As the last step of inclusion removal in tundish, the dissolution of Al
2O
3 in tundish slag is very important and has received many interests by previous researchers. In the present work, the effect of Na
2O addition on dissolution of Al
2O
3 in CaO–Al
2O
3–MgO–SiO
2 slag at 1823 K was investigated by using rotating finger method. The interface between rod and molten slag was investigated using SEM-EDS technique. The dissolution of Al
2O
3 in CaO–Al
2O
3–MgO–SiO
2–Na
2O system increases with increase of rotating speed and immersing time. A linear relationship between logarithm of dissolution rate and logarithm of periphery velocity was found with a slope of 0.53, which indicates that rate determining step for dissolution of Al
2O
3 is the mass transfer of solute in boundary layer of molten slag. The dissolution rate of alumina in CaO–Al
2O
3–MgO–SiO
2–Na
2O slag increases with increase of Na
2O content, which could be attributed to the kinetic and thermodynamic factors. The decrease of viscosity of molten slag with increasing Na
2O content could lead to increased mass transfer in boundary layer of molten slag. On the other hand, the increase of Na
2O would lead to increase of thermodynamic driving force of Al
2O
3 dissolution. Some intermediate compounds such as MgAl
2O
4 and CaAl
4O
7 were found at interface between alumina rod and slag, indicating indirect dissolution of Al
2O
3 in slags.
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