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Diffusion of Ti and Sinterability
Chii-Shyang HWANG, Yu-Jing CHANG
1995 Volume 103 Issue 1202 Pages
987-991
Published: October 01, 1995
Released on J-STAGE: August 06, 2010
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To improve mechanical properties of TiO
2-added zirconia-toughened alumina (ZTA), the microstructure and sinterability of ZTA composites fabricated from ZTA powders containing (Zr, Ti)O
2 and sintered in an atmosphere of N
2+5%H
2 were investigated. In the sintered ZTA, the concentration of Ti in grains of Al
2O
3 or (Zr, Ti)O
2, was analyzed with EDS attached to an AEM apparatus. Experimental results indicated that some Ti ions diffused to the grain boundary and into Al
2O
3 grains, thereby enhancing the densification of ZTA powders sintered in N
2+5%H
2, the grain growth is less than that of powders sintered in air. The solubility of TiO
2 in (Zr, Ti)O
2 in ZTA sintered in N
2+5%H
2 was smaller than that of ZTA sintered in air, which diminished the tetragonal zirconia phase in the ZTA sintered body.
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Mamoru AIZAWA, Taro ISHIKAWA, Kiyoshi ITATANI, F. S. HOWELL, Makio KIN ...
1995 Volume 103 Issue 1202 Pages
992-995
Published: October 01, 1995
Released on J-STAGE: August 06, 2010
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Nine kinds of composite powders in CaO-P
2O
5-SiO
2-Al
2O
3 system were prepared by the sol-gel process. Although the as-prepared powders were amorphous, hydroxyapatite (HAp) and tricalcium phosphate (TCP) were formed as a calcium phosphate phase when they were heated from 800 to 1300°C. Additionally, anorthite (CaAl
2Si
2O
8) was formed in the composites containing 25mol% of Al
2O
3 and 25mol% of SiO
2 at 1100°C. The dense composite of 2.69g·cm
-3 bulk density was obtained by sintering powders with compositions of 38.48CaO⋅11.52P
2O
5⋅25SiO
2⋅25Al
2O
3 at 900°C for 5h. When this composite was hydrothermally treated at 160°C for 24h, β-TCP was changed into HAp to form a porous layer with the -8μm thickness on the surfaces of composites. The porous composite of 2.33g·cm
-3 bulk density was obtained when the powders with the compositions of 40CaO⋅10P
2O
5⋅10SiO
2⋅40Al
2O
3 were sintered at 1200°C for 5h. Ricelike HAp particles were formed on the surfaces and fracture surfaces of the porous composite treated hydrothermally at 160°C for 12h.
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Atsumu ISHIDA, Hideaki MATSUBARA, Katsuya FURUKAWA, Masaru MIYAYAMA, H ...
1995 Volume 103 Issue 1202 Pages
996-999
Published: October 01, 1995
Released on J-STAGE: August 06, 2010
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Two-dimensional computer simulations were conducted on percolative structure in which second phases of various aspect ratios were arranged in a matrix phase. The second phases were randomly arranged in an array with two different computational programs; one prohibiting an overlap among second phases and the other allowing the overlap. From the simulation prohibiting the overlap, it was predicted that a continuous path was formed at less amounts of the second phase with higher aspect ratios. In the simulation allowing the overlap, a continuous path throughout the array was formed by arranging the second phase of an aspect ratio of 100 with less than 4% in the array. These results agreed well with the conduction path formation in hotpressed ceramic composites consisting of an insulator matrix and electrically conductive whisker additives.
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Yasushi FUKUZAWA, Takayuki TANI, Eiji IWANE, Naotake MOHRI
1995 Volume 103 Issue 1202 Pages
1000-1005
Published: October 01, 1995
Released on J-STAGE: August 06, 2010
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As the electro discharge phenomena can only occur between electro conductive materials and electrodes, the insulating materials could not been machined by electrical discharge machining (EDM) method. In this report, the new machining system is proposed and the machining characteristics of Sialon insulating ceramics are discussed. It is clarified that the insulating ceramics are also able to be machined using the standard EDM technique with the adhesive metal plate and soft metal electrodes. It is accomplished by using one of the surface modification techniques for continuously making an electro conductive surface layer on the insulating surface.
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Naoyuki TSUDA, Makoto KUWABARA
1995 Volume 103 Issue 1202 Pages
1006-1010
Published: October 01, 1995
Released on J-STAGE: August 06, 2010
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Interface states at the grain boundaries in La, Mncodoped Ba
0.5Sr
0.5TiO
3 ceramics have been characterized by using the isothermal transient capacitance method. The ceramic materials doped with 0.05, 0.06 and 0.075mol% Mn were used for the present experiments, all of which had the Curie point around -70°C and a room temperature resistivity>10
7Ω·m with a positive temperature coefficient of resistivity effect of more than seven orders of magnitude. The results indicate the existence of grain boundary interface states at a level of about 1.0eV below the conduction band edge in all the materials. On the other hand, it has been found from an analysis of the resistivity-temperature characteristics in the materials that barrier layers with a potential height of about 0.85eV were built at the grain boundaries above the temperature giving the maximum resistivity in the respective materials.
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Hideoki FUKUSHIMA, Hiroyuki MORI, Tatsuya HATANAKA, Masao MATSUI
1995 Volume 103 Issue 1202 Pages
1011-1016
Published: October 01, 1995
Released on J-STAGE: August 06, 2010
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The feasibility of microwave sintering of lead zirconate titanate (PZT) ceramics was examined. Microwave sintering was performed at low temperature and short soaking time, using a heating control system with single mode cavity (2.45GHz). Higher density and electric properties were obtained compared with the conventional process, because the sintering reaction was accelerated by microwave radiation. Moreover, higher strength was obtained due to smaller grain size. The microwave sintering was expected to give both high strength and high electric properties.
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Tomohiro YANAI, Toyohiro HAMASAKI, Kozo ISHIZAKI
1995 Volume 103 Issue 1202 Pages
1017-1021
Published: October 01, 1995
Released on J-STAGE: August 06, 2010
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Highly densified sintered Si
3N
4 bodies are conventionally obtained through liquid phase sintering by adding sintering aids to overcome difficulty of sintering due to the strong covalent bonding in Si
3N
4. Sintered Si
3N
4 ceramics contain a weak grain boundary phase, which is produced from a reaction between the sintering aids and the raw Si
3N
4 powder, especially oxide phase of surface contamination on the Si
3N
4 powder. Therefore, the grain boundary phase influences mechanical properties of Si
3N
4 ceramics. The present paper discusses a method to enhance mechanical properties by forming nano SiC particles in Si
3N
4 system with additives, especially in grain boundary phase. The Si
3N
4 ceramics with dispersed nano SiC particles were obtained by using a Si
3N
4 powder coated by carbon, which was obtained by thermal decomposition of methane (CH
4) gas. The nano SiC particles were formed by in-situ reaction between the oxide phase on the surface of the Si
3N
4 powder and the coated carbon. The sintered bodies were obtained by hot-pressing at 1800°C for 1h in N
2 atmosphere under 30 MPa of applied pressure. Results of mechanical property measurements showed that the bending strength and fracture toughness increased about 20-25%, and the high temperature mechanical strength was also improved by the carbon coating method. TEM observation showed that the precipitated SiC particles were dispersed in three different types of locations, i.e., in the grain boundary layer, at the Si
3N
4-Si
3N
4 interface penetrating the grain boundary layer and inside of the Si
3N
4 grain. SiC particles dispersed at the Si
3N
4-Si
3N
4 interface block grain boundary sliding and slow crack growth at high temperatures. For carbon coated samples, the quantity of grain boundary phase was smaller than the non-coated samples as shown by cryogenic specific heat measurements. The quantity of grain boundary phase decreases, which leads the improvement of high temperature mechanical strength also. Therefore, the high temperature strength was improved by precipitated SiC particles dispersion and decreasing the quantity of grain boundary phase.
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Duan-Fen QIAN, Yutaka OHYA, Zenbe-e NAKAGAWA, Kenya HAMANO
1995 Volume 103 Issue 1202 Pages
1022-1026
Published: October 01, 1995
Released on J-STAGE: August 06, 2010
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Aluminum titanate ceramics were fabricated from compacts of aggregated mixture of alumina and titania. The mixture was prepared by precipitation of aluminum hydroxide from aqueous solution of aluminum nitrate, containing rutile powder. After calcination, the mixture was crushed and classified to fractions' 2-5, 5-10, 10-20, 20-47 and 47-77μm sizes. The SEM observation of compacts of the aggregates revealed that the aggregates were not broken by the compaction. The fired bodies of the compacts consisted of oriented aluminum titanate grains. The sizes of the oriented regions were about 4 times larger than the initial aggregate sizes. The reasons for the formation of the oriented grains were considered as follows: the formation of aluminum titanate has low change in free energy, increases elastic energy, and is endothermic. Because of these reasons, grain boundary energy becomes significant in nucleation of aluminum titanate and, therefore, the nucleation occurs epitaxially to result in the oriented texture. The semi-quantitative estimation of change in energies during formation of aluminum titanate agrees with the argument.
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Toshio SHIMOO, Shin-ichiro ADACHI, Kiyohito OKAMURA
1995 Volume 103 Issue 1202 Pages
1027-1032
Published: October 01, 1995
Released on J-STAGE: August 06, 2010
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In relation to the joining of silicon nitride ceramics to metal, the reaction products and reaction mechanism between Si
3N
4 and Mn have been investigated in Ar or N
2 at temperatures from 1073 to 1573K. Using an Si
3N
4-Mn powder mixture, the reaction rate was determined thermogravimetrically, and the reaction products were examined by X-ray diffraction. Under an Ar atmosphere, from 1223 to 1423K, MnSiN
2, Mn
0.815Si
0.815 and Mn
3Si were produced, and above 1423K, MnSiN
2 disappeared. At higher temperatures and on prolonged heating, the suicide composition changed in the following order: Mn
0.815Si
0.185, Mn
3Si, Mn
5Si
3, and MnSi. Under an N
2 atmosphere, the reaction between Mn, Si
3N
4 and N
2 produced Mn nitrides and MnSiN
2. Below 1223K, the reaction products were Mn
6N
2.58 and Mn
4N. At higher temperatures, MnSiN
2 appeared, while Mn nitrides disappeared. Above 1423K, only MnSiN
2 was produced. By relating these results to TG measurements, a full understanding of the reaction mechanism between Si
3N
4 and Mn was acquired.
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Yoshitaka KAMINO, Yoshihiro HIRATA, Tetsuro KOKUSHO, Kazuto HAMAISHI, ...
1995 Volume 103 Issue 1202 Pages
1033-1036
Published: October 01, 1995
Released on J-STAGE: August 06, 2010
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Si-C-O long fiber (20vol%)/alumina matrix composites have been fabricated by infiltration of aqueous alumina suspensions into fiber-sheets and sintered at 1000-1400°C by firing in air, vacuum (0.01Pa) and hotpressing (39MPa). The sinterability of monolithic alumina and the composites was higher in an atmosphere of air rather than under vacuum. The flexural strength of composites sintered in vacuum showed a maximum (300MPa) at a sintering temperature of 1300°C. The vacuum sintering at 1200°C-1300°C produced a significant non-linear fracture behavior in stress-strain curves based on the pull-out of fibers from the matrix. Increase of sintering temperature of the composite to 1400°C resulted in brittle fracture behavior, suggesting that the interfacial strength increased with an increase in density of the composite. Sintering of the composite in air produced the intermediate layers of the SiO
2-Al
2O
3 system between the alumina matrix and the Si-C-O fibers due to oxidation of the fibers. The formation of SiO
2-Al
2O
3 layers reduced the strength of composite with brittle fracture behavior. Hot-pressing of the composite at 1200°C using Si-C-O fibers coated with fine BN particles led to an increase in strength (420MPa) as well as in non-linearity of the fracture behavior.
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Yoshihito KONDO, Yutaka HASHIZUKA, Masae NAKAHARA, Kozo YOKOTA
1995 Volume 103 Issue 1202 Pages
1037-1040
Published: October 01, 1995
Released on J-STAGE: August 06, 2010
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In applications of ceramics as a structural component, the forming technology and the strength reliability are the most important. One of the factors, which control the strength reliability of ceramics, is large pores as defect, and it is produced in forming process. In this study, the influence of granule properties on the structure of green bodies and the strength of sintered bodies in uniaxial press forming of alumina ceramics was investigated. The sintered bodies from several kinds of granules showed the bending strength of 450-310 MPa, and the granule with low breaking strength gave the sintered bodies with high bending strength due to a small number of large pores. The breaking strength of granule was affected significantly by the amount of dispersant and the type of binder.
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Fumio MUNAKATA, Makoto TANIMURA, Kumi TAKAMOTO, Hiroaki KANEKO, Hideno ...
1995 Volume 103 Issue 1202 Pages
1041-1045
Published: October 01, 1995
Released on J-STAGE: August 06, 2010
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The solid-state reaction between La
1-xCo
1-yFe
yO
3-δ (
x=0.0, 0.1;
y=0.0, 0.5) and Al
2O
3 was investigated by X-ray diffraction, transmission electron microscopy, and electron energy loss spectroscopy. LaAlO
3 and spinel phases formed from a mixture of LaCoO
3 and Al
2O
3 with the increase in the reaction temperature. However, substitution of Fe for Co and La-site deficiency in LaCoO
3 inhibited the formation of LaAlO
3 and spinel phases. Moreover, the electron diffraction pattern of LaCoO
3 after the reaction suggests the possibility that the solid-state reaction enhance the formation of the La-site deficiency of La
1-xCoO
3.
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Kazuya YABUTA, Hiroaki NISHIO, Keizo UEMATSU
1995 Volume 103 Issue 1202 Pages
1046-1050
Published: October 01, 1995
Released on J-STAGE: August 06, 2010
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To study the effect of process-related oxidation on microstructure and densification of β′-o′ sialon, green compacts of a silicon nitride powder and boehmite sol were prepared. With progressive oxidation of the silicon nitride powder, the amount of o′-phase increased and grain size of o′-phase was changed. The different densification was caused by o′-phase content. The experimental result showed that, the transition liquid phase in the specimen of low oxygen contents formed at higher tempeature than that of high oxygen contents.
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Masae NAKAHARA, Yoshihito KONDO, Kenya HAMANO
1995 Volume 103 Issue 1202 Pages
1051-1056
Published: October 01, 1995
Released on J-STAGE: August 06, 2010
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The effect of talc grain size on the microstructure of cordierite ceramics prepared from the talc, kaolin and alumina was studied. Six kinds of talc materials with various grain size distributions were prepared by classification and grinding. Enstatite formed by decomposition of fine talc grains contributed to the cordierite formation at a lower temperature of 1200°C without transformation to protoenstatite. When the grain size of the talc was larger than that of kaolin, behavior of melt of the talc grains was so complicated that the melt affected the pore formation of fired bodies. By grinding the talc to submicron size, it was possible to densify the bodies at a temperature lower than that of cordierite formation, and high strength of fired bodies was achieved.
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1995 Volume 103 Issue 1202 Pages
1056
Published: 1995
Released on J-STAGE: August 06, 2010
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Kunio KITAJIMA, Yoshihiro IHARA, Nobuo TAKUSAGAWA
1995 Volume 103 Issue 1202 Pages
1057-1062
Published: October 01, 1995
Released on J-STAGE: August 06, 2010
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Various Ni
2+-substituted tetrasilicic micas having high contents of Ni
2+, such as KNiMgLi(Si
4O
10)F
2, KNi
2Li(Si
4O
10)F
2 and KNi
2.5(Si
4O
10)F
2, were synthesized at ca. 900°C through solid-state reaction techniques. Lattice constants
a,
b,
c decreased with increasing Ni
2+-substitutions, reflecting the decrease in the ionic radius of Ni
2+ against Mg
2+. UV-visible spectra of Ni
2+-micas were very similar to those of [Ni(H
2O)
6]
2+, This can be explained in terms of the nephelauxetic series F
-<H
2O<O
a (apical oxygen) as well as the spectrochemical series F
-<H
2O<O
a. IR spectra showed that the tetrahedral distortion changes with increasing Ni
2+-substitutions, i.e., the interatomic distance of Si-O
a lengthens while that of Si-O
b (basal oxygen) shortens. Ni
2+-micas exhibited paramagnetism when the Ni
2+ content was smaller than 2.0 mol in octahedral sites, however, antiferromagnetism seemed to appear at larger substitutions of 2.5 mol Ni
2+ per formula unit.
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Toshio OGASAWARA, Naoto HIROSAKI, Yoshio AKIMUNE, Eiichi YASUDA
1995 Volume 103 Issue 1202 Pages
1063-1068
Published: October 01, 1995
Released on J-STAGE: August 06, 2010
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The effect of microstructure in silicon nitride on fracture toughness and Subcritical crack growth (SCG) behavior at room temperature was investigated. Three kinds of silicon nitride materials containing 5 mass% of Y
2O
3 and Al
2O
3 were sintered under different conditions, and they showed different microstructures. Fracture toughness of the materials was obtained by single edge precracked beam (SEPB) method and controlled surface flaw (CSF) method with Knoop indentation-crack in order to investigate the dependence of the fracture toughness on microstructure. The fracture toughness data measured by the CSF method increased with increasing crack size for all kinds of the materials. The increment of the fracture toughness per crack length was more considerable for coarser grain sizes. It can be due to stress shielding at crack tip by such toughening mechanism as crack bridging. The static fatigue behavior of the materials was investigated by the dynamic fatigue technique at room temperature. The fatigue parameter
n in SCG model (d
a/d
t=
AKIn) increased with increasing as fracture toughness and grain size increased. Based on stress shielding model at crack tip, the fatigue crack growth parameters in SCG model were calculated. The predicted value agreed to the experimental results.
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Silvester TURSILOADI, Hiroaki IMAI, Hiroshi HIRASHIMA
1995 Volume 103 Issue 1202 Pages
1069-1072
Published: October 01, 1995
Released on J-STAGE: August 06, 2010
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Powder precipitates and monolithic gels of lead zirconate-titanate (PZT) were prepared by hydrolysis of metal alkoxides in 1-propanol and acetylacetone/1-propanol solutions, respectively. The as-dried precipitates and gels were amorphous. Deposition of pyrochlore and perovskite at a relatively low temperature, 450°C, was observed for both the precipitate and gel. However, crystalline PbO was found in the gels heated at 300°C. The results showed that the homogeneity of the powder precipitate was better than that of the gel. After heating at 600°C, the diffraction peaks of only perovskite were found for both samples. Powder-compacts and gel compacts were sintered at temperatures higher than 900°C. The shrinkage of the gel-compacts after sintering was greater than that of the powder-compacts because of its small particle size.
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Hyun Gyu KIM, Takayuki KOMATSU, Ryuji SATO, Kazumasa MATUSITA
1995 Volume 103 Issue 1202 Pages
1073-1076
Published: October 01, 1995
Released on J-STAGE: August 06, 2010
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A transparent mixed alkali tellurite glass of 10Li
2O-10Na
2O-80TeO
2 containing LiNbO
3 crystals with a diameter of about 4μm and with the amount of about 6 mass% is prepared using an incorporation method, and LiNbO
3-doped tellurite glass fibers are drawn. LiNbO
3 particles in the fiber and bulk samples are well dispersed. The samples also have a good transparency. The mixed alkali tellurite glass with a high thermal stability against crystallization and with a high refractive index of
n=1.98 is very suitable for incorporation of LiNbO
3 crystals and for LiNbO
3-doped fiber drawing. This technique will be applicable for fabrications of nonlinear optical glass fibers containing various nonlinear optical crystals.
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Shiro TORIZUKA, Hiroaki NISHIO, Teruo KISHI
1995 Volume 103 Issue 1202 Pages
1077-1081
Published: October 01, 1995
Released on J-STAGE: August 06, 2010
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A commercial TiB
2 powder with the grain size of 2μm was milled by an attriter and the powder having the average grain size of 0.9μm and the oxygen content of 3.4 mass% was obtained. Sinterability of the powder without additives and mechanical properties of hotisostatically pressed compacts were investigated. The density of fired compacts improved with rising firing temperature. However, compacts with densities approaching 100% were difficult to obtain by pressureless firing. Abnormal grain growth with cracks and residual pores occurred in the compact fired at 2000°C and its density was 92%. A compact having 99.5% density could be obtained by firing at 1800°C and sequential hot isostatic pressing with encapsulation at 1700°C. Fracture toughness, 3-point bending strength and Vickers hardness of the hot-isostatically pressed compact were 3.3 MPa·m
1/2, 420MPa and 2500, respectively.
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Kazuhito SUGAI, Akira KISHIMOTO, Yoshinobu NAKAMURA, Naobumi MOTOHIRA, ...
1995 Volume 103 Issue 1202 Pages
1082-1084
Published: October 01, 1995
Released on J-STAGE: August 06, 2010
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The effect of thickness deviation on the apparent strength distribution through simultaneous loading measurement was estimated. Some thickness deviations were generated by computer simulation. An apparent strength was calculated from the intrinsic strength of a sample and thickness difference taking into account of the sample setup of the simultaneous loading measurement. For a hundred samples with thickness deviation which accords with a normal distribution, the apparent strength distribution was calculated based on Weibull statistics and compared to the ideal one. Almost equivalent strength distribution shape was proved to be obtainable from samples with standard deviation of thickness deviation up to 6.5μm in the case of titanium dioxide ceramics. This critical thickness deviation was larger than 1μm for all ceramic materials calculated, which could be controllable using a micrometer.
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Mika OGISO, Osami ABE
1995 Volume 103 Issue 1202 Pages
1085-1089
Published: October 01, 1995
Released on J-STAGE: August 06, 2010
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Silicon nitride powder calcined with yttria-rich or alumina-rich additives (total 10 mol%) was alternately accumulated into layers by centrifugal filter-pressing; a combination of filter-pressing and centrifugal shape forming. The subsequent sintering at 1800°C in 1.0 MPa N
2 atmoshere provided sintered composites (SN-MLCs) with more than 98% density and 60μm thick of each layer. Elongated rodlike grains characteristic of yttria-rich additives were periodically observed in the SN-MLCs at the calcination temperature of 1400°C. At a high calcination temperature (1450°C), the difference in microstructure between layers became smaller. It was considered that the diffusion of a part of the additives through the layer interface reduced the interlayer stress to prevent delamination during sintering. The crack length propagated from Vickers indents on the SN-MLCs was shorter than that on the monolithic materials. The shorter crack length and interlayer fracture observed for SN-MLCs suggested a possibility of toughening.
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Koretomo ENDO, Akira KISHIMOTO, Naobumi MOTOHIRA, Yoshinobu NAKAMURA, ...
1995 Volume 103 Issue 1202 Pages
1090-1092
Published: October 01, 1995
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The effect of high voltage screening on ceramics parts composed of titania ceramics with relative densities of 60 and 90%, was examined. Before screening, strength distribution was clearly descriminated into two regions, high strength region and low strength region. The dielectric strength was measured on the low strength samples, and the electric field below which all of the low strength parts would break was estimated as a screening field. After electric screening, the mechanical strength was measured and compared with the original one. Ceramic parts composed of only high strength region were obtained by eliminating the low strength parts electrically.
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Morito Akiyama, Kazuhiro Nonaka, Kazuhisa Shobu, Tadahiko Watanabe
1995 Volume 103 Issue 1202 Pages
1093-1096
Published: October 01, 1995
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Highly
c-axis oriented AIN thin films were prepared on the polycrystalline substrates of MoSi
2, Al
2O
3 and SiC by rf magnetron sputtering. Crystal orientation of the thin films was not influenced by the difference in the polycrystalline substrate materials. Crystal structure of the thin film was hexagonal and its texture was consisted of many columnar grains. It was thought that the thin films were
c-axis oriented because the interaction between the thin films and the substrate surfaces was small and the growth of (100) and (110) planes of AlN was fast. The orientation of the thin films deposited on the polycrystalline substrates was worse than that of thin films deposited on single crystal substrates, however, the thin films showed appreciable piezoelectricity.
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Kazuyori URABE, Takayuki KOJIMA, Yoshiaki GOTO
1995 Volume 103 Issue 1202 Pages
1097-1098
Published: October 01, 1995
Released on J-STAGE: August 06, 2010
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Effect of additives on the sintering of calcite under the atmospheric pressure was studied. Calcite could be sintered at about 793K by adding a small amount of lithium fluoride. The microstructure of the sintered calcite was consistent with that of ceramics fabricated by liquid-phase sintering.
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