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Author: search.filters.author.Sano, NoriakiSubject: search.filters.subject.Freeze 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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    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.