Activity-composition relations of MnO in MnO-CrO x -CaO-SiO 2 -containing melts
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I.
INTRODUCTION
CHROMIUM and manganese are two of the most important alloying elements in high-manganese stainless steels. Of major concern to potential high-manganese stainless steel producers, however, is a high loss of manganese through volatilization, due to high manganese partial pressures under steelmaking conditions (i.e., high temperatures and highly reducing conditions). It is therefore of fundamental as well as great practical importance to determine to what extent the recovery of both manganese and chromium, but specifically manganese, can be optimized in the smelting and subsequent refining processes of these stainless steels. Theoretical considerations indicate that high manganese losses can be minimized by keeping the steelmaking temperature as low as possible, and by the use of slags with high MnO activities at low concentrations of MnO. Consequently, it is important to determine MnO activitycomposition relations in MnO-CrOx-CaO-SiO2 slags, as a starting point for a better understanding of the behavior of MnO in slags which contain both MnO and CrOx. This was done by equilibrating selected slag samples with platinum at 1500 7C under an oxygen partial pressure of 1028.99 atm. The activities of MnO in these slags were calculated from a knowledge of the previously determined activities of manganese in platinum, which were calculated from the coefficients IMn, aPt-Mn, aPt-Cr, and aCr-Mn, using Darken’s
quadratic formalism for binary and ternary metallic solutions.[1] II.
THERMODYNAMIC EQUATIONS
The activity of MnO (aMnO) in the (MnO-CrOx-CaOSiO2)-containing melt was determined by alloying the sample with platinum, thereby establishing the following equilibrium: [Mn]platinum 1 1/2O2 (g) ⇔ MnO (
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