Tantalum: Fused Fluoride Bath with Tantalum Oxide Electrolysed at 700 °C (Driggs, US 1,815,054)

A melt of potassium and sodium fluorides with potassium tantalum fluoride carries dissolved tantalum oxide; a direct current of about 20 A deposits tantalum powder on the graphite crucible while oxygen leaves at the carbon anode. Feeding in more oxide keeps it running. Result: crystalline tantalum powder, ready for pressing and sintering. Source: F. H. Driggs (Westinghouse), US patent 1,815,054 (filed 1928), pp. 1-3. When the oxide runs out the voltage jumps and fluorine is set free: stop at once. Picture drawn by Youblob.