Niobium Plating Processes in Alkali Chloride Melts

Abstract

Niobium deposits were prepared from alkali chloride melts on nickel and AISI316 stainless steel substrates both by constant current and by pulse current methods. The influence of electrolysis conditions on the nature, morphology and purity of the deposits was investigated by X-ray diffraction, scanning electron microscopy and energy dispersive X-ray analysis. No metallic niobium was obtained at temperatures below 500 ∘C. At temperatures between 550 and 650 ∘ C, the deposits were dendritic and non-adherent, whereas pure niobium layers could be obtained at 750 ∘ C. Detailed analysis showed that a large negative overpotential during the pulse current period lead to the presence of suboxides, such as Nb6O, in the metallic phase. Suitable electrolysis conditions gave pure oxygen-free niobium. Cross section analysis showed that on nickel a thin layer of niobium–nickel alloy such as NbNi3, was formed at the metal interface. In contrast no alloys were detected at the niobium-stainless steel interface, where homogenous adherent layers of thickness around 50 μm were obtained.