The corrosion behavior of 304 stainless steel in NaNO3-NaCl-NaF molten salt and vapor

Abstract

Corrosion behavior of 304 stainless steel in molten NaNO3-NaCl-NaF salt and NaNO3-NaCl-NaF vapor has been studied at 450 °C. The results showed that the samples suffered weight loss, and surface oxides, i.e. Fe2O3 and FeCr2O4 characterized by XRD, were formed after corrosion. The surface oxide layer was about 1.1 μm in thickness after corrosion in molten NaNO3-NaCl-NaF salt, which was relatively homogeneous and dense. Whereas, the distribution of surface oxides was not even, and a shedding phenomenon was observed after corrosion molten NaNO3-NaCl-NaF vapor. This is mainly attributed to the existence of NO2 and NO in the molten NaNO3-NaCl-NaF vapor determined by thermogravimetric infrared spectroscopy, which affected the adherence between oxides and the matrix. Additionally, the corrosion rate of 304 stainless steel in molten NaNO3-NaCl-NaF salt is almost close to that in solar salt, which demonstrates that the synergy influence of Cl− and F− on the rate of 304 stainless steel is not significant. This work not only enriches the database of molten salt corrosion, but provides references for the selection of alloy and molten salt in the CSP.