• Korean Journal of Materials Research
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• v.27 no.4
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• pp.184-191
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• 2017

This present study deals with the effect of micro-alloying elements and transformation temperature on the correlation of microstructure and tensile properties of low-carbon steels with ferrite-pearlite microstructure. Six kinds of low-carbon steel specimens were fabricated by adding micro-alloying elements of Nb, Ti and V, and by varying isothermal transformation temperature. Ferrite grain size of the specimens containing mirco-alloying elements was smaller than that of the Base specimens because of pinning effect by the precipitates of carbonitrides at austenite grain boundaries. The pearlite interlamellar spacing and cementite thickness decreased with decreasing transformation temperature, while the pearlite volume fraction was hardly affected by micro-alloying elements and transformation temperature. The room-temperature tensile test results showed that the yield strength increased mostly with decreasing ferrite grain size and elongation was slightly improved as the ferrite grain size and pearlite interlamellar spacing decreased. All the specimens exhibited a discontinuous yielding behavior and the yield point elongation of the Nb4 and TiNbV specimens containing micro-alloying elements was larger than that of the Base specimens, presumably due to repetitive pinning and release of dislocation by the fine precipitates of carbonitrides.

• Journal of Environmental Science International
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• v.9 no.4
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• pp.345-349
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• 2000

Activated carbons were prepared from Korean coal by steam activation in this study. The variation of pore structure of the activated carbons were investigated according to different carbonization temperatures. Yield, surface area, pore volume and pore structure of this activated carbon were compared with those of activated carbon prepared without carbonization. The investigated carbonization temperature ranged from 700${\circ}C$ to 1,000${\circ}C$. Carbonization was carried out in nitrogen atmosphere for 70 minutes and activation was performed by steam at 950${\circ}C$ for 210 minutes. Surface area and pore volume of the resulting activated carbons increased with carbonization temperature. Also pore volume increased by 20% compared to the activated carbon without carbonization. Especially, in mesopore region, the activated carbon carbonized at 900${\circ}C$ had more pores by 60% than that of activated carbon carbonized at other temperature.

• Journal of Microbiology and Biotechnology
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• v.12 no.3
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• pp.518-521
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• 2002

Poly(3-hydroxyalkanoate) copolyesters containing both carbon-carbon double and carbon-carbon triple bonds were produced by Pseudomonas oleovorans grown in mixtures of 10-undecynoic acid (10-UND($\equiv$)) and 10-undecenoic acid (10-UND(=)). The PHA content in the dry cells was usually 40 wt%. The bioconversion yield of ($10-UND({\equiv})$) to PHA by P. oleovorans was remarkably enhanced from 1% to over 24% as the fraction of 10-UND(=) in the carbon substrate mixtures increased from 0 to 50%. These values were higher than those obtained when P. oleovorans was grown in the same molar mixtures of ($10-UND({\equiv})$) and nonanoic acid (NA), indicating that 10-UND(=) was more efficient than NA as a cosubstrate in inducing cometabolic PHA production.

• Fibers and Polymers
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• v.2 no.4
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• pp.178-183
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• 2001

A pitch precursor for a general purpose carbon fiber was prepared by condensation of pyrolized fuel oil (petroleum residual oil) with bromine under nitrogen blowing. such a condensation raised the softening point of the pitch from 4$0^{\circ}C$ to $265^{\circ}$ with a yield of 43%. The pitch precurosr showed an enhanced aromaticity and enlarged molecular size, which led to a reduction in molecular mobility and optical isotropy. The precursor was spun into fibers of $20\mu\textrm{m}$ diameter at a take-up speed of 700m/min. The fiber was stepwise stabilized in air and carbonized in Ar gas to obtain an isotropic carbon fiber. The carbon fiber exhibited tensile strengths of 500-800 ㎫though the fiber was formed via a crude method. The electric conductivity of the carbon fiber was relatively high, 2.2$\times$$10^2$S/cm, sufficient to be used as electrode materials.

• Journal of the Korean Ceramic Society
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• v.37 no.4
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• pp.345-353
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• 2000

Carbon nanofibers were prepared from the decomposition of various carbon-containing gases over pure Ni, pure Fe and their alloys with Cu. They yields, properties, and structure of carbon nanofibers obtained from the various reaction conditions were analyzed. Type of reacting gas, reaction temperature and catalyst composition were changed as the reaction variable. With Ni-Cu catalysts, the maximum yields of carbon nanofibers were obtained at temperatures between 550 and 650$^{\circ}C$ according to the reacting gas mixtures of C2H2-H2, C2H4-H2 and C3H8-H2, and the surface areas of the carbon nanofibers produced were 20∼350㎡/g. In the case of CO-H2 mixture, the rapid deposition of carbon nanofibers occurred with Fe-Cu catalyst and the maximum yield were obtained around 550$^{\circ}C$ with the range of surface areas of 140∼170㎡/g. The electrical resistivity of carbon nanofiber regarded as the key property of filler for the application of electromagnetic interference shielding was very sensitive to the type of reactant gas and the catalyst composition ranging 0.07∼1.5Ωcm at a pressure of 10000 psi, and the resistivity of carbon nanofibers produced over pure nickel catalyst were lower than those over alloy catalysts. SEM observation showed that the carbon nanofibers produced had the diameters ranging 20∼300 nm and the straight structure of carbon nanofibers changed into the twisted or helical conformation by the variation of reacting gas and catalyst composition.

• Bulletin of the Korean Chemical Society
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• v.26 no.11
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• pp.1743-1748
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• 2005

This work presents that carbon dioxide, which is a main contributor to the global warming effect, could be utilized as a selective oxidant in the oxidative dehydrogenation of ethylbenzene. The dehydrogenation of ethylbenzene over alumina-supported vanadium-antimony oxide catalyst has been studied under different atmospheres such as inert nitrogen, steam, oxygen or carbon dioxide as diluent or oxidant. Among them, the addition of carbon dioxide gave the highest styrene yield (up to 82%) and styrene selectivity (up to 97%) along with stable activity. Carbon dioxide could play a beneficial role of a selective oxidant in the improvement of the catalytic behavior through the oxidative pathway.

• Carbon letters
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• v.20
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• pp.32-38
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• 2016

In this study, cellulose nanoplates (CNPs) were fabricated using cellulose nanocrystals obtained from commercial microcrystalline cellulose (MCC). Their pyrolysis behavior and the characteristics of the product carbonaceous materials were investigated. CNPs showed a relatively high char yield when compared with MCC due to sulfate functional groups introduced during the manufacturing process. In addition, pyrolyzed CNPs (CCNPs) showed more effective chemical activation behavior compared with MCC-induced carbonaceous materials. The activated CCNPs exhibited a microporous carbon structure with a high surface area of 1310.6 m²/g and numerous oxygen heteroatoms. The results of this study show the effects of morphology and the surface properties of cellulose-based nanomaterials on pyrolysis and the activation process.

• Carbon letters
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• v.3 no.1
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• pp.25-32
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• 2002

Aligned multi-wall carbon nanotubes (MWNTs) were synthesized through the catalytic decomposition of hydrocarbons in a quartz tube reactor. In this study, we investigated the influence of reaction parameters such as gas flow rate, ferrocene-xylene ratio and partial pressure, and reaction time on the yield and structure of vertically aligned carbon nanotubes produced by the floating catalyst method. The MWNTs produced had diameters in the range of 20~l00 nm, length around $100{\mu}m$ and bulk density about $0.51g/cm^3$ at a pressure of l0000 psi. It was possible to produce MWNTs with much faster growth rate of $12{\mu}m/min$ than that reported previously by the increase of ferrocene-xylene partial pressure.

• 한국신재생에너지학회:학술대회논문집
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• 2007.11a
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• pp.93-96
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• 2007

Catalytic activities of color and conductive carbon blacks in ethane decomposition for $CO_2-free$ hydrogen production were investigated. The ethane decomposition was carried out in a conventional fixed bed reactor under atmospheric pressure at 973-1173 K for 2 hours. When the decomposition in the presence of carbon black was compared with the non-catalytic thermal decomposition, the former exhibited significantly higher ethane conversion, higher C(s) selectivity and lower ethylene selectivity with small increase of the methane selectivity, which resulted in higher hydrogen yield. This indicates that carbon black is catalytically effective for dehydrogenation of ethane as well as subsequent decomposition of ethylene. All the carbon blacks exhibited stable catalytic activity with time. In durability tests, fluffy N-330 and BP2000 maintained their activities for 36 hours.

• KSBB Journal
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• v.13 no.4
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• pp.391-398
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• 1998

The effect of culture medium copper availability on the specific growth rate(${\mu}$) and carbon conversion efficiency (CCE) was sutided for an obligatory methanotroph Methylosinus trichosporium OB3b under various combinations of carbon and nitrogen sources. Methane or methanol was used as a carbon source, and nitrate or ammonium was used as a nitrogen source. Medium copper availability determined the intracellular location or kind of methane monooxygenase (MMO), cell-membrane (particulate or pMMO) when copper was present and cytoplasm (soluble or sMMO) when copper was deficient. When methane was used as a carbon source, copper-containing medium exhibited higher ${\mu}$ and CCE than copper-free medium regardless of the kind of nitrogen source. When methanol was used as a carbon source, however, the effect of copper disappeared. Ammonium gave the higher ${\mu}$ and CCE than nitrate for both methane and methanol. Those observation suggest that there exist an important difference in energy utilization efficiency for methane assimilation between sMMO and pMMO.