电热法CVD热解碳及CCVD生长纳米碳的研究

发布时间：2018-04-24 05:38

本文选题：炭纤维 + 电热法　；参考：《华东交通大学》2015年硕士论文

【摘要】：炭/炭复合材料（C/C复合材料）作为新一代高性能的复合材料有着无限广阔的应用前景，随着C/C复合材料应用领域的拓展，更加苛刻的使用环境对其性能及生产效率等的提高提出了更高的要求。本文采用了一种新的C/C复合材料的制备方法即电热法，即利用炭纤维自身的导电性对其直接通电加热，再利用化学气相沉积（CVD）的方法沉积热解碳（PyC），研究了热解碳的结构、形成机理及其对炭纤维表面微晶结构的影响，并通过催化化学气相沉积（CCVD）的方法在炭纤维表面生长了纳米碳，研究了不同电镀工艺和CCVD工艺下纳米碳的形态、生长机理及其影响因素。实验结果表明：（1）较高的加热功率下（50W），热解碳有两种沉积模式。沉积初期，热解碳主要以小球状分子沉积生成球状微晶组织的生长方式生长，随着沉积时间延长为60min，大片状分子沉积的生长方式占主导地位。（2）降低初始加热功率（30W），即降低沉积温度，热解碳的沉积方式主要为大片状的分子沉积生成层状微晶，且沉积1h后形成了结构致密的C/C复合材料。（3）在大的气流作用下，电热法生成的热解碳沿垂直于纤维轴向方向定向生长。（4）CVD热解碳会优先在炭纤维表面的刻蚀点、孔洞等更大的活性点生长，，形成一些无序堆叠的细小碳原子团，使炭纤维表面微晶结构的有序度降低，而碳原子团会组装形成一些小的石墨微晶，故而使炭纤维表面的平均微晶尺寸降低。（5）不同电镀时间下生成的纳米碳可能是颗粒状、木耳状、竹节状、树枝状等，也可能是CNT/CNF。合适的电镀时间下，电镀镍颗粒分布均匀，尺寸合适，有利于生长出CNT/CNF，电镀时间过长，几乎不能生成CNT/CNF。可以通过控制电镀时间来控制镍颗粒的数量、形态和分布等，并进一步控制生成的纳米碳的形态。单晶的镍颗粒催化生长出较直的CNT/CNF或螺旋状的CNT/CNF，多晶的镍颗粒催化生成木耳状、竹节状、树枝状或颗粒状的纳米碳。本实验最佳电镀时间为3min。（6）CCVD生长CNT/CNF后，炭纤维的晶化程度和表面平均微晶尺寸都增大。（7）CCVD工艺3下生长的CNT/CNT晶粒尺寸更大，石墨化度更高。本实验最佳气体流量为：C2H2=80mL/min，N2=200mL/min。（8）沉积时间对CNT/CNF的影响主要有两个阶段。第一阶段为沉积初期，CNT/CNF和热解碳（PyC）的沉积同时进行，前者速率大且CNT/CNF的形貌由镍颗粒的大小和分布决定；第二阶段为沉积后期，镍颗粒失去活性，CNT/CNF几乎停止生长，此时主要为PyC的沉积，另外，镍催化剂和生长的CNT/CNF都能促进和加快PyC的沉积。
[Abstract]:Carbon / carbon composites (C / C composites) as a new generation of high performance composites have an unlimited application prospects, with the expansion of the field of application of C / C composites, The more demanding environment for its performance and production efficiency to raise higher requirements. In this paper, a new preparation method of C / C composite, electrothermal method, is used to deposit pyrolytic carbon PyCn by means of direct electric heating of carbon fiber itself and chemical vapor deposition (CVD) method, and the structure of pyrolytic carbon is studied. The formation mechanism of carbon fiber and its effect on the microcrystalline structure of carbon fiber surface were studied. The carbon nanocrystalline was grown on the carbon fiber surface by catalytic chemical vapor deposition (CVD) method. The morphology of nano-carbon was studied under different electroplating and CCVD processes. Growth mechanism and influencing factors. The experimental results show that: 1) at higher heating power, pyrolytic carbon has two deposition modes. In the early stage of deposition, pyrolytic carbon mainly grew in the form of globular microcrystalline structure formed by the deposition of small globular molecules. With the increase of deposition time to 60 min, the growth mode of large flake molecules was dominant. (2) to reduce the initial heating power by 30 W / W, that is to say, to reduce the deposition temperature, the deposition mode of pyrolytic carbon is mainly formed by large flake molecular deposition to form layered microcrystals, and a compact C / C composite is formed after 1 hour of deposition. 3) under the action of large airflow, the pyrolytic carbon generated by electrothermal method grows in a direction perpendicular to the axial direction of the fiber. Carbon pyrolytic carbon will be preferentially grown at larger active points such as etching points and pores on the surface of carbon fibers, forming some small carbon atoms which are stacked disorderly, thus reducing the order of microcrystalline structures on the surface of carbon fibers. The carbon cluster assembles some small graphite microcrystals, which reduces the average microcrystalline size of the carbon fiber surface. The nanocrystalline carbon produced under different electroplating time may be granular, auricular-shaped, bamboo-shaped, dendritic, or CNT / CNF. When the electroplating time is suitable, the distribution of nickel particles is uniform and the size is suitable, which is beneficial to the growth of CNT / CNF, and the electroplating time is too long to produce CNT / CNF. The amount, morphology and distribution of nickel particles can be controlled by controlling the electroplating time, and further controlling the morphology of the resulting carbon nanoparticles. Single crystal nickel particles catalyze the growth of straight CNT/CNF or spiral CNT / CNF, and polycrystalline nickel particles catalyze the formation of auricular-shaped, bamboo-shaped, dendritic or granular nano-carbon. The optimum electroplating time is 3 min. The degree of crystallization and the average surface microcrystalline size of carbon fibers increased after CNT/CNF growth. The grain size and graphitization degree of CNT/CNT grown under CCVD process 3 are larger and higher. The best gas flow rate in this experiment is 80 mL / min N _ 2N _ 2 N _ 2N _ 2 / min. The influence of deposition time on CNT/CNF has two stages. The first stage is the deposition of CNT / CNF in the early stage of deposition and the deposition of pyrolytic carbon (PyC) at the same time. The former has a high rate and the morphology of CNT/CNF is determined by the size and distribution of nickel particles, the second stage is the late stage of deposition, when the nickel particles lose their activity, the CNT / CNF almost stops growing. In addition, both the nickel catalyst and the growing CNT/CNF can promote and accelerate the deposition of PyC.
【学位授予单位】：华东交通大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TQ127.11;TB383.1

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