Preliminary experiments have shown that hafnia (HfO 2 ) NPs behave qualitatively similar to silica NPs when CO 2 -laser pre-heated. The initially transparent HfO 2 NPs begin to adsorb 532 nm efficiently, emitting blackbody-like thermal spectra, and when exposed to O 2 , they etch with rates similar to those for Hf NPs, suggesting that pre-heated hafnia NPs also become surface-reduced. Therefore, experiments comparing passivation of surface-reduced hafnia and Hf NPs over a range of temperatures and O 2 pressures should help test the Hf passivation mechanism. We also are carrying out pulsed heating experiments on both HfO 2 and Hf NPs to examine the question of whether mass gain from oxide layer formation can be observed for NPs briefly heated to high T NP to desorb oxides, then cooled at 10 5 K/sec to temperatures where a surface oxide layer should be stable. These experiments as well as experiments at different temperatures and pressures should allow clearer interpretation of the Hf oxidation kinetics.