Electrochemical deposition of tantalum carbide coatings in molten LiCl-KCl-K2CO3

A method for the preparation of tantalum carbide (TaC) coatings on tantalum by electrochemical reduction in carbonate ions in molten LiCl-KCl was developed. Carbide coatings were obtained on the tantalum substrate at 900 degrees C with a bias voltage of -1.8V versus the graphite counter electrode. The phase composition, morphology and strength of the carbide coating were characterized by XRD, SEM, and XPS analyses, as well as scratch testing. Kinetic mechanism for the formation of TaC coatings and evolution of chemical bonds between the carbide layer and substrate were schematically discussed. The coatings consist of a single phase of TaC with a thickness of approximately 5m. Ta2O5 and tantalate derivatives in molten salt restrict TaC formation. Electro-deoxidation of Ta substrate can favorably eliminate tantalum-involved compounds to produce TaC. TaC coatings improve the surface strength of Ta substrate obviously. The formation of a metal-carbon solid solution in molten salt determines the existence of excess carbon on Ta substrate. Chemical bonds on the TaC coating were investigated in comparison with those at the interface of the metal-oxygen-carbon and carbon film.