  The kinetics for O2 oxidation of individual graphite and graphene platelet
nanoparticles (NPs) were studied as a function of temperature (1200 to 2200 K)
at varying oxygen partial pressures, using a single nanoparticle mass
spectrometry method. NP temperature (TNP) was measured by measuring the NP
thermal emission spectra during the kinetics studies. The initial oxidation
efficiency is found to peak in the 1200 to 1500 K range, dropping by an order
of magnitude as TNP was increased above 2000 K. There were large NP-to-NP
variations in the oxidation rates, attributed to variations in the NP surface
structure. In addition, the oxidation efficiencies decreased,
non-monotonically, as the NPs reacted, by factors of between 10 and 300. This
evolution of reactivity is attributed to changes in the NP surface structure
due to the combination of oxidation and annealing. The optical properties,
including wavelength dependence of the emissivity, and the absorption cross
section for the 532 nm heating laser, also tend to evolve as the NPs oxidize,
but differently for each individual NP, presumably reflecting differences in
the initial structures, and how they evolve under different reaction
conditions.
