The fatigue behavior for mullite ceramics containing 71, 72 and 74wt%Al₂O₃ (71A, 72A and 74A) was measured at 1200°C by the static fatigue technique. The fracture toughness was evaluated from the slow crack growth magnitude (fatigue fracture surface) combined with the applied stress. The crack growth parameter (N) of 71A, 72A and 74A was 17, 23-24 and 26, and the fracture toughness (K_IC) was 4.3, 2.4 and 1.7MPa⋅m^1/2, respectively. These tendencies correspond to a decrease of the glass phase in the grain boundary. The fracture modes of the grains in the fatigue fracture surface for 71A was intergranular fracture in equiaxial crystals and transgranular fracture broken in the rod-like crystals, for 72A intergranular fracture in equiaxial crystals and transgranular fracture broken in slightly remained rod-like crystals, and for 74A only intergranular fracture. The fracture mode in the catastrophic fracture surface was transgranular for 71A, 72A and 74A. It was considered that the fracture toughness of mullite at 1200°C increased with a decrease of Al₂O₃ content because the crack tip became blunter by increasing the glass phase.

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To improve the gas selectivity for carbon monoxide from hydrogen, the complex impedance characteristics under DC bias voltages were studied on a pn semiconductor heterocontact comprised of 1mol%Na₂O-added CuO (as a p-type semiconductor) and ZnO (as an n-type), in the atmosphere of air-balanced CO or H₂ gas (concentration: 4000ppm) at 250 and 400°C. In this heterocontact system, the capacitance component of the equivalent-circuit at the interface at 250°C was larger in the CO mixture, but smaller in the H₂ mixture than that in air. As the results of characteristic changes of the equivalent-circuit components to each ambient gas at 250°C, it was shown that CO gas was selectively distinguishable from H₂ gas by using a decrease in the absolute value of reactance at 10kHz under the bias voltage of -1V. Moreover, the identification of CO and H₂ gases was shown to be feasible by DC bias dependence of reactance at a fixed frequency and by frequency dependence of reactance at a fixed DC bias. The CO gas identification by use of Na-modified CuO/ZnO was found to be feasible at a lower temperature of 250°C than that for Na-free CuO/ZnO (at 400°C).

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Substituted yttrium iron garnet (Bi, Al:YIG, Bi_XY_3-XAl_YFe_5-YO₁₂) were prepared by sol-gel process. Nitrates of bismuth, aluminium, yttrium and iron were used as the starting materials. The highly oriented thin film was obtained on a substrate of gadolinium gallium garnet (GGG) single crystal. The square type ratio (magnetization of the plane perpendicular to the magnetic field (σ_S⊥)/magnetization of the plane parallel to the magnetic field (σ_S//)) of the thin film, preferentially oriented in the perpendicular plane as a result of the Al substitution for the iron at the Fe site, exhibited a very large value, greater than 3.5. The Faraday rotation angle (θ_F) was 50°/μm for the Bi₂YAl_0.4Fe_4.6O₁₂ film.

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The present authors previously reported that a dense and uniform bone-like apatite layer with a desired thickness can be formed on any kind and shape of solid substance by the following biomimetic method at normal temperature and pressure. First, a substrate is set in contact with particles of CaO-SiO₂-based glass soaked in a simulated body fluid (SBF) with ion concentrations nearly equal to those of human blood plasma. Second, the substrate is soaked in another solution highly supersaturated with respect to the apatite. In the present study, the CaO-SiO₂-based glass as the nucleating agent was replaced by Na₂O-SiO₂ glasses, SiO₂ glass and SiO₂ gel. The induction periods for the apatite nucleation on poly-ethersulfone substrates were ∞, a little longer than 168, 96, 48, 1.5 and 0.5h for SiO₂ glass, SiO₂ gel, Na₂O 10⋅SiO₂ 90, Na₂O 20⋅SiO₂ 80, Na₂O 30⋅SiO₂ 70 and Na₂O 40⋅SiO₂ 60mol% glasses, respectively, whereas 24h for MgO 4.6⋅CaO 44.7⋅SiO₂ 34.0⋅P₂O₅ 16.2⋅CaF₂ 0.5wt% glass G. The short induction period for the glasses with high Na₂O contents is attributed to high dissolution rates of sodium and silicate ions from them. The adhesive strengths of the formed apatite layer to the poly (ethylene terephthalate), poly (methyl methacrylate), poly-ethersulfone and polyamide 6 were 5.37, 1.63, 6.80 and 2.91MPa for Na₂O 30⋅SiO₂ 70mol% glass, whereas 3.48, 1.06, 4.40 and 0.63MPa for glass G. It is considered that highly polar carboxyl or sulfinyl groups were formed on the polymer surfaces by the hydrolysis of their ester, amide or sulfonyl group in SBF with its pH considerably increased by the Na⁺ dissolution from the glass, and that these polar groups formed a fairly strong bond with the apatite. Thus formed apatite-organic polymer composites are expected to be useful as the bone-repairing as well as soft tissue-repairing materials.

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Phenolic resin is widely used as a binder for carbon-containing refractories for its relatively high amount of carbon yield. Carbon from it, however, is the so-called non-graphitizing carbon, therefore its crystallization and oxidation resistance are low. In this study, the effects of B₄C which is usually added to carbon-containing refractories as an antioxidant on the crystallization and oxidation resistance of carbon from resin have been investigated. The results show that B₄C can accelerate the crystallization of carbon from resin and thus improve the oxidation resistance of the carbon.

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The mechanical behavior of an iron carbide base material processed by an ingot route was compared with that of the same composition material processed by a powder route. Thermo-mechanical processing routes have been developed to refine the coarse as-cast ingot microstructure. Structural refinement is a result of creation of strain-free regions by carbon dissolution from high strain energy subgrain boundaries and slip bands. The ingot-processed iron carbide material exhibits superplastic behavior and deforms by the same grain boundary sliding mechanism as for the powder-processed material. It is proposed that thermo-mechanical processing of ingot-cast eutectic-composition ceramics to achieve a superplastic structure is feasible.

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Mixtures of Zr(SO₄)₂-Zr(OH)₄-H₂O system were hydrothermally treated at temperatures from 160 to 240°C for various time periods. A metastable compound, pseudo-zirconium oxide sulfate (PZOS), was formed at the early stage of the hydrothermal process. In solutions containing 0.4mol/l of H₂SO₄, an isotropic, elongated, flaky m-ZrO₂ particles were formed subsequently, and the particle size increased with increase in treatment time. The m-ZrO₂ particles crystallized from the PZOS by discharging SO₄^2- ions. In solutions containing 1.0 or 1.5mol/l of H₂SO₄, however, the subsequent product was zirconium oxide sulfate (ZOS) particles, which probably resulted by the nucleation and crystal growth mechanism. The yield of ZOS particles or elongated, flaky m-ZrO₂ particles from Zr(SO₄)₂-Zr(OH)₄-H₂O system was higher than that from Zr(SO₄)₂-H₂O system. This method in this study is expected to be useful in the mass volume production of ZOS or m-ZrO₂ particles.

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Dense barium metaplumbate (BaPbO₃) ceramics with relative sintered densities>99% have been prepared with the addition of 0.5mol% ZnO by a conventional method. The electrical resistivity, thermal conductivity and thermal expansion coefficient were measured at room temperature to 600°C, which were found to be typically 6×10^-4Ω⋅cm, 4.19W/m⋅K and 15×10^-6/°C, respectively, at room temperature. The obtained ceramic materials with these physical properties have been evaluated from the view point of utilizing as an electrode material for ferroelectric thin-film devices.

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The dc electrical conductivity of annealed V₂O₅-Sb₂O₃-TeO₂ glasses prepared by quenching was studied. In the high temperature range from room temperature to 473K, conduction of annealed glasses was confirmed to be due to small polaron hopping. An increase in annealing time increased the glass density, and decreased the oxygen molar volume, resulting in a decrease in mean V-ion spacing. This decrease also caused an increase in polaron band width, and a decrease in hopping energy, W_H. At temperatures lower than room temperature, the relationship between log σ and T^-1/4 was linear. The conductivity analysis based on Mott's variable-range hopping (VRH) theory gave disorder energy, W_D=0.06-0.08 eV (at 250K), the density of the states, N(E_F)=1.26×10²¹-9.30×10²²cm^-3⋅eV^-1 (at 250K) and the mean distance in VRH, R_VRH=(5.26-19.31)×10^-1nm (at 250K). The fact that VRH takes place at such a high temperature as T=243-293K was explained by relatively large W_D.

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SrTiO₃ ceramics were sintered under various oxygen partial pressures. The relationship between the oxygen partial pressure and properties of sintered samples was investigated by TEM, EDX and XRD measurements. At lower oxygen partial pressure, the Ti₈O₁₅ phase about 5μm in diameter existed at triple points. On the contrary, at higher oxygen partial pressure the Ti₃O₅ phase about 0.5μm in diameter existed at triple points. The stability of Magnéli phases was discussed on the basis of thermodynamic data. Lowering of oxygen partial pressure resulted in an increase in oxygen vacancies and lattice parameters and further in a decrease in electric resistivity.

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Al₂O₃/SiC composites were prepared by hot-pressing in order to investigate the microstructural characteristics and nano-disperse behavior of alumina matrix composites. The grain size of the monolithic alumina ceramics increased with increasing hot-pressing temperature, and the exaggerated grain growth occurred above 1800°C. However, the addition of SiC particulates effectively suppressed the growth of the alumina matrix in the composites. The average matrix grain size was smaller and the grain size distribution was narrower than those of the monolithic alumina ceramics. Very fine SiC particulates were well dispersed in composites as nano-sized intragranular grains in the alumina matrix, on the other hand, coarse SiC particulates were found to exist at grain boundaries of the alumina matrix. The intragranular SiC seems to be trapped like a pores in the matrix grains during the densification by hot-pressing. It is concluded that nano-sized SiC particulates are grain growth inhibitors and microstructural stabilizers thus giving a uniform microstructures with fine grains.

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Temperature distribution of ceramic disks subjected to suddenly heating from outside under constant heat flux conditions was measured to estimate the thermal stress history and evaluate the first kind thermal shock resistance parameter of ceramic materials. Also, numerical calculations were conducted to compare with experimental data for each heating condition. Temperature dependence of thermal conductivity and thermal diffusivity was introduced into the calculation to realize the practical heat conductive condition. Two types of ceramics were used for the experiment; alumina ceramics having high and varying thermal conductivies and mica ceramics having low and constant thermal conductivities. As a result, it was found that the thermal stress history of heated disks is easily estimated from measurement of temperature distribution of the specimen. Temperature dependence of thermal properties was substantially affected on temperature distribution and thermal stress history, and it is shown that varying thermal properties in alumina ceramics can lead to a significant increase in the maximum tensile thermal stress generated in the center of the disks. As demonstrated by the numerical calculation for many kinds of other ceramics, maximum thermal stress of heated disks under constant heat flux condition shows non-steady-state value.

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Fine β-Si₃N₄ powders containing 5mass% of large β-Si₃N₄ particles were gas-pressure sintered at 1900°C for 4h using Y₂O₃ and Al₂O₃ as sintering aid. A core/rim structure was observed by scanning and transmission electron microscopy. The core was pure β-Si₃N₄ and the rim was β-sialon. The electron dffraction patterns indicated that the core and rim had the same orientation, showing that the rim was epitaxially grown on the core. Lattice mismatch was observed at the core/rim boundary by HREM. These results show that the relatively large β-Si₃N₄ particles in raw material powder acted as seeds for grain growth and that the rim was formed by epitaxial precipitation from liquid containing Al. When β-Si₃N₄ is used as the raw material powder, the particle size distribution is especially important for the development of in-situ composite microstructure.

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C-SiC composite fiber was obtained by heating a C-SiO₂ precursor, prepared from carbon fiber (Kynol) impregnated with ethylsilicate. The mechanism of SiC formation from the precursor has been investigated. The reaction rate was determined by means of a thermobalance in an atmosphere of Ar at temperatures from 1673 to 1973K. The reaction products were examined by X-ray diffraction and chemical analyses. The reaction products were SiC and SiO. The yield of SiC increased with increasing SiO₂ content in the precursor and heat treatment temperature. The particles of SiC coarsened at high temperatures. The SiC layer grew from the surface to the fiber core. The continuous concentration gradient of Si was observed in the reaction layer. The reaction rate was described by the two dimensional contracting-disc formula for diffusion control. The activation energy was 304kJ/mol. The rate-determining step is probably the diffusion through the SiC layer.

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The influence of grain size on the fraction of transgranular fracture in polycrystalline ceramics was investigated with a stochastic model. Crack propagation path was divided into three cases according to the arrival position of a crack and the angle between a main crack and a cleavage plane. The probability that a crack propagates transgranularly or intergranularly was derived from the above model with stochastic calculation. The influence of grain size on the fraction of transgranular fracture was formulated as a function of grain size. This stochastic model could well explain the influence of grain size on the fraction of transgranular fracture in polycrystalline Al₂O₃ reported previously.

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Silicon nitride powders containing 5mass% Y₂O₃ and 5mass% MgAl₂O₄ as sintering additives were sintered with β-Si₃N₄ whisker of 0-90mass% at 1800°C for 1-3h at 0.1-1MPa of N₂ atmosphere. The silicon nitride with 0-15mass% β-Si₃N₄ whisker was densified above 90% of theoretical density in the above conditions. Rod-like β-Si₃N₄ grains grew on seeded-β-Si₃N₄ whisker. The fracture toughness of Si₃N₄ with 15mass% β-Si₃N₄ whisker was 35% higher than that of monolithic Si₃N₄.

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Chromium boride crystals were obtained by the high-temperature metal (copper, lead or tin) solutions using chromium metal and boron powders as starting materials in an argon atmosphere. CrB and CrB₂ crystals were obtained as a single phase, however, Cr₃B₄ and Cr₂B₃ were obtained invariably as a phase mixture for various atomic ratios of the starting material in molten metal solutions. The largest CrB and CrB₂ crystals were obtained from Cu solution. CrB crystals were obtained in the form of pillar shape extending to a-axis or c-axis and thin plates with well-developed {010} faces, and CrB₂ crystals were obtained in the form of nearly spherical polyhedron. The largest crystals prepared had the maximum dimensions of about 0.12mm×0.13mm×3.30mm for CrB and 30μm for CrB₂. The results of unit cell dimension and chemical analysis of CrB and CrB₂ crystals are also present.

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