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Author: search.filters.author.Sano, Noriaki

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    Influence of evaporation drying on the porous properties of carbon/carbon composite xerogels
    (2021-08-02)
    Kraiwattanawong, Kriangsak
    ;
    Sano, Noriaki
    ;
    Tamon, Hajime
    Carbon/carbon (C/C) composite xerogels dried by evaporation were prepared in this study to observe the change of their porous properties and their morphology by nitrogen sorption apparatus and a scanning electron microscope. Resorcinol and formaldehyde (RF) sols as a matrix phase and cotton fibers (CF) as a dispersed phase were mixed and gelated to be CF/RF composite hydrogels. The composite hydrogels were exchanged by t-butanol (TBA), dried by evaporation at 50<sup>◦</sup>C, and carbonized at 1000<sup>◦</sup>C to become the C/C composite xerogels. The results show that the CF addition does not decrease the mesoporous properties of the C/C composite xerogels. Moreover, the CF addition can alleviate the pore shrinkage, and it can maintain the mesopore structure. The mesopore size and the micropore size of C/C composites are insignificantly changed because the CF addition and the solvent exchange using TBA may suppress the pore shrinkage despite the gas-liquid interface existing during the evaporation drying.
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    Investigation on porous properties of carbon/carbon composite cryogels by using weighted arithmetic mean
    (2016-09-01)
    Kraiwattanawong, Kriangsak
    ;
    Sano, Noriaki
    ;
    Tamon, Hajime
    Cotton fibers (CF) and resorcinol and formaldehyde (RF) sol were used to synthesize composite cryogels. They were carbonized to prepare carbon/carbon (C/C) composite cryogels. In this work, the molar ratio of resorcinol to sodium carbonate (R/C), the mass concentration of resorcinol to distilled water (R/W) and the mass ratio of CF to RF (CF/RF) were changed as 100 and 200 mol/mol, 0.25 and 0.50 g/cm<sup>3</sup> and 0.00 up to 0.64 g/g, respectively. The C/C composites were characterized by nitrogen adsorption and scanning electron microscopy. The results showed that the mesopore structure of C/C composites could be controlled by the adjustment of an R/W or R/C ratio. Moreover, the mean micropore sizes of C/C composite cryogels were kept equivalently to those of normal carbon cryogels. The weighted arithmetic mean was well applied to the BET surface area and micropore surface area of C/C composites with the deviation of about 21% for the high R/C ratio; however, it poor for the low R/C ratio. The weighted arithmetic mean also estimated the micropore volume of C/C composite cryogels with the deviation of about 20% for the CF/RF ratio smaller than 0.40 g/g. Moreover, the weighted arithmetic mean can be used as a guideline to estimate the mesopore volume.
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    Capacitive performance of binder-free carbon/carbon composite cryogels
    (2013-01-01)
    Kraiwattanawong, Kriangsak
    ;
    Sano, Noriaki
    ;
    Tamon, Hajime
    A carbon/carbon (C/C) composite cryogel was prepared by pouring a resorcinol-formaldehyde (RF) sol into vials containing cotton fibers, followed by solvent exchange with t-butanol, freeze drying and pyrolysis under inert atmosphere. The porous properties of C/C composites were analyzed by nitrogen adsorption, and their mesopore texture was observed by a scanning electron microscope. The capacitive performance of C/C composites was also analyzed by galvanostatic charge/discharge method and cyclic voltammetry. The results demonstrate that the capacitance can be increased with the increase of amount of cotton fibers added to C/C composites, because the broader micropore size distribution and the carbon tunnels of C/C composites promote the charge propagation inside the pore structure. The suitable pore texture and the carbon tunnels can play the crucial role relevant to the high surface area in order to obtain the high capacitance value. © 2012 Elsevier Inc. All rights reserved.
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    Carbon tunnels formed in carbon/carbon composite cryogels
    (2012-05-01)
    Kraiwattanawong, Kriangsak
    ;
    Sano, Noriaki
    ;
    Tamon, Hajime
    A carbon/carbon (C/C) composite cryogel was prepared by putting almost the maximum content of cotton fibers in vials and then filling them with resorcinol-formaldehyde (RF) sols, followed by solvent exchange with t-butanol, freeze drying and pyrolysis under inert atmosphere. The mesopore structure of C/C composite cryogels was observed by a scanning electron microscope (SEM) and their porous structures were characterized by nitrogen adsorption and mercury porosimetry. The SEM images confirm that the C/C composite cryogels, being heterogeneous carbon materials, possess ordinary carbon cryogels and carbon tunnels. Here, the tunnels are comprised of (i) carbon fibers, (ii) spaces between carbon fibers and nanoporous carbon spheres, (iii) nanoporous carbon spheres with surrounding nanocages, and (iv) dense ring structures. The formation model of carbon tunnels is also proposed. The porous properties of cryogels could be changed by the cotton fiber addition and the synthesis conditions. The results support that the synthesis condition of RF sol determines the porous properties of C/C composite cryogels. © 2011 Elsevier Inc. All rights reserved.
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    Low-cost production of mesoporous carbon/carbon composite cryogels
    (2011-09-01)
    Kraiwattanawong, Kriangsak
    ;
    Sano, Noriaki
    ;
    Tamon, Hajime
    A carbon/carbon (C/C) composite cryogel was prepared by dispersing cotton fibers (CF) in a resorcinol and formaldehyde (RF) sol, followed by solvent exchange with t-butanol, freeze drying and pyrolysis under inert atmosphere. The mass ratio of CF to RF was increased from 0% up to 25% to observe the mesopore structure change of C/C composites under a selected RF synthesis condition. The porous structures were characterized by nitrogen adsorption and mercury porosimetry, and their structure was observed by a scanning electron microscope (SEM). The mesopore diameter of the C/C composites increases slightly with the increase of CF content. The preparation can increase the mesopore volume and also reduce the production cost compared with carbon cryogels prepared without CF. The SEM images show that nanoporous gel spheres appeared after the freeze drying step. These spheres are converted to be nanoporous carbon spheres with surrounding nanocages, and CF are converted into carbon fibers at the same time by pyrolysis. © 2011 Elsevier Ltd. All rights reserved.