Mineral transition and formation mechanism of calcium aluminate compounds in CaO-Al2O3-Na2O system during high-temperature sintering

The mineral transition and formation mechanism of calcium aluminate compounds in CaO-Al 2 O 3 -Na 2 O system during the high-temperature sintering process were systematically investigated using DSC-TG, XRD, SEM-EDS, FTIR, and Raman spectra, and the crystal structure of Na 4 Ca 3 (AlO 2 ) 10 was also simulated by Material Studio software. The results indicated that the minerals formed during the sintering process included Na 4 Ca 3 (AlO 2 ) 10 , CaOAl 2 O 3 , and 12CaO·7Al 2 O 3 , and the content of Na 4 Ca 3 (AlO 2 ) 10 could reach 92wt% when sintered at 1200°C for 30 min. The main formation stage of Na 4 Ca 3 (AlO 2 ) 10 occurred at temperatures from 970 to 1100°C, and the content could reach 82wt% when the reaction temperature increased to 1100°C. The crystal system of Na 4 Ca 3 (AlO 2 ) 10 was tetragonal, and the cells preferred to grow along crystal planes (110) and (210). The formation of Na 4 Ca 3 (AlO 2 ) 10 was an exothermic reaction that followed a secondary reaction model, and its activation energy was 223.97 kJ/mol.