Inconsumable electrodes

#The invention relates to a process and a device for the electrolysis of a molten charge using inconsumable electrodes, in particular for the production of aluminum with a purity of more than 99.5 %.

#In the electrolytic production of aluminum by the Hall-Heroult process a cryolite melt with Al.sub.2l O.sub.3 dissolved in it is electrolysed at 940.degree. - 1000.degree. C. The aluminum which separates out in the process collects on the cathodic carbon floor of the electrolysis cell whilst CO.sub.2 and to a small extent CO are formed at the carbon anode. The anode is thereby burnt away.

#For the reaction

#The figures show:

#FIG. 1. A ceramic oxide anode with sides completely shielded

#FIG. 2 A ceramic oxide anode with sides partly shielded by solidified electrolytic material.

#In all figures the part leading the power to the anode is indicated by the number 1. It is made of metal or another electron conductive material such as a carbide, nitride or boride. The protective layer 2 on the anode 3 is made of a poorly conducting material which is resistant to attack by the molten electrolyte. The ceramic oxide anode 3 consists, advantageously, of doped SnO.sub.2 and is at least partly in contact with the electrolyte 4.

#In the embodiment shown in FIG. 1, the protective layer 2 on the cylindrically shaped anode 3 of ceramic oxide material, is a ring of electrically melted A1.sub.2 O.sub.3 or MgO which has been prefabricated and bonded, or sprayed onto the anode surface before immersing the anode in the melt. This protective ring completely covers the sidewalls of the ceramic anode 3 which is only partly immersed in the molten electrolyte 4. In this way a mainly uniform distribution of current is obtained on the exposed bottom face which is immersed in the molten electrolyte.

#It is however not necessary that the protective ring covers the whole of the side wall area, it may also be less extensive but must protect that part in the three phase zone.