The pyrolytic carbon is a new family of carbonaceous materials with structure and properties that can be controlled over wide ranges.
One of the purposes of this research is to develop the tumbling bed as a new system in which the pyrolytic carbon can be obtained. This system consists of a parallel reaction tube equiped so that the gas composition, gas flow rate, temperature and RPM can be controlled. A batch of silica particles and graphite substrate is introduced into reaction tube in order to mix the gas and to rub the surfaces of substrate by rotation of reaction tube.
Another purpose of this research is to study the influences of process variables on the coating density, microstructure, crystallite size and deposition rate. The process variables employed is the deposition temperature in the range of 900 to 1230℃, RPM in the range of 10 to 60 and total gas flow rate in the range of 0.5 to 3.0 1/min.
In the case of the 1050-1230℃, 10-60 RPM and 1.0-3.0 1/min, the pyrolytic carbon has the isotropic structure, which is composed of the small columns. As the temperature increases, the coating density and growth rate increases and the crystallite size is constant. As the RPM increases, the coating density increases, the crystallite size is constant and the growth rate shows the minimum point. As the total gas flow rate increases, the density and crystallite size is constant and the growth rate increases.
Considering the variation of growth rates, it is believed that the rate controlling step is both pyrolysis of propane gas to high molecular weight polymer and diffusion through the gas film. From the studies of microstructure, it is thought that the pyrolytic carbon is deposited both by the homogenious nucleation in the gas phase and by the heterogenious nucleation on the surfaces of substrate.
