| Summary: | 碩士 === 國立成功大學 === 機械工程學系碩博士班 === 95 === In the present study, we aim at investigating the synthesis of carbon nano-structures including carbon nanotubes (CNTs) and carbon nano-spheres on a catalytic nickel substrate using normal jet diffusion flames, with particular emphasis on the influence of mixed fuel (methane and ethylene) on carbon nanomaterials growth. The flame appearance, flame structure, flame stability, and soot layer are experimentally observed using image processing techniques. Meanwhile, the temperature distributions at various axial and radial positions are measured by using an R-type thermocouple. Moreover, we employ the bare nickel substrate or Ni(NO3)2-coated nickel substrate to collect deposit materials. Finally, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Raman spectroscopy are utilized to characterize the morphology and microstructure of condensed carbon deposits and their formation mechanism in the combustion environment.
The SEM, TEM, HR-TEM and EDS images show that carbon nanotubes and carbon nano-spheres are successfully synthesized at suitable operating conditions. Many carbon nanotubes are harvested in the soot zone of flame whose temperature range is about 750~1250℃. Curved and entangled tubular multi-walled canbon nanotubes are found, which have only typical straight tubular structures. In addition to curved CNTs, a small amount of helically coiled tubular CNTs are also synthesized when the sampling position is located at a distance of 1.5~2 mm from the soot zone where the temperature is about 1048~1082℃. However, carbon nano-spheres can be observed only at higher height above of burner (i.e. 15 and 10 mm) and higher methane concentration, 30%, for fixed ethylene concentration, 5%. The temperature range of carbon nano-spheres formation is around 1000℃ and 1300~1400℃. It is of interests to note that the formation zones of carbon nanotubes and carbon nano-spheres are different although they can be synthesized at the same operating conditions.
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