Corrosion of refractories by slag is explained by 3 complex mechanisms:
1- Dissolution or conversely the precipitation of new phases
The equation d[C]/dt = h (C saturation – C slag) with C  concentration of the refractory component and h transfer coefficient indicates that an effective way to slow corrosion is to enrich the slag with refractory components that can be dissolved.
 
2- Capillary infiltration of slag into the open porosity of refractory
 
3- Erosion of the transformed surface under the action of friction forces applied by the moving bath in the furnace.
 
Two parameters play an essential role: the limit of solubility and the viscosity of the slags.
The limit of solubility is involved in the kinetics of surface dissolution and in the transformation layer. In the case of an indirect dissolution, it is possible to precipitate protective mineral phases.
By acting on the thickness of the diffusion boundary layer, the viscosity affects the kinetics of infiltration of the slag into the porosity and the kinetics of dissolution at the interface. There is a correlation between viscosity and chemical diffusivity. Moreover, the slag viscosity changes during the dissolution of the refractory.
 
In the solubility / viscosity space, a map of the different dominant corrosion modes is presented. Specifically, the transition from infiltration-erosion mechanism to surface dissolution takes place when solubility increases. For example, this occurs during the corrosion of MgO-C refractories in contact with acidic CaO-SiO2 slags (25% saturation and viscosity not exceeding a few hundred mPas).
 
The effect of the solubility of refractory oxides in the different slags and the viscosity evolution during this dissolution are studied using thermodynamic calculations.
 
As illustration, the refractory-slag compatibility at the different stages of steelmaking process, from the blast furnace to the steel ladle is detailed.