Corrosion evaluation of alloy 800 in sulfate/vanadate molten salts

This paper is devoted to the evaluation of the corrosion behavior of Alloy 800 (UNS N08800) when exposed to 80 mol% Na2SO4-20V(2)O(5) (80 mol% sodium sulfate-20vanadium pentoxide; high sulfate) and 80 mol% V2O5-20Na(2)SO(4) (high vanadate) at 700degreesC and 900degreesC. Applying electrochemical techniques, namely potentiodynamic polarization curves that led to the calculation of Tafel slopes and the electrochemical noise technique (ENT), corrosion rates and the type of corrosion (localized or generalized) attack was determined by ENT and compared with conventional weight-loss methods. A statistical and spectral noise analysis of noise-time records was performed, providing the noise resistance, pitting index, and noise impedance. The results showed that Alloy 800 is liable to suffer localized corrosion when it is exposed to molten salt solution high in sulfate at 700degreesC and 900degreesC, showing a higher degree of localized attack at the higher temperature. When exposed to the vanadium-rich solution, a more generalized corrosion was observed at both temperatures. Comparison of mass loss obtained with electrochemical noise measurements is in agreement. The pitting index proved to be an indicator for the type of corrosion observed.