E. MgO–Al2O3–ZrO2 Refractories
The eutectic points corresponding to the two subsystems in the MgO–Al2O3–
ZrO2 system are all higher than 18008C (18308C for Al2O3–MgAl2O4–ZrO2
and 18408C for MgO–MgAl2O4–ZrO2) (65). This fact, along with the unique
properties of ZrO2, confers many excellent properties such as high refractoriness,
mechanical strength, thermal shock resistance, and slag corrosion resistance on
refractories in the MgO–Al2O3–ZrO2 system. Consequently, MgO–Al2O3–
ZrO2 refractories have potential uses in many applications such as steel-making
furnaces and waste-melting furnaces (66,67). Table 7 compares properties of
MgO–MA–ZrO2 castables developed by Sakamoto and Miyagishi with those
of Al2O3–Cr2O3 castables currently used in waste-melting furnaces. MgO–
MA–ZrO2 castables show better corrosion resistance and spalling resistance
and so may replace Al2O3–Cr2O3 castables in such applications.