Improved quantification of alite and belite in anhydrous Portland cements by 29Si MAS NMR: Effects of paramagnetic ions

• Published in: Solid state nuclear magnetic resonance Vol. 36; no. 1; pp. 32 - 44
• Main Authors: Poulsen, Søren L., Kocaba, Vanessa, Le Saoût, Gwenn, Jakobsen, Hans J., Scrivener, Karen L., Skibsted, Jørgen
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 01.09.2009
• Subjects: 29Si MAS NMR; Alite (Ca 3SiO 5); Belite (Ca 2SiO 4); Guest-ion substitution; High-speed spinning; Paramagnetic ions (Fe 3+); Portland cement; Spin-lattice relaxation; Taylor–Bogue calculation; XRD-Rietveld refinement; Alite (Ca 3SiO 5); Guest-ion substitution; Spin-lattice relaxation; XRD-Rietveld refinement; Belite (Ca 2SiO 4); High-speed spinning; Paramagnetic ions (Fe 3+); Portland cement; 29Si MAS NMR; Taylor–Bogue calculation
• ISSN: 0926-2040; 1527-3326
• DOI: 10.1016/j.ssnmr.2009.05.001

The applicability, reliability, and repeatability of 29Si MAS NMR for determination of the quantities of alite (Ca 3SiO 5) and belite (Ca 2SiO 4) in anhydrous Portland cement was investigated in detail for 11 commercial Portland cements and the results compared with phase quantifications based on powder X-ray diffraction combined with Rietveld analysis and with Taylor–Bogue calculations. The effects from paramagnetic ions (Fe 3+) on the spinning sideband intensities, originating from dipolar couplings between 29Si and the spins of the paramagnetic electrons, were considered and analyzed in spectra recorded at four magnetic fields (4.7–14.1 T) and this has led to an improved quantification of alite and belite from 29Si MAS NMR spectra recorded at “high” spinning speeds of ν R=12.0–13.0 kHz using 4 or 5 mm rotors. Furthermore, the impact of Fe 3+ ions on the spin-lattice relaxation was studied by inversion-recovery experiments and it was found that the relaxation is overwhelmingly dominated by the Fe 3+ ions incorporated as guest-ions in alite and belite rather than the Fe 3+ sites present in the intimately mixed ferrite phase (Ca 2Al x Fe 2− x O 5).