The stability of the superconducting phase of Ba₂EuCu₃O_7-x was studied under various humid atmospheres at 25°C by XRD, SEM and EPMA. The superconducting oxide completely disintegrated within 1400h above 80% RH, while it remained stable for a long time below 60% RH. The superconducting oxide would disintegrate by forming BaCO₃ via Ba(OH)₂ above 80% RH. It formed only a small amount of precipitate which was considered to be BaCU(OH)₄ below 60% RH.

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Mg(OH)₂ particles of hexagonal plate and prism are prepared by hydration of magnesia clinker in magnesium salt solution. The hydration mechanism of magnesia was investigated by measuring reaction rates and SEM observations. The hydration rate was proportional to the surface area of MgO particles, suggesting that the reaction proceeds by the dissolution of MgO particles followed by the precipitation of Mg(OH)₂ and that the dissolution was rate-controlling. In Mg(CH₃COO)₂ system, the reaction was divided roughly into two stages. The rate of the first stage was about half that of the second stage. MgO surface was covered with dense Mg(OH)₂ layer during the first stage. At the second stage, however, Mg(OH)₂ layer peeled off from MgO surface. These results suggested that the rate-controlling mechanism in the dissolution of MgO was diffusion through the product layer of Mg(OH)₂ at the first stage, and surface reaction at the second stage. In MgCl₂ system, the rate remained constant only in a short period and decreased gradually with reaction time. Mg(OH)₂ films on MgO were observed as in Mg(CH₃COO)₂ system, though it did not peel off completely. Hence, this product layer prevented MgO from dissolution and limited the rate in MgCl₂ system.

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Effect of IIIa oxide additives on bending strength and micro-structure of mullite ceramics produced using two different kinds of powders were investigated. For the mullite powder produced by the arc-melting method, the maximum bending strength of 250MPa at room temperature was obtained with addition of 5.5mol% Y₂O₃, and no degradation of strength was observed at 1200°C. Y₂SiO₅ was detected at grain boundaries by TEM observation, and this seemed to be the cause for the high strength at high temperatures. For the mullite powder produced by the sol-gel method, on the other hand, no effect of Y₂O₃ addition on the bending strength was observed.

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Defect frozen phenomenon in hydrogenated amorphous silicon (a-Si: H) was investigated with studying temperature dependence of dc conductivity and excess heat capacity in samples which were cooled at various cooling rates from a thermal equilibrium state kept at 250°C for 1h. Differential scanning calorimetry (DSC) studies of P-doped a-Si: H show the behavior governed by relaxation of defect frozen state which is characterized by the equilibrium temperature T_E. The T_E detected by DSC agrees with the one determined by the temperature dependence of dc conductivity. The temperature dependence of excess heat capacity is successfully interpreted by a simulation based on the model of defect specific heat which is caused by the relaxation process of defect frozen states. The temperature dependence of dc conductivity above T_E is characterized by the activation energy E_a. The experimental relation between T_E and E_a in P-doped and compensated a-Si: H was discussed semi-quantitatively on the basis of a model for frozen defect states. It is suggested that a large amount of D⁰ (neutral dangling bond state) in the compensated sample plays an important role in the relaxation phenomena of defect frozen states.

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As barium titanate series dielctric ceramics is ferroelecricity, the decline of the capacitance occurred caused in applying high voltage by the material's characteristics of voltage dependent. It was already reported that a present material, which had been developed from (Sr, Ba)TiO₃ series ceramics, had a high dielectric constant and moreover is little under the influence of its voltage dependent characteristics. However, for the CRT circuit, etc. operated by DC high voltage, it has been required that the capacitor material have not to be at all under the influence of voltage dependent characteristic, or rather enhance capacitance in applying voltage. Completing the requirement, a new material from (Sr, Ca, Pb)TiO₃ series ceramics was developed. The explanation of the author's fundamental way of thinking in developing the new material, and the study on the electric characteristics and the microstructure of the material, are discussed in this paper.

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Joining of SiC ceramics by active metal brazing method was studied. Sintered bodies of TiC, Ti₅Si₃ and Ti₃SiC₂, which have been reported to be the reaction products between SiC and active metal Ti, were fabricated. Some properties for these products, i.e., microhardness, four point bending strength and thermal expansion coefficient, were investigated. Their influences on the joining strength were discussed: the formation of Ti₅Si₃ is thought to be undesirable as a reaction product due to its weakness, and the large difference of thermal expansion coefficients between the reaction products and SiC, which means that the thicker the reaction layer grows, the larger the residual thermal stress develops. Some possibilities for the good wettability of Ag-Cu-2% Ti braze to SiC were discussed, while Ag-Cu braze did not wet. The wetting behavior of Ag-Cu and Ag-Cu-2% Ti alloys on SiC and the reaction products mentioned above was investigated by the sessile drop method. The variations of their contact angles as a function of temperature were observed, which showed the same behaviors on SiC and the reaction products, respectively. These results are thought to mean that the phenomenon that Ti promotes the wetting of Ag-Cu-2% Ti alloy on SiC does not depend on reaction products, but on adsorption.

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Fracture toughness (K_IC) of polycrystalline silicon carbide and alumina was evaluated using a single edge precracked beam (SEPB) technique. A Knoop indentation-induced microcrack was introduced into a specimen, and then a sharp pop-in precrack was followed by appling the bridge indentation method The relative precrack length (a/W) was varied by changing the indentation load (20, 30, 50kgf) and/or the width of support groove (4, 5, 6mm). The precracked specimens were fractured by three-point bending under a cross-head speed of 0.5mm/min at room temperature. K_IC values decreased with the increase in the indentation load in the range of 0.2<a/W<0.8 for silicon carbide and a/W<0.35 for alumina, respectively. The indentation load dependence on the K_IC values was discussed from the residual stress around the indentation-induced crack and the crack mouth opening displacement (CMOD) of SEPB specimens.

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Electro-conductive Si₃N₄ bonded ZrN ceramics with 15-30% porosity were produced by sintering green compacts of Si and ZrN powders in nitrogen gas atmosphere. Si and ZrN powders were mixed and molded using thermoplastic resin binder. The amount of ZrN was varied from 20 to 70vol%. The green bodies were dewaxed and sintered in the 0.88MPa nitrogen gas atmosphere. Si particles changed into Si₃N₄ and the Si₃N₄ connected ZrN particles in the green compacts. The dimensional change in sintering stage was under 0.2% for each sample. The ceramics containing 20vol% of ZrN showed electrical resistivity of 1×10^-3Ω·m, bending strength of 370MPa and a thermal expansion coefficient of 3.4×10^-6°C^-1. A lower electrical resistivity of 9×10^-6Ω·m was obtained when ZrN content was 70vol%, but its bending strength was decreased to 120MPa.

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Fibrous II-gypsum anhydride was synthesized without destroying fibrous form in dehydration (heating at 700°-800°C) of fibrous gypsum hemihydrate as the reaction product of CaSO₄-CH₃OH-H₂O system in our previous paper. Direct preparation of fibrous II-gypsum anhydride was studied by removing methanol rapidly from organogel of gypsum, which was deposited as the precipitate CaSO₄ nucleus aggregated with CH₃OH molecules by the reaction CaCl₂-H₂SO₄ system in methanol. Gelatinous conditions of the organogel and characteristics of fibrous II-gypsum anhydride were investigated by means of X-ray diffraction, thermal analysis (TG-DTA), scanning electron microscopic observation and dissolution test, The organogel was deposited by adding calcium chloride of 0.090mol dm^-3 to sulfuric acid of 0.023-1.126mol dm_-3, which were previously dissolved in 99.6% methanol. The water content in initial solutions, temperature, aging time and concentration of sulfuric acid in excess to equivalence for formation of gypsum, effected remarkably the formation area of fibrous II-gypsum anhydride in the further crystallization process. For an example, gypsum dihydrate with prismoidal or platy crystals crystallized by removing methanol from the gel which deposited in excess sulfuric acid of less than 0.05mol dm^-3 after aging for 5h at temperature below 15°C. Whereas, the fibrous II-gypsum anhydride with an aspect ratio of larger than 100 (diameter 0.15μm, length 15-30μm) was obtained under the following gelatinous conditions, water content of below 1% in the both initial solutions, temperature range of 30°-40°C, excess sulfuric acid of 0.095mol dm^-3 and aging time for 40-72h, The X-ray diffraction pattern of the fibrous II-gypsum anhydride showed strong orientation by rapid crystal growth of (020) and (002) planes. Its solubility at 20°C was 0.20g CaSO₄/100cm³ H₂O after 30 days.

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The effects of carrier concentration on the electrical resistivity and electrical barrier height at grain boundaries in SiC ceramics with BeO addition are described. The carrier concentration of the SiC ceramics was controlled by the doping of nitrogen of Si₃N₄ as a donor or aluminum of Al₂O₃ as an acceptor. The barrier height and the electrical resistivity of the SiC ceramics with grains of p-type conduction are higher than those with grains of n-type conduction by 0.3-0.6eV in the barrier height and the factor of 10-10⁵ in the electrical resistivity. In p-type conduction, the barrier height and the electrical resistivity decrease steeply at the carrier concentration above -10¹⁸ cm^-3 in SiC grains. These phenomena are explained by the filling of trapping levels in the grain boundaries with the carriers with increase of the carrier concentration in the SiC grains.

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Fine powders of diopside, CaMgSi₂O₆, were prepared by the spray pyrolysis method. Ca(NO₃)₂4H₂O, Mg(NO₃)₂6H₂O and Si (OC₂H₅)₄ were dissolved into ethanol and refluxed under various time-temperature conditions before pyrolysis. Refluxing at 70°C for 1 day was necessary to prepare homogeneously mixed diopside precursor powders. Spray pyrolysis was made between 800° and 1000°C under the following conditions: volume of flowing solution, 2 to 15ml/min, volume of flowing air, 2 to 15l/min, and concentration of solution, 0.05 to 0.33mol/l. Almost all powder particles were hollow spheres of a few micron meter, which were composed of fine primary particles of submicron or less. These powders were calcined at 1000°C and sintered at 1275° to 1350°C after ground with a vibration mill. Relative densities up to 97.4% were achieved by firing at 1300°C for 1h without additives. This specimen showed dielectric losses much lower than those sintered with additives reported before.

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The residual stress of metal to ceramic laminates (Al₂O₃/Nb, Y₂O₃/Nb, stabilized ZrO₂/Nb) produced by solid state bonding was studied. Two typical models, disk coated on one side with different materials and disk coated on both sides were chosen for finite element method (FEM) analysis. The results indicated that the dimensionless residual stress at the ceramic coating decreases with increasing the coating thickness ratio, h_c/h_s, and the elastic modulus ratio, (1-μ_s)E_c/((1-μ_c)E_s). The four point bending strength at room temperature for sintered ceramics (Al₂O₃, Y₂O₃, stabilized ZrO₂) enabled us to estimate critical heating temperature for ceramics coating from the analysis of residual stress described above.

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The behavior of Nd³⁺ ions in aluminophosphate glasses was investigated by spectrophotometry, scanning electron microscopy, energy dispersive X-ray spectroscopy, wavelength dispersive X-ray spectroscopy and X-ray powder diffraction analysis. It is shown that (1), the crystallization of NdAlO₃ with simple cubic structure having a₀=3.744Å occurred in the glass-forming process; (2), The values of J-O parameters Ω_t(t=2, 4, 6) were an order of magnitude smaller than those in an ordinary phosphate glass; and, (3), Addition of NdAlO₃ powder to potassium aluminometaphosphate glass gave a fluorescence lifetime at 1.06μm wavelength, longer than that of the same mother glass containing Nd₂O₃.

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The uniazial compression was applied with a hot press apparatus for the partially sintered preforms with three chemical compositions, 3mol% Y₂O₃-ZrO₂ (TZ-3 Y), 6mol% Y₂O₃-ZrO₂ (TZ-6 Y), and 8mol% Y₂O₃-ZrO₂ (TZ-8 Y). The change in size was measured after pressing. Obviously, the densification occurred below 1350°C and superplastic defomation appeared mainly over 1350°C. The grain size at 1500°C was 2μm in TZ-8 Y in comparison with 0.4μm in TZ-3 Y. TZ-6 Y and TZ-8 Y had a porosity of 5-15% because of the rapid grain growth. Consequently, small bending strengths in the range of 20-30kgf/mm² were obtained. In TZ-3 Y, the compressive deformation gave a rapid increase in strength up to 140kgf/mm². But the strength decreased above 1450°C, due to the formation of R-phase, by Kitano et al. (1987).

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A computer program is presented for finding the unit-cell constants for a crystal phase from X-ray powder data containing multi-phase diffraction lines. Input data are observed diffraction angles, 2θ_obs (or d-values), allowable errors in diffraction angles, Δ2θ, approximate unit-cell constants and space group (or lattice type). The procedure of the program is as follows:
(1) Five consecutive low-angle lines are selected by using the input cell constants and the space group (or lattice type).
(2) Trial unit-cell constants are obtained from the first 35 lines by using the algorithms given by Takaki et al. [Yogyo-Kyokai-Shi, 95, 610 (1987), Seramikkusu Ronbunshi, 96, 13 (1988)].
(3) For each of the trial cell constants, diffraction angles are calculated and compared with observed ones. Then, number of indexed lines N and the reliability index R for the trial unit cell are calculated.
(4) After the calculation, the 10 sets of the unit-cell constants having largest values of N×R are selected. The user can obtain the most suitable unit-cell constants comparing the values of N, R, and NÅR.
The reliability index R is given by R=100Å(Number of observed reflections)/(Number of all calculated reflections), where the observed reflections are those belonging to the observed lines within window widths, ±Δ2θ. The program is written in N₈₈-BASIC.

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A sintering model in which sintering occurs at necks between edges and faces of polyhedral particles has been proposed. Kinetic equations for densification derived from this model indicate 1/4 power dependence of time for sintering controlled by the grain boundary diffusion mechanism, and the obtained shrinkage data of Al₂O₃ compacts were best fitted by these equations. Furthermore, satisfactory agreement was found between theoretical and experimental specific surface areas.

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