Dissolution Behavior of MgAl2O4 Spinel Inclusions in Mold Slag

This study investigates the dissolution behavior of single crystal MgAl2O4 particle in CaO-SiO2-Al2O3-MgO-CaF2-Na2O slags using single hot thermocouple technique (SHTT) from 1550 to 1650 degrees C. MgAl2O4 contents of the slag are set at 5, 15, and 25 wt%, and the basicity (CaO/SiO2) of the slags is fixed at 0.9. Dissolution rate is determined by image analysis of the MgAl2O4 spinel size over time in the slag. In the experimental results, the dissolution rate increases as the temperature increases and as the contents of MgAl2O4 in the slag decreases. During the dissolution, the cube or trapezoid cube shaped MgAl2O4 particles change into a truncated cube, a cube with rounded corners and a sphere. The shrinking core model is modified into a volume ratio and found that the MgAl2O4 dissolution kinetic varies with the slag chemical composition. At high temperature, it appears to be chemical controlled. The dissolution firstly occurs at the corners and edges of the cube particle which can be understood by the Gibbs-Thomson equation. The activation energies of MgAl2O4 dissolution are 205 kJ mol(-1) at 5 wt% MgAl2O4, 181 kJ mol(-1) at 15 wt% MgAl2O4 and 594 kJ mol(-1) at 25 wt% MgAl2O4. The activation energy calculated should be started as similar to other inclusions of Al2O3 and MgO.