Long-term stability of ceramics in liquid lithium

Two candidate materials for insulating coatings in a lithium-cooled fusion reactor have been exposed to lithium in 1000 h isothermal tests from 400–800°C to determine their maximum compatibility temperature. Bulk samples of AlN+5 wt%Y2O3 showed significant mass loss at 600°C and higher temperatures. The amount of attack was reduced when AlN+0.04 wt%Y was tested. Characterization by Auger spectroscopy of a AlN+0.04 wt%Y specimen exposed at 600°C indicated the possibility of a lithium aluminate compound formation. Bulk, polycrystalline specimens of CaO (99.9% purity) showed mass losses above 500°C indicating a possible dissolution problem that had not been observed in previous short-term screening tests and is not predicted based on thermodynamic calculations. Doping of the lithium with oxygen (in the case of CaO) did not appear effective in reducing the mass loss at 600°C.