Current production of aluminum in the United States is approximately 3.8 x 106 metric tons per year. The presently used system for the production of aluminum is the Hall-Herault cell. It is operated at 950 to 980 C and consists of a carbon cavity (lining) which conducts current from a molten aluminum cathode on the bottom of the cathode cavity. Consumable carbon anodes are suspended in a cryolite electrolyte (bath) which floats on the aluminum cathode (metal pad). Alumina powder is fed periodically or continuously, carbon anodes are consumed continuously (with periodic replacement in prebaked anode plants), and molten metal product is siphoned approximately daily. In this work the PI will examine new electrode materials and new concepts for electrochemical cell design and operation which could save energy and lower operating costs on retrofit older plants, as well as decrease both capital and operating costs for new aluminum reduction plants. The aluminum industry has for decades been pursuing a non- consumable anode that can be substituted for the consumable carbon anodes in the Hall-Herault cells. The PI plans to test a new alumina/carbon composite anode made of a Ni-Fe-Cu cermet material. This composite anode technology utilizes the same reaction as the Hall-Herault technology but the alumina in the anode is dissolved at the anode-bath interface at exactly the location where oxide ions are discharged on the carbon matrix. The result is that high alumina solubility in the bath is not required, and low-temperature baths could be used. The bath to be used in this research project is a mixture of sodium and lithium cryolites having a freezing point less than 670 C and operating at about 700 C Titanium diboride sleeves inside the crucible will serve as an alternate cathode to graphite. The phase I objectives include: o Maintenance of slurry in suspension without formation of deposits. o Limiting current density as a function of Al2O3 particle size in the feed and slurry density. o Effect of bath temperature on limiting current density and other operating parameters in the range of 700 to 800 C. o Mixed fluoride-chloride bath performance compared to all- fluoride bath. o Potential distribution in respect to thermodynamic overpotentials and ohmic drops. o Corrosion of cermet anode contamination of aluminum metal by cermet anode components.
