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.