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 °C are 12CaO·7Al2O3, 2CaO·Al2O3·SiO2 and 2CaO·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·7Al2O3 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·Al2O3·SiO2 decreases with the increase of Na2O addition. Na2O forms solid solution in 12CaO·7Al2O3, which increases the volume of elementary cell of 12CaO·7Al2O3. The formation temperature of 12CaO·7Al2O3 is decreased by 30 °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.