预氧化的56Cu-22Ni-12Fe-8Al-2La合金在低温铝电解熔盐中的腐蚀行为研究

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

摘要:

在800℃下，对未氧化与预氧化的56Cu-22Ni-12Fe-8Al-2La合金阳极在Na3AlF6-K3AlF6-AlF3-Al2O3铝电解熔盐体系中的腐蚀行为进行了研究。结果表明：预氧化合金在800℃氧气气氛下形成的氧化层主要为铝、镍、铁、铜及镧的氧化物。铝电解3小时后，未氧化合金阳极表面腐蚀产物呈三层结构，不连续且多孔的氧化腐蚀产物层在电解过程中形成连通通道，导致电解质直接渗透至金属基体约320微米深度。预氧化合金阳极的腐蚀氧化层厚度约为190微米，外层与内层均含有连续的富镍/铁/铝/铜氧化物（以NiFe2O4、CuAlO2为主），中间层为厚度约15微米且致密连续的NiFe2O4层。该氧化层内仅出现少量电解质渗透现象，且向金属基体渗透程度较浅。与未氧化合金相比，预氧化合金在铝电解过程中表现出更优的耐腐蚀性和稳定性。同时对金属阳极在铝电解熔盐中的电化学性能进行了测试，并探讨了合金在低温铝电解熔盐电解质中的腐蚀机理。

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.