Phase formation in the CaO–Al ₂ O ₃ –ZnO system as an analogue to CaO–Al ₂ O ₃ –MgO in spinel containing refractories

Abstract Recently, gahnite (ZnAl 2 O 4 ) is gaining attraction as a potential refractory ceramic because of the similarity of its structure and properties with those of magnesium aluminate (MgAl 2 O 4 ) spinel refractories. Formation of MgO and hibonite solid solution (CaMg x Al 12− x O 19−0.5 x ; 0 ≤ x ≤ 0.18), CAM‐I (Ca 2 Mg 2−3 x Al 28+2 x O 46 (0 ≤ x ≤ 0.3), and CAM‐II (CaMg 2−3 x Al 16+2 x O 27 , 0 ≤ x ≤ 0.2) phases with platelet and interlocking microstructure in the CaO–Al 2 O 3 –MgO ternary system significantly enhances the high temperature mechanical properties of refractory castables. The CaO–Al 2 O 3 –ZnO ternary system has been studied, for the first time to our knowledge, in a selected compositional range with reference to the CaO–Al 2 O 3 –MgO system from 1650°C to 1700°C. The formation of ZnO and hibonite solid solution (CaZn x Al 12− x O 19−0.5 x ; 0 < x < 0.18), CAZ‐I (Ca 2 Zn 2−3 x Al 28+2 x O 46 ; 0 ≤ x ≤ 0.3), and CAZ‐II (CaZn 2−3 x Al 16+2 x O 27 ; 0 ≤ x ≤ 0.2) phases with platelet and interlocking morphology have been found. The crystal structures and lattice parameters of ZnO and hibonite solid solution, CAZ‐I, and CAZ‐II are comparable, respectively, with MgO and hibonite solid solution, CAM‐I, and CAM‐II. Furthermore, CAZ‐I and CAZ‐II phases also form due to reaction between hibonite (CaO·6Al 2 O 3 ) and ZnAl 2 O 4 .