Effect of MgO contents on the dissolution rate of alumina into molten CaO-SiO₂-Al₂O₃-MgO slags

Dissolution rates of sintered alumina into molten CaO-SiO₂-9mass%Al₂O₃-MgO(CaO/SiO₂=0.80) slags were measured by a rotating specimen method. The dissolution rates into slags containing 5, 10, and 15mass% MgO were measured at 1773, 1823 and 1873K, and the revolution speed varied from 100 to 600 rpm. The microstructures of specimens after experiments were examined by an electron probe microanalyzer(EPMA), and the dissolution mechanism was discussed. The dissolution rate of alumina increased with increasing revolution speed and temperature. The dissolution rate of alumina into the slags containing more than 10mass% MgO were increased more rapidly with increasing revolution speed and temperatures, compared with that into the slag containing 5mass% MgO. The dissolution rate of alumina decreased with increasing MgO content up to 15mass%. According to the EPMA analysis, a deposition of MgO · Al₂O₃ spinel particles was observed in slag adjacent to the alumina specimen. The spinel particles formed a layer in slags containing more than 10mass% MgO, and the thickness of the layer was increased with increasing MgO content in slags. These morphological differences of the spinel layers suggest that the spinel layers suppress the flow of slag components, and the dissolution rate decreases with increasing MgO content. Moreover, the morphology of spinel layer was changed with revolution speed, this morphological change is considered to be the reason why the dependence of the dissolution rate on revolution speed differs by the MgO content in slag.