Production of Tungsten Electrode Used in Rare Earth Fused Salt Electrolysis by Activated Sintering Method

Using fused salt electrolysis method for rare earth metals production need to use refractory and corrosion metal as cathode and cathode material usually chooses molybdenum electrode or tungsten electrode. Fused salt electrolysis method for rare earth metals production usually requires high temperature and the cathode should has corrosion resistance property. Tungsten electrode and molybdenum electrode has good high temperature performance and corrosion resistance property, therefore become the preferred cathode material. However, comparing molybdenum electrode with tungsten electrode, molybdenum electrode corrosion resistance is poorer than tungsten electrode, and consumption is faster. On the other hand, some rare earth has a strict requirement on impurity content and molybdenum is one of impurity element of rare earth. So many manufacturers will use tungsten electrode as cathode using in fused salt electrolysis for rare earth production instead of using molybdenum electrode.

Tungsten electrode production usually uses powder metallurgy method and the key process of this method is sintering. When tungsten bar diameter is less than 20mm, they usually directly use vertical furnace for tungsten bar sintering. When tungsten bar diameter is larger than 20mm need to use intermediate frequency sintering furnace for sintering and after sintering need to process forge. However, both methods require higher sintering equipment and there will have welding difficult as well. Thus, most manufacturers choose activated sintering method for tungsten electrode sintering. This method is using physical or chemical means to reduce sintering temperature and increase sintering speed, thereby increasing the density and associated performance of electrode.

Using activated sintering method to produce tungsten electrode so it can use in fused salt electrolysis for rare earth metal production and the detail production processes are as follow:
1. Mixing powder: making a small amount of the activator nickel salt dissolves in ethanol, and then pours this solution into tungsten powder and mixing well.
2. Pressing: mixed tungsten powder to dry under the protection of hydrogen, nickel will coat on tungsten particle surface, then using cold isostatic pressing presses tungsten powder into a billet.
3. Sintering: after pressing to sinter pressed tungsten powder into a billet can obtain tungsten electrode.

The experiment found that using nickel-coated tungsten powder as raw material for tungsten electrode production which produces by activated sintering method has better property than traditional tungsten and molybdenum electrodes.