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Volume 50, Issue 6
Displaying 1-11 of 11 articles from this issue
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Nobuyoshi Takabatake, Shizuo Nakamura, Masayuki Kojima, Kentaro Ohhash ...2003 Volume 50 Issue 6 Pages 439-443
Published: June 15, 2003
Released on J-STAGE: May 22, 2009
JOURNAL FREE ACCESSTiO2 films with doping transition metals were prepared by sol-gel processing. The absorbance of the TiO2 films in the range of 500-700 nm was increased by doping V, Mn or Cu ions. Their photocatalytic ability for decomposing methylene blue was less than that of the original TiO2 films under illumination of both uv-and vis-light. Upon the heat treatment above 650°C, a new compound V2TiO6 showed up leading to formation of non-transparent films and thus its photocatalytic ability for decomposing methylene blue was not determined. The method for testing of photocatalysis was developed in a semi-quantitative manner.View full abstractDownload PDF (1843K) -
Gaku Obara, Hiroshi Yamamoto, Masayasu Senda2003 Volume 50 Issue 6 Pages 444-447
Published: June 15, 2003
Released on J-STAGE: December 04, 2009
JOURNAL FREE ACCESSSr-La-Co M-type ferrite powders were prepared by the mechanical compounding method using the planetary ball-mill and subsequent heat treatment. This experiment was carried out to investigate magnetic properties of bonded magnet using M-type ferrite powders prepared by Mechanical compounding method. The properties and making condition of typical sample are as follows; Chemical composition: SrO⋅6.3Fe2O3 in addition with 2.0 wt% La2O3 and 0.3 wt% Co3O4; planetary ball-mill condition: 300 rpm × 1 h; heat treatment condition: 1200°C×4h in air; centrifugal mill time: 1 h; binder: Nylon6 (ejection molding); magnetic properties are Jr= 0.252T; HcJ=307kA/m; (BH)max=12.3 kJ/m3 and density: 3.57 Mg/m3.View full abstractDownload PDF (2863K) -
[in Japanese]2003 Volume 50 Issue 6 Pages 450
Published: June 15, 2003
Released on J-STAGE: May 22, 2009
JOURNAL FREE ACCESSDownload PDF (77K) -
Shigeru Katsuyama, Mikio Ito, Hiroshi Nagai2003 Volume 50 Issue 6 Pages 451-457
Published: June 15, 2003
Released on J-STAGE: May 22, 2009
JOURNAL FREE ACCESSWe have prepared the thermoelectric materials, where the small particles are dispersed in the matrix, by mechanical grinding (MG) or alloying (MA). Si and C powers were added to the p-type Fe0.92Mn0.08Si2 or n-type Fe0.98Co0.02Si2 powders, and they were mechanically milled followed by being hot-pressed. The amounts of the β-phase, ε-phase, α-SiC and C in the sintered samples depend on the amount of the added (Si+C) and the Si/C molar ratio, which affect the values of the Seebeck coefficient and electrical resistivity of the samples. A lot of fine α-SiC particles around 20nm were dispersed in the samples, which decreases the thermal conductivity of the samples. The maximum figure of merit values appear at Si/C=1.5 for p-type Fe0.92Mn0.08Si2 containing 4 mass%(Si+C) and Si/C=1.75 for n-type Fe0.98Co0.02Si2. We have also prepared the CoSb3-FeSb2 composite where the FeSb2 particles are dispersed in the CoSb3 matrix. The dispersed FeSb2 particles contributed to decreasing the thermal conductivity and maintaining the moderate Seebeck coefficient and electrical resistivity of the samples. As a result, the composite whose molar ratio CoSb3/FeSb2 is 0.7/0.3 and milling time is 25 h has a maximum value of figure of merit of 6.1×10-4 K-1 at 756 K, which is much larger than that of 3.2×10-4 K-1 for CoSb3.View full abstractDownload PDF (2717K) -
Susumu Fukuda, Teruo Asaoka, Taketo Masui2003 Volume 50 Issue 6 Pages 458-463
Published: June 15, 2003
Released on J-STAGE: December 04, 2009
JOURNAL FREE ACCESSIn the results of one-step sintering, the relations between applied pressure, heating rate, densification, and β-FeSi2 formation are as follows. There is a tendency that the higher applied pressure, the higher densification and the easier β-FeSi2 formation. On the other hand, there is a tendency that the lower heating rate, the higher densification, and the higher heating rate, the easier β-FeSi2 formation. However, if the applied pressure and heating rate are too high, it will become a reaction exceeding eutectic temperature. It is supposed that there is no advance in the formation of β-FeSi2 during the heating and the formation of β-FeSi2 proceeds during the holding time. In addition, β-FeSi2 of high density (about 95%TD) was produced by two-step sintering. Results show that, 750°C is suitable for the sintering temperature of 2nd step sintering. At that condition, remaining of some ε-FeSi was observed, while α-FeSi2 almost disappeared.View full abstractDownload PDF (7421K) -
Sunao Sugihara, Manabu Katayose, Takeshi Nakamura, Takamasa Isobe2003 Volume 50 Issue 6 Pages 464-468
Published: June 15, 2003
Released on J-STAGE: May 22, 2009
JOURNAL FREE ACCESSAn oxide is functionally classified into two categories when regarding oxide as thermoelectricity: 1) an oxide itself has thermoelectric properties such as CaMnO3, homologous series of (ZnO)m and NaCo2O4, and they have been researched since around 1995. 2) there are researches on oxide as an additive to conventional thermoelectric material. We have investigated to approach thermoelectric property from the electronic structures by ab initio calculation. We propose to estimate Seebeck coefficient of oxide by regarding movement of electron between energy levels in the electronic structures. Thereby, it will lead to a new thermoelectric material of oxide. Furthermore, we can improve figure of merit by adding oxide to FeSi2 due to reducing thermal conductivity in the present study.View full abstractDownload PDF (381K) -
Yasuhiro Ono, Nobuhiko Kato, Yoshinobu Ishii, Yuzuru Miyazaki, Tsuyosh ...2003 Volume 50 Issue 6 Pages 469-474
Published: June 15, 2003
Released on J-STAGE: December 04, 2009
JOURNAL FREE ACCESSCrystal structure and transport properties of γ-NaxCoO2 have been studied in the range of x=0.67-0.75. Single-phase samples were prepared by sintering mixture of raw materials, Na2CO3 (99.5%) and Co3O4 (99.9%). Na/Co composition ratio (x) was determined by inductively coupled plasma (ICP) analysis. The crystal structure parameters were refined by Rietveld analysis of powder neutron diffraction intensities, assuming P63/mmc type space symmetry. Little changes in the crystal structure are noticed, except for Na contents. Electric resistivity ρ and Seebeck coefficient S were measured at temperatures between 380 K and 1000 K by the standard four-probe method and temperature-gradient method, respectively. The ρ-T curves exhibit the thermal hysteresis in the initial measurement. But, in the following measurement, the thermal hysteresis is significantly surpressed. The S was slightly higher in the sample with x = 0.75 than in the others at any temperatures. Power factor (S2/ρ) reaches its maximum value at x = 0.75 (5.3 × 10-4 W/mK2 at 980 K). Hot pressing technique is effective in removing the thermal hysteresis of ρ as well as increasing the power factor.View full abstractDownload PDF (462K) -
Yuzuru Miyazaki, Tatsuro Miura, Yasuhiro Ono, Tsuyoshi Kajitani2003 Volume 50 Issue 6 Pages 475-479
Published: June 15, 2003
Released on J-STAGE: May 22, 2009
JOURNAL FREE ACCESSPolycrystalline samples of [(Ca1-xSrx)2CoO3]ρCoO2 with 0≤x≤0.20 have been synthesized at 1193 K in flowing oxygen gas. The modulated crystal structure of the samples has been determined in accordance with a four-dimensional formalism from powder neutron diffraction data. With increasing x, the modulation amplitudes in Co-Co conduction paths become less marked. The non-doped sample (x=0) exhibits the resistivity ρ=150μΩm and the thermoelectric power S=130, μV/K at 300 K. Both the ρ and S values decrease with x but the decrease in ρ values is steeper than that of the S values. The power factor S2/ρ increases with x, from 110μW/m/K2 (x=0) to 140μW/m/K2 (x=0.20) at 300 K. This improvement in thermoelectric performance can be explained in terms of the reduction of displacive modulation of the Co-Co conduction paths in the CoO2 sheets.View full abstractDownload PDF (388K) -
Masayuki Eguchi, Shin Nishiyama, Takeo Hattori2003 Volume 50 Issue 6 Pages 480-484
Published: June 15, 2003
Released on J-STAGE: May 22, 2009
JOURNAL FREE ACCESSCa3Co4O9 was synthesized by ultrasonic spray pyrolysis (USP) method. The concentration of metal ions in the starting solution was 0.1 mol/l or 0.01 mol/l as Ca3Co4O9, and as the solvent, each of pure water, H2O2 solution or HNO3 solution was used. The solution was sprayed in the furnace and pyrolyzed at 1073 K. X-ray powder diffraction analysis confirmed that all the powders prepared by USP were Ca-Co oxide. The powders were calcined at 1073 K and then sintered at 1173 K. The same sintering conditions were used for the powders prepared by the solid state reaction. The density of the sintered bodies prepared from USP powders ranged in 2.5-2.8gcm-3 and they differed by the solvent of the starting solution. The density of the sintered bodies prepared by solid state reaction was higher than those by USP. The electrical conductivity of the sintered bodies prepared by USP ranged in 4700-5000 Sm-1 at 1073 K, which was higher than those by solid state reaction. In contrast, Seebeck coefficient of the bodies prepared by USP was 106-108μVK-1 at 1073 K, being smaller than those by solid state reaction.View full abstractDownload PDF (1961K) -
Ryoji Funahashi, Saori Urata, Toyohide Sano, Masaaki Kitawaki2003 Volume 50 Issue 6 Pages 485-489
Published: June 15, 2003
Released on J-STAGE: May 22, 2009
JOURNAL FREE ACCESSHaving recently succeeded in synthesizing large single crystals of (Ca2CoO3)CoO2(Co-349) with superior thermoelectric properties and in high yields of about 30% using a modified flux method, we have prepared a composite material of Co-349 powder and single crystals and examined its thermoelectric properties. The electrical resistivity p of this composite containing 20 wt.% single crystals is found to be lower than that of the sample without the single crystals. Improved grain alignment and the effect of current bypassing grain boundaries through the large single crystals in the composite are thought to cause the suppressed ρ, which consequently results in an enhanced thermoelectric figure of merit about 0.56 at 973 K in air.View full abstractDownload PDF (5259K) -
Saori Urata, Masaaki Kitawaki, Ryoji Funahashi2003 Volume 50 Issue 6 Pages 490-494
Published: June 15, 2003
Released on J-STAGE: May 22, 2009
JOURNAL FREE ACCESSIt has been reported that single crystals of CoO2-based oxides with layered structures show good p-type thermoelectric properties. In order to realize thermoelectric power generation, n-type oxides possessing thermoelectric properties as good as CoO2-based oxides are indispensable. We are exploring new n-type oxides using a combinatorial technique, in which 1000 samples can be prepared and evaluated their thermoelectric properties a day. Aqueous solutions of metal nitrates were used as starting materials. In an hour, a single library of 100 samples can be prepared on a 100 × 100 mm alumina plate for heat treatment. Evaluation of Seebeck coefficient was performed using a "Seebeck tester" at a rate of 600 samples/h. In the binary system, the Nd-Ni-O libraries are found out to show n-type thermoelectric properties.View full abstractDownload PDF (6733K)
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