In Situ Observation of Dissolution Behavior of Aluminum Oxide and Nitride in CaO–Al₂O₃ Slag

In this study, the dissolution behavior of Al 2 O 3 and AlN inclusions in CaO–Al 2 O 3 slag is investigated. Preliminary experiments are conducted to ensure slag homogeneity and AlN stability. Subsequently, the dissolution process of inclusions is investigated through confocal laser scanning microscopy. The dissolution process of Al 2 O 3 inclusion is direct, and no detectable intermediate phase forms during the process. In contrast, the AlN inclusion shows a very intense gas reaction with slag during the dissolution process. Based on the inclusion dissolution mechanism, the Al 2 O 3 directly dissolves as (Al 2 O 3 ) molecules into the slag. However, AlN might undergo an indirect dissolution process within the slag. The initial reaction between AlN and (O 2 ) from the slag phase results in the formation of N 2 bubbles and Al 2 O 3 . Subsequently, the Al 2 O 3 dissolves as (Al 2 O 3 ) into the slag, and partial N 2 bubbles diffuse into the slag. The rate limiting step of AlN and Al 2 O 3 dissolution is both distance‐limited mass transfer in the slag, while the mass transfer distance of AlN is longer than that of Al 2 O 3 . The calculated mass diffusion coefficient of AlN ( D AlN = 6.56 × 10 −9 m 2 s −1 ) is significantly smaller than that of Al 2 O 3 ( = 4.56 × 10 −8 m 2 s −1 ).