1. Ceramic Synthesis and Processing
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Masakazu KOMATSU, Yohei AIDA, Shu YIN, Tsugio SATO
Session ID: 1
Published: 2004
Released on J-STAGE: September 29, 2004
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Nitrogen-doped titania nanocrystals were prepared by “Homogeneous Precipitation-Solvothermal Process” in TiCl
3-hexamethylenetetramine (C
6H
12N
4) mixed solution. The phase composition, crystallinity, microstructure and specific surface area of titania greatly changed depending on pH and temperature. The titania powders prepared in TiCl
3-hexamethylenetetramine solutions at pH 1-6 and 190°C for 2 h consisted of single phase of brookite and that prepared at pH 9 was single phase of rutile. All titania powders prepared in the present study were yellow and showed excellent visible light absorption property and photocatalytic ability for nitrogen monoxide destruction under irradiation of the visible light (λ>510 nm). The photocatalytic activity of brookite prepared at pH 1-6 was superior to that of rutile prepared at pH 9. The photocatalytic activity under irradiation of visible light (λ>510 nm) slightly decreased with increasing calcination temperature up to 700°C and then greatly decreased at 800°C.
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Hideyuki NEGISHI, Tomohiro IMURA, Dai KITAMOTO, Toru IKEGAMI, Hiroshi ...
Session ID: 1
Published: 2004
Released on J-STAGE: September 29, 2004
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Zeolite has been recognized as one of the materials used for inorganic membranes. To improve the reproducibility of preparation and high permselectivity, the seed technique has been applied to the zeolite membrane under hydrothermal synthesis. Here, electrophoretic deposition (EPD) mechanism of zeolite (A-4) powder, as with the fabrication of the separation membrane, has been investigated under constant applied voltages as one of seed crystal coating techniques. Zeolite- n-propanol suspension is used as the EPD bath. The potential gradient in the n-propanol depended on the distance between the electrodes and the applied voltages. The zeta potential of zeolite particles was -26.5 mV in n-propanol and the resistibility of the EPD bath decreased by dispersing zeolite powder. On the other hand, potential gradient in the bulk EPD bath was constant with the progress of EPD, and the actual working potential gradient decreased 35% against the applied potential and electrode distance. Moreover, current density was constant with the progress of EPD, and the deposition layer in the EPD bath had low resistivity. Therefore, the velocity of zeolite particles was constant in the progress of EPD and the amount of deposited zeolite powder increased linearly against the deposition time and applied voltage. In addition, EPD efficiency is approximately 80% up to the amount of deposit at 25 g/m
2. EPD is a useful technique for the coating of zeolite particles onto substrates because deposition can be easily controlled and it has high deposition efficiency.
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Yuko Sawaki, Kazutaka Matsuo, Mikio Kishimoto
Session ID: 1
Published: 2004
Released on J-STAGE: September 29, 2004
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We synthesized various kinds of nanosize oxide particles with the particle size of 2-100 nm by the combination of precipitation method and hydrothermal treatment at temperature lower than 200°C. The cerium oxide particles obtained only by the hydrothermal treatment were single crystal with platelet shape even at a particle size of about 2 nm, and the platelet plane was identified to be (111) from the observation of lattice images. By the heating at 100-600°C in air, the particle size was increased from about 2 nm to 15 nm maintaining the platelet shape with elevating the temperature. In the zirconium oxide particles, it was confirmed that both monoclinic and tetragonal phases were obtained by the control of synthesis conditions in the precipitation hydrothermal treatment at a temperature lower than 200°C without heating at higher temperature. The typical particle sizes of monoclinic and tetragonal phases were about 7 nm and 100 nm. The crystal constants of these cerium and zirconium oxide particles were nearly in agreement with those of balk oxides.
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Tomohiro YAMAGUCHI, Tetsuji ITO, Yoichi YAJIMA, Seiichi TARUTA, Kunio ...
Session ID: 1
Published: 2004
Released on J-STAGE: September 29, 2004
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Unique mica ceramics with micropores were fabricated from alumina-pillared fluorine micas by pulse electric current sintering (PECS) at a temperature range of 600-800°C under a uniaxial pressure range of 10-30 MPa. The effects of PECS conditions and the nature of alumina-pillared mica powders on the formation and properties of the mica ceramics were studied. The mica ceramics obtained at lower temperatures and lower uniaxial pressures retained the pillared structure of alumina-pillared micas and gave a maximum BET specific surface area of ∼300 m
2 g
-1, while those obtained at higher temperatures and higher uniaxial pressures lost the pillared structure and microporous characteristics. The mica ceramics thus obtained were machinable due to the interlocking microstructure of the flaky pillared mica crystals. Fully densified mica ceramics could be also produced by PECS at ∼1035°C under a uniaxial pressure range of 10-30 MPa.
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Ranbo YU, Dan WANG, Mikio TAKANO, Nobihiro KUMADA, Nobukazu KINOMURA
Session ID: 1
Published: 2004
Released on J-STAGE: September 29, 2004
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Three new zirconium phosphates, [NH
4]
2[H
3N(CH
2)
2NH
3]
2[Zr
3(OH)
6(PO
4)
4] (ZrPO-1), [NH
4]
2[Zr(OH)
3(PO
4)] (ZrPO-2) and [NH
4]
3[Zr(OH)
2(PO
4)(HPO
4)] (ZrPO-3), have been prepared in ZrOCl
2-H
3PO
4—organic anime-NH
4F—organic solvent systems, and characterized by single crystal X-ray diffraction, powder X-ray diffraction, thermal analysis, scanning electron microscope, infrared spectroscopy, ICP, and CHN elemental analysis. Through the systematical investigation of crystal structures and synthesis conditions, the effects of organic solvents, organic amines and F
- cations on product crystallization are further clarified. Moreover, the ion-exchange properties of the compounds have also been investigated.
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Dan WANG, Ranbo YU, Hong WANG, Mikio TAKANO, Shouhua FENG, Wenjun ZHEN ...
Session ID: 1
Published: 2004
Released on J-STAGE: September 29, 2004
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A series of giant magnetoresistance materials La
0.5A
0.5MnO
3 (A=Ba, Sr, Ca) was hydrothermally prepared at 240°C for 1∼3 days and characterized by powder X-ray diffraction, scanning electron microscope, iodometry, and DC four-terminal method. The alkalinity and molar ratio of Mn(VII)/Mn
2+ in the initial reaction mixture, associated with hydrothermal reaction temperature, dominate the crystallization of the products. The SEM images of the as-prepared La
0.5Sr
0.5MnO
3 indicated that the product is cubic crystal about 2-5 μm, and the La
0.5Ba
0.5MnO
3 is cubic crystal about 100-500 nm. The average valence state of manganate in all the products is 3.5.
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Fumiko KAMIYAMA, Takashi TAKEDA, Shinichi KIKKAWA
Session ID: 1
Published: 2004
Released on J-STAGE: September 29, 2004
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GaN powder, in carbon crucibles was heated at various temperatures in an induction furnace in a nitrogen atmosphere. Deposition of Ga
2O
3 was observed on a substrate that covered the crucible during heating at above 800°C. The recrystallization of GaN was detected in the deposit formed only at 850°C probably because Ga metal deposited on the substrate reacted with an active nitrogen released in the decomposition of GaN powder. GaN also recrystallized on the substrate at 1000°C in a reaction of the evaporated Ga metal with nitrogen atmosphere. Such recrystallization was also observed when GaN powder was heated to above 850°C in an evacuated sealed quartz tube. Hexagonal thin platy crystals of about 4 μm diameter were obtained. Short duration heating at temperature close to 850°C was preferable to grow crystals because its decomposition simultaneously occurred with the recrystallization. It appears that GaN crystals do not grow in the sublimation process proposed previously but rather in the recrystallization.
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Naofumi Uekawa, Takuji Kudo, Yong Jun Wu, Kazuyuki Kakegawa
Session ID: 1
Published: 2004
Released on J-STAGE: September 29, 2004
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The complex between the Nb-peroxo compound and KNO
3 was prepared by heating the Nb-peroxo compound aqueous solution with KNO
3 at 573 K for 1 h. The single phase of KNbO
3 was obtained by firing the complex between the Nb-peroxo compound and KNO
3 at 873 K for 2 h. The obtained KNbO
3 had tetragonal crystal system. On the other hand, when the stoichiometric mixed powder of Nb
2O
5 and K
2CO
3 with the molar ratio of Nb : K=1 : 1 was fired at 873 K for 2 h, orthorhombic KNbO
3 was obtained. In general, tetragonal phase can be obtained under high pressure condition at more than 6.6 GPa. When the complex between the Nb-peroxo compound and KNO
3 was used for the KNbO
3 preparation, the tetragonal KNbO
3 was obtained at normal pressure condition. The lattice parameter of a axis of the KNbO
3 obtained from the Nb-peroxo compound solution was less than that of the stoichiometric one. According to this fact and the result of UV-VIS spectra, the KNbO
3 prepared by firing the complex between the Nb-peroxo compound and KNO
3 had oxygen vacancies, which affected the lattice parameter and the crystal system.
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Yarong WANG, Toshiyuki MORI, John DRENNAN, Ji-Guang LI, Yoshiyuki YAJI ...
Session ID: 1
Published: 2004
Released on J-STAGE: September 29, 2004
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10 mol% Gd
2O
3-doped CeO
2 solid-solution (20GDC) powders have been synthesized via carbonate coprecipitation using nitrates as the starting salts and ammonium hydrogen carbonate (AHC) as the precipitant. Characterizations were achieved by elemental analysis, XRD, DTA/TG, and FESEM. The thus-processed precursor is an amorphous hydroxyl carbonate with an approximate formula of Ce
0.8Gd
0.2(OH)(CO
3)•2H
2O, which directly yield oxide solid-solutions upon thermal decomposition at a very low temperature of approximately 430°C without any phase detected corresponding to Gd
2O
3. The 20GDC oxide powder calcined at 700°C shows excellent reactivity and were densified to >99% of the theoretical via pressureless sintering at a low temperature of 1150°C for 6 h. Electrical conductivity of the densified ceramic was measured in air in the range 400-700°C by the DC three-point method, and an activation energy of ∼60.92 kJ/mol was derived from the experimental data.
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Qing TANG, Ruixing LI, Shu YIN, Tsugio SATO
Session ID: 1
Published: 2004
Released on J-STAGE: September 29, 2004
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Solvothermal treatment of AgNO
3 in alcohol-water mixed solvent dispersed with γ-alumina (γ-Al
2O
3) powders at 498 K for 2 h was conducted to prepare Ag/(γ-Al
2O
3) composite powders for catalysts. The influence of ethanol content on the crystalline phase and microstructure of solvothermal products was investigated. With decreasing ethanol content in the solvent, the alumina matrix phase gradually changes from γ-Al
2O
3 to boehmite (γ-AlOOH), accordingly, the ratio of larger rhombic γ-AlOOH to smaller needle-like γ-Al
2O
3 increased. This phase change resulted in the decrease of the BET specific surface area and total pore volume and a shift of the characteristic pore size and pore size distribution. During the solvothermal treatment in ethanol/water mixed solvents, silver nanoparticles precipitated from the solution to form Ag/(γ-AlOOH, γ-Al
2O
3) nano-composites whereas no precipitation occurred in pure water.
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Yoshiaki MORISADA, Masakatsu MAEDA, Toshiya SHIBAYANAGI, Yoshinari MIY ...
Session ID: 1
Published: 2004
Released on J-STAGE: September 29, 2004
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MWCNTs were coated with SiC layer using SiO vapor. The growth mechanism of SiC and the oxidation resistance of the SiC-coated MWCNTs were studied. The growth of the SiC layer was controlled with the partial pressure of CO using the carbon felt placed in a crucible for SiC coating. The nanometer sized SiC particles were deposited by the reaction between SiO(g) and CO(g). On the other hand, the thin surface of MWCNT was converted to the SiC layer when the carbon felt was not used. The oxidation durability of MWCNTs was improved by the SiC coating. MWCNTs were oxidized completely in air at 650°C for 60 min. However, about 90 mass% of the SiC-coated MWCNTs remained after the same oxidation test.
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Dai MATSUSHIRO, Jun TAMAKI, Yoshifumi YAMAMOTO
Session ID: 1
Published: 2004
Released on J-STAGE: September 29, 2004
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KTaO
3 thin films have been synthesized on single crystal SrTiO
3 substrate with La
0.7Sr
0.3MnO
3 buffer layer (LSMO/STO) by hydrothermal electrodeposition at 80-110°C. At first, the preparation of KTaO
3 powder was investigated under hydrothermal condition. As a result, the powders consisting of single phase KTaO
3 were prepared in high concentration KOH solution of 18.5 M at temperature higher than 80°C. Under this condition, KTaO
3 thin film was grown on LSMO/STO substrate by hydrothermal electrodeposition. The only (
l00) peaks of cubic KTaO
3 were observed in XRD patterns of KTaO
3 thin film grown on LSMO/STO substrate, suggesting the (100) orientation. The KTaO
3 (200) peak appeared at 45.39-45.52° and shifted to lower degree side with increasing film thickness. The film growth started from the deposition of fine and cubic particles (ca. 10 nm). Then the fine particles were united to form larger and flat crystallites (ca. 400 nm). Interestingly, KTaO
3 film was deposited on both positive and negative electrodes, but the growth mode was slightly different from each other.
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Keisuke SHIRAISHI, Young Ho RHO, Kiyoshi KANAMURA
Session ID: 1
Published: 2004
Released on J-STAGE: September 29, 2004
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Phospho-olivine LiFePO
4 as a cathode material for rechargeable lithium batteries was successfully synthesized by hydrothermal process with an additional heat treatment in order to realize a theoretical electrochemical capacity. Several solutions with various concentrations of Li, Fe, and P were examined, and ascorbic acid was also used as a reducing agent. From an x-ray diffraction measurement, all of the samples synthesized with the molar ratio of Li : Fe : P=2.5 : 1 : 1 were characterized as a phospho-olivine LiFePO
4, independent of the addition of ascorbic acid. In order to improve the discharge and charge capacities, a heat-treatment was carried out. A remarkable increase in the charge and discharge capacities was accomplished for all of samples. The best performance was obtained when LiFePO
4 was prepared under the conditions as follows, the molar composition of Li : Fe : P : Ascorbic acid=2.5 : 1 : 1 : 0.2 in the starting solution, and annealing at 400°C for 1 h under argon atmosphere.
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Tetsuo UCHIKOSHI, Yoshio SAKKA
Session ID: 1
Published: 2004
Released on J-STAGE: September 29, 2004
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The electrophoretic deposition characteristics of alumina particles in aqueous media were investigated under a constant current condition. The apparent deposition rate and green density of the deposits were dependent on the pH and salt concentration of the suspensions. The isoelectric point (i.e.p.) of alumina in aqueous media was pH 7.9 and no deposition of the particles was observed for the suspension prepared at the i.e.p. As the pH of the suspension slightly decreased from the i.e.p., the deposition rate rapidly increased. The maximum deposition rate was observed at pH 7.0. As the suspension became more acid, the zeta potential of alumina particles increased, however, the deposition rate decreased. At a fixed pH, the higher concentration of the salt, sodium chloride, produced a smaller amount of deposits and the higher solid concentration produced a the larger amount of deposits. The apparent transport number of the surface-charged alumina particles estimated from the total electrical current and deposit weight was low. The predominate carrier of the electric charge in the solvent was considered to be other ions, such as protons.
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Haruo NARUKE, Toshihiro YAMASE
Session ID: 1
Published: 2004
Released on J-STAGE: September 29, 2004
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Well-formed single crystals of
R4Mo
7O
27 (
R=Ce and Pr), novel phases in the
R2O
3-MoO
3 system, have been obtained by thermal degradation of
R-containing polyoxomolybdate precursor, [
R2(H
2O)
12Mo
8O
27]•
nH
2O, in air at 800°C 12 h. Both compounds crystallize in a flux of the dehydrated precursor as a result of loss of excess MoO
3. The two species are isomorphous with space group
C2/c, Z=8, a=4.6354(2) and 4.6046(2) nm, b=0.74853(3) and 0.74712(2) nm, c=1.43536(9) and 1.42640(5) nm, and β=100.897(2) and 101.006(2)°, for
R4Mo
7O
27 (
R=Ce and Pr), respectively. The structure is built up with two kinds of {
R(MoO
4)}
2 double-layers and one {Mo
3O
11} mono-layer, which are stacked alternately parallel to the (110) plane. An arrangement of [
R(MoO
4)]
+ unit is different between the two {
R(MoO
4)}
2 double-layers. The Mo
3O
11 group in the mono-layer consists of one MoO
5 trigonal bipyramid corner-shared with two MoO
4 tetrahedra. In comparison with other rare earth molybdates, we found that several materials commonly have similar {
R(MoO
4)}
2 double-layers. Details of their layer structures are discussed.
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Changtai XIA, Hiroshi ITAHARA, Shin TAJIMA, Toshihiko TANI
Session ID: 1
Published: 2004
Released on J-STAGE: September 29, 2004
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Well-faceted hexagonal plate-like particles of β-Co(OH)
2 have been prepared by a precipitation method. α-Co(OH)
2 was formed first, and then transformed to β-Co(OH)
2 with a typical size of 0.5×0.1 μm. Growth of β-Co(OH)
2 micro-crystals up to 9×0.5 μm was carried out in NaOH aqueous solutions under hydrothermal conditions. The basal plane of the synthesized β-Co(OH)
2 platelets was {001}, as revealed by oriented particulate monolayer X-ray diffraction (OPML-XRD), which was kept after hydrothermal growth. The obtained platelets are considered to be suitable templates for the fabrication of textured layered-cobaltite thermoelectric ceramics by the reactive-templated grain growth (RTGG) method.
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Jihong SHE, Tatsuki OHJI, Shuzo KANZAKI
Session ID: 1
Published: 2004
Released on J-STAGE: September 29, 2004
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A recently developed shock-sintering technique was employed to fabricate dense titania (TiO
2) ceramics. The densification and grain-growth behaviors as well as the anatase-to-rutile transformation of a nanocrystalline TiO
2 powder without any additives were investigated as a function of sintering temperature and/or sintering time. It has been shown that densification proceeds simultaneously with phase transformation. At 1100°C for a sintering time of 2 min, a 100% density was achieved, while 98% anatase was transformed into rutile. On the other hand, significant grain growth was observed to occur at temperatures above 1100°C.
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Masato SAITO, Takao ANDO, Osamu SUGIYAMA, Kimio HIYOSHI, Kazuo SATO, T ...
Session ID: 1
Published: 2004
Released on J-STAGE: September 29, 2004
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For the utilization of the paper sludge (PS) ash, we investigated a novel method to remove high concentrated Pb ions from water and fix them. PS ash zeolite (PSZ), which was prepared through an alkali hydrothermal treatment of PS ash with the addition of sodium silicate, was soaked into an aqueous solution of Pb(NO
3)
2 to include Pb ions. The PSZ was heated at a temperature more than 400°C to form PS ceramics (PSC) after being mixed with sodium silicate. The PSC was characterized in terms of morphology, constituent minerals and chemical bonding. In addition, we evaluated the Pb ions fixability of PSC by the determination of Pb concentration eluted from PSC. As a result, detected minerals of PSC's were quartz, albite, nepheline and wollastonite. Each of them appeared or disappeared with changing heating temperature and/or amount of sodium silicate added. Especially in the case of high heating temperature (≥800°C) and large amount of sodium silicate added (≥0.03 molSi/10 gPSZ), nepheline and albite were principal assemblage of PSC and mechanical strength of PSC increased. When nepheline existed in PSC, Pb concentration eluted from PSC was extremely low, showing high ability on fixing of Pb ions. At the same time, the PSC that contained nepheline showed high acidic resistant.
Therefore, it was concluded that the transformation of Pb-included PSZ to PSC that contained nepheline as a principal constituent mineral was much effective for fixing of Pb ions. This novel method will be also applicable to the removal of other heavy metal ions in the water.
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Tao SUN, Xiaoshan NING, Kexin CHEN, Yong Sheng HAN, Heping ZHOU
Session ID: 1
Published: 2004
Released on J-STAGE: September 29, 2004
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Nickel aluminate (NiAl
2O
4) spinel has a high electric conductivity and a good stability at high temperature, and it becomes a promising candidate as anode material in aluminum electrolysis. The self-propagating high-temperature synthesis (SHS) technique was employed in the present work to produce NiAl
2O
4 spinel by using Al and NiO as reactants. The synthesized powders were studied by SEM and XRD. The XRD results show that the formation of NiAl
2O
4 depends on the molar ratio (
R) of NiO/Al, and NiAl
2O
4 spinel could only be formed when the molar ratio is higher than 1.5. The amount of the NiAl
2O
4 spinel reaches maximum when the molar ratio was 2. The reaction chemistry and the reaction mechanism are also discussed in this article.
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Lin LI, Hideki NABIKA, Minoru MIZUHATA, Akihiko KAJINAMI, Shigehito DE ...
Session ID: 1
Published: 2004
Released on J-STAGE: September 29, 2004
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The Copper phthalocyanine (CuPc)/transition metal oxide (TiO
2)-CuPc-SDS/TiO
2 composite thin film has been successfully prepared from the aqueous solution by a novel wet process, liquid-phase deposition (LPD) method. It may open up a new way to prepare the CuPc thin film, and develops the formation processes of CuPc thin films. For LPD method, this is the first attempt to prepare the insoluble organic substance/inorganic metal oxide composite thin film with using a surfactant sodium dodecyl sulfate (SDS) as dispersing agent. The CuPc-SDS/TiO
2 composite thin film was formed directly on to the substrate upon immersion into a mixed solution of [NH
4]
2TiF
6, H
3BO
3 and CuPc-SDS aqueous solution. The deposited composite thin films were characterized by ultraviolet-visible (UV-Vis) absorption spectroscopy in the range of 350-850 nm, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and inductive coupled plasma atomic emission spectrometry (ICP-AES). The results revealed that most of the CuPc existed as dimer species both in the film and in the treatment solution, illustrating that the CuPc is not further aggregated by LPD process. According to the study of the XRD patterns of the composite thin films, the CuPc-SDS/TiO
2 composite thin film was proved to be α-form CuPc composite thin film. The effects of changing SDS and CuPc concentration on the composite thin films were studied, indicating that the deposited amount of CuPc increased with an increase of SDS and CuPc concentrations. The dependences between the deposited amount of Ti and Cu with the reaction time were investigated, which indicated that the deposited amount of Ti and Cu are nearly directly proportional to the reaction time, and suggested the growing of the composite thin film was controllable readily.
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Yang ZHOU, Akiko HONDA, Tomokazu TAKEDA, Masato UEHARA, Naoya ENOMOTO, ...
Session ID: 1
Published: 2004
Released on J-STAGE: September 29, 2004
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Surface treatments, such as calcination, acid solution leaching and alkali solution leaching, were used to improve the dispersibility and increase the electrophoretic deposition (EPD) weight for a fine SiC powder. Main impurities including hydrophobic free carbon and hydrocarbon on the particle surface caused the low dispersibility and less deposition for the as-received powder in aqueous suspension. After calcination, the dispersibility and deposition weight were enhanced obviously. Acid leaching and alkali leaching were more effective to improve the dispersibility. The deposition weights of the two kinds of powders were about 4 times larger than that of the as-received powder. Slight oxidation on the particle surface after acid leaching led to the largest deposition weight for the acid leached powder. The reason for the improvement caused by different treatments was discussed according to the results of zeta potential, FTIR, XPS, and surface acidity analyses.
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Sang-Soon OH, Yong-Seog KIM
Session ID: 1
Published: 2004
Released on J-STAGE: September 29, 2004
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In an attempt to improve luminance efficiency of plasma display panel (PDP), its discharge cells were coated with photonic crystal (PC) layer. The powders used were monodispersed SiO
2, which were prepared through hydrolysis and condensation reactions of silicon alkoxides in the presence of ammonia. Polydispersity of the powder was less than 5%. A suspension of the powder was filled into the cells on rear plate of PDP and solvent was evaporated from the cells in a controlled manner to form a PC layer. Luminance efficiency of the cells with the layer was measured and compared with cells without the layer. The results indicated that application of PC layer significantly improved luminance efficiency of the PDP cells.
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Hideaki SANO, Takehiro HIGUCHI, Guo Bin ZHENG, Yasuo UCHIYAMA
Session ID: 1
Published: 2004
Released on J-STAGE: September 29, 2004
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A thin film including beta-silicon carbide (β-SiC) was synthesized by carbon silicification through a reaction between gaseous silicon monoxide (SiO) gas and carbon source derived from polyimide film (PIF). The sample obtained had film shape similar to that of the carbon source film. Two reacted regions were found on both surfaces of the carbon source film, as well as the un-reacted region in the middle of the sample with less than 3 h synthesis time. Formation mechanism of β-SiC film formed by the reaction between SiO gas and carbon source film at 1400°C was investigated based on relationship among SiC conversion ratio, reaction time and atmospheres. Formation processes were simulated thermodynamically and kinetically by the calculations solving differential equations concerning with a rate of chemical species. Results of the simulated curves for the SiC conversion ratio calculated from 6 chemical equations, 12 rate constants, 2 diffusion constants, 9 chemical species and 9 differential equations have a good agreement with the experimental results of the SiC conversion ratio as a function of reaction time.
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Dan S. PERERA, Catherine L. NICHOLSON, Mark G. BLACKFORD, Ross A. FLET ...
Session ID: 1
Published: 2004
Released on J-STAGE: September 29, 2004
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Geopolymers synthesised using New Zealand fly ash have been investigated for their potential application as matrices for encapsulation and immobilisation of hazardous and radioactive waste. Knowledge of the long-term behaviour and macroscopic and microscopic properties of these materials will be essential. Pastes aged for between 1 day and 2 years after were investigated in this study. The material exhibited a complex microstructure, consisting of both crystalline and amorphous regions. While no changes in crystalline phases were detected in fresh and aged samples, significant differences in porosity and surface area were noted on ageing of the samples. Very high early strengths of 85 MPa were achieved but were observed to decline in samples after 7 days ageing. It is believed that on-going reactions within the geopolymer matrix are contributing to these changes after the material has set and hardened.
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2. Processing and Manufacturing
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Satoshi TANAKA, Shinya WATANABE, Nozomu UCHIDA, Keizo UEMATSU
Session ID: 2
Published: 2004
Released on J-STAGE: September 29, 2004
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The packing structure of alumina green body prepared by slip casting method was examined using an optical method based on polarized light microscopy. Minor particle orientation was noted in the green body made by slip casting. The alumina compact was fabricated by slip casting in gypsum molds. Alumina particles in commercial grade powders have an elongated shape. The alumina particles in the green body were always oriented parallel to gypsum surface. The oriented packing structure was observed throughout the compact.
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Kaori JONO, Masayoshi FUJI, Minoru TAKAHASHI
Session ID: 2
Published: 2004
Released on J-STAGE: September 29, 2004
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Use of natural polymers as gelling agents was attempted in order to develop a new gelcasting process under ambient atmosphere for fabrication of porous building materials composed of waste resources. Agar, curdlan and carrageenan were selected as natural polymers. The slurry with an appropriate composition of wastes and polymer was foamed by a mixer after addition of a surfactant. The foamed slurries were
in situ solidified after casting into a plastic mold under ambient atmosphere. Effects of a type and concentration of polymer on the properties of wet-green bodies, dry-green bodies and sintered bodies were examined. The strength of the obtained wet-green bodies was sufficient enough for de-molding and successive handling. The compressive strength of wet-green bodies increased with polymer content and showed the highest value at the addition of agar. However, carrageenan and curdlan have advantages that the foamed slurries can be solidified by heating after casting into the mold. On the other hand, the slurries should be heated before casting and cooled for gelation when agar is used. It is obvious that the gelling is quite easy in the former procedure. The flexural strength of dry-green bodies and sintered bodies depended on their porosity rather than on the type and concentration of the polymer. The values of strength ranged from 15 to 45 MPa enough for application as a ceramic tile, even though the porous materials have high porosities of around 60%. These results revealed the
in situ solidification method using carrageenan and curdlan as a promising technique to produce porous building materials.
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Hisanori YOKOYAMA, Seizo OBATA, Nobuhisa KATO, Tadashi HOTTA, Hiroya A ...
Session ID: 2
Published: 2004
Released on J-STAGE: September 29, 2004
CONFERENCE PROCEEDINGS
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Three-dimensional electroconduction pattern of Si
3N
4-TiN system was prepared using the ink jet printing method. Two kinds of 20 vol% ink were prepared by milling insulative powder (Si
3N
4) and electroconductive powder (TiN), of which the viscosity and the dispersibility were carefully adjusted. The droplet formation process and the compact characters were examined, and the effect of the ink characters on both printing and forming behaviors was studied. It was revealed that the viscosity and the structure of the ink influenced the printing behavior and the compact characters. The laminated body was processed by patterning on a compact of Si
3N
4, followed by firing for 3 h at 1750°C in N
2. The sintered body showed an interesting structure with three-dimensional electroconduction pattern.
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Satoshi KITAOKA, Naoki KAWASHIMA, Kazushi AOYAMA, Craig A. J. FISHER, ...
Session ID: 2
Published: 2004
Released on J-STAGE: September 29, 2004
CONFERENCE PROCEEDINGS
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Porous carbon substrates have been sealed completely with a molten silicate glass, where the wettability of the carbon to the molten glass was improved by infiltration and pyrolysis of perhydropolysilazane. The interfacial structure between the carbon and glass depended on the N
2 partial pressures during sealing. Coating of the glass at a higher N
2 partial pressure was not followed by formation of cristobalite due to oxidation of the products pyrolyzed on the carbon substrate. The molten glass easily infiltrated into the substrate. Under lower N
2 partial pressures such as in Ar, the glass covered only the carbon substrate and seldom penetrated into the substrate. In this case, cristobalite was produced at the interface, with many pores also forming at the interface. The pores are due to the large amount of SiO produced by oxidation of the pyrolyzed species, leading to suppression of molten glass infiltration into the carbon. The structural changes occurring as a result of variation in N
2 partial pressures are described in terms of thermodynamic calculations.
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Osamu SAKURADA, Koichiro SUZUKI, Minoru HASHIBA
Session ID: 2
Published: 2004
Released on J-STAGE: September 29, 2004
CONFERENCE PROCEEDINGS
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Non-aqueous suspensions are preferred for electrophoretic deposition (EPD) to prevent electrolysis of the solvent and to obtain a bubble-free deposit. On the other hand, aqueous systems have the advantages of low cost and low environmental burden. However, water is decomposed into hydrogen and oxygen when a dc current is passed through an aqueous media. It is well known that hydroquinone (HQ) is easily oxidized to quinone (Q), and this reaction decreases the levels of dissolved and electrolytically produced oxygen. In the EPD process, oxygen produced electrolytically would be consumed by the chemical oxidation of HQ, followed by bubble-free deposition on the anode. In this study, we investigated EPD on various anodes of aqueous alumina and zirconia suspensions with HQ and also attempted to fabricate bubble-free alumina/zirconia gradiented composites.
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Sung-Jin AHN, Jooho MOON
Session ID: 2
Published: 2004
Released on J-STAGE: September 29, 2004
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Patterned ceramic structures composed of two different materials with a feature resolution in the micrometer range have been generated by microfluidic lithography. Micro-channels made of poly (dimethylsiloxane) (PDMS) were filled with well-dispersed suspensions followed by solidification upon solvent evaporation. The cross-inserted comb-type ceramic structures with 100 μm in the width were fabricated in a relatively large area of 2×2 cm
2 for Al
2O
3 and NiO. It was found that controls of suspension characteristics and its drying play an important role in determining pattern quality. Micro-channel filling was significantly influenced by viscosity and surface tension of suspension and interfacial interaction of suspension with surfaces of the substrate and PDMS. Once filled, a proper drying condition must be met. Otherwise, the micro-channels were disconnected due to capillary stress, resulting in an incomplete pattern generation.
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Shintaro ISHIYAMA, Shigeki MARUYAMA
Session ID: 2
Published: 2004
Released on J-STAGE: September 29, 2004
CONFERENCE PROCEEDINGS
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Very high tensile strengths of SiC and its joint material over 1200 MPa and 500 MPa were achieved by newly developed reaction sintering (RS) technique. The design study of ceramic type H
2SO
4 vaporizer was performed on the base of these material data and testified its applicability for nuclear heat IS hydrogen production plant. Present study also demonstrated applicability of the RS-technique to full scale ceramic block unit(110 mm×110 mm×110 mm) with heat channels for the vaporizer.
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Masatoshi OTAKE, Kenji SATO, Osamu SUGIYAMA, Shoji KANEKO
Session ID: 2
Published: 2004
Released on J-STAGE: September 29, 2004
CONFERENCE PROCEEDINGS
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Both p- and n-type Si
0.8Ge
0.2 powders (Si : Ge : B=79.7 : 20.1 : 0.20 mol% for p-type and 79.8 : 20.0 : 0.20 mol% for n-type) were prepared by gas atomization of the melts from starting solids, followed by densification using a pulse-current sintering technique. These Si-Ge powders were characterized and their sinterability was studied, and the thermoelectricity of the Si-Ge dense bodies was then elucidated. The effect of ball-milling on both the sinterability and thermoelectricity was discussed. Ball-milling made the particle size of as-prepared powders small, presumably together with the introduction of the distortion to the crystal lattice. The densification of as-prepared powders was abruptly promoted above 1500 K by pulse-current sintering, while this densification behavior of the pulverized powders occurred at a lower temperature by approximately 100 K. The grain size and elemental inhomogeneity of the dense body from pulverized powders were also reduced. The pulse-current sintering of the gas-atomized and their pulverized powders led possibly to a density of the shaped bodies of more than 99% at 1523 and 1433 K, respectively, in a short time of 3 min. The following results obtained here were all attributed to the thermoelectric properties such as thermal conductivity, electrical resistivity and the Seebeck coefficient of the dense bodies. The figure of merit of dense body from gas-atomized n-type powder was the highest among the four kinds of the dense bodies tested. It is proved that the figure of merit of the dense bodies from gas-atomized powders was higher than those from pulverized powders, and that further pulverization by ball-milling was ineffective.
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Hiroyuki Y. SUZUKI, Yuya NARA, Shunzo TASHIMA, Hidenori KUROKI
Session ID: 2
Published: 2004
Released on J-STAGE: September 29, 2004
CONFERENCE PROCEEDINGS
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Tetragonal zirconia polycrystal (TZP) compact was made via colloidal processing by the high-speed centrifugal compaction process (HCP). A pure zirconia powder of 0.14 μm was prepared into aqueous slip and compacted by the HCP under 10,000 g. The compact was presintered, then yttria phase stabilizer was impregnated in the form of an aqueous solution of yttrium nitrate.
The slip with the maximum powder concentration (72.2 mass%) yielded the highest green density of 46% and suppressed the segregation of particles during the HCP. The yttria-doped specimens were densified up to 99% at 1623 K without pressure assistance. The microstructure consisted of grains of 0.5 μm diameter of the tetragonal phase. The highest values of hardness and fracture toughness, Hv 1270 and 9.1 MPa m
1/2, respectively, were obtained with a specimen doped with 2.7 mol% yttria.
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G. C. WEI
Session ID: 2
Published: 2004
Released on J-STAGE: September 29, 2004
CONFERENCE PROCEEDINGS
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Sintering of translucent polycrystalline alumina has improved through optimization of dopants and sintering atmosphere. The role of the magnesia dopant and mechanisms of the densification process in alumina have been active topics for numerous studies in the literature. It is widely recognized that the mass transport required for densification involves grain-boundary diffusion, and oxygen vacancies play an important role. The retardation of grain growth has been ascribed to drags due to solute and/or spinel second phase particles. Some researchers have conceived the notion that magnesia solubility in alumina is dependent on grain size. In this paper, we will report that the solid solubility of magnesia in alumina is indeed a strong function of grain size in the range of submicron to one micron. The grain-boundary enrichment factor and width appear to be a function of grain size. Grain growth occurs in small-grained MgO-doped alumina at temperatures as low as 1150°C. During the initial stage of grain growth and sintering of compacts of magnesia-doped, submicron alumina powders, the grain size, enriched dopant level at grain boundaries, boundary width, and equilibrium dopant content in the lattice, undergo dynamic evolution, in a background of boundary motion, precipitation of spinel second phase, and diffusional flux of the dopant.
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K. TSUCHIYA, T. HOSHINO, H. KAWAMURA, T. TAKAYAMA
Session ID: 2
Published: 2004
Released on J-STAGE: September 29, 2004
CONFERENCE PROCEEDINGS
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Lithium titanate (Li
2TiO
3) pebbles are considered to be a candidate material of the tritium breeders for fusion reactor from viewpoints of good tritium recovery, chemical stability, etc. In the present study, fabrication tests of
6Li-enriched Li
2TiO
3 pebbles were carried out by a wet process with a dehydration reaction and their characteristics were evaluated in preparation of an irradiation experiment in a material testing reactor. Based on the results,
6Li-enriched Li
2TiO
3 pebbles and TiO
2-doped
6Li-enriched Li
2TiO
3 pebbles with the target values (density: 80-85%T.D., grain size:<5 μm, diameter: 0.85-1.18 mm) were successfully fabricated by this wet process. Sphericity of the Li
2TiO
3 pebbles, which is the ratio of the longest diameter to the shortest diameter, was a satisfying value of less than 1.1.
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Seizo OBATA, Hiroyuki ASAKURA, Hiroshi ASANO, Osamu SAKURADA, Minoru H ...
Session ID: 2
Published: 2004
Released on J-STAGE: September 29, 2004
CONFERENCE PROCEEDINGS
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The dispersion and fluidity of aqueous carbon slurries were studied to elucidate the optimum preparation conditions to obtain well-dispersed and fluidized aqueous carbon slurries. The mean particle diameter of the carbon powder used was 13 nm. Styrene/maleic copolymer (SM), polystyrenesulfonic acid (HPSS), and naphthalene sulfonic acid formalin condensate ammonium salts (DEMOL-AS) were selected as dispersants. The rheological behavior of aqueous carbon slurries with various dispersants was examined and evaluated. The electrokinetic behavior of the carbon particles in the presence of DEMOL-AS, SM, or HPSS indicated that the surface properties of the carbon particles changed from hydrophobic to hydrophilic by adsorption of dispersants. The fluidity of aqueous carbon slurries was effectively enhanced by the addition of DEMOL-AS, as compared with the addition of SM or HPSS. DEMOL-AS containing a naphthalene nucleus was an effective dispersant to improve the surface of carbon particles. The dispersion and fluidity of the carbon slurries were dependent on electrokinetic and steric interactions. The carbon slurries with DEMOL-AS were well dispersed and fluidized over a wide range of pH. These observations indicated that DEMOL-AS is an effective dispersant for preparing aqueous carbon slurries.
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3. Sol-Gel, Coating and Products