Continuous synthesis of high-crystalline carbon nanotubes (CNTs) is achieved by reconfguring the injection part in the reactor that is used in the foating catalyst chemical vapor deposition (FC-CVD) process. The degree of gas mixing is divided into three cases by adjusting the confguration of the injection part: Case 1: most-delayed gas mixing (reference experiment), Case 2: earlier gas mixing than Case 1, Case 3: earliest gas mixing. The optimal synthesis condition is obtained using design of experiment (DOE) in the design of Case 1, and then is applied to the other cases to compare the synthesis results. In all cases, the experiments are performed by varying the timing of gas mixing while keeping the synthesis conditions constant.
Production rate (Case 1: 0.63 mg/min, Case 2: 0.68 mg/min, Case 3: 1.29 mg/min) and carbon content (Case 1: 39.6 wt%, Case 2: 57.1 wt%, Case 3: 71.6 wt%) increase as the gas-mixing level increases. The amount of by-products decreases step�wise as the gas-mixing level increases. The IG/ID ratio increases by a factor of 7 from 10.3 (Case 1) to 71.7 (Case 3) as the gas-mixing level increases; a high ratio indicates high-crystalline CNTs. The radial breathing mode (RBM) peak of Raman spectrograph is the narrowest and sharpest in Case 3; this result suggests that the diameter of the synthesized CNTs is the most uniform in Case 3. This study demonstrates the importance of confguration of the injection part of the reactor for CNT synthesis using FC-CVD.