The Corrosion Protection of Nickel Equipment in Chloride-Fluotantalate Melts

The possibility of corrosion protection of nickel equipment at 680–780°C in chloride-fluotantalate melts, used in the sodium-thermal production of tantalum capacitor powder, is investigated. It is shown that preliminarily adding tantalum powder (no less than 0.3 wt. % relative to K₂TaF₇) to the NaCl–K₂TaF₇ (ca. 14 mol %) melt prevents the nickel corrosion from starting just as the melt is fused; the electroless tantalum deposition on nickel starts, which results in the formation of a Ni₃Ta–Ni₂Ta intermetallic protective coating on the nickel surface. The effects of the exposure time and the melt temperature, as well as the tantalum powder content and dispersity, on the tantalum deposition are studied.