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1.
Atsuo Yasumori Hiroshi Matsumoto Shigeo Hayashi Kiyoshi Okada 《Journal of Sol-Gel Science and Technology》2000,18(3):249-258
The magnetic composite materials that consist of transparent matrix and magnetic fine particles are expected to have large residual magnetization and coercive force because of their fine magnetic domain structure, and also to show magneto-optical effects. Silica gels containing magnetite (Fe3O4) fine particles were prepared by sol-gel method. The magnetic, optical and magneto-optical properties of the composites were investigated by measurements of magnetization curves, UV-visible spectra and Faraday rotation in visible range. The saturation magnetization of the composite was almost as same as that expected from the amount of magnetite fine particles in it. Although the composites had large and broad absorption at around 400 nm, they still maintained their transparency. The origins of decrement of transparency attributed to the optical absorption of magnetite and scattering due to magnetite fine particles. The whole composites showed positive Faraday rotation under external static magnetic field due to the large contribution of diamagnetic silica gel matrix. Magnetite contributed negative Faraday rotation with maximum at around 470–480 nm to the magneto-optical spectra of the composites. 相似文献
2.
Yasumori Atsuo Katsuyama Tomokazu Kameshima Yoshikazu Okada Kiyoshi 《Journal of Sol-Gel Science and Technology》2000,19(1-3):237-242
Composite materials which consist of ferro- or ferrimagnetic fine particles in a glass matrix are expected to have a large residual magnetization and coercive force because of their fine magnetic domain structure, and has potential for superior magneto-optical properties compared with single or polycrystalline materials. In this study, the sodium borosilicate (NBS) glass containing Bi-substituted yttrium iron garnet (Bi
x
Y3–x
Fe5O12: BiYIG) fine particles, which show a superior magneto-optical effect, was prepared by the sol-gel method. BiYIG fine particles were stable in NBS gel-glass matrix during densification because the sintering temperature (580°C) of NBS gel was low enough to avoid pyrolysis of BiYIG and the reaction between BiYIG fine particles and the matrix. The Faraday rotation angle spectrum of the composite after deducting the contribution of the NBS glass matrix was intermediate between the reported ones of YIG and Bi0.25YIG polycrystalline thin films. The change of the Faraday rotation angles of the composite with imposing magnetic field showed a hysteresis loop. It was in good agreement with that of the magnetization curve of the composite. 相似文献
3.
S. Shibata T. Taniguchi T. Yano A. Yasumori M. Yamane 《Journal of Sol-Gel Science and Technology》1994,2(1-3):755-759
Organic dyes such as water soluble porphyrins were incorporated into monodispersed SiO2 particles using the sol-gel technique (the Stober synthesis) and their monomeric and dimeric properties were investigated by aiming at the microcavity effect. Doping efficiencies of dyes into SiO2 particles depended on dye's hydrophilic properties. The doping efficiency of a porphyrin, TTMAPP, decreased with increasing the nominal content in the starting solution and the doping content showed the maximum value of 1.6×10–5 mol/g SiO2. With increasing the TTMAPP content, spectra of doped particles were changed from dimeric to monomeric nature; the absorption peak due to dimers disappeared and halfwidth of absorption at Soret band decreased. This unusual change was caused by the decrease of particle sizes by dye doping. The TTMAPP-doped sample having monomeric spectrum showed the fluorescence life time of 8.5 nsec and photochemical hole burning at about 5 K. 相似文献
4.
Okada K Yamamoto N Kameshima Y Yasumori A 《Journal of colloid and interface science》2003,262(1):194-199
Adsorption properties of activated carbons prepared from waste newspaper by chemical and physical activation were investigated using water vapor, ammonia, methane, and methylene blue (MB) as adsorbents. The water vapor adsorption isotherms show type V behavior and the maximum vapor adsorption of the chemically and physically activated products is about 1050 and 450 ml/g, respectively. The higher water vapor adsorption of the chemically activated products is attributed to the higher specific surface area (S(BET)) and greater hydrophilic activity (arising from the surface oxygen-containing functional groups) than in the physically activated products. The adsorption of ammonia and methane was measured by temperature-programmed desorption (TPD). NH(3) adsorption is found to be higher in the chemically activated product than in the physically activated product while methane adsorption is slightly higher in the physically activated products even though these have lower S(BET) values. In the MB adsorption, the chemically activated products show higher adsorption (390 mg/g) than the physically activated product. These results are suggested to be related to the surface characteristics. 相似文献
5.
The effects of drying temperature on the structural evolution of alkoxy-derived silica gel prepared using various catalysts have been investigated. The dependence of specific surface area, Sg, reflecting the structure, on the temperature of drying was remarkable for a non-catalyzed xerogel. The effect of drying temperature on the Sg of an ammonia-catalyzed xerogel was also found but was not very large. The Sg of xerogels obtained by drying at 60°C was always higher by 50% than the gels dried at 30°C without regard to the aging temperature. The Sg of xerogels from HCl-catalyzed solution was of the order of several m2/g, however, the Sg of the aerogel obtained by hypercritical drying of the wet gel from a similar solution was about 800 m2/g. These phenomena were understood on the basis of SAXS measurements on both wet gels and aerogels. 相似文献
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Okada K Nagashima T Kameshima Y Yasumori A 《Journal of colloid and interface science》2002,248(1):111-115
The effect of crystallite size on the thermal phase change and porous properties of boehmite was investigated using boehmites with crystallite sizes of 2.9 to 24.4 nm and boehmite gels prepared by precipitation and hydrothermal methods. The dehydroxylation temperature of boehmite increases, its phase transition temperature from gamma- to theta-Al(2)O(3) decreases and the theta- to alpha-Al(2)O(3) transition temperature increases as the crystallite size of the boehmite increases. Boehmite with a crystallite size of approximately 5 nm shows the highest specific surface area and greatest thermal stability. This boehmite contains pores of about 2-3 nm radius, suggested to be responsible for the superior porous properties and thermal stability. 相似文献
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Yuki Yamaguchi Yukari Emoto Tohru Kineri Masakatsu Fujimoto Hideo Mae Atsuo Yasumori Keishi Nishio 《Ionics》2012,18(5):449-453
A well-known gasochromic material is Pt particle-dispersed tungsten trioxide (Pt/WO3). Its optical properties could make it effective as a hydrogen gas sensor. In this study, Pt nanoparticle-dispersed WO3 thin films were prepared using the sol–gel process, and their optical and electrical properties dependent on the working
environment (i.e., temperature, hydrogen gas concentration, oxygen partial pressure, etc.) were investigated. The Pt/WO3 thin films prepared at 400 °C showed the largest change in optical transmittance and electrical conductivity when exposed
to hydrogen gas compared with the films prepared at other temperatures. The optical absorbance and electrical conductivity
were found to be dependent on the hydrogen and oxygen gas concentration in the atmosphere because generation and disappearance
of W5+ in the thin films depend on the equilibrium reaction between injection and rejection of H+ into and from the thin films. In addition, the equilibrium reaction depends on the hydrogen and oxygen gas concentrations. 相似文献