Spherical and narrow-size lead zirconium titanate (PZT) powders (average diameter: 0.39μm) were prepared by ultrasonic spray pyrolysis of a mixed solution of lead-iso-propoxide, zirconium-buthoxide and titanium-iso-propoxide or lead-acetate, zirconium-buthoxide and titanium-iso-propoxide. From EDX measurement each particle in PZT powders had very little compositional fluctuation. In this process, the homogeneity of Ti, Zr and Pb in PZT precursor particles plays an important role in the formation of homogeneous PZT powders. Inhomogeneity of PbO in PZT precursors resulted in evaporation of PbO from the surface of the precursor on calcination in air. As a result, less PbO in the precursor caused formation of PZT having less Zr and coexistence of ZrO₂ in the particles. Using metal alkoxides as a source of PZT and refluxing starting solutions result in good compositional homogeneity in each PZT particle.

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A water suspension including ultra-fine particles of (Sn, Sb) oxide precursor was prepared by sol-gel process. TEM observation of a dried sample of the suspension at room temperature showed that primary (crystalline) particles with an average diameter of 2-3nm and aggregate particles of about 50nm were formed. A composite which was prepared by firing a dried mixed sample of the suspension and a fine glass powder showed higher electrical conductivity even by relative low temperature (1100°-1200°C) firing than in the case of conventional composite having larger semiconductive particles of about 2-3μm in diameter.

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The Ge, Ag and Br EXAFS spectra were measured for 40AgBr⋅30Ag₂O⋅30GeO₂ glass by using synchrotron radiation. The average Ge-O distance was estimated to be 1.77Å using low-quartz type GeO₂ crystals (Ge-O=1.74Å with 4-fold coordination) as a reference sample. It is concluded that the coordination geometry of the Ge⁴⁺ ions in the glass is primarily tetrahedral. Using Ag₂O(Ag-O=2.05Å with 2-fold coordination) and AgBr (Ag-Br=2.89Å with 6-fold coordination) crystals as reference samples, average Ag-O and Ag-Br distances were estimated from the direct comparison of peak positions on the |F(r)| curves to be 2.17 and 2.63Å, respectively. The Ag-O atomic distance suggests that a part of Ag⁺ ions locate near polygermanate anions which mainly consisted of GeO₄ tetrahedra. The Br-Ag distance was estimated to be 2.76Å by the curve fitting method using AgBr crystals as a reference sample. The Br-Ag distance obtained from the Br EXAFS analysis seems to be more reliable than the Ag-Br distance obtained from the Ag EXAFS analysis, because the former was analyzed by the curve fitting method. It is concluded on the basis of ionic radii of Br^- and Ag⁺ ions that the rest of Ag⁺ ions probably occupy the tetrahedral site surrounded by four Br^- ions. Since the coordination of these Ag⁺ ions is similar to that of Ag⁺ ions in α-AgI crystals which show ionic conductivity, the Ag⁺ ions of this type seem to contribute to the ionic conduction.

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Phase changes in Mn-Co-Ni oxide in firing process for making thermistor materials were investigated in different atmospheres in the temperature range from 1000° to 1400°C. The starting oxide was prepared from a mixture of Mn, Co ana Ni nitrates with molar ratio of 3.0:1.9:1.1 by calcining at 1000°C for three hours in air. The fired samples employed in this study were obtained by quenching them in water after firing the starting oxide at a desired temperature between 1000° and 1400°C for one hour in different atmospheres of oxygen, air and nitrogen. In the X-ray diffraction analysis, changes in diffraction pattern due to the phase separation and phase transition were observed in each firing atmosphere. In air, the cubic spinel at 1000°C changed to a mixed crystal phase composed of tetragonal spinel and rock salt at 1160°C. Similar crystal phase changes were observed in both oxygen and nitrogen atmospheres. However, the temperatures of crystal phase change were dependent on the concentration of oxygen in the firing atmosphere. In oxygen, the temperature of crystal phase change increased to 1240°C. In nitrogen, on the other hand, the crystal phase change occurred at lower temperature than in air. On the basis of these results, a phase diagram of Mn-Co-Ni oxide with molar ratio of 3.0:1.9:1.1 was proposed, in which the temperature of crystal phase change is correlated with the concentration of oxygen.

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Influence of structural homogeneity of CIP-ed compacts on mechanical properties of sintered silicon carbide was investigated at the applying pressure from 100 to 700MPa. Structural homogeneity decreased with increasing pressure up to 500MPa. A compact at 700MPa showed a duplicate structure consisted of homogeneous innner parts and a surface layer with high density. Flexural strength of thin sintered plates degradated with decreasing structural homogeneity. On the contrary, the average strength of thick sintered cylinders was almost constant irrespective of the pressure. Weibull modules of the cylinders decreased with decreasing homogeneity. At 700MPa, the duplicate structure of compacts was retained in the sintered boody, resulting in the two step Weibull plot corresponding to the high-strength surface layer and the low-strength inner parts. By removing of the inhomogeneous surface layer before sintering, Weibull modulus was improved twice at 700MPa, while it was not improved at 100MPa, where the homogeneity was not improved by the removal. The highest strength and Weibull modulus were obtained for the sintered body prepared from the most homogeneous compacts with the highest green density (Pressure: 700MPa, with the surface layer removed). Fracture toughness, grain size and grain shape were not influenced by the pressure for the sintered density higher than 94%. However, there were internal defects, interconnected pores. The size of defects estimated from the mechanical properties was in the range of the size of internal defects. Temperature dependence of the maximum pore size indicated that pores grew extensively during sintering at lower applying pressure, while they were diminished at higher pressure. High CIP-ing pressure was effective to realize highly dense and homogeneous structure of sintered bodies by suppressing the inhomogeneous pore growth. Thus, the prevention of internal defects improves Weibull modulus.

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The major mineral compositions of Amakusa pottery stone are quartz, sericite and kaolin mineral. The refinement of the low-grade of Amakusa pottery stone has been required because of the recent shortage of the resources of high-grade one. This paper concerns an optimum hydrothermal condition to refine the low-grade Amakusa pottery stone of which impurities are feldspar, limonite, siderite and calcite. The results obtained are as follows:
(1) Feldspar included in the sample is converted into kaolin mineral with 0.5wt% HCl solution at the temperature below 200°C and about 15atm. The formation of kaolin mineral is observed to be increased with increases in volume of the solution, temperature, and the treatment time.
(2) Conversion of the feldspar into the kaolin mineral is promorted by adding aluminium chloride under the condition concerned. At the temperature lower than 180°C, no formation of kaolin mineral is observed. Aluminum chloride is considered to supply the insufficient alumium during the conversion of feldspar to kaolin mineral.
(3) A product having SK value higher than 26 and Fe₂O₃ content lower than 0.4wt% is obtained from a raw material with SK value less than 15 by the hydrothermal treatment.
(4) A plasticity index of a product is measured with the Pfefferkorn method to be higher than that of a raw material.
(5) The refined pottery stone obtained in the present study has smaller green strength and higher firing shrinkage than those of common Amakusa pottery clay. This is considered to be due to the difference of its surface state from that of a raw material.

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Ceramics with high-strength and low-thermal-expansion-coefficient was prepared from (ZrO)₂P₂O₇. Overfiring reduced the strength, because the extensive grain growth developed microcracks due to the thermal expansion anisotropy of the crystal. The effects of additives on the densification and grain growth were studied at high temperature. Above 1500°C, the densification was promoted by adding TiO₂. The maximum strength of this ceramic was about 50MPa. SiO₂ was effective in suppressing grain growth responsible for the microcracking. Thus, a ceramic which has a strength of 150MPa was obtained by adding SiO₂ together with sintering aid such as MgO and Nb₂O₅ even after firing at 1500°C. Composites in the system (ZrO)₂P₂O₇-ZrSiO₄ with TiO₂ additive had the strength of 200MPa and thermal expansion coefficient from 1.7 to 4.0×10^-6/°C.

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Thin films of superconductor Ba₂YCu₃O_7-δ (BYCO) were prepared on the yttria-stabilized zirconia substrates by the dipping-pyrolysis process using metal naphthenates and acetylacetonates as starting materials. Barium, yttrium and copper naphthenates and acetylacetonates, with molar ratios of (A) Ba:Y:Cu=2:1:3 and (B) 3:1:4.3, were dissolved in toluene and a mixture of pyridine and propionic acid, respectively, to make homogeneous solutions. After dipping, drying and preheating at 500°C were repeated 10-20 times, final heat treatment at 950°-970°C in O₂ gave 5-10μm thick BYCO films, which showed superconduction at T_{c, zero} of 89-91K. Results of scanning electron microscopy and X-ray diffraction analysis showed dense textures of orthorhombic BYCO grains.

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In the previous paper, sliding wear properties of oxide ceramics was evaluted using an indentation fracture model in which the effect of roughness at the frictional surface was assessed. This model was tested for non-oxide ceramics at various vertical load, and the transition of wear properties was studied with a pin-on-disk tester using SiC, Al₂O₃ and ZrO₂ as pin, and SiC, Si₃N₄ and Al₂O₃ as disk. Wear increased by more than ten times depending on the combination of pin and disk materials. When the frictional surface was smoothed by the increased vertical load, the wear was independent of the load. To explain this phenomenon, an equation was derived to estimate quantitatively the effect of a roughness at the frictional surface on wear. Hence, the wear transition was estimated for the sliding surface, of which roughness depends on the vertical load. However, the effect of material combination on the wear was not able to be explained by this equation completely. This result suggested that the transition of wear by material combination was took place by the changed wear mechanism.

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Preparation of porous substrates (discs) of La_0.6Sr_0.4CoO₃ (LSCO) was investigated as a part of the study on an oxygen semipermeable device based on mixed conductive perovskite-type oxides. Of the several methods attempted, sintering of compacts of an LSCO powder-methylcellulose (MC) mixture and an LSCO-carbon fiber (CF) mixture gave discs with irregular macro-pores which tended to grow parallel to the disc surface or with straight penetrating channels with a uniform diameter, respectively. However, none of them exhibited sufficiently large (physical) air permeability. On the other hand, sintering of a compact of LSCO powder was far more effective if an adequate starting powder was chosen. Thus, when the LSCO powder calcined at 1400°C (LSCO (1400)) with the particle size larger than 10μm was used, the disc sintered at 1400°C showed high air permeability through penetrating channels consisting of a network of intergranular pores. Furthermore, when LSCO (1400) powder was sieved to 44-74μm, the sintered disc had uniform-sized open pores with a diameter of 20 to 30μm, which provided porous structure resistant to heat treatment and high permeability of air. The disc appeared to be suitable as a porous support on which thin membrane of oxygen semipermeable perovskite-type oxides was formed.

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Pure fine-grained barium titanate powder with a particle size of 0.1μm was sintered by the HIP (Hot Isostatic Pressing) method using a platinum capsule. HIP is an effective process for sintering barium titanate for reducing the sintering temperature and grain size. The densification proceeded at the HIP temperature 800°C under the pressure of 500MPa. The HIP sintered fine-grained barium titanate exhibited a lower dielectric constant and broader temperature characteristics at the Curie point (T_c) than that for a normal-sintered sample. A close relationship was obtained between the dielectric constant and the HIP treatment temperature. With lowering the HIP treatment temperature or time, both the dielectric constant and the peak temperature of the dielectric constant decreased. The grain size of the samples ranged under 1μm, much smaller than that of the normal-sintered samples.

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Raw mixtures have been prepared from raw materials of fly ash, slaked lime and type III-gypsum dehydrated at 200°C. The fly ash and the gypsum were supplied from a steam power station. Fine particles under 30μm of the fly ash were collected by a cyclone. The bulk density of the fly ash is 0.97g/cm³. The content of gypsum was varied from 10 to 50wt% as CaSO₄⋅2H₂O with the variation of gypsum/lime molar ratio from 0.1 to 1.0. Slip cast technique into 2×2×8cm moulds was performed using slurry of W/S 0.60. Hardened green bodies demoulded after 10-20min were precured at room temperature for 30min measured from the flooding point of time. Then the steam curing was carried out at 80°C and 90% R. H. for 23.5h. Test pieces thus obtained were subjected to three-point flexural and compressive resistance tests. Flexural strength, 1-3MPa and compressive strength, 2-9MPa were reached. Increasing content of the fly ash makes the strength weak. High strength is obtained in compositional range of 20-60wt% of fly ash. The bulk density of the products is 0.97-1.17g/cm³. Although the porous materials have water absorption property, they show the water resistance and machinable properties. Therefore, the present steam-cured porous hardened bodies of low density will be suitable for the sound and heat insulating materials. Besides those of high strength may be applicable to the constructive materials as well.

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Metallization of Al₂O₃ ceramic by low pressure plasma-spraying (LPPS) was studied for ceramic/metal bonding applications. Metal coating by LPPS had the same phase as the starting powder, but was porous and 80-85% dense. The adhesion strength of the coating depended upon the surface roughness of the ceramic substrates and the strength of 50MPa was attained by blasting at 3.5kg/cm² for 1min. Metallized substrates were brazed and the bonding strength was evaluated using a 4-point bending test. Bending strength of the test piece was about 30MPa. EPMA detected no reaction layer between the coating and substrate.

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Electrical conductivities of molten Li₂O-SiO₂ and K₂O-SiO₂ glasses was measured by the four-electrode method and bridge method with alternating current. For the four-electrode method, the resistances measured at the frequencies in the range of 1 to 5kHz were a constant value, but those at frequencies higher than 7kHz increased with increasing frequency. On the other hand, the resistances measured by the bridge method decreased with increasing frequency. The electrical conductivities calculated from the resistances below 5kHz for the four-electrode method agreed with those calculated from the resistance obtained by extrapolating to the infinitely high frequency for the bridge method. The four-electrode method was considered to be better than the bridge method for measuring the electrical conductivity of molten glasses with high specific conductivities.

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Static leach tests were carried out on a nuclear waste glass (SRL-165) at two different SA/V-ratios of 0.85cm^-1 and 0.079cm^-1 at 90°C. Fourier transform infra-red reflection spectroscopy revealed that Fe tended to precipitate on the surface of the glass when leached at 0.079cm^-1, 90°C for more than 14 days. X-ray photoelectron spectroscopy indicated that Fe which precipitated on the specimen surface was a mixture of Fe²⁺ and Fe³⁺; the ratio of Fe²⁺/Fe³⁺ would be determined by the redox conditions of surrounding water.

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Since, the zeta potential of membranes affect the filtration characteristics of the solid-liquid separation process for membrane bioreactors, the variability of zeta potential with operating conditions was investigated for alumina membranes, used for membrane bioreactor system. The surface hydroxyl group density of alumina mambranes was also investigated. The distilled water immersion test revealed that the isoelectric point of the membrane shifts from 5.5, initial value, to 6.0 in distilled water at 37°C after 1000h, and also, to 6.5 after distilled water reflux for 100h. The measurement of surface hydroxyl group density showed that refluxing for 100h is equivalent to immersion in water at 37°C for several years. This suggests that the variability in zeta potential under normal mambrane operating conditions, for 2-3 years, is negligible. It is also apparent that the variability in pore size distribution has negligible effects.

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The anisotropic mechanical properties were studied in uniaxially hot-pressed silicon nitride. The flexural strength and Weibull modulus of specimens with longitudinal direction perpendicular to the hot-pressing direction were 22% and 38% higher than those of parallel specimens, respectively. The perpendicular specimens had narrower distributions of defect size and 20% higher critical rupture stress for the apparent same-sized defects than the parallel ones. These differences have been attributed to the shape and orientation of defects.

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