Different mechanisms are proposed in the literature to describe the formation and behaviour of inclusions during electroslag remelting: - dissolution in the liquid metal of the inclusions already present in the electrode and then renucleation in the freezing ingot. - total or partial dissolution in the slag. - exchange reactions between inclusions in the metal and the slag. - entrapment in the freezing ingot of pieces of slag skin or droplets of slag. The mechanism of dissolution of alumina inclusions in a 70/30 CaF₂/Al₂0₃ slag has been studied in detail. For this a new equilibrium diagram for the system CaF₂/Al₂0₃ has been proposed and the diffusion coefficient of alumina in the slag has been determined by the rotating disk system. In a 70/30 CaF₂/Al₂0₃ slag at 1518°C the diffusion coefficient was estimated as D = 8.5 10⁻⁹ m² sec⁻¹. Calculations of the extent of the dissolution of alumina particles in the slag predicted that big particles (800 μ) might dissolve only partially in the slag. Particles of this size were introduced artificially in electrodes, but after electroslag remelting a much larger number of relatively small (15 μ max) alumina, iron aluminates and iron oxide inclusions were found in the ingot. The same types of inclusions could also be observed in ingots obtained after remelting a Ferro Vac-E electrode. The presence of these inclusions cannot be explained by one the mechanisms proposed precedently (dissolution in the liquid metal and then renucleation or partial dissolution in the slag), but only by an electrolytic oxidation and electrolytic aluminum dissolution on the electrodes and then nucleation of deoxidation products in the freezing ingot. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

It has been suggested by others that hot working is an extension of high temperature creep because of the similar observed dependencies of stress, strain rate, temperature and the similar activation energies of the two types of deformation. This suggestion has been evaluated for commercial purity aluminum by obtaining stress, strain rate and temperature data in the strain rate range 10⁻⁴ to 10¹/second. Published hot compression, hot torsion, and high temperature creep work of others is used to provide supplementary data. A combination of the published work of others with the present experimental work provides data in the strain rate range 10⁻⁷ to 10⁺²/second. From the present analysis, contradictions arise against the theory that hot working is an extension of high temperature creep. First, the method of evaluation of the material constant α in the hyperbolic stress-strain rate relation, [formula omitted], must change in going from creep to hot working. Secondly, the activation energy varies. Those that have suggested that hot working is an extension of high temperature creep found that α and the activation energy were independent of strain rate. Their work is compared to the present analysis and many discrepancies were found. The work in the literature left a data gap in the strain rate range 10⁻³ to 10⁰/second. Hot tensile tests and hot rolling tests were used to provide data in this gap. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

This investigation is an attempt to verify the original work done by George Antonoff and Anne Rowley, and to contribute specific data on the action of a magnetic field on aluminum cells. Experiments of the type they have described have been performed and an extensive set of data has been collected. It was thought that if the results of Antonoff and Rowley could be duplicated, further investigation would be warranted. However, the experiments have produced negative results. These results are described in detail in these chapters.

The purpose of this work was to determine the liquidus surface of the cryolite-rich portion of the ternary system Na₃AlF₆-CaF₂-AlF₃ and to establish the effect of Al₂O₃ on the operation of the Hall cell electrolysis. A series of isotherm of the cryolite-rich portion were graphed. It was shown that pseudo-binary phase diagrams of Al₂O₃ and bulk composition in the cryolite-rich portion of the Na₃AlF₆-CaF₂-AlF₃ system were found to be simple eutectic. The temperatures and the alumina contents of the double solubility limit, two important parameters for the Hall cell, of the joins 95 Na₃AlF₆/5 AlF₃-Na₃AlF₆, 90 Na₃AlF₆/ 10 NaCaAlF₆ and 85 Na₃AlF₃/15 AlF₃-NaCaAlF₆ were determined. The cryolite liquidus temperature of the quaternary system Na₃AlF₆-CaF₂-AlF₃-Al₂O₃ was found to be expressed by: T_Liq.. (C) = 1009.4 + 4.059(CaF₂) - 1.167(CaF₂)² + 0.968 x (CaF₂)(AlF₃) - 0.105(CaF₂)(AlF₃)² + 0.073 x (CaF₂)²(AlF₃) + 0.002(CaF₂)² (AlF₃)² - 4.165 x (AlF₃) - 0.054(AlF₃)² - 5.33(Al₂O₃) for CaF₂ 3.8~11.25%, AlF₃ 5~20%. / M.S.

The NaCaAlF₆-Al₂O₃ and Na₃AlF₆-Al₂O₃-NaCaAlF₆ phase diagrams were determined using DTA, x-ray diffraction, quench analysis, and optical microscopy. The NaCaAlF₆-Al₂O₃ system was a simple eutectic system with the eutectic located below 0.5 weight percent NaCaAlF₆. The ternary system was a eutectic system showing solid solution of NaCaAlF₆ in both polymorphs of Na₃AlF₆. Alumina exhibited no appreciable solubility in Na₃AlF₆ and, in the ternary system, less than 2% solubility above 15% NaCaAlF₆. / Master of Science