Phase formation in the CaO–Al2O3–ZnO system as an analogue to CaO–Al2O3–MgO in spinel containing refractories

Abstract

Recently, gahnite (ZnAl₂O₄) is gaining attraction as a potential refractory ceramic because of the similarity of its structure and properties with those of magnesium aluminate (MgAl₂O₄) spinel refractories. Formation of MgO and hibonite solid solution (CaMg_xAl_12−xO_19−0.5x; 0 ≤ x ≤ 0.18), CAM-I (Ca₂Mg_2−3xAl_28+2xO₄₆ (0 ≤ x ≤ 0.3), and CAM-II (CaMg_2−3xAl_16+2xO₂₇, 0 ≤ x ≤ 0.2) phases with platelet and interlocking microstructure in the CaO–Al₂O₃–MgO ternary system significantly enhances the high temperature mechanical properties of refractory castables. The CaO–Al₂O₃–ZnO ternary system has been studied, for the first time to our knowledge, in a selected compositional range with reference to the CaO–Al₂O₃–MgO system from 1650°C to 1700°C. The formation of ZnO and hibonite solid solution (CaZn_xAl_12−xO_19−0.5x; 0 < x < 0.18), CAZ-I (Ca₂Zn_2−3xAl_28+2xO₄₆; 0 ≤ x ≤ 0.3), and CAZ-II (CaZn_2−3xAl_16+2xO₂₇; 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·6Al₂O₃) and ZnAl₂O₄.