Effect of Na2O on formation of calcium aluminates in CaO-Al2O3-SiO2 system

The formation characteristics of calcium aluminates in the CaO-Al2O3-SiO2 system with sodium oxide was investigated by XRD, SEM-EDS and DSC-TG technologies. The main phases in the clinker after sintering at 1350 degrees C are 12CaO center dot 7Al(2)O(3), 2CaO center dot Al2O3 center dot SiO2 and 2CaO center dot SiO2 when the mass ratio of Al2O3 to SiO2 is 3.0 and the molar ratio of CaO to Al2O3 is 1.0. The proportion of 12CaO center dot 7Al(2)O(3) increases with the increase of Na2O addition when the molar ratio of Na2O to Al2O3 is from 0 to 0.4, while the proportion of 2CaO center dot Al2O3 center dot SiO2 decreases with the increase of Na2O addition. Na2O forms solid solution in 12CaO center dot 7Al(2)O(3), which increases the volume of elementary cell of 12CaO center dot 7Al(2)O(3). The formation temperature of 12CaO center dot 7Al(2)O(3) is decreased by 30 degrees C when the molar ratio of Na2O to Al2O3 increases from 0 to 0.4 determined by DSC. The alumina leaching property of clinker increases obviously with the increase of Na2O addition.