Abstract:Calcium aluminate clinkers doped with Na₂O were synthesized using analytically pure reagents CaCO₃, Al₂O₃, SiO₂ and Na₂CO₃. The effects of Na₂O-doping on the formation mechanism of calcium aluminate compounds and the crystal property of 12CaO·7Al₂O₃ (C₁₂A₇) cell were studied. The results show that the minerals containing Na₂O mainly include 2Na₂O·3CaO·5Al₂O₃ and Na₂O·Al₂O₃, when the Na₂O content in clinkers is less than 4.26% (mass fraction). The rest of Na₂O is mainly doped in 12CaO·7Al₂O₃, which results in the decrease of the crystallinity of 12CaO·7Al₂O₃. The crystallinity of 2Na₂O·3CaO·5Al₂O₃ is also inversely proportional to the Na₂O content in clinkers. The formation processes of 2Na₂O·3CaO·5Al₂O₃ and 12CaO·7Al₂O₃ can be divided into two ways, which are the direct reactions of raw materials and the transformation of CaO·Al₂O₃, respectively. The simulation shows that the covalency of O—Na bond in Na₂O-doped 12CaO·7Al₂O₃ cell is weaker than those of O—Ca and O—Al bonds. The free energy of the unit cell increases because of Na₂O doping, which results in the improvement of chemical activity of 12CaO·7Al₂O₃. The leaching efficiency of Al₂O₃ in clinker is improved from 34.81% to 88.17% when the Na₂O content in clinkers increases from 0 to 4.26%.

Key words: calcium aluminate; Na₂O-doping; formation mechanism; crystal structure; sintering; computer simulation