Anodic Behavior of Ni₄₈Fe₄₇Cu₅ and Ni₄₂Fe₃₈Cu₂₀ in Potassium-Rich NaF-KF-AlF₃-Al₂O₃ Melts

The anodic behavior of Ni₄₈Fe₄₇Cu₅ and Ni₄₂Fe₃₈Cu₂₀ alloys in NaF-KF-AlF₃-Al₂O₃ electrolyte was studied using electrochemical methods, such as chronopotentiometry, chronoamperometry, and linear sweep voltammetry at 770°C. The cryolite ratio and potassium ratio were 1.3 and 0.7, respectively. The steady-state polarization curves were obtained before and after galvanostatic polarization for 2 h. The current densities in the passivation region were lower for both anodes after polarization than before, indicating the formation of a protective passive layer during polarization. When anodes were subjected to potentiostatic polarization at 2.2 V (vs. reference), a passive film was readily formed. Linear sweep voltammograms were obtained on Ni₄₈Fe₄₇Cu₅ and Ni₄₂Fe₃₈Cu₂₀ alloys, and the polarization resistances were 5.227 Ω cm⁻² and 5.968 Ω cm⁻², respectively. During the galvanostatic electrolysis, the anodic potential (vs. reference) constantly varied with time for the Ni₄₈Fe₄₇Cu₅ anode. In contrast, the anodic potential of Ni₄₂Fe₃₈Cu₂₀ remained almost constant throughout the electrolysis. The thickness of the oxide layer formed on the anodes Ni₄₈Fe₄₇Cu₅ and Ni₄₂Fe₃₈Cu₂₀ after 2 h of electrolysis were around 90 μm and 30 μm, respectively.