Investigation of the codeposition of Fe and Mo from sulphate-citrate acid solutions

This paper presents the study of the electrodeposition of Fe-Mo from sodium citrate solutions at pH 4.0. The behaviour of the deposits was investigated by cyclic voltammetry (CV) for different Fe:Mo ratios and they were characterized by scanning electronic microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) analysis. The XPS results show that, in the solution containing the least Fe, molybdate can only be reduced to a mixture of polyvalent molybdenum oxides and/or hydroxide. On the other hand, when the Fe concentration is higher, molybdate can be reduced to metallic Mo and the alloy can be obtained. However, for 10:1 molar ratio practically only Fe, as oxide and metallic iron, is deposited. In this case, the amounts of Fe-Mo alloy corresponding to 2% of the deposits. In all cases the deposits obtained consisted of the oxide layers doped with Fe-Mo. SEM analysis demonstrated that globular and compact deposits were obtained at higher Fe contents. Regular deposition is observed for Fe and Mo codeposition, at all molar ratios studied, since the Fe:Mo ratio in the alloy was lower than the corresponding [Fe(II)]/[Mo(VI)] ratio in solution.