Kinetics of iron passivation and corrosion in molten alkali nitrates

Abstract

The electrochemical behaviour of iron anodes in molten alkali nitrates has been investigated at temperatures ranging from ca 240–320°C. The E/I curves exhibit a potential region where the electrode passivates. Two different oxidized states of the passive iron surface exist. Within definite potential regions, the oxidation of nitrite and iron occurs, the latter being characterized by a Tafel slope of 2RT/F. At high positive potentials the breakdown of passivity is observed. Results are interpreted in terms of the stability of possible iron oxides during the electrode reaction. The kinetics of nitrite and nitrate ion oxidation on the passive surface is discussed on the basis of previous work. A comparison between iron passivation and corrosion in molten nitrites and nitrates is made.