Resolution of the Two Aluminum Sites in Ettringite by Al-27 MAS and MQMAS NMR at Very High Magnetic Field (22.3 T)

Publication: Research - peer-reviewJournal article

DOI

Ettringite (Ca-6[Al(OH)(6)](2)(SO4)(3)center dot 26H(2)O) is the first hydration product formed during Portland cement hydration. Al-27 MAS NMR has been used in a wide number of studies to detect and quantify ettringite in hydrated cement blends by the observation of a single, narrow resonance at 13-14 ppm. This work reports the first observation of resonances from two distinct Al sites in octahedral coordination for ettringite, employing Al-27 MAS and MQMAS NMR at an ultrahigh magnetic field (22.3 T). Thereby, the Al-27 NMR spectra are in agreement with the most accepted trigonal model for the ettringite structure. Al-27 quadrupole coupling parameters and isotropic chemical shifts for the two Al sites are determined from simulations and least-squares optimization of slow-speed Al-27 MAS NMR spectra of the satellite transitions. These data reveal that the local environments for the two octahedral Al sites are very similar, in accord with the most recent XRD refinements of the ettringite structure. Finally, the significant improvement in spectral resolution by the application of an ultrahigh magnetic field is illustrated by the detection of the two Al sites from ettringite in a hydrated cement mimicking the composition of a calcium sulfoaluminate cement.

Original languageEnglish
JournalThe Journal of Physical Chemistry Part C: Nanomaterials, Interfaces and Hard Matter
Volume121
Issue number7
Pages (from-to)4011-4017
Number of pages7
ISSN1932-7447
DOIs
StatePublished - 23 Feb 2017

    Keywords

  • C-S-H, SOLID-STATE NMR, CRYSTAL-STRUCTURE, SATELLITE TRANSITIONS, QUADRUPOLAR NUCLEI, SPECTROSCOPY, CEMENTS, SI-29, CONCRETE

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