KCl对酚醛树脂炭化生长碳纤维的影响

Effect of KCl on growth of carbon fibers during carbonization of phenolic resin

为了促进酚醛树脂在炭化过程中的石墨化，以工业液态酚醛树脂为碳源，微米尺度的KCl为催化剂，经混合、六亚甲基四胺固化处理后，在埋炭1000℃保温3h热处理条件下，研究了 KCl 添加量（掺入酚醛树脂质量的1％、3％、5％和7％）对树脂碳的物相、微观结构的影响及碳纤维的生长机制。结果表明：KCl催化后提高了树脂碳的石墨化程度，树脂碳中原位生长较多碳纤维和片状碳，碳纤维直径为30～200 nm，长度可达10～20μm；KCl最优添加量为5％（w），此时树脂碳中发现相对较多碳纤维，XRD图谱中出现较明显的石墨d002衍射峰；探索认为碳纤维的生长机制为：高温下KCl熔化后吸收酚醛树脂分解产生的含碳气体，促进固相C原子在液相KCl中扩散，达到C溶解饱和后，在局部不断析出碳原子，再进一步生长成碳纤维或片状碳，同时，熔体中局部C原子形成的浓度梯度，也给碳纤维或片状碳在KCl表面析出提供生长动力。

Effects of the KCl additions （1%,3%,5% and 7% of the phenolic resin mass）on phase composi-tion and microstructure of the resin carbon and the growth mechanism of carbon fibers were investigated by using commercial liquid phenolic resin as carbon source and micron-scaled KCl as catalyzer,mixing,hexa-methylenetetramine solidification treating,carbon-embedded firing at 1 000 ℃ for 3 h in order to accelerate the graphitization of phenolic resin during carbonization.The results show that the graphitization degree of resin carbon is improved by catalysis of KCl,numerous carbon fibers with 30 -200 nm in diameter and 10 -20μm in length and sheet-like carbon in situ grow in resin carbon.The optimal addition of KCl is 5 mass% when relatively large amount of carbon fibers can be found in resin carbon,and d002 diffraction peak of graphite ap-pears obviously in the XRD pattern.The growth mechanism of carbon fiber is that the molten KCl at high tem-peratures absorbs carbonaceous gas from the decomposition of phenolic resin,accelerating the diffusion of solid C atoms in liquid KCl;after the dissolution of C saturates,carbon atoms separate continuously in local parts to form carbon fiber or sheet-like carbon;meanwhile,the concentration gradient formed by local carbon atoms in the melt offers growth drive for the separation of carbon fiber or sheet-like carbon on KCl surface.