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The rather similar structure of the two alites makes it difficult to distinguish them from their XRD patterns. This paper shows that five angular windows in the X-Ray diffraction patterns can be used with synthetic alites as well as industrial compounds, to identify the nature of the actual polymorph (M1 or M3) present and the structural model to be used (with or without superstructure) in subsequent Rietveld analysis of the data.

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M 1 alite / Polymorphism / Powder diffraction structure analysis / X-ray diffraction Abstract. In this paper, we present a structural model for the M 1 polymorph of tricalcium silicate Ca 3 SiO 5 from Powder X-Ray Diffraction (XRD) data, including weak intensity superstructure Bragg lines. As no single crystal is available, this structural model has been deduced using the structural relationships found between the previously known triclinic and monoclinic M 3 polymorphs.We find that the better starting set of atomic positions for Rietveld refinement is the triclinic set and not the monoclinic set. A key observation is that the monoclinic M 1 structure is closer to the low temperature triclinic T 3 structure (within the Golovastikov model) than to the higher temperature monoclinic M 3 structure.The unit cell and the set of atomic positions of the two best models, called 3hMiPc and 3hTiPn models, are provided. We prefer the 3hMiPc model for it better reproduces the weak characteristic Bragg lines of the superstructure.pure: T 1 ÀÀÀ! 620 C T 2 ÀÀÀ! 920 C T 3 ÀÀÀ! 980 C M 1 ÀÀÀ! 990 C M 2 ÀÀÀ! 1070 C R doped (mainly Zn or Mg): M 1 ÀÀÀ! 990 C M 2 ÀÀÀ! 1060 C M 3 ÀÀÀ! 1070 C R

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