Rhenium and Molybdenum as Diffusion Inhibitors in Catalytic Metal Particles for growth of Ultra-Long Carbon Nanotubes (C
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MRS Advances © 2020 Materials Research Society DOI: 10.1557/adv.2020.162
Rhenium and Molybdenum as Diffusion Inhibitors in Catalytic Metal Particles for growth of Ultra-Long Carbon Nanotubes (CNTs) Michael J. Bronikowski1 and Melissa King1 1
Dept. of Chemistry, Biochemistry and Physics, University of Tampa, Tampa, FL
ABSTRACT
Bulk production by Chemical Vapor Deposition (CVD) of ultra-long Carbon Nanotubes (CNTs) with lengths greater than several centimeters is desirable for materials applications, but is not presently feasible. A principal reason for this limitation is cessation of CNT growth due to erosion of the nano-sized catalyst particles from which the CNTs nucleate and grow: at elevated CVD growth temperatures, atoms of catalytic metal detach and diffuse away from the particles, resulting in erosion and eventual deactivation of the particles. Recently, a novel idea was introduced to slow this diffusion and erosion by including heavy refractory metals with the catalyst metals in the nanoparticles. Here are presented recent and ongoing investigations into this method. The metal system investigated uses iron as catalyst and rhenium as diffusion inhibitor. Results show that inclusion of Re in the catalyst particles will substantially increase the catalysts particle lifetimes, and hence the growth time of the CNTs produced. These results are compared to previous results obtained using the iron/molybdenum system of catalyst/inhibitor.
INTRODUCTION There is ongoing interest in developing materials based on Carbon Nanotubes (CNTs) due to CNTs’ outstanding mechanical, electrical and thermal properties [1 - 3]. However, to take full advantage of CNTs’ material properties, it appears necessary to produce large-scale quantities of CNTs with lengths comparable to the macroscopic sizes (centimeters-to-meters) of the envisioned applications [4 - 5]. CNTs are typically produced using metal-catalyzed Chemical Vapor Deposition (CVD): nanometer-sized particles of catalytic metals are exposed to carbonaceous gases at elevated temperatures under conditions in which the gases will decompose to release their carbon atoms, which form into nanotubes. Past work on maximizing the lengths of the CNTs grown has
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consistently shown that, under any such sets of conditions, the CNT formed will continue to grow for only a certain length of time, after which the growth stops, typically giving CNTs with maximum lengths of 1 cm or less [6 - 21]. While exceptions exist for the growth of individual ultra-long (tens of cm) CNTs [6], production of macroscopic quantities (grams to kilograms) of ultra-long CNTs continues to elude researchers. One key mechanism in cessation of CNT growth is believed involve erosion of the catalyst particles due to detachment and diffusion of catalytic metal atoms away from the partic
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