A suitable relationship between free-ion polarizability and metal (or nonmetal) outermost binding energy has been searched on the basis of the similarity in physical nature between electron binding energy and ionization energy. It has been suggested that outermost core-level binding energy can be used for relative measuring the cation polarizability. In general, cation polarizability increases with decreasing metal (or nonmetal) binding energy. Highly polarizable cations possess low outermost binding energy. Simultaneously, a systematic periodic change of the polarizability against the binding energy has been observed in the isoelectronic series. A decreasing of metal (or nonmetal) binding energy in XPS spectra of simple oxides is accompanied with decreasing of O1s binding energy, that is related to increased basicity. This could be explained on the basis of enhanced interaction between outermost metal core level and O2p orbitals responsible to increased electron donor ability of oxide ion.

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Samples of a Si₃N₄ mixed powder with oxide sintering additives, Y₂O₃ 5mass% and Al₂O₃ 3mass%, were sintered separately by pulse electric current sintering (PECS) and by hot pressing to discuss the characteristic features of these two processing techniques. The low-temperature consolidation and the plasma effect, which have been reported to be features of the PECS process, could not be confirmed in this study. In the sintering of Si₃N₄ ceramics as a material for electrical insulators, the rapid consolidation, which enables the nanometer-scale grain size to be maintained in the dense material, was shown to be the only advantage of the PECS process.

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Al₂O₃-TiO₂ thin films and powders were synthesised from acid catalyzed sols of aluminium and titanium alkoxides containing acetyl acetone as a chelating agent. The crystallization of the system was studied as a function of the relative compositions and the firing temperature. Films of four different alumina-titania compositions (10, 20, 30 and 40mol% alumina) were prepared and fired at various temperatures in the range from 300 to 1000°C. The films and powders were amorphous, at any composition, up to about 600°C. Larger molar contents of Al₂O₃ were found to have an inhibitory effect on the crystallization of TiO₂, while larger contents of TiO₂ had only a weak influence on Al₂O₃ crystallization. The formation of a metastable β-Al₂TiO₅ phase was observed in films at 1000°C.

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Redox behaviors of sulfur species in sodium borate, silicate and phosphate melts doped sodium sulfate were studied by means of differential pulse voltammetry. In the 10Na₂O⋅90B₂O₃ melt, three reduction peaks are observed. The peak intensity at -400mV, which appeared as a shoulder of the peak at -300mV, decreases with the elapse of time. In the early stages of melting, noises are superimposed on the peak beyond -600mV. In the 30Na₂O⋅70B₂O₃ melt, the profile of the voltammogram does not change much with time after 92h. The voltammograms of sodium metaphosphate melt at the initial stage of melting have large noises beyond -600mV. The peak at -400mV disappears after 23h. In the sodium borate melts, the intensity of the peak at -450mV decreases and its position shifts to the positive side with an increase in temperature, whereas the intensity of the peak at -600mV increases with an increase in temperature. In the 20Na₂O⋅80B₂O₃⋅0.5Na₂S melt, the peak position shifts to the positive side with an increase in heating time due to the oxidation of S^2- to SO₄^2-. By combination of the Raman signal at 988cm^-1 and the IR signal at 630cm^-1, which are assigned to the fundamental vibration of SO₄^2-, the three peaks of the voltammogram are assigned to the successive reductions of SO₄^2-, SO₂ and S⁰ with the cathodic reduction process. The stability of SO₄^2- increases with an increase in the basicity of the melts and with a decrease in temperature.

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Hydration activity of belite-rich cement, based on the heat evolution for up to -10d, was effectively improved by a remelting reaction of the constituent belite. The modified cement, termed “remelted belite cement, ” is mainly composed of belite in which the remelting reaction occurred for a large extent, and thus distinct from the conventional belite-rich cement. The liquid, exsolved by the reaction, contained a much higher concentration of alkalies than the host belite. The alkalies accelerated the hydration and the main heat evolution peak began -7h earlier during the initial stage up to -30h. The subsequent heat evolution between -30h and -10d was mainly increased by the presence of twin boundaries in the host β-phase belite; the boundaries on the crystal surface behaved like active centers for the reaction with water. The grindability was also improved by the remelting reaction, in agreement with a previous study.

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A multilayer material consisting of hydroxyapatite (HAp) and calcium titanate (CaTiO₃) was hydrothermally synthesized on a titanium substrate. The titanium substrate was treated with a mixed solution of CaCl₂ and KOH at 150°C to form a CaTiO₃ layer. The thickness of the CaTiO₃ layer increased with increasing KOH concentration, but the adhesion between the coating layer and the substrate diminished. In an alkaline solution such as KOH, titanium substrates dissolved and reacted with calcium ions, and a CaTiO₃ layer precipitated on the substrate. A layer of HAp formed on the CaTiO₃ coating layer from the mixed solution containing CaCl₂, K₂HPO₄ and KOH, when the molar ratio of Ca/P was less than 1.67, which was the ratio of stoichiometric HAp. Calcium was supplied from both the reacting solution and the CaTiO₃ layer, and was precipitated as HAp. Decomposition of a part of CaTiO₃, and the consequent supply of Ca from the coating layer were necessary to form the HAp layer. The multilayer formed without peeling, when HAp was precipitated on the CaTiO₃ layer at 220°C for 24h with a pH of 8-10. The adhesion force between the substrate and the CaTiO₃ layer did not decrease after the formation of HAp, though the force decreased with increasing KOH concentration during synthesis of the CaTiO₃ layer. After soaking the HAp/CaTiO₃ multilayer in simulated body fluid (SBF) for 35 d at 37°C, the multilayer was covered with very fine needlelike particles of HAp, though neither the surface of the CaTiO₃ coating layer nor the titanium substrate were altered after the same treatment.

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A Hertzian contact fatigue test was proposed to simulate conventional rolling wear experiments, by which the wear behavior and phase transformation of 3mol%Y₂O₃-partially stabilized zirconia (3Y-PSZ) and 3Y-PSZ/20 mass%Al₂O₃ ceramics in water at 90°C were investigated. The Hertzian stress contact fatigue property was found to be greatly dependent on fracture strength and remarkably improved by the post-HIP treatment. The Hertzian contact stress was revealed to have minor influence on the water-assisted tetragonal-to-monoclinic phase transformation in Y-PSZ-based ceramics at temperatures as low as 90°C. The addition of Al₂O₃ into Y-PSZ effectively suppressed the low-temperature phase transformation, but it did not lead to the improvement in the contact fatigue property probably because the strength of the resultant composite was lower than the monolithic Y-PSZ; however, more work is required to completely understand the Hertzian stress contact fatigue behavior of composites.

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The Griffith concept of energy equilibrium for brittle mode I crack propagation was extended to a combined mode I-II crack extension. First, the maximum energy release rate for an infinitesimally kinked crack extension under combined mode I-II loading, analyzed by other researchers, was successfully expressed with a combined mode stress intensity factor. Second, the fracture energy rate was estimated from the area of the frontal process zone estimated from the area enclosed by the isostress contours of both the maximum principal stress and the maximum shear stress. Third, these considerations led to the estimated K_IIC/K_IC ratio of 1.20, which was close to the experimental results of 1.1 to 1.3 obtained previously. Lastly, the combined mode I-II fracture criterion was formulated by adopting the same procedure, and the predicted criterion coincided well with Shetty's empirical criterion. The fracture toughness values of mode I and mode II, and the combined mode I-II criterion for polycrystalline alumina, float glass and PMMA (polymethyl methacrylate) were also estimated experimentally using a disk method and a rectangular test. The estimated results of the K_IIC/K_IC ratio using the disk method ranged from 1.1 to 1.3, which was very close to the predicted value of 1.20, whereas the rectangular test specimens exhibited considerable stable crack growth at the crack tip and yielded a smaller K_IIC/K_IC ratio, which was related to the mode transformation and stress shielding.

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A melt of Na and Ga with various Ga contents was placed in a BN crucible and reacted at 650°C for 300h with N₂ generated from the decomposition of NaN₃ in a sealed stainless-steel tube. At 0.25 and 0.45 Ga molar fractions (r_Ga=Ga/(Ga+Na)), GaN precipitated at the interface of the melt and gas phases, and on the wall and bottom of the crucible. Platelet single crystals with a maximum size of 2mm grew at the inside of the interface layer. The precipitates on the wall and bottom consisted of hexagonal columnar crystals elongated along the c-axis direction. The size of these crystals was about 10-20μm at r_Ga=0.25 and 50-100μm at r_Ga=0.45. The morphology of the precipitates observed by scanning electron microscopy suggested that the columnar GaN crystals grew from the melt phase. At r_Ga=0.65 and 0.85, thin GaN microcrystalline layers partially covered the Na-Ga melt surface, but the formation of bulk GaN was not observed in the BN crucible.

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The effect of Y₂O₃/SiO₂ ratio on grain growth of Si₃N₄ was systematically investigated using the “seed” fabrication method. The aspect ratio of β-Si₃N₄ crystals heat-treated with an additive composition of Y₂O₃:SiO₂=1:2 was found to be much smaller than that of Y₂O₃:SiO₂=2:1. It was confirmed that this was due to the difference in solubility of Si₃N₄ caused by the change of Y₂O₃/SiO₂ ratio of the liquid phase. The number of β-crystals originally contained in the raw Si₃N₄ powder changed very little in the Y₂O₃:SiO₂=1:2 composition, while it significantly decreased in the Y₂O₃:SiO₂=2:1 composition, which resulted in a considerable difference in aspect ratio. A mechanism for this enhanced solubility of Si₃N₄ in the liquid phase with high Y₂O₃/SiO₂ ratio was proposed.

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Composite cements consisting of different pairs of inorganic filler-resin were prepared by selecting CaO-SiO₂-P₂O₅-CaF₂ glass, glass-ceramic A-W and silica glass powders as inorganic fillers, and combining each of them with bisphenol-a-glycidyl methacrylate/triethylene glycol dimethacrylate (Bis-GMA/TEGDMA) resin. The mechanical behavior of each of the composite resin cements was investigated by examining their fracture strength in a simulated body fluid (SBF) as a function of both the soaking time and the stressing rate. It was found that, among the composite cements studied, the CaO-SiO₂-P₂O₅-CaF₂ glass-filled composite cement showed a rapid strength degradation with increasing the soaking time in SBF and the highest sensitivity to time-dependent fatigue in SBF. On the other hand, the strengths of the resin cements filled with glass-ceramic A-W and silica glass particles did not vary with soaking time up to 336d in SBF. Thus, glass-ceramic A-W and silica glass can strengthen the resin cement without increasing the sensitivity to time-dependent fatigue in SBF. The glass-ceramic A-W can be used as a reliable inorganic filler for the composite cements with the Bis-GMA/TEGDMA resin, because of its bioactivity and good chemical stability.

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A theoretical model is proposed for explaining the increase in thermal conductivity experimentally found upon annealing in an AlN polycrystal doped with ≈3vol%Y₂O₃. The model foresees the concurrent effect of the growth of AlN-matrix grains and of the collapse of grain boundaries filled by the low thermal conductivity Y₂O₃ phase. Such depleted grain boundaries form directly bonded two-grain junctions. Grain growth produces a reduction of scattering of phonons at grain boundaries, and the increase of the number of directly bonded grain boundaries increases the average size of the thermally conductive AlN clusters. Thus, both the phenomena accompanying the microstructural evolution can lead to an increase of thermal conductivity in the polycrystal. The mathematical formulations of phonon scattering at grain boundaries and the percolation model are revisited and rearranged to give a comprehensive model of grain-growth-assisted percolation, which links the microstructural evolution of the polycrystal to the experimentally observed increase in its thermal conductivity.

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The crystal phase, the primary particle size, and the formation rate of hydrous-zirconia fine particles produced by hydrolysis conditions of various ZrOCl₂ concentrations (0.05-0.4mol·dm^-3) and reaction temperatures (358-373K) were measured to clarify the effects of the ZrOCl₂ concentration and the reaction temperature on the formation process. Chemical analysis and X-ray diffraction measurements revealed that hydrous-zirconia particles synthesized from all of the hydrolysis conditions were similar to those observed in monoclinic crystalline ZrO₂, except that the crystal structure changed with increasing chlorine content at the preparation conditions of 0.4mol·dm^-3 and ≤363K. The primary particle size of monoclinic hydrous-zirconia particles decreased with increasing ZrOCl₂ concentration and was independent of the reaction temperature. The rate constants (k) of hydrous-zirconia particles were determined experimentally by applying Avrami-Erofeev's equation. The determined k-value decreased, as the ZrOCl₂ concentration increased and the reaction temperature decreased. From Arrhenius plots of k, the activation energies for hydrous-zirconia particles in the monoclinic phase and containing high chlorine contents were determined to be 3.8×10²-4.0×10² and 2.5×10²kJ·mol^-1, respectively. The nucleation and the particle growth mechanisms of hydrous-zirconia particles were determined on the basis of the present experimental results.

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Lead titanate thin films were prepared on cleaved MgO (100) substrate by cold wall horizontal metallorganic chemical vapor deposition (MOCVD). Crystal structure of films was examined by X-ray 2θ/ω scan and X-ray pole-figure measurements. The growth mechanism of PbTiO₃ thin film at the initial growth stage was characterized using an atomic force microscope (AFM). AFM results show that the growth mechanism of PbTiO₃ thin film on MgO (100) substrate is in accordance with layer-by-layer plus islands of Stranski-Krastanov mode. Islands formed after two lattice layer with 0.8nm PbTiO₃ film deposition on a MgO (100) substrate. The crystal orientation and surface roughness are dependent on deposition rate. (001) and (100) oriented grain were found at higher deposition rate (>2.5nm/min). On the other hand, (212) and (221) oriented triangular-shaped grain growth was observed at relatively lower deposition rate (<2.5nm/min), which lead to an increase of surface roughness.

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Silicon nitride (Si₃N₄) whiskers were coated on a porous Si₃N₄ substrate, which was coated with SiO₂-Al₂O₃-Y₂O₃ oxides, by gas phase processing using amorphous Si₃N₄ and TiO₂ powders as source materials. Coating was carried out in the interval 1350-1550°C in N₂. At temperatures below the melting point of the oxides, α-Si₃N₄ whiskers of high aspect ratio were coated with weak adhesion to the substrate. At temperatures above the melting point, β-Si₃N₄ whiskers with diameters of 0.02 to 0.07μm (low aspect ratio) were coated with strong adhesion to the substrate. When the Si₃N₄ substrates coated with the β-Si₃N₄ whiskers were used as membrane filters, it could separate particles as fine as 0.05μm in diameter.

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Titanium nitride (TiN) slurry was prepared for slip casting with water, and the effects of slurry characters on forming and sintering behaviors were studied. 46.4vol% TiN powder was dispersed in water with triethylamine (TEA) and polycalboxyl ammonium (PCA), and formed in a gypsum mold. Formed compacts were sintered at about 0.7MPa N₂ pressure, at 1750°C for 3h. The slurries with TEA content above 0.02mass% showed low viscosity and non-thixotropy. The slurries with PCA content in the range 0.06-0.08mass% showed the minimum viscosity and minimum thixotropy. High-density specimens (density of 3.8-3.9×10³kg·m^-3) could be sintered from the low viscosity slurry, prepared by the addition of TEA with pH higher than 10 and optimum addition of PCA.

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Monolithic mullite was synthesized from polymer (cross-linked polysiloxane)/filler (alumina) blends. By virtue of a chemical oxidation reaction of ZrSi₂, intentionally added in increasing fractions, a nearly zeroshrinkage mullite based composite could be obtained by conventional sintering. The composites specimen after sintering were composed of mullite and monoclinic ZrO₂, according to the ZrSi₂ fraction added to the starting mixture. Low-shrinkage mullite based ceramics could be obtained when the content of ZrSi₂ was between 30 and 50mol%. In the case of ZrSi₂ 50mol%, the shrinkage was as low as 4.5%, although some specimen was found cracked after sintering. The upper limit for ZrSi₂ addition was considered to be ≈50mol% because of inhomogeneity related to mixing a low fraction of siloxane polymer (liquid) with the filler (solid).

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The structure of piezoelectric multilayer actuator with interdigital-electrode-type structure was investigated in order to improve both its moisture-resistance and displacement. The moisture-resistance was affected by the number of ceramic layers and by the shape of its internal electrode as well. An actuator with 20 layers in which the length of the inactive electrostrictively part was 0.6mm showed high moisture-resistance, and generated 1.7μm in displacement at DC 150V. In addition, it was also observed that inhomogeneous sintering reaction in the actuator affects its moisture-resistance.

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The effect of changing the solution pH inside indentation-induced microcracks on the post-indentation crack-growth behavior was investigated in glass. Buffer solution was used for crack growth experiments in order to suppress the pH change inside the microcracks and then comparison of crack growth behavior was made between the buffered and unbuffered solutions. It was found that the pH change inside the microcracks occurs depending on the initial pH of the solution and that the bonding state at the crack tip region changes depending on the pH change inside the microcracks. The obtained results also showed that the ratio of surface area/solution volume, S/V affects the pH change inside microcracks, which induced the change in the stress corrosion limit, K_scc depending on the pH.

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An arc imaging furnace has various advantages as an apparatus for ceramic synthesis. However, the disadvantage of this furnace is the difficulty of in situ temperature measurement of the sample, because of a very small heating spot in the furnace and the effect of infrared radiation from the light source on the measurement, a monochromatic radiation pyrometer is used. In this paper, a technique for in situ temperature measurement by monochromatic radiation pyrometer is proposed and applied to the melts of a CaO-SiO₂ system above 1700°C. Heating up was performed in an arc imaging furnace equipped with a Xenon lamp. The monochromatic radiation pyrometer was proven to work appropriately for in situ temperature measurement of the melting samples above 1750°C, because it can focus on a small melting drop 2-3mm in diameter, and also because it can avoid the effect of infrared radiation from the Xe lamp, by using a 5μm wavelength to detect the radiation from the sample melts.

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Plasticity of clay dough is strongly influenced by the formation of buffer domain consisted of clay aggregates. Change in plasticity of Georgia kaolin along with heat treatment was analyzed by examining the variation of the particle packing structure of the dough. The plastic behavior did not change by the heat treatment up to 350°C. However, above 350°C, plasticity was reduced together with micron sized pores existing among aggregates. The lower plasticity arose from destruction of buffer domains, caused by the increase of particle size upon sintering.

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