Activity of Chromium Oxide in CaO–SiO₂–MgO–Al₂O₃–MnO–CaF₂–CrO<i>_x</i> Slag for Chromium Reducing Process

Abstract

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-CaF 2 -MgO-Al 2 O 3 -SiO 2 -MnO-CrO x slags at 1823 K (1550℃) under oxygen partial pressure of atm with different chromium oxides contents. It is found 2.57 × 10 -11 that no solid phase appears in the slag when the initial CrO 1.5 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 CrO 1.5 firstly levels off and then rises sharply when the mole fraction of total chromium oxides reaches 0.00198, beyond this point, activity coefficient of CrO 1.5 keeps relatively constant again. Through the Raman spectroscopy analysis, the sharp increase of the activity coefficient of CrO 1.5 is assumed to be caused by the transformation of CrO 1.5 from network former to network modifier. KEY WORDS: activity; chromium oxide; CaO-SiO 2 -MgO-Al 2 O 3 -MnO-CaF 2 -CrO x slag; stainless steel; reducing process.