The ZrB 2 Volatility Diagram

A volatility diagram was calculated for temperatures of 1000, 1800, and 2500 K to understand the oxidation of ZrB 2 . Applying the diagram, it can be seen that exposure of ZrB 2 to air produces ZrO 2 (cr) and B 2 O 3 (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 ∼10 5 Pa at 2500 K. Predictions were consistent with experimental observations that ZrB 2 exhibits passive oxidation below 1200 K, but undergoes active oxidation at higher temperatures due to B 2 O 3 (l) evaporation.