Description: A low-temperature aluminum smelting process being developed differs from the Hall-Heroult process in several significant ways. The low-temperature process employs a more acidic electrolyte than cryolite, an alumina slurry, oxygen-generating metal anodes, and vertically suspended electrodes. Wetted and drained vertical cathodes are crucial to the new process. Such cathodes represent a significant portion of the capital costs projected for the new technology. Athough studies exist of wetted cathode technology with Hall-Heoult cells, the differences make such a study desirable with the new process. This project is such a study. In Phase 1, titanium diboride, zirconium diboride and composites of these with other materials were tested using a statistically useful test matrix. The materials were consolidated both by hot pressing and by a new method, plasma pressure compaction (P2C�). The materials were subject to controlled electrolysis tests under conditions of the low-temperature smelting process. Post-electrolysis characterizations included quantitative atomic analyses and electron microscopic examinations. These methods allowed evaluating the relative merits of the materials, and the mechanisms of their corrosion. Also, a few tests were performed to determine whether oxygen and carbon dioxide bathing vertically suspended cathodes exhibited different current efficiencies. In Phase 2, additional composite materials were fabricated with P2C�, electrolysis tested, and subsequently characterized. The statistical test matrix was not used in this Phase. However, the materials were tested with electrolysis lasting both five and twenty hours. The project demonstrated that good current efficiencies are obtained with the new process at this scale. All of the materials tested except for aluminum infiltrated aluminum nitride wetted well and gave comparable electrolysis voltages. Both hot pressing and P2C� produce grain structures in the consolidated materials. Grain loss to the product metal is the dominant corrosion mechanism of these materials as cathodes. Grain loss is more of a problem with the composites ...
Date: September 30, 2002
Creator: Brown, Craig W.
Item Type: Refine your search to only Report
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