Study On The Process Parameters Of Continuous Growth Of Carbon Nanotubes On Carbon Fiber Surface By CVD Method

Chemical vapor deposition(CVD)is a method for in-situ growth of carbon nanotubes(CNTs)on the surface of carbon fibers.In this method,carbon fiber as the substrate is placed in a carbon source gas,and under the action of a catalyst loaded on the surface of the carbon fiber,the carbon source gas is cracked to generate active carbon atoms,thus growing CNTs.CVD method is considered to be one of the most effective and practical methods for the growth of CNTs on carbon fiber surfaces,which can effectively control the production process parameters and the morphology of CNTs.In this paper,the continuous preparation of CNTs/carbon fiber was successfully realized by using the equipment designed by the laboratory.The influence of different experimental conditions on the preparation of CNTs/carbon fiber was studied by adjusting the process parameters.This paper focuses on the following four aspects:(1)the effects of different current intensities on the surface of carbon fibers and the preparation of CNTs/carbon fibers reinforced by electrochemical oxidation;(2)the effect of copper as catalyst on the growth of CNTs;(3)the effects of different reduction temperatures and time on the morphology of CNTs and the properties of CNTs/carbon fiber;(4)The effects of different growth time,temperature and atmosphere on the preparation of CNTs/carbon fiber during CVD were studied.The electrochemical oxidation treatment on the surface of carbon fiber showed that the carbon fiber could be activated by electrochemical oxidation treatment,adding C-OH,C=O,COOH and other oxygen-containing functional groups.Electrochemical oxidation method can uniformly modify the surface of each monofilament,forming grooves to increase the surface roughness and improve the wettability with the catalyst precursor solution.The resulting grooves can prevent catalyst adhesion caused by solvent flow and promote the uniform loading of catalyst on the surface of carbon fiber,which is conducive to the uniform growth of CNTs.However,the electrochemical treatment will cause damage to the carbon fiber,destroying the graphite structure of the carbon fiber,generating defects in the surface layer and reducing the tensile property.Therefore,the current intensity should be controlled reasonably in the electrochemical treatment process to prevent excessive damage to the carbon fiber.The experimental study shows that,When the current intensity is 0.4A,the uniform loading of catalyst can be realized on the basis of retaining good mechanical properties.Change catalyst component research shows that:metal nickel as catalyst,additives when adding copper as the catalyst,catalytic activity was promoted,the decomposition of acetylene is more efficient,catalyst metal particles on the surface of the carbon fiber dispersion improved,and the optimum process parameters under the condition of the preparation of CNTs/carbon fiber reinforced body,maintain the excellent tensile strength.Studies on temperature and time in catalyst reduction conditions show that the increase of reduction temperature and time will increase the diameter of CNTs.By separating the catalyst reduction process from the growth process of CNTs,CNTs/carbon fiber with higher graphitization degree can be obtained.Studies on the growth temperature,time and atmosphere during the CVD process showed that the increase of the growth temperature could increase the activity of the catalyst and increase the growth abundance,length and diameter of CNTs.However,the combined action of high temperature and catalyst will destroy the ordered graphite structure on the surface of carbon fiber,and when the growth temperature reaches 700?,the catalyst will be poisoned and deactivated,and the activated carbon atoms from cracking will gather on the surface of carbon fiber into amorphous carbon and other impurities.The morphology of CNTs could be changed by adjusting the growth time.When the growth time was 4 min,sparse and short CNTs appeared on the surface of carbon fibers.After 8 min,CNTs covered the surface of carbon fibers,and after 12 min,the length of CNTs on the surface of carbon fibers increased.Excessive growth time leads to high entanglement of CNTs and the formation of impurities on the surface of carbon fiber.Reducing the growth time can reduce the interaction between metal nanoparticles and the surface of carbon fiber,weaken the etching on the surface of carbon fiber,prevent the degradation of mechanical properties of carbon fiber,and also avoid the reduction of catalyst activity.Hydrogen plays an important role in the growth process of CNTs.Adjusting the flow rate of hydrogen can control the cracking rate of carbon source.The flow rate of 0.3L/min hydrogen can inhibit the decomposition of carbon source and grow pure CNTs.