Papers - SAKAI Go
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Synthesis of Nanostructured Platinum by a Mixed Surfactant Templating Method
Yoshimura Takumi, Uota Masafumi, Fuzikawa Daisuke, Kuwahara Takeshi, Sakai Go, Kizima Tuyoshi
Preprints of Annual Meeting of The Ceramic Society of Japan<br>Preprints of Fall Meeting of The Ceramic Society of Japan 2004 ( 0 ) 23 - 23 2004
Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Ceramic Society of Japan
Recently, we found that platinum nanotubes are synthesized from mixed surfactant liquid crystal templates. A similar but a little modified templating method was applied to the reduction of metal salts to obtain sponge- and layer-like platinum with a primary particle diameter of several tens of nanometer.
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Mesoporous Silica Nanoblocks with microporous walls from Mixed-Surfactant Liquid-Crystal Templates
Mori Hiroshi, Uota Masafumi, Yoshimura Takumi, Fujikawa Daisuke, Kuwahara 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 ) 518 - 518 2004
Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Ceramic Society of Japan
Mesoporous silica nanoblocks with microporous walls were synthesized by the hydrolysis of tetraethyl orthosilicate (TEOS) using the mixed-surfactant liquid-crystal templates composed of nonaethylene-glycol monododecyl ether (C12EO9), polyoxyethylene (20) sorbitan monostearate (Tween60) and water, followed by the calcination of the resulting silica/surfactant nanocomplexes. The precursory LC was structurally characterized by X-ray diffraction. It was also found that the ethanol species formed by hydrolysis must be extracted with a large excess of water for the complexation.
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Controlled crystallization of ordered mesoporous anatase-based oxides
Li Donglin, Zhou Haoshen, Honma Itaru, Sakai Go, Kijima Tsuyoshi
日本セラミックス協会 年会・秋季シンポジウム 講演予稿集 2004 ( 0 ) 503 - 503 2004
Language：Japanese Publishing type：Research paper (scientific journal) Publisher：公益社団法人 日本セラミックス協会
A methodology was developed to synthesize crystalline mesoporous metal oxides by help of controlled crystallization process. The proposed methodology has three essential features: (1) Mesoscopically ordered hybrids consisting of multicomponent inorganic precursors and surfactant templates can be obtained by using self-assembly procedure; (2) Subsequent in-situ crystallization of the materials through heat treatment transforms the hybrid into nanocrystal–based oxides; (3) Glass phase is used to control the crystallization. In this way, the nanocomposite consisting of anatase nanocrystals and glass phase can be designed and synthesized. In addition, almost fully crystalline mesoporous oxides can be resulted by decreasing the content of glass phase.
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Ultrasensitive gas sensor using Co3O4-modified SnO2
Choi U., Sakai G., Shimanoe K., Yamazoe N.
Ceramic Engineering and Science Proceedings 24 ( 4 ) 101 - 106 2003.12
Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Ceramic Engineering and Science Proceedings
SnO2 powder was loaded with 0-5 % Co3O4 by mass by a ball milling method. The resulting composites were screen printed onto a substrate to test the sensing properties to CO and H2. It was found that the sensor response, defined as the ratio of electrical resistance in air to that in gas, was greatly promoted with 0.5 or 1.0 % Co 3O4 loading, while further loadings (3 or 5 %) gave an adverse effect. For the 1 % Co3O4-loaded device, for example, the responses to 100, 50 and 10 ppm CO in air were as large as 375, 181 and 23 at 250 °C, respectively, and those to 50, 10 and 1 ppm H 2 in air were 568, 181 and 53 at 300 °C, respectively. The electrical resistance in air increased significantly with increasing Co 3O4 loading, indicating an electronic interaction between Co3O4 and SnO2. The change of the electronic interaction with a change in the redox state of Co3O4 appears to be an origin of the ultra high sensitivity to CO and H2.
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Matsunaga N., Sakai G., Shimanoe K., Yamazoe N.
Sensors and Actuators, B: Chemical 96 ( 1-2 ) 226 - 233 2003.11
Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Sensors and Actuators, B: Chemical
In response and recovery steps of a thin film semiconductor gas sensor, target gas molecules diffuse in and out of the thin film. The gas diffusion dynamics taking place in these steps have been formulated based on a simple reaction-diffusion equation assuming a first-order reaction of target gas. In order to facilitate mathematical treatments, the actual thin film device was replaced by an equivalent model, for which boundary conditions could be set properly. With this model, the reaction-diffusion equation could be solved by using the methods of Fourier expansion and separation of variables. The solutions given as a function of diffusion coefficient D, rate constant k, film thickness L, depth x and time t, are shown to express well how target gas concentration profile in the thin film develops or vanishes in the response or recovery step, respectively. © 2003 Elsevier B.V. All rights reserved.
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Formulation of gas diffusion dynamics for thin film semiconductor gas sensor based on simple reaction-diffusion equation Reviewed
共著者：N. Matsunaga, G. Sakai, K. Shimanoe, N. Yamazoe
Sensors and Actuators B, Vol. 96, 226-233 (2003). 96 226 - 233 2003.11
Language：English Publishing type：Research paper (scientific journal)
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Wet process-prepared thick films of WO<inf>3</inf>for NO<inf>2</inf>sensing
Choi Y., Sakai G., Shimanoe K., Miura N., Yamazoe N.
Sensors and Actuators, B: Chemical 95 ( 1-3 ) 258 - 265 2003.10
Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Sensors and Actuators, B: Chemical
Preparation of an aqueous sol of WO3·2H2O starting from Na2WO4through an ion-exchange method, coupled with post-treatments (ultrasonic and/or centrifugal), was found to give WO3·2H2O gels which differed in morphology and preferred orientation depending on the kinds and conditions of the post-treatments. The morphology of the gels was well inherited topotaxically by the dehydrated phases of WO3·H2O and tungsten trioxide (WO3), allowing to control the morphology of WO3by the wet processing. The WO3thick film devices, fabricated from the gels and calcined at 300°C, were found to show very different sensor responses to NO2in air depending on the morphology of WO3. That is, poorly developed, small lamellas of WO3obtained by the ultrasonic treatment for a prolonged time (5h) gave the most sensitive device at 200°C, which could respond to as low as 10ppb NO2, while well developed, thin lamellas of WO3obtained by the centrifugal treatment for a prolonged time (10h) gave the most sensitive one at 300°C. In order to understand the dependence of sensor response on the morphology of WO3, several other methods were also adopted for preparing WO3. It was found that all of the sensor response data collected at 300°C could be related fairly well with the thickness of WO3lamellas or the diameter of WO3grains, whereas such a relationship became less certain at 200°C. © 2003 Elsevier Science B.V. All rights reserved.
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Wet process-prepared thick films of WO3 for NO2 sensing Reviewed
共著者：Y.-G. Choi, G. Sakai, K. Shimanoe, N. Miura, N. Yamazoe
Sensors and Actuators B, Vol. 95, 258-265 95 258 - 265 2003.10
Language：English Publishing type：Research paper (scientific journal)
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Cr-doped TiO2 gas sensor for exhaust NO2 monitoring
Ruiz A., Sakai G., Cornet A., Shimanoe K., Morante J., Yamazoe N.
Sensors and Actuators, B: Chemical 93 ( 1-3 ) 509 - 518 2003.8
Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Sensors and Actuators, B: Chemical
A set of Cr-highly doped TiO2samples with Cr contents ranging from 5 to 30 at.% were prepared in a sol-gel route and calcined at a temperature between 600 and 900 °C. X-ray diffraction (XRD) analyses revealed the persistence of anatase phase up to the calcination temperature of 700 °C in all samples, above which rutile phase became dominant. The segregation of Cr2O3remained modest, only detectable by surface-sensitive technique like X-ray photoelectron spectra (XPS), for the 5 and 10 at.% Cr-doped samples calcined at 600 or 700 °C, suggesting incorporation of major part of doped Cr in the lattice of TiO2. Higher calcination temperatures or higher Cr contents lead to marked segregation of Cr2O3. XPS spectra in the valence band region of the samples calcined at 600 °C revealed a shift of the binding energy (BE) at the band edge to the lower energy side with increasing Cr contents, suggesting a tendency for the electronic conduction to alter from n- to p-type. As tested preliminarily, the thick and thin film devices prepared with these samples exhibited p-type conduction, and, particularly, a thin film device using 10 at.% Cr-doped sample calcined at 600 °C proved promising performances in the detection of dilute NO2in air at 500 °C. © 2003 Elsevier Science B.V. All rights reserved.
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Fabrication of CO2 sensor using NASICON thick film
Miyachi Y., Sakai G., Shimanoe K., Yamazoe N.
Sensors and Actuators, B: Chemical 93 ( 1-3 ) 250 - 256 2003.8
Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Sensors and Actuators, B: Chemical
The condition of screen-printing paste was explored to densify a thick film of Na+conductor, Na3Zr2Si2PO12(NASICON) deposited on an alumina substrate. A fair well-densified NASICON thick film was found to be obtained from a paste consisting of NASICON powder and ethylene glycol dispersant by screen-printing and calcination at 1000 °C. The resulting planar sensor showed good CO2sensing capability even under humid conditions, although the emf tended to shift upward with increasing relative humidity. In order to reduce the disturbance by humidity, applicability of an oxide-ionic conductor of Bi2Me0.1V0.9O5.35as a counter electrode material was examined. The oxide-incorporated devices, of both disk type and planar, exhibited stable CO2sensing properties under dry as well as humid conditions. In addition, the dependence of emf on RH could be reduced considerably with the oxide-incorporated devices. It was found, however, that the RH dependence of emf originates from both of the sensing and counter electrodes so that the RH dependence of both electrodes should be tackled with to eliminate the RH dependence of the devices. © 2003 Elsevier Science B.V. All rights reserved.
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Preparation of size and habit-controlled nano crystallites of tungsten oxide
Choi Y., Sakai G., Shimanoe K., Teraoka Y., Miura N., Yamazoe N.
Sensors and Actuators, B: Chemical 93 ( 1-3 ) 486 - 494 2003.8
Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Sensors and Actuators, B: Chemical
An aqueous sol dispersing nano crystallites of WO3·2H2O was subjected to a centrifugal treatment for 1 or 10 h, to obtain two kinds of WO3·2H2O gels with very different morphology of crystals. The WO3thick film devices fabricated with these gels were investigated for several properties including NO2sensing characteristics. It was found that the devices prepared under proper conditions exhibited excellent NO2sensing properties to cover environmental standard of NO2. The sensitivity to NO2as well as the rate of response depended markedly on calcination temperature of the devices. The morphology of WO3crystals, i.e. lamellae or disks, was almost the same as that of WO3·2H2O gel unless calcination temperature exceeded 500 °C. Based on the surface analysis using N2adsorption technique, the above changes were estimated to result from a change in microstructure of the WO3crystals. © 2003 Elsevier Science B.V. All rights reserved.
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Fabrication of CO2 sensor using NASICON thick film Reviewed
共著者：Y. Miyachi, G. Sakai, K. Shimanoe, N. Yamazoe
Sensors and Actuators B, Vol. 93, 250-256 93 250 - 256 2003.8
Language：English Publishing type：Research paper (scientific journal)
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Cr-doped TiO2 gas sensor for exhaust NO2 monitoring Reviewed
共著者：A. M. Ruiz, G. Sakai, A. Cornet, K. Shimanoe, J. R. Morante, N. Yamazoe
Sensors and Actuators B, Vol. 93, 486-494 93 486 - 494 2003.8
Language：English Publishing type：Research paper (scientific journal)
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Preparation of size and habit-controlled nano crystallites of tungsten oxide Reviewed
共著者：Y.-G. Choi, G. Sakai, K. Shimanoe, Y. Teraoka, N. Miura, N. Yamazoe
Sensors and Actuators B, Vol. 93, 486-494 93 486 - 494 2003.8
Language：English Publishing type：Research paper (scientific journal)
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Oxide semiconductor gas sensors Reviewed
共著者：N. Yamazoe, G. Sakai, K. Shimanoe
Catalysis Surveys from Asia, Vol. 7, No.1, 63-75 7 ( 1 ) 63 - 75 2003.4
Language：English Publishing type：Research paper (scientific journal)
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Oxide semiconductor gas sensors
Yamazoe N., Sakai G., Shimanoe K.
Catalysis Surveys from Asia 7 ( 1 ) 63 - 75 2003.4
Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Catalysis Surveys from Asia
Semiconductor gas sensors utilize porous polycrystalline resistors made of semiconducting oxides. The working principle involves the receptor function played by the surface of each oxide grain and the transducer function played by each grain boundary. In addition, the utility factor of the sensing body also takes part in determining the gas response. Therefore, the concepts of sensor design are determined by considering each of these three key factors. The requirements are selection of a base oxide with high mobility of conduction electrons and satisfactory stability (transducer function), selection of a foreign receptor which enhances surface reactions or adsorption of target gas (receptor function), and fabrication of a highly porous, thin sensing body (utility factor). Recent progress in sensor design based on these factors is described.
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Oxygen-sorptive and desorptive properties of perovskite-related oxides under temperature-swing conditions for oxygen enrichment Reviewed
共著者：H. Kusaba, G. Sakai, K. Shimanoe, N. Miura, N. Yamazoe
Solid State Ionics, Vol. 152/153, 689-694 152/153 689 - 694 2002.12
Language：English Publishing type：Research paper (scientific journal)
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Kusaba H., Sakai G., Shimanoe K., Miura N., Yamazoe N.
Solid State Ionics 152-153 689 - 694 2002.12
Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Solid State Ionics
A group of A- and/or B-site partially substituted strontium cobaltites was investigated for oxygen-sorptive properties under temperature-swing conditions in air. The cobaltites with perovskite structure desorbed and absorbed significant amounts of oxygen quickly as well as reversibly on heating or cooling in the temperature range between 300 and 1000 °C, while those with brownmillerite or 2H-BaNiO3structure either lacked oxygen-sorptive properties or showed retarded oxygen sorption with hysteresis, respectively. Under temperature-swing cycles between 300 and 550 °C at a heating or cooling rate of 30 °C/min, SrCo0.4Fe0.6O3 - δshowed the largest mass change of 0.96%, or sorption and desorption of 7 cm3oxygen (STP)/g oxide among the perovskite-type oxides tested. This result appears to indicate the potential of a new oxygen enriching method coupled with a temperature-swing technique. © 2002 Published by Elsevier Science B.V.
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Choi Y., Sakai G., Shimanoe K., Miura N., Yamazoe N.
Sensors and Actuators, B: Chemical 87 ( 1 ) 63 - 72 2002.11
Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Sensors and Actuators, B: Chemical
Aqueous sols of tungsten oxide dihydrate (WO3·2H2O) were prepared from Na2WO4by an ion-exchange method. An aqueous solution of Na2WO4was let to flow through a glass column packed with protonated cation-exchange resin. The effluent, initially transparent, turned into an opaque viscous fluid (pale yellow) in a few hours, before yellow precipitate deposited to completion in three days. The precipitate was a mixture of a crystalline phase of WO3·2H2O and an amorphous phase, and the crystalline part could be separated from another by washing with deionized water and centrifuging. The gel of WO3·2H2O thus obtained consisted of platelike crystallite 25nm thick and 42nm wide as evaluated from the X-ray diffractometer (XRD) peaks, and could be dispersed well into deionized water to form a stable suspension of colloidal particles with a mean diameter of about 30nm. The mean particle size as well as the crystallite size tended to increase gradually with the repetition of dispersion in water under ultrasonic wave agitation and gelling by centrifuging. On heating, the gel (WO3·2H2O) changed to the monohydrate (WO3·H2O) at 100°C, which in turn changed to the anhydride (WO3) at 240°C. Remarkably XRD patterns showed conspicuous preferred orientation of WO3·2H2O crystallites in (010) plane after the sol was centrifuged for a long time (10h) and, upon dehydration, it was inherited by the dehydrated phases, resulting in the conspicuous orientation of WO3crystallites in (001). © 2002 Elsevier Science B.V. All rights reserved.
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Preparation of aqueous sols of tungsten oxide dehydrate from sodium tungstate by an ion-exchange method Reviewed
共著者：Y. ?G. Choi, G. Sakai, K. Shimanoe, N. Miura, N. Yamazoe
Sensors and Actuators B,Vol. 87, 63-72 87 63 - 72 2002.11
Language：English Publishing type：Research paper (scientific journal)