Argon Shrouded Plasma Spraying of Tantalum over Titanium for Corrosion Protection in Fluorinated Nitric Acid Media
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Argon Shrouded Plasma Spraying of Tantalum over Titanium for Corrosion Protection in Fluorinated Nitric Acid Media E. Vetrivendan1 • J. Jayaraj1 • S. Ningshen1 • C. Mallika1 • U. Kamachi Mudali2
Submitted: 8 September 2017 / in revised form: 30 November 2017 / Published online: 29 January 2018 Ó ASM International 2018
Abstract Argon shrouded plasma spraying (ASPS) was used to deposit a Ta coating on commercially pure Ti (CPTi) under inert argon, for dissolver vessel application in the aqueous spent fuels reprocessing plant with high plutonium content. Oxidation during plasma spraying was minimized by shrouding argon system. Porosity and oxide content were controlled by optimizing the spraying parameters, to obtain a uniform and dense Ta coating. The Ta particle temperature and velocity were optimized by judiciously controlling the spray parameters, using a spray diagnostic charge-coupled device camera. The corrosion resistance of the Ta coatings developed by ASPS was investigated by electrochemical studies in 11.5 M HNO3 and 11.5 M HNO3 ? 0.05 M NaF. Similarly, the durability of the ASPS Ta coating/substrate was evaluated as per ASTM A262 Practice-C test in boiling nitric acid and fluorinated nitric acid for 240 h. The ASPS Ta coating exhibited higher corrosion resistance than the CP-Ti substrate, as evident from electrochemical studies, and low corrosion rate with excellent coating stability in boiling nitric, and fluorinated nitric acid. The results of the present study revealed that tantalum coating by ASPS is a promising strategy for improving the corrosion resistance in the highly corrosive reprocessing environment.
& S. Ningshen [email protected] 1
Corrosion Science and Technology Division, Metallurgy and Materials Group, Indira Gandhi Centre for Atomic Research, Kalpakkam 603102, India
2
Materials Chemistry and Metal Fuel Cycle Group, Indira Gandhi Centre for Atomic Research, Kalpakkam 603102, India
123
Keywords corrosion electrochemical fluorinated nitric acid shrouded plasma spraying tantalum coating
Introduction Plutonium-rich oxides are reported to dissolve completely in fluorinated nitric acid (Ref 1, 2). In the aqueous reprocessing of spent mixed oxide fuels (with high Pu content) to be discharged from future fast breeder reactors (FBRs) in India by the widely employed PUREX process, boiling fluorinated 11.5 M nitric acid is proposed to be the process medium for effective dissolution (Ref 3). Owing to their good corrosion resistance in the boiling nitric acid medium, titanium is being used as a material for the fabrication of dissolver in CORAL plant (Ref 4, 5). However, the presence of fluoride ions was found to increase the corrosion rates of Ti and Zr alloys (Ref 6). A coating of refractory metals like tantalum, niobium, etc., is expected to offer better protection to the dissolver material from the attack by chloride and fluoride ions (Ref 7, 8). Tantalum with outstanding corrosion resistance and good thermal conductivity is attractive coating material, though it is re
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