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2011, Vol.12, No.1

  • 1.

    Equilibrium Removal of Pb (II) Ions from Aqueous Solution onto Oxidized-KOH-Activated Carbons

    Nady A. Fathy | Iman Y. El-Sherif | 2011, 12(1) | pp.1~7 | number of Cited : 2
    Abstract
    In the present study, the removal of Pb (II) ions on oxidized activated carbons (ACs) was investigated. ACs were derived from activation of indigenous cotton stalks waste with potassium hydroxide (KOH) in two-stage process. The KOH-ACs were subjected to liquid-phase oxidation with hot HNO3 and one untreated sample was included for comparison. The obtained carbons were characterized by Fourier transform infrared (FTIR), slurry pH and N2-adsorption at 77 K, respectively. Adsorption capacity of Pb (II) ions on the resultant carbons was determined by batch equilibrium experiments. The experimental results indicated that the oxidation with nitric acid was associated with a significant increase in mass of yield as well as a remarkable reduction in internal porosity as compared to the untreated carbon. The AC-800N revealed higher adsorption capacity than that of AC-800, although the former sample exhibited low surface area and micropore volume. It was observed that the adsorption capacity enhancement attributed to pore widening, the generation of oxygen functional groups and potassium containing compounds leading to cation-exchange on the carbon surface. These results show that the oxidized carbons represented prospective adsorbents for enhancing the removal of heavy metals from wastewater.
  • 2.

    Thermal Emissivity Of Nuclear Graphite as a Function Of Its Oxidation Degree (3): Structural Study using Scanning Electron Microscope and X-Ray Diffraction

    서승국 | Jaeseung Roh | 김석환 and 2other persons | 2011, 12(1) | pp.8~15 | number of Cited : 0
    Abstract
    We study the relationships between the thermal emissivity of nuclear graphites (IG-110, PCEA, IG-430 and NBG-18) and their surface structural change by oxidation using scanning electron microscope and X-ray diffraction (XRD). The nonoxidized (0% weight loss) specimen had the surface covered with glassy materials and the 5% and 10% oxidized specimens,however, showed high roughness of the surface without glassy materials. During oxidation the binder materials were oxidized first and then graphitic filler particles were subsequently oxidized. The 002 interlayer spacings of the non-oxidized and the oxidized specimens were about 3.38~3.39Å. There was a slight change in crystallite size after oxidation compared to the nonoxidized specimens. It was difficult to find a relationship between the thermal emissivity and the structural parameters obtained from the XRD analysis.
  • 3.

    Tensile Properties and Morphology of Carbon Fibers Stabilized by Plasma Treatment

    이승욱 | 이화영 | 장성연 and 3other persons | 2011, 12(1) | pp.16~20 | number of Cited : 2
    Abstract
    Commercial PAN fibers were thermally stabilized at 220 or 240oC for 30 min. Those fibers were further stabilized using radio-frequency (RF) capacitive plasma discharge during 5 or 15 min. From Fourier transform infrared spectroscopy results, it was observed that an additional plasma treatment led to further stabilization of PAN fibers. After stabilization, carbonization was performed to investigate the final tensile properties of the fabricated carbon fibers (CFs). The results revealed that a combination of thermal and plasma treatment is a possible stabilization process for manufacturing CFs. Morphology of CFs was investigated using scanning electron microscopy. The morphology shows that the plasma stabilization performed by the RF large gap plasma discharge may damage the surface of the CF, so it is necessary to select a proper process condition to minimize the damage.
  • 4.

    Improved Sensitivity of an NO Gas Sensor by Chemical Activation of Electrospun Carbon Fibers

    강석창 | Im Ji Sun | Lee, Young-Seak | 2011, 12(1) | pp.21~25 | number of Cited : 7
    Abstract
    A novel electrode for an NO gas sensor was fabricated from electrospun polyacrylonitrile fibers by thermal treatment to obtain carbon fibers followed by chemical activation to enhance the activity of gas adsorption sites. The activation process improved the porous structure, increasing the specific surface area and allowing for efficient gas adsorption. The gas sensing ability and response time were improved by the increased surface area and micropore fraction. High performance gas sensing was then demonstrated by following a proposed mechanism based on the activation effects. Initially, the pore structure developed by activation significantly increased the amount of adsorbed gas, as shown by the high sensitivity of the gas sensor. Additionally, the increased micropore fraction enabled a rapid sensor response time due to improve the adsorption speed. Overall, the sensitivity for NO gas was improved approximately six-fold, and the response time was reduced by approximately 83% due to the effects of chemical activation.
  • 5.

    Effect of Process Condition on Tensile Properties of Carbon Fiber

    이성호 | Ji Hoon Kim | Bon-Cheol Ku and 2other persons | 2011, 12(1) | pp.26~30 | number of Cited : 5
    Abstract
    For polyacrylonitrile (PAN) based carbon fiber (CF) process, we developed a lab scale wet spinning line and a continuous tailor-made stabilization system with ten columns for controlling temperature profile. PAN precursor was spun with a different spinning rate. PAN spun fibers were stabilized with a total duration of 45 to 110 min at a given temperature profile. Furthermore, a stabilization temperature profile was varied with the last column temperature from 230 to 275oC. Stabilized fibers were carbonized in nitrogen atmosphere at 1200oC in a furnace. Morphologies of spun and CFs were observed using optical and scanning electron microscopy, respectively. Tensile properties of resulting CFs were measured. The results revealed that process conditions such as spinning rate, stabilization time, and temperature profile affect microstructure and tensile properties of CFs significantly.
  • 6.

    Polymerization and Thermal Characteristics of Acrylonitrile/Dicyclohexylammonium 2-Cyanoacrylate Copolymers for Carbon Fiber Precursors

    Kiyoung Kim | 박우리 | Chung Yong Sik and 2other persons | 2011, 12(1) | pp.31~38 | number of Cited : 1
    Abstract
    This study experimentally investigated dicyclohexylammonium 2-cyanoacrylate (CA) as a potential comonomer for polyacrylonitrile (PAN) based carbon fiber precursors. The P(AN-CA) copolymers with different CA contents (0.19-0.78 mol% in the feed)were polymerized using solution polymerization with 2,2-azobis(isobutyronitrile) as an initiator. The chemical structure and composition of P(AN-CA) copolymers were determined by proton nuclear magnetic resonance and elemental analysis, and the copolymer composition was similar to the feeding ratio of the monomers. The effects of CA comonomer on the thermal properties of its copolymers were characterized differential scanning calorimetry (DSC) in nitrogen and air atmospheres. The DSC curves of P(AN-CA) under nitrogen atmosphere indicated that the initiation temperature for cyclization of nitrile groups was reduced to around 235oC. The heat release and the activation energy for cyclization reactions were decreased in comparison with those of PAN homopolymers. On the other hand, under air atmosphere, the P(AN-CA) with 0.78 mol% CA content showed that the initiation temperature of cyclization was significantly lowered to 160.1oC. The activation energy value showed 116 kJ/mol, that was smaller than that of the copolymers with 0.82 mol% of itaconic acids. The thermal stability of P(AN-CA), evidenced by thermogravimetric analyses in air atmosphere, was found higher than PAN homopolymer and similar to P(AN-IA) copolymers. Therefore, this study successfully demonstrated the great potential of P(AN-CA) copolymers as carbon fiber precursors, taking advantages of the temperature-lowering effects of CA comonomers and higher thermal stability of the CA copolymers for the stabilizing processes.
  • 7.

    Hydrogen Storage by Carbon Fibers Synthesized by Pyrolysis of Cotton Fibers

    Maheshwar Sharon | Madhuri Sharon | Golap Kalita and 1other persons | 2011, 12(1) | pp.39~43 | number of Cited : 1
    Abstract
    Synthesis of carbon fibers from cotton fiber by pyrolysis process has been described. Synthesis parameters are optimized using Taguchi optimization technique. Synthesized carbon fibers are used for studying hydrogen adsorption capacity using Seivert’s apparatus. Transmission electron microscopy analysis and X-ray diffraction of carbon fiber from cotton suggested it to be very transparent type material possessing graphitic nature. Carbon synthesized from cotton fibers under the conditions predicted by Taguchi optimization methodology (no treatment of cotton fiber prior to pyrolysis, temperature of pyrolysis 800oC, Argon as carrier gas and paralyzing time for 2 h) exhibited 7.32 wt% hydrogen adsorption capacity.
  • 8.

    Preparation of Activated Carbon Fibers from Cost Effective Commercial Textile Grade Acrylic Fibers

    Mekala Bikshapathi | Nishith Verma | Rohitashaw Kumar Singh and 2other persons | 2011, 12(1) | pp.44~47 | number of Cited : 3
    Abstract
    Activated carbon fibers (ACFs) were prepared from cost effective commercial textiles through stabilization, carbonization,and subsequently activation by carbon dioxide. ACFs were characterized for surface area and pore size distribution by physical adsorption of nitrogen at 77 K. ACFs were also examined for various surface characteristics by scanning electron microscopy, Fourier transform infrared spectroscopy, and CHNO elemental analyzer. The prepared ACFs exhibited good surface textural properties with well developed micro porous structure. With improvement in physical strength, the commercial textile grade acrylic precursor based ACFs developed in this study may have great utility as cost effective adsorbents in environmental remediation applications.
  • 9.

    Preparation and Characteristics of Conducting Polymer-Coated MWCNTs as Electromagnetic Interference Shielding Materials

    김연이 | 윤주미 | Lee, Young-Seak and 1other persons | 2011, 12(1) | pp.48~52 | number of Cited : 14
    Abstract
    The conducting polymer-coated multi-walled carbon nanotubes (MWCNTs) were prepared by template polymerization of aniline and pyrrole on the surface of MWCNTs in order to develop the novel electromagnetic interference (EMI) shielding materials. The conducting polymer phases formed on the surface of MWCNTs were confirmed by field emission-scanning electron microscopy and field emission-transmission electron microscopy. Both permittivity and permeability were significantly improved for the conducting polymer-coated MWCNTs due to the intrinsic electrical properties of MWCNTs and the conducting properties of coated polymers. The electromagnetic waves were effectively absorbed based on the permittivity nature of conducting polymer and MWCNTs preventing the secondary interference from reflecting the electromagnetic waves. The highly improved EMI shielding efficiency was also obtained for the conducting polymer-coated MWCNTs showing the synergistic effects by combining MWCNTs and the conducting polymers.
  • 10.

    Thermal Insulation Properties of Epoxy/Mesoporous Carbon Composites

    허건영 | 서민강 | 오상엽 and 2other persons | 2011, 12(1) | pp.53~56 | number of Cited : 5
    Abstract
    This study aimed to investigate the influence of mesoporous carbons on the thermal insulation properties of epoxy/mesoporous carbon composites. The mesoporous carbon (CMK-3) was prepared by conventional templating method using SBA-15. The epoxy/mesoporous carbon composites were prepared by mixing the synthesized CMK-3 with diglycidylether of bisphenol A (DGEBA). As experimental results, the curing reactivities of the DGEBA/CMK-3 composites were found to decrease with the addition of the CMK-3. Also, the thermal conductivities of DGEBA/CMK-3 composites were found to decrease with increasing CMK-3 content. This could be interpreted in terms of the slow thermal diffusion rate resulting in pore volume existing in the gaps in the interfaces between the mesoporous carbon and the DGEBA matrix.