Papers - SAKAI Go
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Stabilization of counter electrode for nasicon based potentiometric CO 2 sensor
Miyachi Y., Sakai G., Shimanoe K., Yamazoe N.
Ceramic Engineering and Science Proceedings 25 ( 3 ) 471 - 476 2004.12
Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Ceramic Engineering and Science Proceedings
Two kinds of materials, Bi2Cu0.1V0.9O 5.35 (BICUVOX) and NaCoO2, were investigated for their applicability as the counter electrode for a potentiometric CO2 sensor using NASICON (Na+ conductor, Na3Zr 2Si2PO12). The BICUVOX counter electrode was more stable than an Au counter electrode. Thermal cycling between the operating temperature (450°C) and room temperature under various conditions indicated the time needed for the BICUVOX electrode to reach the stationary potential after switching to the operating temperature was unacceptably long. NaCoO 2 was found unsuitable as a counter electrode material due to its reactivity with CO2. This reactivity was suppressed completely when NaCoO2 was coated with a layer of glass (SiO2: Na 2O: B2O3: Al2O3 = 44:20:31:5, in molar ratio). The glass-coated NaCoO2 electrode worked well as a counter electrode at 450°C. Thermal cycling indicated that the glass-coated NaCoO2 electrode exhibited an initial ageing effect. Once aged, glass-coated NaCoO2 showed the properties of a reliable counter electrode, i.e., rapid warm-up characteristics and a reproducible stationary potential at 450°C.
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Microstructural control of SnO2 thin films by using polyethylene glycol-mixed sols
Sakai G., Shimanoe K., Yamazoe N., Sato C.
Ceramic Engineering and Science Proceedings 25 ( 3 ) 477 - 482 2004.12
Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Ceramic Engineering and Science Proceedings
Microstructural control of SnO 2 thin films was attempted by introducing various amounts of polyethylene glycol (PEG) into an aqueous sol of SnO 2 to be spin-coated. As measured for the powder samples derived from the sols, the addition of PEG cut the specific surface area of SnO 2 almost in half, while keeping the crystallite size almost unchanged. Pore size distribution analysis revealed that the average pore diameter was about 6 nm for the powder derived from the neat SnO 2 sol, while it was enlarged to about 20 nm by the addition of PEG1000 by 18 wt%. SEM observation of spin-coated thin films revealed that morphology changed from a dense packing of very fine particles to a more porous packing of larger particles with the addition of PEG1000 or PEG6000. The thickness of spin-coated film could be increased by increasing amount of PEG1000 or PEG6000 added. The sensor response of these films to H 2 gas increased with increasing film thickness. This tendency is considered to result because the porous structure of the film becomes better developed as the amount of PEG increases.
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Yuasa M., Sakai G., Shimanoe K., Teraoka Y., Yamazoe N.
Journal of the Electrochemical Society 151 ( 10 ) 2004.11
Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Journal of the Electrochemical Society
La1-xSrxMn0.8Fe0.2O 3+δ (x = 0-0.4) and La0.8Sr0.2Mn 1-yFeyO3+δ (y = 0-0.8) supported on carbon were successfully prepared by a reverse micelle method. Aqueous solutions dissolving nitrates of constituent metals of the intended oxides and tetramethylammonium hydroxide (precipitant) were separately transformed into reverse micelle dispersions by using poly(oxyethylene)5-lauryl ether (surfactant) and cyclohexane (oil). These dispersions were mixed together to derive a reverse micelle dispersion containing mixed hydroxides as precursors of the oxides, into which carbon powder suspended in cyclohexane was put under agitation. The suspension was destabilized with ethanol, and the resulting precipitate (carbon-supported precursors) was calcined in N2 atmosphere to prevent the carbon matrix from being combusted. Single-phase oxides supported on carbon were obtained by calcination at 700°C unless the oxides were free of Fe. Oxygen reduction activity of the gas-diffusion-type electrodes fabricated with thus prepared carbon-supported oxides increased sharply and decreased gradually with increasing x and y, respectively. Among the prepared oxides, the greatest activity, i.e., 500 mA/cm2 at -67 mV (vs. Hg/HgO electrode) in 9 M NaOH at 85°C under O2 flow, was achieved by the oxide with x = 0.4 and y = 0.2. Optimal loading on carbon as well as durability under oxygen reduction conditions were tested for selected oxides. 17 wt % La0.6Sr0.4Mn0.8Fe 0.2O3+δ loading electrode was compared with 27.7 wt % Pt-loading electrode in an oxygen reduction activity, and it was found that the former electrode was better than the Pt loading electrode. © 2004 the electrochemical society All rights reserved.
DOI： 10.1149/1.1789156
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Stabilization of counter electrode for NASICON based potentiometric CO2 sensor Reviewed
共著者：Y. Miyachi, G. Sakai, K. Shimanoe, N. Yamazoe
Ceramic Engineering and Science Proc., 25 (3), 471-476 (2004). 25 ( 3 ) 471 - 476 2004.11
Language：English Publishing type：Research paper (international conference proceedings)
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Microstructural control of SnO2 thin films by using polyethylene glycol-mixed sols Reviewed
共著者：G. Sakai, C. Sato, K. Shimanoe, N. Yamazoe
Ceramic Engineering and Science Proc., 25 (3), 477-482 (2004). 25 ( 3 ) 477 - 482 2004.11
Language：English Publishing type：Research paper (international conference proceedings)
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Exploration of reverse micelle synthesis of carbon-supported LaMnO <inf>3</inf>
Yuasa M., Sakai G., Shimanoe K., Teraoka Y., Yamazoe N.
Journal of the Electrochemical Society 151 ( 9 ) 2004.10
Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Journal of the Electrochemical Society
Reverse micelle (RM) based synthesis of carbon-supported perovskite type oxide (LaMnO3) was investigated. By using cyclohexane as oil phase, six kinds of nonionic surfactants were tested for the formation of the revere micelle dispersions containing aqueous solutions of mixed nitrates of La 3+ and Mn2+ (RM-N) and tetramethylammonium hydroxide (RM-A) at the water/surfactant molar ratio (Rw) of 3. RM-A was found to be more difficult to form compared with RM-N or the RM containing pure water. At a temperature range of 5-25°C, it was given only by the surfactants with hydrophilic-lipophilic balance (HLB) values of 10.0-10.9. Phase diagrams of oil-surfactant-alkaline solution (or pure water) were constructed at 5 and 15°C for the best two surfactants, i.e., poly-(oxyetylene) 6-nonylphenyl ether and poly-(oxyetylene)5-lauryl ether. Mixing RM-N and RM-A together gave the RM containing a mixed hydroxides-precursor (RM-P), which was further converted into carbon-supported LaMnO3 through a series of treatments including the addition of carbon powder and calcination in N2 atmosphere at 600°C. The size of RM-P as well as that of the LaMnO3 grains supported on carbon could be controlled well by selecting Rw. The carbon-supported LaMnO3 proved to be highly active for the electrochemical reduction of oxygen. © 2004 The Electrochemical Society. All rights reserved.
DOI： 10.1149/1.1782165
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Ruiz A., Sakai G., Cornet A., Shimanoe K., Morante J., Yamazoe N.
Sensors and Actuators, B: Chemical 103 ( 1-2 ) 312 - 317 2004.9
Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Sensors and Actuators, B: Chemical
Nanocrystalline titanium dioxide with enhanced thermal stability was prepared by subjecting the alkoxide-derived TiO2gel to a hydrothermal treatment at 150°C for 3h in dilute HNO3solution (pH 3 or 2). Structural modifications of TiO2were analyzed by XRD and the morphology of the powders observed by FE-SEM. The hydrothermal treatment stabilized TiO2in two ways, i.e., suppressing thermal growth of TiO2crystallites and shifting up the temperature of anatase-to-rutile phase transformation, although the degree of stabilization differed considerably depending on the pH of the HNO3solution used. The TiO2hydrothermally treated at pH 3 consisted of small anatase nanospheres of 13 and 34nm in average diameter after calcination at 600 and 800°C, respectively, whereas the untreated TiO2was predominated by rutile phase at 700°C. Suppression of crystallite growth was even more conspicuous with the treatment at pH 2; the average crystallite size of anatase was 11 and 26nm after calcined at 600 and 800°C, respectively. In this case, however, the transformation was less hindered, with rutile phase occupying 9, 22 and 67% of TiO2after calcinations at 600, 700 and 800°C, respectively. This indicates that the phase transformation is not always related uniquely with crystallite size of anatase phase. The thick films fabricated with these TiO2powders did not show much differences in sensor response (ratio of resistance in air to that in gas) to dilute CO in air at 400-550°C, though the powder hydrothermally treated at pH 3 tended to give the highest response. However, the hydrothermal treatment was found to improve much the sensor response transients, suggesting that it was effective in developing mesopores inside the films. © 2004 Elsevier B.V. All rights reserved.
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Vuong D., Sakai G., Shimanoe K., Yamazoe N.
Sensors and Actuators, B: Chemical 103 ( 1-2 ) 386 - 391 2004.9
Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Sensors and Actuators, B: Chemical
Colloidal dispersions of crystalline SnO2(sols) with a mean grain (crystallite) size controlled between 6 and 16nm were prepared successfully from stannic acid gel by hydrothermal treatments under the condition of pH 10.5 and 200°C or pH 12.2 and 250°C. The growth of crystallites saturated in a few hours of hydrothermal treatment and the saturation values tended to increase with increasing SnO2gel content, pH and temperature. The SnO2grains remained monodispersed unless time of hydrothermal treatment was excessive. Thin films of SnO2prepared on an alumina substrate from the sols by a spin-coating method responded sharply to H2gas. The magnitude of sensor response as well as its dependence on operating temperature were different significantly depending on the grain sizes of the starting sols. Among the sols with a mean grain size of 6, 8.5, and 10nm, the last two gave large response to H2, which reached a maximum at 400 or 350°C, respectively. © 2004 Published by Elsevier B.V.
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Development of FET-type CO<inf>2</inf>sensor operative at room temperature
Shimanoe K., Goto K., Obata K., Nakata S., Sakai G., Yamazoe N.
Sensors and Actuators, B: Chemical 102 ( 1 ) 14 - 19 2004.9
Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Sensors and Actuators, B: Chemical
An FET-type CO2sensor operative at room temperature was developed by stacking a powder mixture of metal carbonate (auxiliary phase) - indium tin oxide (ITO, sensing electrode) as well as Na+-exchanged cation exchange membrane (ionic conductor gate) on an FET chip. Both ITO and the cation exchange membrane were indispensable to obtain stable response to CO2at room temperature, while the auxiliary phase was optimized to be Li2CO3-BaCO3(1:3 in molar ratio) from the stability of response against the disturbance by humidity. The device, Li2CO3-BaCO3-ITO (1:3:1)/Na+-exchanged cation exchange membrane/FET, exhibited excellent CO2-sensing characteristics at 30°C. The response in gate-source voltage (VGS) was linear to the logarithm of CO2concentration, with its slopes indicating n = 2.0 where n is the number of reaction electrons involved in the electrochemical reduction per CO2. The Nernst's correlation was fairly stable against a change in RH between 30 and 70%. The times for 90% response and 90% recovery to switching-on and -off 3000 ppm CO2were 1 and 2 min, respectively. © 2004 Elsevier B.V. All rights reserved.
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Reverse Micelle-Based Preparation of carbon-supported La1-xSrxMn1-yFeyO3+d for Oxygen Reduction Electrode Reviewed
共著者：M. Yuasa, G. Sakai, K. Shimanoe, Y. Teraoka, N. Yamazoe
Journal of the Electrochemcal Society, 151, A1690-A1695 (2004). 151 1690 - 1695 2004.9
Language：English Publishing type：Research paper (scientific journal)
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Exploration for reverse micelle synthesis of carbon-supported LaMnO3 Reviewed
共著者：M. Yuasa, G. Sakai, K. Shimanoe, Y. Teraoka, N. Yamazoe
Journal of the Electrochemcal Society, 151, A1477-A1482 (2004). 151 1477 - 1482 2004.9
Language：English Publishing type：Research paper (scientific journal)
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Preparation of grain size-controlled tin oxide sols by hydrothermal treatment for thin film sensor application
共著者：D. D. Vuong, G. Sakai, K. Shimanoe, N. Yamazoe
Sensors and Actuators B, 103, 386-391 (2004). 2004.9
Language：English Publishing type：Research paper (scientific journal)
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Microstructure control of thermally stable TiO2 obtained by hydrothermal process for gas sensors Reviewed
共著者：A. M. Ruiz, G. Sakai, A. Cornet, K. Shimanoe, J. R. Morante, N. Yamazoe
Sensors and Actuators B, 103, 312-317 (2004). 103 312 - 317 2004.9
Language：English Publishing type：Research paper (scientific journal)
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Development of FET-type CO2 sensor operative at room temperature Reviewed
共著者：K. Shimanoe, K. Goto, K. Obata, S. Nakata, G. Sakai, N. Yamazoe
Sensors and Actuators B, Vol. 102, 14-19 (2004). 102 14 - 19 2004.9
Language：English Publishing type：Research paper (scientific journal)
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Wet process-based fabrication of WO<inf>3</inf>thin film for NO<inf>2</inf>detection
Choi Y., Sakai G., Shimanoe K., Yamazoe N.
Sensors and Actuators, B: Chemical 101 ( 1-2 ) 107 - 111 2004.6
Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Sensors and Actuators, B: Chemical
It was tried to fabricate a WO3thin film device through a wet process starting from an aqueous sol of WO3·2H2O. When mixed with polyethylene glycol (PEG, molecular weight 6000), the sol was made compatible to spin coating on an alumina substrate and the coating could be converted into a WO3thin film by calcination at 300°C for 2h. Starting with a typical coating dispersion containing WO3·2H2O by 5mass% on WO3basis and 2mass% PEG, the WO3film obtained was 450nm in mean thickness. The film was a slim pack of square plates, each of which was a stack of thin lamellar crystals of WO3. The device was sensitive enough to detect 50ppb NO2in air at 200 or 250°C, although the response and recovery transients were rather sluggish. Unexpectedly, the transients were found to be sharpened drastically in humid atmosphere, while sensor response (sensitivity) to NO2was hardly degraded with humidity. © 2004 Elsevier B.V. All rights reserved.
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Wet process-based fabrication of WO3 thin film for NO2 detection Reviewed
共著者：Y.-G. Choi, G. Sakai, K. Shimanoe, N. Yamazoe
Sensors and Actuators B, Vol. 101, 107-111 (2004). 101 107 - 111 2004.6
Language：English Publishing type：Research paper (scientific journal)
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Sensing properties of SnO2-Co3O4 composites to CO and H2
Choi U., Sakai G., Shimanoe K., Yamazoe N.
Sensors and Actuators, B: Chemical 98 ( 2-3 ) 166 - 173 2004.3
Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Sensors and Actuators, B: Chemical
A series of SnO2-Co3O4composite thick films (about 10μm thick) containing 0-100% Co3O4by mass of the composites were prepared from the component oxides through mixing by ball-milling for 24h, screen-printing and sintering at 700°C for 3h. The composite films were found to exhibit n- or p-type response to CO and H2depending on the Co3O4contents of the composites. The n-type response was exhibited at 200°C or above by SnO2-rich composites (Co3O4content up to 5mass%). The sensor response to both CO and H2, defined as Ra/Rg, where Raand Rgare electrical resistances in air and gas, respectively, was promoted strongly by the addition of small amounts of Co3O4to SnO2, and the response at 250°C as correlated with the Co3O4contents went through a sharp maximum at 1mass% Co3O4. The p-type response, obviously originating from Co3O4(p-type), was exhibited at 200°C or below by the composites containing 25-100mass% Co3O4. Remarkably, sensor response to CO, defined as Rg/Ra, was larger with the 50% Co3O4composite than with the neat Co3O4, while the reverse was true for the response to H2. Thus fairly sensitive and selective detection of CO over H2was possible with the 50% Co3O4composite. The physical state of the composites and the mechanisms of promotion of n- and p-type response were discussed. © 2003 Elsevier B.V. All rights reserved.
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Sensing properties of SnO2-Co3O4 composites to CO and H2 Reviewed
共著者：U.-S. Choi, G. Sakai, K. Shimanoe, N. Yamazoe
Sensors and Actuators B, Vol. 98, 166-173 (2004). 98 166 - 173 2004.3
Language：English Publishing type：Research paper (scientific journal)
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Reduction of platinum salts using mixed surfactant liquid crystal as a reaction medium
Kuwahara Takeshi, Uota Masafumi, Yoshimura Takumi, Karasima Takeshi, Sakai Go, Kijima Tsuyoshi
Preprints of Annual Meeting of The Ceramic Society of Japan<br>Preprints of Fall Meeting of The Ceramic Society of Japan 2004 ( 0 ) 631 - 631 2004
Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Ceramic Society of Japan
Previously we reported the synthesis of platinum nanotubes from mixed surfactant liquid crystal(SLC) templates. The present study demonstrates that the structural order of LC is templates largely affected by couter cation species added and their thermal hystories. The effect of these preparation conditions on the morphological properties of the reduced platinum is also reported.
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Synthesis of high surface area hydroxyapatite nanorods by a mixed surfactant templating method
Uota Masafumi, Arakawa Hiroshi, Kitamura Nana, Yoshimura Takumi, Sakai Go, Kijima Tsuyoshi
Preprints of Annual Meeting of The Ceramic Society of Japan<br>Preprints of Fall Meeting of The Ceramic Society of Japan 2004 ( 0 ) 466 - 466 2004
Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Ceramic Society of Japan
Precipitation of calcium phosphate from mixed surfactant liquid crystal templates lead to hydroxyapatite nanorods covered with calcium stearate. On calcination at 500 <sup>o</sup>C the rod particles were deorganized into hydroxyapatite with a surface area of as large as 360 m <sup>2</sup>g<sup>-1</sup>.