Journal of the Ceramic Society of Japan
Online ISSN : 1882-1022
Print ISSN : 0914-5400
ISSN-L : 0914-5400
Volume 101, Issue 1180
Displaying 1-23 of 23 articles from this issue
  • Katsutoshi KOMEYA, Noriyuki MATSUKAZE, Takeshi MEGURO
    1993 Volume 101 Issue 1180 Pages 1319-1323
    Published: December 01, 1993
    Released on J-STAGE: August 06, 2010
    JOURNAL FREE ACCESS
    Direct nitridation of Al-alloys such as Al-Y, Al-Ca, and Al-Li was investigated with particular emphasis on the alloy composition, reaction temperature and reaction time. The alloys Al-2.3wt% Li, Al-5.0wt% Li and Al-5.0wt% Ca converted completely to AlN in very short soaking time at 1000°C. For Al-1.0wt% Li and Al-0.5wt% Li conversion ratios at 1000°C for 5h were 28.2 and 12.6%, respectively. On the other hand, no noticeable reaction was seen for Al-Y alloy and pure Al. The product from Al-Ca alloy was difficult to crush, which seemed to be a disadvantage for AlN powder synthesis. The reaction using Al-2.3wt% Li alloy could be divided into three categories: namely, surface nitridation, volume nitridation and breakaway nitridation. In the surface nitridation, the conversion ratio was very low, indicating the thickness of AlN layer was several tens of micron meters. In the volume nitridation the conversion ratio was in the extent of about 10%, and AlN porous surface layer formed. In the breakaway nitridation, complete conversion to AlN was attained, and the product greatly expanded to show no trace of the original form. The AlN product in the breakaway nitridation consisted of rod-like, plate-like and spherical grains. The size increased with increasing reaction temperature.
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  • Byoung Ouk KIM, Su Jin CHUNG
    1993 Volume 101 Issue 1180 Pages 1324-1329
    Published: December 01, 1993
    Released on J-STAGE: August 06, 2010
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    The mechanism of the changes in the refractive index of sol-gel derived 80TiO2⋅20SiO2 films dip-coated on commercial soda-lime-silicate glass and silicon wafer has been investigated by the ellipsometry and X-ray photoelectron spectroscopy. As the drying time after coating increased, the refractive index increased along with the decrease in film thickness by the evaporation of ethanol and water which were produced by the hydrolysis and polycondensation reaction. The refractive index of films coated on glass substrate was markedly lower than that coated on silicon wafer. This was due to sodium ions in films, which diffused from glass substrate and induced Na2Ti2Ti6O16 phase formation in the film. The refractive index of thick films was higher than that of thin films because sodium ion took more time to diffuse through thick films. The increase in the refractive index along with the decrease in the thickness of films prepared by the fast heating process was due to the sudden collapse and fast shrinkage of gel film before polycondensation reaction and thus to the higher packing density of film.
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  • Yoshiyuki KOWADA, Hirohiko ADACHI, Tsutomu MINAMI
    1993 Volume 101 Issue 1180 Pages 1330-1334
    Published: December 01, 1993
    Released on J-STAGE: August 06, 2010
    JOURNAL FREE ACCESS
    The electronic states of the SiO2-MxOy(MxOy=P2O5, TiO2 and ZrO2) glasses, which have good passivation ability, were calculated by the DV-Xα cluster method. The energy level structure of glasses containing the transition metal oxides, TiO2 and ZrO2, is different from that of pure SiO2 and SiO2-P2O5 glasses. The bond order between oxygen and sodium ion diffusing to the glass matrix in the systems SiO2-P2O5, SiO2-TiO2 and SiO2-ZrO2 is larger than that in SiO2 glass. Such a result is probably the origin of the passivation ability of these glasses.
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  • Isao MATSUSHITA, Yukitoshi HAMADA, Takashi SUZUKI, Yuji NOMURA, Toshih ...
    1993 Volume 101 Issue 1180 Pages 1335-1339
    Published: December 01, 1993
    Released on J-STAGE: August 06, 2010
    JOURNAL FREE ACCESS
    The crystal system of BCC (basic calcium carbonate) was determined by analyzing XRD patterns and SAED spot patterns. It was proved that the BCC was assigned to an orthorhombic system, having the lattice constants of a=7.094Å, b=8.627Å, and c=6.558Å. The decomposition process of BCC in water at 40-80°C was investigated by means of XRD, SEM, TEM, and SAED. XRD measurement showed that BCC decomposed to Ca(OH)2, calcite, and aragonite. Elevation of the slurry temperature resulted in an exponential increase of the decomposition rate and a decrease of the yield of aragonite. SEM, TEM observations and SAED measurement indicated that CaCO3 (calcite and aragonite) deposited on the surface of BCC particles resulting from the dissolution of Ca2+ ion from BCC in the early stage of decomposition. With progress of decomposition, the aragonite grew in the [001] direction and the number of calcite particles increased. Ca2+ ion dissolved into the liquid phase precipitated as Ca(OH)2 and grew to large single crystals with progress of the decomposition.
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  • Tohru KINERI, Masami MORI, Kohei KADONO, Toru SAKAGUCHI, Masaru MIYA, ...
    1993 Volume 101 Issue 1180 Pages 1340-1345
    Published: December 01, 1993
    Released on J-STAGE: August 06, 2010
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    Gold-dispersed BaTiO3 thin films and gold-dispersed SiO2 thin films were prepared by r. f. magnetron sputtering method. The as-deposited films were heat-treated in air at temperature ranging from 700 to 900°C for 1h, and were compared to the optical properties of these films. For the SiO2 matrix, an absorption peak position shifted toward longer wavelength from 520 to 535nm as the volume fraction of gold increases, and gold fine particles were spherical and were uniformly dispersed in the films. In contrast, for the BaTiO3 matrix, an absorption peak position shifted from 580 to 640nm. The matrix had substantially crystallized, and the size of matrix grain and the gold particle size varied widely. The nonlinear optical property of these thin films was measured by the degenerate four-wave mixing (DFWM) method using a frequency-doubled Nd: YAG laser with 7ns pulse duration. Third-order nonlinear susceptibility χ(3) of gold-dispersed BaTiO3 films increased with increasing the heat-treating temperature, volume fraction of gold in these films and the mean particle size of gold. The values of χ(3)532 of BaTiO3 films were much larger than those of SiO2 films. It seemed that BaTiO3 matrix contributes to increase the value of χ(3)532. The resulting maximum value of gold-dispersed BaTiO3 films was 3×10-6esu. The large χ(3) may be ascribed to the high dielectric constant of the films.
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  • Isao SHIMONO, Shoichi NAGATA, Hajime KONISHI, Yoshikazu HAMAGUCHI
    1993 Volume 101 Issue 1180 Pages 1346-1350
    Published: December 01, 1993
    Released on J-STAGE: August 06, 2010
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    The process of the 2223 phase formation from the precursor prepared by the citrate method was investigated X-ray diffraction, thermal analysis, thermal expansion measurement and SEM/EDX. It was found that Bi(Ca0.5Sr0.5)Oz, Ca2PbO4, CuO and SrCO3 coexist before the occurrence of the partial-melt. It was also found that the citrate route accelerates the formation of Bi(Ca0.5Sr0.5)Oz, which decreases the partial-melt temperature by about 40K. Powder mixtures of the above coexisting phases prepared by solid-state reaction could be converted via heat-treatment to a product that contained 2223 phase in a volume fraction as high as that of the specimen prepared by the citrate method.
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  • Hidetsugu MORI, Jun IGARASHI, Hironobu SAKATA
    1993 Volume 101 Issue 1180 Pages 1351-1357
    Published: December 01, 1993
    Released on J-STAGE: August 06, 2010
    JOURNAL FREE ACCESS
    Glasses in the system of V2O5-ZnO-TeO2 glasses were prepared by rapid quenching and their dc-condutivity was studied. A large glass formation region was found i.e., ZnO=0-60mol%, V2O5=0-70mol%, TeO2=30-100mol%. The glasses were found to be n-type semiconductors. Dc-conductivities (σ) were in the range from 9.5×10-7 to 5.7×10-7S⋅cm-1 at 473K for V2O5=30-60mol%. The conduction was due to adiabatic small polaron hopping and non-adiabatic small polaron hopping for the glasses with V2O5>50 and V2O5<50mol%, respectively. The polaron band width (J) was estimated to be 0.01-0.10eV. The evaluated carrier mobilities μ were in the range from 4.1×10-8 to 8.9×10-7cm2⋅V-1⋅s-1 at 473K. The values of J and μ satisfied the conditions for the small polaron hopping conduction. The estimated carrier density (NC) was 0.15×1021-2.89×1021cm-3, depending upon V2O5 concentration. Seebeck coefficients (Q) of the glasses determined in the temperature range of 100-200°C exhibited no temperature dependence, and thus it is concluded that the dominant factor responsible for Q was the amount of V4+.
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  • Akira YAMAKAWA, Takao NISHIOKA, Masaya MIYAKE, Koji WAKAMORI, Akira NA ...
    1993 Volume 101 Issue 1180 Pages 1358-1362
    Published: December 01, 1993
    Released on J-STAGE: August 06, 2010
    JOURNAL FREE ACCESS
    Hugoniot-compression curves for Si3N4 ceramics with controlled microstructure were measured to study the yielding properties under shock compression, and the correlation with the microstructural characterization and the static mechanical strength. Hugoniot-measurement experiments were performed on 4 kinds of Si3N4 ceramics by means of the inclined-mirror method combined with a powder gun. The Hugoniot-elastic limits of fine-grained Si3N4 ceramics and the SiC whisker-reinforced Si3N4 ceramics (within 14-20GPa) were greater than the conventional Si3N4 (10-12.5GPa). It was found that the strength of Si3N4 ceramics under shock compression is strongly influenced by their microstructure, and the key to the high Hugoniot-elastic limit is to achieve a fine-grained microstructure or a composite structure containing high-strength materials such as SiC whiskers. It was also pointed out that the yield strength per unit weight under shock compression of the Si3N4 monolithic ceramics was proportinal to the static strength, but the yield strength per unit weight under shock compression of the SiC whisker reinforced Si3N4 was comparatively larger than that of monolithic Si3N4. In addition, it was suggested that the Hugoniot-measurement experiments are useful for evaluating the performance of ceramics, because the ceramics show the strength close to the intrinsic value under shock compression, due to the very high strain rate at the shock wave front.
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  • Yasuhiro MORIZONO, Minoru NISHIDA, Akira CHIBA
    1993 Volume 101 Issue 1180 Pages 1363-1368
    Published: December 01, 1993
    Released on J-STAGE: August 06, 2010
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    A 0.96 mass% C steel coated with chromium carbides was brazed to Si3N4 by using Ag-Cu/Ti alloy. Chromium carbides were coated on the steel at 1373K for 2.5 to 36h in an (Ar+HCl) mixture gas using the Cr powder pack process. The obtained coating layer consisted of M7C3 and M23C6 (M=Fe, Cr). The bonding treatment was performed at 1173K for 1h in vacuum. The shear strength of the joint increased with increasing coating layer thickness up to 20μm. The average and maximum shear strengths of the joint with a coating layer of 20μm in thickness were 209 and 258MPa, respectively. Those of the joint without the coating layer were 149 and 218MPa, respectively. The Weibull slopes for the shear strength were 9.4 in the former and 3.8 in the latter. It was considered that the coating layer played an important role as an active layer of interfacial reaction and as a relaxation layer of thermal stress in the joint. The difference in interfacial structures between these joints was also discussed on the basis of TEM observation.
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  • Kunio SHINOHARA, Takeshi MURAI
    1993 Volume 101 Issue 1180 Pages 1369-1373
    Published: December 01, 1993
    Released on J-STAGE: August 06, 2010
    JOURNAL FREE ACCESS
    Material characteristics of powder compacts are closely related to the packing structure of particle aggregates. In order to express the microscopic structure, a probability function of regular-shaped voids in the interspaces among particles over a cross section of the compact was studied theoretically and experimentally. It was found that the regular shape of the voids is normally circular, and that the void diameter becomes small and uniform for low voidage and narrow size distribution of particles. The reduction and uniformity of void diameter has been attributed to an increase in the number of smaller particle sections. The actual existence probability of any void is lower than the theoretical prediction because of the ineffective void spaces which are formed in the packing of regular-shaped voids among interparticle void spaces. The difference between theoretical and experimental probabilities of voids was correlated by a simple equation based on the total void spaces available.
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  • Yuichi SATO, Tsutomu KIYA, Haruo TAGUCHI, Syoichi IWAYA, Susumu SATO
    1993 Volume 101 Issue 1180 Pages 1374-1378
    Published: December 01, 1993
    Released on J-STAGE: August 06, 2010
    JOURNAL FREE ACCESS
    Thin films of a mixture system of Pr-Co-O were deposited on quartz glass substrates by RF sputtering. The films of Pr-O were polycrystalline, but addition of Co inhibited the crystallization of the films. As increasing Co content of the films, the electrical conductivities increased and their activation energies decreased. The same films were also deposited on semiconductive BaTiO3 ceramics to form hetero-junctions. Forward current of the junctions abruptly rose at about 2V, and the rising voltage was independent on the film composition. On the other hand, reverse current of the junctions increased with increasing of Co content, but abrupt rising of the current was not observed. Capacitance of Pr-O thin film-BaTiO3 junction was about 0.1μF/cm2, and increased to about 0.9μF/cm2 by addition of Co.
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  • Toshio SHIMOO, Toshihide HAYATSU, Masanori NARISAWA, Michio TAKEDA, Hi ...
    1993 Volume 101 Issue 1180 Pages 1379-1383
    Published: December 01, 1993
    Released on J-STAGE: August 06, 2010
    JOURNAL FREE ACCESS
    The pyrolysis of the low oxygen (1.7% O) SiC fiber prepared by the electron-irradiation curing method has been investigated. The pyrolytic rate was measured with a thermobalance in Ar at temperatures from 1673 to 1973K. The pyrolyzed fiber was examined by X-ray diffraction, SEM observation, specific resistance measurement and tensile test. Lowering of oxygen content in the fiber was found to be effective for the suppression of pyrolysis. The pyrolyzed fiber was composed of β-SiC and amorphous carbon. The growth and coarsening of SiC crystals were observed on the skin of the fiber, while the core was smooth and remained in the microcrystalline state. The tensile strength of the fiber, which was heated at 1973K for 3.6ks, retained 34% of that of the original fiber. The strength was correlated closely with the size of the β-SiC crystal in the fiber.
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  • Kouichi YASUDA, Junichi TATAMI, Kazutoshi ASADA, Yohtaro MATSUO, Shius ...
    1993 Volume 101 Issue 1180 Pages 1384-1389
    Published: December 01, 1993
    Released on J-STAGE: August 06, 2010
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    The influence of crack propagation path on the fracture toughness of polycrystalline Al2O3 was investigated. Polycrystalline Al2O3 with grain size from 1.8μm to 50μm was fabricated by hot pressing. Fracture toughness KIC was measured by the controlled surface flaw method and the chevron notched beam method. The value of KIC by the CSF method was 3.8MPa√m at a grain size of 1.8μm. It increased with the increase in grain size, and reached 4.5MPa√m at grain sizes larger than 30μm. The value of KIC by the CN method nearly agreed to the value of KIC by the CSF method. The fraction of transgranular fracture was 10% at a grain size of 1.8μm. It increased with the increase in grain size, and reached about 30% at grain sizes larger than 30μm. The critical energy release rate calculated from KIC linearly changed depending on the fraction of transgranular fracture. Consequently, it was shown that the change in frature toughness KIC of polycrystalline Al2O3 corresponded to the change in crack propagation path.
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  • Minoru MORIYAMA, Yuuji MAEDA, Kiichiro KAMATA
    1993 Volume 101 Issue 1180 Pages 1390-1394
    Published: December 01, 1993
    Released on J-STAGE: August 06, 2010
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    The D. C. electrical conductivity of nano-composite Si3N4-SiC films prepared by the plasma CVD method at 400°C was measured by the three-terminal technique. It was estimated that the electrical conduction in Si3N4 films was due to the hopping mechanism which gave the ohmic characteristics and Poole-Frenkel mechanism below and above the electric field of 9×106V⋅m-1, respectively. The electrical conduction in SiN1.01C0.28 (abbreviated as ‘SiNC’) and SiC films was estimated to show the hopping mechanism under the whole field studied. The activation enemies of coduction for Si3N4, SiNC and SiC films were approximately 0.72, 1.64 and 0.43eV, respectively at about 130°C; the SiNC film showed an extremely high value. The activation energies of these films were much lower than the optical band gaps (2.7-5.3eV). The electrical conduction in the compositional range from Si3N4 to SiC at a constant temperature showed a maximum near the atomic ratio (C/Si) of 0.3 without obeying the theory of composite. This was assumed that the electrical conduction of the SiNxCy films was influenced by the difference in number of valence electrons between N and C and the structural change from Si3N4 to SiC since N and C atoms around Si were mixed uniformly on an atomic scale.
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  • Kisato TONE, Masanobu KAMORI, Yasuo SHIBASAKI
    1993 Volume 101 Issue 1180 Pages 1395-1399
    Published: December 01, 1993
    Released on J-STAGE: August 06, 2010
    JOURNAL FREE ACCESS
    The relation between the plasticity of green bodies of natural kaolinitic clays (Kibushi- and Gairome-clay, Georgia-, New Zealand-, and Green Bush-kaolins) and the amounts of adsorbed cations on the surface of clay particles were investigated. Based on the Pfefferkorn method, the plasticity of green bodies was evaluated and the water film thickness was determined. For the adsorbed cations, the cation exchange capacities and the amounts of cations extracted with 1N KCl and 1N CH3COON4 solutions were measured. It was found that the plasticity of green bodies was closely related to the water film thickness depending upon the amount of adsorbed cations on the clay particle surface. Obtained results are as follows: (1) the water film thickness is almost independent of the amount of adsorbed mono-valent cations. It increases with increasing amount of adsorbed di-valent cations and decreases with increasing amount of adsorbed tri-valent cations, especially Al3+ ion, (2) kaolinites from weathering origins, i.e. Kibushi- and Gairome-clays are richer in di-valent and mono-valent cations (Ca2+, Mg2+, K+) than those from hydrothermal origins, Georgia-, New Zealand-, and Green Bush-kaolins.
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  • Keizo UEMATSU, Hiroshi TANAKA, Yao ZHANG, Nozomu UCHIDA
    1993 Volume 101 Issue 1180 Pages 1400-1403
    Published: December 01, 1993
    Released on J-STAGE: August 06, 2010
    JOURNAL FREE ACCESS
    This paper presents a novel characterization method which can reveal the presence of large crystalline particles of very low concentration and particle orientation in optically anisotropic granules, i.e. alumina. It involves an adequate immersion liquid which makes granules transparent and subsequent polarized optical microscopic examination. Large alumina particles are easily detected by this method: They are clearly visible under the crossed polarized light mode. Particle orientation in the matrix particles was also noted: Dark cross pattern appeared on the granules, showing the orientation of particle along the tangential direction of granules. The significance of these features for ceramic processing was discussed.
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  • Minoru TAKAHASHI, Kazuyoshi BABA, Osamu NISHIZATO, Akinobu TAKAMURA, M ...
    1993 Volume 101 Issue 1180 Pages 1404-1408
    Published: December 01, 1993
    Released on J-STAGE: August 06, 2010
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    Monoclinic ZrO2 fiber/PZT composites were fabricated by slip casting and pressureless sintering. The isoelectric points of ZrO2 and PZT were 4.8 and 7.6, respectively. Homogeneous composites were obtained by adjusting pH of slurries at 10. Although densification was inhibited by addition of fibers, a composite with 20vol% ZrO2 fibers attained a relatively high bulk density of 93%. The grain size of PZT matrix was almost invariant with addition of fibers. EDS (Energy Dispersion X-Ray Spectroscopy) and XRD (X-Ray Diffractometer) analyses verified that no macroscopic reaction between ZrO2 fibers and PZT occurred.
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  • Shinsuke HAYASHI, Kenji FUKAYA, Hirokazu KAJIMA, Hajime SAITO
    1993 Volume 101 Issue 1180 Pages 1409-1414
    Published: December 01, 1993
    Released on J-STAGE: August 06, 2010
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    Perovskite-type LaCrO3 ceramics substituted with Sr on the La site and with Zn, Cu and Li on the Cr site were prepared and investigated by X-ray diffraction analysis at room temperature and thermal expansion measurement in the range of 25 to 800°C. Single-phase solid solutions were obtained for the substitutions of Zn and Cu up to 20 and 15%, respectively. The transition temperature from an orthorhombic structure to a rhombohedral structure was determined from the inflection of the thermal expansion curve. While the substitution of Sr decreased the volume of the pseudocubic cell, lowering the transition temperature, the substitutions of Zn and Cu increased the volume, raising the transition temperature. The tolerance factor seems to affect the transition behavior. The substitutions of Sr, Zn, Cu and Li resulted in an increase in the thermal expansion coefficient. The relation between the thermal expansion coefficient and the melting point of component oxides as well as the transition temperature was discussed.
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  • Toyokazu KURUSHIMA, Kozo ISHIZAKI
    1993 Volume 101 Issue 1180 Pages 1415-1418
    Published: December 01, 1993
    Released on J-STAGE: August 06, 2010
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    Thermal shock resistant zirconia ceramics reinforced with zirconia fibers have been developed. Zirconia ceramics with 12wt% fiber having an average length of 2.5 or 0.2mm and without fibers were studied. Sintered bodies with different bulk densities were obtained by firing in air at temperatures between 1250 and 1650°C. Dispersed ZrO2 fibers remarkably improved the thermal shock resistance of the ZrO2 ceramics. The bending strength and thermal shock resistance of the samples in which ZrO2 fibers were spheroidized by diffusion during sintering decreased, even though they had high densities. The bending strength did not change after water quenching from 625 to 25°C for the zirconia ceramics reinforced with long fibers.
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  • Kenji WATANABE, Sanae TAKATSU, Matsuhiro SATO, Yo TAJIMA
    1993 Volume 101 Issue 1180 Pages 1419-1422
    Published: December 01, 1993
    Released on J-STAGE: August 06, 2010
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    Surface oxygen content in as received and oxidized silicon nitride powders was measured by X-ray photoelectron spectroscopy (XPS) analysis and chemical analysis. In the as received powders, the average difference in the measured values by the two methods was about 40%. It is suggested that the difference is due to some irrelevancies of the models on which these methods are based. On the other hand, the correlation of the results for the oxidized powders was reasonable. The agreement between the increment of the surface oxygen content and that of the total oxygen content in the oxidized powders was better for the XPS measurements.
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  • Osamu SAKURAI, Kazumasa KUMAGAI, Nobuo KIEDA, Atsushi OGURA, Kazuo SHI ...
    1993 Volume 101 Issue 1180 Pages 1423-1426
    Published: December 01, 1993
    Released on J-STAGE: August 06, 2010
    JOURNAL FREE ACCESS
    Ni-Zn ferrite thin films were prepared on fused silica plates by an inductively coupled plasma (ICP) flash evaporation method using ultrasonically atomized aqueous solutions of corresponding metal ions in the reduced Ar gas of 30kPa. All the films consisted same-size columnar particles and the particle size increased from 0.1 to 0.5μm in diameter with deposition time. The growth rate of the films was about 2.9μm/h. In this method, the metal composition agreed with that of the starting solution. Therefore, the ICP flash evaporation method using the mists of aqueous solutions was more advantageous to control the composition of complex metal oxide films than the method using the mixed oxide powders.
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  • Tatsuo HARA, Rikuo OTA, Takashi WAKASUGI, Jiro FUKUNAGA, Akiko MIYAKE
    1993 Volume 101 Issue 1180 Pages 1427-1429
    Published: December 01, 1993
    Released on J-STAGE: August 06, 2010
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    Accelerated gelation on the alumina surfaces in the sols of the Na2O-ZrO2-SiO2 system without water addition has been shown by model experiments. From the surface-to-surface adhesion test, it was demonstrated that water-free Na2O-ZrO2-SiO2 sols gelated in 1h-1d period preferentially on/between the contacted alumina surfaces. Formation of gel films was confirmed by BS images and EDX analysis. A similar result was obtained for slide glass plates. Gelation was not observe, however, for PTFE (polytetrafluoroethylene or teflon) plates, which was explained as due to the absence of hydroxyl group or adsorbed water on the PTFE surface.
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  • Yoshio UKYO, Toshio KANDORI, Shigetaka WADA
    1993 Volume 101 Issue 1180 Pages 1430-1431
    Published: December 01, 1993
    Released on J-STAGE: August 06, 2010
    JOURNAL FREE ACCESS
    Si3N4-SiC particle composites constaining up to 30wt% SiC were sintered to a neary full density using gas pressure sintering and HIPing process (post-HIPing). Fine SiC powder with an average particle size of about 0.03μm, and Y2O3 as sintering additive were used. Si3N4-30wt% SiC sintered composite with a strength of about 700MPa at 1400°C was obtained by post-HIPing.
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