• Applied Chemistry for Engineering
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• v.29 no.2
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• pp.191-195
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• 2018

In this study, the influence of microporous structures of activated carbon fibers (ACFs) on dimethyl methylphosphonate (DMMP) gas sensing properties as a nerve agent simulant was investigated. The pore structure was given to carbon fibers by chemical activation process, and an electrode was fabricated for gas sensors by using these fibers. The PAN based ACF electrode, which is an N-type semiconductor, received electrons from a reducing gas such as DMMP, and then electrical resistance of its electrode finally decreased because of the reduced density of electron holes. The sensitivity of the fabricated DMMP gas sensor increased from 1.7% to 5.1% as the micropore volume increased. It is attributed that as micropores were formed for adsorbing DMMP whose molecular size was 0.57 nm, electron transfer between DMMP and ACF was facilitated. In conclusion, it is considered that the appropriate pore structure control of ACFs plays an important role in fabricating the DMMP gas sensor with a high sensitivity.

• Carbon letters
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• v.19
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• pp.99-103
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• 2016

Porous carbons have attracted much attention for their novel application in gas storage. In this study, porous graphite nano-fiber (PGNFs)-based graphite nano fibers (GNFs) were prepared by KOH activation to act as adsorbents. The GNFs were activated with KOH by changing the GNF/KOH weight ratio from 0 through 5 at 900℃. The effects of the GNF/KOH weight ratios on the pore structures were also addressed with scanning electron microscope and N₂ adsorption/desorption measurements. We found that the activated GNFs exhibited a gradual increase of CO₂ adsorption capacity at CK-3 and then decreased to CK-5, as determined by CO₂ adsorption isotherms. CK-3 had the narrowest micropore size distribution (0.6–0.78 nm) among the treated GNFs. Therefore, KOH activation was not only a significant method for developing a suitable pore-size distribution for gas adsorption, but also increased CO₂ adsorption capacity as well. The study indicated that the sample prepared with a weight ratio of ‘3’ showed the best CO₂ adsorption capacity (70.8 mg/g) as determined by CO₂ adsorption isotherms at 298 K and 1 bar.

• Carbon letters
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• v.6 no.4
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• pp.243-247
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• 2005

Plasma polymerization of allylamine subsequently after plasma pre-treatment was conducted on the activated carbon fibers (ACFs) for the immobilization of amine groups in the surface of ACFs. The change of structural properties of ACFs with respect to different polymerization conditions was investigated through BET method. The change of surface morphologies of ACFs with respect to different plasma polymerization power was also studied through AFM. It was found that the structural properties such as specific surface area and micropore volume could be optimized under certain plasma deposition conditions. It was reckoned that treatment and deposition showed adverse effect on plasma polymerization, in which the former developed the micro-structures of the ACFs and the latter tended to block the micro pores. The Fourier transform infrared spectroscopy (FTIR) revealed that the poly(allylamine) was successfully immobilized on the surface of ACFs and the amount of the deposited polymer layer was related to the plasma polymerization power. SEM results showed that the plasma deposited polymer layer were small and homogenously distributed. The size and the distribution of particles deposited were closely related to the plasma polymerization power, too.

• International Journal of Concrete Structures and Materials
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• v.8 no.1
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• pp.15-26
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• 2014

In order to study the capacities of a new occurrence of Brazilian clay samples as partial replacements of cement, a bentonite sample was selected for utilization in the natural and modified forms for present study. The natural bentonite (BBT) was modified by anchorament of 3-aminopropyltrietoxisilane ($BBT_{APS}$) and 3,2-aminoethylaminopropyltrimetoxisilane (BBTAEAPS) in the surface of component minerals of bentonite sample. The original and organo-bentonite samples were characterized by elemental analysis, scanning electron microscopic and textural analyses. The values of micropore area were varying from $7.2m^2g^{-1}$ for the BBT to $12.3m^2g^{-1}$ for the $BBT_{AEAPS}$. The bentonite samples were characterized by the main variable proportion of bentonite in the natural and intercalated forms (2, 5, 10, 15, 20, 25, 30, and 35 % by weight of cement) in the replacement mode whiles the amount of cementations material. The workability, density of fresh concrete, and absorption of water decreased as the substitution of ordinary Portland cement by perceptual of natural and modified bentonite increased. The results reveal that workability decreased with decrease of the amount of natural bentonite in the concrete, same behavior is observed for bentonite functionalized, varying from 49 to 28 mm. The energetic influence of the interaction of calcium nitrate in the structure of blends was determined through the calorimetric titration procedure.

• Carbon letters
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• v.2 no.1
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• pp.15-21
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• 2001

In this work, activated carbon fibers (ACFs) were plated with copper metal using electroless plating method and the effects of surface properties and pore structures on chromium adsorption properties were investigated. Surface properties of ACFs have been characterized using pH and acid/base values. BET data with $N_2$ adsorption were used to obtain the structural parameters of ACFs. The electroless copper plating did significantly lead to a decrease in the surface acidity or to an increase in the surface basicity of ACFs. However, all of the samples possessed a well-developed micropore. The adsorption capacity of Cr(III) for the electroless Cu-plated ACFs was higher than that of the as-received, whereas the adsorption capacity of Cr(VI) for the former was lower than that of the latter. The adsorption rate constants ($K_1$, $K_2$, and $K_3$) were also evaluated from chromium adsorption isotherms. It was found that $K_1$ constant for Cr(III) adsorption depended largely on surface basicity. The increase of Cr(III) adsorption and the decrease of Cr(VI) adsorption were attributed to the formation of metal oxides on ACFs, resulting in increasing the surface basicity.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.14 no.5
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• pp.1081-1089
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• 1994

Polypropylene Fibers have been used to increase the toughness of concrete and to increase the resistance to crack formation. However, there are many contradictory argument about the effectiveness of the fiber due to the lack of knowledge about the mechanism of fiber in concrete. One of the mechanism which changes the concrete properties on the addition of fiber is the change of the micropore structures. In this study, the change of pore structure due to the addition of fiber has been analysized by a permeability and a pore size distributuion test. The added fiber is found to provide a path for moisture movement, which increases drying shrinkage and pore size. It is found that the size of pores formed around the fiber ranges from $0.05{\mu}m$ to $5.0{\mu}m$.

• Carbon letters
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• v.14 no.3
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• pp.180-185
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• 2013

In this study, activated carbons nanofibers (ACNFs) were prepared from polyacrylonitrile-based nanofibers by physical ($H_2O$ and $CO_2$) and chemical (KOH) activation. The surface and structural characteristics of the porous carbon were observed by scanning electron microscopy and X-ray diffraction, respectively. Pore characteristics were investigated by $N_2$/77K adsorption isotherms. The specific surface area of the physically ACNFs was increased up to $2400m^2/g$ and the ACNFs were found to be mainly composed of micropore structures. Chemical activation using KOH produced ACNFs with high specific surface area (up to $2500m^2/g$), and the micropores were mainly found in the ACNFs. The physically and chemically ACNFs showed both mainly type I from the International Union of Pure and Applied Chemistry classification.

• Macromolecular Research
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• v.13 no.6
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• pp.521-528
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• 2005

Electrospun polyacrylonitrile (PAN) nanofibers were carbonized with or without iron (III) acetylacetonate to induce catalytic graphitization within the range of 900-1,500$^{circ}C$, resulting in ultrafine carbon fibers with a diameter of about 90-300 nm. Their structural properties and morphologies were investigated. The carbon nanofibers (CNF) prepared without a catalyst showed amorphous structures and very low surface areas of 22-31 $m^{2}$/g. The carbonization in the presence of the catalyst produced graphite nanofibers (GNF). The hydrogen storage capacities of these CNF and GNF materials were evaluated through the gravimetric method using magnetic suspension balance (MSB) at room temperature and 100 bar. The CNFs showed hydrogen storage capacities which increased in the range of 0.16-0.50 wt$\%$ with increasing carbonization temperature. The hydrogen storage capacities of the GNFs with low surface areas of 60-253 $m^{2}$/g were 0.14-1.01 wt$\%$. Micropore and mesopore, as calculated using the nitrogen gas adsorption-desorption isotherms, were not the effective pore for hydrogen storage.

• Journal of the Korean Wood Science and Technology
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• v.38 no.3
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• pp.205-212
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• 2010

This study was carried out to investigate the characterization of aerogel made by holocellulose, the thermal properties of the aerogel, and its shapes and porous structures. The aerogel was made by holocellulose through the gelation in alkali hydroxide-urea solution and freeze drying processes. Holocellulose aerogel had porous structure such as net or sponge. The density of holocellulose aerogel was 0.04 g/$cm^3$, and the specific surface area 145.3 $m^2$/g. Although thermal degradation occurred in the range of $210{\sim}350^{\circ}C$, significant thermal degradation occurred at low temperature with low heating rate, Micropore volume was sharply increased with low heating rate. Holocellulose aerogel char obtained by carbonization with $900^{\circ}C$ and $0.5^{\circ}C$/min. heating rate had the highest surface area, 656.7 $m^2$/g. The deformed and irregular structures of holocellulose aerogel chars due to the thermal degradation were observed in SEM.

• Korean Journal of Veterinary Research
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• v.28 no.2
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• pp.379-385
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• 1988

For the comparison of surface fine structures in the proliferative forms of two major protoroan parasites, Toxoplasma gondii and Sarcocystis species in mammalian hosts, isolated from the artificially infected mice and from the naturally infected cattle, respectively, an SEM(Hitachi S-570) was applied to the fixed, dried and coated with gold ion on the microslide glasses. The tachyzoites of T gondii from the peritoneal cavity of the mouse showed the crescent-like feature and measured as $5.57{\mu}m$ in length and $2.33{\mu}m$ in width, while the bradyzoites of Sarcocystis species from the heart muscle of slaughtered cattle was banana-shaped and measured as $14.18{\mu}m$ in length and $2.85{\mu}m$ in width. On the surface of Sarcocystis species bradyzoite, a distinct elliptical micropore was identified in the high magnification observation of 60,000X, and it measured as $0.35{\mu}m$ in length and $0.18{\mu}m$ in width.