Pore size estimation of materials, whose surface areas and volumes are so small that nitrogen adsorption cannot be measured, is investigated by applying krypton adsorption at 77K. The krypton adsorption-desorption isotherms at 77K on the porous silicas whose pore radii are in the range of 1.36 to 5.20nm showed capillary condensation and evaporation phenomena, and exhibited definite hysteresis loops. The measurement of the pore sizes using the Kelvin equation revealed that the pore sizes estimated from the krypton desorption isotherms did not coincide with the values estimated from nitrogen desorption isotherms. These differences in pore size estimation will be attributed to the changes in the physical properties (surface tension and density) of the adsorbed krypton in the narrow pores. Considering these changes, the modified Kelvin equation and t-curve for calculating the correct pore size from krypton desorption isotherms are proposed. In the range of pore radii from 1.36 to 5.20nm, the measurement of krypton adsorption-desorption at 77K is useful for estimating the pore sizes of porous materials which have small surface areas and pore volumes, such as membranes, coating films and sintered bodies.

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An infrared irradiation heating method has previously been proposed as a technique for directly estimating thermal shock parameters from an electric charge. In this method, a thin circular disk is irradiated with infrared rays over its central area at a constant heat flux. In this report, we analyzed the temperature/thermal stress distributions in the disk in relation to the temperature-dependent material properties of ceramics, namely the temperature distributions relating to temperature-dependent thermal conductivity and thermal diffusivity, and the thermal stress distributions relating to temperature-dependent thermal conductivity, thermal diffusivity and thermal expansion. The results reveal that these temperature-dependent properties yield marked effects on the temperature/stress distributions in the disk. A number of possibilities are suggested for decreasing thermal stresses in ceramic structures by selecting appropriate combinations of temperature-dependent properties.

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The dependence of green and sintered densities of zirconia-toughened alumina (ZTA: Al₂O₃/15vol% ZrO₂) on the properties of spray-dried granules and compaction pressures was studied to differentiate the dominant processing parameter controlling sintered properties. Two sets of spray-dried granules, which differed largely in terms of the morphology and yield stress of granules, were compacted at various uniaxial pressures in the range of 80MPa to 120MPa. The green and sintered densities varied depending on the granule properties and compaction pressure. However, both sets of granules formed by cold isostatic pressing at 500MPa exhibited the same green and sintered densities of about 63% and 99%, respectively, relative to the theoretical density, regardless of the variation of granule properties. This work confirmed that high cold isostatic pressure could overcome the effect of granule properties on the green and sintered densities. The strength of sintered specimens was determined from the size of large hollows in the spray-dried granules remaining after compaction. Details of the compaction behavior in terms of the granule properties were discussed.

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The lithium ion conductivity of perovskite-type solid-solutions La_1/3-xLi_3xTaO₃ was measured by the ac impedance method and the activation energy for conduction was determined. The lithium ion mobility was calculated in order to discuss the conductivity behavior. While the ordering at the A-sites as well as the tetragonal distortion lowered the mobility for tetragonal perovskites (x≤0.06), the mobility decreased with decreasing the lattice parameter for cubic perovskites (0.075≤x≤1/6). The logarithm of the mobility was found to decrease linearly with increasing the activation energy. It was concluded that the lithium ion mobility was the major factor in influencing lithium ion conduction in this solid-solution system.

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Alumina bicrystals with (0001) twist boundary were fabricated by joining two alumina single crystals at 1900°C in Ar flow in a tungsten furnace. Single edge V-notched plate tension method was applied to evaluate the fracture toughness of the twist boundaries of the bicrystals. The fracture toughness of glass and single crystal alumina was also measured to make sure the validity of this method. The measured fracture toughness of (0001) twist boundaries were 3.6MPa√m at 0° twist angle, 2.8MPa√m at 10°, 2.1MPa at 28°, 1.8MPa√m at 38° and 2.7MPa√m at 60°, respectively. The dependence of twist angle of fracture toughness of grain boundary of alumina was discussed with changes in surface energy, boundary enemy and plastic dissipative energy.

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Ag-doped NdBa₂Cu₃O_7-δ superconducting ceramics were prepared by a sol-gel method. Ag was distributed uniformly in the sintered samples. The incongruent melting temperature of the NdBa₂Cu₃O_7-δ samples prepared by our sol-gel method was lower than that of the samples prepared by the conventional powder method. The incongruent melting temperature was further decreased by doping with Ag. The authors consider that the incongruent melting is induced by reaction between NdBa₂Cu₃O_7-δ and Ag. The superconducting transition width ΔT(ΔT=T_c(onset)-T_c(end)) was decreased by doping with Ag. The electrical resistivity of a 10mass% Ag-doped sample dropped sharply from 93K (T_c(onset)) and showed zero resistivity at 86K (T_c(end)).

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Formation and characterization of thin films of indium hydroxide, In(OH)₃⋅nH₂O were carried out. The indium hydroxide sample was prepared in the gel form via the reaction of indium nitrate solution with ammonium hydroxide solution. After the precipitated gel was extracted using a centrifugal separator, the gel was dispersed in deionized water for several days to prepare a colloidal solution. Films dip-coated on glass substrates were heated at several temperatures. Thin films were characterized by means of XRD, SEM, AFM, thickness measurement, TG-DTA and conductivity measurement. Although only one weak peak of the (200) plane was observed in XRD patterns, the thin films could be regarded as almost amorphous. Surfaces of all the samples were found to be smooth with roughness R_max=7nm, and the thickness of each film was about 40nm. Depending on both the heat-treatment temperature of thin films and the relative humidity, the conductivity varied in the range of 10^-7-10^-3S/cm at room temperature. In addition, the conductivity measured along the surface of the sample was on the order of 10^-6S/cm which was comparable with the value measured in the direction perpendicular to the surface. These results suggested that the carriers of conduction were protons based on water incorporated in the crystallographic channels and grain boundaries of the thin films.

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Four kinds of cordierite ceramics were fabricated by firing the glass compacts having the composition of 2MgO⋅2Al₂O₃⋅5SiO₂ and the same composition with small amount of ZrO₂ at 1373K for 1h at heating rate of 6K/min and 20K/min. Their thermal shock fracture resistance was investigated through a rapid change in bending strength of quenched specimen. The critical quenching temperature difference (ΔT_c) of the sintered bodies with the chemical composition close to cordierite fired at 6K/min was about 650K, while the ΔT_c=550K for the sintered bodies fired at 20K/min. On the other hand, the cordierite ceramics with small amount of ZrO₂ revealed to have 500-550K as their ΔT_c. Although an addition of ZrO2 to cordierite composition and high heating rate have given rise to higher strength of sintered bodies, no effect on an increase in ΔT_c was recognized because Young's modulus and the thermal expansion coefficient of sintered bodies increased simultaneously.

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The relationship between the fracture toughness and the work-of-fracture of ceramics toughened by crack bridging was discussed using a constant crack closure stress model including irreversible energy loss in the bridging region during crack propagation. The Irwin similarity relationship could not be applied to the bridged crack without modifying stress intensity factor and energy release rate considering the crack closure stress and the energy loss. Moreover, the fracture toughness was not simply related with the work-of-fracture even if the modified Irwin similarity was applied. The fracture toughness was determined as a function of the crack closure stress and the length of the bridging region regardless of the energy loss. On the other hand, the work-of-fracture of bridged crack was increased by the irreversible energy consumption as well as crack closure stress.

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Electrical properties of the sol-gel derived amorphous films containing P₂O₅ have been investigated. In the binary system of P₂O₅-SiO₂, the surface resistivities at 25°C under a relative humidity ranging from 50 to 90% RH were 2-3 orders of magnitude higher than that of the P₂O₅-TiO₂ films. In a nominal composition of P₂O₅⋅9SiO₂ (molar ratio), the conductivity at 25°C of the film prepared by using H₃PO₄ for the starting materials of P was 10^-6S⋅cm^-1. This was 1 or 2 orders of magnitude higher than that of the films prepared by using partially hydrolyzed P₂O₅: PO[OCH(CH₃)₂]_3-x(OH)_x or PO(OCH₃)₃ as starting materials of P, respectively. In the former case of PO[OCH(CH₃)₂]_3-x(OH)_x, however, the conductivity of the film obtained from a coating solution kept for 40d after preparation increased up to 10^-6S⋅cm^-1. In these films, we observed absorption band at 1300cm^-1, which was assigned to P=O stretching vibration. The high proton-conductivities come from the increase of hydrogen-bonded protons in the glass structure with increasing the P=O bonding content.

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Self-bonding aluminum borate (9Al₂O₃⋅2B₂O₃) needle-like crystals were synthesized by the reaction of aluminum hydroxide (Al(OH)₃) with boric acid (H₃BO₃). The powders were mixed (B/Al=4/9) and fired at 1250°C to obtain self-bonding needle-like crystals of 3-20μm in length and 0.4-0.8μm in diameter and to form frame-work of needle-like crystals. Amorphous aluminum oxide (Al₂O₃) were coated with melted boron oxide (B₂O₃) at high temperature. The seeds of needle-like crystals were formed on the surface of Al₂O₃ particles, namely solid-liquid interface. Then the seeds grew as needle-like crystals. In this way boric acid act not only as a reactant, but also as a flux. In this reaction, nickel oxide (NiO) act as an additive so that the surface of Al₂O₃ had been well wetted by flux. Excess of H₃BO₃ in the raw materials caused by-products in RD patterns. The B₂O₃ were removed by water. Needle-like crystals grew on the single crystal surface in the Al₂O₃ particles. On the large particles, several needle-like crystals grew on one plane. On the other hand, a needle-like crystal grew on one plane in the small particles, Then needle-like crystals grew in random directions from each plane.

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Synthesis of Ln³⁺-substituted tetrasilicic fluorine micas [K_1-xLn_xMg_2-2xLi_1+2x(Si₄O₁₀)F₂; Ln=Ce, Nd, Eu; x=0.0-0.2] was undertaken by solid state reaction and melting methods. Eu3+-substituted mica synthesized by the melting method had the largest solid solubility, i.e., x=0.10. The solid solubility of rare earth ions in mica structure depends on the radius of rare earth cations, resulting in the order Eu³⁺>Nd³⁺>Ce³⁺. Highly Ln³⁺-substituted fluorine micas were synthesized by ion exchange-fixation method from expandable Nataeniolite [Na_0.8Mg_2.2Li_0.8(Si₄O₁₀)F₂] and altered tetrasilicic fluorine mica [K_xNa_1-xMg_2.5(Si₄O₁₀)F₂; x≥0.18]. Homoionic Ln³⁺-exchanged micas obtained from Na-taeniolite didn't lose their rehydration properties upon heating even at 900°C. The degree in rehydration upon heating for homoionic Ln³⁺-exchanged micas also decreased in the same order Eu³⁺>Nd³⁺>Ce³⁺. This order is explained in terms of the polarizing power of interlayer Ln³⁺ ions. However, (Ln³⁺, K⁺)-exchanged micas obtained from altered tetrasilicic micas with NaB(C₆H₅)₄ treatment showed complete fixation of interlayer Ln³⁺ ions upon heating at 400°C, probably due to the effect of residual K⁺. They lost thoroughly rehydration property. This allows us to synthesize nonexpandable fluorine micas having the highest content of rare earth cations. Ce³⁺-substituted micas thus obtained showed strong UV-absorptivity.

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X-ray photoelectron spectra were measured on the fresh surfaces of silica, binary alkali silicate and mixed alkali silicate glasses fractured in ultra-high vacuum by irradiating with focusing monochromatic AlKα X-ray. Binding energies and chemical shifts of O1s, Si2p, Li1s, Na1s, K2p, Rb3d_5/2 and Cs4d_5/2 have been investigated, and charge densities of oxide, silicon and other alkali ions have been discussed. For xNa₂O⋅(100-x)SiO₂ glasses, electron densities of bridging oxide ion (BO), non-bridging oxide ion (NBO) and sodium ions increased with increasing the Na₂O content, suggesting that the bond order between O2p and Na3s (or 3p) increased with increasing the Na₂O content. In addition, the difference in binding energies between BO1s and NBO1s decreased with increasing Na₂O content indicating that electrons were delocalized considerably in O2p-Si3d π bonds. For 33.3R₂O⋅66.7SiO₂ (R=Li, Na, K, Rb, Cs) glasses, charge densities of BO increased with increasing ionic radius of alkali ions (Li→Na→K, Rb→Cs). The degree of polarization of BO increased with increasing ionic radius of alkali ions. For 33.3{(1-y)Li₂O⋅yCs₂O}⋅66.7SiO₂ glasses, O1s peak of NBO could not been discriminated between the components belonging to Si-O^-…Li⁺ and Si-O^-…Cs⁺. O1s chemical shifts of 33.3{(1-x)Li₂O⋅xCs₂O}⋅66.7SiO₂ glasses with increasing Cs₂O content were similar to the shifts of 33.3R₂O⋅66.7SiO₂ glasses with increasing ionic radius of alkali ions. The area-weighed mean values of O1s peaks appeared to have good correlation with an empirical expression of optical basicity.

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A method of simulating crack propagation in single-phase polycrystals and two-phase composites containing dispersoids is proposed. The microstructures for simulation were generated by the Monte Carlo method using a two-dimensional triangular lattice. The criterion for crack path selection is based on the total released energy rate of the system on crack extension. The crack path is determined by selecting the neighboring lattice in front of the crack tip corresponding to the smallest released energy rate from five possible crack extension scenarios; cracking along the cleavage plane in a matrix grain, a non-cleavage plane in a matrix grain, along a grain boundary, dispersoid, or the interface between a matrix grain and dispersoid. The crack propagation behavior was analyzed by calculating the surface ratio of the transgranular fracture, crack length ratio and effective fracture energy. The crack paths depended significantly on the constitution of the simulated microstructures such as average matrix grain size, distribution of the dispersoids and ratios of the fracture surface formation energies.

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To investigate the possibility of developing a humidity self-control material, the shaping and firing of mesoporous-powder (mainly γ-alumina phase), made by selective leaching method, were investigated adding 10mass% of coal kaolin. The specific surface area, total pore volume, pore size distribution and water vapor adsorption of fired bodies were measured for samples prepared with various calcination and firing temperatures to evaluate the humidity controlling properties. The amount of water vapor adsorbed on the fired bodies decreased compared with that of the powder. However, this decrease was larger at relative humidifies between 0 and 60% than that between 0 and 90%, namely, an increase in water vapor adsorption at around the relative humidity of 50-70% was found. The present mesoporous γ-alumina fired body is thought to be a promising candidate as humidity self-control material.

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Carbonate ions incorporated into two hydroxyapatites of different origins cattle bone-originated (r-HAp) and chemically-synthesized (s-HAp), were compared with emphasis placed on the morphology of these two hydroxyapatites. In r-HAp pretreated at 1073K, a PO₄-substituted and an OH-substituted carbonate ions were observed. On the other hand, s-HAp had only the PO₄-subsituted carbonate ion. This difference suggested that r-HAp had a more calcium-deficient structure and a larger density of OH-vacancies to compensate the decrease of Ca²⁺, which moves the OH-substituted carbonate ion forming more easily. This was in agreement with the difference of morphology in the two HAp's observed by field emission-scanning electron microscopy: the r-HAp was constituted by assemblies of relatively round particles of 50-100nm in diameter, while the s-HAp was bar-shaped particles of 100-300nm in length, meaning that the r-HAp does not grow so easily as the s-HAp along crystallographic c-axis.

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Porous alumina ceramics were sintered by conventional sintering (CSing) and hot isostatic pressing (HIPing) without encapsulating at temperatures between 1200°C and 1400°C under pressures between 0.1MPa and 200MPa of Ar gas. Pending strength and Weibull modulus of sintered porous aluminas were evaluated by three-point bending tests. The HIPed samples have well-grown necks and roundish pore shape compared to the CSed ones due to enhanced surface diffusivity, which results in lower specific surface area of HIPed samples than that of CSed ones with the same porosity and pore size. As increasing gas pressure, the bending strength increased for porous materials with same porosity. The bending strength of samples HIPed under 200MPa was about 30% higher than that of CSed ones having the same porosity of about 40%. The increase in bending strength by HIPing was significant as decrease in sintering temperature. The enhancement of bending strength by HIPing is caused by well-grown necks that reduce stress concentration around necks. On Weibull plots, kinks were observed for HIPed samples. As increasing gas pressure, Weibull modulus for weak samples increased, while that of strong samples was constant. Enhanced surface diffusivity by high gas pressure causes deviation of defect distribution from single Weibull distribution. As a result, a kink appears on Weibull plots. The increase in Weibull modulus for weak samples is caused by removal of insufficiently grown necks by enhanced surface diffusivity.

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The microstructure in silicon nitride ceramics containing Y₂O₃-Nd₂O₃ additive sintered at 2473K under 30MPa in N₂ was investigated by transmission electron microscopy (TEM). TEM analysis suggested that the second phase existed in silicon nitride grains, and this structure was similar to β-Si₃N₄ structure. EDX analysis suggested that the second phase consisted of Y, Nd, Si, O, and N elements.

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Sinterability of low-temperature calcined α-alumina powder and the bending strength of sintered bodies were investigated. The α-alumina powder was made from commercial aluminum hydroxide with seeding of abrasion powder worn in the wet ball milling. The low-temperature calcined α-alumina powder was very fine and achieved the density of more than 3.8Mg/m³ by hot pressing at 1200°C. The microstructure of the sample sintered at low temperature was composed of very fine equiaxial gains in spite of low purity. The bending strength of this sample was more than 800MPa.

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