Review of alkali metal and refractory alloy compatibility for Rankine cycle applications

The principal corrosion mechanisms in refractory metal--alkali systems are dissolution, mass transfer, and impurity reactions. In general, Nb, Ta, Mo, and tungsten have low solubilities in the alkali metals, even to very high temperatures, and static corrosion studies have verified that the systems are basically compatible. Loop studies with Nb and Ta based alloys have not indicated any serious problems due to temperature gradient mass transfer. Above 1000K, dissimilar metal mass transfer was noted between the refractory metals and Fe or Ni based alloys. The most serious corrosion problems encountered are related to impurity reactions associated with oxygen. Photomicrographs. 35 ref.--AA