The corrosion mechanisms of MgO–MA refractories depend on the environment
in which they are used. In CaO–Al2O3–SiO2 (CAS) model steel-making slags, if
the slag Al2O3 content is high, it will react with MgO from the refractories to
form a protective secondary spinel layer on the MgO surface, leading to indirect
corrosion of MgO in the slag (Figure 11 after Goto et al. (36)). If the slag Al2O3
content is low, no continuous spinel layer forms on MgO; in this case, MgO will
react with CaO and SiO2 from the slag to form low-melting phases such as CMS
and C3MS2 and then dissolve into the slag directly. If the slag CaO is high, MA
from the MgO–MA refractories can react with it to form low-melting calcium
aluminate phases; on the other hand, if the slag CaO is low, MA will react
with CaO and SiO2 from the slag to form low-melting phases such as C2AS or
CAS2 and thus dissolve into the slag directly (37). Figure 12 shows schematically
the corrosion process of an MgO–MA brick in a CAS slag (C/S ¼ 1,
Al2O3 ¼ 20 wt%) (36). In such a slag, MgO dissolves in the slag indirectly via
formation of a secondary spinel on its surface while MA dissolves in the slag
directly.
The corrosion mechanisms of MgO–MA refractories depend on the environmentin which they are used. In CaO–Al2O3–SiO2 (CAS) model steel-making slags, ifthe slag Al2O3 content is high, it will react with MgO from the refractories toform a protective secondary spinel layer on the MgO surface, leading to indirectcorrosion of MgO in the slag (Figure 11 after Goto et al. (36)). If the slag Al2O3content is low, no continuous spinel layer forms on MgO; in this case, MgO willreact with CaO and SiO2 from the slag to form low-melting phases such as CMSand C3MS2 and then dissolve into the slag directly. If the slag CaO is high, MAfrom the MgO–MA refractories can react with it to form low-melting calciumaluminate phases; on the other hand, if the slag CaO is low, MA will reactwith CaO and SiO2 from the slag to form low-melting phases such as C2AS orCAS2 and thus dissolve into the slag directly (37). Figure 12 shows schematicallythe corrosion process of an MgO–MA brick in a CAS slag (C/S ¼ 1,Al2O3 ¼ 20 wt%) (36). In such a slag, MgO dissolves in the slag indirectly viaformation of a secondary spinel on its surface while MA dissolves in the slagdirectly.
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