Early-stage corrosion of IN 740H alloy in eutectic NaCl-KCl molten salt at high temperatures

The next generation concentrated solar power plants are expected to operate at temperatures above 700 degrees C and this would necessitate heat storage media such as chloride salt mixtures to be used for better heat transfer and energy storage. In this perspective, the corrosion behaviour of a commercial grade IN 740H alloy is being investigated in the eutectic equimolar NaCl-KCl salt mixture, at 700 degrees C and 800 degrees C. To evaluate and understand the early stages of corrosion of IN 740H, electrochemical and gravimetric tests were carried out after exposure to molten eutectic NaCl-KCl salt mixture for 1.5 and 24 h, respectively. The quantitative outcomes of the gravi-metric studies suggest that IN 740H corrodes at 0.29 +/- 0.03 and 0.59 +/- 0.17 mg cm(-2) day(- 1) at 700 degrees C and 800 degrees C, respectively. Tafel measurements reveal corrosion rates similar to those measured by gravimetric method. Electrochemical impedance spectroscopy analysis indicated the diffusion-controlled corrosion behav-iour, but the passive layer does not inhibit corrosion at early stages. A correlation between the underlying mechanism and the oxide scale microstructure has been presented using electrochemical and cross-sectional studies.