Cu-ni-fe anodes having improved microstructure

#This invention relates to electrolytic production of aluminum from alumina and more particularly, it relates to an improved anode for use in a cell for the electrolytic production of aluminum.

#In the electrolytic production of aluminum, there is great interest in utilizing an anode substantially inert to the electrolyte and which does not react with oxygen during cell operation. Anodes of this type are described in U.S. Pat. No. 4,399,008 which discloses a composition suitable for fabricating into an inert electrode for use in the electrolytic production of metal from a metal compound dissolved in a molten salt. The electrode comprises at least two metal oxides combined to provide a combination metal oxide.

#Also, U.S. Pat. No. 5,284,562 discloses an oxidation resistant, non-consumable anode for use in the electrolytic reduction of alumina to aluminum, which has a composition comprising copper, nickel and iron. The anode is part of an electrolytic reduction cell comprising a vessel having an interior lined with metal which has the same composition as the anode. The electrolyte is preferably composed of a eutectic of AlF3 and either (a) NaF or (b) primarily NaF with some of the NaF replaced by an equivalent molar amount of KF or KF and LiF.

#FIG. 1 is a vertical cross-sectional view of a test cell used for testing anodes of the invention.

#FIG. 2 is a micrograph showing multiple phase metallurgical structure of Cu—Ni—Fe cast anodes.

#FIG. 3 is a micrograph showing single phase microstructure of a Cu—Ni—Fe cast anode of FIG. 3 after heating.

#Anodes of the present invention may be employed in any aluminum producing electrolytic cell. Further, the anodes may be used with any electrolyte which does not oxidize or cause degradation of the electrode during electrolysis. Preferred electrolytes are set forth in our U.S. Pat. No. 5,284,562 incorporated herein by reference as if specifically set forth.

#Referring to FIG. 1, there is shown a laboratory electric cell referred to generally as 10 used for testing anodes in accordance with the invention. Cell 10 comprises an alumina crucible 11 containing an anode 12, a cathode 13, and a molten electrolyte bath 14. Alumina crucible 11 is positioned within a stainless steel container 15. As shown in FIG. 1, the inner surface of the sidewall of container 15 and the outer surface of the sidewall of crucible 11 are in abutting relation. In practice, a space can exist between the respective sidewalls of container 15 and crucible 11. In such a case, the space may be filled with graphite or petroleum coke particles to assist in the uniform distribution of heat to the sidewall of crucible 11.

#Cathode 13 is typically a slab of titanium diboride, a composite of titanium diboride and graphite, or molybdenum. Anode 12 is in the form of a metal disc overlying and substantially covering the bottom 16 of crucible 11. A vertical copper conductor 17 has a lower end connected to disc 12 and an upper end connected to a source of electric current (not shown). Vertical conductor 17 is insulated with an alumina tube 18 so as to confine the anodic current to disc 12. Cathode 13 is connected in a conventional manner to the source of electric current. Cell 10 is placed in a furnace and held at a temperature at which electrolyte bath 14 is molten (e.g., 680-800° C.). The temperature of bath 14 is measured continuously with a chromel-alumel thermocouple contained in a closed-end fused alumina tube (not shown).