The microstructures of pyrolytic carbons deposited in the tumbling bed at various conditions have been examined by polarized light microscopy, scanning electron microscopy and transmission electron microscopy.
It has been proved from the experimental results that the structures of pyrolytic carbons were directly determined by the gas flow patterns adjacent to the deposition surface. The isotropic or laminar structure was deposited in the regions which was affected by gas recirculation while columnar structure was deposited where the gas flow pattern near the deposition surface was laminar viscous or static. The difference between laminar and isotropic structures arised from the relative amount of directly deposited planar carbon and droplet in the deposites, i.e. isotropic structure was mainly composed of droplets or droplet aggregates and laminar structure was formed by continual droplet deposition subsequent to planar carbon deposition over it.
The role of the bed particles in the tumbling bed and density defects in the pyrolytic carbon have been discussed. The deposition kinetics of pyrolytic carbon at low propane concentration showed the apparent activation energy decreasing with temperatures.