Aspects of the oxidation of liquid aluminium alloys.
Agema, Klaas Sybren
University of Cambridge
Department of Materials Science and Metallurgy
Doctor of Philosophy (PhD)
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Agema, K. S. (1989). Aspects of the oxidation of liquid aluminium alloys. (Doctoral thesis). https://doi.org/10.17863/CAM.11452
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Nearly all the research on the oxidation of molten aluminium alloys was carried out on quiescent melts. However, in most industrial processes in which molten aluminium is handled, the liquid metal will be under dynamic flowing conditions. Therefore the oxidation behaviour of a melt of aluminium alloy will, in practical circumstances, not be determined by the diffusion of species through thick oxide scales, but by the strength and the deformation characteristics of the oxide skin, and by the short-time oxidation rate of the molten aluminium. The deformation behaviour of the oxide layer covering liquid molten aluminium alloys was investigated by subjecting the oxide scale in a controllable manner to tension and compression forces. Most of the deformation was found to take place in regions with a relative fresh oxide skin which had considerable flexibility. The old oxide scale does not seem to have any flexibility and fractures when subjected to deformation. The short-time oxidation rate of molten aluminium alloys was investigated using two different techniques. In the first technique a closed gas atmosphere was used and the oxidation rate after a disturbance of the protective oxide layer was determined by the change of oxygen partial pressure of the gas atmosphere. The short-time oxidation rate was also measured as an electric current using a fused salt layer situated on top of the molten aluminium alloy together with a conventional potentiostatic electrochemical arrangement. The results show that the oxidation rate can increase momentarily by a factor 100 when the oxide layer is removed, but within a matter of seconds a new protective oxide skin is formed after which the oxidation rate becomes very small. The formed oxide scales were investigated using SEM, optical microscopy, EDX and x-ray analysis.
This record's DOI: https://doi.org/10.17863/CAM.11452
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