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

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 (CaMgxAl12-xO19-0.5x; 0 <= x <= 0.18), CAM-I (Ca2Mg2-3xAl28+2xO46 (0 <= x <= 0.3), and CAM-II (CaMg2-3xAl16+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 degrees C to 1700 degrees C. The formation of ZnO and hibonite solid solution (CaZnxAl12-xO19-0.5x; 0 < x < 0.18), CAZ-I (Ca2Zn2-3xAl28+2xO46; 0 <= x <= 0.3), and CAZ-II (CaZn2-3xAl16+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<middle dot>6Al(2)O(3)) and ZnAl2O4.