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Crystal structures of calcium hemicarboaluminate and carbonated calcium hemicarboaluminate from synchrotron powder diffraction data

DOI: 10.1107/S010876811203042X DOI Help
PMID: 22992794 PMID Help

Authors: Tomce Runcevski (Max-Planck-Institute for Solid State Research, Germany) , Robert E. Dinnebier (Max-Planck-Institute for Solid State Research, Germany) , Oxana V. Magdysyuk (Max-Planck-Institute for Solid State Research, Germany) , Herbert Pöllmann (Institut für Geowissenschaften und Geographie, Germany)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Acta Crystallographica Section B Structural Science , VOL 68 (5) , PAGES 493 - 500

State: Published (Approved)
Published: October 2012

Abstract: One of the main phases formed at the beginning of the carbonation reaction of cementitious building materials is the calcium hemicarboaluminate (abbreviated as Hc). This AFm (shorthand for hydrated calcium aluminate phases structurally related to hydrocalumite) phase was synthesized, crystallized and then studied by synchrotron X-ray powder diffraction and micro-Raman spectroscopy. At room temperature and standard experimental conditions two major cementitious phases were detected, the Hc phase (as a major phase) and carbonated calcium hemicarboaluminate (abbreviated as cHc). By increasing the temperature the Hc form transforms into cHc. The crystal structures of these important AFm phases were successfully solved and refined in the space group of the trigonal crystal system. Hc has the unit-cell parameters a = 5.7757 (1) and c = 48.812 (2) Å, and cHc the unit-cell parameters a = 5.7534 (1) and c = 46.389 (1) Å. The two crystal structures are composed of positively charged main layers, [Ca4Al2(OH)12]2+, and negatively charged interlayers, [OH2n(CO3)1 - n·4H2O]2-. The structure of the main layers is typical of the AFm family. Conversely, the interlayer region has a characteristic structure built up from water molecules and statistically distributed anions. In the interlayer, the Hc carbonate and hydroxyl anions are distributed in a 0.25:0.5 ratio, whereas the ratio of the anions in the cHc interlayers is 0.4:0.2.

Journal Keywords: Synchrotron Powder Diffraction; Cementitious Building Material; Micro-Raman Spectroscopy.

Subject Areas: Materials

Instruments: I11-High Resolution Powder Diffraction