## 1 Introduction  
Magneisia is one of the widely used refractory components in pyro-metallurgy and cement industries [1; 2; 3; 4; 5]. When applied to a working lining, it is susceptible to corrosion owing to the corrosive charge at elevated temperatures, including dissolution in melts. Refractory corrosion often seriously hampers the production performance of vessels and the product quality [6].  
To design a resource- and cost-efficient refractory with a longer service life, the dissolution of the refractory component must be studied thoroughly in different corrosive melts [7; 8]. Diffusivity is the primary parameter used to quantify dissolution [2; 7; 9; 10; 11]. The diffusivities of the dissolving species can be experimentally determined. In the last two and half decades, high-temperature confocal laser scanning microscopy (HT-CLSM) has become a popular tool for dissolution studies [9; 10; 12; 13; 14; 15; 16; 17; 18; 19; 20; 21; 22; 23; 24; 25]. The in situ measurements and possibility of maintaining a high slag-to-particle mass ratio make this method important for dissolution studies. However, only small particles can be studied using this apparatus. In several reported CLSM dissolution studies [9; 10; 12; 13; 14; 15; 16; 17; 18; 19; 20; 21; 22; 23], all of the influencing phenomena and parameters, particularly the effects of slag bath motion and Stefan flow, were not incorporated into the evaluation methods. [PERSON] and [PERSON] [26] accounted for Stefan flow, but the effect of bath motion was not considered. However, both of the phenomena were incorporated in Ref. [11]. The main hurdle in determining the diffusivity from CLSM studies is the appropriate depiction of the effective diffusive boundary layer thickness. In Ref. [11], a method for appropriately depicting the effective diffusive boundary layer thickness by integrating the effect of bath motion and related flow parameters using the Sherwood relation is described in detail. The same method for determining the diffusivity was employed in this study.  
Few dissolution studies on magnesia using HT-CLSM and their diffusivities are available in the literature [10; 16; 21; 23]. In these studies, the effects of slag bath motion and Stefan flow on diffusivity determination were not considered. However, the effect of slag basicity on magnesia dissolution has not been extensively studied. In the present study, the dissolution of magnesia particles in three silicate slags at 1450, 1500, and 1550 \({}^{\circ}\)C have been studied to enrich the literature with effective binary diffusivities of magnesia determined with the consideration of all influencing phenomena and parameters. Furthermore, we tried to establish a parameter for the qualitative estimation of dissolution, which is not possible with slag basicity only. The aforesaid parameter consisted of the dimensionless concentration difference (\(B\)), thermodynamic factor (\(f\)), effective diffusive boundary layer thickness (\(\delta\)), and slag viscosity (\(\eta\)). Additionally, the diffusivities of magnesia in one of these three slags were weighed against the findings obtained from dynamic finger test experiments [8] where the \(\delta\) could be accurately controlled.