An investigation of the evaporation of B2O3 and Na2O in f-free mold slags

The present paper deals with the investigation of evaporation of B ₂O₃ and Na₂O from F-free mold slags in the temperature range of 1 573 to 1 673 K by Thermogravimetric Analysis (TGA) method. The study was aimed at elucidating the evaporation mechanism during continuous casting and identifying the resulting effect on the flux composition. The basicity was found to slightly enhance the evaporation rate of mold slags, suggesting that the mass transport in the liquid phase plays a role in controlling the evaporation. TiO₂ addition resulted in an increasing evaporation rate due to the decrease of viscosity of the slag. The diffusional flux resulting from gas phase mass transfer from the gas/slag interface to the bulk gas was theoretically estimated and the results suggest that this process is not the controlling step. The evaporation rate was found to increase with increasing ZrO₂ addition possibly due to the fact that the solid particles existing in the slag act as nucleation sites of bubbles formation. The evaporation rate was also found to increase with increasing experimental temperatures.