High-Temperature Corrosion Behavior of Al-Coated Ni-Base Alloys in Lithium Molten Salt for Electroreduction

Abstract

The electrolytic reduction of a spent oxide fuel involves the liberation of oxygen in a molten salt LiCl–Li2O electrolyte, which creates a corrosive environment for typical structural materials. In this study, the corrosion behaviors of Al–Y-coated specimens in a Li molten salt kept under an oxidizing atmosphere at 650 °C for 72 and 168 h were investigated. The weight loss fraction of the coated specimen to bare specimen was approximately 60% for 3% Li2O and 54% for 8% Li2O at 72 h, and approximately 38% for 3% Li2O and 30% for 8% Li2O at 168 h. Corrosion was induced in the LiCl–Li2O molten salt by the basic oxide ion O2− via the basic flux mechanism, and the corrosion product was found to be dependent on the activity of the O2− ion. The increase in weight loss may have been caused by the increase in the O2− concentration due to the increase in the Li2O concentration rather than being because of the increased reaction time. The Al–Y coating was found to be beneficial for hot corrosion resistance, which can be useful for handling high-temperature lithium molten salt under an oxidizing atmosphere.

Behavior of Ni20Cr Alloy in Molten Nitrate Salts

“…These reactions are favored by the basic character of the molten salt (high concentration of oxide ion, O 2− ) whose reaction product is soluble in the melt and can precipitate as a porous layer on the surface of the alloy [ 33 ]. The formation of Na 2 CrO 4 and K 2 CrO 4 is favored with increasing temperature; therefore, the corrosion resistance of the alloy could be diminished as its formation depletes the Cr content of the protective layer [ 33 , 34 ]. Recent studies [ 12 ] have shown that Solar Salt dissolves pure Cr by similar reactions.…”

Effect of reaction temperature on the corrosion behaviour of Inconel alloys in lithium molten salt under an oxidising atmosphere

“…22 Specifically, during the electrolytic reduction of spent oxide nuclear fuel in a molten lithium salt system containing highly corrosive and strongly basic Li 2 O, the oxygen generated at the anode and resulting high-temperature molten lithium salt can lead to a chemically aggressive environment, which is excessively corrosive for ordinary structural materials. 2,[24][25][26][27][28] Hence, studies on the hot corrosion of Ni-base alloys, which are used to fabricate the equipment related to the handling of high-temperature molten salts owing to their excellent resistance to corrosion at elevated temperatures, [29][30][31][32][33][34][35] have been conducted. In addition, long-term corrosion resistance is an important parameter, which is used to determine the suitability of structural materials requiring continuous exposure to high-temperature molten salts.…”

“…Few reports on the high-temperature corrosion behaviours of Ni-base alloys in a LiCl-Li 2 O molten salt are available. [24][25][26][27][28] According to these reports, in addition to the formation, maintenance and spalling of the external corrosion layer and the shape and growth of the internal corrosion layer, the depletion region of major alloying elements formed beneath the corrosion layer has a significant effect on the weight loss of the alloy. Many alloys for hightemperature applications are based on Ni and/or Co due to their better corrosion resistance and rely on the formation of Cr 2 O 3 layers for protection against corrosion.…”

Effect of Cr Content on Hot Corrosion Behavior of Inconel Alloys in Molten LiCl–Li2O

“…During the electrolytic reduction of spent oxide nuclear fuel in molten lithium salts, the oxygen generated at the anode and the hot strongly basic lithium oxide make ordinary structural materials highly susceptible to corrosion [6, [31][32][33][34][35]. Therefore, a suitable structural material is required to handle the molten salts during the electrolytic reduction of the spent oxide nuclear fuel.…”

“…However, there have been only a few studies on the hot corrosion behavior of Ni-base alloys in molten LiCl-Li 2 O salts [31][32][33][34][35]. According to these studies, the formation, maintenance, and spalling of the external corrosion layer and the shape and growth of the internal corrosion layer as well as the depletion of the major alloying elements beneath the corrosion layer signi cantly affect the weight loss of the alloy.…”