Effect of In-situ Self-Generated MgO on Corrosion Resistance of KCl-MgCl2 Molten Salt

Abstract:

Molten chloride salt is excellent candidature for third-generation solar energy storage media due to its good energy storage advantages and low price. However, in the actual working environment, molten chloride salt has strong corrosion to metal pipes (Inconel 625 alloy). Inconel 625 welding wire is usually used as a repair material for solar pipeline. In order to solve the problem of strong corrosion of molten chloride salt to Inconel 625 cladding metal, Inconel 625 cladding metal was welded by MAG welding, and the effect of nano-MgO particles and MgCl₂·6H₂O in-situ self-generated MgO on the corrosion of KCl-MgCl₂ molten salt was investigated. The results show that after 72 h of corrosion in KCl-MgCl₂, KCl-MgCl₂+5wt% MgO and KCl-MgCl₂+5wt% MgCl₂·6H₂O, the mass loss of Inconel 625 cladding metal is 0.00714, 0.00512, and 0.00308 g·cm^-2, respectively. The corrosion rate of Inconel 625 cladding metal in molten salt with in-situ self-generated MgO is decreased by 56.86% and 39.85%. Although the addition of nano-MgO particles in the molten salt can alleviate the corrosion of the chloride molten salt, the molten salt is agglomerated or settled, leading to a non-uniform distribution of MgO and MgCr₂O₄ protective shell layers. Adding MgCl₂·6H₂O to the molten salt can generate in-situ MgO, and the generated MgO and MgCr₂O₄ protective shells are more uniform, which hinder the erosion of corrosive media, so it is an effective method to reduce the corrosion of chloride molten salt.