Peter Jozef Vrugt

Sodium corrosion resistance of translucent alumina: effect of additives and sintering conditions

The resistance of Al2O3 against corrosion by sodium in the temperature range 800 to 1000° C was studied by holding samples in liquid sodium in molybdenum containers for several hundred hours. Thermodynamic calculations indicating that Al2O3 is unstable in contact with sodium were confirmed by testing sapphire samples. A remarkable aspect was the large anisotropy in the corrosion resistance of sapphire. The effect of the sintering atmosphere and the amount of MgO and CaO dopant in polycrystalline alumina on the corrosion resistance was considered. Vacuum sintering yielded more resistant materials than hydrogen sintering. Low firing temperatures as well as low dopant levels also proved beneficial. In particular, the absence of CaO improves the corrosion resistance considerably. Consequently, the use of this additive should be avoided.