Development of a rotating ring-disc electrode for high temperature studies in cryolite-based melts

A compact rotating ring-disc electrode incorporating a molybdenum disc, gold ring and boron nitride insulator has been designed, constructed and evaluated in molten cryolite-based electrolytes at temperatures up to 1000°C and rotation rates between 0 and 2000 rpm. The electrode design is extremely versatile and relatively maintenance free, with no visible evidence of melt leakage at the ring-insulator and disc-insulator interfaces. The operating performance of the gold-molybdenum rotating ring-disc electrode was evaluated from collection efficiency measurements based on the dissolution of the disc surface and subsequent detection of soluble species transported to the ring. The observed collection efficiency was less than the theoretical value determined from the geometry of the electrode, primarily because of noncoplanarity of the electrode surface at the working temperature. The results confirm that the electrode should be useful for mechanistic studies in high temperature molten fluoride electrolytes.