Electrodeposition of tungsten from ZnCl2-NaCl-KCl-WO3 melt and analysis on tungsten species in the melt

Abstract

The electrodeposition of tungsten in ZnCl2-NaCl-KCl-WO2 melt at low temperature was further studied to obtain a thicker deposit. In the ordinary electrolysis at 0.05 V vs. Zn(II)/Zn, the current density decreased from 1.2 mA cm-2 to 0.3 mA cm-2 in 6h. It was found that the soluble tungsten species slowly changes to insoluble ones in the melt. The soluble species was suggested to be WO3F- anoin. One of the insoluble species was confirmed to be ZnWO4 and the other one was suggested to be K2WO2F4. Electrodeposition was carried out under the same condition as above except for the intermittent addition of WO3 every 2h. The Voltage was kept at the initial value and the thickness was 20 μm. The intermittent addition of WO3 was confirmed to be effective to obtain a thicker tungsten film. The deposited W films are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM).