increases the raw mass loss rate (but not EEO2), and hastens passivation. One more 1200 K example is shown in Fig. , in which a pre-heated NP with initial mass just under 54 MDa was oxidized at constant PO2 = 2.1 x 10 -5 Torr, i.e., half the PO2 value used in Figs. and. For this NP, EEO2 was initially ~10 -3 Da/O2 collision, but increased by a factor of ~four over the first ~hour of oxidation, and continued to increase slowly thereafter, eventually reaching ~5 x 10 -3 Da/ O2 collision after ~2.5 hours, at which point the experiment was terminated.