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

Technical Report · Tue May 01 04:00:00 EDT 1990

DOI:https://doi.org/10.2172/6979456· OSTI ID:6979456

Windisch, Jr, C F; Stice, N D

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-Heroult 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. The results of potential-step studies, electrochemical impedance spectroscopy, and post-mortem microscopic analysis of polarized anodes suggest that the processes of corrosion of the metallic phase of the anode and the production of oxygen gas are separable and exhibit very different kinetic behavior. The corrosion reactions occur predominantly at low anode potentials, appear to show diffusion control, and may be related to the porosity of the anode. The oxygen production reaction is the predominant reaction above 2.2 V, exhibits activation control, occurs primarily on the surface of the anode, and is accompanied by an increase in surface roughness at higher current densities. Evidence presented in this report indicates that the production of oxygen shuts down the corrosion reactions, possibly through a pore-blocking mechanism. In addition, roughness effects may help explain some of the impedance relationships previously observed by PNL for these anodes. Although the present results do not rule out the formation of a protective layer or film, they strongly indicate mechanisms other than the formation of a macroscopic protective film for the apparent attenuation of corrosion reactions at typical operating current densities. 11 refs.

• Research Organization: Pacific Northwest Lab., Richland, WA (USA)
• Sponsoring Organization: DOE/CE
• DOE Contract Number: AC06-76RL01830
• OSTI ID: 6979456
• Report Number(s): PNL-7326; ON: DE90010364
• Country of Publication: United States
• Language: English

Related Subjects

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATION
320303* -- Energy Conservation
Consumption
& Utilization-- Industrial & Agricultural Processes-- Equipment & Processes
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400400 -- Electrochemistry
ALUMINIUM
ALUMINIUM COMPOUNDS
ALUMINIUM OXIDES
ANODES
CHALCOGENIDES
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
CHEMISTRY
CORROSION
CORROSION PROTECTION
CURRENT DENSITY
DATA
DOCUMENT TYPES
ELECTROCHEMICAL CELLS
ELECTROCHEMISTRY
ELECTRODES
ELEMENTS
EXPERIMENTAL DATA
FILMS
INFORMATION
KINETICS
MATHEMATICAL MODELS
METALS
NUMERICAL DATA
OXIDES
OXYGEN COMPOUNDS
PRODUCTION
PROGRESS REPORT
REACTION KINETICS