Single crystal and sintered alumina corrosion in liquid sodium

Corrosion tests were conducted under static conditions at 450 and 550 C for various oxygen contents and durations with single crystal and sintered alumina regarded as model materials for ceramics. Extremely pure and dense sintered alumina exhibited no intergranular corrosion and identical behavior as single crystal. Corrosion appeared to proceed by reaction of Al₂O₃ with dissolved oxygen (Na₂O) to form sodium aluminate (NaAlO₂). Then, sodium aluminate was dissolved in liquid sodium by a mechanism that is still to be elucidated. The corrosion morphology was equivalent to dissolution. From weight loss measurement, linear kinetics were found with a constant dissolution rate of (61 ± 2)10^-4 mg dm^-2 h^-1 at 550 C and low oxygen content (≤1 ppm). No significant corrosion rate could be measured at 450 C and low oxygen content. An order reaction kinetics with respect to dissolved oxygen content of 0.6 ± 0.2 was found. (authors)