Niobium deposits were prepared from alkali chloride melts on nickel and AIS
I316 stainless steel substrates both by constant current and by pulse curre
nt methods. The influence of electrolysis conditions on the nature, morphol
ogy and purity of the deposits was investigated by X-ray diffraction, scann
ing electron microscopy and energy dispersive X-ray analysis. No metallic n
iobium was obtained at temperatures below 500 degrees C. At temperatures be
tween 550 and 650 degrees C, the deposits were dendritic and non-adherent,
whereas pure niobium layers could be obtained at 750 degrees C. Detailed an
alysis showed that a large negative overpotential during the pulse current
period lead to the presence of suboxides, such as Nb6O, in the metallic pha
se. Suitable electrolysis conditions gave pure oxygen-free niobium. Cross s
ection 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 wer
e detected at the niobium-stainless steel interface, where homogenous adher
ent layers of thickness around 50 mu m were obtained.