Stability of ternary oxygen compounds of molybdenum in liquid sodium

Abstract

The ternary system Na-Mo-O is of interest in sodium loops such as in the heat transport systems of LMFBRs. This paper reports the results of our investigations with a view to identifying the phases which could co-exist with liquid sodium and molybdenum. The limited number of studies reported in literature are first critically reviewed and shown to be inconsistent. Experiments involving in-sodium equilibrations, solid state reactions and pseudo-isopiestic equilibrations were carried out to understand the phase relations in the Na-Mo-O system. In addition to the above, oxygen potentials were measured in sodium to which molybdates of sodium were added, using a galvanic cell. From these results it could be deduced that Na₂O(s) coexists with molybdenum and liquid sodium metal up to 681.1 K. Above this temperature the ternary oxygen compound, Na₄MoO₅(s) appears as the coexisting phase with the two metals. From the oxygen potential data, the Gibbs energy of formation of Na₄MoO₅(s) could be deduced.