Electrochemical preparation of W coatings in Na2WO4-WO3-ZrO2 molten salt

Abstract

In this paper, the flat tungsten coatings with uniform grains were prepared via electrolytic tungsten at 1173 K in ternary molten salt system formed by tungstate, tungsten oxide and different mass fractions of ZrO2. Dense tungsten coatings containing the second phase of ZrO2 were obtained by constant direct current electrodeposition in molten salt, and the coatings have preferential growth orientation along the (2 1 1) crystal plane. These coatings were characterized via X–ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectrometry (EDS) and laser scanning confocal microscope (LSCM). The results show that W-ZrO2 coating obtained at Na2WO4-WO3-ZrO2. In addition, the existence of zirconia in molten salt reduced the coating roughness from 13.567 μm to 3.017 μm, the current efficiency was lost from 84.15% to 70.76%, and the grains became fine and uniform. What’s more, the mechanical properties and thermal cycle performance of the coating have been effectively improved. To further illustrate the electrochemical process, the electrochemical behavior of tungsten ions and zirconium ions during the electrodeposition was investigated by cyclic voltammetry (CV) and square wave voltammetry (SWV). The results indicated that the reduction reactions of tungsten ions and zirconium ions are divided into two steps, and the reaction processes are as follows: W(VI) → W(IV) → W, Zr(IV) → Zr(II) → Zr.