Niobium: Fused Potassium Niobium Oxyfluoride Electrolysed at 400-600 A in a Water-Jacketed Iron Pot (Balke, US 1,905,882)

Balke made the first workable niobium. He cleaned the potassium niobium salt of tin, tungsten and tantalum, dried it completely, melted it with an electric arc in a water-cooled iron pot and electrolysed it with a big carbon anode at 20 volts; crystals of niobium grow on the bottom of the pot. Result: crystals of pure niobium, ready for pressing and vacuum sintering. Source: C. W. Balke (Fansteel), US patent 1,905,882 (filed 1928), pp. 1-3, Fig. 1 (shown above). Hydrofluoric acid and the fuming melt are poisonous; the arc and 400-600 A need proper electrical gear.