A new formation mechanism of isotropic, laminar, and columnar carbons is suggested. For this, a low RPM (≤2.4 RPM) tumbling bed and a stationary bed were used. Deposits were made on graphite substrates from propane and methane at low temperatures below 1200℃.
Flow visualizations were made to support the new deposition mechanism.
The microstructures of pyrolytic carbons were very dependent on the flow pattern of reactant gas, RPM, hydrocarbon concentration, the nature of hydrocarbon, and on the geometry of the bed.
The suggested deposition mechanism can also be applied to the pyrolytic carbons deposited in fluidized bed or in stationary bed as well as in tumbling bed. Especially isotropic carbon can be obtained even in stationary bed, only if the requirements for deposition of isotropic carbon suggested by this study are satisfied.
Deposition rate of pyrolytic carbons deposited in a tumbling bed was analysed with respect to the deposition mechanism.
Scanning electron microscopies of fracture surfaces of crossection of pyrolytic carbons deposited in the tumbling bed could clarify the factors influencing the size of growth features of isotropic carbon and explain the role of gas-recirculation on the microstructures of pyrolytic carbons. And the process of the deposition of gas-borne droplets on substrate in tumbling bed below 2.4 RPM was sugqested.
The reason why the size of soot collected on trap in fluidized bed is smaller than that of growth feature of isotropic carbon observed with TEM was explained.
It is suggested how and why each type of microstructural component could be formed with deposition temperature, transmission electron microscopies of which can explain the change of its density with deposition temperature.