Growth and passivation of individual carbon nanoparticles by C2H2 addition at high temperatures: Dependence of growth rate and evolution on material and size

Absolute kinetics for reactions of C2H2 with a series of similar to 60 individual carbon nanoparticles (NPs) from graphite, graphene, graphene oxide, carbon black, diamond, and nano-onion feedstocks were measured for temperatures (T-NP) ranging from 1200 to 1700 K. All the NPs were observed to gain mass by carbon addition under conditions that varied with feedstock but with large variations in initial growth rate. Long reaction periods were studied to allow the evolution of growth rates over time to be observed. Diamond NPs were found to passivate against C2H2 addition if heated above similar to 1400 K, and the highly variable initial reactivity for carbon nano-onions was found to depend on the presence of non-onion-structure surface carbon. For graphitic and carbon black NPs, three distinct growth modes were observed, correlated with the initial NP mass (M-initial). Smallest graphitic and carbon black NPs, with masses 50 MDa, grew rapidly and continuously, adding up to similar to 300% of M-initial with no sign of rate slowing as long as C2H2 was present. The efficiencies for C2H2 addition and etching by O-2 are strongly correlated, but the correlation changes as the NPs passivate. Growth and passivation mechanisms are discussed.

Automated summary

We measured the absolute kinetics for reactions of C2H2 with a series of approximately 60 individual carbon nanoparticles from different feedstocks. The growth rates of the nanoparticles varied significantly depending on the feedstock. Diamond nanoparticles passivated against C2H2 addition above a certain temperature, and the reactivity of carbon nano-onions was found to depend on the presence of non-onion-structure surface carbon. Graphitic and carbon black nanoparticles exhibited three distinct growth modes correlated with their initial mass. The efficiencies of C2H2 addition and O-2 etching were strongly correlated, but this correlation changed as the nanoparticles passivated.