文章信息/Info

Title:

Influence of Initial Surface Area / Volume Ratio of the Fiber Preform on Kinetics of Chemical Vapor Infiltration and Texture of Infiltrated Carbon

作者:

張偉剛1; 2;  Hüttinger K.J. 1

(1.卡爾斯魯厄理工學(xué)院 化學(xué)技術(shù)與高分子化學(xué)研究所，德國卡爾斯魯厄 76131)(2.中國科學(xué)院過程工程研究所 多相復(fù)雜系統(tǒng)國家重點(diǎn)實(shí)驗(yàn)室，北京100190)

Author(s):

ZHANG Weigang1; 2;  Hüttinger K.J. 1

(1. Institute of Chemical Technology and Polymer ChemistryKarlsruhe Institute of Technology, Karlsruhe 76131, Germany)
(2.State Key Laboratory of Multiphase Complex Systems, Institute of Process Engineering, CAS, Beijing 100190, China)

關(guān)鍵詞:

熱解炭; 化學(xué)氣相滲透; 壓汞儀孔隙率測試; 光學(xué)顯微鏡; 織態(tài)結(jié)構(gòu)

DOI:

10.7502/j.issn.1674-3962.2013.11.02

摘要:

采用體積含量分別為7.1%和14.2%的兩種炭纖維各向同性針刺氈為預(yù)制體，研究了預(yù)制體內(nèi)部初始炭纖維表面積與自由體積比值（A/V值）對熱解炭的等溫等壓化學(xué)氣相滲透動力學(xué)以及熱解炭織態(tài)結(jié)構(gòu)變化的影響。實(shí)驗(yàn)研究以22.5kPa純甲烷為碳源氣體，沉積溫度為1095℃，氣體平均停留時間0.1s，沉積時間從20小時到120小時不等。熱解炭沉積后測量了C/C復(fù)合材料的表觀密度、開氣孔率、熱解炭的真密度及其內(nèi)部分布。利用正交偏光顯微鏡測試了熱解炭的織態(tài)結(jié)構(gòu)。研究結(jié)果表明，熱解炭的初始沉積過程主要受氣相-表面形核機(jī)制控制，隨著致密化的進(jìn)行，逐漸轉(zhuǎn)變?yōu)楸砻魃�長機(jī)制。這種從形核到表面生長機(jī)制的轉(zhuǎn)化，導(dǎo)致了熱解炭的織態(tài)結(jié)構(gòu)相應(yīng)地從低織構(gòu)向中織構(gòu)、最后到高織構(gòu)的轉(zhuǎn)化。上述沉積機(jī)制和結(jié)構(gòu)的變化，都是由于炭纖維編制體初始A/V值的不同以及由于熱解炭不斷沉積導(dǎo)致的A/V值的不斷增大引起的。增大炭纖維編制體的初始A/V值，可以導(dǎo)致這些轉(zhuǎn)化在致密化過程中提前發(fā)生。上述結(jié)果能夠很好地證明以前相關(guān)研究的結(jié)論。

Abstract:

Isothermal, isobaric chemical vapor infiltration of carbon fiber felts with fiber volume fractions of 7.1% and 14.2% were investigated to analyze the influence of initial surface area / volume ratio, [A/V], of the fiber preform on infiltration kinetics and texture of infiltrated carbon. Experiments were performed at a temperature of 1095oC, a methane pressure of 22.5kPa, a residence time of 0.1s and infiltration times being stepwise increased from 20 to 120h. Global bulk density and bulk density, porosity as well as density of matrix carbon as a function of infiltration depth were determined. Carbon texture was analyzed with polarized杔ight microscopy. The results show that infiltration kinetics in the initial stage of infiltration are dominated by the nucleation mechanism and afterwards by the growth mechanism of carbon formation. These changes of deposition chemistry and kinetics lead to changes of carbon texture from low / medium to medium / high. All changes are caused by an increase of [A/V] ratio. They occur in a significantly earlier stage in the case of the felt with the higher initial [A/V] ratio, as to be expected. These results are a perfect confirmation of conclusions from earlier studies.