Fig. shows the next section of the experiment, in which TNP was held constant at 1800 K, while PN2O was stepped up by factors of ~2, covering two orders of magnitude. At each step, Rbaseline (≈ Rsublimation at 1800 K) was measured in Ar (white background) before and after periods with N2O added (pink background). Note that the mass loss rates in Ar were initially constant but began to decrease noticeably starting at the ~4 hour mark, implying that Rsublimation gradually slowed over the course of the experiment. Kinetics slowing over time was observed previously for sublimation of graphite/graphene NPs, and was attributed to sublimation preferentially removing material from the least stable surface sites, thus gradually increasing the average stability of the remaining sites, slowing sublimation.