Activity of Chromium Oxide in CaO-SiO2-MgO-Al2O3-MnO-CaF2-CrOx Slag for Chromium Reducing Process

Thermodynamic data of chromium oxide activities in molten slags are important for improvement of the reduction treatment process of chromium oxides in stainless steel slags. The chemical equilibrium experiments were conducted in the present work to measure the activity coefficients of chromium oxides in the CaO-CaF2-MgO-Al2O3-SiO2-MnO-CrOx slags at 1 823 K (1 550 degrees C) under oxygen partial pressure of 2.57x10(-11) atm with different chromium oxides contents. It is found that no solid phase appears in the slag when the initial CrO1.5 mole fraction of the slag is no more than 0.00390 (0.5 mass%), which could ensure the accuracy of the chromium valence analysis. The activity coefficient of CrO keeps almost constant with the increase of mole fraction of total chromium oxides, which indicates that CrO obeys Henry's law under the present conditions. The activity coefficient of CrO1.5 firstly levels off and then rises sharply when the mole fraction of total chromium oxides reaches 0.00198, beyond this point, activity coefficient of CrO1.5 keeps relatively constant again. Through the Raman spectroscopy analysis, the sharp increase of the activity coefficient of CrO1.5 is assumed to be caused by the transformation of CrO1.5 from network former to network modifier.