Inert Electrodes Program: Characterization of the reaction layer or film on PNL (Pacific Northwest Laboratory) inert anodes: Progress Report for April-December 1989

Abstract

This progress report addresses activities conducted at Pacific Northwest Laboratory (PNL) between April 1989 and December 1989 to characterize the reaction layer or film previously proposed by PNL to form on cermet anodes during the electrolytic production of aluminum in Hall-Herault cells. Formation of this resistive film was thought to protect the cermet anode from corrosion reactions that would otherwise occur in the molten cryolite electrolyte. i i; ACKNOWLEDGMENTS The authors acknowledge the assistance of the staff at Pacific Northwest Laboratory (PNL), in particular the managerial guidance provided by L. G. Morgan, the technical contributions of 0. H. Koski and D. M. Strachan, the microscopy work done by N. T. Saenz, and the secretarial support by D. L. Schneider. We are also grateful for the programmatic assistance provided by

Final report on the characterization of the film on inert anodes

“…The mechanism for the corrosion of the cermet anode at low current densities is not certain, but, based on the results of potential-step studies, it appears to be diffusion-controlled and to occur in the cermet's pores. The production of oxygen gas at 2.2 V and above may attenuate this corrosion process by blocking popes in the surface region and reducing access by the molten electrolyte to the Cu meta] phase (Windisch and Stice 1990). Another possibility is that the redox conditions present at low oxygen fugacities favor the corrosion/dissolution of the cermet anode.…”

Fabrication of advanced design (grooved) cermet anodes

“…This issue is complex and is not discussed further in the text. Refer to previous PNL publications for a more thorough description of anode wear (Strachan et al 1989;Windisch and Stice 1991;Windisch et al 1992a). lt is also important to note that the wear rates given in the text are extrapolated from short-term tests, assuming linearity.…”