SYNTHESIS OF CARBON NANOTUBES BY CVD: EFFECT OF ACETYLENE PRESSURE ON NANOTUBES CHARACTERISTICS

MARIANO ESCOBAR; SERGIO MORENO; ROBERTO J. CANDAL; M. CLAUDIA MARCHI; ALVARO CASO; PABLO POLOSECKI; GERARDO H. RUBIOLO; SILVIA GOYANES

San Carlos de Bariloche, Argentina

Conferencia; 13th International Conference on Solid Films and Surfaces; 2006

Applied Surface Science

It is known that CNTs can be grown on fewtransition metals nanoparticles (Fe, Co, Ni) or with irondoped with transition metals. The dopant has differenteffects on the morphological and structuralcharacteristics of the nanotubes. In this work we describethe effect of tungsten on the morphology on CNT grownon W-doped iron nanoparticles, included into a SiO2matrix.Iron catalyst nanoparticles containing 0, 2, 5 or 10% mol/mol tungsten, were prepared by sol-gel. The solprecursor was prepared by mixing an ethanol solution ofiron nitrate with the adequate amount of tungsten (VI)ethoxide, tetra ethyl orto-silicate and water. Thehydrolysis was catalyzed with hydrofluoric acid. The solwas dried at 80 ºC and firing at 450 º during 10 hr. Thefired xerogel was reduced under a 10% H2/N2atmosphere at 600 ºC. The CNTs were grown under thefollowing general conditions: 2.5% C2H2/N2 with a flowrate of 110 cm3/min, 600 °C synthesis temperature, 180torr over pressure. The products were characterized byHR-TEM, SEM, IR, UV-Vis TGA-DTA and DRX.CNT grown on pure iron nanoparticles were themultiple wall type (MWCNT). They displayed 11-19 nmexternal diameter, with an inner channel of 4-6 nm wide.The walls were 5-4 nm thick, well crystallized, andalmost free of amorphous carbon. The CNT were severalmicrometers long.The presence of 2% mol/mol W(VI) is enough toproduce important changes in the yielding andmorphology of the CNT. The yield was reduced morethan ten times The nanotubes display walls with similarcharacteristics that those grown on pure ironnanoparticles, but the length of the nanotubes wasconsiderably lower: no more than several hundrednanometres.