Corrosion of construction materials of separator in molten carbonates of alkali metals

Abstract

The mitigation of steels and alloys corrosion is one of the great challenges for application of high-temperature devices in contact with molten salts. The current research estimates corrosion resistance of the following construction materials: Crofer APU 22, austenitic steel 12Cr18Ni10Ti and two types of austenitic nickel-chromium alloy: CrNi78Ti, CrNi78Ti + 5% wt. W. The measurements are performed by exposition of samples within 24 h in the molten mixture of carbonates of lithium and potassium at 650 °C. The rates and mechanism of materials corrosion under these conditions are determined. The process occurring on the surface while contact of the materials and steels with carbonate melt are investigated.Accurate quantitative data on materials interaction with alkali carbonate melt have been obtained by gravimetrical and physico-chemical methods. The high-temperature corrosion of Fe and Ni austenitic materials has turned dramatically different from both their low-temperature corrosion and each other. There are mixed passivating oxide films on the surface of the only iron-based materials.In addition, the resulting layers of corrosion products are well bonded to the substrate and have protective properties and can be used as protective coatings in molten salts of other compositions, including alkali metal fluorides.