• Title/Summary/Keyword: carbon preform

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RBSC Prepared by Si Melt Infiltration into the Y2O3 Added Carbon Preform (Y2O3 첨가 탄소 프리폼에 Si 용융 침투에 의해 제조한 반응 소결 탄화규소)

  • Jang, Min-Ho;Cho, Kyeong-Sik
    • Journal of Powder Materials
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    • v.28 no.1
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    • pp.51-58
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    • 2021
  • The conversion of carbon preforms to dense SiC by liquid infiltration is a prospectively low-cost and reliable method of forming SiC-Si composites with complex shapes and high densities. Si powder was coated on top of a 2.0wt.% Y2O3-added carbon preform, and reaction bonded silicon carbide (RBSC) was prepared by infiltrating molten Si at 1,450℃ for 1-8 h. Reactive sintering of the Y2O3-free carbon preform caused Si to be pushed to one side, thereby forming cracking defects. However, when prepared from the Y2O3-added carbon preform, a SiC-Si composite in which Si is homogeneously distributed in the SiC matrix without cracking can be produced. Using the Si + C → SiC reaction at 1,450℃, 3C and 6H SiC phases, crystalline Si, and Y2O3 were generated based on XRD analysis, without the appearance of graphite. The RBSC prepared from the Y2O3-added carbon preform was densified by increasing the density and decreasing the porosity as the holding time increased at 1,450℃. Dense RBSC, which was reaction sintered at 1,450℃ for 4 h from the 2.0wt.% Y2O3-added carbon preform, had an apparent porosity of 0.11% and a relative density of 96.8%.

The Effect of Pressure on the Properties of Carbon/Carbon Composites during the Carbonization Process

  • Joo, Hyeok-Jong;Oh, In-Hwan
    • Carbon letters
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    • v.3 no.2
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    • pp.85-92
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    • 2002
  • 4D carbon fiber preforms were manufactured by weaving method and their carbon fiber volume fractions were 50% and 60%. In order to form carbon matrix on the preform, coal tar pitch was used for matrix precursor and high density carbon/carbon composites were obtained by high densification process. In this process, manufacture of high density composites was more effective according to pressure increasement. When densificating the preform of 60% fiber volume fraction with 900 bar, density of the composites reached at 1.90 $g/cm^3$ after three times processing. Degree of pressure in the densification process controls macro pore but it can not affect micro pore. During the carbonization process, micro pore of the preform were filled fully by once or twice densification processing. But micro pore were not filled easily in the repeating process. Therefore, over three times densification processing is the filling micro pore.

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Effect of Y2O3 Additive Amount on Densification of Reaction Bonded Silicon Carbides Prepared by Si Melt Infiltration into All Carbon Preform (완전 탄소 프리폼으로부터 Si 용융 침투에 의해 제조한 반응 소결 탄화규소의 치밀화에 미치는 Y2O3 첨가량의 영향)

  • Cho, Kyeong-Sik;Jang, Min-Ho
    • Korean Journal of Materials Research
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    • v.31 no.5
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    • pp.301-311
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    • 2021
  • The conversion of all carbon preforms to dense SiC by liquid infiltration can become a low-cost and reliable method to form SiC-Si composites of complex shape and high density. Reactive sintered silicon carbide (RBSC) is prepared by covering Si powder on top of 0.5-5.0 wt% Y2O3-added carbon preforms at 1,450 and 1,500℃ for 2 hours; samples are analyzed to determine densification. Reactive sintering from the Y2O3-free carbon preform causes Si to be pushed to one side and cracking defects occur. However, when prepared from the Y2O3-added carbon preform, an SiC-Si composite in which Si is homogeneously distributed in the SiC matrix without cracking can be produced. Using the Si + C = SiC reaction, 3C and 6H of SiC, crystalline Si, and Y2O3 phases are detected by XRD analysis without the appearance of graphite. As the content of Y2O3 in the carbon preform increases, the prepared RBSC accelerates the SiC conversion reaction, increasing the density and decreasing the pores, resulting in densification. The dense RBSC obtained by reaction sintering at 1,500 ℃ for 2 hours from a carbon preform with 2.0 wt% Y2O3 added has 0.20 % apparent porosity and 96.9 % relative density.

Numerical Simulation of Diffusion and Flow in Fabrication of Carbon/Carbon Composite Using Chemical Vapor Infiltration (다단계 화학반응과 밀도화 모델을 이용한 탄소/탄소 복합재 화학기상침투 공정의 확산 및 유동 수치해석)

  • Kim, Hye-gyu;Ji, Wooseok;Jo, Namchun;Park, Jonggyu
    • Composites Research
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    • v.32 no.1
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    • pp.56-64
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    • 2019
  • In this paper, a model is developed to simulate carbon/carbon composite fabrication using chemical vapor infiltration, considering density and porosity change in the preform and multi-step hydrocarbons reactions. The model considers the preform as a porous medium whose diffusion and flow properties changes due to the porosity. To verify the theoretical model, two numerical analyses were performed for the case that the flow inside the preform is zero and the case that the flow inside the preform is calculated by fluid mechanics. The numerical results showed good agreement with the experimental data.

Properties of Silicon Carbide-Carbon Fiber Composites Prepared by Infiltrating Porous Carbon Fiber Composites with Liquid Silicon

  • Lee, Jae-Chun;Park, Min-Jin;Shin, Kyung-Sook;Lee, Jun-Seok;Kim, Byung-Gyun
    • The Korean Journal of Ceramics
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    • v.3 no.4
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    • pp.229-234
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    • 1997
  • Silicon carbide-carbon fiber composites have been prepared by partially Infiltrating porous carbon fiber composites with liquid silicon at a reaction temperature of $1670^{\circ}C$. Reaction between molten silicon and the fiber preform yielded silicon carbide-carbon fiber composites composed of aggregates of loosely bonded SiC crystallites of about 10$\mu\textrm{m}$ in size and preserved the appearance of a fiber. In addition, the SiC/C fiber composites had carbon fibers coated with a dense layer consisted of SiC particles of sizes smaller than 1$\mu\textrm{m}$. The physical and mechanical properties of SiC/C fiber composites were discussed in terms of infiltrated pore volume fraction of carbon preform occupied by liquid silicon at the beginning of reaction. Lower bending strength of the SiC/C fiber composites which had a heterogeneous structure in nature, was attributed to the disruption of geometric configuration of the original carbon fiber preform and the formation of the fibrous aggregates of the loosely bonded coarse SiC particles produced by solution-precipitation mechanism.

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Effects of the Gas Flow Inside a CVI Reactor on the Densification of a C/C Composite (화학기상침투법 반응로 내부 유동에 따른 탄소/탄소 복합재 밀도화)

  • Kim, Hye-gyu;Ji, Wooseok;Kwon, Hyang Joo;Yoon, Sungtae;Kim, Jung-il
    • Composites Research
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    • v.34 no.4
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    • pp.249-256
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    • 2021
  • In this paper, the densification of a carbon/carbon composite during a chemical vapor infiltration (CVI) process is studied using a chemo-mechanical model. The multi-physics numerical model, developed in the previous research, couples computational fluid dynamics and major chemical reactions in the reactor. The model is especially utilized to study the effect of flow behavior around the preform on the densification. Four different types of "flow-guide" structures are placed to alter the gas flow around the preform. It is shown that the flow pattern and speed around the preform can be controlled by the guide structures. The process simulations demonstrate that the average density and/or density distribution of the preform can be improved by controlling the gas flow around the perform. In this study, a full industrial-scale reactor and process parameter were used.

Fabrication and Mechanical Characterization of Braided Carbon Fiber Reinforced Al Matrix Composites (Braided 탄소섬유강화 알루미늄 기지 금속복합재료의 제조 및 기계적 특성평가)

  • 김경태;이상관;홍순형
    • Proceedings of the Korean Society For Composite Materials Conference
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    • 2002.10a
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    • pp.131-134
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    • 2002
  • Braided carbon fiber reinforced Al matrix composites were developed and characterized. Braided carbon fiber preforms with braiding angles of $30^{\circ}$, $45^{\circ}$ and $60^{\circ}$ were manufactured by using a braiding machine. The manufactured braided carbon fibers were used as reinforcement to fabricate Al matrix composites by employing a pressure infiltration casting method. In the processing of pressure infiltration casting, important processing parameters such as melting temperature, preheating temperature of preform and applied pressure were optimized. Prediction of elastic constants on composites was performed by using the volume averaging method, which utilizes the coordinate transformation and the averaging of stiffeness and compliance constants based upon the volume of each reinforcement and matrix material. The elastic moduli of composites were evaluated by using Resonant Ultrasound Spectroscopy(RUS) method and compared with the elastic moduli obtained from static tensile test method.

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Thermophysical Properties of 4D Carbon/Carbon Composites with Preform Architectures (프리폼 구조에 따른 4방향성 탄소/탄소 복합재의 열물리적 특성)

  • Kim, Zeong-Baek;Lee, Ki-Woong;Park, Jong-Min;Joo, Hyeok-Jong
    • Applied Chemistry for Engineering
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    • v.18 no.6
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    • pp.580-586
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    • 2007
  • In this study, 4 directional carbon/carbon composites with different preform architectures were manufactured and their thermophysical properties are studied. Carbon fiber preforms are fabricated with fiber bundles using four different spaces. The density of the fabricated preforms were increased through pressure impregnation and carbonizing process. The increased density of the composites was graphitized at $2300^{\circ}C$. Microstructures of these composite were observed under scanning electron microscope. This was to understand the effect the preform architectures has on the thermophysical properties of carbon/carbon composites. Also, the behavior of thermal conduction and heat expansion was investigated and studied in association with the factors of the reinforced direction of fibers and unit cell of preforms.

Film Boiling Chemical Vapor Infiltration of C/C Composites: Influence of Mass and Thermal Transfers

  • Delhaes, P.;Trinquecoste, M.;Derre, A.;Rovillain, D.;David, P.
    • Carbon letters
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    • v.4 no.4
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    • pp.163-167
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    • 2003
  • The "Film boiling" Chemical Vapor Infiltration (CVI) process is a rapid densification one developed in particular for the elaboration of carbon/carbon composite materials. In order to optimize this new thermal gradient process, we have carried out several studies, on one hand, about the nature of the complex chemical reactions in a confined medium, and on the other hand, relative to the role of heat and mass transfers inside the preform. We show in this study that the introduction of a permeable sheath around the preform leads to hybrid liquid/gas CVI process which presents the advantages of very high densification rates associated with a moderate input energy.

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Fabrication and Characterization of Carbon Fiber Reinforced (탄소섬유강화 유리복합재료의 제조 및 특성분석)

  • Cho, H.S.;Kim, S.D.;Cho, H.J.;Kong, S.S.;Choi, W.B.;Baek, Y.K.;Kim, H.J.;Kim, H.
    • Journal of the Korean Ceramic Society
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    • v.29 no.8
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    • pp.601-608
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    • 1992
  • We investigated the influence of several processes, including the preparation of slurry and preform and the heat-treatment of the preform, on the properties of composites to fabricate the carbon-fiber reinforced glass composites having good mechanical properties. Cerander was determined to be the best binder among Cerander, Rhoplex and Elvacite 2045 by the dipping test and the binder within a preform could be completely eliminatd by burning out the specimen under 10-6 Torr at 400$^{\circ}C$ for more than 1h. The fracture behavior of a composite was largely dependent on the uniformity of carbon-fiber distribution within the composite and the heat-treatment condition of the composite. The higher the glass content, the more difficult to obtain uniform distribution of carbon-fiber. As the hot-pressing temperature increased, the densification process of the composite and the formation of pore due to oxidation of carbon fiber occurred competitively. But, above 1000$^{\circ}C$ the latter played a predominant role. We could fabricated the densest 15 vol.% carbon-fiber-content glass composite having the highest toughness and flexural strength of 250 MPa by hot-pressing under 15 MPa at 900$^{\circ}C$ for 30 min.

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