【作者】 冯建民；

【导师】 李亚利；

【作者基本信息】 天津大学 ， 材料学， 2012， 博士

【摘要】 碳纳米管是高强高导电并有其它多功能特性的一维纳米材料,由其构成的宏观纤维有巨大的应用潜力,可用于新型超强纤维,传感器和智能纺织等方面。纤维的规模化制备是实现上述应用的前提。化学气相法是在气流中生长碳管,碳管在气流中组装成纤维,机械操纵连续纺出纤维的方法。化学气相法一步高效,易规模化,但气相流须使用氢气,存在潜在危险。本论文针对化学气相法制备纤维安全问题,以氩气替代氢气,在水为控制助剂的条件下,乙醇为碳源,二茂铁为催化剂,噻吩为促进剂,在安全气相流中纺出连续碳管纤维。纤维比强为0.75GPa/(g/cm3),导电率为0.5×105S/m,与氢气流中制备的纤维相当。纤维抗氧化性优,空气流中氧化失重开始温度为550oC,比对应氢气流中制备的纤维高50oC。水是纤维形成关键,水去除非晶碳,保持碳管表面干净,促进碳管组装形成纤维。同样通过加水，在氮气和氦气气流中也纺出了碳管纤维。水助氩气流纺出的纤维中的碳管表面缺陷多，活性高,是由于高温下水具有氧化刻蚀作用。X射线光电子能谱分析纤维碳管表面,氧含量高,原子百分比为10.2at.%,是氢气流纤维(4.6at.%)的2.2倍。纤维表面富含含氧基团,活性高,能溶于乙醇,而氢气流中制备的纤维则不能。碳管外层覆盖的缺陷翘曲碳层,在纤维拉伸断裂时,能阻碍中碳管间的滑移,可增强纤维强度。通过观察分析氢气流,氩气流和水助氩气流产物结构,对比气流中纤维形成的行为,推断出小直径碳管利于在气相流中组装成纤维。碳管直径越小越利于组装,且可纺性趋好。氢气流和水助氩气流产物多为双壁管,直径1-5nm。氩气流中不能形成纤维是因为碳管直径粗,80-200nm,相互间范德华力作用小,不利于组装形成纤维。氩气流产物结构为双壁碳管外裹非晶碳层。双壁碳管与非晶碳层分立,机械力作用下能将双壁碳管抽出。水蒸汽氧化也可将包裹层剥离,端部非晶碳层首先被剥离,形成以双壁碳管为凸出端的针型结构的纤维。借助非晶碳层,可操纵移动难于用现有的一般微纳操纵办法移动的双壁碳管。在扫描电镜的监控下,用微机械手拾取针型结构,将其竖立粘在原子力显微镜商用探针上,构建出了双壁碳管为凸出针尖的探针示意模型。此外用水蒸汽氧化处理氩气流碳管,在碳管壁上氧化形成缺陷,再通入碳源乙醇,在碳管表面原位生长出石墨烯翘曲结构,获得了碳管/石墨烯复合材料。碳管/石墨烯缺陷多,富含氧基团,氧含量为12.9at.%碳管/石墨烯表面起伏的翘曲石墨层结构利于增强复合材料,与聚硅氧烷(PDMS)复合,能有效提到材料强度，优于商用多壁碳管;利于负载纳米颗粒,能均匀负载CdS量子点,而商用光滑壁碳管则不能。更多还原

【Abstract】 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.更多还原