Formation of Cr-metallized layer on the surface of Si₃N₄ ceramic by the vapor-diffusion method was studied. The metallization was carried out in a quartz capsule at 1273K for up to 72ks. As a vapor source, pure Cr powder was used. The kinetics of layer growth was parabolic with the rate constant of 1.0×10^-14m²·s^-1 at 1273K. The metallized layer was composed of two lyers; Cr₂N and CrN at the surface layer and Cr₂Si at the inner layer as identified by the X-ray diffraction analysis. The hardness of the metallized layer increased gradually from H_v 668 at surface to H_v 1179 at inner part.

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Preparation of precipitates for obtaining Zn₂SnO₄ is examined by the homogeneous precipitation method in which SnCl₄, ZnCl₂ and (CH₂)₆N₄ are used. The precipitation becomes difficult with increasing concentration of SnCl₄ and decreasing ratio of (CH₂)₆N₄ to SnCl₄. The homogeneous precipitation method becomes difficult to apply with increasing ratios of ZnCl₂ to SnCl₄ and of (CH₂)₆N₄ to SnCl₄. The amount of zinc contained in the obtained precipitate increases with increasing ratios of ZnCl₂ to SnCl₄ and of (CH₂)₆N₄ to SnCl4. The precipitate obtained is SnO₂ with poor crystallinity and contains zinc. Heating at 700°C resulted in the mixture of ZnO, SnO₂ and Zn₂SnO₄. The amount of zinc in the calcined material which dissolves into 2N HCl solution increases with increasing calcining temperature.

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Kaolinite mixed with 5 to 15wt% magnesia was fired at 1100°-1250°C and the phase transformation during firing was studied by powder X-ray diffraction analysis. The addition of MgO markedly promoted formation of mullite and cristobalite from kaolinite, and lowered their crystallization temperatures. In the samples containing 10 and 15wt% MgO, a large amount of Mg-Al spinel appeared with increasing firing temperature, and mullite decreased. Formation of the spinel increased the amount of isolated amorphous silica and promoted its crystallization. A quartz-like compound was formed at 1100°-1150°C and the cristobalite formed at 1150°-1250°C.

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A program for finding the unit-cell constants and the possible space groups of orthorhombic substances from X-ray powder diffraction data is presented. The program is written in N₈₈-BASIC. The program is based on the assumption that reflections with indices h00, hk0 and h0l exist in the observed diffraction lines. Trial unit-cell parameters a are obtained by assuming that all low-angle observed lines have indices h00. Then, the b and c parameters for a particular a parameter are derived by assuming that the observed lines have indices 0k0, 00l, hk0 or h0l. For each set of the a, b and c parameters thus obtained, 2θ_cal are calculated for various indices hkl and compared with 2θ_obs. Then, if all 2θ_obs up to the 20th line are explained in terms of 2θ_cal within given window widths ±Δ2θ, the a, b and c parameters are saved as a possible set of the unit-cell constants. After the above calculation, the systematic extinctions for the space groups belonging to the orthorhombic system are applied to the calculated reflections, and the unit cells with high reliability indices R are selected. Final unit-cell constants and possible space groups are obtained by least-squares refinement of the cell parameters and reexamination of the reliability indices using input data up to about 35th line. The reliability index R used in the program is given by R=(Number of observed reflections)/(Number of calculated reflections for a given space group), where the calculated reflections are those having essentially different d-values. Note that the above program includes a program which gives information concerning the presence of insufficient higher-angle diffraction lines, such as those produced by impurities or those having uncertainty in 2θ due to weak diffraction intensities.

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The permeation characteristics of water, methanol, benzene and heptane through six kinds of porous glass membranes with pore diameters of 4, 12, 50, 70, 100, 200nm were studied. For 4nm membranes, the liquid flow was different from Poiseuille flow and was affected by the pore wall. Further, the porous glass membranes were modified with trimethylchlorosilane (TMS) and propane sultone (PS). For 4nm membrane, high fluxes of hydrophobic and hydrophilic liquids were obtained for hydrophobic and hydrophilic surfaces, respectively. For example, the flux of liquid through the porous glass membrane modified with TMS was, in the decreasing order, heptane>benzene>methanol=water. This order corresponded with the results of measurement of contact angle.

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The dispersion of fine magnetic powders synthesized from metal alkoxides was studied. The powders were treated with an alkali, and then oleic ions were adsorped in sodium oleate aqueous solution. This as-wetted powders were dispersed in water or alkylnaphthalene containing a surfactant. It is concluded that;
(1) Fine particles below 10-15nm are required to prepare stable suspensions,
(2) To be fully adsorped with oleic ions, the powder synthesized have to be treated with an alkali,
(3) The surfactant more than 25wt% of the powder is repuired to disperse the powder,
(4) The effective surfactant is sodium oleate for water suspension medium and ethoxylated alcohol phosphate for alkylnaphthalene suspension medium.

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Reactions of niobium metal powder with high temperature-high pressure water were studied in an open system under the conditions of 300°-800°C, 10-100MPa and 3-72h. Niobium pentaoxide (Nb₂O₅), niobium hydride (NbH_x), and NbO₂ were obtained from niobium. Niobium changed into orthorhombic Nb₂O₅ and niobium hydride at 400°C under 100MPa for 3h. Only orthorhombic, or/and monoclinic Nb₂O₅ were obtained above 700°C under 100MPa for 3h. The formation of oxides and hydrides caused cracking on the surface above 400°C (100MPa, 3h) resulting in disintegration of grains above 500°C (100MPa, 3h). The partial crystal growth of Nb₂O₅ was observed above 700°C (100MPa, 3h). Temperature and reaction duration affected the hydrothermal oxidation of Nb metal, but pressure did not.

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The early stage of hydration of CaO⋅2Al₂O₃ was investigated. Hydration was carried out mainly in a diluted water suspension. The rate of hydration of CaO⋅2Al₂O₃ was greatly affectted by the water/solid ratio and the synthetic condition of specimen, while the mechanism of hydration remained unchanged under these conditions. In particular, formation of crystalline hydrates was retarded with increasing water/solid ratio. At the earliest period of hydration, the reaction rate was slow and hydrates were not found. It appears that this period corresponds to a nucleation stage of gibbsites. In the following period precipitation of gibbsite was observed, in which the concentrations of CaO and Al₂O₃ in the liquid increased rapidly, accompanied by an increase in CaO/Al₂O₃ molar ratio. In this period the reaction proceed by the dissolution-crystallization mechanism. Finally, different hydrates such as 2CaO⋅Al₂O₃⋅8H₂O began to precipitate and the rate of hydration was accelerated.

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Strain-induced tetragonal (t)→monoclinic martensitic transformation in ZrO₂ crystals has been effectively used for increasing toughness of oxide ceramic composites. The t-ZrO₂ crystal generally transforms to the monoclinic one at room temperature, and thus various experiments have been tried to decrease the spontaneous martensitic transformation temperature of ZrO₂ crystals. In the present experiment, stability of t-ZrO₂ crystals in Al₂O₃-ZrO₂ composites has been investigated by in situ experiments with a 3MV electron microscope as a function of the following four factors; (a) grain size of ZrO₂ crystals, (b) relative position of ZrO₂ particles in Al₂O₃ grains, (c) effect of additive elements, and (d) grain size of surrounding Al₂O₃ grains.

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Far infrared reflection spectra of complex perovskite-type ceramics, Ba (Zn_1/3Ta_2/3) O₃, Ba (Ni_1/3Ta_2/3) O₃ and Ba (Mn_1/3Ta_2/3) O₃, were measured in the frequency range between 100 and 4000cm^-1 at room temperature with a Fourier transform infrared spectrometer. The data were analyzed according to the Kramers-Kronig relation. The Q-values of these ceramics were discussed using the obtained dispersion parameters, and the reason was given why the former two ceramics showed better Q-values than the latter one. A possibility that the presence of other vibration-modes affecting the dielectric constants and Q-values of the materials in the frequency range below 100cm^-1 was discussed.

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The liquidus and eutectic temperatures in the system Ga₂O₃-Nd₂O₃ were measured from the cooling curves by the specular reflection method with a heliostat-type solar furnace. Quenched specimens from the melt were examined by X-ray diffractometry and chemical analysis. Four types of binary compounds were found to exist; garnet-type 3 Nd₂O₃⋅5Ga₂O₃, perovskitetype NdGaO₃, monoclinic 2Nd₂O₃⋅Ga₂O₃ and orthorhombic 3Nd₂O₃⋅Ga₂O₃. Except 3Nd₂O₃⋅Ga₂O₃, these binary compounds, showed no phase transition during repeated heating and cooling cycles. However, 3Nd₂O₃⋅Ga₂O₃ decomposed to Nd₂O₃ and 2Nd₂O₃⋅Ga₂O₃ at about 1500°C, which was detected with a high-temperature X-ray diffractometer. The lattice parameters of each compound are as follows; a₀=12.504Å for 3Nd₂O₃⋅5Ga₂O₃, a₀=5.411Å, b₀=5.490Å, c₀=7.708Å for NdGaO₃, a₀=7.739Å, b₀=10.899Å, c₀=11.562Å, β=108.901 for 2Nd₂O₃⋅Ga₂O₃ and a₀=11.537Å, b₀=5.573Å, c₀=9.182Å for 3Nd₂O₃⋅Ga₂O₃. The solidification points of 3Nd₂O₃⋅5Ga₂O₃, NdGaO₃ and 2Nd₂O₃⋅Ga₂O₃ are measured as 1640±20°C, 1670±20°C and 1704±20°C, respectively. The phase diagram shows eutectic points with the composition of 25, 45, 58 and 73mol% Nd₂O₃ at 1485°, 1600°, 1620° and 1650°C, respectively. Each cooling curve of Ga₂O₃, 3Nd₂O₃⋅5Ga₂O₃, NdGaO₃ and 2Nd₂O₃⋅Ga₂O₃ showed an exothermic peak which was assigned to the solidification point, while Nd₂O₃ showed two exothermic peaks corresponding to solid state phase transition and solidification. A high temperature phase diagram of the system Ga₂O₃-Nd₂O₃ has been presented.

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Effect of Al₂O₃ on the sintering of SrSiO₃ and (Sr_1-xBa_x)SiO₃(x≤0.2) ceramics was studied. Bulk densities, microstructures, chemical compositions and lattice constants of metasilicates were measured for the fired bodies. (1) An orthosilicate was formed as a precursor when an equimolor mixture of SrCO₃ and SiO₂ was heated above 700°C, and the orthosilicate and SiO₂ reacted to form a metasilicate at higher temperature. (2) The calcined powders of SrCO₃ and SiO₂ did not sinter at 1450°C. (3) Substitutional solid solutions were formed in the composition range (Sr_1-xBa_x)SiO₃(x≤0.2) at 1300°C. They did not sinter like SrSiO₃ powders. (4) When 3-5wt% of Al₂O₃ was added, the powder of (Sr_1-xBa_x)SiO₃(0≤x≤0.1) densified rapidly at about 1300°C. A glassy phase was formed at grain boundaries. (5) The average chemical composition of this glassy phase was 2 (Sr, Ba)O⋅2SiO₂⋅Al₂O₃ and that of the crystalline phase was (Sr, Ba)O⋅SiO₂. (6) When Al₂O₃ was added, the sintering temperature decreased with increasing BaO content. The BaO content in the metasilicate crystal was less than that expected from the mixing ratio indicating that BaO was concentrated at the glassy phase preferentially.

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Hydrolysis and polycondensation of Al and Si alkoxides are controlled to design a mullite precursor. Infrared spectroscopy, powder X-ray diffraction, transmission electron microscopy comfirmed that the mullite precursor prepared by this method is in the stoichiometric Al₂O₃/SiO₂ ratio and is more homogeneous than powders prepared by the hydrolysis of Al and Si mixed alkoxides. The mullite precursor was found to crystallize into mullite via Al, Si-spinel above 900°C, and ultra-fine mullite powders with 6-11nm particle size was obtained at 1100°C.

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A detailed comparison of the electrical properties between β-type and γ-type manganese (IV) oxides is presented on high-purity samples. Thermal stability of MnO₂ in terms of its transition to Mn₂O₃ was examined by TG and β-type was found to be more stable the γ-type. The temperature dependence of Seebeck coeffecient and resistivity was measured. The effect of annealing temperature on the resistivity was also studied. Both β- and γ-MnO₂ showed n-type semiconduction, but the differences found were: (1) β-type showed higher conductivity than γ-type; (2) The temperature dependence of resistivity for β-MnO₂ was smaller than that of γ-MnO₂; (3) Resistivity at 100°C showed a “U” shape relation with annealing temperature for γ-MnO₂, while it increased monotonically with increasing annealing temperature for β-MnO₂. These differences were explained by the distinctions in crystal structure based on a hopping conduction model. β-type is built up with MnO₆ octahedron chains having 1×1 tunnels and shows high electrical conductivity. γ-type has the intergrowth structure of β-type and groutite containing 1×1 and 1×2 tunnels, and has low electrical conductivity. Annealing of γ-MnO₂ at high temperature shifts 1×2 tuunels to 1×1 tunnels, and the structure approaches β-type. This structural change was explained to be responsible for the “U” shape relation between resistivity and annealing temperature.

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Highly dispersed tetragonal or cubic zirconia solid solution hydrosols composed of ultrafine particles were prepared by aging coprecipitated hydroxides both of Zr-Y and Zr-Ca below 200°C for a long duration. In ZrO₂-Y₂O₃ system, 10-30mol% Y₂O₃ solid solutions crystallized easily at 97°C for 5 days. The solid solution particles with cubic shape of 60-120Å formed, when 10mol% Y₂O₃ was added. The solid solutions in the ZrO₂-CaO system were also obtained at 150°C for 3 days. When the coprecipitated hydroxides containing 0-20mol% CaO was washed by saturated Ca(OH)₂ solution before aging, the produced solid solution contained 15.3-18.8mol% CaO and they were composed of spherical particles of 30-60Å. Translucent thin films of cubic zirconia, both of ZrO₂-Y₂O₃ and ZrO₂-CaO solid solutions, were obtained and they were composed of grains of 1-4μm after firing at 1350°C for 30min.

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Mechanical properties of SiO₂-Al₂O₃ ceramics were studied in relation to the chemical composition. Raw powders of the composition ranging from 60 to 78wt% Al₂O₃ were synthesized by the spray pyrolysis method and sintered at 1650°C for 4h. The room temperature flexural strength and fracture toughness of the specimens showed no significant difference with the composition ranging from 66 to 78wt% Al₂O₃. But for the SiO₂-rich specimens containing less than 66wt% Al₂O₃, those values decreased slightly. For the Al₂O₃-rich specimens which contain no glassy phase, the high-temperature strength and fracture toughness decreased gradually with increasing temperature. In contrast, the strength and the K_IC of the specimens containing both mullite and a glassy phases increased with increasing silica content and increasing temperature up to 1300°C. While the flexural strength decreased drastically at 1400°C. The maximum fracture strength at high temperature depends on both chemical composition and the amount of grain boundary glassy phase. The increase in strength and fracture toughness for the SiO₂-rich specimens at high temperatures is explained in terms of stress relaxation and/or crack healing in the grain boundary glassy phase, and pull out of acicular mullite grains due to decrease in viscosity of the glassy phase, respectively.

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The formation and structure of spinel solid solutions were studied in the system Li₂O-MO-GeO₂ (M=Zn, Go, Ni). Specimens were prepared by calcining mixtures of zinc, cobalt and germanium oxides, lithium and nickel carbonates at 950°C for 16h, and were analyzed by X-ray powder diffraction diagrams and visible reflectance spectra. The crystal structure of Li₂O⋅MO⋅3GeO₂ (M=Zn, Go, Ni) was refined by the pattern fitting method for X-ray powder diffraction.
(1) Spinel solid solutions with superstructure are obtained over the whole region of Li₂O-(1-x-y)ZnO-xCoO-yNiO-3GeO₂ system.
(2) The structure of Li₂O⋅MO⋅3GeO₂ (M=Zn, Co, Ni) is cubic, with the space group P4₃32 and Z=4. These compounds have the cell dimensions: a=8.193Å (M=Zn), 8.204Å (M=Co), 8.181Å (M=Ni). The cation distribution of Li₂O⋅MO⋅3GeO₂ (M=Zn, Co) is nearly Li_0.5M_0.5 [Li_0.5Ge_1.5] O₄, while that of Li₂O⋅NiO⋅3GeO₂ is nearly Li [Ni_0.5Ge_1.5] O₄. The octahedral site cations have 1:3 order. As Ni²⁺ content increases, Ni²⁺ ions occupy octahedral sites and Li⁺ ions migrate from octahedral to tetrahedral sites. The intensities of superlattice lines decrease because of decrease in the difference of atomic scattering factor between octahedral site cation. The sizes of two kinds of octahedra depend on the ionic radii of central cation.
(3) Reflectance spectra show the typical absorption of 4-coordinated Co²⁺ ion and 6-coordinated Ni²⁺ ion.

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Large single crystals of Ba-Al-priderite (BATO) and K-Zn-priderite (KZTO) which are characterized by the one-dimensional tunnel structure with the hollandite type were grown by the floating zone (FZ) method. The chemical compositions, lattice parameters and melting temperatures of the obtained crystals are determined. BATO crystals melt congruently at 1510°C±10°C with a Ba_1.18Al_2.36Ti_5.64O₁₆ composition, and KZTO crystals at 1388°±10°C with a K_1.56Zn_0.75Ti_7.25O₁₆ composition. The frequency-dependence of complex ionic conductivities for BATO and KZTO single crystals was measured at room temperature. The BATO indicates complex behavior of a mixed conduction. The electronic conduction is predominant below 100Hz, but the ionic conduction becomes gradually predominant above 100Hz. The ac ionic conductivities of BATO and KZTO at 100kHz are 9.2×10^-4S·cm^-1 and 2.4×10^-3S·cm^-1, respectively.

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Effects of additives on the thermal conductivity and electrical resistivity of SiC ceramics prepared by pressureless sintering were studied. α-SiC powder with an average particle size of 0.5μm was treated with HF+HNO₃. Additions of 2wt% BeO, 0.2-0.4wt% B₄C and 0.2-0.3wt% C to SiC powder gave 92-95% of the theoretical density of SiC after sintering at 2200°C for 0.5h in an argon atmosphere. The highest values of the electrical resistivity and the thermal conductivity at 25°C of dense SiC ceramics were 5×10¹²Ω·cm and 140W/m·K, respectively. Electrical resistivities and thermal conductivities of SiC ceramics depend on to the amount of additives.

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Mixtures of β-tricalcium phosphate (β-TCP) and zirconia containing 0, 2, 3, 4 and 8mol% Y₂O₃ were hot-pressed for 10min at 1300°C-1400°C and 20MPa, and the mechanical properties (bending strength, fracture toughness, Vickers hardness and modulus of elasticity) of the hot-pressed bodies were measured. The zirconia content was up to 50vol%. The obtained ceramics consisted of β-TCP and zirconia. The above-mentioned mechanical properties increased with increasing zirconia content. Zirconia containing 2 and 3mol% Y₂O₃ (TZ-2Y and TZ-3Y) gave better results than other zirconias. Ceramics containing 50vol% zirconia (TZ-2Y or TZ-3Y) fired at 1350° and 1400°C had a bending strength of about 440MPa and a fracture toughness of about 2.7MPa·m^1/2. These values were two or three times as large as those of β-TCP monolithic compacts.

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Hydroxyapatite fine powders prepared from (NH₄)₂HPO₄ and Ca(NO₃)₂ by a wet method were treated under hydrothermal conditions at 200°C under 2MPa for 10h. The obtained single-crystal fine powders of 90nm×25nm were sintered in air at a temperature from 1000° to 1100°C for 3h. The obtained ceramics with relative densities of 73±2% (1000°C)-92±2% (1100°C) were HIP'ed at 1000°C under 200MPa of Ar for 1h without any capsules. The post-sintering brought about densification up to 99% for the samples more than 90% dense having closed pores, but it barely increased the density of samples with lower densities. Transparent apatite ceramics were obtained by HIP.

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