Journal of the Ceramic Society of Japan
Online ISSN : 1882-1022
Print ISSN : 0914-5400
ISSN-L : 0914-5400
Volume 102, Issue 1190
Displaying 1-19 of 19 articles from this issue
  • Atsuomi FUKUURA, Yasumichi OISHI
    1994 Volume 102 Issue 1190 Pages 897-901
    Published: October 01, 1994
    Released on J-STAGE: August 06, 2010
    JOURNAL FREE ACCESS
    The grain-boundary diffusion equation, Eq. (1.11), was derived for the small-grain deep-penetration diffusion, and solved for the instantaneous source condition. The obtained solution, Eq. (2.9), consists of two terms, one is the simple diffusion solution for the grain-boundary diffusion only, and the other is the factor which expresses the effect of the flux from the grain boundary toward the interior of the grains.
    Equation (3.4), which gives the average concentration at given distance and time, should be useful for determination of the diffusion parameters for the grain boundary and the bulk by tracer technique, and also for the analysis of kinetics in the formation of a grain-boundary phase by preferential diffusion in dielectric ceramics.
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  • Kiyosumi FUJII
    1994 Volume 102 Issue 1190 Pages 902-907
    Published: October 01, 1994
    Released on J-STAGE: August 06, 2010
    JOURNAL FREE ACCESS
    Selective adsorption of lithium ions from molten NaNO3 containing a slight amount of lithium ions was examined using various inorganic adsorbents. Consequently, activated alumina was found to be the most promising adsorbent for adsorption of lithium ions because of its high recovery. Adsorption by activated alumina involved chemisorption with the activation energy of 70.7kJ/mol. It was confirmed that activated alumina showed high stability when mixed with molten salt because no changes of specific pore volume, surface area, or pore size distribution were observed throughout adsorption at high temperatures. Since the adsorption of lithium ions by activated alumina obeyed Freundlich's equation, it was found that the adsorption can be treated as that of lithium ions in dilute solution. The enrichment of lithium ions on activated alumina was much higher than that of sodium ions, indicating that the selective adsorption of lithium ions from molten salt by activated alumina is feasible.
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  • Osamu FUNAYAMA, Yuji TASHIRO, Tomoko AOKI, Takeshi ISODA
    1994 Volume 102 Issue 1190 Pages 908-912
    Published: October 01, 1994
    Released on J-STAGE: August 06, 2010
    JOURNAL FREE ACCESS
    Polyaluminosilazane was synthesized by the reaction of perhydropolysilazane with (ethyl acetoacetate) aluminumdiisopropoxide. The chemical structure of this polymer was investigated by infrared spectroscopy and nuclear magnetic resonance and it was found that this polymer contains some Al-N bonds. Amorphous SiAlON was obtained by pyrolysis of this polymer in a stream of anhydrous ammonia to 1000°C with a high ceramic yield. Crystallization to fine crystalline β′-SiAlON or mixture of J′-SiAlON and mullite proceeded on heat treatment at 1500°C under N2. These results indicate that polyaluminosilazane is a good precursor for SiAlON-based materials.
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  • Shigeki TAKEUCHI, Mototsugu SAKAI
    1994 Volume 102 Issue 1190 Pages 913-918
    Published: October 01, 1994
    Released on J-STAGE: August 06, 2010
    JOURNAL FREE ACCESS
    Stress-induced microcrack toughening is studied through the numerical fracture mechanics with the finite element method. In our numerical model, the stress-induced microcrack zone is represented by the local reduction of the Young's modulus. The microcrack toughening is discussed in terms of the changes in the Young's modulus, Poisson's ratio, and the dimension and the shape of the process zone. The reduction of the local stress intensity factor at the crack-tip, KITIP, results in toughening. The reduction of KITIP is proportional to the decrease in the Young's modulus, and enhanced through the decrease in the Poisson's ratio. The KITIP reduces significantly with increasing the dimension of the process zone, and then followed by saturation. This toughening effect diminishes for an infinitely large process zone. The shape of the process zone makes an important influence on stress shielding, as well.
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  • Yoshihiko OKADA, Tsuguya MASUDA, Hideki ISHIDA, Hirotsugu NISHIDO
    1994 Volume 102 Issue 1190 Pages 919-924
    Published: October 01, 1994
    Released on J-STAGE: August 06, 2010
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    The silicate anion structure and thermal decomposition behavior of okenite were studied mainly using solid 29Si NMR. The silicate anion structure of okenite is very close to some parts of the sheet structure of gyrolite. Dehydration occurs at around 119 and 315°C which are caused by the decomposition of the double-chain and sheet structure, and the sheet structure, respectivly. Although, the dehydration is caused by the water in the interlayer of okenite, and the main silicate anion structure remains untill around 350°C. From 350 to 700°C, the silicate anion structure decompose gradually as the temperature increases and many kinds of silicate anions are formed from the double-chain and the sheet structure of okenite. By the thermal treatment above 800°C, wollastonite, pseudo-wollastonite and amorphous silica are formed and pseudo-wollastonite, cristobalite, quartz and silica glass are formed over 1200°C.
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  • Hideaki SANO, Huiming CHENG, Yasuo UCHIYAMA, Kazuo KOBAYASHI
    1994 Volume 102 Issue 1190 Pages 925-929
    Published: October 01, 1994
    Released on J-STAGE: August 06, 2010
    JOURNAL FREE ACCESS
    Oxidation of a carbon/B4C/SiC/ZrB2 composite was investigated at 900°C in moist air atmospheres. From mass change measurement, scanning electron microscopy (SEM) observation, X-ray powder diffraction analysis and ion microprobe mass analysis before and after oxidations, the structure of oxidized layer was examined. The mass of the sample decreased with oxidation time and linearly with an increase in partial pressure of the moisture. Cross sectional observation showed that the oxidized layer was formed on the sample and the oxidized layer was porous in comparison with the sample core. The oxidized layer consisted of SiC and ZrO2, but carbon and boron were not detected. To discuss the formation process of the oxidized layer, thermodynamic calculations were performed. The equilibrium partial pressure of boric acids was calculated as a function of temperature or partial pressure of moisture. It is clarified that B2O3(s, l) formed from B4C and ZrB2 by oxidation reacted with H2O(g) to produce HBO2(g), (HBO2)3(g) and H3BO3(g) at elevated temperatures and the equilibrium partial pressure of these boric acids became high at 900°C in H2O(g)-containing atmospheres. Based on the experimental results and thermodynamic considerations, the formation process of the oxidized layer at 900°C in moist air was discussed.
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  • Takao NISHIOKA, Yoshio TANAKA, Akira YAMAKAWA, Masaya MIYAKE
    1994 Volume 102 Issue 1190 Pages 930-935
    Published: October 01, 1994
    Released on J-STAGE: August 06, 2010
    JOURNAL FREE ACCESS
    Si3N4 ceramics were surface-ground under different conditions, and the grindability was evaluated by specific grinding energy and stock removal rate. Statistical analysis was conducted on the specific grinding energy and stock removal rate with respect to the maximum grain depth of cut by a new method of directly evaluation successive cutting point spacing. Main results are summarized as follows; (1) The specific grinding energy decreases with increasing stock removal rate. This result shows that the fraction of brittle fracture of Si3N4 increases with increase in the stock removal rate. (2) By a new method for determining successive cutting point spacing, a difference in distribution of cutting edges between resinoid-bonded and metal-bonded wheels with the same grain size and concentration was evaluated. Furthermore, the maximum grain depth of cut of each wheel was represented by statistical analysis. (3) Decrease in the specific grinding energy was caused by the increase in statistical mean value of the maximum grain depth of cut. The stock removal of Si3N4 including brittle fracture was observed even at its level less than 1μm.
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  • Motoyuki MIYATA, Yoshiyuki YASUTOMI
    1994 Volume 102 Issue 1190 Pages 936-939
    Published: October 01, 1994
    Released on J-STAGE: August 06, 2010
    JOURNAL FREE ACCESS
    The Sintering Behavior of powder mixture compacts of Si and B4C in nitrogen atmosphere at 1350°C was investigated. Mainly, Si was changed into α-Si3N4 and β-Si3N4 by a reaction with nitrogen, and B4C was changed into BN and C, and C was converted into β-SiC by a reaction with Si. BN seemed to have an effect on reducing the number of pores in the nitrided body. B4C retarded nitridation of Si. An Si-B-C-N-O layer and BN were formed on the surface of unnitrided Si particle in the nitrided body. An SiO2-B2O3 layer formed on the surface of the Si particle in the nitriding stage seemed to retard nitridation of Si.
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  • Tsuyoshi HAGIO, Yuji MIYAZAKI, Kazuo KOBAYASHI
    1994 Volume 102 Issue 1190 Pages 940-943
    Published: October 01, 1994
    Released on J-STAGE: August 06, 2010
    JOURNAL FREE ACCESS
    Pressureless sintered products of h-BN were fabricated by heating ground BN powders at temperatures between 900 and 2000°C. The BN products with bending strengths of 40 to 70MPa were obtained at the sintering temperatures above 1400°C, while they contained an appreciable amount of oxygen as impurity, except for the 2000°C products. The strength of sintered bodies increased with increasing sintering temperature up to 1600°C, with the release of boron compounds such as boric oxide. SEM and TEM observations indicated that grain growth or coarsening of BN particles took place above 1800°C with the vaporization of boron compounds, which reduced lowered slightly the strength of BN products.
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  • Minoru TAKAHASHI, Terumoto FUJIWARA, Hideo HAYASHI, Osamu NISHIZATO, M ...
    1994 Volume 102 Issue 1190 Pages 944-949
    Published: October 01, 1994
    Released on J-STAGE: August 06, 2010
    JOURNAL FREE ACCESS
    Tetragonal ZrO2 fiber/PZT composites were fabricated by slip casting and normal sintering in order to improve mechanical properties of PZT. With increasing fiber content from 0 to 20vol%, green densities increased from 57 to 63%, but fired densities decreased from 97.5 to 89.1%. Anisotropic shrinkage due to orientation of the fibers in casting occurred during firing. Mechanical properties were measured on the unpoled composites by applying the load in the direction perpendicular to the fiber orientation. In spite of the considerable decrease in fired density, bending strength of the composites remained at a constant value of 80MPa. On the other hand, fracture toughness KIC increased from 0.91 to 1.29MPa⋅m1/2. The composites were poled by applying a DC field in the direction perpendicular to the fiber orientation. Addition of fibers reduced both permittivity and electromechanical coupling factor k31 in the tetragonal ZrO2 fiber/PZT systems like in the monoclinic ZrO2 fiber/PZT systems.
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  • Toshio SHIMOO, Kazuo OHATA, Masaki NARISAWA, Kiyohito OKAMURA
    1994 Volume 102 Issue 1190 Pages 950-956
    Published: October 01, 1994
    Released on J-STAGE: August 06, 2010
    JOURNAL FREE ACCESS
    The conversion mechanism from oxidation-cured polycarbosilane to SiC ceramic fibers have been investigated. The fibers were heated isothermally and the conversion rate was determined by thermogravimetry at temperatures from 553 to 1673K in an Ar stream. The heat-treated fiber was examined by X-ray diffraction, infra-red spectroscopy, specific resistance measurement and tensile test. Below 800K, the fiber was in organic state. In the temperature range of 800 to 1000K, the conversion produced a very large increase in tensile strength. And then, in the temperature range from 1000 to 1500K, β-SiC crystallites grew and the maximum strength was obtained. Above 1500K, the pyrolysis coarsened the SiC crystals and lowered the strength. The conversion rate was described by the first order rate equation. The activation energy was 42.8kJ⋅mol-1. The conversion is considered to be controlled by the chemical reaction and the mass transfer through the gas film.
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  • Akira KAMIYA, Kikuo NAKANO, Sigeharu MORIBE, Toru IMURA, Hiroshi ICHIK ...
    1994 Volume 102 Issue 1190 Pages 957-960
    Published: October 01, 1994
    Released on J-STAGE: August 06, 2010
    JOURNAL FREE ACCESS
    Conventional NICALON fiber has a refractoriness of only about 1200°C because of its high oxygen content. Recently a new fiber HI-NICALON with improved refractoriness has been developed. The slurry process developed by the authors was adopted for the fabrication of HI-NICALON fiber-reinforced Si3N4 composites. Carbon-coated HI-NICALON fiber-reinforced composites showed high strength and toughness. At room temperature, samples hot-pressed at 1550°C showed a flexural strength of 890±10MPa and KIC of 29±8MPa√m, respectively. Samples hot-pressed at 1600°C showed high values at 1200°C; 640±70MPa of flexural strength and 18.3±0.8MPa√m of KIC. On the other hand, non-coated HI-NICALON fiber-reinforced composites showed a higher flexural strength at 1400°C than the coated ones, however, they showed a brittle fracture and KIC values were only 3 to 4MPa√m.
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  • Koichi AWAZU, Hideo ONUKI
    1994 Volume 102 Issue 1190 Pages 961-965
    Published: October 01, 1994
    Released on J-STAGE: August 06, 2010
    JOURNAL FREE ACCESS
    In-situ measurements of optical absorption in silica glass were carried out under irradiation of VUV light using undulator radiation. Optical loss at 6.7eV and 7.6eV increased with increasing of total dosage. It was also observed that the increase in the optical loss depends on the preparation method of silica glass. Optical loss caused by the VUV irradiation was restricted in silica glass having fluorine and OH groups.
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  • Kazumichi YANAGISAWA, Koji IOKU, Nakamichi YAMASAKI
    1994 Volume 102 Issue 1190 Pages 966-971
    Published: October 01, 1994
    Released on J-STAGE: August 06, 2010
    JOURNAL FREE ACCESS
    Porous silica ceramics with homogeneous pore distribution were prepared by the hydrothermal hot-pressing of silica gels. The recovered porous ceramics had high mechanical strengths with large pore volumes. The ceramics prepared at 300°C and 20MPa for 1h with 17.2mass% water showed the following properties; high compressive strength (60MPa), low bulk density (0.68g/cm3), large pore volume (0.98cm3/g), and uniform pore distribution with average pore size of 65nm. The average pore diameter of the ceramics was controlled from 25 to 100nm by selecting hydrothermal hot-pressing conditions and starting silica gels. The formation mechanism of large pores in the silica ceramics could be elucidated by capillary effects.
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  • Takayasu IKEGAMI, Varanasi SRIKANTH, Hajime HANEDA, Takebumi MITSUHASH ...
    1994 Volume 102 Issue 1190 Pages 972-975
    Published: October 01, 1994
    Released on J-STAGE: August 06, 2010
    JOURNAL FREE ACCESS
    In scanning electron microscopy (SEM) observation, ceramic insulators are usually coated with conductive elements such as gold, palladium-gold alloy and carbon to avoid charging-up. In the present investigation, it was observed that charging is not serious above a certain temperature, even without coating. Those particular temperatures are 150°C for yttria-doped zirconia, 400°C for alumina and silicon nitride and 500°C for hexagonal boron nitride. The order of these temperatures is consistent with the order of reported electric resistances of them. Disappearance of the charging problem has been explained as due to transport of electrons through enhanced diffusion layers on the surfaces.
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  • Mechanical and Thermal Properties of C/SiC/B4C Composites
    Ichitaro OGAWA
    1994 Volume 102 Issue 1190 Pages 976-981
    Published: October 01, 1994
    Released on J-STAGE: August 06, 2010
    JOURNAL FREE ACCESS
    Mechanical and thermal properties of the C/SiC/B4C composites made by a normal pressure sintering process were examined as a function of SiC and B4C content. The composites showed an increase in bending strength due to dispersions of the particles, which was more markedly than that of the composites made by hot press method. The increase in mechanical strength was due to not interactions between cracks and dispersed particles but an increase in Young's modulus of the composites. The thermal expansion coefficient decreased with an increase of SiC and B4C content, which showed the same feature in temperature dependence as conventional carbon bodies, that is, the slopes of the increases became small at around 400°C. The particle dispersions of SiC and B4C improved the thermal conductivity at room temperatures. Thermal shock fracture resistance, R and R′, showed the maximum values when the SiC and B4C content was around 30vol%.
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  • Takayuki NAGANO, Fumihiro WAKAI
    1994 Volume 102 Issue 1190 Pages 982-985
    Published: October 01, 1994
    Released on J-STAGE: August 06, 2010
    JOURNAL FREE ACCESS
    Cyclic bending fatigue tests were performed on Y-TZP, Y-TZP/Al2O3 composite (3Y20A), and superplastic diffusion-bonded materials. The relation between the maximum stress (σmax) and the number of cycles to failure (N) was expressed as N=Bmaxn. The fatigue exponents (n) of Y-TZP and 3Y20A were 26 and 61, respectively. Every fatigue specimen of 3Y20A-3Y20A bonded material was fractured at the bonding interface with the fatigue exponent of 24. In the fatigue test of TZP-TZP bonded material, 33% of specimens were fractured at the bonding interface with the fatigue exponent of 16. The fatigue exponent of TZP-TZP bonded materials which were fractured at Y-TZP part was the same with that of Y-TZP. When fracture occurred at the bonding interface, ground marks were observed on the fracture surface. The bonded materials were more susceptible to cyclic fatigue than the base materials.
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  • Takayuki NAGANO, Fumihiro WAKAI
    1994 Volume 102 Issue 1190 Pages 986-989
    Published: October 01, 1994
    Released on J-STAGE: August 06, 2010
    JOURNAL FREE ACCESS
    Fracture strength and fracture behavior using tensile and bending specimens machined from superplastic diffusion bonded bodies between ZrO2 and ZrO2/Al2O3 composite were compared and examined. The difference in fracture behavior by testing methods was not observed for all kinds of specimens. The strength ratio calculated by effective volume, effective area and Weibull modulus was influenced by fracture behavior. If we estimate the fracture strength of bonded material from those in different testing methods, fracture behavior of bonded material must be considered.
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  • Satoru YOSHIHARA, Fumiaki MIYAJI, Tadashi KOKUBO, Naomi NISHIMURA, Tak ...
    1994 Volume 102 Issue 1190 Pages 990-993
    Published: October 01, 1994
    Released on J-STAGE: August 06, 2010
    JOURNAL FREE ACCESS
    Bioactive cement which can set in a few minutes and bond to living bone is obtained by mixing CaO-SiO2-P2O5-CaF2 glass powders with ammonium phosphate solution. The mechanical strength of the cement has been investigated as a function of phosphate ion concentration and pH of the ammonium phosphate solution and powder to liquid ratio. A glass powder with a composition CaO 47.1, SiO2 35.8, P2O5 17.1, CaF2 0.75 in mass ratio was mixed with ammonium phosphate solution, placed in 100% humidity at 37°C for 1h and immersed into a simulated body fluid (SBF). The compressive strengths of the cements soaked in SBF for 23h increased with increase in phosphate ion concentration and pH of the ammonium phosphate solution and in powder to liquid ratio. It has been found that the cements using ammonium phosphate solution with pH 7.4 and phosphate ion concentration of 3.7M give the highest compressive strength of 58MPa. It has been indicated that for the fixed ratio of powder to liquid, the compressive strength of the cement soaked in SBF increases with increasing amount of the hydroxyapatite layer formed at the intergranular spaces in the glass powders.
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