• Title/Summary/Keyword: whisker

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Fabrication of SiCf/SiC Composite by Chemical Vapor Infiltration (화학기상침착법에 의한 SiCf/SiC 복합체의 제조)

  • Park, Ji Yeon;Kim, Daejong;Kim, Weon-Ju
    • Composites Research
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    • v.30 no.2
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    • pp.108-115
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    • 2017
  • Among several fabrication processes of $SiC_f/SiC$ composites, the chemical vapor infiltration (CVI) process has attractive advantages in manufacturing complex net-or near-net-shape components at relatively low temperatures, easily controlling the microstructure of the matrix and obtaining the highest SiC purity level. However, it has disadvantages in that the ratio of residual pores in matrix is higher than other processes and processing time is relatively long. To reduce the residual porosity, the whisker-growing-assisted CVI process, which is composed of whisker growth and matrix filling steps has been developed. The whiskers grown before matrix filling may serve to divide the large natural pores between the fibers or bundles so that the matrix can be effectively filled into the finely divided pores. In this paper, the fundamentals of the CVI process for preparation of $SiC_f/SiC$ composites and some experimental results prepared by CVI and whisker-growing-assisted CVI processes are briefly introduced.

Growth Behavior of Aluminum Borate Whisker under 2.45 GHz Electromagnetic Irradiation (2.45 GHz 전자기파 조사하에서 Aluminum Borate Whisker의 성장 거동)

  • 김성완;이상근;김지경;이창희;안진모;신준식;박성수;박희찬
    • Journal of the Korean Ceramic Society
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    • v.40 no.10
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    • pp.998-1004
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    • 2003
  • With starting materials of two different powder mixtures, $Al_2$(S $O_4$)$_3$+xNa$_2$B$_4$ $O_{7}$$.$10$H_2O$(㏖ ratio; x=0.1, 0.7) and ${\gamma}$-Al$_2$ $O_3$+xNa$_2$B$_4$ $O_{7}$$.$10$H_2O$(㏖ ratio; x=0.1, 0.7), whisker-type $Al_{18}$B$_4$ $O_{33}$ particles were synthesized by using conventional and microwave heat-treatment. The effects of microwave, amount of flux and temperature on the growth of whisker-type $Al_{18}$B$_4$ $O_{33}$ particles were investigated by using X-Ray Diffractometry (XRD) and Scanning Electron Microscopy (SEM). With increase of heat-treatment temperature and amount of flux, the size of whisker-type $Al_{18}$B$_4$ $O_{33}$ particles increased in both conventional and microwave heat-treated samples. However, compared to the conventional heat-treated samples, whisker-type $Al_{18}$B$_4$ $O_{33}$ particles were well grown for the microwave heat-treated samples.ted samples.

Synthesis of Lithium Titanate Whisker Using Ion-Exchange of Acid Treatment

  • Um Myeong-Heon;Lee Jin-Sik
    • Korean Journal of Materials Research
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    • v.14 no.9
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    • pp.627-633
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    • 2004
  • Lithium titanate whiske($Li_{x}Ti_{4}O_9$) was prepared by an ion-exchange reaction. To this end, the initial material, potassium tetratitanate ($K_{2}Ti_{4}O_9{\cdot}nH_{2}O$) was prepared by calcination of a mixture of $K_{2}CO_3\;and\;TiO_2$ with a molar ratio of 2.8 at $1050^{\circ}C$ for 3 h, followed by boiling water treatment of the calcined products for 10 h. Fibrous potassium tetratitanate could be transformed into layered hydrous titanium dioxide ($H_{2}Ti_{4}O_9{\cdot}nH_{2}O$) through an exchange of $K^{+}\;with\;H^{+}$ using 0.075 M HCl. Also, lithium titanate whisker was finally prepared as $Li^{+}\;and\;H^{+}$ ions were exchanged by adding 20 mL of a mixture solution of LiOH and $LiNO_3$ to 1g whisker and stirring for $5\~15$ days. The average length and diameter of the $Li_{x}Ti_{4}O_9$ whiskers were $10\~20{\mu}m\;and\;1\~3{\mu}m$, respectively.

Preparation and Application of Functional Carbon Whisker Membrane for Separation Process

  • Bae, Sang-Dae;Son, Hee-Jong;Jung, Chul-Woo
    • Journal of Environmental Science International
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    • v.17 no.11
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    • pp.1235-1241
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    • 2008
  • Membrane separation is extensively used for water/wastewater treatment because of its efficiency separation processes. However, particles in the feed water can deposit and accumulate on the membrane surface to created cake layer. As a consequence, the selectivity of the membrane and flux through the membrane are decreased, which is called fouling/blocking phenomenon. In order to solve fouling problem, we developed a novel membrane named Carbon Whisker Membrane (CWM) which contains vapor-grown carbon fibers/whiskers on the surface of the membrane and a layer of carbon film coated on the ceramic substrate. We firstly employed polymethyl methacrylate (PMMA) as a testing material to investigate the fouling mechanism. The results suggested that Carbon Whiskers on the surface of the membrane can prevent the directly contact between the membrane body and particles so that the fouling/blocking could not occurred easily compared to the membrane without carbon whiskers. We also researched the relationship with the diameter, density of carbon whisker on the membrane surface and total flux of solutions. Finally, we will be able to control the diameter and density of carbon whiskers on the membrane and existence of carbon whiskers on the membrane, it is important factor, might be prevent fouling/blocking in the water treatment.

High Strain Rate Superplasticity of Whisker Reinforced Aluminum Alloy Matrix Composites Fabricated by Squeeze Casting (용탕단조법에 의한 휘스커강화 Al합금기 복합재료의 고속초소성)

  • Lim, Suk-Won;Nishida, Yoshinori
    • Journal of Korea Foundry Society
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    • v.21 no.6
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    • pp.359-365
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    • 2001
  • The superplastic behavior of whisker reinforced aluminum alloy matrix composites fabricated by squeeze casting as one of high pressure routes was investigated. The preforms of ${\alpha}-Si_3N_4$ and ${\beta}-SiC$ whiskers without any binder as a reinforcement were used. The matrix materials were 2024 and 7075 aluminum alloys. For the purpose of optimum superplastic condition, respectively, the whiskers volume fraction, extrusion temperature, tensile test temperature and initial strain rate were changed. Fracture surface of tested specimens were observed by SEM. By the results, it became possible to produce superplastic composites by applying only a hot extrusion process to composites obtained by the squeeze casting. The superplastic composites developed are ${\alpha}-Si_3N_4w/7075$, ${\alpha}-Si_3N_4w/2024$ and ${\beta}-SiCw/2024$ systems at high strain rate.

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Effect of Hot Extrusion on the Mechanical Properties of 6061 Aluminum Alloy composites Reinforced with SiC whisker (SiC휘스커로 강화한 6061 Al합금 복합재료의 기계적 특성에 미치는 열간압출의 영향)

  • Kim, Jun-Su;Lim, Su-Geun
    • Journal of Korea Foundry Society
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    • v.16 no.2
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    • pp.132-140
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    • 1996
  • Both cast and extruded composites of SiC whisker reinforced 6061 Al alloy matrix were fabricated by high pressure infiltration of the alloy melt into the SiC preform and subsequent hot extrusion of the composite ingots. The micro structures, age hardening behavior and mechanical properties have been examined on the both cast and extruded composites of SiCw/6061. The cast composites of SiCw/6061 were obtained in which SiC whiskers were randomly oriented. Hot extrusion of these cast composites lead to alignment of the whisker in the direction of extrusion. Strengthening effect of whisker in the extruded composites is lower than that of the cast composites. The cast composites of SiCw/6061 showed higher thensile strength and lower elongation than extruded composites of SiCw/6061 at all testing temperatures. Lower tensile strength and higher elongation of the extruded composites were attributable to fine grain structures in which grain boundary sliding occruued preferentially at elevated temperatures.

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Fabrication of Aluminum Alloy Composites Reinforced with SiC whisker an $Al_2O_3-SiO_2$ Short Fiber by Squeeze Casting (용탕단조에 의한 $Al_2O_3-SiO_2$ 단섬유 및 SiC whisker강화 알루미늄 합금기 복합재료의 제조)

  • Hong, Sung-Kil;Yun, Jung-Yul;Choi, Jung-Chul
    • Journal of Korea Foundry Society
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    • v.17 no.1
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    • pp.28-35
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    • 1997
  • SiC whisker and $Al_2O_3-SiO_2$ short fiber reinforced AC8A, AC8B and AC8B(J) marix composites were fabricated by squeeze casting method. Preform deformation, change of reinforcement volumefraction and formation of macro-segregation in two composites were investigated by using micro Vickers hardness test, analysis of macro and micro structures with OM, SEM and EDAX. $Al_2O_3-SiO_2$ short fiber preform manufactured with 5% $SiO_2$ binder in this study was considerably deformed and cracked, nevertheless, the short fibers were distributed homogeneously in the composites. In SiC whisker reinforced composites, on the other hand, preform deforming and cracking were not occurred, however, macro segregation zone formed along the infiltration routes by interface reaction during infiltration of molten metal into the preform was observed at center-low area in the composites. The decrease of hardness in the macro segregation zone resulted from the depletion of Si and Mg atoms.

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Synthesis of Silicon Carbide Whiskers (I) : Reaction Mechanism and Rate-Controlling Reaction (탄화규소 휘스커의 합성(I) : 반응기구의 율속반응)

  • 최헌진;이준근
    • Journal of the Korean Ceramic Society
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    • v.35 no.12
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    • pp.1329-1336
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    • 1998
  • A twt -step carbothermal reduction scheme has been employed for the synthesis of SiC whiskers in an Ar or a H2 atmosphere via vapor-solid two-stage and vapor-liquid-solid growth mechanism respectively. It has been shown that the whisker growth proceed through the following reaction mechanism in an Ar at-mosphere : SiO2(S)+C(s)-SiO(v)+CO(v) SiO(v)3CO(v)=SiC(s)whisker+2CO2(v) 2C(s)+2CO2(v)=4CO(v) the third reaction appears to be the rate-controlling reaction since the overall reaction rates are dominated by the carbon which is participated in this reaction. The whisker growth proceeded through the following reaction mechaism in a H2 atmosphere : SiO2(s)+C(s)=SiO(v)+CO(v) 2C(s)+4H2(v)=2CH4(v) SiO(v)+2CH4(v)=SiC(s)whisker+CO(v)+4H2(v) The first reaction appears to be the rate-controlling reaction since the overall reaction rates are enhanced byincreasing the SiO vapor generation rate.

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