MECHANISMS OF CALCIUM OXIDE DISSOLUTION IN CaO-Al_2O_3-SiO_2-BASED SLAGS

摘要

The dissolution of solid lime particles into liquid slags at high temperatures was investigated by means of confocal laser scanning microscopy (CLSM). An additional solid layer around the lime particle was observed at the intermediate stage of the dissolution into CaO-Al_2O_3-SiO_2 slags. The dissolution rate was decelerated due to the existence of the additional layer and the dissolution profile could be clearly distinguished into three stages, i.e. an early, intermediate and late stage. By adding 10 wt% MgO, this layer could be effectively eliminated and the slope of the whole dissolution profile kept relatively constant. The dissolution path and mechanisms were subsequently evaluated by incorporating thermodynamic calculations. Both direct and indirect dissolutions could be distinguished. It was realized that the decrease in composition range for solid precipitating after adding MgO could significantly reduce the interfacial reaction (IR) layer formation. Post-mortem analyses on quenched samples were further carried out to confirm the theoretical calculations. It was found that the solid layer in slags without MgO was (CaO)_2SiO_2 and (CaO)_3SiO_2 which is in line with the thermodynamic calculations. However, only (CaO)_2-SiO_2 was noticed in slags with MgO which both (CaO)_2SiO_2 and MgO phases should be present according to the calculations. The non-equilibrium during dissolution may play an important role on phase transformation and MgO particles in much smaller quantity may have dissolved into (CaO)_2·SiO_2 phase.