Effect of temperature and dissolved oxygen content on the dissolved iron concentration in liquid sodium at equilibrium

Overview & Synopsis

This study aims to determine the effect of temperature and dissolved oxygen content on the dissolved iron concentration in liquid sodium at equilibrium. Based on the mass variation of the samples, the ap- plied experimental approach avoids the conventional but inaccurate chemical analysis that requires rep- resentative samples of liquid metal so that trace amounts of corrosion products can be measured. The results obtained show that, under isothermal conditions at 550 ◦C , the equilibrium iron concentration fol- lows a power law of an order very close to 2 as a function of the initial oxygen content. These results demonstrate unequivocally that the increase in the iron solubility, in the presence of dissolved oxygen, is directly related to a chemical reaction of complexation. The presence in solution of this corrosion product was hypothesized over more than 50 years ago. The stoichiometry of this soluble complex is thought to be NaF e O 2 . Based on this interpretation and on our experimental measurements, an equilibrium law of this complex in liquid sodium was developed as a function of temperature and dissolved oxygen content. This analytical law can be extrapolated to low dissolved oxygen contents, provided that the contribution of atomic iron to the total dissolved iron in solution is taken into account.