Abstract
The oxidation behaviour of iron in NaNO 3-NaNO 2 melt has been studied by potentiodynamic polarisation and electrochemical noise measurements in the temperature range of 250–550°C. The open circuit potential and the repassivation potential shifted in a noble direction with temperature up to 450°C due to the formation of stable oxide film. An opposite effect was found at 550°C due to breakdown of the oxide film. An increase of noise power values with the increase of temperature was observed which indicated an increased diffusion of iron ions in the formation of oxide film. X-ray diffraction investigation of the surface film formed on iron showed the presence of a sodium ferrite layer on the iron surface. The oxidation rate obtained by the Tafel extrapolation method was in agreement with the harmonic current measurements. The activation energy of the process was 57.43 kJ mol −1.
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