Transmission Electron Microscopy and X-Ray Diffraction of Doped Tricalcium Silicate

Member of oxides, including MgO, ZnO, La₂O₃, Al₂O₃, TiO₂, and F were reacted with C₃S, either individually or in combination, in order to stabilize a variety of polymorphic forms. The resultant phases were examined by both XRD and TEM. It was found that the results obtained by the conventional means of observing groups of reflections in powder X-ray diffraction patterns were not in agreement with the structure types identified by electron diffraction. In particular, the rhombohedral form of alite, synthesized by the addition of either ZnO or Al₂ O₃+ F to C₃S, was not observed by TEM although the corresponding X-ray patterns all displayed single peaks characteristic of the rhombohedral cell. Electron diffraction of C,S doped with 2.02 and 4.43% ZnO gave mono-clinic patterns, whereas C₃S doped with Al + F gave several forms, all of them different from the form produced by ZnO-doped C₃S. The addition of La₂0₃ produced a new hexagonal lattice with cell dimensions of a = 2.575 and c = 2.50 nm. When Al + F was incorporated in C₃S, the modifications found included the triclinic lattice characteristic of pure C₃S, the hexagonal lattice characteristic of La-doped C₃S, and a complex lattice distinguished by the presence of incommensurate doublet reflections and sometimes extra weak spots. A similar incommensurate superlattice was found in alites containing Mg, Al, and a large amount of Ti (0.13 mole). The Jeffery cell for the Mm modification of C₃S doped with 1.63% MgO was confirmed.