Electrodeposition of Beta-Tantalum from Molten Salts

摘要

An adherent coating of beta-tantalum (beta-tantalum) has been electrodeposited oncopper in an NaF-KF-LiF (FLINAK) molten salt electrolyte. Electrolyte temperatures ranged from 700 to 800 deg C using pulse current electrolysis at current densities higher than 100 mA/sq cm. The hardness of the beta-tantalum was ten times higher than body-centered-cubic tantalum (BCC-tantalum, also called alpha-tantalum). Electrolytic etching, using 25 percent hydrofluoric acid and 75 percent sulfuric acid, revealed a columnar grain structure. At current densities higher than 100 mA/sq cm, the beta-tantalum was found to deposit to a maximum thickness of 70 micrometer after 3 hours of electrodeposition. The beta-tantalum deposits were determined to be metastable and began to partially revert to the BCC-tantalum after 2 hours of heating at 800 deg C. (RH)