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Crystal Structures and Phase Transition of Cementitious Bi‐Anionic AFm‐(Cl − , CO 3 2− ) Compounds
Author(s) -
Mesbah Adel,
Rapin JeanPhilippe,
François Michel,
CauditCoumes Céline,
Frizon Fabien,
Leroux Fabrice,
Renaudin Guillaume
Publication year - 2011
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1551-2916.2010.04050.x
Subject(s) - crystallography , monoclinic crystal system , crystal structure , chemistry , carbonate , chloride , phase transition , salt (chemistry) , organic chemistry , physics , quantum mechanics
A single crystal X‐ray diffraction study was performed on the compounds [Ca 2 Al(OH) 6 ]·[Cl ∼0.5 (CO 3 ) ∼0.25 ·∼2.25H 2 O] belonging to the cementitious AFm family of general formulae [Ca 2 Al(OH) 6 ]·[ X · n H 2 O], where X is a monovalent anion, or half a divalent anion. The so‐called chloro‐carboaluminate compound crystallizes in the rhombohedralspace group with: a =5.7400(4) Å, c =46.7402(4) Å, V =1333.7(2) Å 3 , D x =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 (6 a 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 [Ca 2 Al(OH) 6 ]·[Cl·2H 2 O]. Three powdered samples of composition [Ca 2 Al(OH) 6 ]·[Cl 1− x (CO 3 ) x /2 ·∼2.25H 2 O], 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.