The Effect of CaF_2 on Thermodynamics of CaO-CaF_2-SiO_2-Al_2O_3(-MgO) Slags

摘要

The slag system of CaO-CaF_2-SiO_2-Al_2O_3(-MgO) was thermodynamically assessed at by equilibratingit with liquid iron at 1873 K using a CaO or MgO crucible. To solve the experimental difficulties in treating CaF_2-containing slags, the pre-saturation with a piece of CaO crucible and the application of carbon paste to the crucible surface were made. The experimental results lead to the following conclusions. 1. The saturation point with CaO-containing phases (2CaO·SiO_2, 3CaO·SiO_2, and CaO) moves toward the region of low SiO_2 with the increase in CaF_2 content. It is also the case for the double saturation point with MgO and the CaO-containing phases. In addition, the solubility of MgO in the doubly saturated slags decreases with increasing CaF_2 content. 2. The sulfide capacities of the present slags increase significantly by increasing CaF_2 content and then become almost constant. 3. The activity coefficients of Fe_tO of the present slags initially maintain a nearly constant value but increase a little when CaF_2 exceeds 15 pet.