High Temperature Oxidation of Single Carbon Nanoparticles: Dependence on Surface Structure, and Probing Real-Time Structural Evolution via Kinetics.

Abstract

O2-oxidation and sublimation kinetics for >30 individual nanoparticles (NPs) of five different feedstocks (graphite, graphene oxide, carbon black, diamond, and nano-onion) were measured using single nanoparticle mass spectrometry at temperatures (TNP) in 1100 – 2900 K range. It was found that oxidation, studied in the 1200 to 1600 K range, is highly sensitive to NP sur-face structure, with etching efficiencies (EEO2) varying by up to four orders of magnitude, whereas sublimation rates, significant only for TNP ≥ ~1700 K, varied by only a factor of ~3. Its sensitivity to NP surface structure makes O2 etching a good real-time structure probe, which was used to follow evolution of the NP surface structures over time as they were either etched or an-nealed at high TNP. All types of carbon NPs were found to have initial EEO2 values in the range near 10-3 Da/O2 collision, and all eventually evolved to become essentially inert to O2 (EEO2 < 10-6 Da/O2 collision), however, the dependence of EEO2 on time and mass loss was very different for NPs from different feedstocks. For example, diamond NPs evolved rapidly and monoton-ically toward inertness, and evolution occurred in both oxidizing and inert atmospheres. In contrast, graphite NPs evolved only under oxidizing conditions, and etched with complex time dependence, with multiple waves of fast-but-non-monotonic etching, separated by periods of near-inertness. Possible mechanisms to account for the complex etching behavior are pro-posed.

High Temperature Reaction of Individual Graphite Nanoparticles with N2O: Etching, Passivation, Sublimation, and Comparison to O2

“…previously. 1,2,15,[27][28][29] In brief, graphite NPs (Alfa Aesar, 99.9999% metals basis) were injected into a quadrupole trap, 30 with 15 mTorr of ultrahigh purity (UHP) argon added to aid trapping.…”

“…We recently reported studies of O2 etching of individual carbon nanoparticles (NPs) in the temperature (TNP) range from 1200 to 2400 K, with several unexpected results. 1,2 O2 reaction with graphite in this temperature range proceeds by O2 dissociative adsorption at undercoordinated carbon sites ("-C * "), at exposed basal plane edges and defects, [3][4][5][6][7][8][9] creating oxidized surface sites ("-C(O)") that can decay by desorption of oxygen, resulting in no net reaction, or by CO/CO2 desorption, etching the surface. 10 The mechanisms are not as well established for other forms of carbon, but almost certainly involve O2 dissociative adsorption at under-coordinated sites, followed by desorption of oxygen or COx.…”