A wide range of experimental data on the oxidation of ZrB2 and HfB2 as a function of temperature (800°–2500°C) 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°C) 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.
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Document Type: Research Article
UES Inc., Dayton, Ohio 45432
The Ohio State University, Columbus, Ohio 43235
Air Force Research Laboratory, Materials and Manufacturing Directorate, AFRL/MLLN, Wright-Patterson AFB, Ohio 45433-7817
Publication date: May 1, 2009