• Title, Summary, Keyword: Polymer precursor

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Fabrication of Flake-like LiCoO2 Nanopowders using Electrospinning (전기 방사법을 이용한 플레이크형 LiCoO2 나노 분말의 제조)

  • Koo, Bon-Ryul;An, Geon-Hyoung;Ahn, Hyo-Jin
    • Journal of Korean Powder Metallurgy Institute
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    • v.21 no.2
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    • pp.108-113
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    • 2014
  • Flake-like $LiCoO_2$ nanopowders were fabricated using electrospinning. To investigate their formation mechanism, field-emssion scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy were carried out. Among various parameters of electrospinning, we controlled the molar concentration of the precursor and the PVP polymer. When the molar concentration of lithium and cobalt was 0.45 M, the morphology of $LiCoO_2$ nanopowders was irregular and round. For 1.27 M molar concentration, the $LiCoO_2$ nanopowders formed with flake-like morphology. For the PVP polymer, the molar concentration was set to 0.011 mM, 0.026 mM, and 0.043 mM. Irregular $LiCoO_2$ nanopowders were formed at low concentration (0.011 mM), while flake-like $LiCoO_2$ were formed at high concentration (0.026 mM and 0.043 mM). Thus, optimized molar concentration of the precursor and the PVP polymer may be related to the successful formation of flake-like $LiCoO_2$ nanopowders. As a results, the synthesized $LiCoO_2$ nanopowder can be used as the electrode material of Li-ion batteries.

Synthesis of Cross-Linked Polyurethane-Based Gel Polymer Electrolyte and Its Electrochemical Properties (가교형 폴리우레탄기 겔 폴리머 전해질의 합성과 전기화학적 특성)

  • Kim, Hyun-Soo;Kim, Sung-Il;Choi, Gwan-Young;Moon, Seong-In;Yun, Mun-Soo;Kim, Sang-Pil
    • Journal of the Korean Electrochemical Society
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    • v.6 no.2
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    • pp.98-102
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    • 2003
  • Urethane acrylate oligomer was synthesized and used in a gel polymer electrolyte (GPE) and then its electrochemical performances were evaluated. $LiCoO_2/GPE/graphite$ cells were prepared and their performances depending on discharge currents and temperatures were evaluated. The precursor containing $5 vol\%$ curable mixture had a low viscosity relatively. ionic conductivity of the gel polymer electrolyte at room temperature and $-20^{\circ}C$ was ca. $5.9\times10^{-3}S{\cdot}cm^{-1}\;and\;1.4times10^{-3}S{\cdot}cm^{-1}$, respectively. GPE showed good electrochemical stability up to potential of 4.5V vs. RLi/Li^+.\;LiCoO_2/GPE/graphite$ cell showed a good high-rate and low-temperature performance.

Au/Titania Composite Nanoparticle Arrays with Controlled Size and Spacing by Organic-Inorganic Nanohybridization in Thin Film Block Copolymer Templates

  • Li, Xue;Fu, Jun;Steinhart, Martin;Kim, Dong-Ha;Knoll, Wolfgang
    • Bulletin of the Korean Chemical Society
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    • v.28 no.6
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    • pp.1015-1020
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    • 2007
  • A simple approach to prepare arrays of Au/TiO2 composite nanoparticles by using Au-loaded block copolymers as templates combined with a sol-gel process is described. The organic-inorganic hybrid films with closely packed inorganic nanodomains in organic matrix are produced by spin coating the mixtures of polystyrene-block-poly(ethylene oxide) (PS-b-PEO)/HAuCl4 solution and sol-gel precursor solution. After removal of the organic matrix with deep UV irradiation, arrays of Au/TiO2 composite nanoparticles with different compositions or particle sizes can be easily produced. Different photoluminescence (PL) emission spectra from an organic-inorganic hybrid film and arrays of Au/TiO2 composite nanoparticles indicate that TiO2 and Au components exist as separate state in the initial hybrid film and form composite nanoparticles after the removal of the block copolymer matrix.

Processing and properties of $Al_{2}O_{3}/SiC$ nanocomposites by polycarbosilane infiltration

  • Jung-Soo Ha;Chang-Sung Lim;Chang-Sam Kim
    • Journal of the Korean Crystal Growth and Crystal Technology
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    • v.12 no.2
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    • pp.80-86
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    • 2002
  • $Al_{2}O_{3}/SiC$ nanocomposites were made by infiltrating partially sintered alumina bodies with polycarbosilane (PCS) solutions, which is a SiC polymer precursor, with pressureless sintering. The SiC content, densification, phases, strength, and microstructure were investigated with the processing parameters such as PCS solution concentration and heat treatment condition for PCS pyrolysis and sintering. The results were compared with those for pure alumina and nanocomposite samples made by the existing polymer precursor route (i.e. the PCS addition process). The SiC contents of up to 1.5 vol% were obtained by the PCS infiltration. PCS pyrolysis, followed by air heat treatment, was needed before sintering to avoid a cracking problem and to attain a densification as high as 98 % of theoretical. The nanocomposites exhibited significantly higher strength than pure alumina and those prepared by the PCS addition process despite larger grain size. Besides $\alpha-Al_{2}O_{3}/SiC$ and $\beta-SiC$ phases, mullite was present a little in the nanocomposites, which resulted from the reaction of $SiO_{2}$ in the pyrolysis product of PCS with the $Al_{2}O_{3}$ matrix during sintering. The nanocomposites had intagranular particles believed to be SiC, which is a typical feature of $Al_{2}O_{3}/SiC$ nanocomposites.

Synthesis of Tetra-armed Star Shaped Poly(tetrahydrofuran) via Photocationic Mechanism (광양이온 중합을 이용한 별모양 4가닥 폴리(테트라히드로퓨란)의 합성)

  • Ma, Seok-Il;Hwang, Hyeon-Seon;Sin, Jong-Ho
    • Textile Science and Engineering
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    • v.31 no.7
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    • pp.543-550
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    • 1994
  • The synthesis of tetra-armed star shaped poly(tetrahydrofuran)(THF) has been attempted using pentaerythritol tetrakis(3,4-epoxybutanoate(PETE) as a precursor by photoinduced cationic polymerization. The cationic polymerization of THF was initiated by photoirradiation with 500w high pressure mercury lamp, using PETE as a precursor, in the presence of diphenylidonium hexafluorophosphate(initiator) and followed by dark reaction. The polymerization behaviors, i.e., oyo conversion to polymer, the number of arms and gel formation have been discussed in relation to reaction parameters such as concentrations of PETE, salt and THF. The number of arms in star shaped polymers were determined by dividing the molecluar weight of polymer before alkaline hydrolysis by those of after alkaline hydrolysis. The number of arms of star shaped polymers were found to be strongly dependent on the molar ratio of THF/PETE and varied in the range of 2.5-11.2. It was observed that tetra-armed star shaped polymers was obtainable in the early stage of dark reaction from the systems where the molar ratio of THF/PETE in the feed was kept at around 1000.

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Fabrication of SiCN microstructures for super-high temperature MEMS using photopolymerization and its characteristics (광중합에 의한 초고온 MEMS용 SiCN 미세구조물 제작과 그 특성)

  • Chung, Gwiy-Sang
    • Journal of Sensor Science and Technology
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    • v.15 no.2
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    • pp.148-152
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    • 2006
  • This paper describes the fabrication of SiCN microstructures for super-high temperature MEMS using photopolymerization of pre-ceramic polymer. In this work, polysilazane liquide as a precursor was deposited on Si wafers by spin coating, microstructured and solidificated by UV lithography, and removed from the substrate. The resulting solid polymer microstructures were cross-linked under HIP process and pyrolyzed to form a ceramic of withstanding over $1400^{\circ}C$. Finally, the fabricated SiCN microstructures were annealed at $1400^{\circ}C$ in a nitrogen atmosphere. Mechanical characteristics of the SiCN microstructure with different fabrication process conditions were evaluated. The elastic modules, hardness and tensile strength of the SiC microstructure implemented under optimum process condtions are 94.5 GPa, 10.5 GPa and 11.7 N/min, respectively. Consequently, the SiCN microstructure proposed in this work is very suitable for super-high temperature MEMS application due to very simple fabrication process and the potential possiblity of sophisticated mulitlayer or 3D microstructures as well as its good mechanical properties.

Fabrication of SiCN microstructures for super-high temperature MEMS using PDMS mold and its characteristics (PDMS 몰드를 이용한 초고온 MEMS용 SiCN 미세구조물 제작과 그 특성)

  • Chung, Gwiy-Sang;Woo, Hyung-Soon
    • Journal of Sensor Science and Technology
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    • v.15 no.1
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    • pp.53-57
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    • 2006
  • This paper describes a novel processing technique for fabrication of polymer-derived SiCN (silicone carbonitride) microstructures for super-temperature MEMS applications. PDMS (polydimethylsiloxane) mold is fabricated on SU-8 photoresist using standard UV photolithographic process. Liquid precursor is injected into the PDMS mold. Finally, solid polymer structure is cross-linked using HIP (hot isostatic pressure) at $400^{\circ}C$, 205 bar. Optimum pyrolysis and annealing conditions are determined to form a ceramic microstructure capable of withstanding over $1400^{\circ}C$. The fabricated SiCN ceramic microstructure has excellent characteristics, such as shear strength (15.2 N), insulation resistance ($2.163{\times}10^{14}{\Omega}$) and BDV (min. 1.2 kV) under optimum process condition. These fabricated SiCN ceramic microstructures have greater electric and physical characteristics than bulk Si wafer. The fabricated SiCN microstructures would be applied for supertemperature MEMS applications such as heat exchanger and combustion chamber.

Fabrication of SiCN Microstructures for Super-High Temperature MEMS and Its Characteristics (초고온 MEMS용 SiCN 미세구조물 제작과 그 특성)

  • Lee, Gyu-Chul;Chung, Gwiy-Sang
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • pp.392-393
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    • 2006
  • This paper describes the fabrication of SiCN microstructures for super-high temperature MEMS using photopolymerization of pre-ceramic polymer. In this work. polysilazane liquide as a precursor was deposited on Si wafers by spin coating. microstructured and solidificated by UV lithography. and removed from the substrate. The resulting solid polymer microstructures were cross-linked under HIP process and pyrolyzed to form a ceramic of withstanding over $1400^{\circ}C$. Finally, the fabricated SiCN microstructures were annealed at $1400^{\circ}C$ in a nitrogen atmosphere. Mechanical characteristics of the SiCN microstructure with different fabrication process conditions were evaluated. The elastic modules. hardness and tensile strength of the SiC microstructure implemented under optimum process conditions are 94.5 GPa, 10.5 GPa and 11.7 N/min, respectively. Consequently, the SiCN microstructure proposed in this work is very suitable for super-high temperature MEMS application due to very simple fabrication process and the potential possiblity of sophisticated multlayer or 3D microstructures as well as its good mechanical properties.

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Synthesis of Silica Nanopowder via Change in Polymer Gel Concentration (고분자 젤 농도변화에 의한 실리카 나노분말의 합성)

  • Kim, Ji-Kyung;Lee, Sang-Geun;Kwon, Jae-Youl;Seo, Geum-Seok;Park, Seong-Soo;Park, Hee-Chan
    • Journal of the Korean Ceramic Society
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    • v.42 no.3
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    • pp.205-210
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    • 2005
  • Nanoscale silica powder was synthesized from $SiO_2$ precursor solution using Tetraethyl Orthosilicate (TEOS) by polyacrylamide gel method. This process was of simplicity and provided ultrafine powders at relatively low calcination temperatures because polymer network could inhibit aggregation of $SiO_2$ powder. The particle size of Si02 powder was affected by the concentration of ammonium persulphate and N, N'-methylene-bis-acrylamide(BIS) in the gel precursor. The particle size decreased with increasing ammonium persulphate and was mininum size of 10 nm at 0.01 M. Also, the size decreased with increasing BIS concentration and was 5 nm at its concentration of 0.05 M.