Preparation of tantalum carbide layers on carbon using the metalliding process

Abstract

This work concerns the preparation of tantalum carbide films on carbon based substrates using the metalliding process in LiF-NaF molten medium (60-40% mol.), containing tantalum heptafluorotantalate ions TaF72-, in the 800-900 °C temperature range. The process uses a metalliding cell symbolized as: (+) C, TaCx/LiF-NaF-K2TaF7/Ta (-) involving the dissolution of Ta at the anode and the reduction of Ta ions in TaCx at the cathode. The experiments of this process were performed with different carbon substrates as cathodic material: graphite, glassy carbon and carbon braid. Samples analysis (SEM-EDS and XRD) after metalliding showed the formation of tantalum carbides (TaC and Ta2C) at the surface of the substrate at a relatively low temperature. A kinetic study, based on the control of the cathodic reaction by the intermetallic diffusion, allowed the diffusion parameters, such as Ta-C diffusion coefficient, to be determined at several temperatures. Furthermore, the results are shown to be independent of the type of carbon substrate.