Impact of rhenium ion stability on coating quality in chloride molten salts

Abstract

Rhenium (Re) has received considerable attention due to its excellent mechanical properties at high temperatures and resistance to gas corrosion, making it suitable for high-temperature environments as a substrate and coating. Among various preparation methods, electrodeposition offers high efficiency, cost-effectiveness, and substrate shape insensitivity, making it a promising approach for Re coating and component fabrication. Research on chloride molten salt systems is prevalent; however, coating defects often arise from disproportionation reactions, a critical determinant of coating quality. To assess Re ion stability in molten salts and optimise electrodeposition, the effects of atmospheric conditions, molten salt composition, and electrode materials were investigated. Our findings revealed poor Re ion stabilisation in molten salts, susceptible to disproportionation reactions at interfaces forming ReCl₅ and Re. The presence of oxygen in an argon atmosphere promoted the disproportionation reaction, whereas, chlorine inhibited the reaction. The composition of the molten salt affected the Re ion structure; a larger cation radius increased Re ion stability. Similar catalytic behaviour was observed on electrode surfaces, where unstable Re ions disproportionated, weakening interfacial bonding and increasing defects.