Phase equilibrium studies in the Na-Fe-O system

Abstract

In high temperature sodium-steel systems, the corrosion of structural steels by sodium is enhanced by the presence of dissolved oxygen. As iron is the major constituent in steel, the interaction between iron and sodium containing oxygen plays a decisive role in this corrosion process. A knowledge of the various phase relationships that exist in the Na-Fe-O system is essential to understand this phenomenon. In order to elucidate the equilibrium phase fields, various experiments such as in-sodium equilibrations, pseudo-isopiestic equilibrations, differential thermal analysis and solid state reactions between the oxides of iron and sodium of various compositions were carried out. On the basis of the results of these experiments an isothermal cross-section of the partial phase diagram of the Na-Fe-O system above 773 K is reported.