Synthesis of Fe-Mo catalyst surfaces using plasma-assisted surface alloying for carbon nanotube growth by PECVD

Abstract

Transition metal nanoparticles can act as seeds for the nucleation and growth of carbon nanotubes (CNTs). Adding molybdenum (Mo) to an iron (Fe) catalyst offers synergistic and beneficial features that enhance the yield of these nanostructures and influence their morphological and structural aspects. This study explored the development of Fe-Mo catalyst surfaces for CNT synthesis using a novel plasma-assisted surface alloying process. AISI 1005 low-carbon steel specimens were surface-alloyed with Mo by employing a DC argon-hydrogen mixed glow discharge at three different temperatures (800 °C, 1150 °C, and 1200 °C with an additional diffusion step). Subsequently, the Fe-Mo surfaces were used for CNT synthesis at 700 °C under a plasma-carburizing atmosphere (20 % CH₄ + 80 % H₂). The morphological, chemical, and structural aspects were assessed using material characterization techniques. The results indicate that Mo-enrichment temperatures and the resulting Mo content on Fe-Mo surfaces directly influence catalytic CNT growth and nanostructure morphology. Mo-rich intermetallic phases up to 71 wt% Mo hinders the CNT nucleation, while Mo in solid solution (0.7 wt% Mo) enhances CNT yield and improves their structural aspects. This study proves the feasibility of plasma surface alloying to produce Fe-Mo catalytic surfaces by controlling the processing parameters.