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.
Alite is the major compound of anhydrous Portland cement: it is composed of tricalcium silicate Ca3SiO5 (C3S) modified in composition and crystal structure by ionic substitutions. Alite is also the main hydraulic phase of cement and the most important for subsequent strength development. Using raw meals (rich in Ca3P2O8) as alternative fuels in cement plants raises the question about the effect of phosphorus on C3S and its consequences on reactivity with water. This paper deals with a systematic study of C3S triclinic T1 polymorph doped with P2O5 in the range 0–0.9 wt%. All the samples were characterized by X‐ray powder diffraction (XRD), scanning electron microscopy (SEM), and electron‐microprobe analysis. The appearance of a phase rich in phosphorus is shown. It displays a structure derivative of the α′H–Ca2SiO4 polymorph, noted α′H–C2S(P). As phosphorus content increases, C3S is more and more decomposed into free lime and α′H–C2S(P). The α′H phase was detected from 0.1 wt% P2O5 and located at the interfaces of C3S grains. Two identification keys are proposed in order to highlight the α′H–C2S(P) phase: the XRD angular window at 2θCu=32.8°–33.2° and a smooth aspect on SEM micrographs.
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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