The effect of pyrolysis temperature on the synthesis of carbon nanotubes by a flame method

Abstract

Nowadays, many investigations have been done for the synthesis of carbon nanotubes by diffusion flame using a variety of carbon sources. However, the change law of the temperature required for the reaction is the lack of attention. Carbon nanotubes have been synthesized from methane on a Fe–Mo/Al2O3 catalyst by a V-shape pyrolysis flame in this paper. The effect of pyrolysis temperature on the growth of the carbon nanotubes has been studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Raman spectroscopy. The optimum pyrolysis temperature of pyrolysis-flame-synthesized carbon nanotubes using methane as the carbon source has been confirmed to be 1100 degrees C, at this pyrolysis temperature, the yield of CNTs was the higher, the diameter was the smaller and the graphitization degree was the higher. Four optimum pyrolysis temperatures using different carbon sources (CH4, C2H4, C2H2, and CO) have been compared and analyzed. The variation of the optimum pyrolysis temperature was consistent with the change of the chemical bond energy of the four carbon sources. And the ionization rate coefficients of these gas molecules in an electric field have been calculated to verify that breaking the chemical bonds of the different gas molecules required corresponding amounts of energy. Therefore chemical bond energy directly affected the pyrolysis temperature for these carbon sources during the synthesis of CNTs.