Liquid Penetration and Dissolution-Corrosion

When a hot face of a refractory is exposed to a liquid, various microstruc-tural features of the refractory interact with the hot liquid. The features that could be present in a refractory are refractory crystal, orientation boundary, phase boundary, segregated impurity, unbonded boundary, matrix, liquid boundary film, connected porosity, and open joint. 

The r ractory crystal is a unit of the one or more principal phases chosen to provide thermal stability and corrosion resistance in the material. Orientation boundaries are narrow, but not quite atomically narrow even if free from impurities. Phase boundaries are still somewhat thicker, atomically less dense, and crystallographically more disordered because they join crystals 

Penetration, which takes place in open joints, connected porosity, unbonded boundary, and liquid film, establishes the overall pace of corrosion, that is, its increasing depth into the refractory with time [77]. Matrix and segregated impurity are the vulnerable ones. They are solid regions their invasion has to be by dissolution [77]. Phase, orientation boundaries, and refractory crystal are equally exposed to the penetrating liquid, but their resistance to invasive dissolution is the highest among all features present. 

Both physical penetration and chemical invasion are favored by the effective liquid-solid wetting and by the low viscosity of the liquid. Wetting is decided by the contact angle. As it decreases, wetting is increased. In the liquid state, silicate slags and glasses are the most viscous, oxidic compounds are less so, and halides and elemental metals are the least viscous. 

the weakened zone of a refractory is less deep than the penetrated zone. 

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