INTERACTION OF ZR2AL WITH OXYGEN AT HIGH-TEMPERATURES

The oxidation of Zr//2Al in dry oxygen in the temperature range 730-875 K follows a parabolic rate law. An activation energy of 371. 5 kJ mol** minus **1 is estimated. The oxidation results in the formation of the following sequence of layers: tetragonal ZrO//2, monoclinic ZrO//2, Zr//2Al and tetragonal Zr//5Al//3. During oxidation aluminum diffuses from the oxide layer into the Zr//2Al bulk, thus forming a Zr//5Al//3 phase at some distance from the oxide-alloy interface. The excess zirconium is therefore selectively oxidized, yielding monoclinic and/or tetragonal ZrO//2 containing no alumina.