• Title, Summary, Keyword: Polymer precursor

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Mechanical Properties of Carbon Fiber/Si/SiC and Carbon Fiber/C/SiC Composites (탄소섬유/Si/SiC 및 탄소섬유/탄소/SiC 복합재의 기계적 물성)

  • 신동우;박삼식;김경도;오세민
    • Composites Research
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    • v.12 no.3
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    • pp.8-16
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    • 1999
  • Carbon woven fabric/C/SiC composites were fabricated by multiple impregnations of carbon woven fabric/carbon preform with the polymer precursor of SiC, i.e., polycarbosilane. In addition, two kinds of low density carbon/carbon preforms which had different fiber volume fraction and fiber orientation, i.e., a carbon woven fabric(${\thickapprox}$55 vol%)/carbon and a chopped carbon fiber${\thickapprox}$40 vol%)/carbon composites, were reaction-bonded with a silicon melt at 1$700^{\circ}C$ in a vacuum to fabricate dense carbon fiber/Si/SiC composites. The reaction-bonding process increased the density to ~2.1 g/$cm^3$ from 1.6 g/$cm^3$ and 1.15 g/$cm^3$ of a carbon woven and a chopped carbon preforms, respectively. All of the composites fractured with extensive fiber pull-out. The higher the density the higher the stiffness and proportional limit stress. The mechanical properties obtained from a three-point bend and tension tests were compared. The ratios of the peak tensile stresses to the bending strengths of a carbon woven and a chopped carbon composites were about one-third, respectively. The carbon woven fabric/Si/SiC composites with density of 2.06 g/$cm^3$ showed ~120 MPa of ultimate strength and ~80 MPa of proportional limit in bend testing.

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Fabrication of Stack-Structured Gas Sensor of LaCrxCo1-xO3/Li1.3Al0.3Ti1.7(PO4)3 and Its NOx Sensing Properties (LaCrxCo1-xO3/Li1.3Al0.3Ti1.7(PO4)3의 적층구조를 가지는 가스센서 제조와 그의 NOx 검지특성)

  • Lee, Young-Sung;Shimizu, Y.;Song, Jeong-Hwan
    • Korean Journal of Materials Research
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    • v.25 no.8
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    • pp.423-428
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    • 2015
  • Impedancemetric $NO_x$ (NO and $NO_2$) gas sensors were designed with a stacked-layer structure and fabricated using $LaCr_xCo_{1-x}O_3$ (x = 0, 0.2, 0.5, 0.8 and 1) as the receptor material and $Li_{1.3}Al_{0.3}Ti_{1.7}(PO_4)_3$ plates as the solid-electrolyte transducer material. The $LaCr_xCo_{1-x}O_3$ layers were prepared with a polymeric precursor method that used ethylene glycol as the solvent, acetyl acetone as the chelating agent, and polyvinylpyrrolidone as the polymer additive. The effects of the Co concentration on the structural, morphological, and $NO_x$ sensing properties of the $LaCr_xCo_{1-x}O_3$ powders were investigated with powder X-ray diffraction, field emission scanning electron microscopy, and its response to 20~250 ppm of $NO_x$ at $400^{\circ}C$ (for 1 kHz and 0.5 V), respectively. When the as-prepared precursors were calcined at $700^{\circ}C$, only a single phase was detected, which corresponded to a perovskite-type structure. The XRD results showed that as the Co concentration of the $LaCr_xCo_{1-x}O_3$powders increased, the crystal structure was transformed from an orthorhombic phase to a rhombohedral phase. Moreover, the $LaCr_xCo_{1-x}O_3$ powders with $0{\leq}x<0.8$ had a rhombohedral symmetry. The size of the particles in the $LaCr_xCo_{1-x}O_3$powders increased from 0.1 to $0.5{\mu}m$ as the Co concentration increased. The sensing performance of the stack-structured $LaCr_xCo_{1-x}O_3/Li_{1.3}Al_{0.3}Ti_{1.7}(PO_4)_3$ sensors was found to divide the impedance component between the resistance and capacitance. The response of these sensors to NO gas was more sensitive than that to $NO_2$ gas. Compared to other impedancemetric sensors, the $LaCr_{0.8}Co_{0.2}O_3/Li_{1.3}Al_{0.3}Ti_{1.7}(PO_4)_3$ sensor exhibited good reversibility and reliable sensingresponse properties for $NO_x$ gases.

Fabrication and Property of Ba0.5Sr0.5Co0.8Fe0.2O3-δ Hollow Fiber Membranes (Ba0.5Sr0.5Co0.8Fe0.2O3-δ 중공사 분리막의 제조 및 물성)

  • Jeon, Sung Il;Park, Jung Hoon;Kim, Jong Pyo;Sim, Woo Jong;Lee, Yong Taek
    • Korean Chemical Engineering Research
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    • v.50 no.1
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    • pp.1-5
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    • 2012
  • $Ba_{0.5}Sr_{0.5}Co_{0.8}Fe_{0.2}O_{3-{\delta}}$ hollow fiber with o.d. 1.02 mm and i.d. 0.437 mm were fabricated by a phase-inversion spinning technique.The starting $Ba_{0.5}Sr_{0.5}Co_{0.8}Fe_{0.2}O_{3-{\delta}}$ precursor was synthesized by the polymerized complex method and then calcined at $900^{\circ}C$. As-prepared powder was dispersed in a polymer solution, and extruded as form of hollow fiber through a spinneret. Finallydense $Ba_{0.5}Sr_{0.5}Co_{0.8}Fe_{0.2}O_{3-{\delta}}$ hollow fiber membrane was obtained by sintering for 2 h at $1,080^{\circ}C$ for the application of oxygen separation. In addition, despite a very thin membrane with 0.58 mm, the BSCF hollow fiber membrane possessed a proper mechanical strength of 602.5 MPa.

Fabrication of Carbon Microneedle Arrays with High Aspect Ratios and The Control of Hydrophobicity of These Arrays for Bio-Applications (고종횡비 탄소 마이크로니들 어레이의 제조 및 생체응용을 위한 소수성 표면의 제어)

  • Lee, Jung-A;Lee, Seok-Woo;Lee, Seung-Seob;Park, Se-Il;Lee, Kwang-Cheol
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.34 no.11
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    • pp.1721-1725
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    • 2010
  • This paper reports the fabrication of geometry-controlled carbon microneedles by a backside exposure method and pyrolysis. The SU-8 microneedles are a polymer precursor in a carbonization process, which geometries such as base diameter, spacing, and aspect ratio can be controlled in a photolithography step. Using this fabrication method, highly reproducible carbon microneedles, which have high aspect ratios of more than 10 and very sharp nanotips, can be realized. The quartz surface with carbon microneedles becomes very hydrophilic and its wettability is adjusted by carrying out the silane treatment. In the carbon microneedle array ($3\;{\mu}m{\times}3\;{\mu}m$), the contact angle is extremly enhanced (${\sim}180^{\circ}$); this will be advantageous in developing low-drag microfluidics and labs-on-a-chip as well as in other bio-applications.