si₃N₄, on the other hand, flat dense and powder-like or whisker-like porous films were deposited at t_d longer or smaller than 200μs, respectively. These results suggest that in this process the clusters produced in the flame may play an important role in the formation of dense films. One of the essentials to obtain dense films at a high deposition rate is to regulate t_d as well as deposition temperature.

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Thermal diffusivity and conductivity as well as specific heat were studied for capsule-HIP sintered Si₃N₄. Yttria and alumina additives with a total amount of 6mol% were used. For a given additive percentage, specimens of higher β phase fraction had higher thermal diffusivity and conductivity, as expected However, samples with larger amounts of Y₂O₃ additive had higher thermal diffusivity and conductivity in spite of a lower β phase fraction than those with more Al₂O₃ additive. The highest thermal conductivity was 70W/(m·K) with 6mol% Y₂O₃ additive alone. The reason is that aluminium and oxygen ions are soluble in β-Si₃N₄ particles, in the case for Al₂O₃ addition.
Oxygen, presented as an impurity, also had a profound effect on the thermal diffusivity and conductivity. Higher oxygen contents reduced the thermal diffusivity and conductivity. This may be due to the amount of grain boundary glassy phase.
The specific heat of sintered Si₃N₄ was 0.67±0.02kJ/(K·g). The crystalline structure (α or β-Si₃N₄), additive composition, and raw material particle size did not show any effect on the specific heat.

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High density titanium nitride having various non-stoichiometries (TiN_x: x=0.56-0.97) was prepared by hot isostatic pressing between 1350° and 1650°C and at 50 to 60MPa. Thermoelectrical properties were measured at the temperature region 25° to 1000°C, Temperature and/or pressure needed for densification increased with increasing nitrogen content. The lattice constant increased linearly with increasing nitrogen content. Thermoelectrical powers were small and increased with increasing temperature. They were, however, only slightly affected by the non-stoichiometry, and had a maximum at approximately x=0.75. Electrical conductivities decreased with increasing temperature and with decreasing nitrogen content. These results were explained by the quasi-free electron model for the carrier transport.

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The wetting of water on two-phased model material plates, consisting of hydrophilic and hydrophobic phases, has been studied with an emphasis on the effect of relative phase area and phase configuration. The model material plates were prepared from aluminum sheets by arranging the two phases in check and stripe patterns with different pattern unit sizes. The wetting behavior was found to be best characterized by the advancing contact angle and capillary rise. It is shown also that the wetting behavior depends both on the phase fraction and phase pattern. In some cases, pulse type wetting was observed depending on model plate pattern and immersion rate. Dynamic analysis rather than static analysis has been more useful in evaluating the wetting behavior of multiphase materials.

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A new dispersing process based on a surface property of cobalt-modified γ-Fe₂O₃(Co-γ-Fe₂O₃) magnetic particles was developed in order to improve the dispersibility of Co-γ-Fe₂O₃ in magnetic coating. Heat of immersion into water and adsorption isotherm of water revealed that Co-γ-Fe₂O₃ particles have strongly hydrophilic surfaces. The Co-γ-Fe₂O₃ particles with the hydrophilic surface showed better dispersibility in water than that in organic solvent. Drying of aqueous suspension of particles caused hard agglomerations of particles which were difficult to redisperse in paint using organic solvent. To overcome this problem, the displacement of water in the aqueous suspension by organic solvent such as alcohol, ketone and so on, was investigated. The dispersibility of Co-γ-Fe₂O₃ particles in the magnetic paint using organic solvent was significantly improved by the combination of dispersion in water and subsequent displacement of water by organic solvent. Thus, saturation magnetization and surface roughness of the coating made by the new process were improved about 10% and 50%, respectively, compared with the coating by a conventional process.

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Composite ceramics of MgO mixed with SiC fine powder up to 90vol% were fabricated by the hot-pressing at 1700°-1900°C under 30MPa for 30min. The properties (bending strength, fracture toughness, hardness, oxidation-resistance et al.) of the hot-pressed bodies were measured. Fairly dense MgO-SiC composite ceramics with relative densities above 95% were obtained in the region of SiC content up to 50vol% at a sintering temperature of 1850°C. The composites containing 30-50vol% SiC had higher strength, hardness and thermal shock resistance than MgO monolithic compacts. Little decrease in the strength was observed at temperatures up to 1400°C because of surpressing the fracture of MgO at grain boundary by SiC particles. The fracture toughness (about 5MPa·m^1/2) of composite with a SiC content of 30vol% was two and half times as large as that of hot pressed MgO at 1400°C. This is considered to be due to the crack deflection by SiC particles. This composite ceramics showed poor oxidation-resistance, so that the high-temperature uses must be limited in certain range.

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Silicon nitride, doped with 2.5, 5.0, and 7.5wt% MgO, was hot-pressed under various temperature-time conditions. Fracture toughness and Vickers hardness were measured, and these properties have been correlated with the fraction of β phase determined by X-ray diffractometory. Comparison with a theoretical curve confirmed that the crack deflection at rod-like crystal contributed to the increase in fracture toughness.

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Sintered silicon nitride ceramics were joined, employing the joule heating by electric current through the joining paste containing CaF₂. The flexual strength of the joint was dependent on the thickness of the joint layer. The thickness was controlled by the time of joule heating. For instance, heating for 10 minutes gave the thickness about 10 to 30μm. This sample showed the maximum strength around 300MPa up to 800°C. But the strength decreased rapidly above 900°C, perhaps because of the softening of the joint layer.

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The sol-gel coating process of stainless steel sheets with SiO₂ films has been studied using CH₃Si(OC₂H₅)₃ as a starting material. The obtained SiO₂ films had improved extensibility over that obtained from Si(OC₂H₅)₄. Results of DTA-TG and infrared spectra showed that CH₃ groups remained in the films even after the heat-treatment at 400°C for 1min. Thus, extensibility of these SiO₂ films was ascribed to the flexible structure resulting from the remaining CH₃ groups.

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