Thermodynamic stability of aluminium ceramics in liquid lithium

Thermochemical analysis is performed in the systems Li-Al-O and Li-Al-N taking into account the compounds Li2O, LI3N, Li5AlO4, LiAl5O8, Al2O3, Li9Al4, Li3Al2, LiAl,LiAlO2, AlN. In the range Li-Li2O-LiAlO2Li3Al2 the oxygen pressures of the numerous possible equilibria are too close together to select the relevant equilibria. In consequence, equilibria in this range may be easily modified by changes in composition of the compounds involved (impurities, thermal decomposition, nuclear transmutation). In the system Li-Al-N, aluminum nitride has a very broad field of stability in lithium. The solubility of AlN in Li is estimated to be very low. So aluminum can act as a getter for dissolved nitrogen in Li. It is concluded that the unusual low nitrogen concentration in the ELS at Hanford is caused by the observed presence of aluminum which is bonded as AlN and filtered out during the filling of the loop. Corrosion tests of AlN in Li agree well with the results of the analysis. (author)