Investigation of hafnium, tantalum, and ruthenium as catalyst stabilizers in the iron-catalyzed growth of carbon nanotubes from ethylene

We investigated growth of carbon nanotubes (CNTs) by catalytic chemical vapor deposition (CVD), using catalysts of iron combined with heavy refractory metals including hafnium, tantalum, and ruthenium to increase the ultimate length to which the CNTs grow. The refractories act as diffusion inhibitors, slowing erosion, and deactivation of catalyst nanoparticles, resulting in the growth of longer CNTs than grow from pure iron catalyst. Inclusion of hafnium or tantalum prolongs the CNT growth time; however, both metals decrease the growth rate of CNTs vs pure iron. CNTs grown from Fe/Hf catalysts reach greater ultimate length than CNTs grown from pure Fe despite the slower growth rate, while ultimate CNT length from Fe/Ta catalysts is substantially less than given by pure Fe. Fe/Ru catalyst behaves interestingly, showing faster growth rate, shorter growth time, and greater ultimate length than CNTs grown from Fe. For all catalysts, the CNTs produced were primarily double-walled (DWCNTs).