Fluidized bed chemical vapor deposition of pyrolytic carbon - I. Effect of deposition conditions on microstructure

The effect of deposition temperature and precursor concentration on the microstructure of pyrolytic carbon (PyC) has been studied by using SEM, TEM, Raman spectroscopy, X-ray diffraction and porosimetry. PyC was produced by fluidized bed chemical vapor deposition (FBCVD) at deposition temperatures from 1250 to 1450 °C and with acetylene and acetylene/propylene mixtures at different concentrations. Changes in the density, anisotropy, and microstructure of PyC, controlled by the deposition temperature and precursor concentration, were correlated to variations in the CVD growth or nucleation mechanism. Raman spectroscopy of PyC showed that the changes in the intensity of the D band and G band, generally used for the measurement of domain size (L_a), cannot be applied for low texture pyrolytic carbons. Previous models explaining fluidized bed chemical vapor deposition have been reviewed and compared with recently developed deposition theories in order to establish a better description of the deposition process.