Chemical vapor deposition synthesis of carbon spheres: Effects of temperature and hydrogen

Carbon spheres (CS) of relatively uniform size, ranging from 200 to 350 nm, were synthesized using the noncatalytic thermal Chemical Vapor Deposition (CVD) method. The effect of temperature (650 degrees C-1050 degrees C) along with hydrogen (H-2) and argon (Ar) in acetylene (C2H2) on the carbon spheres were studied using Scanning Electron Microscopy (SEM) and Raman spectroscopy. Morphological studies show that relatively uniform carbon spheres can be synthesized by pyrolysis of acetylene under H-2 and Ar at temperatures above 950 degrees C in an atmospheric pressure CVD. The broad peaks in the XRD spectrum and I-D/I-G ratio of 0.85 obtained from Raman Spectroscopy reveals that the carbon spheres synthesized are amorphous in nature. The morphological studies using SEM on different concentrations of Ar and H-2 during the synthesis indicate that the concentration of carrier gases profoundly affects the morphology. The presence of Ar gives smooth carbon spheres and H-2 contributes to the relative uniformity of the carbon spheres synthesized. A detailed study was carried out to analyze the influence of the concentration of H-2 using SEM, Raman spectroscopy and FTIR. The effect of low concentration of H-2 along with Ar and acetylene reduces the defects and the graphitization degree obtained was 0.85. The present study also infers that high concentrations of H-2 deteriorates the morphology of carbon spheres due to the excess of C-H functional group formation.