The Corrosion Behavior of Pre-oxidized 56Cu-22Ni-12Fe-8Al-2La Anode Alloy in Low Temperature Molten Electrolyte for Aluminum Electrolysis

Abstract:

The corrosive behaviors of unoxidized and pre-oxidized 56Cu-22Ni-12Fe-8Al-2La anode alloys are investigated in Na3AlF6-K3AlF6-AlF3-Al2O3 electrolytes for aluminum electrolysis at 800℃. Results show that the oxide layer formed on the pre-oxidized alloy at 800 °C under O2 atmosphere is mainly oxides of aluminum, nickel, iron, copper, and lanthanum. After 3h aluminum electrolysis, the corrosion products formed on unoxidized anode alloy is a tri-layered structure and the discontinuous and porous oxide layer provides a connected channels during electrolysis, allowing direct electrolyte penetrate into the metal matrix for about 320 μm thickness. The corrosion oxide layer formed on pre-oxidized anode alloy is about 190 μm thickness. The out and inner oxide layer includes a continuous Ni/Fe/Al/Cu-rich (mainly NiFe2O4, CuAlO2) oxides. The middle layer containing of a dense and continuous NiFe2O4 with a thickness about 15 μm. A small amount of electrolyte appears in the oxide layer and penetrate into the metal matrix. The pre-oxidized alloy exhibited a better corrosion resistance and stability in comparison with that unoxidized alloy during aluminum electrolysis. The electrochemical performances testing of the metal anodes in molten salt for aluminum electrolysis are carried out and the corrosion mechanism of the alloys are also investigated.