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Kenji UCHINO, Nam-Yang LEE, Tamaki TOBA, Narikazu USUKI, Hideaki ABURA ...
1992 Volume 100 Issue 1165 Pages
1091-1093
Published: September 01, 1992
Released on J-STAGE: August 06, 2010
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The crystal structure of BaTiO
3 thin films fabricated by RF-magnetron sputtering has been investigated. As-sputtered films exhibited a cubic structure with a small grain size of about 6-8nm. After annealing at a temperature above 1100°C, the crystal structure changed from cubic to tetragonal, because the annealing process caused grain growth. The critical grain size of the thin films which provided the cubic structure existed in the range of 0.1-0.2μm. This value agreed well with the critical grain size of BaTiO
3 fine particles, 0.12μm.
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Atsunori MATSUDA, Yoshihiro MATSUNO, Shinya KATAYAMA, Toshio TSUNO, No ...
1992 Volume 100 Issue 1165 Pages
1094-1097
Published: September 01, 1992
Released on J-STAGE: August 06, 2010
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Alkali passivation mechanism of sol-gel derived TiO
2-SiO
2 glass films with different TiO
2 contents coated on a soda-lime-silica glass substrate has been studied by SIMS and XPS analyses, and compared with the results of a sol-gel derived pure SiO
2 film. An increase in TiO
2 content in the TiO
2-SiO
2 film increased the sodium concentration in the film, which was induced by sodium migration from the glass substrate during the heat-treatment. It was also found that the chemical state of sodium ions in the TiO
2-SiO
2 films was different from the state of those either in the glass substrate or in the sol-gel derived pure SiO
2 film. It is thus concluded that the TiO
2-SiO
2 films serve not as a barrier but as an effective getter of alkli ions and thereby effectively improve the weathering resistance of the glass substrate.
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Yasuhisa IKEDA, Yoshiyuki YASUIKE, Mikio KUMAGAI, Yoon-Yul PARK, Masay ...
1992 Volume 100 Issue 1165 Pages
1098-1102
Published: September 01, 1992
Released on J-STAGE: August 06, 2010
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The results obtained are summarized as follows:
(1) Syn-Tob is decomposed by reacting with CO
2 into CaCO
3 and silica gel.
(2) In the decomposition process, CaCO
3 is present as three crystal forms (vaterite, aragonite and calcite) in the low carbonated Syn-Tobs. With the progress of carbonation, the fraction of calcite increases and in the complete carbonation all CaCO
3 is transformed into calcite.
(3) Silicate phase in Syn-Tob is composed of the double chain structure with some Si-O-Si bridges between the chains. This double chain structure is destroyed with the carbonation and finally silica gel with the three-dimensional cross-linked framework structure is formed.
(4) The double chain structure is kept even at a considerably high degree of carbonation (around 70%). This may cause the pseudomorphism phenomenon.
(5) In the completely carbonated Syn-Tob, two
29Si NMR peaks are observed at around -111 and -102ppm, which are assigned to the silicon atoms of Si*(OSi_??_)
4 and (HO)Si*(OSi_??_)
3 structures in silica gel.
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Hideya INAGAKI, Toshio SHIMOO, Kiyohito OKAMURA, Kuniaki HONJO
1992 Volume 100 Issue 1165 Pages
1103-1108
Published: September 01, 1992
Released on J-STAGE: August 06, 2010
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The effect of SiC coating on the pyrolysis of SiC fiber (Nicalon) has been investigated. SiC coating was carried out by chemical vapor deposition at 1473K using a mixture of CH
3SiCl
3 and H
2 as source gases. The composition and crystallinity of the coating changed with the flow rates of CH
3SiCl
3 and H
2. The composition of the coating with an increase in H
2 gas flow rate was close to that of stoichiometric SiC as determined by the scanning Auger electron spectroscopy. X-ray diffraction patterns showed that the coating was β-SiC crystallites. The rate of pyrolysis of Nicalon with and without SiC coating was measured with a thermobalance in an argon atmosphere at temperatures from 1673 to 1973K. The rate of pyrolysis of SiC coated Nicalon was mixed-controlled by both diffusion of SiO and CO gases through the coating and crystal growth of SiC in the fiber. These results showed that high-temperature pyrolytic reaction of Nicalon was suppressed by coating SiC on the fiber.
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Shinsuke HAYASHI, Shinji SAITO, Hajime SAITO
1992 Volume 100 Issue 1165 Pages
1109-1112
Published: September 01, 1992
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MgO-based composites containing 10 to 30vol% Mg
4Ta
2O
9 were fabricated by pressureless sintering of MgO and Ta
2O
5 powders at 1400° to 1600°C. Mechanical properties and the thermal expansion coefficient of the composites were studied. Under all sintering conditions, Ta
2O
5 reacted with MgO completely to form Mg
4Ta
2O
9 and dense (>95% of theoretical density) composites were obtained. Dispersion of Mg
4Ta
2O
9 particles inhibited the grain growth of MgO and improved mechanical properties. The maximun bending strength and fracture toughness of composites were 260MPa and 3.2MPa⋅m
1/2, respectively, in contrast with 150MPa and 1.6MPa⋅m
1/2 for a MgO monolith. The composites may be toughened by the crack deflection due to Mg
4Ta
2O
9 particles. The thermal expansion coefficient of the composites decreased slightly with increasing Mg
4Ta
2O
9 content and was 12.9×10
-6°C
-1 for the composite with 30vol% Mg
4Ta
2O
9.
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Akio NISHIDA, Kenji TERAI
1992 Volume 100 Issue 1165 Pages
1113-1116
Published: September 01, 1992
Released on J-STAGE: August 06, 2010
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MgO-ZrO
2 composites prepared by the pressureless sintering at 1350°C for 24h were annealed at 1600°C, and the effects of annealing on the properties such asgrain size, phase transformation, bending strength and fracture toughness were investigated. The grain size of ZrO
2 in sintered MgO-ZrO
2 containing more than 20wt% ZrO
2 was too large for t-ZrO
2 to be stable at room temperature, so that the t-ZrO
2 to m-ZrO
2 phase transformation occurred during cooling from the sintering temperature. Microcracks formed during cooling decreased the bending strength and increased the fracture toughness. When m-ZrO
2 was transformed into c- or t-ZrO
2 by annealing, microcracks in MgO-ZrO
2 composites recombined. Consequently, flaw size in MgO-ZrO
2 composites decreased, resulting in an increase of bending strength. However, fracture toughness decreased due to reduced effect of microcrack toughening mechanism.
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Chihiro KAWAI, Jun-ichi TERAKI, Tohru HIRANO, Toshio NOMURA
1992 Volume 100 Issue 1165 Pages
1117-1121
Published: September 01, 1992
Released on J-STAGE: August 06, 2010
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Oxidation-resistant coating using chemical vapor deposition on continuous fiber reinforced ceramics having lower thermal expansion coefficient (α) than the coated layer (SiC) was studied. A SiC-fiber reinforced TiC matrix composite (SiC/TiC composite, α=5.6×10
-6K
-1) was used as a substrate and the TiC-SiC system was chosen as a coating. The CVD was carried out in TiCl
4-SiCl
4-CH
4-H
2 system at deposition temperature of 1350°C and total gas pressure of 60 Torr. Compositionally gradient TiC-SiC layers were formed by stepwise change of the Ti/(Ti+Si) ratio in the feed gas. Peeling occurred along the edges of the coating in the case of SiC coating, but it did not occur at all in a TiC-SiC coating with an optimum gradient composition. These results agreed with the thermal stress analysis using F. E. M.
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Toshikazu NISHIDE, Fujio MIZUKAMI
1992 Volume 100 Issue 1165 Pages
1122-1126
Published: September 01, 1992
Released on J-STAGE: August 06, 2010
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The TiO
2 films were prepared on glass or silicon wafer substrates by sol-gel method using glycols or their ether derivatives as ligands, directed toward control of optical properties. The effect of ligands on the indices and crystal phases of TiO
2 films was investigated. On the glass substrates, the refractive indices of TiO
2 films depended on the ligands used, although all the films were fired under the same conditions. The 2-(2-methoxyethoxy) ethanol (MEE) ligand gave the most high refractive indices among the ligands used. On the other hand, the 2-methyl-2, 4-pentanediol (MPO) ligand gave the most low refractive indices when the films were fired under 510°C. The change in refractive indices is discussed in connection with crystal phases of TiO
2 films measured by X-ray diffraction analysis. In the TiO
2 film prepared using MEE as the ligand, the anatase crystal appeared at low temperature (400°C). It gave high refractive indices. In the TiO
2 film prepared using MPO as the ligand, amorphous TiO
2 appeared under 510°C and gave low refractive indices. The ligands influence size of titanium oxide sols and TiO
2 crystal phases, and change the refractive indices of the films. In other words, the ligands can control the refractive indices of TiO
2 films on glass substrates. The crystal phases of TiO
2 films on silicon wafer also depended on the ligand used. The MPO and triethylene glycol monomethyl ether (TME) ligand accelated the transformation from anatase to rutile form. In contrast MEE ligand inhibited the change to rutile form even at 900°C. Thus, anatase or rutile in the TiO
2 film on the silicon wafer can be selectively formed by the selection of ligands used in sol-gel process.
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Explanation of Formation Condition
Katsuyoshi SHIMOKAWA, Itsuma SEKIGUCHI, Yoshikazu SUZUKI, Yoshinobu UE ...
1992 Volume 100 Issue 1165 Pages
1127-1134
Published: September 01, 1992
Released on J-STAGE: August 06, 2010
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In our previous studies, ceramic materials were synthesized by reactions of oxy-silicate minerals such as siliconoxide (SiO
2), talc (3MgO⋅4SiO
2⋅H
2O), olivin (2(Mg, Fe)O⋅SiO
2) and chlorite (H
4Mg
2Al
2SiO
9) with carbon, or obtained from carbide of rice husk which is one of natural organic materials. In the previous report, a ceramic fiber with a two or three-layered structure was synthesized; each layer has different concentrations of constituents, Si, O, and C. The aspect ratio of the fiber was large. The yield of the ceramic fiber, however, was small. In this study, an attempt to find suitable experimental conditions for greater yield and homogeneous definite quality of the ceramic fibers was carried out. In addition, the reaction mechanism from rice husk carbide to the fiber was investigated. The obtained optimum conditions were as follows. (1) Reaction temperature was 1480°C; (2) the ratio of mixing N
2 and H
2 was 1:2 in volume; (3) the linear velocity of gas flow was about 0.7cm/s. A gaseous reaction of SiO with CO was clearly shown to be responsible for the production of the ceramic fibers, in comparison with the experiments using standard samples and gases such as Si, SiO and SiO
2, and Ar, N
2, H
2, CO and CO
2.
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Hideto KURAMOCHI, Hidehiko KOBAYASHI, Toshiyuki MORI, Hiroshi YAMAMURA ...
1992 Volume 100 Issue 1165 Pages
1135-1139
Published: September 01, 1992
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Ca
0.20Zr
0.80-xTi
xO
y composition (
x=0.04-0.25) powders, whose phases were the tazheranite (
x=0.04-0.10) and the calzirtite (
x=0.20) of single phases, were prepared at 1300°C for 10h by the solid phase reaction. The range of the tazheranite composition was broadened up to
x=0.15 by firing them at 1500°C for 4-10h. The conductivity of the sintered bodies, fabricated at 1500°C for 4h in
x=0.04-0.15 and 10h in
x=0.20, was measured at 400°-900°C using the complex impedance method in the air. The activation energies of the conductivity were 120-130kJ/mol, thus it is presumed that the mechanism of electric conduction was dominated by an oxygen ion conduction in the range of these temperatures. In the case of
x=0.04-0.15 composition samples, the resistance of grain decreased with an increase of
x, while that of grain boundary increased. With regard to the calzirtite (
x=0.20) composition sintered body, it is made ascertained that the specific resistance took a figure up one place. The results have suggested that the elevation of conductivity is due to the increase of dissolved TiO
2 amount, the valence deviation of Ti, the change of grain size and the segregation of a trace amount of calzirtite phase at the grain boundaries of the tazheranite of single phase.
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Seok-Keun LEE, Kazuo SHINOZAKI, Nobuyasu MIZUTANI
1992 Volume 100 Issue 1165 Pages
1140-1144
Published: September 01, 1992
Released on J-STAGE: August 06, 2010
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Effects of hydrolysis-rate-control-additives (carbonyl compounds such as ethylacetoacetate and acetylacetone) on the hydrolysis behavior of aluminium secondary butoxide and condition for the formation of monodispersed alumina particles were investigated. The reactive enol form of the carbonyl compounds substituted butoxyl group of aluminium secondary butoxide and chelated the aluminium atom. The chelating ligand would not be easily removed upon hydrolysis reaction because the aluminium-ligand bond was sufficiently strong. As a consequence, the rate of hydrolysis and polycondensation of modified precursor decreased. By hydrolyzing this modified stable precursor, the monodispersed alumina particles were prepared in the wide range of water concentration; about 8 times that of non-modified precursor when 0.006mol/l ethylacetoacetate was added and about 4 times when 0.006mol/l acetylacetone was added. The average particle size of obtained monodispersed particles and the geometrical standard deviation were 0.2μm and 1.18, respectively. The morphology of particles changed with increasing water concentration as follows; agglomerates of coarse texture→monodispersed particles→agglomerates of fine texture.
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Yoshiyuki KOJIMA, Akiko SADOTOMO, Tamotsu YASUE, Yasuo ARAI
1992 Volume 100 Issue 1165 Pages
1145-1153
Published: September 01, 1992
Released on J-STAGE: August 06, 2010
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The control of three modifications and crystal shape of calcium carbonate which precipitated by outgassing dissolved CO
2 in calcium hydrogencarbonate solution was studied. The starting saturated solution (10.3×10
-3mol CaCO
3⋅dm
-3) of calcium hydrogencarbonate was prepared by passing a stream of CO
2 through the suspension of fine limestone powder at 2°C and then diluted with pure water to concentrations of 2.8-8.5×10
-3mol CaCO
3⋅dm
-3 (initial supersaturation degree: 20-60). Characteristics of the precipitated calcium carbonate were determined by means of X-ray diffraction, infrared spectroscopy, scanning electron microscopy and chemical analysis. The formation region of three modifications was affected remarkably by synthetic conditions such as stirring, pH (6.2-8.0), heating temperature (20°-100°C) and concentration (initial supersaturation degree: 20-60) of calcium hydrogencarbonate solution. When calcium carbonate was precipitated by outgassing dissolved CO
2 in calcium hydrogencarbonate solution under stirring with 240rpm, rhombohedral-like calcite about 10μm in size and prismoidal-like aragonite with 2×50μm in size and 99.7% in purity were independently formed at temperatures below 30°C and above 50°C respectively, while no vaterite was observed. However, vaterite was found as an independent phase by adding an alkaline solution of NaOH or NH
4OH into calcium hydrogencarbonate solution without stirring. Especially, NH
4OH solution was excellent as additive to form hexagonal plate-like crystals of vaterite as compared with NaOH solution. For example, hexagonal plate-like vaterite crystals 20μm in size and 99.7% in purity formed from calcium hydrogencarbonate solution with a supersaturation degree of 20 at pH 7.5-7.8 without stirring. These vaterite-crystals were unstable and transformed to the stable phase of hexagonal plate-like calcite by heating at 600°C. The uniform hexagonal plate-like crystals of calcium carbonate can be expected as a new functional inorganic filler for paper, plastics and rubber.
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Yoshiyasu ITOH, Yutaka ISHIWATA, Matsuo MIYAZAKI, Hideo KASHIWAYA
1992 Volume 100 Issue 1165 Pages
1154-1158
Published: September 01, 1992
Released on J-STAGE: August 06, 2010
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The thermal stress of a graphite body coated with Y
2O
3 by plasma spraying was analyzed using a finite element method program. Especially, the effect of the intermediate layer Nb on the thermal stresses of the Y
2O
3 surface was studied by considering the stress relaxation. The analytical results indicated that the thermal stresses, σ
r, σ
t at the Y
2O
3 surface decreased with increasing thickness of Y
2O
3 and Nb layers. It was confirmed by experiments that the failure mode of the Y
2O
3/Nb/graphite composite was surface cracking by the thermal stresses, σ
r, σ
t induced during cooling. The critical heating temperature of the Y
2O
3/Nb/graphite composites was estimated by the finite element analysis. On the other hand, it was also confirmed that the strength and ductility of as-sprayed films of Y
2O
3 and Nb were improved by the recrystallization and sintering during the heating test.
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Phase Transformation and Sinterability
Chii-Shyang HWANG, Der-Yang FANG
1992 Volume 100 Issue 1165 Pages
1159-1164
Published: September 01, 1992
Released on J-STAGE: August 06, 2010
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The effect of addition of Y
2O
3 on the sinterability and microstructure of mullite was studied by differential thermal analysis, X-ray powder diffraction, scanning and transmission electron microscopy, and dilatometry. The mullite powder compacts containing 2-10wt% Y
2O
3 were sintered at 1500°C in air. The solid state reaction of Y
2O
3 and mullite during the sintering process produced some crystalline phases of yittrium silicates and α-Al
2O
3. The product phases were dependent on the amount of Y
2O
3 addition. The yittrium silicate and Al
2O
3 melted into a liquid phase at higher sintering temperature, which enhanced the sinterability of mullite powders. During the furnace cooling process, the liquid phase crystallized, and different crystalline phases were obtained depending on the amount of Y
2O
3.
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Jae-Sang RYU, Yuichi WATANABE, Masasuke TAKATA
1992 Volume 100 Issue 1165 Pages
1165-1168
Published: September 01, 1992
Released on J-STAGE: August 06, 2010
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Investigations on preferential orientation of tin oxide films were carried out under various conditions of film fabrication from the view point of the effect on sensing mechanism. The preferential orientation of (110) crystallographic plane resulted in the increase of sensitivity for H
2 gas. The observed relationship between the sensitivity and preferential orientation has been understood by considering the maximum atomic density on the (110) plane, which ensures the large numbers of adsorption sites for atomospheric gas as well as of direct reaction sites for H
2 gas.
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Kazuo NAKAMURA, Yasuharu OKASHIRO, Masayoshi OHASHI, Kiyoshi HIRAO, Ta ...
1992 Volume 100 Issue 1165 Pages
1169-1171
Published: September 01, 1992
Released on J-STAGE: August 06, 2010
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Ce/Si ratio increased with the formation of Si
2N
2O in Ce-doped Si
3N
4 based ceramics with SiO
2 addition. The intergranular liquid remained as a glass on cooling until the ratio exceeded a certain level when the intergranular liquid crystallized as cerium nitrogen apatite (Ce
5(SiO
4)
3N-Ce
4.67(SiO
4)
3O) during cooling. There were large differences in flexural strength, fracture toughness between the specimens with the intergranular glassy phase and the ones with the intergranular crystalline phase. Mechanical properties of the bulk bodies depended on those of the intergranular phases.
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Kenji OHSHIMA, Seiji TAKAHASHI, Makoto KUWABARA
1992 Volume 100 Issue 1165 Pages
1172-1174
Published: September 01, 1992
Released on J-STAGE: August 06, 2010
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An investigation has been made on the grain size dependence of the dielectric properties in 0.99Pb
0.7La
0.2TiO
3+0.01MnO
2 ceramics exhibiting two anomalous peaks of dielectric constant; One is a sharp peak at the Curie point (-160°C), and the other a broad one above the Curie point. The sharp dielectric constant peak showed no significant change with grain size, while the broad dielectric constant peak significantly increased as the grain size increased. Complex impedance analysis revealed that the dielectric properties of the present materials can well be described using an equivalent circuit with two sets of
R-C parallel circuits being connected in series. Evidently, these two
R-C parallel circuits give the dielectric properties of the bulk of the grains which provide the sharp dielectric peak and those of the grain boundary region, which yield the broad one, respectively. The origin of the broad dielectric peak is most likely interpreted to be interfacial polarization at the grain boundaries.
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Tatsuo NOMA, Noriyuki SHOJI, Satoshi WADA, Takeyuki SUZUKI
1992 Volume 100 Issue 1165 Pages
1175-1178
Published: September 01, 1992
Released on J-STAGE: August 06, 2010
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Hydroxyapatite (HAp) powders with SiC platelets dispersion were synthesized by a wet process (at 98°C for 24h) and hydrothermal process (at 150°C, 0.5MPa for 4h). The transmission electron microscopy showed that SiC platelets were homogeneously surrounded by fine HAp crystals. The SiC-HAp composites were sintered at various temperatures. SiC loading obstructed the densification but improved the Vickers hardness up to 1.3 times that of pure HAp ceramics.
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