Alumina particulate and platelet-reinforced glass matrix composites with an anorthite phase precipitated at the interface were fabricated by hot pressing. In order to evaluate the mechanical properties of the materials, four-point bending tests in air and in vacuum, and indentation fracture tests in air were performed. The acoustic emission (AE) signals of the alumina particulate glass composite were measured during bending tests in air. The relative density and the elastic modulus of the samples sintered by hot pressing were higher than those of the samples sintered under atmospheric pressure. The bending strength of the samples with larger amount of precipitated phase decreased compared with that of the samples without precipitation both for tests in air and in vacuum due to coarse precipitation but there was a monotonic increase of fracture toughness because of the interfacial precipitation. SEM observation of the crack paths indicated that the crack propagated through the precipitated phase. The results of AE location were related to the bending strength behavior of the particulate samples.

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Microwave (Hybrid) Heating (MHH) was used to oxidize Al-Al₂O₃ powder mixture and sinter the oxidized alumina to produce low shrinkage porous alumina. Compared with conventional fast firing, MHH gave fast oxidation rate due to the surface ohmic current on Al powder. Porous alumina with low thickness change (+1%) and bulk density (2.78g/cm³) was produced. SEM analysis was used to explain the oxidation and sintering behaviours of Al-Al₂O₃ powder mixture.

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The metal-to-insulator (MIT) characteristics of the multiphase vanadium oxide films including V²⁺, V³⁺, V⁴⁺ and V⁵⁺ ions prepared by reactive magnetron sputtering were studied. The average valency of vanadium ion increased when the residence time of active vanadium atom near the oxygen injection pipe, because the oxygen potential of this region is much higher than other part of chamber. Therefore, the final phases of the films depend on the configuration of sputtering system. For two phase films, resistivity changed by a factor of -10³Ω·cm. However, MIT characteristics is getting weaker for the films consisting of more than two phases. Therefore, the strain sensitive phase transition is suggested as a mechanism of MIT of multiphase vanadium oxide thin films.

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Amorphous tungsten trioxide films were prepared from iso-polytungstic acid as a precursor and by RF magnetron sputtering method. Framework structure was investigated based on X-ray diffraction analyses, in which amplitude function as well as radial distribution function was used. And the previously reported films prepared by vacuum evaporation and an ion exchange method using Na₂WO₄⋅2H₂O as a precursor were also re-examined. It was found that, in the films derived from iso-polytungstic acid, the framework had a similar manner to that in hexagonal-WO₃ crystal, whose framework was constructed by 3-, 4- and 6-membered rings formed by WO₆ octahedra. It was supposed that edge-sharing polyhedra and tungsten and/or WO₆ defects were present in the as-prepared film and changed to corner-sharing connection and continuous framework by post-annealing. It was also suggested that structural water was present in a hexagonal tunnel in the framework. These structural characteristics were also observed in the films prepared by vacuum evaporation and ion exchange methods. As for the sputtered films, formation of two framework-types without structural water was confirmed. The hexagonal-WO₃ like framework was formed in the films prepared under a low O₂ partial pressure, and tetragonal-WO₃ like one with an ordinary ReO₃-type structure made up with 4-membered rings was produced at a high O₂ pressure.

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The ferroelectric ceramics of solid solutions xSr(Li_1/4Nb_3/4)O₃-(1-x)PbTiO₃ (0.05≤x≤0.40) were fabricated by conventional solid state sintering. The dielectric constants, Curie temperature, electromechanical coupling factors, and linear thermal expansion were measured as a function of x. The piezoelectric constants, elastic compliance constants, and Poisson's ratio of the specimens were calculated from the measured piezoelectric properties. Maximum coupling factors k₃₁ and k₃₃, and maximum piezoelectric constants d₃₁ and d₃₃ were obtained for the composition x=0.30, which is located close to the phase boundary between the ferroelectric tetragonal and the paraelectric cubic phases.

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The behavior and the effect of Al₄SiC₄, an excellent hydration-resistant compound, as an antioxidant for carbon-containing refractories have been investigated, and the corresponding mechanisms have been discussed. Al₄SiC₄ added to the refractories initially reacts with CO to form Al₂O₃, SiC and C. After the reaction, if the temperatures are below -1560°C, the formed SiC and Al₂O₃ will further react with CO to form mullite (Al₆Si₂O₁₃) and C. The above reaction processes can form protective layers on the surfaces of the refractories, which inhibit the oxidation of the refractories. From the results obtained, Al₄SiC₄ was found to markedly inhibit the oxidation of the carboncontaining refractories.

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The pyrolysis process of basic calcium carbonate (BCC) in air was studied by TG-DTA and high temperature X-ray diffractometry, and obtained results were compared with our previous results in a flowing N₂ gas. The decomposition of Ca(OH)₂ and calcite was observed at higher temperatures than those in a flowing N₂ gas. An exothermic peak appeared in DTA around 370°C before the decomposition of Ca(OH)₂. The difference between the results in air and in a flowing N₂ gas was caused by carbonation of intermediate products by a slight amount of CO₂ in air. The carbonation was promoted by H₂O. The exothermic peak around 370°C was attributed to the crystallization of CaCO₃.

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Silica gel fibers made from TEOS by the sol-gel method were preheat-treated in the temperature range of 200 to 500°C, and were converted to silica glass fibers by further heat-treating up to 800°C.
Tensile strength of the glass fiber preheat-treated at 300°C for 10h was about 1.4 times larger than that obtained without the preheat treatment.
Such an effect of the preheat treatment on the tensile strength of the sol-gel-derived silica glass fiber was discussed in relation to the reconstructive change of overall atomic scale-structure of the gel network consisting of OH-terminated 4-membered siloxane rings to three-dimensional network constructed with 6-membered siloxane rings which occurs in the starting gel fibers at 200-500°C and often causes the destruction of the silica network when heat-treated rapidly. As a result, it was considered that the preheat treatment made the reconstructive change moderate to avoid the destruction of the network.

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The present study was concerned with the grain size and the boundary layer properties of (Sr, Ca) (Ti, Nb)O₃ based ceramics which were applied for capacitive-varistor devices. The results were summarized as follows: (1) The addition of SiO₂ resulted in making same average grain sizes both of A-site excess and B-site excess- (Sr, Ca) (Ti, Nb)O₃ based semiconductive ceramics, which had appreciably different ones without SiO₂ addition, (2) A liquid phase sintering was considered to be the case with SiO₂ both of A-site and B-site excess samples from the TEM observations, (3) SiO₂ addition promoted a reproducible varistor effect even after 1 mA current flow, (4) Insulator composition with Bi₂O₃ to form the insulated boundary layer showed the occurrence of lower varistor coefficients, α<6. Bi₂O₃, which has been widely used for the capacitor, was not necessary to add the varistor property.

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Sintering behavior of SiC with oxide additives is controlled by SiO₂ content and particle size of starting powders at temperatures below 1900°C and chemical reactions, which evolve gaseous products (possibly SiO, Al₂O, CO), between SiC, free carbon, SiO₂ on SiC and oxide additives at temperatures above 1900°C.
The higher SiO₂ content leads to a higher sinterability at temperatures below 1900°C. The higher carbon content leads to a lower sintered density at temperatures above 1900°C. The β→α phase trasformation might be affected by the amount of 2H phase in raw materials. The materials sintered at 1950°C show homogeneous microstructure although significant β→α transformation has occurred during sintering. The α-SiC is more compatible with oxide liquid than β-SiC at temperatures above 1950°C.
Acknowledgment Stay of Young-Wook Kim in National Institute for Research in Inorganic Materials was supported by Japan-Korea Industrial Technology Co-operation Foundation (JKF).

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The formation process of 11CaO⋅7Al₂O₃⋅Ca(OD)₂ (C₁₁A₇⋅Ca(OD)₂) and its thermal stability were studied in controlled atmospheres containing heavy water vapor. The formation of 12CaO⋅7Al₂O₃(C₁₂A₇) solid solution in the system C₁₂A₇-C₁₁A₇⋅Ca(OD)₂ was examined by X-ray powder diffraction, and OD group included in C₁₁A₇⋅Ca(OD)₂ was identified by means of Fourier transform infrared spectroscopy (FT-IR). C₁₁A₇⋅Ca(OD)₂ was formed above 1050°C in a flow of air containing heavy water vapor. It was difficult to make the distinction of X-ray diffraction patterns among C₁₂A₇, C₁₁A₇⋅Ca(OH)₂ and C₁₁A₇⋅Ca(OD)₂, but the stretching vibration band of O-D at about 2620cm^-1 by FT-IR identified the hydrate. In a flow of dried helium gas, C₁₁A₇⋅Ca(OD)₂ decomposed into 5CaO⋅3Al₂O₃ (C₅A₃) in the temperature range from 1150 to 1250°C and finally changed into C₁₂A₇ at temperatures above 1250°C. On the contrary, C₅A₃ changed into C₁₁A₇⋅Ca(OD)₂ by heating at about 1100°C in a flow of air containing heavy water vapor. It seemed that the reaction between C₁₁A₇⋅Ca(OD)₂ and C₅A₃ proceeded reversibly. C₁₁A₇⋅Ca(OH, OD)₂ including both OH and OD group was formed by burning in a flow of wet air with controlled mixing ratio of light and heavy water.

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In order to discuss the effect of grain size on material removal mechanism and crack type beneath the groove, the single point grinding tests of alumina ceramics with three kinds of grain sizes were carried out by use of conical diamond. The specimens of dense alumina ceramics were prepared by hot isostatic pressing (HIP) after presintering at various temperatures. The state of grooves were observed by SEM, and grinding force were measured by dynamometer. Main conclusions are obtained as follows: (1) Material removal mechanism changed from pseudo-plastic flow type to brittle fracture type with increase in depth of cut. The depth of cut, which varied from pseudo-plastic flow type to brittle fracture type, was increased with decrease in grain size. (2) The crack type varied from lateral and median type to microcrack with increase in grain size. (3) The normal grinding force was influenced by material removal mechanism of alumina ceramics.

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Phenolic resin has been widely used as a binder for carbon-containing refractories. Carbon from phenolic resin, however, is so called non-graphitizing carbon and its oxidation resistance is poor. In this paper, oxidation resistance and crystallization of carbon from phenolic resin added to carbon-containing refractories were investigated. In MgO-C refractory, owing to the effect of Mg(g) and CO₂(g) formed by the reaction between MgO and C, the crystallization of the carbon from phenolic resin was enhanced and the oxidation resistance was improved, whereas in Al₂O₃-C refractory, owing to the low equilibrium partial pressure of Al(g), no changes were found in the crystallization and the oxidation resistance of the carbon.

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The dc electrical conductivity, σ, of 60V₂O₅⋅10ZnO⋅30TeO₂ glass (mol%) prepared by press-quenching was measured under Ar and O₂ gas atmospheres and oxygen gas-sensing properties were investigated at temperatures ranging from 303 to 473K. Sigma at 443K in 100% Ar was determined to be 8.53×10^-4S·cm^-1, which was higher than σ in air (σ_443K=7.82×10^-4S·cm^-1), while σ_443K in 100% O₂ gas was 3.57×10^-4S·cm^-1, lower than the σ value in air. This means that V⁴⁺ ions in the glass were oxdized by O₂ gas which diffused into the glass, resulting in an increase in V⁵⁺ with time. The experimental relationship between σ and oxygen partial pressure P_O2 agreed well with the theoretical relation σ ∝ P_O2^-1/4. From data of dynamic change O₂ gas sensitivity, S, defined as the ratio of dcresistivity in Ar gas to that in O₂ gas, at 473K was obtained to be 1.3 under 100% O₂ gas. Changes in σ by switching between 100% O₂ and 100% Ar were found to be reproducible. These changes were explained by the oxygen diffusion and desorption model. Good agreements was found between calculated σ and the experimental σ-t relationship. From these discussions, it is concluded that the present tellurite glass has a potential applicability to O₂ gas sensor.

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In order to prepare carbon-ceramics composites having spherical shape, a powder mixture of carbon and zirconium diboride (ZrB₂) was heat-treated at 2400, 2600 and 2800°C. Carbon black, calcined pitch coke and natural graphite were used. Above 2600°C, spherical bodies of silver color, about 20μm-2mm in diameter, were formed for all carbon powders. The spherical body was the spherical composites in the system carbon-ZrB₂; the surface was covered with polyhedral graphite and the inside was composed of small graphite and ZrB₂ particles. The formation process of the spherical composites is considered as follows: ZrB₂ in contact with carbon fuses in the temperature range of 2400 to 2600°C, carbon dissolves in the fused ZrB₂, the ZrB₂ containing carbon changes into spheres by surface tension, and the carbon dissolved in ZrB₂ separates out as graphite during cooling.

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Mechanical properties of Si-Ti-C-O fiber-bonded-ceramic materials synthesized from pre-oxidized Si-Ti-C-O fibers with a surface oxide layer of 90 to 190nm in thickness were investigated. The Si-Ti-C-O fiber-bonded-ceramic material was synthesized by hot-pressing the pre-oxidized Si-Ti-C-O fiber at 2123K under 50 MPa. Flexural strength and fracture toughness of the Si-Ti-C-O fiber-bonded-ceramic material increased with an increase in the thickness of the oxide layer, whereas the inter-laminar-shear strength decreased under the same condition. These changes were considered to be due to differences in formation condition of the interfacial carbon layer formed by the excess carbon which was isolated from the Si-Ti-C-O fiber during hot-pressing. Moreover, the interfacial carbon layer was found to be formed when the rawmaterial's fiber with a thick surface oxide layer was used.

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A precursor of nickel silicate was synthesized by the reaction of nickel nitrate with sodium metasilicate in an aqueous solution. The reaction was carried out by adding a sodium metasilicate solution of 0.75mol/l to a refluxed nickel nitrate solution of 1.5mol/l in a dropwise way and reacted for 1h. The precursor was then sintered at 1200°C for 2h. The reaction can be assumed to proceed by the following process.
Na₂SiO₃+2Ni(NO₃)₂+3.5H₂O→Ni₂SiO₄⋅2.5H₂O+2HNO₃+2NaNO₃
The precursor and sintered samples were analyzed by XRD, atomic absorption spectrometry and TG/DTA. The sintered sample was confirmed to be nickel silicate, Ni₂SiO₄. Nickel hydroxide remaining unreacted in the sintered sample was removed by treating the nickel silicate precursor with an anmmonia solution, and cristobalite was also removed from the sintered product by dissolving it in a hydrofluoric acid. The resulting sample was shown to be pure nickel silicate, Ni₂SiO₄, by XRD.

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Highly c-axis-oriented lanthanum- and magnesium-modified PbTiO₃ (PLMT) thin films were successfully prepared on (100)-oriented Pt film electrodes/(100)MgO single-crystal substrate by rf-magnetron sputtering method. The c-axis orientation, crystallinity, and structure of surface and cross section of films obtained were investigated in details. As a result, thin films with the compositions of {(1-x)Pb_0.9La_0.1Ti_0.975O₃+xMgO}, where x=0.005-0.010, show great promise as new element thin-film materials, from the viewpoint of the crystallographic properties.

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Thick Zn₂SnO₄ films have the highest sensitivities to NO₂ among the examined complex oxides with spinel structure. Although the NO₂-gas sensitivities of thick Zn₂SnO₄ films decrease with increasing temperature, high sensitivities are obtained in the temperature range of 573 to 673K. The sensitivities of the present Zn₂SnO₄ films are comparable to those of NO₂-sensitive oxides such as WO₃ and ZnO.

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Zirconium oxide gel was prepared by electrochemical reduction of aqueous solution containing zirconium oxychloride octahydrate and zirconium oxynitrate dihydrate. The gel was formed at a Pt electrode below -1.0V (vs. Ag/AgCl). The gel formation by potentiostatic reduction at -1.8V occurred continuously with evolution of hydrogen gas, which caused the gel to drop off from the Pt electrode. It is found that the gel obtained from zirconium oxychloride decomposed to tetragonal zirconium oxide when the freeze-dried gel was heated up to 600°C.

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La, Mn-codoped BaTiO₃ ceramics were prepared by using high purity starting materials to clarify the influence of Mn addition on the positive temperature coefficient of resistivity (PTCR) effect. No sintering aids such as SiO₂ and excess TiO₂ were used. Resistivity at room temperature, grain growth and Curie temperature (T_C) were studied as functions of Mn content. The Curie temperature of La-doped BaTiO₃ increased initially and then decreased with increasing Mn addition, and the Mn concentration of giving the maximun T_C depended on the doping concentration of La. This newly observed phenomenon is interpreted in terms of the state of Mn in the compound in connection with the variation of its bulk and grain boundary resistivity. The largest PTCR effect was observed around the concentration of Mn giving the maximum T_C.

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The effect of structure and chemistry of interphase on the fracture behaviour of the SiC fibre/pyrex composites has been examined using TEM and PEELS. For all Nicalon/pyrex samples investigated, interfacial layers of -30-35nm thickness were observed, regardless of variations in the interfacial stress and difference in fracture mode. The sample of Tyranno fibre-reinforced pyrex which fractured in a brittle manner, and showed extensive diffusion of matrix elements into the fibres had a much thicker interfacial layer of -100nm thickness. SAD pattern and PEELS data confirmed that the interfacial layer in Tyranno/pyrex was carbon-rich. This indicates that the presence of a carbon-rich interfacial layer does not necessarily lead to damage-tolerant composites.

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Electrically equivalent circuits for the paraelectric phase of layer-structured BaBi₄Ti₄O₁₅ single crystals in the parallel and perpendicular directions to the (Bi₂O₂)²⁺ layer were identified by complex impedance and modulus analysis at 600 to 767°C. The same form of single semicircle in complex impedance plots for both directions could be differentiated by using complex modulus plots. The equivalent circuits for the parallel and perpendicular directions to the (Bi₂O₂)²⁺ layer were identified as a single parallel RC circuit and two parallel RC circuits in a series array, respectively.

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