Abstract: Calcium fluoride-doped tricalcium silicate（3CaO·SiO₂，C₃S） were synthesized by co-precipitation process with calcium nitrate tetrahydrate［Ca（NO₃）₂·4H₂O］，sodium silicate nonahydrate（Na₂SiO₃·9H₂O），sodium carbonate（Na₂CO₃）， and ammonium fluoride（NH₄F） as raw materials.Effects of different doping amounts of CaF₂ on the content of free CaO（f-CaO） in the synthesized C₃S were investigated.The content of f-CaO in C₃S was determined by glycol-anhydrous alcohol method，and the micro morphology and phase composition of C₃S were characterized by X-ray diffraction（XRD） and scanning electron microscopy（SEM）.Results indicated that the addition of CaF₂ caused the formation of eutectic mixture，apparently reduced the content of f-CaO，shorten the reaction time and decreased the sintering temperature；and while the doping content of CaF₂ （mass fraction） was 0.6%，C₃S with little f-CaO could be obtained at 1 350 ℃ for 4 h.

Key words: calcium fluoride, tricalcium silicate, free calcium oxide