Perspectives on selected alloys in contact with eutectic melts for thermal storage: Nitrates, carbonates and chlorides
Esraa Hamdy, Johanna Nockert Olovsjö, Christine Geers
Abstract
Increasing the operating temperature of molten salt-based concentrated solar power plants is of paramount importance to enable next-generation gas turbines and an overall increase in power conversion efficiency. The issue is how to mitigate the degradation of necessary metallic components in highly corrosive salt environments. In this study, three eutectic salt mixture candidates, nitrates, carbonates, and chlorides, are brought into contact with stainless steel (316H or 304L) and the FeCrAl alloy Kanthal® APMT. The post-exposure analysis is discussed in terms of the overall performance of each alloy as concerns mass change, scale growth, internal attack, and leaching. Significant reduction of corrosion is realised through the ability of Kanthal® APMT to form aluminium oxide species at the surface in contact with alkali nitrates and carbonates. On the other hand, aluminium is leached most efficiently in contact with chlorides, which causes a deeper attack on Kanthal® APMT than alloy 304L. The overall conclusion is that only by employing a holistic perspective on all individual measurements can a long-term performance estimation be formulated.