Phase equilibria studies of the CaO–SbOx system in air

Abstract The phase equilibria information of the CaO–SbO x system in the range of 700–1580°C in air was obtained for the first time using quenching method and thermal analysis. The equilibrium phase compositions were determined using x‐ray diffraction and Scanning Electron Microscopy‐Energy Dispersion Spectrum. The invariant reaction temperatures were determined using thermogravimetry‐differential scanning calorimetry. A perovskite solid solution between Ca 2 Sb 2 O 7 and CaO, designated as (Ca 6 Sb 2 O 11 ) s.s , was observed. Within this solid solution, three polymorphic forms were identified: orthorhombic, tetragonal, and cubic. The transition temperatures between these polymorphic forms vary with compositional changes. Additionally, the crystal structure of cubic Ca 6 Sb 2 O 11 was analyzed. CaSb 2 O 6 was observed to decompose into Ca 2 Sb 2 O 7 , Sb 4 O 6 , and O 2 above 1336 ± 5°C. The eutectic temperature of α‐Sb 2 O 4 and CaSb 2 O 6 was found to be 1220 ± 5°C.