a contamination of the produced aluminium by 200 ppm of nickel which corresponds to the experimentally measured quantities in typical tests the wear rate of a nickel iron sample corresponds to approximately 1 2 micron day therefore it will theoretically take about 80 to 85 days to wear 0 1 mm of the anode a multi layer non carbon metal based anode was prepared comprising a self formed electrochemically active outer oxide based surface layer according to the invention the anode was made by coating by electro deposition a structure in the form of an rod having a diameter of 12 mm consisting of 74 weight nickel 17 weight chromium and 9 weight iron such as inconel u00ae first with a nickel layer about 200 micron thick and then a copper layer about 100 micron thick by plasma spraying the coated structure was heat treated at 1000 u00b0 c in argon for 5 hours this heat treatment provides for the interdiffusion of nickel and copper to form an intermediate protective layer the structure was then heat treated for 24 hours at 1000 u00b0 c in air to form a chromium oxide cr 2 o 3 barrier layer on the structure and oxidising at least partly the interdiffused nickel copper layer thereby forming the intermediate layer thereby forming an inner core for an anode according to the invention a.