Abstract
Acoustically modulated methane jet diffusion flames were used to enhance carbon nanostructure synthesis. A catalytic nickel substrate was employed to collect the deposit materials at sampling position z = 10 mm above the burner exit. The fabrication of carbon nano-onions (CNOs) and carbon nanotubes (CNTs) was significantly enhanced by acoustic excitation at frequencies near the natural flickering frequency (ƒ = 20 Hz) and near the acoustically resonant frequency (ƒ = 90 Hz), respectively. At these characteristic frequencies, flow mixing was markedly enhanced by acoustic excitation, and a flame structure with a bright slender core flame was generated, which provided a favorable flame environment for the growth of carbon nanomaterials. The production rate of CNOs was high at 20 Hz (near the natural flickering frequency), at which the gas temperature was about 680 °C. Additionally, a quantity of CNTs was obtained at 70–95 Hz, near the acoustically resonant frequency, at which the gas temperature was between 665 and 830 °C. However, no carbon nanomaterials were synthesized at other frequencies. The enhanced synthesis of CNOs and CNTs is attributed to the strong mixing of the fuel and oxidizer due to the acoustic excitation at resonant frequencies.
Highlights
IntroductionCarbon nanotubes (CNTs) have excellent mechanical, thermal, optical, and electrical properties [1,2]
Carbon nanotubes (CNTs) have excellent mechanical, thermal, optical, and electrical properties [1,2].They have been used for many electronic, optical, and magnetic applications, such as gas sensors [3], high-temperature superconductors [4], scanning microscope tips [5], and hydrogen storage media [6].Many methods have been proposed for the synthesis of carbon nanotubes (CNTs), including arc discharge [7], laser ablation [8], spray pyrolysis [9], and chemical vapor deposition (CVD) [10]
It is noteworthy that carbon nano-onions (CNOs) were synthesized in a sooty yellow core flame, whereas CNTs were fabricated in a blue core flame
Summary
Carbon nanotubes (CNTs) have excellent mechanical, thermal, optical, and electrical properties [1,2]. Many methods have been proposed for the synthesis of CNTs, including arc discharge [7], laser ablation [8], spray pyrolysis [9], and chemical vapor deposition (CVD) [10]. Most of these methods are expensive and complex. It has been shown that flame synthesis makes possible the low-cost mass production of CNTs [11]
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