Fabrication Of Continuous Carbon Nanotube Fibers By A Safe CVD Method

Carbon nanotubes (CNTs) have one-dimensional nanostructure, ultra-highstrength, high electrical conductivity and other functional properties. The chemicalvapor deposition (CVD) spinning process is a promising method for the fabrication ofcarbon nanotube yarns, CNT assembling into macroscopic yarns in the gas flow andspun continuously by a mechanical maniplication. The current process relies on ahydrogen flow in the high-temperature CVD gas-flow reaction which brings a safetyconcern in the production, especially at mass production.In this thesis, we report the fabrication of carbon nanotube (CNT) yarns by thisCVD process from a gas flow reaction in an argon flow. The spinning is achieved bythe introduction of a certain amount of water in the ethanol carbon source to suppressthe amorphous carbon deposition on the CNTs. With the addition of water in thereaction, assembling CNTs are achieved in the gas flow forming a continuous CNTintegrate that allows continuous spinning as a CNT yarn. The yarn specific strength is0.75GPa/(g/cm3), electrical conducitity is0.5×105S/m, which is about equivalentwith the yarn spinning from hydrogen. The yarns have a good oxidation resistance.The initial temperature of oxidization loss weight is550oC in the air, which is50oChigher than that of the yarn from hydrogen. The spinning of CNT yarns is alsoachieved in helium or nitrogen flows in the water-assisted CVD reaction.The CNTs in yarn spun from argon flow assisting with water have many surfacedefects owe to the oxidization corrosion of water at high temperature. The oxygencontent on the surface of CNTs in the yarn is10.2at.%(atom percentage), which is2.2times higher than that of the yarn from hydrogen flow (4.6at.%). The yarn couldbe dissoloved in ethanol solution through ultrasound treatment due to the rich oxgencontaining groups on the surface of CNTs.Through observation and analysis of the yarn prepration process in hydrogen,argon and argon assisting with water, the small diameter CNT is believed to beconductive when assemble into yarns in the gas flow. The CNTs assembly into yarnsin hydrogen flow and argon flow with water are double walled CNT with the diameterof1-6nm. The CNTs can not assemble into yarns in argon are multi-walled CNT withdiameter of80-200nm. The mutual van der Waals’ forces among big diameter CNT isweak, which does not favor CNTs assembly into fibers. Multi-walled CNTs from argon flow have a core-shell structure, which is composed of inner core double walledCNT and amorphous carbon layer shell. The inner core and shell could be seperated.The inner double walled CNT could be extracted out. The amorphous carbon layershell can also be peeled off by water vapor. Normally, the amorphous carbon shell atthe end of CNT is first removed and obtains a needle structure with a protrudingdouble walled CNT end. With the help of amorphous carbon layer shell, the needlestructure can be manipulated to move in three-dimensional space. Under scanningelectron microscopy observation, micro mechanical hand is used to pick up the needlestructure and vertically stick to a commercial atomic force microscope probe, adouble-walled CNT atomic force microscope probe model is constuctued.In addition, multi-walled CNT from argon flow is treated by water vapor, andthen put into ethanol as the carbon source. Graphene nano sheet (GNS) warp structurein-situ grows on the surface of CNT. The warp GNS on the surface of the structure ishelpful for reinforcing composite materials and is favor of supported nanoparticles,the comosiptes combining with polydimethylsiloxane (PDMS) are more stronger thancommercial multi walled CNT with a smooth surface. The warp GNS is also helpfulto load CdS quantum dots on its surface uniformly.