Study On The Growth Of Carbon Nanotubes On Continuous Carbon Fibers Surface And Their Structure And Properties

At the present stage,the growth of carbon nanotubes(CNTs)on the carbon fibers surface by chemical vapor deposition(CVD)is one of the most commonly used method for the preparation of carbon fibers/CNTs multi-scale reinforcements.However,CVD method currently used to grow CNTs on the surface of carbon fibers is batch-style,that is,the CVD reaction is carried out in the sealed CVD furnace.This method can't carry out continuously on large-scale industrial production,and it is difficult to meet the huge market demand.Therefore,the research idea of continuous growth of CNTs in this paper was put forward and the preparation technology of CNTs on the surface of continuous carbon fibers was successfully realized.The major contents include:(1)the effects of different electrochemical modification time on the structure and property of carbon fibers,and the catalyst particles reduced and the growing CNTs morphologies on the carbon fibers surface,(2)the influence ofdeposition temperature,velocity of continuous carbon fibers and catalyst concentration on the growth of CNTs were studied by the one-step and two-step growth,according to whether the reduction of catalysts or the growth of CNTs are carried out at the same time during the CVD process,(3)the structure and property of carbon fibers/CNTs multi-scale reinforcements were investigated.Study on the electrochemical modification of carbon fibers surface shows that electrochemical anodic oxidation could effectively modify the carbon fibers surface,oxidize etching graphite microcrystal structure,increase the surface roughness and the amount of grooves.With the increase of electrochemical treatment time,the oxidation the etching degree of the graphite microcrystalline structure on the surface of carbon fibers became more and more serious and the fine grain strengthening was occurring.The R value of carbon fibers increased and the ordering degree was reduced and the mechanical properties of carbon fibers gradually decreased with the increase of electrochemical treatment time.When the electrochemical modification time was 80s,a large amount of oxygen-containing functional groups,including-C-OH,-C=O,and-COOH,were produced on the surface of the carbon fibers with an increase of 11.46%,8.06%,and 1.10%,respectively.At the same time,the uniform distribution of catalyst particles and CNTs could be obtained by catalytic CVD on carbon fibers surface.Study on the process of growth of CNTs on continuous carbon fibers surface shows that when the deposition temperature was low,few CNTs could be catalyzed.While when the deposition temperature was too high,the catalysts would deactivate and form the ball-shaped impurity.When the velocity of continuous carbon fibers was high,that was the growth time of CNTs was shorter,the amount of CNTs on carbon fibers surface was few with the budding shape.When the velocity of continuous carbon fibers was low,the amount and length of CNTs increased obviously,but the distribution was not very uniform.When the catalyst concentration was low,it couldn't provide enough active sites to grow CNTs.But when the catalyst concentration was high,the CNTs grown on the surface of carbon fibers was easy to agglomerate.In the two-step CVD,when the deposition temperature was 650 ?,the velocity of continuous carbon fibers was 6 cm min-1 and the catalyst concentration was 0.05 M,the uniform distribution of CNTs could be grown on the continuous carbon fibers surface.In the one-step CVD,when the deposition temperature was 650 ?,the velocity of continuous carbon fibers was 3 cm min-1 and the catalyst concentration was 0.05 M,the uniform distribution of CNTs could be grown on the continuous carbon fibers surface.After the growth of CNTs on continuous carbon fibers surface,the thermal stability of carbon fibers became poor,indicated the thermal stability of CNTs was not high.CNTs was a hollow tubular structure with multi-wall,and was the bamboo characteristic.The root of CNTs had penetrated into the graphite structure of carbon fibers,indicated the interaction force between carbon fibers and CNTs was strong which was also proved by the ultrasonic vibration analysis experiment.And the top growth type gave priority to the growth of CNTs.The growth mechanism of CNTs on the surface of carbon fiber was analyzed,and the corresponding model was established.The results of the wetting test showed that the multi-scale reinforcements after CNTs growth had a good wetting with resin under the effect of capillary.The optimum technological parameters were beneficial to prepare the multi-scale reinforcements with high mechanical property.The tensile strength of the multi-scale reinforcements was even increased.The cross section of composites was tested and analyzed.It showed that there was an abrupt interface transition of composites resulting in weak wetting between carbon fibers and resin,as well as debonding and couldn't perform the stress transfer under external force load.However,there was a transition buffer interface in multi-scale reinforced composites,and there was no debonding phenomenon between matrix and resin,which helped to eliminate the internal stress produced by the curing of the composites.It played a critical role in the stress transfer and transfer from resin matrix to carbon fibers reinforcements,which was of great significance for the preparation of high-performance carbon fiber reinforced composites.