Development of carbon nanotube synthesis mechanism based on effects of thermo-physical properties of carrier gases

This study proposes a new synthesis mechanism of carbon nanotubes (CNTs) or carbon nanotube fibers (CNTFs) by a deep-injection floating catalyst chemical vapor deposition (DI-FCCVD), where a heavier inert gas, such as Ar, plays critical roles in simultaneously improving the crystallinity and productivity of CNTs or CNTFs. Heavier inert gases have lower thermal conductivities than lighter inert gases. Hence the addition of heavier inert gases in H₂ ambient leads to the formation of a larger space at an exit of the injection tube with a lower temperature gradient to the synthesis temperature (1350 °C). This larger space allows carbon and catalyst precursors to fully decompose and prevents decomposed catalyst particles from agglomerating into too large catalyst particles, resulting in the significantly enhanced synthesis of CNTs or CNTFs.