Influence of bath composition on the electrodeposition of amorphous Ni‐Mo alloys using potassium‐sodium tartrate as complexing agent

Abstract

AbstractCurrently, sodium citrate is the most used complexing agent for electrodeposition of Ni‐Mo coatings, especially for studying the effect of bath temperature and current density on the proprieties of Ni‐Mo coatings. This study evaluates the influence of the concentrations of nickel sulphate and sodium molybdate on the electrodeposition of Ni‐Mo alloys in baths using tartrate as a complexing agent. Electrodepositions were carried out in a two‐electrode cell. A 32 complete factorial design of experiments along with response surface methodology (RSM) was used for the optimization of bath variables for electrodeposition of Ni‐Mo alloys. The coatings obtained were characterized in terms of chemical composition and surface morphology. The chemical composition of the coatings was most influenced by the sodium molybdate concentration. Ni‐Mo coatings of good quality were obtained in potassium‐sodium tartrate baths with Mo content in the range 18‐44 wt%; some results present even higher Mo content than coatings obtained from citrate baths. The coating with the highest Mo content was deposited from the bath with a concentration ratio of nickel sulphate to sodium molybdate of 1:1. Surface morphology varied according to chemical composition, and microcracks were observed for the coating with 41 wt% Mo, for which scanning electron microscopy (SEM) images also show the presence of nodules. The most homogeneous coating surface was obtained at a concentration ratio of nickel sulphate to sodium molybdate of 10:3. X‐ray diffraction analyses have shown that all coatings obtained in this work are amorphous.