Micropyretic synthesis of nickel aluminide intermetallic composites and nonconsumable anodes in the Hall-Heroult cells for aluminum electrolysis.

摘要

Ni{dollar}sb3{dollar}Al and NiAl intermetallic compounds and their composites are potential structural materials for high temperature applications. Among the composites with different types of reenforcements, particulate-reinforced composites possess several advantages, such as isotropic properties, lower costs of reenforcement and easy fabrication. Particulate-reinforced composites also allow for a wider range of component geometry. In this dissertation, Nickel aluminide matrix composites based on Ni{dollar}sb3{dollar}Al+Cu and NiAl+Cu with CeO{dollar}sb2{dollar} particulates were prepared using the micropyretic synthesis techniques. The effect of processing parameters such as chemical composition, powder particle size, compaction pressure, combustion furnace temperature (heating rate) on the processing response parameters, phases of products, microstructure and mechanical properties of the composites were studied. The processing parameters played an important role on some of the processing response parameters, the microstructure and mechanical properties.; Several CeO{dollar}sb2{dollar} coated Ni-Al-Cu metallic and intermetallic anodes, and Ni-Al-Cu-CeO{dollar}sb2{dollar} intermetallic composite micropyretic anodes for the possible use in the Hall-Heroult cells for aluminum electrolysis were studied for their efficacy. Tests were made in laboratory size Hall-Heroult cells. An adherent, protective and electrically conductive CeO{dollar}sb2{dollar} coating of 0.5 to 2 mm thickness was obtained on the anode substrates under the electrolysis conditions which included the addition of 0.5-2.0 wt% CeF{dollar}sb3{dollar} in the cryolite-alumina electrolyte. Stable voltages were sustained for as long as 15 to 100 hours with very low wear rates with the Ni-Al-Cu and Ni-Al-Cu-CeO{dollar}sb2{dollar} anodes. The effect of the anode composition, the cell operating parameters such as current density, Al{dollar}rmsb2Osb3{dollar} and CeF{dollar}sb3{dollar} concentrations in the electrolyte on the deposition of CeO{dollar}sb2{dollar} coating and anode corrosion rate were studied. The microstructure of the coating, the anodes substrates after electrolysis tests were examined by SEM. The chemical composition of the coating, oxide layer and anode substrate was analyzed by EDS/SEM, and was aimed at revealing the possible dissolution mechanisms for the coated anodes.