The ZrB2 Volatility Diagram

A volatility diagram was calculated for temperatures of 1000, 1800, and 2500 K to understand the oxidation of ZrB₂. Applying the diagram, it can be seen that exposure of ZrB₂ to air produces ZrO₂ (cr) and B₂O₃ (l) over the temperature range considered. The pressure of the predominant vapor species was predicted to increase from ∼10⁻⁶ Pa at 1000 K, to 344 Pa at 1800 K, and to ∼10⁵ Pa at 2500 K. Predictions were consistent with experimental observations that ZrB₂ exhibits passive oxidation below 1200 K, but undergoes active oxidation at higher temperatures due to B₂O₃ (l) evaporation.