Corrosion and Microstructure Correlation in Molten LiCl-KCl Medium

Abstract

Pyrochemical reprocessing in molten chloride salt medium has been considered as one of the best options for the reprocessing of spent metallic fuels of future fast breeder reactors. The unit operations such as salt preparation, electrorefining, and cathode processing involve the presence of molten LiCl-KCl eutectic salt from 673 to 1373 K (400 to 1100°C). The present work discusses the corrosion behavior of electroformed nickel (EF Ni) without and with nickel-tungsten (Ni-W) coating, 316L SS, and INCONEL 625 alloy in molten LiCl-KCl eutectic salt at 673 K, 773 K, and 873 K (400°C, 500°C, and 600°C) in the presence of air. The weight percent loss of the exposed samples was determined by the weight loss method and surface morphology of the salt exposed, and product layers were examined by scanning electron microscopy (SEM). X-ray diffraction (XRD) and energy-dispersive X-ray (EDX) analysis were also carried out on the exposed and corrosion product layers to understand the phases present and the corrosion mechanism involved. The results of the present study indicated that INCONEL 625 alloy showed superior corrosion resistance compared to electroformed nickel (EF Ni), EF Ni with nickel-tungsten (Ni-W) coating (EF Ni-W), and 316L SS. The EF Ni with Ni-W coating exhibits better corrosion resistance than EF Ni without tungsten coating. Based on the surface morphology, XRD, and EDX analysis of corrosion product layers, the mechanism of corrosion of INCONEL 625 and 316L involves formation of chromium-rich compound at the surface and subsequent spallation. For the EF Ni, the porous thick NiO corrosion product allows the penetration of salt, thus accelerating the corrosion. Improved corrosion resistance of EF Ni-W was attributed to the W-rich NiO layer, while for INCONEL 625, the adherent and protective NiO layer improved the corrosion resistance. The article highlights the results of the present investigation.

Corrosion of Nickel-Containing Alloys in Molten LiCl-KCl Medium

“…Our earlier studies on Type 316L (UNS S31603) stainless steel exposed to molten LiCl-KCl salt also revealed the selective outward diffusion of Cr and formation of a Cr-rich compound at the surface and spallation. [15][16] These results are in good agreement with the EDX analysis carried out on the attacked surfaces and scales. Oxygen is present in all the top layers, indicating that these layers comprise predominantly oxides.…”

Corrosion Behavior of Commercial Alloys in LiCl–KCl Molten Salt Containing EuCl3

“…As the formation of the protective oxide layer on the alloy surface is challenged in molten chloride media, the structural alloys used for the construction of an electrorefiner may suffer corrosion attack during its design life (e.g., 40 years). To screen the candidate alloys, several studies have evaluated the corrosion resistance of commercial alloys in LiCl-KCl molten salt (Shankar et al, 2010;Shankar et al, 2013a;Shankar et al, 2013b;Rao et al, 2015). In general, alloys exhibit preferential dissolution or oxidation of the active element Cr, which is induced by impurities such as moisture and oxygen in the molten salt.…”

Corrosion of Nanocrystalline Ni-W Coated Copper

“…Another peak at 810 cm −1 could be assigned to the W-O stretching mode [13], which indicates the existence of crystalline WO 3 . The broad Raman band detected at 507 cm −1 can be correspond to the formation of NiO on the surface of the corroded specimen [14]. Thus, it was confirmed, with the aid of Raman spectroscopy, that the main corrosion products were WO 3 and NiO.…”