Carbon/carbon composites were fabricated by pulse chemical vapor infiltration (Pulse CVI) in which cycles of evacuation of the vessel and introduction of the source gas were repeated sequentially. A propane gas was used as a source gas and a nitrogen gas was used as a carrier gas.
The effects of deposition temperature (900, 1100 ℃), reactant gas concentration (20, 100 %), gas flow rate (600, 1800 SCCM), gas introducing time (2, 10 $\sec$), evacuation time (10, 30 $\sec$) and pulse number (1000, 5000) on the degree of densification of phenol-based carbon/carbon preform were studied adopting experimental design method.
According to the analysis of variance (ANOVA) of the experimental data, the important parameters were deposition temperature, gas introducing time and pulse number. An optimum processing parameters on pulse CVI for densification under given conditions were found to be 900℃ of deposition temperature, 100 % of reactant gas concentration, 1800 SCCM of flow rate, 10 sec of gas introducing time, 30 sec of evacuation time and 5000 of pulse number.
Each parameter was varied with the other parameters being constant. Deposition rate increased with increasing deposition temperature at low deposition temperature region, but decreased with increasing deposition temperature at high deposition temperature region. Weight gain increased with increasing gas concentration. Gas flow rate did not affect the bulk density so much. Bulk density increased with increasing gas introducing time. When the ratio of evacuation time to gas introducing time was 4, weight gain was maximum. Bulk density increased with increasing pulse number.
The deposition temperature at which deposition rate was maximum was changed when gas introducing time was changed. When gas introducing time became longer, the deposition temperature became lower.
The optimum deposition condition is thought to be 850℃ of deposition temperature, 100% of reactant gas concentration, 3600 SCCM of gas flow rate, 5 sec of gas introducing time, 20 sec of evacuation time and 10,000 of pulse number.
