Anodic behaviour of oxidised Ni-Fe alloys in cryolite-alumina melts

Nickel-iron alloys have been identified as promising inert anode candidates for the Hall-Heroult process. In this study. binary Ni-Fe alloys of various compositions were subjected to short-term galvanostatic electrolysis in a cryolite-alumina bath at 960 degrees C. Prior to electrolysis, the anodes were oxidised at 800 degrees C for 48 h, forming a protective scale. Fe2O3, Ni,Fe3-xO4 and NixFe1-xO were identified as the major scale components using a combination of X-ray diffraction (XRD) analysis and energy dispersive X-ray spectroscopy (EDX). Anodes having Ni content of 50-65 wt% performed adequately during short-term electrolysis. operating at a steady potential of 3-3.5V vs. AlF3/Al. Overall, it was found that the pre-formed oxide scale was effective in reducing anode wear and fluoridation. In the absence of a pre-formed scale, anodes were shown to undergo appreciable internal corrosion and/or passivation due to metal fluoride formation. Analysis of the anodes following electrolysis was performed using XRD and electron microprobe analysis (EPMA). (C) 2010 Elsevier Ltd. All rights reserved.