The Growth And Mechanism Of CuO Nanowires Formed On Carbon Fibers By Thermal Oxidation

Cupric oxide (CuO) nanowire is an important kind of semiconductor nanomaterial. Thermal oxidation is a convenient and easily controlled route of CuO nanowires preparation. The functional composites with microwave absorption behavior can be synthesized by thermal oxidizing copper (Cu) coated carbon fibers.In this thesis, CuO nanowires are prepared on the surface of carbon fibers through combining thermal oxidation and electroless plating. The obtained samples are characterized and analyzed by thermogravimetry analysis, X-ray diffraction (XRD), scanning electron microscope and transmission electron microscope.(1) In this thesis, the regular and uniform copper coating is obtained on the carbon fibers by electroless plating. The CuO nanowires are obtained on the carbon fibers by thermal oxidizing the copper coated carbon fibers,(2) The copper coated carbon fibers are thermal oxidized in air from room temperature to 600℃by 10℃/min, and this process is analyzed via thermogravimetry analysis. The result shows that carbon fibers are beginning to oxidize at about 140℃, and oxidize violently at about 450℃.(3) The nanowires formed by thermal oxidizing copper coated carbon fibers at 400℃for 2h are characterized. The obtained nanowires are dense and almost grow perpendicular to the surface of carbon fiber. The length of nanowires is range from 2μm to 4,4μm, while the diameter of nanowires is about 100nm. The nanowire is characterized to be monoclinic CuO monocrystalline structure.(4) The copper coated carbon fibers are thermal oxidized at different temperature for 2h in order to study the influence of the temperature on the growth of CuO nanowires. The density and size of CuO nanowires obtained at different temperature are both increasing along with the increase of thermal oxidation temperature. The density and size of CuO nanowires reach to maximum at 400℃, and then decrease along with the increase of temperature. When the thermal oxidation temperature increases to 500℃, CuO nanowires disappear, and the surface of oxide is composed of plat particles. The result of XRD exhibits that carbon fibers are completely oxidized and the remains are tube-like CuO.(5) The copper coated carbon fibers are thermal oxidized at 400℃for different time to study the influence of thermal oxidation time on the growth of CuO nanowires. At the prior period of thermal oxidation, there are many hill-like protuberances on the surface. Along with the increase of oxidation time, the density and size of CuO nanowires increase. The hill-like protuberances reduce and tend to be gently. When the thermal oxidation time prolongs to 2h, the density and size of CuO nanowires reach to maximum. The XRD results exhibit that the relative content of Cu and cuprous oxide (Cu₂O) phase reduce with the prolonging of oxidation time, while the relative content of CuO phase increases. After 2h oxidation, Cu₂O phase disappear and there is no CuO nanowires growth, which illustrates that the Cu₂O phase plays an important role in the growth of CuO nanowires. The optimum condition of CuO nanowires synthesis on carbon fibers by thermal oxidation is being thermal oxidized at 400℃for 2h.(6) The growth mechanism of CuO nanowires on carbon fibers is believed to be the combining of stress driven mechanism and short-circuit diffusion. The hill-like protuberances appearing at the prior period of thermal oxidation shows the existence of internal stress. The formation of protuberances is in order to release the internal stress. And the formation of CuO nanowires is also to release the internal stress. The formation of CuO nanowires is a process of short circuit diffusion along the grain boundary of Cu₂O. The important role of Cu₂O phase during the CuO nanowires growth is that Cu₂O phase can not only provide the internal stress but also short circuit diffusion paths which are necessary for CuO nanowires growth during thermal oxidation. Under high thermal oxidation temperature or long oxidation time, the termination of CuO nanowires growth is the result of disappear of Cu₂O phase.In this thesis the flower-like ZnO nanostructures are also synthesized by a convenient solution method.