Influence of B-Containing Compound on Electrodeposition of Mo and W in Molten Fluoride-Oxide Electrolyte

Abstract

The production of molybdenum (Mo) and tungsten (W) utilizes ultra-high temperatures, resulting in high production costs. If Mo and W plates can be directly produced at relatively low temperatures, drastic cost reduction and energy savings are expected. It is known that molten fluoride-oxide electrolytes containing boron oxides exhibit good adhesion to substrates and provide the smoothest surface; however, the role of boron oxides is unclear. Therefore, in this study, the effect of K2B4O7 on the electrodeposition of Mo and W in molten LiF−KF−KCl−K2MO4 (M=Mo, W) at 1223 K was investigated. The apparent current efficiency for Mo and W deposition decreased drastically with increasing cathode current density in the absence of K2B4O7 addition. In Mo deposition, the apparent current efficiency reached approximately 100% with the addition of 0.1 mol% K2B4O7. In W deposition, the apparent current efficiency reached approximately 100% with the addition of 5 mol% K2B4O7. The electrodeposited films comprised columnar crystals growing from the cathode to the electrolyte, and the Mo and W films contained 0.46 mol% of B and 0.10 mol% B, respectively. It was concluded that the morphology of deposits changed from particle/dendritic crystal to flat film crystal with the addition of K2B4O7.