Effects of Phase Change and Oxygen Permeability in Oxide Scales on Oxidation Kinetics of ZrB2 and HfB2 (POSTPRINT)
Journal article postprint
AIR FORCE RESEARCH LAB WRIGHT-PATTERSON AFB OH MATERIALS AND MANUFACTURING DIRECTORATE
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A wide range of experimental data on the oxidation of ZrB2 and HfB2 as a function of temperature 800 - 1500 degrees Celsius is interpreted using a mechanistic model that relaxes two significant assumptions made in prior work. First, inclusion of the effect of volume change associated with monoclinic to tetragonal phase change of the MeO2 phases is found to rationalize the observations by several investigators of abrupt changes in weight gain, recession, and oxygen consumed, as the temperature is raised through the transformation temperatures for ZrO2 and HfO2. Second, the inclusion of oxygen permeability in ZrO2 is found to rationalize the enhancement in oxidation behavior at very high temperatures 1800 degrees Celsius of ZrB2, while the effect of oxygen permeability in HfO2 is negligible. Based on these considerations, the significant advantage of HfB2 over ZrB2 is credited to the higher transformation temperature and lower oxygen permeability of HfO2 compared with ZrO2.
- Physical Chemistry
- Ceramics, Refractories and Glass