The dissolution kinetics and mechanisms of solid calcium aluminate inclusions (CaO∙2Al₂O₃ (CA2) and CaO∙6Al₂O₃ (CA6)) in CaO-Al₂O₃-SiO₂-(MgO) metallurgical slags at 1550 °C were investigated using high temperature confocal laser scanning microscopy (HT-CLSM). The effects of slag viscosity, CaO/Al₂O₃ (C/A) ratio, and MgO content on the dissolution time of CA6 and slag MgO content on that of CA2 particles were examined by tracking the time dependent changes of particle projection areas. The obtained results showed that the dissolution kinetics of CA2 and CA6 particles was enhanced by an increase in slag MgO content. Moreover, increasing C/A ratio of slag or decreasing slag viscosity improved the dissolution rate of CA6 particles. Post dissolution analysis using scanning electron microscopy equipped with energy dispersive X-ray spectroscopy (SEM-EDS) combined with thermodynamic calculations revealed the dissolution paths of CA6 particles in slag S3 with C/A ratio 3.8 and S6 with 8.0 wt% MgO, where the dissolution time is out of expectation. It was found that an intermediate solid layer melilite formed around the undissolved CA6 particle in slag S3 with C/A ratio 3.8, reducing its dissolution rate. Conversely, the formation of randomly dispersed intermediate solid products around the undissolved CA6 particle in slag S6 with 8 wt% MgO did not impend their dissolution rate. Finally, based on the obtained findings, two distinct dissolution mechanisms were proposed advancing the understanding of solid inclusion dissolution in metallurgical slags. The findings obtained from this study aim to provide new insights to further improve steel cleanliness for a longevity of the product service life.

The dissolution process of CaO·2Al₂O₃ (CA2) particles in CaO-SiO₂-Al₂O₃ steelmaking slags was in situ investigated at 1550 °C. To better understand the role of particle porosity in dissolution kinetics, the particles with two different porosity levels, i.e., 0.08 and 0.20 were used in this study. The porosity (φ) and surface area of CA2 particles were characterized through X-ray Computed Tomographic Imaging (XCT), and the surface area ratio (f(φ)) between the porous and full dense particles was expressed as f(φ)=0.9398e5.9498φ. The obtained results indicated that an increase in the porosity from 0.08 to 0.20 led to an increase in the average dissolution rate from 0.35 to 0.59 μm/s. Moreover, the motion of CA2 particles during the dissolution process was observed, suggesting its importance to include in the modeling approach. A novel mathematical model was developed to predict the dissolution time of inclusion particles by incorporating both the motion and porosity of particles. This model was validated against the existing literature data and aligned well with the current experimental findings. The model predictions demonstrated that the dissolution time of CA2 particles was decreased with an increase in the velocity and porosity of particles and concentration difference of dissolving species between particle–slag interface and molten slag (∆C), and a decrease in slag viscosity.

Dissolution kinetics of CaO·2Al₂O₃ (CA₂) particles in a synthetic CaO–Al₂O₃–SiO₂ steelmaking slag system have been investigated using the high-temperature confocal laser scanning microscope. Effects of temperature (i.e., 1500, 1550, and 1600 °C) and slag composition on the dissolution time of CA2 particles are investigated, along with the time dependency of the projection area of the particle during the dissolution process. It is found that the dissolution rate was enhanced by either an increase in temperature or a decrease in slag viscosity. Moreover, a higher ratio of CaO/Al₂O₃ (C/A) leads to an increased dissolution rate of CA₂ particle at 1600 °C. Thermodynamic calculations suggested the dissolution product, i.e., melilite, formed on the surface of the CA₂ particle during dissolution in slag with a C/A ratio of 3.8 at 1550 °C. Scanning electron microscopy equipped with energy dispersive X-ray spectrometry analysis of as-quenched samples confirmed the dissolution path of CA₂ particles in slags with C/A ratios of 1.8 and 3.8 as well as the melilite formed on the surface of CA₂ particle. The formation of this layer during the dissolution process was identified as a hindrance, impeding the dissolution of CA₂ particle. A valuable reference for designing or/and choosing the composition of top slag for clean steel production is provided, especially using calcium treatment during the secondary refining process.