Molten nitrate salts at 600 and 680 °C: Thermophysical property changes and corrosion of high-temperature nickel alloys

This paper examines the effects of long-term, high-temperature corrosion processes on materials used in concentrated solar power tower systems. More specifically, the heat transfer fluid and the containment metal are examined at operating temperatures of 600 and 680 °C. A 60/40% NaNO3/KNO3 mixture of molten salt and nickel-based alloys HA230 and In625 were tested for up to 4000 h at the given temperatures. HA230 and In625 alloys showed metal losses of 688 and 594 μm/year, respectively, after 1000 h at 680 °C. The solar salt used in this study showed significant decreases (as much as 60 °C) in melting point. Further experiments showed that the primary reason for the decrease in melting point is due to high nitrite concentrations in the molten salt. However, other thermophysical properties of aged solar salt appear to change little during high-temperature corrosion tests.