Corrosion and Microstructure Correlation in Molten LiCl-KCl Medium
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RODUCTION
MOLTEN chloride salts are widely used for electrowinning of metals and alloys, for annealing and normalizing of steels, in high-temperature batteries, fuel cells, etc.[1] Pyrochemical reprocessing has evolved as the bestsuited process for reprocessing of short cooled and high burn up metallic fuels of sodium-cooled fast reactors and has been chosen as the best option for the reprocessing of spent metallic fuels for the future Indian fast breeder reactors.[2] Towards this, molten LiCl-KCl eutectic salt has been considered as the process medium for electrorefining of spent metallic fuels. Due to the high-temperature operation in molten chlorides, pyrochemical reprocessing requires high corrosion-resistant materials for the application. Various studies have been reported on the corrosion of A. RAVI SHANKAR, Scientific Officer-D, K. THYAGARAJAN, Scientific Officer-C, and U. KAMACHI MUDALI, Head, Reprocessing Research and Development Division, Head, Corrosion Science and Technology Section–RPM, Head, IGCAR–Technology Transfer Cell, and Professor, Homi Bhabha National Institute (University), are with the Corrosion Science and Technology Division, Indira Gandhi Centre for Atomic Research, Kalpakkam – 603 102, India. Contact e-mail: [email protected] S. MATHIYA, M. Phil. Student, is with Lady Doak College, Madurai – 625 002, TN, India. Manuscript submitted April 15, 2009. Article published online April 30, 2010 METALLURGICAL AND MATERIALS TRANSACTIONS A
structural materials in molten chlorides, focusing on the corrosion under inert atmosphere or in the presence of oxygen and mechanisms involved.[3–6] In the present study, electroformed nickel (EF Ni), electroformed nickel with nickel-tungsten (Ni-W) coating (EF Ni-W), 316L SS, and INCONEL* 625 were chosen as the *INCONEL is a trademark of Special Metals Corporation, New Hartford, NY.
candidate materials for testing. Electroforming is an effective and economical alternative for fabricating precision parts that are difficult to make by conventional manufacturing means.[7] EF Ni shows excellent strength, toughness, and ductility and is extremely resistant to corrosion in a wide range of environments.[8] Nickel also shows high corrosion resistance in molten chloride as well as in molten fluoride[9] and is regularly employed at elevated temperature[10] as the NiO saturated film developed was not expected to dissolve and provide good corrosion resistance.[11] Arons et al.[12] reported that tungsten is the only material known to be capable of withstanding the corrosive attack of a wide range of liquid metals. Electrodeposition of Ni-W alloys was used for various applications due to their unique combination of tribological, magnetic, electrical, and electro-erosion VOLUME 41A, JULY 2010—1815
properties. They also exhibit good mechanical properties (e.g., high tensile strength and hardness, as well as superior abrasion resistance), good resistance to strong oxidizing acids, and high-temperature corrosion.[13] In the present study, EF Ni and EF Ni-W were selected for corrosion s
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