• Bulletin of the Korean Chemical Society
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• v.30 no.8
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• pp.1719-1723
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• 2009

The LiFeP$O_4$ powder was synthesized by using the solid state reaction method with Fe($C_2O_4){\cdot}2H_2O,\;(NH_4)_2HPO_4,\;Li_2CO_3$, and chitosan as a carbon precursor material for a cathode of a lithium-ion battery. The chitosan added LiFePO4 powder was calcined at 350 ${^{\circ}C}$ for 5 hours and then 800 ${^{\circ}C}$ for 12 hours for the calcination. Then we calcined again at 800 ${^{\circ}C}$ for 12 hours. We characterized the synthesized compounds via the crystallinity, the valence states of iron ions, and their shapes using TGA, XRD, SEM, TEM, and XPS. We found that the synthesized powders were carbon-coated using TEM images and the iron ion is substituted from 3+ to 2+ through XPS measurements. We observed voltage characteristics and initial charge-discharge characteristics according to the C rate in LiFeP$O_4$ batteries. The obtained initial specific capacity of the chitosan added LiFeP$O_4$ powder is 110 mAh/g, which is much larger than that of LiFeP$O_4$ only powder.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.130.2-130.2
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• 2013

Today, chemical vapor deposition (CVD) of hydrocarbon gases has been demonstrated as an attractive method to synthesize large-area graphene layers. However, special care should be taken to precisely control the resulting graphene layers in CVD due to its sensitivity to various process parameters. Therefore, a facile synthesis to grow graphene layers with high controllability will have great advantages for scalable practical applications. In order to simplify and create efficiency in graphene synthesis, the graphene growth by thermal annealing process has been discussed by several groups. However, the study on growth mechanism and the detailed structural and optoelectronic properties in the resulting graphene films have not been reported yet, which will be of particular interest to explore for the practical application of graphene. In this study, we report the growth of few-layer, large-area graphene films using rapid thermal annealing (RTA) without the use of intentional carbon-containing precursor. The instability of nickel films in air facilitates the spontaneous formation of ultrathin (<2~3 nm) carbon- and oxygen-containing compounds on a nickel surface and high-temperature annealing of the nickel samples results in the formation of few-layer graphene films with high crystallinity. From annealing temperature and ambient studies during RTA, it was found that the evaporation of oxygen atoms from the surface is the dominant factor affecting the formation of graphene films. The thickness of the graphene layers is strongly dependent on the RTA temperature and time and the resulting films have a limited thickness less than 2 nm even for an extended RTA time. The transferred films have a low sheet resistance of ~380 ${\Omega}/sq$, with ~93% optical transparency. This simple and potentially inexpensive method of synthesizing novel 2-dimensional carbon films offers a wide choice of graphene films for various potential applications.

• Journal of the Korean Electrochemical Society
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• v.16 no.1
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• pp.52-58
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• 2013

In order to overcome the cost issue for commercialization of polymer electrolyte membrane fuel cell (PEMFC), this research was conducted for replacing platinum cathode catalyst with non-precious metal catalyst. The non-precious metal catalyst (Co-PANI-C) was synthesized by the simple reduction method with polyaniline (PANI), carbon black, and cobalt precursor without any heat treatment. Characterization of new Co-PANI-C composite catalysts was done by the measurement of X-ray diffraction (XRD) and thermogravimetric analysis (TGA) for structure analysis and performed by rotating disk electrode (RDE) and rotating ring disk electrode (RRDE) for electrochemical analysis. As a result, Co-PANI-C catalyst showed 60 mV lower on-set potential for oxygen reduction reaction (ORR) than Pt/C catalyst, but the overall reduction current of Co-PANI-C catalysts by ORR was still smaller than that of Pt/C. In addition, the ORR behavior of Co-PANI-C catalysts depending on the rotation speed of electrode and the stability of Co-PANI-C catalyst under potential cycling and the performance of fuel cell conditions are also discussed.

• Composites Research
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• v.30 no.2
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• pp.116-125
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• 2017

The purpose of this study is to develop silicon carbide fiber showing an excellent mechanical properties under highly oxidative conditions at high temperature. Polycarbosilane(PCS) as a preceramic precursor was used for making the SiC fiber. PCS fiber was taken by melt spinning method followed by melting the PCS at $300{\sim}350^{\circ}C$ in N2 gas. The Curing of PCS fiber was carried out in air oxygen chamber, prior to high temperature pyrolysis. Degree of cure was calculated by characteristic peak's ratio of Si-H to $Si-CH_3$ in FT-IR spectra before and after curing of PCS fiber. The properties of SiC fiber was affected greatly by the degree of cure. The SiC fiber produced by controlling fiber tension during heat treatment showed good properties. The SiC fiber exposed to $1000^{\circ}C$ at air from 1 min. up to maximum 50 hrs showed around 60% reduction in tensile strength. We found that large amount of carbon content on the fiber surface after long-term exposure has resulted in lower tensile strength.

• Journal of the Korean Magnetics Society
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• v.2 no.3
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• pp.244-250
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• 1992

Iron nitride $Fe_4N$ by partial substitution of nitrogen by carbon was prepared by nitriding the iron oxalate whose thermal decomposition gives a carburating atmosphere. Iron oxalates, the precursors, were prepared by precipitation and co-precipitation. The size and shape of the carbonitride particles could be controlled by modifying the conditions of preparation of the oxalate precursor. From the results of electron micrographs, it is clear that the $Fe_4N$ pigment particle maintains the original shape(needle shape) of the starting materials and that it consists of fine unit particles which link together to form a stereo-network structure. An investigation of the $Fe^{II}_3\;Fe^I_{1-x}\;Sn_xN_{1-y}C_y$ solid solution has shown that Sn plays the role of a growth inhibitor of the elementary microcrystallites of the iron carbonitride. The coercive force and saturation magnetization of iron carbonitride obtained from co-precipitated iron oxalate were 500 Oe and 120 emu/g, respectively.

• Polymer(Korea)
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• v.36 no.6
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• pp.739-744
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• 2012

In this work, we prepared the carbons from synthesized styrene-acrylonitrile carbon precursor. The prepared carbons were chemically activated, and then the activated SAN-based carbons were named as A-SANs. The activations were carried out at different temperatures to investigate the effect of activation temperature on the surface and electrochemical properties of the activated SAN-based carbons for using as an electrode of electric double layer capacitors (EDLC). The characteristics of A-SAN were determined by X-ray diffraction (XRD), scanning electron microscopy (SEM), surface area and pore size analysis. Also, the electrochemical behaviors were observed by cyclic voltammetry and galvanostatic charge-discharge method. From the results, the A-SAN 700 showed excellent electrochemical property and the highest specific capacitance, but these properties decreased when the activation temperature was above $700^{\circ}C$. This is due to the fact that the activation at a temperature over $700^{\circ}C$ causes deformation of micropore structures.

• Corrosion Science and Technology
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• v.17 no.2
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• pp.60-67
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• 2018

The compounds associated with corrosion, in metallic archaeological samples of carbon steel of insular origin were evaluated to establish their degree of deterioration and structural damage against air pollution. The iron phases present in samples of archaeological artifacts were detected by Raman spectroscopy and confocal Raman microcopy. These samples mainly exhibited ing mainly ${\beta}$-FeO(OH) type goethite oxyhydroxides and small amounts of akaganeite ${\alpha}$-FeO(OH) lepidocrocite ${\gamma}$-FeO(OH) due to dominant chloride in a marine environment and non-stoichiometric oxyhydroxides Fe (II + / III +) as indicators of early corrosion. Some parts showed the presence of magnetic maghemite indicating high corrosion. ${\gamma}$-FeO(OH) is a precursor of phases associated with advanced marine corrosion. By studying its decomposition by Raman spectroscopy, it was synthesized with the following sequence: ${\gamma}-FeO(OH){\rightarrow}{\alpha}-FeO(OH)+{\gamma}-FeO(OH)$, ${\rightarrow}{\gamma}-Fe_2O_3+Fe_3O_4$. Ferric compounds provided evidence for the effect of intensity of laser on them, constituting a very useful input for the characterization of oxidation of iron in this type of artifacts. Thus, destructive analysis techniques should be avoided in addition to the use of small amounts of specimen.

• Applied Chemistry for Engineering
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• v.10 no.5
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• pp.666-671
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• 1999

In this work, sulfonated poly(phenylene sulfide) (SPPS) was prepared by demethylation with aqueous NaOH solution after poly[methyl[4-(phenylthio)phenyl]sulfonium trifluoromethanesulfonate](PPST) was sulfonated with fumic sulfonic acid(10% $SO_{3}-H_{2}SO_{4}$). PPST soluble in organic solvents was synthesiszed by self-condensation polymerization of methyl-(phenylthio)phenyl sulfoxide(MPPSO). SPPS showed IR bands of asymmetric O=S=O stretching at $1200cm^{-1}$ and S-O stretching at $621cm^{-1}$ from $-SO_{3}H$ group. From the result, it could be known that sulfonic acid groups were introduced to poly(phenylene sulfide). when PPST was sulfonated for 12hr at $150^{\circ}C$, 1.48 sulfonic acid groups were introduced per repeat unit. The weight average molecular weight(Mw) of PPST and SPPS determined by high temperature GPC were 118323 and 131204, respectively. The SPPS exhibited adsorption capacity of ammonia gas $9.67mmol\;NH_{3}/g$ and it was much higher than that of active carbon or silica gel.

• Journal of the Korean Applied Science and Technology
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• v.13 no.3
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• pp.15-24
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• 1996

Essentiality was proposed in the field of lipid by Burr and Burr in 1929. When rats were raised on the fat-free diet, their growth retarded and their skin and tails showed the characteristic deficient symptoms, which were relieved by the addition of ${\omega}6(n-6)$ polyunsaturated fatty acids as linoleic(LA) and arachidonic(AA) acids to the basal diet. LA is dehydrogenated to ${\gamma}-linolenic$ acid(GLNA) by ${\Delta}6$ desaturase, then GLNA is 2 carbon chain elongated by elongase to $dihomo-{\gamma}-linolenic$ acid(DGLNA), which is desaturated by ${\Delta}5$ desaturase to AA. These acids are called LA family or ${\omega}6(n-6)$ polyunsaturated fatty acids(PUFA). ${\alpha}-Linolenic$ acid(ALNA) is converted through the series of desaturation and elongation steps to docosahexaenic acid(DHA) via eicosapentaenoic acid(EPA). These acids belong to ALNA family or ${\omega}3(n-3)$PUFA. Human who consume large amounts of EPA and DHA, which are present in fatty fish and fish oils, have increased levels of these two fatty acids in their plasma and tissue lipids at the expense of LA and AA. Alternately, vegetarians, whose intake of LA in high, have more elevated levels of LA and AA and lower levels of EPA and DHA in plasma lipids and in cell membranes than omnivores. AA and EPA are metabolized to substances called eicosanoids. Those derived form AA are known as prostanocids(prostaglandins and prostacyclins) of the 2-types and leukotrienes of the 4-series, whereas those derived from EPA are known as prostanoids of the 3-types and leukotrienes of the 5-series. DGLNA is a precursor of the 1-types of prostaglandins. The metabolites of AA and EPA have competitive functions. Ingestion of EPA from fish or fish oil replaces AA from membrane phospholipids in practically all cells. So this leads to a more physiological state characterized by the production of proatanoids and leukotrienes that have antithrombic, antichemotactic, antivasoconstrictive and antiinflammatory properties. It is evident that ${\omega}3$ fatty acids can affect a number of chronic diseases through eicosanoids alone.

• Journal of Microbiology and Biotechnology
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• v.1 no.3
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• pp.188-196
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• 1991

The ${\beta}-glucosidase$ was purified to homogeneity from the culture filtrate of P. verruculosum by column chromatography. The enzyme was a glycoprotein with a relative size of approximately 220 kDa with an isoelectric point of 4.8, which was composed of dimeric protein of 105 kDa. The enzyme was stable up to $60^{\circ}C$ and the presence of glycerol significantly increased its thermostability. The enzyme was found to hydrolyze both ${\beta}-aryl$ and ${\beta}-alkyl-glucosides$ in addition to ${\beta}-glucosyl$ glucose and catalyzed glucosyl transfer to cellobiose. The enzyme attacked laminarin in an exotype-like fashion. The apparent Km's of the enzyme toward cellobiose, laminaribiose, laminarin were 0.53 mM, 0.35 mM and 1.11 mM, respectively. Glucose and glucono-${\delta}-lactone$ were competitive inhibitors for the enzyme. Copper ($Cu^{2+}$), mercury ($Hg^{2+}$) and p-chloromercuribenzoate were strong inhibitors of the enzyme. The immunoblotting result revealed that one form of ${\beta}-glucosidase$ was biosynthesized, irrespective of carbon sources used. Polyacrylamide gel electrophoresis analysis of the in vitro translated product of total RNA from avicel grown mycelium established that the P. verruculosum ${\beta}-glucosidase$ precursor was approximately 95 kDa in size. The amino acid composition and N-terminal amino acid sequence are given.