Session: Physical Chemistry Poster:

The kinetics of carbon nanoparticle (NP) growth by high-temperature reaction with unsaturated hydrocarbons such as acetylene are important in soot growth, but also of interest from a fundamental perspective. For example, the reaction is expected to depend strongly on the surface structure of individual NPs, which evolve during a reaction.
Understanding the effects of structural heterogeneity requires the use of a single NP kinetics method, and we have developed NPMS as a practical tool for such studies. NPMS works by monitoring the temperature and mass of an individual NP as it is laser-heated in a 3D trap and allowed to react with gases such as acetylene or oxygen. In our experiments, single NPs of graphite, graphene, carbon black, and nanodiamond were first heated to sublime or oxidize away a surface layer, ensuring the surface was clean, then exposed to acetylene at high temperatures. The kinetics for growth was observed to depend on the NP structure, size, temperature. Several growth modes were observed. For most NPs studied, growth was initially fast, slowly abruptly as the reactive sites saturated, then growing slowly, sometimes non-monotonically as additional layers added. Some large carbon black NPs, in contrast, simply grew continuously at a roughly constant rate when exposed to acetylene. Some NPs became essentially inert to acetylene, and to test if this results from the formation of nano-onion surface layers, we studied nanodiamonds, which are known to undergo this transformation. We found that growth rates of nanodiamond NPs were much slower than other NP types.

Scott Anderson

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