The thermal expansion of CeO₂ and rare-earth-doped ceria (Ce_0.8R_0.2O_1.9, R: Yb, Y, Gd, Sm, Nd and La) was measured in the temperature range from 298 to 1473 K. The coefficients of thermal expansion (CTE) were determined by differentiating the thermal expansion expressed by a polynominal equation of temperature with respect to temperature. The CTE (α₁) for Ce_0.8R_0.2O_1.9 was in the range from 10×10^-6 to 14×10^-6K^-1 and increased nonlinearly with increasing temperature. This result was explained by the asymmetric curve of potential energy based on the lattice energy theory. The kinds of dopant gave small effect on the α₁ of rare-earth-doped ceria. On the other hand, the average CTE for CeO₂ and rare-earth-doped ceria (12.0-12.5×10^-6K^-1), determined from a linear approximation of thermal expansion with respect to temperature at 298-1273 K, was lower than the α₁ and close to the previously reported values.

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An improved understanding of currently used bioceramics in human implants and in bone replacement materials could contribute significantly to the design of new generation prostheses and post-operative patient management strategies. Overall, the benefits of advanced ceramic materials in biomedical applications have been universally appreciated, specifically, in terms of their strength, biocompatibility and wear resistance. However, the amount of supporting data is not large and the continuous development of new characterization tools is pertinent for better understanding of the microstructure-properties relationship and in general for obtaining new directives for their further improvement. This paper gives an overview and re-examines key-issues which concern both processing and applications of ceramics as biomaterials. With doing this, we attempt to bring to the attention of the ceramic community the issues in current bioceramics.

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Temperature-induced bridge flocculation of aqueous zirconia suspensions in the presence of polyacrylic acid (PAA) has been studied. The viscosity (20vol%) of zirconia suspensions with different concentrations of PAA as a function of temperature was measured. The results showed that the viscosity of the suspension in the absence of PAA suddenly increased with increasing temperature above 35°C due to the depletion of zirconium and yttrium cations. In contrast, heating the suspension over 45°C in the presence of PAA led to a sudden increase in viscosity, which can be rationalized by considering the increase in the ionic strength of the suspension as a result of leaching of both yttrium and zirconium cations and also the extent of adsorption of the PAA on the suspension particles. To confirm the bridge flocculation or gelation of the zirconia suspensions in the presence of PAA, viscoelastic measurements in terms of complex, storage and loss moduli (G* and G′ and G″, respectively) as a function of temperature were studied. Preliminary tests on temperature-induced bridge flocculation of high solid suspension (40vol%) in the presence of PAA were also carried out. It was found that with increasing the temperature up to 85°C, the height stability of the samples reached to an optimum level and no deformation was detected. To reach the optimum stability for the samples at lower temperatures, the polymer dosage must be increased. G*, G′ and G″ of high solid suspensions (40vol%) were measured to evaluate the gel formation. The abrupt changes of G* and G′ values from <50kPa to about 300kPa, where G″ was approximately constant at <50kPa at -55°C, can be taken to indicate the formation of gel-like stable solids.

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The chemical states of (Co-Fe)-Al-O magnetic thin films with various compositional ratios were investigated by X-ray photoelectron spectroscopy (XPS). Samples were prepared by using inductively coupled RF sputtering. A non-reactive Ar atmosphere for both a Co-Fe alloy target and an Al₂O₃ ceramic target was used. Compositions of samples were varied to control the cathode power of the Co-Fe alloy target. Those with high (Co-Fe)/(Al-O) volume ratios exhibited excellent saturation magnetization (M_s) arising from the ideal chemical state of the non-oxidised Co-Fe alloy. Samples with low (Co-Fe)/(Al-O) volume ratios highlighted a problem that the increase in volume of the Al-O layer could cause some degree of Fe oxidation in the Co-Fe alloy, which would lead to a decrease of M_s.

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A material consisting of (La_1-xY_x)_0.7Sr_0.3MnO₃ was synthesized and evaluated to enhance the thermal expansion compatibility with an electrolyte material of Solid Oxide Fuel Cells (SOFC) compared with the standard system La_0.7Sr_0.3MnO₃. In addition, its crystal structure, chemical stability, electrical conductivity and electrode performance were examined. For the substitution range x=0.0-0.2 in the (La_1-xYx)_0.7Sr_0.3MnO₃ system, a single perovskite phase was observed. The mixture of (La_1-xYx)_0.7Sr_0.3MnO₃ (x=0.0-0.6) and YSZ, which was fired at 1400°C after mixing, did not contain the reaction products, such as La₂Zr₂O₇, Y₄Zr₃O₁₂, and SrZrO₃. The average thermal expansion coefficients between 50°C and 1000°C at x=0.0 and x=0.2 were 12.2×10^-6K^-1 and 11.5×10^-6K^-1, respectively. The electrical conductivity of the phases with x=0.0 and 0.2, at 1000°C in air, were 172 and 217S·cm^-1, respectively. The electrode performance of (La_0.8Y_0.2)_0.7Sr_0.3MnO₃ was almost equal to that of La_0.7Sr_0.3MnO₃ at 1000°C. Substitution of Y at the content of x=0.2 proved to be effective in obtaining higher expansion compatibility and electrical conductivity than the standard system without any degradation of the other properties.

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BaTiO₃-Cu ferroelectric/metal composite was successfully fabricated by sintering a Cu₂O-added BaTiO₃ pellet using a 100ml/min nitrogen gas flow rate. Abnormal grain growth was found to occur above 1280°C by scanning electron microscopy (SEM). Electron probe micro-analysis (EPMA) results indicated that crystalline spheres within abnormally grown grains were generated from excess titanium-contained BaTiO₃ and copper melt. Transmission electron microscopy (TEM) revealed that copper metal had twins and that BaTiO₃ had faceted boundaries.

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Among porous ceramic with unidirectionally aligned pores, synthesized from a water-based slurry using unidirectional freezing and freeze-drying process, porous silicon nitride showed a characteristic microstructure wherein the macroscopically aligned open pores contained many fibrous grains protruding from their internal walls. Pressure loss of the porous material was measured at room temperature using a filter media tester. A filtering test using fly ash was carried out with a reverse air-cleaning at constant intervals. The developed material had a low pressure loss and a strength which could withstand use. Air-cleaning worked effectively through the aligned pores and almost 100% of the ash was trapped, maintaining low pressure loss.

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Woody waste materials were used for the preparation of titanium carbide ceramics (TiC) by utilizing combustion synthesis or self-propagating high temperature synthesis (SHS). The outer and inner barks and wood of the sugi (Cryptomeria japonica) were used to react with titanium powder as raw materials, as well as commercially available reagents of cellulose and lignin. It was detected by X-ray diffractometry that the TiC phase was obtained directly arose from the mixture of the woody waste materials and titanium powder, without formation of any major oxide phase. Broadening of half width and shift in diffraction peaks of the obtained TiC phase suggest that the TiC phase included lattice deformation and had a non-stoichiometric composition. This latter observation may imply the release of carbon, i.e., formation of carbon mono- or dioxide. The carbide phase had a mean particle size of 1-5μm, and showed a shape similar to a TiC synthesized from a mixture of graphite and titanium powders. The combustion velocity of the mixtures tended to increase with the relative amount of carbon included in the woody materials. On the other hand, the velocity indicated a tendency to decrease with hydrogen and oxygen contents in the materials, which resulted from an endothermic reaction, accompanied with pyrolysis of the woody waste materials during SHS reaction.

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The pyroelectric properties of (Pb_1-x, Ca_x) [(Co_1/2W_1/2)Ti]O₃ ceramics have been studied by substituting Ca for Pb and by measuring spontaneous polarization using the Sawyer-Tower method in order to clarify the mechanism responsible for the improvement of pyroelectric property. With an increase in the Ca concentration range of x=0.20-0.30, spontaneous polarization, P_s increases and reaches large values of 40-42μC/cm² at 100°C, as compared to the 2-3.5μC/cm² of the representative PbTiO₃ ceramics containing small amounts of La and Mn. The Curie temperature decreases according to the Vegard law. The coercive electric field E_c markedly decreases from 28kV/cm at a Ca concentration of x=0.10 to 4kV/cm at a Ca concentration of x=0.40, compared with the 60kV/cm of PbTiO₃ ceramics. Increasing spontaneous polarization might be explained in terms of lattice distortion by Ca ions. It is found that a significant improvement of pyroelectric properties is related to an increase in spontaneous polarization P_s and a decrease in the Curie temperature.

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The effect of impurities, such as Fe₂O₃, Al₂O₃, TiO₂, MgO and CaO, contained in silica-containing natural substances on the growth of SiC whiskers were investigated, with emphasis placed on the yield and length of the whiskers. The yield of SiC whiskers synthesized from silica-containing natural substances was improved by the addition of cryolite. The-most remarkable effect appeared on volcanic ash and led to a total maximum yield of 21mass%. Fe₂O₃ contributed to increasing the length and yield of SiC whiskers on the graphite boat. On the other hand, Al₂O₃ only slightly affected the improvement of the yield on the graphite tube and the length on the graphite boat. The dominant factor in the growth of the whiskers due to transition metal component was clarified based on EDX analysis of the droplet existing at the tip of the whiskers. The content of the metal component in the droplet at the tip of SiC whiskers was related to the solubility of metal in Si, and the content of Fe in the droplet was greatest among other metal elements. The increase in the yield and the higher Fe content in the droplet in the case of using volcanic ash, containing more Fe₂O₃ among other natural substances, supported the belief that Fe₂O₃ is very effective in growth promotion of whiskers deposited on a graphite boat.

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Fundamental and 3rd-harmonic voltages between a pair of electrodes, appearing due to nonlinearity, were theoretically calculated in a piezoelectric rectangular vibrator which was driven by a sinusoidal constant current having the resonance frequency of length-extensional 1/2λ-mode vibration. The theoretical calculation was performed using the electrical equivalent circuit of a piezoelectric rectangular vibrator. Since the fundamental and 3rd-harmonic voltages were generated with cosine distributions in the sample and the motional impedance to each generated voltage also has a cosine distribution, Millman's theorem was used in the analysis of the fundamental and 3rd-harmonic voltages between a pair of electrodes. This analysis clarifies quantitatively the relationship between the nonlinear voltages between electrodes and a nonlinear coefficient used as a material constant.

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Filtering characteristics of porous silicon carbide candle filters with high surface area were investigated. Cogwheel type silicon carbide ceramic filters consisting of a highly porous support and a filtration layer were fabricated by extrusion forming. Tube typed ceramic candle filters were also fabricated for comparison. The cogwheel type filter showed much less pressure drops than the tube typed one according to an increase of flow rate or continuous mass loading. While the cogwheel shape did not greatly affect the separation efficiency, it clearly affected the cleaning efficiency. Additionally, the cogwheel type filter showed better cleaning characteristics. It is suggested that the cogwheel shape is beneficial to decrease pressure drop and thus improves the operating performance.

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Microstructure and mechanical properties of hot-pressed ALON-based composite ceramics were investigated. Microstructure of hot-pressed bodies prepared from a starting mixture of Al₂O₃, AlN and BN, consisted of γ-ALON phase as a matrix and a homogeneously distributed BN phase. The γ-ALON phase was discontinuous in a composite with BN amount >20vol%. However, addition of 2vol% Y₂O₃ as sintering aid made the microstructure to maintain a continuous γ-ALON network even for BN addition >20vol%. It is considered that grain growth of the γ-ALON phase was enhanced by the addition of Y₂O₃. The flexural strength of the hot-pressed bodies decreased with increasing the amount of BN addition up to 20vol%, however, addition of BN >50vol% resulted in an increase of strength up to 80-100MPa. The thermal shock resistance of all samples tested was about 200°C. However, strength degradation due to thermal shock decreased with increasing the BN fraction. It was considered that the mechanical properties of hot-pressed ALON-based composite ceramics are significantly affected by the formation of BN phase through the pressurized sintering.

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Reactivity of hydrogenated diamond surface was investigated with peroxide radical initiators. The radical initiators used in this study were diacyl peroxide (R-COO-OOC-R) and dialkyl peroxide (R₃CO-OCR₃). Hydrogen abstraction reaction of hydrogenated diamond surface was attempted in liquid phase using these radical initiators. The radical species generated from diacyl peroxide such as benzoyl peroxide and lauroyl peroxide could extract the hydrogen atoms from the diamond surface, regardless of the kind of solvent. From the results of the spectra, we presume that the functional group is related to the radical species introduced on the diamond surface. On the other hand, the radical species generated from dialkyl peroxide such as di-t-butyl peroxide and dicumyl peroxide did not fully extract the hydrogen atoms from the diamond surface, regardless of the kind of solvent. Although oxygen radicals are generated from both diacyl peroxide and dialkyl peroxide, the molecular structure of the generated radical species is different for each radical species. The radical species generated from diacyl peroxide is R-COO·, and the radical species generated from dialkyl peroxide is R₃CO·. It was revealed that the reactivity of hydrogenated diamond surface with radical species depended not on the functional group in the radical initiator but on the molecular structure of the generated radical species.

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We studied the characteristics of Ni paste used for the fabrication of internal electrodes of multilayer ceramic chip capacitors (MLCC). The effect of addition of BaTiO₃ powders to Ni paste on green density and sintering characteristics of electrode films were also evaluated. Green density of Ni electrode film increased monotonically with an increase in the amount of BaTiO₃ powder up to 10mass%. From the measurement of shrinkage of electrode films, it was observed that the shrinkage of Ni electrode film prepared from CVD powder was smaller than that of WCP Ni electrode film at the addition of 10mass% BaTiO₃ powder. The results indicated that properties of Ni powder influenced on the shrinkage of electrode films.

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Oxide spinels containing Zn, Mn and Al were synthesized from powder mixtures of Al(OH)₃ and IZC (Itomuka zinc calcine), the latter of which is derived from the waste of dead batteries and consists of ZnO and MnO. Heating of the powders with different Al₂O₃/(ZnO+MnO) molar ratio (A/I value) ranging from 0.44 to 0.88 resulted in the formation of a single phase of spinel solid solution above 1000°C. The lattice parameter of the spinel s. s. with different cation ratios decreased almost linearly with increasing Al₂O₃ content. The chemical formulae of the solid solutions were estimated to be Zn(II)_0.74Mn(II)_0.26Mn(III)_0.60Al(III)_1.40O₄ and Zn(II)_0.50Mn(II)_0.50Mn(III)_0.09Al(III)_1.91O₄ for the samples with A/I=0.44 and A/I=0.88, respectively. Sintering of spinel powders calcined at 1100°C was enhanced at 1450°C to produce densified spinel ceramics with 90-93% of theoretical density. The addition of 4 mass%B₂O₃ or 4mass% Bi₂O₃ to synthesized powders caused the sintering temperature at which highly densified bodies were obtainable to be substantially lowered down to 1200°C, without any appreciable effect on the electrical properties of the sintered samples. The spinel s. s. ceramics having a composition of A/I=0.66 showed a negative linear temperature dependence of electrical resistivity with a thermistor constant (B) of 3240-3390 K.

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Lightweight porcelain has been developed by forming closed pores in the porcelain body through the use of hollow micro-spheres made from volcanic ash. These micro-spheres are called Shirasu-balloon. A green for lightweight porcelain was prepared by mixing the Shirasu-balloon with the green by hand. Experimental specimens were obtained by pressing the green, and drying and firing it at temperatures from 1160 to 1400°C for 2h in air. Bulk density, liner shrinkage, and flexural strength were measured, and the morphology and structure of the Shirasu-balloon in the porcelain bodies were observed using SEM. When the Shirasu-balloon was mixed with green of less than 10 mass%, the bulk density was reduced from 2.38 to 1.77 (×10³kg·m^-3) along the ideal value. The Shirasu-balloon was deformed and was shrunk over 13% by the addition of the Shirasu-balloon at more than 20mass%. The density reduction did not progress ideally beyond this point and approached the saturation value. When the mixing ratio was less than 10 mass%, the reduction of the flexural strength of the lightweight porcelain was slightly suppressed. This might be explained by the residual stress formed in the porcelain body.

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Several common modes of crystal growth provide particularly simple and elegant examples of spontaneous pattern formation in not only nature but also artificial circumstance. ZnO whiskers epitaxially grown using a chemical vapor deposition technique often show remarkable secondary growth. This growth develops the elegant side-branch on the edge of the hexagonal columnar structure.

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We examined the effect of raw materials on the properties of alumina-magnesia powders. In particular, we investigated about the amorphous structure of alumina-magnesia powders (AMA20 and AMH20, MgO content=20mol%) prepared by sol-gel method. The specific surface area of an AMA20 powder prepared from ethyl acetoacetate aluminum diisopropoxide and magnesium acetate tetrahydrate was larger than that of an AMH20 powder prepared from ethyl acetoacetate aluminum diisopropoxide and magnesium hydroxide. Crystallization behavior and true density depended on the raw materials used for magnesia. It is considered that the alumina and magnesia components in alumina-magnesia amorphous powder AMA20 were homogeneously mixed at the atomic level.

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