Electrochemical Investigation of Cathodic Deposition of Mo Coating from Oxofluoride Molten Salt and Characterization

Adherent, thick, nonporous metallic molybdenum (Mo) coating was successfully obtained on two different kinds of substrates Cu and 316L stainless steel by molten salt electrolysis from a eutectic mixture containing potassium molybdate (K₂MoO₄), sodium tetraborate (Na₂B₄O₇) and potassium fluoride (KF). Cyclic voltammetric analysis of the molten mixture in the temperature range 800 °C–920 °C revealed that the presence of both KF and Na₂B₄O₇ were necessary for cathodic discharge of MoO₄ ⁻² to Mo via two-step processes. It also confirmed that the reduction of Mo(VI) species was a diffusion controlled process and higher temperature favored the cathodic deposition up to 860 °C and thereafter it decreased. X-ray diffraction (XRD) of coatings confirmed about the deposition of single phase body centered cubic (bcc) Mo. The Mo coating thickness, microstructure and substrate/coating interface integrity were investigated in detail from cross-section FESEM images.