THERMODYNAMIC STUDY ON CROX CONTAINING SLAGS

Activities of chromium oxides, CrO and CrO1.5, were determined in CaO- SiO2-CrO(x) based slags by the electromotive force method. Equilibrium was achieved between a slag arid a Cr-saturated Cr-Ag alloy, and the oxidation state of chromium in the slags was evaluated by chemical ana lysis. The standard states of CrO and CrO1.5 were pure liquid and pure solid, respectively. The iso-activity contours of CrO and CrO1.5 in C aO-SiO2-CrO(x) slag system were obtained at 1600-degrees-C, and die ef fects of temperature and slag composition on the oxidation state of ch romium and the activities of chromium oxides in the slags were investi gated. When the temperature was raised in the range of 1500 - 1600-deg rees-C, the divalent chromium fraction in the slags increased but the activities of chromium oxides decreased. The effect of slag basicity w as significant. The higher the slag basicity, the lower the divalent c hromium fraction, and the higher the activities of chromium oxides. By partially substituting MgO for CaO, the activities of CrO and CrO1.5 decreased, but the oxidation state of chromium in the slag did not cha nge noticeably. Increasing the Al2O3 content from 0 to 10 mol% resulte d in a lower divalent chromium fraction and higher activities of chrom ium oxides at the slag basicity of 1.0 in mole ratio. A further increa se in the Al2O3 content to 20 mol% did not cause obvious change. The e xperimental results in the CaO-SiO2-CrO(x) quasi-ternary system indica te that the activities of both CrO and CrO1.5 have a positive deviatio n from the ideal solution. Based on the Gibbs-Duhem equation, the meas ured activities of chromium oxides were utilized to determine the acti vities of CaO and SiO2 in a quaternary CaO-SiO2-CrO-CrO1.5 system. Iso -activity diagrams for CaO and SiO2 were obtained at 1600-degrees-C in equilibrium with metallic chromium Finally, IRSID's slag model was at tempted to describe the thermodynamic properties of chromium containin g slags, and a group of model parameters was optimized by applying the present experimental data. The calculated results were in agreement w ith experimentally measured values at the low CrO(x) domain.