Crystal Structures and Phase Transition of Cementitious Bi-Anionic AFm-(Cl, CO32−) Compounds

Authors

  • Adel Mesbah,

    1. Commissariat à l'Energie Atomique et aux Energies Alternatives, CEA DEN/DTCD/SPDE, 30207 Bagnols sur Cèze, France
    2. CNRS, UMR 6002, LMI, 63000 Aubière, France
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  • Jean-Philippe Rapin,

    1. Institut Jean Lamour – UMR 7198, Université Henri Poincaré, Nancy Université, 54500 Vandoeuvre les Nancy, France
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    • ‡‡Present address: University of Geneva, 24 quai Ernest-Ansermet, CH-1211 Geneva 4, Switzerland.

  • Michel François,

    1. Institut Jean Lamour – UMR 7198, Université Henri Poincaré, Nancy Université, 54500 Vandoeuvre les Nancy, France
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  • Céline Cau-dit-Coumes,

    1. Commissariat à l'Energie Atomique et aux Energies Alternatives, CEA DEN/DTCD/SPDE, 30207 Bagnols sur Cèze, France
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  • Fabien Frizon,

    1. Commissariat à l'Energie Atomique et aux Energies Alternatives, CEA DEN/DTCD/SPDE, 30207 Bagnols sur Cèze, France
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  • Fabrice Leroux,

    1. CNRS, UMR 6002, LMI, 63000 Aubière, France
    2. Clermont Université, Université Blaise Pascal, Laboratoire des Matériaux Inorganiques, 63000 Clermont-Ferrand, France
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  • Guillaume Renaudin

    Corresponding author
    1. CNRS, UMR 6002, LMI, 63000 Aubière, France
    2. Clermont Université, ENSCCF, Laboratoire des Matériaux Inorganiques, 63000 Clermont-Ferrand, France
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  • P. Brown—contributing editor

†Author to whom correspondence should be addressed. e-mail: guillaume.renaudin@ensccf.fr

Abstract

A single crystal X-ray diffraction study was performed on the compounds [Ca2Al(OH)6]·[Cl∼0.5(CO3)∼0.25·∼2.25H2O] belonging to the cementitious AFm family of general formulae [Ca2Al(OH)6]·[X·nH2O], where X is a monovalent anion, or half a divalent anion. The so-called chloro-carboaluminate compound crystallizes in the rhombohedralinline imagespace group with: a=5.7400(4) Å, c=46.7402(4) Å, V=1333.7(2) Å3, Dx=2.054 g/cm−3, and Z=6. Refinement of 283 independent reflections led to a residual R factor of 0.020. Chloride and carbonate anions are statistically distributed into the same crystallographic site (6a Wyckoff site). The structure of the chloro-carboaluminate compound corresponds to the high temperature phase of Friedel's salt, the equivalent chloride AFm compound with composition [Ca2Al(OH)6]·[Cl·2H2O]. Three powdered samples of composition [Ca2Al(OH)6]·[Cl1−x(CO3)x/2·∼2.25H2O], with x=0.25, 0.5, and 0.75, were synthesized and characterized in order to investigate the structure transition of Friedel's salt (from the rhombohedral HT-structure to the monoclinic LT-structure) versus the carbonate substitution level. Whereas a structure transition is observed around 35°C for the carbonate-free Friedel's salt, sample with x=0.25 shows a similar structure transition around −15°C. The two other samples with x=0.5 and 0.75, multiphase, exhibit a more complicated thermal behavior.

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