Experimental Determination of Mg Activities in Fe-Mg Solutions
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gnesium and other alkaline earth metals, especially their oxides, are used widely in the production of highquality steels. Magnesium metal is used mostly as a desulfurization agent of hot metal, whereas its oxide serves as the main component in refractory linings for different kinds of steelmaking reactors. The use of MgO lining and MgO-containing slag result in a certain amount of dissolved Mg in the liquid metal. The content of Mg dissolved in the metal has great impact on the stability of MgO containing inclusions. In addition, the carbothermic reduction of MgO in MgO-C linings is suggested to be one of the mechanisms behind formation of spinel type nonmetallic inclusions in molten steel,[1–3] leading to an increase in the total magnesium content in ladle processing. Because of the its crucial role, the deoxidation equilibrium for the reaction Mg(wt pct Fe) + O(wt pct Fe) = MgO(s) has been studied by several research groups.[4–8] Unfortunately, the results from different research groups show a poor consistency. The reported equilibrium constant of this reaction varies even three orders of magnitude. Zhang et al.[9] investigated the dissolution equilibrium of magnesium vapor in liquid iron, trying to exclude oxygen from the system. Their data treatment was later discussed by Hillert[10] and Tarby.[11] The self-interaction parameter of magnesium, derived by Tarby[11] from the data of Zhang et al.[9] was, as described by the author, of ‘‘unusual magnitude.’’ To have better process control and optimization toward clean steelmaking, reliable thermodynamic data for magnesium in liquid iron is essential. Therefore, the objective of the current work is to determine the JIMMY GRAN, Researcher, and DU SICHEN, Professor, are with the Department of Materials Science and Engineering, Royal Institute of Technology, 100 44 Stockholm, Sweden. Contact e-mail: [email protected] Manuscript submitted March 8, 2011. Article published online August 9, 2011. METALLURGICAL AND MATERIALS TRANSACTIONS B
activities of magnesium in liquid iron by measuring experimentally the distribution ratio of magnesium between silver and iron. The principle of the experiment is to use a semienclosed vessel that would allow gas to escape when there is a pressure difference between the inside and outside of the vessel, but not allow extensive gas exchange with the outside at mechanical equilibrium. For this purpose, a Mo-vessel equipped with a conical lid was used. To check the reliability of the setup to maintain 1 atmosphere inside the container and at the same time avoid any gas entering from the surrounding into the vessel, a series of tests were made at room temperature. The Mo-vessel was filled with a well-weighed amount of ethanol. The conical Mo lid was put on the vessel by hand and a small hammer, using slight force not to seal the chamber completely. The Mo vessel with ethanol was placed in the water bath of a thermostat kept at predetermined temperature. After a certain period of time, the vessel was withdrawn from the bath and dried carefully on the o
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