During ramp 1, fast oxidative etching was observed at low TNP, with EEO2 nearly constant from 1200 to 1400 K, but dropping rapidly at higher TNP values, to near zero by 1900 K, seen in the raw data as little change in the slope of M vs. time when O2 was added. In ramp 2, the NP was substantially less reactive than it had been in ramp 1, particularly at low TNP, indicating that the NP had become largely passivated against O2 attack at low TNP. EEO2 increased to a peak at 1500 K then fell again at higher TNP.