预氧化56Cu-22Ni-12Fe-8Al-2La阳极在铝电解高温熔盐电解质中的腐蚀行为

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

摘要:

研究了未氧化和预氧化的56Cu-22Ni-12Fe-8Al-2La阳极合金在800 ℃的Na₃AlF₆-K₃AlF₆-AlF₃-Al₂O₃铝电解用熔盐电解质中的腐蚀行为。测试了金属阳极在铝电解熔盐中的电化学性能，并研究了合金的腐蚀机理。结果表明，合金在800 ℃、O₂气氛下预氧化形成的氧化层主要由含铝、镍、铁、铜和镧元素的氧化物组成。电解3 h后，未氧化的金属阳极形成的腐蚀产物呈三层结构，腐蚀产物中不连续且多孔的氧化层在电解过程中提供了连通通道，使电解质易直接渗透进入金属基体，深度约为320 μm；预氧化后的金属阳极形成的腐蚀产物氧化层厚度约为190 μm，外层和内层氧化层包含连续的富Ni/Fe/Al/Cu氧化物（主要为NiFe₂O₄、CuAlO₂），中间层为致密连续的NiFe₂O₄层，厚度约为15 μm，氧化层中出现少量电解质，并渗入金属基体。在铝电解过程中，预氧化后的合金较未氧化的金属阳极合金表现出更优的耐腐蚀性能和稳定性。

Abstract:

The corrosion behavior of unoxidized and pre-oxidized 56Cu-22Ni-12Fe-8Al-2La anode alloys was investigated in a Na₃AlF₆-K₃AlF₆-AlF₃-Al₂O₃ electrolyte for aluminum electrolysis at 800 °C. Electrochemical tests of the metal anodes in molten salt for aluminum electrolysis were conducted, and the corrosion mechanism of the alloys was investigated. Results show that the oxide layer formed on the pre-oxidized alloy at 800 °C in an O₂ atmosphere mainly consists of oxides of aluminum, nickel, iron, copper, and lanthanum. After aluminum electrolysis for 3 h, the corrosion products formed on the unoxidized anode alloy demonstrate a tri-layered structure, and the discontinuous and porous oxide layer provides a connected channel during electrolysis, allowing the electrolyte to directly penetrate the metal matrix to a depth of approximately 320 μm. The corrosion oxide layer formed on the pre-oxidized anode alloy is about 190 μm in thickness. The outer and inner oxide layers include continuous Ni-/Fe-/Al-/Cu-rich oxides (mainly NiFe₂O₄ and CuAlO₂). The middle layer, with a thickness of about 15 μm, contains a dense and continuous NiFe₂O₄ layer. A small amount of electrolyte appears in the oxide layer and penetrates into the metal matrix. The pre-oxidized alloy exhibits better corrosion resistance and stability than the unoxidized alloy during aluminum electrolysis.