Fluidized bed chemical vapor deposition of pyrolytic carbon - II. Effect of deposition conditions on anisotropy

Pyrolytic carbon coatings were deposited on top of alumina particles at deposition temperatures from 1250 °C to 1450 °C and with acetylene and acetylene/propylene mixtures at concentrations between 25% and 70%, v/v. The anisotropy of pyrolytic carbon coatings was quantified using electron diffraction and Raman peak intensities, and related to the deposition conditions and microstructure. In correlation with the TEM images, it was found that the value of orientation angle (OA) measured from selected area electron diffraction patterns, increased with increasing deposition temperature and precursor concentration corresponding to a reduction in texture. The effect of temperature was more pronounced for the acetylene/propylene mixture and at low temperatures highly anisotropic material was obtained on a local scale. However, the use of larger TEM selecting apertures showed that the majority of coatings were isotropic overall. A correlation was found between OA and Raman D band intensity which allows quick classification of pyrolytic carbon texture.