Polymorph transformation of tricalcium silicate doped with heavy metal

The aim of the present study was to investigate the influence of heavy metals on the polymorph transformation of tricalcium silicate. Heavy metal (0.1wt% to 3.0wt%) of Cr, Zn, Cu, Ni and Pb (in oxides form) was added into the raw mixtures and then sintered together three times at 1450 degrees C for 2 h. The f-CaO content of doped C3S was determined by the glycerol-ethanol method, and their polymorph transformation was investigated by means of XRD and FTIR. Thermal analysis (DTA/DTG) was conducted to determine the reaction temperatures and mass losses during the sintering process of raw mixtures. The concentration of heavy metal in C3S after sintering was determined by ICP-AES. The experimental results indicate that heavy metal doping contributes to a higher symmetry of C3S except for Pb. Addition of up to 3.0wt%, Cr will lead to a decomposition of C3S into C2S and CaO; Zn will cause a transformation from T1 to M2 polymorph, and then to R polymorph; Cu and Ni cause a gradual transformation from T1 to T2 and then to M1 and/or M2 polymorph. During the sintering process, all the Pb releases into atmosphere because of evaporation.

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