Phase equilibria studies of the CaO–SbOx system in air

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.