Effect of depositions condition on the microstructure of C/C minicomposite

C/C minicomposites were manufactured by CVI with propylene as resource gas and Ar as diluent gas. Effects of deposition temperature, the flow rate of propylene and total system pressure on the microstructure of C/C minicomposites were investigated. Deposition conditions are as follows: deposition temperature ranging from 870 °C to 1000 °C, the flow rate of propylene from 10 to 60 ml/min, and total system pressure from 3 to 16 kPa. The results revealed: The deposit distributes non-uniformly as increasing the deposition temperature or total system pressure. The effect of the flow rate of propylene on the distribution of deposit observes different principles at different deposition temperatures. If the deposition temperature rises to 900 °C, the deposit distributes more non-uniformly as increasing the flow rate of propylene. The morphology of deposit varies with deposition condition, such as smooth, droplet-like or spike-like. Deposition mechanism varies with deposition condition. It can be surface reaction nucleation and growth, heterogeneous nucleation of liquid droplet on carbon fiber or gas-borne nuclei-growth. With the principle of nuclei-growth of crystal and the method of phenomenology, the changes of deposition mechanism and the morphology of pyrolytic carbon with deposition condition were explained successfully. The effect of deposition condition on deposit homogeneity stems from the effect of deposition condition on the CVI kinetics and the deposition mechanism of pyrolytic carbon.