• Title/Summary/Keyword: graphite oxidation

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Nanodispersion-Strengthened Metallic Materials

  • Weissgaerber, Thomas;Sauer, Christa;Kieback, Bernd
    • Journal of Powder Materials
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    • v.9 no.6
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    • pp.441-448
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    • 2002
  • Dispersions of non-soluble ceramic particles in a metallic matrix can enhance the strength and heat resistance of materials. With the advent of mechanical alloying it became possible to put the theoretical concept into practice by incorporating very fine particles in a flirty uniform distribution into often oxidation- and corrosion- resistant metal matrices. e.g. superalloys. The present paper will give an overview about the mechanical alloying technique as a dry, high energy ball milling process for producing composite metal powders with a fine controlled microstructure. The common way is milling of a mixture of metallic and nonmetallic powders (e.g. oxides. carbides, nitrides, borides) in a high energy ball mill. The heavy mechanical deformation during milling causes also fracture of the ceramic particles to be distributed homogeneously by further milling. The mechanisms of the process are described. To obtain a homogeneous distribution of nano-sized dispersoids in a more ductile matrix (e.g. aluminium-or copper based alloys) a reaction milling is suitable. Dispersoid can be formed in a solid state reaction by introducing materials that react with the matrix either during milling or during a subsequent heat treatment. The pre-conditions for obtaining high quality materials, which require a homogeneous distribution of small dis-persoids, are: milling behaviour of the ductile phase (Al, Cu) will be improved by the additives (e.g. graphite), homogeneous introduction of the additives into the granules is possible and the additive reacts with the matrix or an alloying element to form hard particles that are inert with respect to the matrix also at elevated temperatures. The mechanism of the in-situ formation of dispersoids is described using copper-based alloys as an example. A comparison between the in-situ formation of dispersoids (TiC) in the copper matrix and the milling of Cu-TiC mixtures is given with respect to the microstructure and properties, obtained.

Simultaneous Exfoliation and Dispersion of Graphene/Carbon Nanotube via Intercalation Reaction and Its Application as Conductive Composite Film (층간삽입 반응을 이용한 그래핀/탄소나노튜브 동시 개별 분산 및 전도성 복합 필름으로의 응용)

  • Kim, Jungmo;Kim, Jin;Yoon, Hyewon;Park, Minsu;Novak, Travis;Ashraful, Azam;Lee, Jinho;Jeon, Seokwoo
    • Composites Research
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    • v.29 no.3
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    • pp.104-110
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    • 2016
  • This paper reports a novel method for simultaneous exfoliation of graphene and dispersion of carbon nanotube by using intercalation method. In common, graphene flake and carbon nanotubes can be produced through individual exfoliation or debundling process, but the process require significant amount of time. Here, potassium sodium tartrate was thermally intercalated into graphite and carbon nanotube bundle for simultaneous exfoliation and dispersion of graphene and carbon nanotubes. We confirmed expansion of interlayer distance via XRD, and also found that oxidation level of the exfoliated materials were significantly low (below 8.3 at%). The produced materials are fabricated in to conductive composite film via vacuum filtration and spray deposition to show enhancement of conductive properties.

Ex Vivo Assay of Trace Nicotine Using a Voltammetric Modified Biosensor

  • Ly, Suw Young;Jang, Myung-Ho;Cha, Jae-Min;Kim, Min-Young;Oh, Hyun-Seok;Jo, Dong-Hyeon;Choi, Seong-Sik
    • Journal of the Korean Applied Science and Technology
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    • v.29 no.1
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    • pp.40-46
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    • 2012
  • In vivo nicotine is associated with Alzheimer's, Parkinson's and lung cancer. Diagnostic assays of these diseases depend on very low analytical detection limits. In this study, a sensitive analytical method was examined using a voltammetric graphite pencil electrode (GPE) and a modified carbon nanotube paste electrode (CNE). The optimum analytical conditions for both electrodes were compared using square wave anodic stripping voltammetry (SW) and cyclic voltammetry (CV) obtaining 400 sec accumulation time and oxidation peak. Under optimum parameters, the stripping working range of GPE was $5.0-40.0{\mu}g/L$, CNE: 0.1-0.8 and $5-50{\mu}g/L$. Quantification limits were $5.0{\mu}g/L$ for GPE and $0.1{\mu}g/L$ for CNE, while detection limits were $0.6{\mu}g/L$ for GPE and $0.07{\mu}g/L$ for CNE. A standard deviation of $10.0{\mu}g/L$ was observed for 0.064 GPE and 0.095 CNE (n = 12) using 400 sec accumulation time. The results obtained can be applied to non.treated urine and ex vivo biological diagnostics.

Regeneration of PCB Etchants and Copper Recovery in a Batch-type Electrolytic Cell (회분식 전해조에서 PCB 식각폐수의 재생 및 구리의 회수)

  • Nam, Sang Cheol;Nam, Chong Woo;Tak, Yongsug;Oh, Seung Mo
    • Applied Chemistry for Engineering
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    • v.8 no.2
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    • pp.161-171
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    • 1997
  • Anodic regeneration of PCB enchant and cathodic deposition of copper using electrochemical method has been studied. Cu(I)/Cu(II) concentration ratio as a function of Cu(I) oxidation at the anode was measured from the potential difference between platinum and Ag/AgCl/4M KCl electrodes. Chlorine gas evolution was minimized by maintaining Cu(I) concentration above a specific concentration and using non-porous graphite electrode. Dendritic copper deposition was observed at the cathode and the optimum conditions for Cu deposition was identified as the current density of $360mA/cm^2$, and copper concentration of 12 g/l. Titanium was the most effective cathode material which showed a higher current efficiency and copper recovery. The current efficiency decreased with increasing temperature, but the highest power efficiency was achieved at $50^{\circ}C$.

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Effects of Oxygen Plasma-treated Graphene Oxide on Mechanical Properties of PMMA/Aluminum Hydroxide Composites (산소 플라즈마 처리된 그래핀 산화물이 PMMA/수산화알루미늄 컴포지트의 기계적 물성에 미치는 영향)

  • Kim, Hyo-Chul;Jeon, Son-Yeo;Kim, Hyung-Il;Choi, Ho-Suk;Hong, Min-Hyuk;Choi, Ki-Seop
    • Polymer(Korea)
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    • v.35 no.6
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    • pp.565-573
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    • 2011
  • The nanocomposites containing graphene oxide (GO) were prepared in order to improve the mechanical properties of poly(methyl methacrylate)/aluminum hydroxide (PMMA/AH) composites. GO was prepared from graphite by oxidation of Hummers method followed by exfoliation with thermal treatment. The surface of GO was modified by oxygen plasma in various exposure times from 0 to 70 min to improve interfacial compatibility. Compared with PMMA/AH composites, the nanocomposites containing GO modified with oxygen plasma for the exposure time up to 50 min showed significant increases in flexural strength, flexural modulus, Rockwell hardness, Barcol hardness, and Izod impact strength. The morphology of fracture surface showed an improved interfacial adhesion between PMMA/AH composites and GO, which was properly treated with oxygen plasma. The mechanical properties of nanocomposites were deteriorated by increasing the content of GO above 0.07 phr due to the nonuniform dispersion of GO.

Effect of Monomers and Initiators on Electrochemical Properties of Gel Polymer Electrolytes (젤 고분자 전해질의 전기화학적 특성에 대한 단량체 및 개시제의 영향)

  • Park, Hyoun-Gyu;Ryu, Sang-Woog
    • Polymer(Korea)
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    • v.34 no.4
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    • pp.357-362
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    • 2010
  • Poly(ethyleneglycol diacrylate)(PEGDA) or 2-ethylhexyl acrylate(2EHA)-based gel polymer electrolytes(GPEs) which have a solid content in the range of 8~54 wt% were synthesized and their ionic conductivity and electrochemical properties were measured at room temperature. It was observed that the ionic conductivity over $1\times10^{-3}$ S/cm was obtained in a homogeneous PEGDA-based GPE with 21 wt% of solid content. However the electrochemical stability of the GPE was lower than that of a liquid electrolyte. The presence of AIBN initiator which can produce a N2 gas during polymerization process might be the reason of this low oxidation decomposition potential. As an alternative, benzoyl peroxide was used as an initiator and GPE with enhanced electrochemical stability was obtained. Finally, the formation of stable solid electrolyte interphase on a graphite anode was evidenced by cyclic voltammetry measurement.

Identification of Internal Resistance of Microbial Fuel Cell by Electrochemical Technique and Its Effect on Voltage Change and Organic Matter Reduction Associated with Power Management System (전기화학적 기법에 의한 미생물연료전지 내부저항 특성 파악 및 전력관리시스템 연계 전압 변화와 유기물 저감에 미치는 영향)

  • Jang, Jae Kyung;Park, Hyemin;Kim, Taeyoung;Yang, Yoonseok;Yeo, Jeongjin;Kang, Sukwon;Paek, Yee;Kwon, Jin Kyung
    • Journal of Biomedical Engineering Research
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    • v.39 no.5
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    • pp.220-228
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    • 2018
  • The internal resistance of microbial fuel cell (MFC) using stainless steel skein for oxidizing electrode was investigated and the factors affecting the voltage generation were identified. We also investigated the effect of power management system (PMS) on the usability for MFC and the removal efficiency of organic pollutants. The performance of a stack microbial fuel cell connected with (PMS) or PMS+LED was analyzed by the voltage generation and organic matter reduction. The maximum power density of the unit cells was found to be $5.82W/m^3$ at $200{\Omega}$. The maximum current density was $47.53A/m^3$ without power overshoot even under $1{\Omega}$. The ohmic resistance ($R_s$) and the charge transfer resistance ($R_{ct}$) of the oxidation electrode using stainless steel skein electrode, were $0.56{\Omega}$ and $0.02{\Omega}$, respectively. However, the sum of internal resistance for reduction electrode using graphite felts loaded Pt/C catalyst was $6.64{\Omega}$. Also, in order to understand the internal resistance, the current interruption method was used by changing the external resistance as $50{\Omega}$, $300{\Omega}$, $5k{\Omega}$. It has been shown that the ohm resistance ($R_s$) decreased with the external resistance. In the case of a series-connected microbial fuel cell, the reversal phenomenon occurred even though two cells having the similar performance. However, the output of the PMS constantly remained for 20 hours even when voltage reversal occurred. Also the removal ability of organic pollutants (SCOD) was not reduced. As a result of this study, it was found that buffering effect for a certain period of time when the voltage reversal occurred during the operation of the microbial fuel cell did not have a serious effect on the energy loss or the operation of the microbial fuel cell.

Effects of Oxyfluorinated Graphene Oxide Flake on Mechanical Properties of PMMA Artificial Marbles (함산소불소화 처리된 그래핀 산화물 플레이크가 PMMA 인조대리석의 기계적 물성에 미치는 영향)

  • Kim, Hyo-Chul;Jeon, Son-Yeo;Kim, Hyung-Il;Lee, Young-Seak;Hong, Min-Hyuk;Choi, Ki-Seop
    • Polymer(Korea)
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    • v.36 no.3
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    • pp.251-261
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    • 2012
  • The nanocomposites containing graphene oxide flakes were prepared in order to improve the mechanical properties of artificial marbles based on poly(methyl methacrylate)(PMMA) matrix. Graphene oxide flakes were prepared from graphite by oxidation with Hummers method followed by exfoliation with thermal treatment. Surface of graphene oxide flakes were modified with oxyfluorination in various oxygene:fluorine compositions to improve the interfacial compatibility. The nanocomposites containing graphenes modified with oxyfluorination in the oxygen content of 50% and higher showed the significant increase in flexural strength, flexural modulus, Rockwell hardness, Barcol hardness, and Izod impact strength. The morphology of fractured surface showed the improved interfacial adhesion between PMMA matrix and the graphenes which were properly treated with oxyfluorination. The mechanical properties of nanocomposite were deteriorated by increasing the content of graphene above 0.07 phr due to the nonuniform dispersion of graphenes.

Structures and Double Layer Performances of Carbons Pyrolized from Carbon Oxides (산화탄소로부터 열분해한 탄소의 구조 및 전기이중층 거동)

  • Kim, Ick-Jun;Yang, Sunhye;Jeon, Min-Je;Moon, Seong-In;Kim, Hyun-Soo;An, Kye-Hyeok
    • Applied Chemistry for Engineering
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    • v.18 no.5
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    • pp.522-526
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    • 2007
  • Structural features and electrochemical performances of cokes pyrolized from oxidized cokes were examined, and compared with KOH-activated coke. Needle cokes ($d_{002}=3.5{\AA} $), having a graphene layer structure, were changed to a single phase of graphite oxide after oxidation treatment with an acidic solution having an $NaCLO_3$/needle coke composition ratio of above 7.5, and the inter-layer distance of the oxidized coke was expanded to $6.9{\AA} $ with increasing oxygen content. After heating at $200^{\circ}C$, the oxidized coke was pyrolized to the graphene layer structure with inter-layer distance of $3.6{\AA} $. However, the change of the inter-layer distance of the needle coke was not observed in the KOH activation process. On the other hand, an intercalation of electrolyte ions into the pyrolized coke, observed at first charge, occurred at 1.0 V, in which the value was lower than that of KOH-activation coke. The cell capacitor using pyrolized coke exhibited a lower internal resistance of $0.57{\Omega}$ in 1 kHz, and a larger capacitance per weight and volume of 30.3 F/g and 26.9 F/ml at the two-electrode system in the potential range 0~2.5 V than those of the cell capacitor using KOH-activation of coke. This better electrochemical performance may be associated with structure defects in the graphene layer derived from the process of the inter-layer expansion and shrinkage.

Effect of Vinylene Carbonate as an Electrolyte Additive on the Electrochemical Properties of Micro-Patterned Lithium Metal Anode (미세 패턴화된 리튬금속 전극의 Vinylene Carbonate 첨가제 도입에 따른 전기화학 특성에 관한 연구)

  • Jin, Dahee;Park, Joonam;Dzakpasu, Cyril Bubu;Yoon, Byeolhee;Ryou, Myung-Hyun;Lee, Yong Min
    • Journal of the Korean Electrochemical Society
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    • v.22 no.2
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    • pp.69-78
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    • 2019
  • Lithium metal anode with the highest theoretical capacity to replace graphite anodes are being reviewed. However, the dendrite growth during repeated oxidation/reduction reaction on lithium metal surface, which results in poor cycle performance and safety issue has hindered its successful implementation. In our previous work, we solved this problem by using surface modification technique whereby a surface pattern on lithium metal anode is introduced. Although the micro-patterned Lithium metal electrode is beneficial to control Li metal deposition efficiently, it is difficult to control the mossy-like Li granulation at high current density ($>2.0mA\;cm^{-2}$). In this study, we introduce vinylene carbonate (VC) electrolyte additive on micro patterned lithium metal anode to suppress the lithium dendrite growth. Owing to the synergetic effect of micro-patterned lithium metal anode and VC electrolyte additive, lithium dendrite at a high current density is dense. As a result, we confirmed that the cycle performance was further improved about 6 times as compared with the reference electrode.