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 degrees C-920 degrees 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 degrees 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.

Automated summary

A thick and nonporous metallic molybdenum coating was successfully obtained on copper and 316L stainless steel substrates using molten salt electrolysis. Analysis revealed that the presence of potassium fluoride and sodium tetraborate was necessary for the cathodic discharge of MoO4-2 to Mo, with higher temperatures favoring cathodic deposition. X-ray diffraction confirmed the deposition of single phase body centered cubic Mo.