Study On Pyrolytic Carbon By CVD And The Nano Carbon By CCVD Under The Electric Heating Method

As a new generation of high performance composite materials, carbon/carboncomposites (C/C composites) have a broad application values. With the expandingapplications of C/C composites, more requirements for the properties of C/C composites arebrought forward in harsh application environment.In this paper, a new method of preparation of C/C composites was adopted which iselectric heating method, the method used the conductivty of carbon fiber to heat carbon fiber.The structure and formation mechanism of pyrolytic carbon (PyC) were studied by themethod of chemical vapor deposition (CVD). The effects of pyrolytic carbon on the surfacemicrocrystalline structure of carbon fibers were also studied. The nano carbons were grownon carbon fibers by the method of catalytic chemical vapor deposition (CCVD). Themorphology and growth mechanism of nano carbon and the influence factors by differentplating and CCVD process were studied. The experimental results show that:(1)There are two kinds of deposition of pyrolytic carbon under a high heating powerdensity (50W). The pyrolytic carbon grows to spherical microcrystalline tissue by thedeposition mode of small globular molecules in the intitial deposition. The deposition modeof large patches of molecular was dominant with the deposition time extend to60min.(2)The pyrolytic carbon is mainly a laminated structure with the reducing of the initialheating power (30W) which means the reducing of deposition temperature. The C/Ccomposites with a dense structure were prepared after deposite for1h.(3)The pyrolytic carbon grows along the vertical deriction of the axial deriction ofcarbon fibers in large airflow.(4)The CVD pyrolytic carbon preferentially grows on the active point on the surface ofcarbon fibers to formating some disordered stacking carbon clusters which made the orderdegree of carbon fibers decreased. The surface average crystallite size of carbon fiber reduceswhile the carbon atomic assemble to form some graphite crystallite.(5)The structure of nano carbons can be granular, fungus shaped, bamboo shaped,dendritic and even CNT or CNF. Uniformly distributed and appropriate size of electroplatingnickel particles can be obtained by reasonable electroplating time which is favor to the growthof CNT/CNF. CNT/CNF almost can not generate by too long plating time. The size, quantity,morphology and the distribution of nickel particles can be controlled by controlling theplating time. Straight and spiral CNT/CNF can be obtained by single-crystal nickel particles. Fungus shaped, bamboo shaped, dendritic shaped and granular shaped nano carbon can beobtained by polycrystalline nickel particles. The best plating time in this paper is3min.(6)The crystallization degree and average crystallite size both increased after the growthof CNT/CNF by CCVD.(7)The grain size and graphitization degree of CNT/CNF under CCVD craft3is larger.The best gas flow in this experiment were: C2H2=80mL/min，N2=200mL/min.(8)The effects of deposition time on CNT/CNF mainly have two stages. The first stage isthe initial stage of deposition, the growth of CNT/CNF and deposition PyC are bothexistences. The former has a higher rate and the morphology of CNT/CNF is determined bythe size and distribution of nickel particle; The second stage is the post stage of deposition,catalyst particle lose its activity, so the CNT/CNF is even stop growing, at this time, thedeposition is mainly the depositon of PyC. Besides, The depositon of PyC can be promotingand accelerating by both nickel catalyst and the growth of CNT/CNF.